Move LikeMatch to Rdbms namespace

[mediawiki.git] / includes / Title.php

<?php
/**
 * Representation of a title within %MediaWiki.
 *
 * See title.txt
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */
use MediaWiki\Linker\LinkTarget;
use MediaWiki\Interwiki\InterwikiLookup;
use MediaWiki\MediaWikiServices;

/**
 * Represents a title within MediaWiki.
 * Optionally may contain an interwiki designation or namespace.
 * @note This class can fetch various kinds of data from the database;
 *       however, it does so inefficiently.
 * @note Consider using a TitleValue object instead. TitleValue is more lightweight
 *       and does not rely on global state or the database.
 */
class Title implements LinkTarget {
        /** @var HashBagOStuff */
        static private $titleCache = null;

        /**
         * Title::newFromText maintains a cache to avoid expensive re-normalization of
         * commonly used titles. On a batch operation this can become a memory leak
         * if not bounded. After hitting this many titles reset the cache.
         */
        const CACHE_MAX = 1000;

        /**
         * Used to be GAID_FOR_UPDATE define. Used with getArticleID() and friends
         * to use the master DB
         */
        const GAID_FOR_UPDATE = 1;

        /**
         * @name Private member variables
         * Please use the accessor functions instead.
         * @private
         */
        // @{

        /** @var string Text form (spaces not underscores) of the main part */
        public $mTextform = '';

        /** @var string URL-encoded form of the main part */
        public $mUrlform = '';

        /** @var string Main part with underscores */
        public $mDbkeyform = '';

        /** @var string Database key with the initial letter in the case specified by the user */
        protected $mUserCaseDBKey;

        /** @var int Namespace index, i.e. one of the NS_xxxx constants */
        public $mNamespace = NS_MAIN;

        /** @var string Interwiki prefix */
        public $mInterwiki = '';

        /** @var bool Was this Title created from a string with a local interwiki prefix? */
        private $mLocalInterwiki = false;

        /** @var string Title fragment (i.e. the bit after the #) */
        public $mFragment = '';

        /** @var int Article ID, fetched from the link cache on demand */
        public $mArticleID = -1;

        /** @var bool|int ID of most recent revision */
        protected $mLatestID = false;

        /**
         * @var bool|string ID of the page's content model, i.e. one of the
         *   CONTENT_MODEL_XXX constants
         */
        private $mContentModel = false;

        /**
         * @var bool If a content model was forced via setContentModel()
         *   this will be true to avoid having other code paths reset it
         */
        private $mForcedContentModel = false;

        /** @var int Estimated number of revisions; null of not loaded */
        private $mEstimateRevisions;

        /** @var array Array of groups allowed to edit this article */
        public $mRestrictions = [];

        /** @var string|bool */
        protected $mOldRestrictions = false;

        /** @var bool Cascade restrictions on this page to included templates and images? */
        public $mCascadeRestriction;

        /** Caching the results of getCascadeProtectionSources */
        public $mCascadingRestrictions;

        /** @var array When do the restrictions on this page expire? */
        protected $mRestrictionsExpiry = [];

        /** @var bool Are cascading restrictions in effect on this page? */
        protected $mHasCascadingRestrictions;

        /** @var array Where are the cascading restrictions coming from on this page? */
        public $mCascadeSources;

        /** @var bool Boolean for initialisation on demand */
        public $mRestrictionsLoaded = false;

        /** @var string Text form including namespace/interwiki, initialised on demand */
        protected $mPrefixedText = null;

        /** @var mixed Cached value for getTitleProtection (create protection) */
        public $mTitleProtection;

        /**
         * @var int Namespace index when there is no namespace. Don't change the
         *   following default, NS_MAIN is hardcoded in several places. See bug 696.
         *   Zero except in {{transclusion}} tags.
         */
        public $mDefaultNamespace = NS_MAIN;

        /** @var int The page length, 0 for special pages */
        protected $mLength = -1;

        /** @var null Is the article at this title a redirect? */
        public $mRedirect = null;

        /** @var array Associative array of user ID -> timestamp/false */
        private $mNotificationTimestamp = [];

        /** @var bool Whether a page has any subpages */
        private $mHasSubpages;

        /** @var bool The (string) language code of the page's language and content code. */
        private $mPageLanguage = false;

        /** @var string|bool|null The page language code from the database, null if not saved in
         * the database or false if not loaded, yet. */
        private $mDbPageLanguage = false;

        /** @var TitleValue A corresponding TitleValue object */
        private $mTitleValue = null;

        /** @var bool Would deleting this page be a big deletion? */
        private $mIsBigDeletion = null;
        // @}

        /**
         * B/C kludge: provide a TitleParser for use by Title.
         * Ideally, Title would have no methods that need this.
         * Avoid usage of this singleton by using TitleValue
         * and the associated services when possible.
         *
         * @return TitleFormatter
         */
        private static function getTitleFormatter() {
                return MediaWikiServices::getInstance()->getTitleFormatter();
        }

        /**
         * B/C kludge: provide an InterwikiLookup for use by Title.
         * Ideally, Title would have no methods that need this.
         * Avoid usage of this singleton by using TitleValue
         * and the associated services when possible.
         *
         * @return InterwikiLookup
         */
        private static function getInterwikiLookup() {
                return MediaWikiServices::getInstance()->getInterwikiLookup();
        }

        /**
         * @access protected
         */
        function __construct() {
        }

        /**
         * Create a new Title from a prefixed DB key
         *
         * @param string $key The database key, which has underscores
         *      instead of spaces, possibly including namespace and
         *      interwiki prefixes
         * @return Title|null Title, or null on an error
         */
        public static function newFromDBkey( $key ) {
                $t = new Title();
                $t->mDbkeyform = $key;

                try {
                        $t->secureAndSplit();
                        return $t;
                } catch ( MalformedTitleException $ex ) {
                        return null;
                }
        }

        /**
         * Create a new Title from a TitleValue
         *
         * @param TitleValue $titleValue Assumed to be safe.
         *
         * @return Title
         */
        public static function newFromTitleValue( TitleValue $titleValue ) {
                return self::newFromLinkTarget( $titleValue );
        }

        /**
         * Create a new Title from a LinkTarget
         *
         * @param LinkTarget $linkTarget Assumed to be safe.
         *
         * @return Title
         */
        public static function newFromLinkTarget( LinkTarget $linkTarget ) {
                if ( $linkTarget instanceof Title ) {
                        // Special case if it's already a Title object
                        return $linkTarget;
                }
                return self::makeTitle(
                        $linkTarget->getNamespace(),
                        $linkTarget->getText(),
                        $linkTarget->getFragment(),
                        $linkTarget->getInterwiki()
                );
        }

        /**
         * Create a new Title from text, such as what one would find in a link. De-
         * codes any HTML entities in the text.
         *
         * @param string|int|null $text The link text; spaces, prefixes, and an
         *   initial ':' indicating the main namespace are accepted.
         * @param int $defaultNamespace The namespace to use if none is specified
         *   by a prefix.  If you want to force a specific namespace even if
         *   $text might begin with a namespace prefix, use makeTitle() or
         *   makeTitleSafe().
         * @throws InvalidArgumentException
         * @return Title|null Title or null on an error.
         */
        public static function newFromText( $text, $defaultNamespace = NS_MAIN ) {
                // DWIM: Integers can be passed in here when page titles are used as array keys.
                if ( $text !== null && !is_string( $text ) && !is_int( $text ) ) {
                        throw new InvalidArgumentException( '$text must be a string.' );
                }
                if ( $text === null ) {
                        return null;
                }

                try {
                        return Title::newFromTextThrow( strval( $text ), $defaultNamespace );
                } catch ( MalformedTitleException $ex ) {
                        return null;
                }
        }

        /**
         * Like Title::newFromText(), but throws MalformedTitleException when the title is invalid,
         * rather than returning null.
         *
         * The exception subclasses encode detailed information about why the title is invalid.
         *
         * @see Title::newFromText
         *
         * @since 1.25
         * @param string $text Title text to check
         * @param int $defaultNamespace
         * @throws MalformedTitleException If the title is invalid
         * @return Title
         */
        public static function newFromTextThrow( $text, $defaultNamespace = NS_MAIN ) {
                if ( is_object( $text ) ) {
                        throw new MWException( '$text must be a string, given an object' );
                }

                $titleCache = self::getTitleCache();

                // Wiki pages often contain multiple links to the same page.
                // Title normalization and parsing can become expensive on pages with many
                // links, so we can save a little time by caching them.
                // In theory these are value objects and won't get changed...
                if ( $defaultNamespace == NS_MAIN ) {
                        $t = $titleCache->get( $text );
                        if ( $t ) {
                                return $t;
                        }
                }

                // Convert things like &eacute; &#257; or &#x3017; into normalized (bug 14952) text
                $filteredText = Sanitizer::decodeCharReferencesAndNormalize( $text );

                $t = new Title();
                $t->mDbkeyform = strtr( $filteredText, ' ', '_' );
                $t->mDefaultNamespace = intval( $defaultNamespace );

                $t->secureAndSplit();
                if ( $defaultNamespace == NS_MAIN ) {
                        $titleCache->set( $text, $t );
                }
                return $t;
        }

        /**
         * THIS IS NOT THE FUNCTION YOU WANT. Use Title::newFromText().
         *
         * Example of wrong and broken code:
         * $title = Title::newFromURL( $wgRequest->getVal( 'title' ) );
         *
         * Example of right code:
         * $title = Title::newFromText( $wgRequest->getVal( 'title' ) );
         *
         * Create a new Title from URL-encoded text. Ensures that
         * the given title's length does not exceed the maximum.
         *
         * @param string $url The title, as might be taken from a URL
         * @return Title|null The new object, or null on an error
         */
        public static function newFromURL( $url ) {
                $t = new Title();

                # For compatibility with old buggy URLs. "+" is usually not valid in titles,
                # but some URLs used it as a space replacement and they still come
                # from some external search tools.
                if ( strpos( self::legalChars(), '+' ) === false ) {
                        $url = strtr( $url, '+', ' ' );
                }

                $t->mDbkeyform = strtr( $url, ' ', '_' );

                try {
                        $t->secureAndSplit();
                        return $t;
                } catch ( MalformedTitleException $ex ) {
                        return null;
                }
        }

        /**
         * @return HashBagOStuff
         */
        private static function getTitleCache() {
                if ( self::$titleCache == null ) {
                        self::$titleCache = new HashBagOStuff( [ 'maxKeys' => self::CACHE_MAX ] );
                }
                return self::$titleCache;
        }

        /**
         * Returns a list of fields that are to be selected for initializing Title
         * objects or LinkCache entries. Uses $wgContentHandlerUseDB to determine
         * whether to include page_content_model.
         *
         * @return array
         */
        protected static function getSelectFields() {
                global $wgContentHandlerUseDB, $wgPageLanguageUseDB;

                $fields = [
                        'page_namespace', 'page_title', 'page_id',
                        'page_len', 'page_is_redirect', 'page_latest',
                ];

                if ( $wgContentHandlerUseDB ) {
                        $fields[] = 'page_content_model';
                }

                if ( $wgPageLanguageUseDB ) {
                        $fields[] = 'page_lang';
                }

                return $fields;
        }

        /**
         * Create a new Title from an article ID
         *
         * @param int $id The page_id corresponding to the Title to create
         * @param int $flags Use Title::GAID_FOR_UPDATE to use master
         * @return Title|null The new object, or null on an error
         */
        public static function newFromID( $id, $flags = 0 ) {
                $db = ( $flags & self::GAID_FOR_UPDATE ) ? wfGetDB( DB_MASTER ) : wfGetDB( DB_REPLICA );
                $row = $db->selectRow(
                        'page',
                        self::getSelectFields(),
                        [ 'page_id' => $id ],
                        __METHOD__
                );
                if ( $row !== false ) {
                        $title = Title::newFromRow( $row );
                } else {
                        $title = null;
                }
                return $title;
        }

        /**
         * Make an array of titles from an array of IDs
         *
         * @param int[] $ids Array of IDs
         * @return Title[] Array of Titles
         */
        public static function newFromIDs( $ids ) {
                if ( !count( $ids ) ) {
                        return [];
                }
                $dbr = wfGetDB( DB_REPLICA );

                $res = $dbr->select(
                        'page',
                        self::getSelectFields(),
                        [ 'page_id' => $ids ],
                        __METHOD__
                );

                $titles = [];
                foreach ( $res as $row ) {
                        $titles[] = Title::newFromRow( $row );
                }
                return $titles;
        }

        /**
         * Make a Title object from a DB row
         *
         * @param stdClass $row Object database row (needs at least page_title,page_namespace)
         * @return Title Corresponding Title
         */
        public static function newFromRow( $row ) {
                $t = self::makeTitle( $row->page_namespace, $row->page_title );
                $t->loadFromRow( $row );
                return $t;
        }

        /**
         * Load Title object fields from a DB row.
         * If false is given, the title will be treated as non-existing.
         *
         * @param stdClass|bool $row Database row
         */
        public function loadFromRow( $row ) {
                if ( $row ) { // page found
                        if ( isset( $row->page_id ) ) {
                                $this->mArticleID = (int)$row->page_id;
                        }
                        if ( isset( $row->page_len ) ) {
                                $this->mLength = (int)$row->page_len;
                        }
                        if ( isset( $row->page_is_redirect ) ) {
                                $this->mRedirect = (bool)$row->page_is_redirect;
                        }
                        if ( isset( $row->page_latest ) ) {
                                $this->mLatestID = (int)$row->page_latest;
                        }
                        if ( !$this->mForcedContentModel && isset( $row->page_content_model ) ) {
                                $this->mContentModel = strval( $row->page_content_model );
                        } elseif ( !$this->mForcedContentModel ) {
                                $this->mContentModel = false; # initialized lazily in getContentModel()
                        }
                        if ( isset( $row->page_lang ) ) {
                                $this->mDbPageLanguage = (string)$row->page_lang;
                        }
                        if ( isset( $row->page_restrictions ) ) {
                                $this->mOldRestrictions = $row->page_restrictions;
                        }
                } else { // page not found
                        $this->mArticleID = 0;
                        $this->mLength = 0;
                        $this->mRedirect = false;
                        $this->mLatestID = 0;
                        if ( !$this->mForcedContentModel ) {
                                $this->mContentModel = false; # initialized lazily in getContentModel()
                        }
                }
        }

        /**
         * Create a new Title from a namespace index and a DB key.
         * It's assumed that $ns and $title are *valid*, for instance when
         * they came directly from the database or a special page name.
         * For convenience, spaces are converted to underscores so that
         * eg user_text fields can be used directly.
         *
         * @param int $ns The namespace of the article
         * @param string $title The unprefixed database key form
         * @param string $fragment The link fragment (after the "#")
         * @param string $interwiki The interwiki prefix
         * @return Title The new object
         */
        public static function makeTitle( $ns, $title, $fragment = '', $interwiki = '' ) {
                $t = new Title();
                $t->mInterwiki = $interwiki;
                $t->mFragment = $fragment;
                $t->mNamespace = $ns = intval( $ns );
                $t->mDbkeyform = strtr( $title, ' ', '_' );
                $t->mArticleID = ( $ns >= 0 ) ? -1 : 0;
                $t->mUrlform = wfUrlencode( $t->mDbkeyform );
                $t->mTextform = strtr( $title, '_', ' ' );
                $t->mContentModel = false; # initialized lazily in getContentModel()
                return $t;
        }

        /**
         * Create a new Title from a namespace index and a DB key.
         * The parameters will be checked for validity, which is a bit slower
         * than makeTitle() but safer for user-provided data.
         *
         * @param int $ns The namespace of the article
         * @param string $title Database key form
         * @param string $fragment The link fragment (after the "#")
         * @param string $interwiki Interwiki prefix
         * @return Title|null The new object, or null on an error
         */
        public static function makeTitleSafe( $ns, $title, $fragment = '', $interwiki = '' ) {
                if ( !MWNamespace::exists( $ns ) ) {
                        return null;
                }

                $t = new Title();
                $t->mDbkeyform = Title::makeName( $ns, $title, $fragment, $interwiki, true );

                try {
                        $t->secureAndSplit();
                        return $t;
                } catch ( MalformedTitleException $ex ) {
                        return null;
                }
        }

        /**
         * Create a new Title for the Main Page
         *
         * @return Title The new object
         */
        public static function newMainPage() {
                $title = Title::newFromText( wfMessage( 'mainpage' )->inContentLanguage()->text() );
                // Don't give fatal errors if the message is broken
                if ( !$title ) {
                        $title = Title::newFromText( 'Main Page' );
                }
                return $title;
        }

        /**
         * Get the prefixed DB key associated with an ID
         *
         * @param int $id The page_id of the article
         * @return Title|null An object representing the article, or null if no such article was found
         */
        public static function nameOf( $id ) {
                $dbr = wfGetDB( DB_REPLICA );

                $s = $dbr->selectRow(
                        'page',
                        [ 'page_namespace', 'page_title' ],
                        [ 'page_id' => $id ],
                        __METHOD__
                );
                if ( $s === false ) {
                        return null;
                }

                $n = self::makeName( $s->page_namespace, $s->page_title );
                return $n;
        }

        /**
         * Get a regex character class describing the legal characters in a link
         *
         * @return string The list of characters, not delimited
         */
        public static function legalChars() {
                global $wgLegalTitleChars;
                return $wgLegalTitleChars;
        }

        /**
         * Returns a simple regex that will match on characters and sequences invalid in titles.
         * Note that this doesn't pick up many things that could be wrong with titles, but that
         * replacing this regex with something valid will make many titles valid.
         *
         * @deprecated since 1.25, use MediaWikiTitleCodec::getTitleInvalidRegex() instead
         *
         * @return string Regex string
         */
        static function getTitleInvalidRegex() {
                wfDeprecated( __METHOD__, '1.25' );
                return MediaWikiTitleCodec::getTitleInvalidRegex();
        }

        /**
         * Utility method for converting a character sequence from bytes to Unicode.
         *
         * Primary usecase being converting $wgLegalTitleChars to a sequence usable in
         * javascript, as PHP uses UTF-8 bytes where javascript uses Unicode code units.
         *
         * @param string $byteClass
         * @return string
         */
        public static function convertByteClassToUnicodeClass( $byteClass ) {
                $length = strlen( $byteClass );
                // Input token queue
                $x0 = $x1 = $x2 = '';
                // Decoded queue
                $d0 = $d1 = $d2 = '';
                // Decoded integer codepoints
                $ord0 = $ord1 = $ord2 = 0;
                // Re-encoded queue
                $r0 = $r1 = $r2 = '';
                // Output
                $out = '';
                // Flags
                $allowUnicode = false;
                for ( $pos = 0; $pos < $length; $pos++ ) {
                        // Shift the queues down
                        $x2 = $x1;
                        $x1 = $x0;
                        $d2 = $d1;
                        $d1 = $d0;
                        $ord2 = $ord1;
                        $ord1 = $ord0;
                        $r2 = $r1;
                        $r1 = $r0;
                        // Load the current input token and decoded values
                        $inChar = $byteClass[$pos];
                        if ( $inChar == '\\' ) {
                                if ( preg_match( '/x([0-9a-fA-F]{2})/A', $byteClass, $m, 0, $pos + 1 ) ) {
                                        $x0 = $inChar . $m[0];
                                        $d0 = chr( hexdec( $m[1] ) );
                                        $pos += strlen( $m[0] );
                                } elseif ( preg_match( '/[0-7]{3}/A', $byteClass, $m, 0, $pos + 1 ) ) {
                                        $x0 = $inChar . $m[0];
                                        $d0 = chr( octdec( $m[0] ) );
                                        $pos += strlen( $m[0] );
                                } elseif ( $pos + 1 >= $length ) {
                                        $x0 = $d0 = '\\';
                                } else {
                                        $d0 = $byteClass[$pos + 1];
                                        $x0 = $inChar . $d0;
                                        $pos += 1;
                                }
                        } else {
                                $x0 = $d0 = $inChar;
                        }
                        $ord0 = ord( $d0 );
                        // Load the current re-encoded value
                        if ( $ord0 < 32 || $ord0 == 0x7f ) {
                                $r0 = sprintf( '\x%02x', $ord0 );
                        } elseif ( $ord0 >= 0x80 ) {
                                // Allow unicode if a single high-bit character appears
                                $r0 = sprintf( '\x%02x', $ord0 );
                                $allowUnicode = true;
                        } elseif ( strpos( '-\\[]^', $d0 ) !== false ) {
                                $r0 = '\\' . $d0;
                        } else {
                                $r0 = $d0;
                        }
                        // Do the output
                        if ( $x0 !== '' && $x1 === '-' && $x2 !== '' ) {
                                // Range
                                if ( $ord2 > $ord0 ) {
                                        // Empty range
                                } elseif ( $ord0 >= 0x80 ) {
                                        // Unicode range
                                        $allowUnicode = true;
                                        if ( $ord2 < 0x80 ) {
                                                // Keep the non-unicode section of the range
                                                $out .= "$r2-\\x7F";
                                        }
                                } else {
                                        // Normal range
                                        $out .= "$r2-$r0";
                                }
                                // Reset state to the initial value
                                $x0 = $x1 = $d0 = $d1 = $r0 = $r1 = '';
                        } elseif ( $ord2 < 0x80 ) {
                                // ASCII character
                                $out .= $r2;
                        }
                }
                if ( $ord1 < 0x80 ) {
                        $out .= $r1;
                }
                if ( $ord0 < 0x80 ) {
                        $out .= $r0;
                }
                if ( $allowUnicode ) {
                        $out .= '\u0080-\uFFFF';
                }
                return $out;
        }

        /**
         * Make a prefixed DB key from a DB key and a namespace index
         *
         * @param int $ns Numerical representation of the namespace
         * @param string $title The DB key form the title
         * @param string $fragment The link fragment (after the "#")
         * @param string $interwiki The interwiki prefix
         * @param bool $canonicalNamespace If true, use the canonical name for
         *   $ns instead of the localized version.
         * @return string The prefixed form of the title
         */
        public static function makeName( $ns, $title, $fragment = '', $interwiki = '',
                $canonicalNamespace = false
        ) {
                global $wgContLang;

                if ( $canonicalNamespace ) {
                        $namespace = MWNamespace::getCanonicalName( $ns );
                } else {
                        $namespace = $wgContLang->getNsText( $ns );
                }
                $name = $namespace == '' ? $title : "$namespace:$title";
                if ( strval( $interwiki ) != '' ) {
                        $name = "$interwiki:$name";
                }
                if ( strval( $fragment ) != '' ) {
                        $name .= '#' . $fragment;
                }
                return $name;
        }

        /**
         * Escape a text fragment, say from a link, for a URL
         *
         * @param string $fragment Containing a URL or link fragment (after the "#")
         * @return string Escaped string
         */
        static function escapeFragmentForURL( $fragment ) {
                # Note that we don't urlencode the fragment.  urlencoded Unicode
                # fragments appear not to work in IE (at least up to 7) or in at least
                # one version of Opera 9.x.  The W3C validator, for one, doesn't seem
                # to care if they aren't encoded.
                return Sanitizer::escapeId( $fragment, 'noninitial' );
        }

        /**
         * Callback for usort() to do title sorts by (namespace, title)
         *
         * @param LinkTarget $a
         * @param LinkTarget $b
         *
         * @return int Result of string comparison, or namespace comparison
         */
        public static function compare( LinkTarget $a, LinkTarget $b ) {
                if ( $a->getNamespace() == $b->getNamespace() ) {
                        return strcmp( $a->getText(), $b->getText() );
                } else {
                        return $a->getNamespace() - $b->getNamespace();
                }
        }

        /**
         * Determine whether the object refers to a page within
         * this project (either this wiki or a wiki with a local
         * interwiki, see https://www.mediawiki.org/wiki/Manual:Interwiki_table#iw_local )
         *
         * @return bool True if this is an in-project interwiki link or a wikilink, false otherwise
         */
        public function isLocal() {
                if ( $this->isExternal() ) {
                        $iw = self::getInterwikiLookup()->fetch( $this->mInterwiki );
                        if ( $iw ) {
                                return $iw->isLocal();
                        }
                }
                return true;
        }

        /**
         * Is this Title interwiki?
         *
         * @return bool
         */
        public function isExternal() {
                return $this->mInterwiki !== '';
        }

        /**
         * Get the interwiki prefix
         *
         * Use Title::isExternal to check if a interwiki is set
         *
         * @return string Interwiki prefix
         */
        public function getInterwiki() {
                return $this->mInterwiki;
        }

        /**
         * Was this a local interwiki link?
         *
         * @return bool
         */
        public function wasLocalInterwiki() {
                return $this->mLocalInterwiki;
        }

        /**
         * Determine whether the object refers to a page within
         * this project and is transcludable.
         *
         * @return bool True if this is transcludable
         */
        public function isTrans() {
                if ( !$this->isExternal() ) {
                        return false;
                }

                return self::getInterwikiLookup()->fetch( $this->mInterwiki )->isTranscludable();
        }

        /**
         * Returns the DB name of the distant wiki which owns the object.
         *
         * @return string|false The DB name
         */
        public function getTransWikiID() {
                if ( !$this->isExternal() ) {
                        return false;
                }

                return self::getInterwikiLookup()->fetch( $this->mInterwiki )->getWikiID();
        }

        /**
         * Get a TitleValue object representing this Title.
         *
         * @note Not all valid Titles have a corresponding valid TitleValue
         * (e.g. TitleValues cannot represent page-local links that have a
         * fragment but no title text).
         *
         * @return TitleValue|null
         */
        public function getTitleValue() {
                if ( $this->mTitleValue === null ) {
                        try {
                                $this->mTitleValue = new TitleValue(
                                        $this->getNamespace(),
                                        $this->getDBkey(),
                                        $this->getFragment(),
                                        $this->getInterwiki()
                                );
                        } catch ( InvalidArgumentException $ex ) {
                                wfDebug( __METHOD__ . ': Can\'t create a TitleValue for [[' .
                                        $this->getPrefixedText() . ']]: ' . $ex->getMessage() . "\n" );
                        }
                }

                return $this->mTitleValue;
        }

        /**
         * Get the text form (spaces not underscores) of the main part
         *
         * @return string Main part of the title
         */
        public function getText() {
                return $this->mTextform;
        }

        /**
         * Get the URL-encoded form of the main part
         *
         * @return string Main part of the title, URL-encoded
         */
        public function getPartialURL() {
                return $this->mUrlform;
        }

        /**
         * Get the main part with underscores
         *
         * @return string Main part of the title, with underscores
         */
        public function getDBkey() {
                return $this->mDbkeyform;
        }

        /**
         * Get the DB key with the initial letter case as specified by the user
         *
         * @return string DB key
         */
        function getUserCaseDBKey() {
                if ( !is_null( $this->mUserCaseDBKey ) ) {
                        return $this->mUserCaseDBKey;
                } else {
                        // If created via makeTitle(), $this->mUserCaseDBKey is not set.
                        return $this->mDbkeyform;
                }
        }

        /**
         * Get the namespace index, i.e. one of the NS_xxxx constants.
         *
         * @return int Namespace index
         */
        public function getNamespace() {
                return $this->mNamespace;
        }

        /**
         * Get the page's content model id, see the CONTENT_MODEL_XXX constants.
         *
         * @param int $flags A bit field; may be Title::GAID_FOR_UPDATE to select for update
         * @return string Content model id
         */
        public function getContentModel( $flags = 0 ) {
                if ( !$this->mForcedContentModel
                        && ( !$this->mContentModel || $flags === Title::GAID_FOR_UPDATE )
                        && $this->getArticleID( $flags )
                ) {
                        $linkCache = LinkCache::singleton();
                        $linkCache->addLinkObj( $this ); # in case we already had an article ID
                        $this->mContentModel = $linkCache->getGoodLinkFieldObj( $this, 'model' );
                }

                if ( !$this->mContentModel ) {
                        $this->mContentModel = ContentHandler::getDefaultModelFor( $this );
                }

                return $this->mContentModel;
        }

        /**
         * Convenience method for checking a title's content model name
         *
         * @param string $id The content model ID (use the CONTENT_MODEL_XXX constants).
         * @return bool True if $this->getContentModel() == $id
         */
        public function hasContentModel( $id ) {
                return $this->getContentModel() == $id;
        }

        /**
         * Set a proposed content model for the page for permissions
         * checking. This does not actually change the content model
         * of a title!
         *
         * Additionally, you should make sure you've checked
         * ContentHandler::canBeUsedOn() first.
         *
         * @since 1.28
         * @param string $model CONTENT_MODEL_XXX constant
         */
        public function setContentModel( $model ) {
                $this->mContentModel = $model;
                $this->mForcedContentModel = true;
        }

        /**
         * Get the namespace text
         *
         * @return string|false Namespace text
         */
        public function getNsText() {
                if ( $this->isExternal() ) {
                        // This probably shouldn't even happen,
                        // but for interwiki transclusion it sometimes does.
                        // Use the canonical namespaces if possible to try to
                        // resolve a foreign namespace.
                        if ( MWNamespace::exists( $this->mNamespace ) ) {
                                return MWNamespace::getCanonicalName( $this->mNamespace );
                        }
                }

                try {
                        $formatter = self::getTitleFormatter();
                        return $formatter->getNamespaceName( $this->mNamespace, $this->mDbkeyform );
                } catch ( InvalidArgumentException $ex ) {
                        wfDebug( __METHOD__ . ': ' . $ex->getMessage() . "\n" );
                        return false;
                }
        }

        /**
         * Get the namespace text of the subject (rather than talk) page
         *
         * @return string Namespace text
         */
        public function getSubjectNsText() {
                global $wgContLang;
                return $wgContLang->getNsText( MWNamespace::getSubject( $this->mNamespace ) );
        }

        /**
         * Get the namespace text of the talk page
         *
         * @return string Namespace text
         */
        public function getTalkNsText() {
                global $wgContLang;
                return $wgContLang->getNsText( MWNamespace::getTalk( $this->mNamespace ) );
        }

        /**
         * Could this title have a corresponding talk page?
         *
         * @return bool
         */
        public function canTalk() {
                return MWNamespace::canTalk( $this->mNamespace );
        }

        /**
         * Is this in a namespace that allows actual pages?
         *
         * @return bool
         */
        public function canExist() {
                return $this->mNamespace >= NS_MAIN;
        }

        /**
         * Can this title be added to a user's watchlist?
         *
         * @return bool
         */
        public function isWatchable() {
                return !$this->isExternal() && MWNamespace::isWatchable( $this->getNamespace() );
        }

        /**
         * Returns true if this is a special page.
         *
         * @return bool
         */
        public function isSpecialPage() {
                return $this->getNamespace() == NS_SPECIAL;
        }

        /**
         * Returns true if this title resolves to the named special page
         *
         * @param string $name The special page name
         * @return bool
         */
        public function isSpecial( $name ) {
                if ( $this->isSpecialPage() ) {
                        list( $thisName, /* $subpage */ ) = SpecialPageFactory::resolveAlias( $this->getDBkey() );
                        if ( $name == $thisName ) {
                                return true;
                        }
                }
                return false;
        }

        /**
         * If the Title refers to a special page alias which is not the local default, resolve
         * the alias, and localise the name as necessary.  Otherwise, return $this
         *
         * @return Title
         */
        public function fixSpecialName() {
                if ( $this->isSpecialPage() ) {
                        list( $canonicalName, $par ) = SpecialPageFactory::resolveAlias( $this->mDbkeyform );
                        if ( $canonicalName ) {
                                $localName = SpecialPageFactory::getLocalNameFor( $canonicalName, $par );
                                if ( $localName != $this->mDbkeyform ) {
                                        return Title::makeTitle( NS_SPECIAL, $localName );
                                }
                        }
                }
                return $this;
        }

        /**
         * Returns true if the title is inside the specified namespace.
         *
         * Please make use of this instead of comparing to getNamespace()
         * This function is much more resistant to changes we may make
         * to namespaces than code that makes direct comparisons.
         * @param int $ns The namespace
         * @return bool
         * @since 1.19
         */
        public function inNamespace( $ns ) {
                return MWNamespace::equals( $this->getNamespace(), $ns );
        }

        /**
         * Returns true if the title is inside one of the specified namespaces.
         *
         * @param int|int[] $namespaces,... The namespaces to check for
         * @return bool
         * @since 1.19
         */
        public function inNamespaces( /* ... */ ) {
                $namespaces = func_get_args();
                if ( count( $namespaces ) > 0 && is_array( $namespaces[0] ) ) {
                        $namespaces = $namespaces[0];
                }

                foreach ( $namespaces as $ns ) {
                        if ( $this->inNamespace( $ns ) ) {
                                return true;
                        }
                }

                return false;
        }

        /**
         * Returns true if the title has the same subject namespace as the
         * namespace specified.
         * For example this method will take NS_USER and return true if namespace
         * is either NS_USER or NS_USER_TALK since both of them have NS_USER
         * as their subject namespace.
         *
         * This is MUCH simpler than individually testing for equivalence
         * against both NS_USER and NS_USER_TALK, and is also forward compatible.
         * @since 1.19
         * @param int $ns
         * @return bool
         */
        public function hasSubjectNamespace( $ns ) {
                return MWNamespace::subjectEquals( $this->getNamespace(), $ns );
        }

        /**
         * Is this Title in a namespace which contains content?
         * In other words, is this a content page, for the purposes of calculating
         * statistics, etc?
         *
         * @return bool
         */
        public function isContentPage() {
                return MWNamespace::isContent( $this->getNamespace() );
        }

        /**
         * Would anybody with sufficient privileges be able to move this page?
         * Some pages just aren't movable.
         *
         * @return bool
         */
        public function isMovable() {
                if ( !MWNamespace::isMovable( $this->getNamespace() ) || $this->isExternal() ) {
                        // Interwiki title or immovable namespace. Hooks don't get to override here
                        return false;
                }

                $result = true;
                Hooks::run( 'TitleIsMovable', [ $this, &$result ] );
                return $result;
        }

        /**
         * Is this the mainpage?
         * @note Title::newFromText seems to be sufficiently optimized by the title
         * cache that we don't need to over-optimize by doing direct comparisons and
         * accidentally creating new bugs where $title->equals( Title::newFromText() )
         * ends up reporting something differently than $title->isMainPage();
         *
         * @since 1.18
         * @return bool
         */
        public function isMainPage() {
                return $this->equals( Title::newMainPage() );
        }

        /**
         * Is this a subpage?
         *
         * @return bool
         */
        public function isSubpage() {
                return MWNamespace::hasSubpages( $this->mNamespace )
                        ? strpos( $this->getText(), '/' ) !== false
                        : false;
        }

        /**
         * Is this a conversion table for the LanguageConverter?
         *
         * @return bool
         */
        public function isConversionTable() {
                // @todo ConversionTable should become a separate content model.

                return $this->getNamespace() == NS_MEDIAWIKI &&
                        strpos( $this->getText(), 'Conversiontable/' ) === 0;
        }

        /**
         * Does that page contain wikitext, or it is JS, CSS or whatever?
         *
         * @return bool
         */
        public function isWikitextPage() {
                return $this->hasContentModel( CONTENT_MODEL_WIKITEXT );
        }

        /**
         * Could this page contain custom CSS or JavaScript for the global UI.
         * This is generally true for pages in the MediaWiki namespace having CONTENT_MODEL_CSS
         * or CONTENT_MODEL_JAVASCRIPT.
         *
         * This method does *not* return true for per-user JS/CSS. Use isCssJsSubpage()
         * for that!
         *
         * Note that this method should not return true for pages that contain and
         * show "inactive" CSS or JS.
         *
         * @return bool
         * @todo FIXME: Rename to isSiteConfigPage() and remove deprecated hook
         */
        public function isCssOrJsPage() {
                $isCssOrJsPage = NS_MEDIAWIKI == $this->mNamespace
                        && ( $this->hasContentModel( CONTENT_MODEL_CSS )
                                || $this->hasContentModel( CONTENT_MODEL_JAVASCRIPT ) );

                return $isCssOrJsPage;
        }

        /**
         * Is this a .css or .js subpage of a user page?
         * @return bool
         * @todo FIXME: Rename to isUserConfigPage()
         */
        public function isCssJsSubpage() {
                return ( NS_USER == $this->mNamespace && $this->isSubpage()
                                && ( $this->hasContentModel( CONTENT_MODEL_CSS )
                                        || $this->hasContentModel( CONTENT_MODEL_JAVASCRIPT ) ) );
        }

        /**
         * Trim down a .css or .js subpage title to get the corresponding skin name
         *
         * @return string Containing skin name from .css or .js subpage title
         */
        public function getSkinFromCssJsSubpage() {
                $subpage = explode( '/', $this->mTextform );
                $subpage = $subpage[count( $subpage ) - 1];
                $lastdot = strrpos( $subpage, '.' );
                if ( $lastdot === false ) {
                        return $subpage; # Never happens: only called for names ending in '.css' or '.js'
                }
                return substr( $subpage, 0, $lastdot );
        }

        /**
         * Is this a .css subpage of a user page?
         *
         * @return bool
         */
        public function isCssSubpage() {
                return ( NS_USER == $this->mNamespace && $this->isSubpage()
                        && $this->hasContentModel( CONTENT_MODEL_CSS ) );
        }

        /**
         * Is this a .js subpage of a user page?
         *
         * @return bool
         */
        public function isJsSubpage() {
                return ( NS_USER == $this->mNamespace && $this->isSubpage()
                        && $this->hasContentModel( CONTENT_MODEL_JAVASCRIPT ) );
        }

        /**
         * Is this a talk page of some sort?
         *
         * @return bool
         */
        public function isTalkPage() {
                return MWNamespace::isTalk( $this->getNamespace() );
        }

        /**
         * Get a Title object associated with the talk page of this article
         *
         * @return Title The object for the talk page
         */
        public function getTalkPage() {
                return Title::makeTitle( MWNamespace::getTalk( $this->getNamespace() ), $this->getDBkey() );
        }

        /**
         * Get a title object associated with the subject page of this
         * talk page
         *
         * @return Title The object for the subject page
         */
        public function getSubjectPage() {
                // Is this the same title?
                $subjectNS = MWNamespace::getSubject( $this->getNamespace() );
                if ( $this->getNamespace() == $subjectNS ) {
                        return $this;
                }
                return Title::makeTitle( $subjectNS, $this->getDBkey() );
        }

        /**
         * Get the other title for this page, if this is a subject page
         * get the talk page, if it is a subject page get the talk page
         *
         * @since 1.25
         * @throws MWException
         * @return Title
         */
        public function getOtherPage() {
                if ( $this->isSpecialPage() ) {
                        throw new MWException( 'Special pages cannot have other pages' );
                }
                if ( $this->isTalkPage() ) {
                        return $this->getSubjectPage();
                } else {
                        return $this->getTalkPage();
                }
        }

        /**
         * Get the default namespace index, for when there is no namespace
         *
         * @return int Default namespace index
         */
        public function getDefaultNamespace() {
                return $this->mDefaultNamespace;
        }

        /**
         * Get the Title fragment (i.e.\ the bit after the #) in text form
         *
         * Use Title::hasFragment to check for a fragment
         *
         * @return string Title fragment
         */
        public function getFragment() {
                return $this->mFragment;
        }

        /**
         * Check if a Title fragment is set
         *
         * @return bool
         * @since 1.23
         */
        public function hasFragment() {
                return $this->mFragment !== '';
        }

        /**
         * Get the fragment in URL form, including the "#" character if there is one
         * @return string Fragment in URL form
         */
        public function getFragmentForURL() {
                if ( !$this->hasFragment() ) {
                        return '';
                } else {
                        return '#' . Title::escapeFragmentForURL( $this->getFragment() );
                }
        }

        /**
         * Set the fragment for this title. Removes the first character from the
         * specified fragment before setting, so it assumes you're passing it with
         * an initial "#".
         *
         * Deprecated for public use, use Title::makeTitle() with fragment parameter,
         * or Title::createFragmentTarget().
         * Still in active use privately.
         *
         * @private
         * @param string $fragment Text
         */
        public function setFragment( $fragment ) {
                $this->mFragment = strtr( substr( $fragment, 1 ), '_', ' ' );
        }

        /**
         * Creates a new Title for a different fragment of the same page.
         *
         * @since 1.27
         * @param string $fragment
         * @return Title
         */
        public function createFragmentTarget( $fragment ) {
                return self::makeTitle(
                        $this->getNamespace(),
                        $this->getText(),
                        $fragment,
                        $this->getInterwiki()
                );
        }

        /**
         * Prefix some arbitrary text with the namespace or interwiki prefix
         * of this object
         *
         * @param string $name The text
         * @return string The prefixed text
         */
        private function prefix( $name ) {
                $p = '';
                if ( $this->isExternal() ) {
                        $p = $this->mInterwiki . ':';
                }

                if ( 0 != $this->mNamespace ) {
                        $p .= $this->getNsText() . ':';
                }
                return $p . $name;
        }

        /**
         * Get the prefixed database key form
         *
         * @return string The prefixed title, with underscores and
         *  any interwiki and namespace prefixes
         */
        public function getPrefixedDBkey() {
                $s = $this->prefix( $this->mDbkeyform );
                $s = strtr( $s, ' ', '_' );
                return $s;
        }

        /**
         * Get the prefixed title with spaces.
         * This is the form usually used for display
         *
         * @return string The prefixed title, with spaces
         */
        public function getPrefixedText() {
                if ( $this->mPrefixedText === null ) {
                        $s = $this->prefix( $this->mTextform );
                        $s = strtr( $s, '_', ' ' );
                        $this->mPrefixedText = $s;
                }
                return $this->mPrefixedText;
        }

        /**
         * Return a string representation of this title
         *
         * @return string Representation of this title
         */
        public function __toString() {
                return $this->getPrefixedText();
        }

        /**
         * Get the prefixed title with spaces, plus any fragment
         * (part beginning with '#')
         *
         * @return string The prefixed title, with spaces and the fragment, including '#'
         */
        public function getFullText() {
                $text = $this->getPrefixedText();
                if ( $this->hasFragment() ) {
                        $text .= '#' . $this->getFragment();
                }
                return $text;
        }

        /**
         * Get the root page name text without a namespace, i.e. the leftmost part before any slashes
         *
         * @par Example:
         * @code
         * Title::newFromText('User:Foo/Bar/Baz')->getRootText();
         * # returns: 'Foo'
         * @endcode
         *
         * @return string Root name
         * @since 1.20
         */
        public function getRootText() {
                if ( !MWNamespace::hasSubpages( $this->mNamespace ) ) {
                        return $this->getText();
                }

                return strtok( $this->getText(), '/' );
        }

        /**
         * Get the root page name title, i.e. the leftmost part before any slashes
         *
         * @par Example:
         * @code
         * Title::newFromText('User:Foo/Bar/Baz')->getRootTitle();
         * # returns: Title{User:Foo}
         * @endcode
         *
         * @return Title Root title
         * @since 1.20
         */
        public function getRootTitle() {
                return Title::makeTitle( $this->getNamespace(), $this->getRootText() );
        }

        /**
         * Get the base page name without a namespace, i.e. the part before the subpage name
         *
         * @par Example:
         * @code
         * Title::newFromText('User:Foo/Bar/Baz')->getBaseText();
         * # returns: 'Foo/Bar'
         * @endcode
         *
         * @return string Base name
         */
        public function getBaseText() {
                if ( !MWNamespace::hasSubpages( $this->mNamespace ) ) {
                        return $this->getText();
                }

                $parts = explode( '/', $this->getText() );
                # Don't discard the real title if there's no subpage involved
                if ( count( $parts ) > 1 ) {
                        unset( $parts[count( $parts ) - 1] );
                }
                return implode( '/', $parts );
        }

        /**
         * Get the base page name title, i.e. the part before the subpage name
         *
         * @par Example:
         * @code
         * Title::newFromText('User:Foo/Bar/Baz')->getBaseTitle();
         * # returns: Title{User:Foo/Bar}
         * @endcode
         *
         * @return Title Base title
         * @since 1.20
         */
        public function getBaseTitle() {
                return Title::makeTitle( $this->getNamespace(), $this->getBaseText() );
        }

        /**
         * Get the lowest-level subpage name, i.e. the rightmost part after any slashes
         *
         * @par Example:
         * @code
         * Title::newFromText('User:Foo/Bar/Baz')->getSubpageText();
         * # returns: "Baz"
         * @endcode
         *
         * @return string Subpage name
         */
        public function getSubpageText() {
                if ( !MWNamespace::hasSubpages( $this->mNamespace ) ) {
                        return $this->mTextform;
                }
                $parts = explode( '/', $this->mTextform );
                return $parts[count( $parts ) - 1];
        }

        /**
         * Get the title for a subpage of the current page
         *
         * @par Example:
         * @code
         * Title::newFromText('User:Foo/Bar/Baz')->getSubpage("Asdf");
         * # returns: Title{User:Foo/Bar/Baz/Asdf}
         * @endcode
         *
         * @param string $text The subpage name to add to the title
         * @return Title Subpage title
         * @since 1.20
         */
        public function getSubpage( $text ) {
                return Title::makeTitleSafe( $this->getNamespace(), $this->getText() . '/' . $text );
        }

        /**
         * Get a URL-encoded form of the subpage text
         *
         * @return string URL-encoded subpage name
         */
        public function getSubpageUrlForm() {
                $text = $this->getSubpageText();
                $text = wfUrlencode( strtr( $text, ' ', '_' ) );
                return $text;
        }

        /**
         * Get a URL-encoded title (not an actual URL) including interwiki
         *
         * @return string The URL-encoded form
         */
        public function getPrefixedURL() {
                $s = $this->prefix( $this->mDbkeyform );
                $s = wfUrlencode( strtr( $s, ' ', '_' ) );
                return $s;
        }

        /**
         * Helper to fix up the get{Canonical,Full,Link,Local,Internal}URL args
         * get{Canonical,Full,Link,Local,Internal}URL methods accepted an optional
         * second argument named variant. This was deprecated in favor
         * of passing an array of option with a "variant" key
         * Once $query2 is removed for good, this helper can be dropped
         * and the wfArrayToCgi moved to getLocalURL();
         *
         * @since 1.19 (r105919)
         * @param array|string $query
         * @param string|string[]|bool $query2
         * @return string
         */
        private static function fixUrlQueryArgs( $query, $query2 = false ) {
                if ( $query2 !== false ) {
                        wfDeprecated( "Title::get{Canonical,Full,Link,Local,Internal}URL " .
                                "method called with a second parameter is deprecated. Add your " .
                                "parameter to an array passed as the first parameter.", "1.19" );
                }
                if ( is_array( $query ) ) {
                        $query = wfArrayToCgi( $query );
                }
                if ( $query2 ) {
                        if ( is_string( $query2 ) ) {
                                // $query2 is a string, we will consider this to be
                                // a deprecated $variant argument and add it to the query
                                $query2 = wfArrayToCgi( [ 'variant' => $query2 ] );
                        } else {
                                $query2 = wfArrayToCgi( $query2 );
                        }
                        // If we have $query content add a & to it first
                        if ( $query ) {
                                $query .= '&';
                        }
                        // Now append the queries together
                        $query .= $query2;
                }
                return $query;
        }

        /**
         * Get a real URL referring to this title, with interwiki link and
         * fragment
         *
         * @see self::getLocalURL for the arguments.
         * @see wfExpandUrl
         * @param string|string[] $query
         * @param string|string[]|bool $query2
         * @param string $proto Protocol type to use in URL
         * @return string The URL
         */
        public function getFullURL( $query = '', $query2 = false, $proto = PROTO_RELATIVE ) {
                $query = self::fixUrlQueryArgs( $query, $query2 );

                # Hand off all the decisions on urls to getLocalURL
                $url = $this->getLocalURL( $query );

                # Expand the url to make it a full url. Note that getLocalURL has the
                # potential to output full urls for a variety of reasons, so we use
                # wfExpandUrl instead of simply prepending $wgServer
                $url = wfExpandUrl( $url, $proto );

                # Finally, add the fragment.
                $url .= $this->getFragmentForURL();
                // Avoid PHP 7.1 warning from passing $this by reference
                $titleRef = $this;
                Hooks::run( 'GetFullURL', [ &$titleRef, &$url, $query ] );
                return $url;
        }

        /**
         * Get a URL with no fragment or server name (relative URL) from a Title object.
         * If this page is generated with action=render, however,
         * $wgServer is prepended to make an absolute URL.
         *
         * @see self::getFullURL to always get an absolute URL.
         * @see self::getLinkURL to always get a URL that's the simplest URL that will be
         *  valid to link, locally, to the current Title.
         * @see self::newFromText to produce a Title object.
         *
         * @param string|string[] $query An optional query string,
         *   not used for interwiki links. Can be specified as an associative array as well,
         *   e.g., array( 'action' => 'edit' ) (keys and values will be URL-escaped).
         *   Some query patterns will trigger various shorturl path replacements.
         * @param string|string[]|bool $query2 An optional secondary query array. This one MUST
         *   be an array. If a string is passed it will be interpreted as a deprecated
         *   variant argument and urlencoded into a variant= argument.
         *   This second query argument will be added to the $query
         *   The second parameter is deprecated since 1.19. Pass it as a key,value
         *   pair in the first parameter array instead.
         *
         * @return string String of the URL.
         */
        public function getLocalURL( $query = '', $query2 = false ) {
                global $wgArticlePath, $wgScript, $wgServer, $wgRequest;

                $query = self::fixUrlQueryArgs( $query, $query2 );

                $interwiki = self::getInterwikiLookup()->fetch( $this->mInterwiki );
                if ( $interwiki ) {
                        $namespace = $this->getNsText();
                        if ( $namespace != '' ) {
                                # Can this actually happen? Interwikis shouldn't be parsed.
                                # Yes! It can in interwiki transclusion. But... it probably shouldn't.
                                $namespace .= ':';
                        }
                        $url = $interwiki->getURL( $namespace . $this->getDBkey() );
                        $url = wfAppendQuery( $url, $query );
                } else {
                        $dbkey = wfUrlencode( $this->getPrefixedDBkey() );
                        if ( $query == '' ) {
                                $url = str_replace( '$1', $dbkey, $wgArticlePath );
                                // Avoid PHP 7.1 warning from passing $this by reference
                                $titleRef = $this;
                                Hooks::run( 'GetLocalURL::Article', [ &$titleRef, &$url ] );
                        } else {
                                global $wgVariantArticlePath, $wgActionPaths, $wgContLang;
                                $url = false;
                                $matches = [];

                                if ( !empty( $wgActionPaths )
                                        && preg_match( '/^(.*&|)action=([^&]*)(&(.*)|)$/', $query, $matches )
                                ) {
                                        $action = urldecode( $matches[2] );
                                        if ( isset( $wgActionPaths[$action] ) ) {
                                                $query = $matches[1];
                                                if ( isset( $matches[4] ) ) {
                                                        $query .= $matches[4];
                                                }
                                                $url = str_replace( '$1', $dbkey, $wgActionPaths[$action] );
                                                if ( $query != '' ) {
                                                        $url = wfAppendQuery( $url, $query );
                                                }
                                        }
                                }

                                if ( $url === false
                                        && $wgVariantArticlePath
                                        && preg_match( '/^variant=([^&]*)$/', $query, $matches )
                                        && $this->getPageLanguage()->equals( $wgContLang )
                                        && $this->getPageLanguage()->hasVariants()
                                ) {
                                        $variant = urldecode( $matches[1] );
                                        if ( $this->getPageLanguage()->hasVariant( $variant ) ) {
                                                // Only do the variant replacement if the given variant is a valid
                                                // variant for the page's language.
                                                $url = str_replace( '$2', urlencode( $variant ), $wgVariantArticlePath );
                                                $url = str_replace( '$1', $dbkey, $url );
                                        }
                                }

                                if ( $url === false ) {
                                        if ( $query == '-' ) {
                                                $query = '';
                                        }
                                        $url = "{$wgScript}?title={$dbkey}&{$query}";
                                }
                        }
                        // Avoid PHP 7.1 warning from passing $this by reference
                        $titleRef = $this;
                        Hooks::run( 'GetLocalURL::Internal', [ &$titleRef, &$url, $query ] );

                        // @todo FIXME: This causes breakage in various places when we
                        // actually expected a local URL and end up with dupe prefixes.
                        if ( $wgRequest->getVal( 'action' ) == 'render' ) {
                                $url = $wgServer . $url;
                        }
                }
                // Avoid PHP 7.1 warning from passing $this by reference
                $titleRef = $this;
                Hooks::run( 'GetLocalURL', [ &$titleRef, &$url, $query ] );
                return $url;
        }

        /**
         * Get a URL that's the simplest URL that will be valid to link, locally,
         * to the current Title.  It includes the fragment, but does not include
         * the server unless action=render is used (or the link is external).  If
         * there's a fragment but the prefixed text is empty, we just return a link
         * to the fragment.
         *
         * The result obviously should not be URL-escaped, but does need to be
         * HTML-escaped if it's being output in HTML.
         *
         * @param string|string[] $query
         * @param bool $query2
         * @param string|int|bool $proto A PROTO_* constant on how the URL should be expanded,
         *                               or false (default) for no expansion
         * @see self::getLocalURL for the arguments.
         * @return string The URL
         */
        public function getLinkURL( $query = '', $query2 = false, $proto = false ) {
                if ( $this->isExternal() || $proto !== false ) {
                        $ret = $this->getFullURL( $query, $query2, $proto );
                } elseif ( $this->getPrefixedText() === '' && $this->hasFragment() ) {
                        $ret = $this->getFragmentForURL();
                } else {
                        $ret = $this->getLocalURL( $query, $query2 ) . $this->getFragmentForURL();
                }
                return $ret;
        }

        /**
         * Get the URL form for an internal link.
         * - Used in various CDN-related code, in case we have a different
         * internal hostname for the server from the exposed one.
         *
         * This uses $wgInternalServer to qualify the path, or $wgServer
         * if $wgInternalServer is not set. If the server variable used is
         * protocol-relative, the URL will be expanded to http://
         *
         * @see self::getLocalURL for the arguments.
         * @return string The URL
         */
        public function getInternalURL( $query = '', $query2 = false ) {
                global $wgInternalServer, $wgServer;
                $query = self::fixUrlQueryArgs( $query, $query2 );
                $server = $wgInternalServer !== false ? $wgInternalServer : $wgServer;
                $url = wfExpandUrl( $server . $this->getLocalURL( $query ), PROTO_HTTP );
                // Avoid PHP 7.1 warning from passing $this by reference
                $titleRef = $this;
                Hooks::run( 'GetInternalURL', [ &$titleRef, &$url, $query ] );
                return $url;
        }

        /**
         * Get the URL for a canonical link, for use in things like IRC and
         * e-mail notifications. Uses $wgCanonicalServer and the
         * GetCanonicalURL hook.
         *
         * NOTE: Unlike getInternalURL(), the canonical URL includes the fragment
         *
         * @see self::getLocalURL for the arguments.
         * @return string The URL
         * @since 1.18
         */
        public function getCanonicalURL( $query = '', $query2 = false ) {
                $query = self::fixUrlQueryArgs( $query, $query2 );
                $url = wfExpandUrl( $this->getLocalURL( $query ) . $this->getFragmentForURL(), PROTO_CANONICAL );
                // Avoid PHP 7.1 warning from passing $this by reference
                $titleRef = $this;
                Hooks::run( 'GetCanonicalURL', [ &$titleRef, &$url, $query ] );
                return $url;
        }

        /**
         * Get the edit URL for this Title
         *
         * @return string The URL, or a null string if this is an interwiki link
         */
        public function getEditURL() {
                if ( $this->isExternal() ) {
                        return '';
                }
                $s = $this->getLocalURL( 'action=edit' );

                return $s;
        }

        /**
         * Can $user perform $action on this page?
         * This skips potentially expensive cascading permission checks
         * as well as avoids expensive error formatting
         *
         * Suitable for use for nonessential UI controls in common cases, but
         * _not_ for functional access control.
         *
         * May provide false positives, but should never provide a false negative.
         *
         * @param string $action Action that permission needs to be checked for
         * @param User $user User to check (since 1.19); $wgUser will be used if not provided.
         * @return bool
         */
        public function quickUserCan( $action, $user = null ) {
                return $this->userCan( $action, $user, false );
        }

        /**
         * Can $user perform $action on this page?
         *
         * @param string $action Action that permission needs to be checked for
         * @param User $user User to check (since 1.19); $wgUser will be used if not
         *   provided.
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @return bool
         */
        public function userCan( $action, $user = null, $rigor = 'secure' ) {
                if ( !$user instanceof User ) {
                        global $wgUser;
                        $user = $wgUser;
                }

                return !count( $this->getUserPermissionsErrorsInternal( $action, $user, $rigor, true ) );
        }

        /**
         * Can $user perform $action on this page?
         *
         * @todo FIXME: This *does not* check throttles (User::pingLimiter()).
         *
         * @param string $action Action that permission needs to be checked for
         * @param User $user User to check
         * @param string $rigor One of (quick,full,secure)
         *   - quick  : does cheap permission checks from replica DBs (usable for GUI creation)
         *   - full   : does cheap and expensive checks possibly from a replica DB
         *   - secure : does cheap and expensive checks, using the master as needed
         * @param array $ignoreErrors Array of Strings Set this to a list of message keys
         *   whose corresponding errors may be ignored.
         * @return array Array of arrays of the arguments to wfMessage to explain permissions problems.
         */
        public function getUserPermissionsErrors(
                $action, $user, $rigor = 'secure', $ignoreErrors = []
        ) {
                $errors = $this->getUserPermissionsErrorsInternal( $action, $user, $rigor );

                // Remove the errors being ignored.
                foreach ( $errors as $index => $error ) {
                        $errKey = is_array( $error ) ? $error[0] : $error;

                        if ( in_array( $errKey, $ignoreErrors ) ) {
                                unset( $errors[$index] );
                        }
                        if ( $errKey instanceof MessageSpecifier && in_array( $errKey->getKey(), $ignoreErrors ) ) {
                                unset( $errors[$index] );
                        }
                }

                return $errors;
        }

        /**
         * Permissions checks that fail most often, and which are easiest to test.
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkQuickPermissions( $action, $user, $errors, $rigor, $short ) {
                if ( !Hooks::run( 'TitleQuickPermissions',
                        [ $this, $user, $action, &$errors, ( $rigor !== 'quick' ), $short ] )
                ) {
                        return $errors;
                }

                if ( $action == 'create' ) {
                        if (
                                ( $this->isTalkPage() && !$user->isAllowed( 'createtalk' ) ) ||
                                ( !$this->isTalkPage() && !$user->isAllowed( 'createpage' ) )
                        ) {
                                $errors[] = $user->isAnon() ? [ 'nocreatetext' ] : [ 'nocreate-loggedin' ];
                        }
                } elseif ( $action == 'move' ) {
                        if ( !$user->isAllowed( 'move-rootuserpages' )
                                        && $this->mNamespace == NS_USER && !$this->isSubpage() ) {
                                // Show user page-specific message only if the user can move other pages
                                $errors[] = [ 'cant-move-user-page' ];
                        }

                        // Check if user is allowed to move files if it's a file
                        if ( $this->mNamespace == NS_FILE && !$user->isAllowed( 'movefile' ) ) {
                                $errors[] = [ 'movenotallowedfile' ];
                        }

                        // Check if user is allowed to move category pages if it's a category page
                        if ( $this->mNamespace == NS_CATEGORY && !$user->isAllowed( 'move-categorypages' ) ) {
                                $errors[] = [ 'cant-move-category-page' ];
                        }

                        if ( !$user->isAllowed( 'move' ) ) {
                                // User can't move anything
                                $userCanMove = User::groupHasPermission( 'user', 'move' );
                                $autoconfirmedCanMove = User::groupHasPermission( 'autoconfirmed', 'move' );
                                if ( $user->isAnon() && ( $userCanMove || $autoconfirmedCanMove ) ) {
                                        // custom message if logged-in users without any special rights can move
                                        $errors[] = [ 'movenologintext' ];
                                } else {
                                        $errors[] = [ 'movenotallowed' ];
                                }
                        }
                } elseif ( $action == 'move-target' ) {
                        if ( !$user->isAllowed( 'move' ) ) {
                                // User can't move anything
                                $errors[] = [ 'movenotallowed' ];
                        } elseif ( !$user->isAllowed( 'move-rootuserpages' )
                                        && $this->mNamespace == NS_USER && !$this->isSubpage() ) {
                                // Show user page-specific message only if the user can move other pages
                                $errors[] = [ 'cant-move-to-user-page' ];
                        } elseif ( !$user->isAllowed( 'move-categorypages' )
                                        && $this->mNamespace == NS_CATEGORY ) {
                                // Show category page-specific message only if the user can move other pages
                                $errors[] = [ 'cant-move-to-category-page' ];
                        }
                } elseif ( !$user->isAllowed( $action ) ) {
                        $errors[] = $this->missingPermissionError( $action, $short );
                }

                return $errors;
        }

        /**
         * Add the resulting error code to the errors array
         *
         * @param array $errors List of current errors
         * @param array $result Result of errors
         *
         * @return array List of errors
         */
        private function resultToError( $errors, $result ) {
                if ( is_array( $result ) && count( $result ) && !is_array( $result[0] ) ) {
                        // A single array representing an error
                        $errors[] = $result;
                } elseif ( is_array( $result ) && is_array( $result[0] ) ) {
                        // A nested array representing multiple errors
                        $errors = array_merge( $errors, $result );
                } elseif ( $result !== '' && is_string( $result ) ) {
                        // A string representing a message-id
                        $errors[] = [ $result ];
                } elseif ( $result instanceof MessageSpecifier ) {
                        // A message specifier representing an error
                        $errors[] = [ $result ];
                } elseif ( $result === false ) {
                        // a generic "We don't want them to do that"
                        $errors[] = [ 'badaccess-group0' ];
                }
                return $errors;
        }

        /**
         * Check various permission hooks
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkPermissionHooks( $action, $user, $errors, $rigor, $short ) {
                // Use getUserPermissionsErrors instead
                $result = '';
                // Avoid PHP 7.1 warning from passing $this by reference
                $titleRef = $this;
                if ( !Hooks::run( 'userCan', [ &$titleRef, &$user, $action, &$result ] ) ) {
                        return $result ? [] : [ [ 'badaccess-group0' ] ];
                }
                // Check getUserPermissionsErrors hook
                // Avoid PHP 7.1 warning from passing $this by reference
                $titleRef = $this;
                if ( !Hooks::run( 'getUserPermissionsErrors', [ &$titleRef, &$user, $action, &$result ] ) ) {
                        $errors = $this->resultToError( $errors, $result );
                }
                // Check getUserPermissionsErrorsExpensive hook
                if (
                        $rigor !== 'quick'
                        && !( $short && count( $errors ) > 0 )
                        && !Hooks::run( 'getUserPermissionsErrorsExpensive', [ &$titleRef, &$user, $action, &$result ] )
                ) {
                        $errors = $this->resultToError( $errors, $result );
                }

                return $errors;
        }

        /**
         * Check permissions on special pages & namespaces
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkSpecialsAndNSPermissions( $action, $user, $errors, $rigor, $short ) {
                # Only 'createaccount' can be performed on special pages,
                # which don't actually exist in the DB.
                if ( NS_SPECIAL == $this->mNamespace && $action !== 'createaccount' ) {
                        $errors[] = [ 'ns-specialprotected' ];
                }

                # Check $wgNamespaceProtection for restricted namespaces
                if ( $this->isNamespaceProtected( $user ) ) {
                        $ns = $this->mNamespace == NS_MAIN ?
                                wfMessage( 'nstab-main' )->text() : $this->getNsText();
                        $errors[] = $this->mNamespace == NS_MEDIAWIKI ?
                                [ 'protectedinterface', $action ] : [ 'namespaceprotected', $ns, $action ];
                }

                return $errors;
        }

        /**
         * Check CSS/JS sub-page permissions
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkCSSandJSPermissions( $action, $user, $errors, $rigor, $short ) {
                # Protect css/js subpages of user pages
                # XXX: this might be better using restrictions
                # XXX: right 'editusercssjs' is deprecated, for backward compatibility only
                if ( $action != 'patrol' && !$user->isAllowed( 'editusercssjs' ) ) {
                        if ( preg_match( '/^' . preg_quote( $user->getName(), '/' ) . '\//', $this->mTextform ) ) {
                                if ( $this->isCssSubpage() && !$user->isAllowedAny( 'editmyusercss', 'editusercss' ) ) {
                                        $errors[] = [ 'mycustomcssprotected', $action ];
                                } elseif ( $this->isJsSubpage() && !$user->isAllowedAny( 'editmyuserjs', 'edituserjs' ) ) {
                                        $errors[] = [ 'mycustomjsprotected', $action ];
                                }
                        } else {
                                if ( $this->isCssSubpage() && !$user->isAllowed( 'editusercss' ) ) {
                                        $errors[] = [ 'customcssprotected', $action ];
                                } elseif ( $this->isJsSubpage() && !$user->isAllowed( 'edituserjs' ) ) {
                                        $errors[] = [ 'customjsprotected', $action ];
                                }
                        }
                }

                return $errors;
        }

        /**
         * Check against page_restrictions table requirements on this
         * page. The user must possess all required rights for this
         * action.
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkPageRestrictions( $action, $user, $errors, $rigor, $short ) {
                foreach ( $this->getRestrictions( $action ) as $right ) {
                        // Backwards compatibility, rewrite sysop -> editprotected
                        if ( $right == 'sysop' ) {
                                $right = 'editprotected';
                        }
                        // Backwards compatibility, rewrite autoconfirmed -> editsemiprotected
                        if ( $right == 'autoconfirmed' ) {
                                $right = 'editsemiprotected';
                        }
                        if ( $right == '' ) {
                                continue;
                        }
                        if ( !$user->isAllowed( $right ) ) {
                                $errors[] = [ 'protectedpagetext', $right, $action ];
                        } elseif ( $this->mCascadeRestriction && !$user->isAllowed( 'protect' ) ) {
                                $errors[] = [ 'protectedpagetext', 'protect', $action ];
                        }
                }

                return $errors;
        }

        /**
         * Check restrictions on cascading pages.
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkCascadingSourcesRestrictions( $action, $user, $errors, $rigor, $short ) {
                if ( $rigor !== 'quick' && !$this->isCssJsSubpage() ) {
                        # We /could/ use the protection level on the source page, but it's
                        # fairly ugly as we have to establish a precedence hierarchy for pages
                        # included by multiple cascade-protected pages. So just restrict
                        # it to people with 'protect' permission, as they could remove the
                        # protection anyway.
                        list( $cascadingSources, $restrictions ) = $this->getCascadeProtectionSources();
                        # Cascading protection depends on more than this page...
                        # Several cascading protected pages may include this page...
                        # Check each cascading level
                        # This is only for protection restrictions, not for all actions
                        if ( isset( $restrictions[$action] ) ) {
                                foreach ( $restrictions[$action] as $right ) {
                                        // Backwards compatibility, rewrite sysop -> editprotected
                                        if ( $right == 'sysop' ) {
                                                $right = 'editprotected';
                                        }
                                        // Backwards compatibility, rewrite autoconfirmed -> editsemiprotected
                                        if ( $right == 'autoconfirmed' ) {
                                                $right = 'editsemiprotected';
                                        }
                                        if ( $right != '' && !$user->isAllowedAll( 'protect', $right ) ) {
                                                $pages = '';
                                                foreach ( $cascadingSources as $page ) {
                                                        $pages .= '* [[:' . $page->getPrefixedText() . "]]\n";
                                                }
                                                $errors[] = [ 'cascadeprotected', count( $cascadingSources ), $pages, $action ];
                                        }
                                }
                        }
                }

                return $errors;
        }

        /**
         * Check action permissions not already checked in checkQuickPermissions
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkActionPermissions( $action, $user, $errors, $rigor, $short ) {
                global $wgDeleteRevisionsLimit, $wgLang;

                if ( $action == 'protect' ) {
                        if ( count( $this->getUserPermissionsErrorsInternal( 'edit', $user, $rigor, true ) ) ) {
                                // If they can't edit, they shouldn't protect.
                                $errors[] = [ 'protect-cantedit' ];
                        }
                } elseif ( $action == 'create' ) {
                        $title_protection = $this->getTitleProtection();
                        if ( $title_protection ) {
                                if ( $title_protection['permission'] == ''
                                        || !$user->isAllowed( $title_protection['permission'] )
                                ) {
                                        $errors[] = [
                                                'titleprotected',
                                                User::whoIs( $title_protection['user'] ),
                                                $title_protection['reason']
                                        ];
                                }
                        }
                } elseif ( $action == 'move' ) {
                        // Check for immobile pages
                        if ( !MWNamespace::isMovable( $this->mNamespace ) ) {
                                // Specific message for this case
                                $errors[] = [ 'immobile-source-namespace', $this->getNsText() ];
                        } elseif ( !$this->isMovable() ) {
                                // Less specific message for rarer cases
                                $errors[] = [ 'immobile-source-page' ];
                        }
                } elseif ( $action == 'move-target' ) {
                        if ( !MWNamespace::isMovable( $this->mNamespace ) ) {
                                $errors[] = [ 'immobile-target-namespace', $this->getNsText() ];
                        } elseif ( !$this->isMovable() ) {
                                $errors[] = [ 'immobile-target-page' ];
                        }
                } elseif ( $action == 'delete' ) {
                        $tempErrors = $this->checkPageRestrictions( 'edit', $user, [], $rigor, true );
                        if ( !$tempErrors ) {
                                $tempErrors = $this->checkCascadingSourcesRestrictions( 'edit',
                                        $user, $tempErrors, $rigor, true );
                        }
                        if ( $tempErrors ) {
                                // If protection keeps them from editing, they shouldn't be able to delete.
                                $errors[] = [ 'deleteprotected' ];
                        }
                        if ( $rigor !== 'quick' && $wgDeleteRevisionsLimit
                                && !$this->userCan( 'bigdelete', $user ) && $this->isBigDeletion()
                        ) {
                                $errors[] = [ 'delete-toobig', $wgLang->formatNum( $wgDeleteRevisionsLimit ) ];
                        }
                }
                return $errors;
        }

        /**
         * Check that the user isn't blocked from editing.
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkUserBlock( $action, $user, $errors, $rigor, $short ) {
                global $wgEmailConfirmToEdit, $wgBlockDisablesLogin;
                // Account creation blocks handled at userlogin.
                // Unblocking handled in SpecialUnblock
                if ( $rigor === 'quick' || in_array( $action, [ 'createaccount', 'unblock' ] ) ) {
                        return $errors;
                }

                // Optimize for a very common case
                if ( $action === 'read' && !$wgBlockDisablesLogin ) {
                        return $errors;
                }

                if ( $wgEmailConfirmToEdit && !$user->isEmailConfirmed() ) {
                        $errors[] = [ 'confirmedittext' ];
                }

                $useSlave = ( $rigor !== 'secure' );
                if ( ( $action == 'edit' || $action == 'create' )
                        && !$user->isBlockedFrom( $this, $useSlave )
                ) {
                        // Don't block the user from editing their own talk page unless they've been
                        // explicitly blocked from that too.
                } elseif ( $user->isBlocked() && $user->getBlock()->prevents( $action ) !== false ) {
                        // @todo FIXME: Pass the relevant context into this function.
                        $errors[] = $user->getBlock()->getPermissionsError( RequestContext::getMain() );
                }

                return $errors;
        }

        /**
         * Check that the user is allowed to read this page.
         *
         * @param string $action The action to check
         * @param User $user User to check
         * @param array $errors List of current errors
         * @param string $rigor Same format as Title::getUserPermissionsErrors()
         * @param bool $short Short circuit on first error
         *
         * @return array List of errors
         */
        private function checkReadPermissions( $action, $user, $errors, $rigor, $short ) {
                global $wgWhitelistRead, $wgWhitelistReadRegexp;

                $whitelisted = false;
                if ( User::isEveryoneAllowed( 'read' ) ) {
                        # Shortcut for public wikis, allows skipping quite a bit of code
                        $whitelisted = true;
                } elseif ( $user->isAllowed( 'read' ) ) {
                        # If the user is allowed to read pages, he is allowed to read all pages
                        $whitelisted = true;
                } elseif ( $this->isSpecial( 'Userlogin' )
                        || $this->isSpecial( 'PasswordReset' )
                        || $this->isSpecial( 'Userlogout' )
                ) {
                        # Always grant access to the login page.
                        # Even anons need to be able to log in.
                        $whitelisted = true;
                } elseif ( is_array( $wgWhitelistRead ) && count( $wgWhitelistRead ) ) {
                        # Time to check the whitelist
                        # Only do these checks is there's something to check against
                        $name = $this->getPrefixedText();
                        $dbName = $this->getPrefixedDBkey();

                        // Check for explicit whitelisting with and without underscores
                        if ( in_array( $name, $wgWhitelistRead, true ) || in_array( $dbName, $wgWhitelistRead, true ) ) {
                                $whitelisted = true;
                        } elseif ( $this->getNamespace() == NS_MAIN ) {
                                # Old settings might have the title prefixed with
                                # a colon for main-namespace pages
                                if ( in_array( ':' . $name, $wgWhitelistRead ) ) {
                                        $whitelisted = true;
                                }
                        } elseif ( $this->isSpecialPage() ) {
                                # If it's a special page, ditch the subpage bit and check again
                                $name = $this->getDBkey();
                                list( $name, /* $subpage */ ) = SpecialPageFactory::resolveAlias( $name );
                                if ( $name ) {
                                        $pure = SpecialPage::getTitleFor( $name )->getPrefixedText();
                                        if ( in_array( $pure, $wgWhitelistRead, true ) ) {
                                                $whitelisted = true;
                                        }
                                }
                        }
                }

                if ( !$whitelisted && is_array( $wgWhitelistReadRegexp ) && !empty( $wgWhitelistReadRegexp ) ) {
                        $name = $this->getPrefixedText();
                        // Check for regex whitelisting
                        foreach ( $wgWhitelistReadRegexp as $listItem ) {
                                if ( preg_match( $listItem, $name ) ) {
                                        $whitelisted = true;
                                        break;
                                }
                        }
                }

                if ( !$whitelisted ) {
                        # If the title is not whitelisted, give extensions a chance to do so...
                        Hooks::run( 'TitleReadWhitelist', [ $this, $user, &$whitelisted ] );
                        if ( !$whitelisted ) {
                                $errors[] = $this->missingPermissionError( $action, $short );
                        }
                }

                return $errors;
        }

        /**
         * Get a description array when the user doesn't have the right to perform
         * $action (i.e. when User::isAllowed() returns false)
         *
         * @param string $action The action to check
         * @param bool $short Short circuit on first error
         * @return array Array containing an error message key and any parameters
         */
        private function missingPermissionError( $action, $short ) {
                // We avoid expensive display logic for quickUserCan's and such
                if ( $short ) {
                        return [ 'badaccess-group0' ];
                }

                return User::newFatalPermissionDeniedStatus( $action )->getErrorsArray()[0];
        }

        /**
         * Can $user perform $action on this page? This is an internal function,
         * with multiple levels of checks depending on performance needs; see $rigor below.
         * It does not check wfReadOnly().
         *
         * @param string $action Action that permission needs to be checked for
         * @param User $user User to check
         * @param string $rigor One of (quick,full,secure)
         *   - quick  : does cheap permission checks from replica DBs (usable for GUI creation)
         *   - full   : does cheap and expensive checks possibly from a replica DB
         *   - secure : does cheap and expensive checks, using the master as needed
         * @param bool $short Set this to true to stop after the first permission error.
         * @return array Array of arrays of the arguments to wfMessage to explain permissions problems.
         */
        protected function getUserPermissionsErrorsInternal(
                $action, $user, $rigor = 'secure', $short = false
        ) {
                if ( $rigor === true ) {
                        $rigor = 'secure'; // b/c
                } elseif ( $rigor === false ) {
                        $rigor = 'quick'; // b/c
                } elseif ( !in_array( $rigor, [ 'quick', 'full', 'secure' ] ) ) {
                        throw new Exception( "Invalid rigor parameter '$rigor'." );
                }

                # Read has special handling
                if ( $action == 'read' ) {
                        $checks = [
                                'checkPermissionHooks',
                                'checkReadPermissions',
                                'checkUserBlock', // for wgBlockDisablesLogin
                        ];
                # Don't call checkSpecialsAndNSPermissions or checkCSSandJSPermissions
                # here as it will lead to duplicate error messages. This is okay to do
                # since anywhere that checks for create will also check for edit, and
                # those checks are called for edit.
                } elseif ( $action == 'create' ) {
                        $checks = [
                                'checkQuickPermissions',
                                'checkPermissionHooks',
                                'checkPageRestrictions',
                                'checkCascadingSourcesRestrictions',
                                'checkActionPermissions',
                                'checkUserBlock'
                        ];
                } else {
                        $checks = [
                                'checkQuickPermissions',
                                'checkPermissionHooks',
                                'checkSpecialsAndNSPermissions',
                                'checkCSSandJSPermissions',
                                'checkPageRestrictions',
                                'checkCascadingSourcesRestrictions',
                                'checkActionPermissions',
                                'checkUserBlock'
                        ];
                }

                $errors = [];
                while ( count( $checks ) > 0 &&
                                !( $short && count( $errors ) > 0 ) ) {
                        $method = array_shift( $checks );
                        $errors = $this->$method( $action, $user, $errors, $rigor, $short );
                }

                return $errors;
        }

        /**
         * Get a filtered list of all restriction types supported by this wiki.
         * @param bool $exists True to get all restriction types that apply to
         * titles that do exist, False for all restriction types that apply to
         * titles that do not exist
         * @return array
         */
        public static function getFilteredRestrictionTypes( $exists = true ) {
                global $wgRestrictionTypes;
                $types = $wgRestrictionTypes;
                if ( $exists ) {
                        # Remove the create restriction for existing titles
                        $types = array_diff( $types, [ 'create' ] );
                } else {
                        # Only the create and upload restrictions apply to non-existing titles
                        $types = array_intersect( $types, [ 'create', 'upload' ] );
                }
                return $types;
        }

        /**
         * Returns restriction types for the current Title
         *
         * @return array Applicable restriction types
         */
        public function getRestrictionTypes() {
                if ( $this->isSpecialPage() ) {
                        return [];
                }

                $types = self::getFilteredRestrictionTypes( $this->exists() );

                if ( $this->getNamespace() != NS_FILE ) {
                        # Remove the upload restriction for non-file titles
                        $types = array_diff( $types, [ 'upload' ] );
                }

                Hooks::run( 'TitleGetRestrictionTypes', [ $this, &$types ] );

                wfDebug( __METHOD__ . ': applicable restrictions to [[' .
                        $this->getPrefixedText() . ']] are {' . implode( ',', $types ) . "}\n" );

                return $types;
        }

        /**
         * Is this title subject to title protection?
         * Title protection is the one applied against creation of such title.
         *
         * @return array|bool An associative array representing any existent title
         *   protection, or false if there's none.
         */
        public function getTitleProtection() {
                // Can't protect pages in special namespaces
                if ( $this->getNamespace() < 0 ) {
                        return false;
                }

                // Can't protect pages that exist.
                if ( $this->exists() ) {
                        return false;
                }

                if ( $this->mTitleProtection === null ) {
                        $dbr = wfGetDB( DB_REPLICA );
                        $res = $dbr->select(
                                'protected_titles',
                                [
                                        'user' => 'pt_user',
                                        'reason' => 'pt_reason',
                                        'expiry' => 'pt_expiry',
                                        'permission' => 'pt_create_perm'
                                ],
                                [ 'pt_namespace' => $this->getNamespace(), 'pt_title' => $this->getDBkey() ],
                                __METHOD__
                        );

                        // fetchRow returns false if there are no rows.
                        $row = $dbr->fetchRow( $res );
                        if ( $row ) {
                                if ( $row['permission'] == 'sysop' ) {
                                        $row['permission'] = 'editprotected'; // B/C
                                }
                                if ( $row['permission'] == 'autoconfirmed' ) {
                                        $row['permission'] = 'editsemiprotected'; // B/C
                                }
                                $row['expiry'] = $dbr->decodeExpiry( $row['expiry'] );
                        }
                        $this->mTitleProtection = $row;
                }
                return $this->mTitleProtection;
        }

        /**
         * Remove any title protection due to page existing
         */
        public function deleteTitleProtection() {
                $dbw = wfGetDB( DB_MASTER );

                $dbw->delete(
                        'protected_titles',
                        [ 'pt_namespace' => $this->getNamespace(), 'pt_title' => $this->getDBkey() ],
                        __METHOD__
                );
                $this->mTitleProtection = false;
        }

        /**
         * Is this page "semi-protected" - the *only* protection levels are listed
         * in $wgSemiprotectedRestrictionLevels?
         *
         * @param string $action Action to check (default: edit)
         * @return bool
         */
        public function isSemiProtected( $action = 'edit' ) {
                global $wgSemiprotectedRestrictionLevels;

                $restrictions = $this->getRestrictions( $action );
                $semi = $wgSemiprotectedRestrictionLevels;
                if ( !$restrictions || !$semi ) {
                        // Not protected, or all protection is full protection
                        return false;
                }

                // Remap autoconfirmed to editsemiprotected for BC
                foreach ( array_keys( $semi, 'autoconfirmed' ) as $key ) {
                        $semi[$key] = 'editsemiprotected';
                }
                foreach ( array_keys( $restrictions, 'autoconfirmed' ) as $key ) {
                        $restrictions[$key] = 'editsemiprotected';
                }

                return !array_diff( $restrictions, $semi );
        }

        /**
         * Does the title correspond to a protected article?
         *
         * @param string $action The action the page is protected from,
         * by default checks all actions.
         * @return bool
         */
        public function isProtected( $action = '' ) {
                global $wgRestrictionLevels;

                $restrictionTypes = $this->getRestrictionTypes();

                # Special pages have inherent protection
                if ( $this->isSpecialPage() ) {
                        return true;
                }

                # Check regular protection levels
                foreach ( $restrictionTypes as $type ) {
                        if ( $action == $type || $action == '' ) {
                                $r = $this->getRestrictions( $type );
                                foreach ( $wgRestrictionLevels as $level ) {
                                        if ( in_array( $level, $r ) && $level != '' ) {
                                                return true;
                                        }
                                }
                        }
                }

                return false;
        }

        /**
         * Determines if $user is unable to edit this page because it has been protected
         * by $wgNamespaceProtection.
         *
         * @param User $user User object to check permissions
         * @return bool
         */
        public function isNamespaceProtected( User $user ) {
                global $wgNamespaceProtection;

                if ( isset( $wgNamespaceProtection[$this->mNamespace] ) ) {
                        foreach ( (array)$wgNamespaceProtection[$this->mNamespace] as $right ) {
                                if ( $right != '' && !$user->isAllowed( $right ) ) {
                                        return true;
                                }
                        }
                }
                return false;
        }

        /**
         * Cascading protection: Return true if cascading restrictions apply to this page, false if not.
         *
         * @return bool If the page is subject to cascading restrictions.
         */
        public function isCascadeProtected() {
                list( $sources, /* $restrictions */ ) = $this->getCascadeProtectionSources( false );
                return ( $sources > 0 );
        }

        /**
         * Determines whether cascading protection sources have already been loaded from
         * the database.
         *
         * @param bool $getPages True to check if the pages are loaded, or false to check
         * if the status is loaded.
         * @return bool Whether or not the specified information has been loaded
         * @since 1.23
         */
        public function areCascadeProtectionSourcesLoaded( $getPages = true ) {
                return $getPages ? $this->mCascadeSources !== null : $this->mHasCascadingRestrictions !== null;
        }

        /**
         * Cascading protection: Get the source of any cascading restrictions on this page.
         *
         * @param bool $getPages Whether or not to retrieve the actual pages
         *        that the restrictions have come from and the actual restrictions
         *        themselves.
         * @return array Two elements: First is an array of Title objects of the
         *        pages from which cascading restrictions have come, false for
         *        none, or true if such restrictions exist but $getPages was not
         *        set. Second is an array like that returned by
         *        Title::getAllRestrictions(), or an empty array if $getPages is
         *        false.
         */
        public function getCascadeProtectionSources( $getPages = true ) {
                $pagerestrictions = [];

                if ( $this->mCascadeSources !== null && $getPages ) {
                        return [ $this->mCascadeSources, $this->mCascadingRestrictions ];
                } elseif ( $this->mHasCascadingRestrictions !== null && !$getPages ) {
                        return [ $this->mHasCascadingRestrictions, $pagerestrictions ];
                }

                $dbr = wfGetDB( DB_REPLICA );

                if ( $this->getNamespace() == NS_FILE ) {
                        $tables = [ 'imagelinks', 'page_restrictions' ];
                        $where_clauses = [
                                'il_to' => $this->getDBkey(),
                                'il_from=pr_page',
                                'pr_cascade' => 1
                        ];
                } else {
                        $tables = [ 'templatelinks', 'page_restrictions' ];
                        $where_clauses = [
                                'tl_namespace' => $this->getNamespace(),
                                'tl_title' => $this->getDBkey(),
                                'tl_from=pr_page',
                                'pr_cascade' => 1
                        ];
                }

                if ( $getPages ) {
                        $cols = [ 'pr_page', 'page_namespace', 'page_title',
                                'pr_expiry', 'pr_type', 'pr_level' ];
                        $where_clauses[] = 'page_id=pr_page';
                        $tables[] = 'page';
                } else {
                        $cols = [ 'pr_expiry' ];
                }

                $res = $dbr->select( $tables, $cols, $where_clauses, __METHOD__ );

                $sources = $getPages ? [] : false;
                $now = wfTimestampNow();

                foreach ( $res as $row ) {
                        $expiry = $dbr->decodeExpiry( $row->pr_expiry );
                        if ( $expiry > $now ) {
                                if ( $getPages ) {
                                        $page_id = $row->pr_page;
                                        $page_ns = $row->page_namespace;
                                        $page_title = $row->page_title;
                                        $sources[$page_id] = Title::makeTitle( $page_ns, $page_title );
                                        # Add groups needed for each restriction type if its not already there
                                        # Make sure this restriction type still exists

                                        if ( !isset( $pagerestrictions[$row->pr_type] ) ) {
                                                $pagerestrictions[$row->pr_type] = [];
                                        }

                                        if (
                                                isset( $pagerestrictions[$row->pr_type] )
                                                && !in_array( $row->pr_level, $pagerestrictions[$row->pr_type] )
                                        ) {
                                                $pagerestrictions[$row->pr_type][] = $row->pr_level;
                                        }
                                } else {
                                        $sources = true;
                                }
                        }
                }

                if ( $getPages ) {
                        $this->mCascadeSources = $sources;
                        $this->mCascadingRestrictions = $pagerestrictions;
                } else {
                        $this->mHasCascadingRestrictions = $sources;
                }

                return [ $sources, $pagerestrictions ];
        }

        /**
         * Accessor for mRestrictionsLoaded
         *
         * @return bool Whether or not the page's restrictions have already been
         * loaded from the database
         * @since 1.23
         */
        public function areRestrictionsLoaded() {
                return $this->mRestrictionsLoaded;
        }

        /**
         * Accessor/initialisation for mRestrictions
         *
         * @param string $action Action that permission needs to be checked for
         * @return array Restriction levels needed to take the action. All levels are
         *     required. Note that restriction levels are normally user rights, but 'sysop'
         *     and 'autoconfirmed' are also allowed for backwards compatibility. These should
         *     be mapped to 'editprotected' and 'editsemiprotected' respectively.
         */
        public function getRestrictions( $action ) {
                if ( !$this->mRestrictionsLoaded ) {
                        $this->loadRestrictions();
                }
                return isset( $this->mRestrictions[$action] )
                                ? $this->mRestrictions[$action]
                                : [];
        }

        /**
         * Accessor/initialisation for mRestrictions
         *
         * @return array Keys are actions, values are arrays as returned by
         *     Title::getRestrictions()
         * @since 1.23
         */
        public function getAllRestrictions() {
                if ( !$this->mRestrictionsLoaded ) {
                        $this->loadRestrictions();
                }
                return $this->mRestrictions;
        }

        /**
         * Get the expiry time for the restriction against a given action
         *
         * @param string $action
         * @return string|bool 14-char timestamp, or 'infinity' if the page is protected forever
         *     or not protected at all, or false if the action is not recognised.
         */
        public function getRestrictionExpiry( $action ) {
                if ( !$this->mRestrictionsLoaded ) {
                        $this->loadRestrictions();
                }
                return isset( $this->mRestrictionsExpiry[$action] ) ? $this->mRestrictionsExpiry[$action] : false;
        }

        /**
         * Returns cascading restrictions for the current article
         *
         * @return bool
         */
        function areRestrictionsCascading() {
                if ( !$this->mRestrictionsLoaded ) {
                        $this->loadRestrictions();
                }

                return $this->mCascadeRestriction;
        }

        /**
         * Compiles list of active page restrictions from both page table (pre 1.10)
         * and page_restrictions table for this existing page.
         * Public for usage by LiquidThreads.
         *
         * @param array $rows Array of db result objects
         * @param string $oldFashionedRestrictions Comma-separated list of page
         *   restrictions from page table (pre 1.10)
         */
        public function loadRestrictionsFromRows( $rows, $oldFashionedRestrictions = null ) {
                $dbr = wfGetDB( DB_REPLICA );

                $restrictionTypes = $this->getRestrictionTypes();

                foreach ( $restrictionTypes as $type ) {
                        $this->mRestrictions[$type] = [];
                        $this->mRestrictionsExpiry[$type] = 'infinity';
                }

                $this->mCascadeRestriction = false;

                # Backwards-compatibility: also load the restrictions from the page record (old format).
                if ( $oldFashionedRestrictions !== null ) {
                        $this->mOldRestrictions = $oldFashionedRestrictions;
                }

                if ( $this->mOldRestrictions === false ) {
                        $this->mOldRestrictions = $dbr->selectField( 'page', 'page_restrictions',
                                [ 'page_id' => $this->getArticleID() ], __METHOD__ );
                }

                if ( $this->mOldRestrictions != '' ) {
                        foreach ( explode( ':', trim( $this->mOldRestrictions ) ) as $restrict ) {
                                $temp = explode( '=', trim( $restrict ) );
                                if ( count( $temp ) == 1 ) {
                                        // old old format should be treated as edit/move restriction
                                        $this->mRestrictions['edit'] = explode( ',', trim( $temp[0] ) );
                                        $this->mRestrictions['move'] = explode( ',', trim( $temp[0] ) );
                                } else {
                                        $restriction = trim( $temp[1] );
                                        if ( $restriction != '' ) { // some old entries are empty
                                                $this->mRestrictions[$temp[0]] = explode( ',', $restriction );
                                        }
                                }
                        }
                }

                if ( count( $rows ) ) {
                        # Current system - load second to make them override.
                        $now = wfTimestampNow();

                        # Cycle through all the restrictions.
                        foreach ( $rows as $row ) {
                                // Don't take care of restrictions types that aren't allowed
                                if ( !in_array( $row->pr_type, $restrictionTypes ) ) {
                                        continue;
                                }

                                // This code should be refactored, now that it's being used more generally,
                                // But I don't really see any harm in leaving it in Block for now -werdna
                                $expiry = $dbr->decodeExpiry( $row->pr_expiry );

                                // Only apply the restrictions if they haven't expired!
                                if ( !$expiry || $expiry > $now ) {
                                        $this->mRestrictionsExpiry[$row->pr_type] = $expiry;
                                        $this->mRestrictions[$row->pr_type] = explode( ',', trim( $row->pr_level ) );

                                        $this->mCascadeRestriction |= $row->pr_cascade;
                                }
                        }
                }

                $this->mRestrictionsLoaded = true;
        }

        /**
         * Load restrictions from the page_restrictions table
         *
         * @param string $oldFashionedRestrictions Comma-separated list of page
         *   restrictions from page table (pre 1.10)
         */
        public function loadRestrictions( $oldFashionedRestrictions = null ) {
                if ( $this->mRestrictionsLoaded ) {
                        return;
                }

                $id = $this->getArticleID();
                if ( $id ) {
                        $cache = ObjectCache::getMainWANInstance();
                        $rows = $cache->getWithSetCallback(
                                // Page protections always leave a new null revision
                                $cache->makeKey( 'page-restrictions', $id, $this->getLatestRevID() ),
                                $cache::TTL_DAY,
                                function ( $curValue, &$ttl, array &$setOpts ) {
                                        $dbr = wfGetDB( DB_REPLICA );

                                        $setOpts += Database::getCacheSetOptions( $dbr );

                                        return iterator_to_array(
                                                $dbr->select(
                                                        'page_restrictions',
                                                        [ 'pr_type', 'pr_expiry', 'pr_level', 'pr_cascade' ],
                                                        [ 'pr_page' => $this->getArticleID() ],
                                                        __METHOD__
                                                )
                                        );
                                }
                        );

                        $this->loadRestrictionsFromRows( $rows, $oldFashionedRestrictions );
                } else {
                        $title_protection = $this->getTitleProtection();

                        if ( $title_protection ) {
                                $now = wfTimestampNow();
                                $expiry = wfGetDB( DB_REPLICA )->decodeExpiry( $title_protection['expiry'] );

                                if ( !$expiry || $expiry > $now ) {
                                        // Apply the restrictions
                                        $this->mRestrictionsExpiry['create'] = $expiry;
                                        $this->mRestrictions['create'] =
                                                explode( ',', trim( $title_protection['permission'] ) );
                                } else { // Get rid of the old restrictions
                                        $this->mTitleProtection = false;
                                }
                        } else {
                                $this->mRestrictionsExpiry['create'] = 'infinity';
                        }
                        $this->mRestrictionsLoaded = true;
                }
        }

        /**
         * Flush the protection cache in this object and force reload from the database.
         * This is used when updating protection from WikiPage::doUpdateRestrictions().
         */
        public function flushRestrictions() {
                $this->mRestrictionsLoaded = false;
                $this->mTitleProtection = null;
        }

        /**
         * Purge expired restrictions from the page_restrictions table
         *
         * This will purge no more than $wgUpdateRowsPerQuery page_restrictions rows
         */
        static function purgeExpiredRestrictions() {
                if ( wfReadOnly() ) {
                        return;
                }

                DeferredUpdates::addUpdate( new AtomicSectionUpdate(
                        wfGetDB( DB_MASTER ),
                        __METHOD__,
                        function ( IDatabase $dbw, $fname ) {
                                $config = MediaWikiServices::getInstance()->getMainConfig();
                                $ids = $dbw->selectFieldValues(
                                        'page_restrictions',
                                        'pr_id',
                                        [ 'pr_expiry < ' . $dbw->addQuotes( $dbw->timestamp() ) ],
                                        $fname,
                                        [ 'LIMIT' => $config->get( 'UpdateRowsPerQuery' ) ] // T135470
                                );
                                if ( $ids ) {
                                        $dbw->delete( 'page_restrictions', [ 'pr_id' => $ids ], $fname );
                                }
                        }
                ) );

                DeferredUpdates::addUpdate( new AtomicSectionUpdate(
                        wfGetDB( DB_MASTER ),
                        __METHOD__,
                        function ( IDatabase $dbw, $fname ) {
                                $dbw->delete(
                                        'protected_titles',
                                        [ 'pt_expiry < ' . $dbw->addQuotes( $dbw->timestamp() ) ],
                                        $fname
                                );
                        }
                ) );
        }

        /**
         * Does this have subpages?  (Warning, usually requires an extra DB query.)
         *
         * @return bool
         */
        public function hasSubpages() {
                if ( !MWNamespace::hasSubpages( $this->mNamespace ) ) {
                        # Duh
                        return false;
                }

                # We dynamically add a member variable for the purpose of this method
                # alone to cache the result.  There's no point in having it hanging
                # around uninitialized in every Title object; therefore we only add it
                # if needed and don't declare it statically.
                if ( $this->mHasSubpages === null ) {
                        $this->mHasSubpages = false;
                        $subpages = $this->getSubpages( 1 );
                        if ( $subpages instanceof TitleArray ) {
                                $this->mHasSubpages = (bool)$subpages->count();
                        }
                }

                return $this->mHasSubpages;
        }

        /**
         * Get all subpages of this page.
         *
         * @param int $limit Maximum number of subpages to fetch; -1 for no limit
         * @return TitleArray|array TitleArray, or empty array if this page's namespace
         *  doesn't allow subpages
         */
        public function getSubpages( $limit = -1 ) {
                if ( !MWNamespace::hasSubpages( $this->getNamespace() ) ) {
                        return [];
                }

                $dbr = wfGetDB( DB_REPLICA );
                $conds['page_namespace'] = $this->getNamespace();
                $conds[] = 'page_title ' . $dbr->buildLike( $this->getDBkey() . '/', $dbr->anyString() );
                $options = [];
                if ( $limit > -1 ) {
                        $options['LIMIT'] = $limit;
                }
                $this->mSubpages = TitleArray::newFromResult(
                        $dbr->select( 'page',
                                [ 'page_id', 'page_namespace', 'page_title', 'page_is_redirect' ],
                                $conds,
                                __METHOD__,
                                $options
                        )
                );
                return $this->mSubpages;
        }

        /**
         * Is there a version of this page in the deletion archive?
         *
         * @return int The number of archived revisions
         */
        public function isDeleted() {
                if ( $this->getNamespace() < 0 ) {
                        $n = 0;
                } else {
                        $dbr = wfGetDB( DB_REPLICA );

                        $n = $dbr->selectField( 'archive', 'COUNT(*)',
                                [ 'ar_namespace' => $this->getNamespace(), 'ar_title' => $this->getDBkey() ],
                                __METHOD__
                        );
                        if ( $this->getNamespace() == NS_FILE ) {
                                $n += $dbr->selectField( 'filearchive', 'COUNT(*)',
                                        [ 'fa_name' => $this->getDBkey() ],
                                        __METHOD__
                                );
                        }
                }
                return (int)$n;
        }

        /**
         * Is there a version of this page in the deletion archive?
         *
         * @return bool
         */
        public function isDeletedQuick() {
                if ( $this->getNamespace() < 0 ) {
                        return false;
                }
                $dbr = wfGetDB( DB_REPLICA );
                $deleted = (bool)$dbr->selectField( 'archive', '1',
                        [ 'ar_namespace' => $this->getNamespace(), 'ar_title' => $this->getDBkey() ],
                        __METHOD__
                );
                if ( !$deleted && $this->getNamespace() == NS_FILE ) {
                        $deleted = (bool)$dbr->selectField( 'filearchive', '1',
                                [ 'fa_name' => $this->getDBkey() ],
                                __METHOD__
                        );
                }
                return $deleted;
        }

        /**
         * Get the article ID for this Title from the link cache,
         * adding it if necessary
         *
         * @param int $flags A bit field; may be Title::GAID_FOR_UPDATE to select
         *  for update
         * @return int The ID
         */
        public function getArticleID( $flags = 0 ) {
                if ( $this->getNamespace() < 0 ) {
                        $this->mArticleID = 0;
                        return $this->mArticleID;
                }
                $linkCache = LinkCache::singleton();
                if ( $flags & self::GAID_FOR_UPDATE ) {
                        $oldUpdate = $linkCache->forUpdate( true );
                        $linkCache->clearLink( $this );
                        $this->mArticleID = $linkCache->addLinkObj( $this );
                        $linkCache->forUpdate( $oldUpdate );
                } else {
                        if ( -1 == $this->mArticleID ) {
                                $this->mArticleID = $linkCache->addLinkObj( $this );
                        }
                }
                return $this->mArticleID;
        }

        /**
         * Is this an article that is a redirect page?
         * Uses link cache, adding it if necessary
         *
         * @param int $flags A bit field; may be Title::GAID_FOR_UPDATE to select for update
         * @return bool
         */
        public function isRedirect( $flags = 0 ) {
                if ( !is_null( $this->mRedirect ) ) {
                        return $this->mRedirect;
                }
                if ( !$this->getArticleID( $flags ) ) {
                        $this->mRedirect = false;
                        return $this->mRedirect;
                }

                $linkCache = LinkCache::singleton();
                $linkCache->addLinkObj( $this ); # in case we already had an article ID
                $cached = $linkCache->getGoodLinkFieldObj( $this, 'redirect' );
                if ( $cached === null ) {
                        # Trust LinkCache's state over our own
                        # LinkCache is telling us that the page doesn't exist, despite there being cached
                        # data relating to an existing page in $this->mArticleID. Updaters should clear
                        # LinkCache as appropriate, or use $flags = Title::GAID_FOR_UPDATE. If that flag is
                        # set, then LinkCache will definitely be up to date here, since getArticleID() forces
                        # LinkCache to refresh its data from the master.
                        $this->mRedirect = false;
                        return $this->mRedirect;
                }

                $this->mRedirect = (bool)$cached;

                return $this->mRedirect;
        }

        /**
         * What is the length of this page?
         * Uses link cache, adding it if necessary
         *
         * @param int $flags A bit field; may be Title::GAID_FOR_UPDATE to select for update
         * @return int
         */
        public function getLength( $flags = 0 ) {
                if ( $this->mLength != -1 ) {
                        return $this->mLength;
                }
                if ( !$this->getArticleID( $flags ) ) {
                        $this->mLength = 0;
                        return $this->mLength;
                }
                $linkCache = LinkCache::singleton();
                $linkCache->addLinkObj( $this ); # in case we already had an article ID
                $cached = $linkCache->getGoodLinkFieldObj( $this, 'length' );
                if ( $cached === null ) {
                        # Trust LinkCache's state over our own, as for isRedirect()
                        $this->mLength = 0;
                        return $this->mLength;
                }

                $this->mLength = intval( $cached );

                return $this->mLength;
        }

        /**
         * What is the page_latest field for this page?
         *
         * @param int $flags A bit field; may be Title::GAID_FOR_UPDATE to select for update
         * @return int Int or 0 if the page doesn't exist
         */
        public function getLatestRevID( $flags = 0 ) {
                if ( !( $flags & Title::GAID_FOR_UPDATE ) && $this->mLatestID !== false ) {
                        return intval( $this->mLatestID );
                }
                if ( !$this->getArticleID( $flags ) ) {
                        $this->mLatestID = 0;
                        return $this->mLatestID;
                }
                $linkCache = LinkCache::singleton();
                $linkCache->addLinkObj( $this ); # in case we already had an article ID
                $cached = $linkCache->getGoodLinkFieldObj( $this, 'revision' );
                if ( $cached === null ) {
                        # Trust LinkCache's state over our own, as for isRedirect()
                        $this->mLatestID = 0;
                        return $this->mLatestID;
                }

                $this->mLatestID = intval( $cached );

                return $this->mLatestID;
        }

        /**
         * This clears some fields in this object, and clears any associated
         * keys in the "bad links" section of the link cache.
         *
         * - This is called from WikiPage::doEditContent() and WikiPage::insertOn() to allow
         * loading of the new page_id. It's also called from
         * WikiPage::doDeleteArticleReal()
         *
         * @param int $newid The new Article ID
         */
        public function resetArticleID( $newid ) {
                $linkCache = LinkCache::singleton();
                $linkCache->clearLink( $this );

                if ( $newid === false ) {
                        $this->mArticleID = -1;
                } else {
                        $this->mArticleID = intval( $newid );
                }
                $this->mRestrictionsLoaded = false;
                $this->mRestrictions = [];
                $this->mOldRestrictions = false;
                $this->mRedirect = null;
                $this->mLength = -1;
                $this->mLatestID = false;
                $this->mContentModel = false;
                $this->mEstimateRevisions = null;
                $this->mPageLanguage = false;
                $this->mDbPageLanguage = false;
                $this->mIsBigDeletion = null;
        }

        public static function clearCaches() {
                $linkCache = LinkCache::singleton();
                $linkCache->clear();

                $titleCache = self::getTitleCache();
                $titleCache->clear();
        }

        /**
         * Capitalize a text string for a title if it belongs to a namespace that capitalizes
         *
         * @param string $text Containing title to capitalize
         * @param int $ns Namespace index, defaults to NS_MAIN
         * @return string Containing capitalized title
         */
        public static function capitalize( $text, $ns = NS_MAIN ) {
                global $wgContLang;

                if ( MWNamespace::isCapitalized( $ns ) ) {
                        return $wgContLang->ucfirst( $text );
                } else {
                        return $text;
                }
        }

        /**
         * Secure and split - main initialisation function for this object
         *
         * Assumes that mDbkeyform has been set, and is urldecoded
         * and uses underscores, but not otherwise munged.  This function
         * removes illegal characters, splits off the interwiki and
         * namespace prefixes, sets the other forms, and canonicalizes
         * everything.
         *
         * @throws MalformedTitleException On invalid titles
         * @return bool True on success
         */
        private function secureAndSplit() {
                # Initialisation
                $this->mInterwiki = '';
                $this->mFragment = '';
                $this->mNamespace = $this->mDefaultNamespace; # Usually NS_MAIN

                $dbkey = $this->mDbkeyform;

                // @note: splitTitleString() is a temporary hack to allow MediaWikiTitleCodec to share
                //        the parsing code with Title, while avoiding massive refactoring.
                // @todo: get rid of secureAndSplit, refactor parsing code.
                // @note: getTitleParser() returns a TitleParser implementation which does not have a
                //        splitTitleString method, but the only implementation (MediaWikiTitleCodec) does
                $titleCodec = MediaWikiServices::getInstance()->getTitleParser();
                // MalformedTitleException can be thrown here
                $parts = $titleCodec->splitTitleString( $dbkey, $this->getDefaultNamespace() );

                # Fill fields
                $this->setFragment( '#' . $parts['fragment'] );
                $this->mInterwiki = $parts['interwiki'];
                $this->mLocalInterwiki = $parts['local_interwiki'];
                $this->mNamespace = $parts['namespace'];
                $this->mUserCaseDBKey = $parts['user_case_dbkey'];

                $this->mDbkeyform = $parts['dbkey'];
                $this->mUrlform = wfUrlencode( $this->mDbkeyform );
                $this->mTextform = strtr( $this->mDbkeyform, '_', ' ' );

                # We already know that some pages won't be in the database!
                if ( $this->isExternal() || $this->mNamespace == NS_SPECIAL ) {
                        $this->mArticleID = 0;
                }

                return true;
        }

        /**
         * Get an array of Title objects linking to this Title
         * Also stores the IDs in the link cache.
         *
         * WARNING: do not use this function on arbitrary user-supplied titles!
         * On heavily-used templates it will max out the memory.
         *
         * @param array $options May be FOR UPDATE
         * @param string $table Table name
         * @param string $prefix Fields prefix
         * @return Title[] Array of Title objects linking here
         */
        public function getLinksTo( $options = [], $table = 'pagelinks', $prefix = 'pl' ) {
                if ( count( $options ) > 0 ) {
                        $db = wfGetDB( DB_MASTER );
                } else {
                        $db = wfGetDB( DB_REPLICA );
                }

                $res = $db->select(
                        [ 'page', $table ],
                        self::getSelectFields(),
                        [
                                "{$prefix}_from=page_id",
                                "{$prefix}_namespace" => $this->getNamespace(),
                                "{$prefix}_title" => $this->getDBkey() ],
                        __METHOD__,
                        $options
                );

                $retVal = [];
                if ( $res->numRows() ) {
                        $linkCache = LinkCache::singleton();
                        foreach ( $res as $row ) {
                                $titleObj = Title::makeTitle( $row->page_namespace, $row->page_title );
                                if ( $titleObj ) {
                                        $linkCache->addGoodLinkObjFromRow( $titleObj, $row );
                                        $retVal[] = $titleObj;
                                }
                        }
                }
                return $retVal;
        }

        /**
         * Get an array of Title objects using this Title as a template
         * Also stores the IDs in the link cache.
         *
         * WARNING: do not use this function on arbitrary user-supplied titles!
         * On heavily-used templates it will max out the memory.
         *
         * @param array $options Query option to Database::select()
         * @return Title[] Array of Title the Title objects linking here
         */
        public function getTemplateLinksTo( $options = [] ) {
                return $this->getLinksTo( $options, 'templatelinks', 'tl' );
        }

        /**
         * Get an array of Title objects linked from this Title
         * Also stores the IDs in the link cache.
         *
         * WARNING: do not use this function on arbitrary user-supplied titles!
         * On heavily-used templates it will max out the memory.
         *
         * @param array $options Query option to Database::select()
         * @param string $table Table name
         * @param string $prefix Fields prefix
         * @return array Array of Title objects linking here
         */
        public function getLinksFrom( $options = [], $table = 'pagelinks', $prefix = 'pl' ) {
                $id = $this->getArticleID();

                # If the page doesn't exist; there can't be any link from this page
                if ( !$id ) {
                        return [];
                }

                $db = wfGetDB( DB_REPLICA );

                $blNamespace = "{$prefix}_namespace";
                $blTitle = "{$prefix}_title";

                $res = $db->select(
                        [ $table, 'page' ],
                        array_merge(
                                [ $blNamespace, $blTitle ],
                                WikiPage::selectFields()
                        ),
                        [ "{$prefix}_from" => $id ],
                        __METHOD__,
                        $options,
                        [ 'page' => [
                                'LEFT JOIN',
                                [ "page_namespace=$blNamespace", "page_title=$blTitle" ]
                        ] ]
                );

                $retVal = [];
                $linkCache = LinkCache::singleton();
                foreach ( $res as $row ) {
                        if ( $row->page_id ) {
                                $titleObj = Title::newFromRow( $row );
                        } else {
                                $titleObj = Title::makeTitle( $row->$blNamespace, $row->$blTitle );
                                $linkCache->addBadLinkObj( $titleObj );
                        }
                        $retVal[] = $titleObj;
                }

                return $retVal;
        }

        /**
         * Get an array of Title objects used on this Title as a template
         * Also stores the IDs in the link cache.
         *
         * WARNING: do not use this function on arbitrary user-supplied titles!
         * On heavily-used templates it will max out the memory.
         *
         * @param array $options May be FOR UPDATE
         * @return Title[] Array of Title the Title objects used here
         */
        public function getTemplateLinksFrom( $options = [] ) {
                return $this->getLinksFrom( $options, 'templatelinks', 'tl' );
        }

        /**
         * Get an array of Title objects referring to non-existent articles linked
         * from this page.
         *
         * @todo check if needed (used only in SpecialBrokenRedirects.php, and
         *   should use redirect table in this case).
         * @return Title[] Array of Title the Title objects
         */
        public function getBrokenLinksFrom() {
                if ( $this->getArticleID() == 0 ) {
                        # All links from article ID 0 are false positives
                        return [];
                }

                $dbr = wfGetDB( DB_REPLICA );
                $res = $dbr->select(
                        [ 'page', 'pagelinks' ],
                        [ 'pl_namespace', 'pl_title' ],
                        [
                                'pl_from' => $this->getArticleID(),
                                'page_namespace IS NULL'
                        ],
                        __METHOD__, [],
                        [
                                'page' => [
                                        'LEFT JOIN',
                                        [ 'pl_namespace=page_namespace', 'pl_title=page_title' ]
                                ]
                        ]
                );

                $retVal = [];
                foreach ( $res as $row ) {
                        $retVal[] = Title::makeTitle( $row->pl_namespace, $row->pl_title );
                }
                return $retVal;
        }

        /**
         * Get a list of URLs to purge from the CDN cache when this
         * page changes
         *
         * @return string[] Array of String the URLs
         */
        public function getCdnUrls() {
                $urls = [
                        $this->getInternalURL(),
                        $this->getInternalURL( 'action=history' )
                ];

                $pageLang = $this->getPageLanguage();
                if ( $pageLang->hasVariants() ) {
                        $variants = $pageLang->getVariants();
                        foreach ( $variants as $vCode ) {
                                $urls[] = $this->getInternalURL( $vCode );
                        }
                }

                // If we are looking at a css/js user subpage, purge the action=raw.
                if ( $this->isJsSubpage() ) {
                        $urls[] = $this->getInternalURL( 'action=raw&ctype=text/javascript' );
                } elseif ( $this->isCssSubpage() ) {
                        $urls[] = $this->getInternalURL( 'action=raw&ctype=text/css' );
                }

                Hooks::run( 'TitleSquidURLs', [ $this, &$urls ] );
                return $urls;
        }

        /**
         * @deprecated since 1.27 use getCdnUrls()
         */
        public function getSquidURLs() {
                return $this->getCdnUrls();
        }

        /**
         * Purge all applicable CDN URLs
         */
        public function purgeSquid() {
                DeferredUpdates::addUpdate(
                        new CdnCacheUpdate( $this->getCdnUrls() ),
                        DeferredUpdates::PRESEND
                );
        }

        /**
         * Check whether a given move operation would be valid.
         * Returns true if ok, or a getUserPermissionsErrors()-like array otherwise
         *
         * @deprecated since 1.25, use MovePage's methods instead
         * @param Title $nt The new title
         * @param bool $auth Whether to check user permissions (uses $wgUser)
         * @param string $reason Is the log summary of the move, used for spam checking
         * @return array|bool True on success, getUserPermissionsErrors()-like array on failure
         */
        public function isValidMoveOperation( &$nt, $auth = true, $reason = '' ) {
                global $wgUser;

                if ( !( $nt instanceof Title ) ) {
                        // Normally we'd add this to $errors, but we'll get
                        // lots of syntax errors if $nt is not an object
                        return [ [ 'badtitletext' ] ];
                }

                $mp = new MovePage( $this, $nt );
                $errors = $mp->isValidMove()->getErrorsArray();
                if ( $auth ) {
                        $errors = wfMergeErrorArrays(
                                $errors,
                                $mp->checkPermissions( $wgUser, $reason )->getErrorsArray()
                        );
                }

                return $errors ?: true;
        }

        /**
         * Check if the requested move target is a valid file move target
         * @todo move this to MovePage
         * @param Title $nt Target title
         * @return array List of errors
         */
        protected function validateFileMoveOperation( $nt ) {
                global $wgUser;

                $errors = [];

                $destFile = wfLocalFile( $nt );
                $destFile->load( File::READ_LATEST );
                if ( !$wgUser->isAllowed( 'reupload-shared' )
                        && !$destFile->exists() && wfFindFile( $nt )
                ) {
                        $errors[] = [ 'file-exists-sharedrepo' ];
                }

                return $errors;
        }

        /**
         * Move a title to a new location
         *
         * @deprecated since 1.25, use the MovePage class instead
         * @param Title $nt The new title
         * @param bool $auth Indicates whether $wgUser's permissions
         *  should be checked
         * @param string $reason The reason for the move
         * @param bool $createRedirect Whether to create a redirect from the old title to the new title.
         *  Ignored if the user doesn't have the suppressredirect right.
         * @param array $changeTags Applied to the entry in the move log and redirect page revision
         * @return array|bool True on success, getUserPermissionsErrors()-like array on failure
         */
        public function moveTo( &$nt, $auth = true, $reason = '', $createRedirect = true,
                array $changeTags = [] ) {

                global $wgUser;
                $err = $this->isValidMoveOperation( $nt, $auth, $reason );
                if ( is_array( $err ) ) {
                        // Auto-block user's IP if the account was "hard" blocked
                        $wgUser->spreadAnyEditBlock();
                        return $err;
                }
                // Check suppressredirect permission
                if ( $auth && !$wgUser->isAllowed( 'suppressredirect' ) ) {
                        $createRedirect = true;
                }

                $mp = new MovePage( $this, $nt );
                $status = $mp->move( $wgUser, $reason, $createRedirect, $changeTags );
                if ( $status->isOK() ) {
                        return true;
                } else {
                        return $status->getErrorsArray();
                }
        }

        /**
         * Move this page's subpages to be subpages of $nt
         *
         * @param Title $nt Move target
         * @param bool $auth Whether $wgUser's permissions should be checked
         * @param string $reason The reason for the move
         * @param bool $createRedirect Whether to create redirects from the old subpages to
         *     the new ones Ignored if the user doesn't have the 'suppressredirect' right
         * @param array $changeTags Applied to the entry in the move log and redirect page revision
         * @return array Array with old page titles as keys, and strings (new page titles) or
         *     getUserPermissionsErrors()-like arrays (errors) as values, or a
         *     getUserPermissionsErrors()-like error array with numeric indices if
         *     no pages were moved
         */
        public function moveSubpages( $nt, $auth = true, $reason = '', $createRedirect = true,
                array $changeTags = [] ) {

                global $wgMaximumMovedPages;
                // Check permissions
                if ( !$this->userCan( 'move-subpages' ) ) {
                        return [
                                [ 'cant-move-subpages' ],
                        ];
                }
                // Do the source and target namespaces support subpages?
                if ( !MWNamespace::hasSubpages( $this->getNamespace() ) ) {
                        return [
                                [ 'namespace-nosubpages', MWNamespace::getCanonicalName( $this->getNamespace() ) ],
                        ];
                }
                if ( !MWNamespace::hasSubpages( $nt->getNamespace() ) ) {
                        return [
                                [ 'namespace-nosubpages', MWNamespace::getCanonicalName( $nt->getNamespace() ) ],
                        ];
                }

                $subpages = $this->getSubpages( $wgMaximumMovedPages + 1 );
                $retval = [];
                $count = 0;
                foreach ( $subpages as $oldSubpage ) {
                        $count++;
                        if ( $count > $wgMaximumMovedPages ) {
                                $retval[$oldSubpage->getPrefixedText()] = [
                                        [ 'movepage-max-pages', $wgMaximumMovedPages ],
                                ];
                                break;
                        }

                        // We don't know whether this function was called before
                        // or after moving the root page, so check both
                        // $this and $nt
                        if ( $oldSubpage->getArticleID() == $this->getArticleID()
                                || $oldSubpage->getArticleID() == $nt->getArticleID()
                        ) {
                                // When moving a page to a subpage of itself,
                                // don't move it twice
                                continue;
                        }
                        $newPageName = preg_replace(
                                        '#^' . preg_quote( $this->getDBkey(), '#' ) . '#',
                                        StringUtils::escapeRegexReplacement( $nt->getDBkey() ), # bug 21234
                                        $oldSubpage->getDBkey() );
                        if ( $oldSubpage->isTalkPage() ) {
                                $newNs = $nt->getTalkPage()->getNamespace();
                        } else {
                                $newNs = $nt->getSubjectPage()->getNamespace();
                        }
                        # Bug 14385: we need makeTitleSafe because the new page names may
                        # be longer than 255 characters.
                        $newSubpage = Title::makeTitleSafe( $newNs, $newPageName );

                        $success = $oldSubpage->moveTo( $newSubpage, $auth, $reason, $createRedirect, $changeTags );
                        if ( $success === true ) {
                                $retval[$oldSubpage->getPrefixedText()] = $newSubpage->getPrefixedText();
                        } else {
                                $retval[$oldSubpage->getPrefixedText()] = $success;
                        }
                }
                return $retval;
        }

        /**
         * Checks if this page is just a one-rev redirect.
         * Adds lock, so don't use just for light purposes.
         *
         * @return bool
         */
        public function isSingleRevRedirect() {
                global $wgContentHandlerUseDB;

                $dbw = wfGetDB( DB_MASTER );

                # Is it a redirect?
                $fields = [ 'page_is_redirect', 'page_latest', 'page_id' ];
                if ( $wgContentHandlerUseDB ) {
                        $fields[] = 'page_content_model';
                }

                $row = $dbw->selectRow( 'page',
                        $fields,
                        $this->pageCond(),
                        __METHOD__,
                        [ 'FOR UPDATE' ]
                );
                # Cache some fields we may want
                $this->mArticleID = $row ? intval( $row->page_id ) : 0;
                $this->mRedirect = $row ? (bool)$row->page_is_redirect : false;
                $this->mLatestID = $row ? intval( $row->page_latest ) : false;
                $this->mContentModel = $row && isset( $row->page_content_model )
                        ? strval( $row->page_content_model )
                        : false;

                if ( !$this->mRedirect ) {
                        return false;
                }
                # Does the article have a history?
                $row = $dbw->selectField( [ 'page', 'revision' ],
                        'rev_id',
                        [ 'page_namespace' => $this->getNamespace(),
                                'page_title' => $this->getDBkey(),
                                'page_id=rev_page',
                                'page_latest != rev_id'
                        ],
                        __METHOD__,
                        [ 'FOR UPDATE' ]
                );
                # Return true if there was no history
                return ( $row === false );
        }

        /**
         * Checks if $this can be moved to a given Title
         * - Selects for update, so don't call it unless you mean business
         *
         * @deprecated since 1.25, use MovePage's methods instead
         * @param Title $nt The new title to check
         * @return bool
         */
        public function isValidMoveTarget( $nt ) {
                # Is it an existing file?
                if ( $nt->getNamespace() == NS_FILE ) {
                        $file = wfLocalFile( $nt );
                        $file->load( File::READ_LATEST );
                        if ( $file->exists() ) {
                                wfDebug( __METHOD__ . ": file exists\n" );
                                return false;
                        }
                }
                # Is it a redirect with no history?
                if ( !$nt->isSingleRevRedirect() ) {
                        wfDebug( __METHOD__ . ": not a one-rev redirect\n" );
                        return false;
                }
                # Get the article text
                $rev = Revision::newFromTitle( $nt, false, Revision::READ_LATEST );
                if ( !is_object( $rev ) ) {
                        return false;
                }
                $content = $rev->getContent();
                # Does the redirect point to the source?
                # Or is it a broken self-redirect, usually caused by namespace collisions?
                $redirTitle = $content ? $content->getRedirectTarget() : null;

                if ( $redirTitle ) {
                        if ( $redirTitle->getPrefixedDBkey() != $this->getPrefixedDBkey() &&
                                $redirTitle->getPrefixedDBkey() != $nt->getPrefixedDBkey() ) {
                                wfDebug( __METHOD__ . ": redirect points to other page\n" );
                                return false;
                        } else {
                                return true;
                        }
                } else {
                        # Fail safe (not a redirect after all. strange.)
                        wfDebug( __METHOD__ . ": failsafe: database sais " . $nt->getPrefixedDBkey() .
                                                " is a redirect, but it doesn't contain a valid redirect.\n" );
                        return false;
                }
        }

        /**
         * Get categories to which this Title belongs and return an array of
         * categories' names.
         *
         * @return array Array of parents in the form:
         *        $parent => $currentarticle
         */
        public function getParentCategories() {
                global $wgContLang;

                $data = [];

                $titleKey = $this->getArticleID();

                if ( $titleKey === 0 ) {
                        return $data;
                }

                $dbr = wfGetDB( DB_REPLICA );

                $res = $dbr->select(
                        'categorylinks',
                        'cl_to',
                        [ 'cl_from' => $titleKey ],
                        __METHOD__
                );

                if ( $res->numRows() > 0 ) {
                        foreach ( $res as $row ) {
                                // $data[] = Title::newFromText($wgContLang->getNsText ( NS_CATEGORY ).':'.$row->cl_to);
                                $data[$wgContLang->getNsText( NS_CATEGORY ) . ':' . $row->cl_to] = $this->getFullText();
                        }
                }
                return $data;
        }

        /**
         * Get a tree of parent categories
         *
         * @param array $children Array with the children in the keys, to check for circular refs
         * @return array Tree of parent categories
         */
        public function getParentCategoryTree( $children = [] ) {
                $stack = [];
                $parents = $this->getParentCategories();

                if ( $parents ) {
                        foreach ( $parents as $parent => $current ) {
                                if ( array_key_exists( $parent, $children ) ) {
                                        # Circular reference
                                        $stack[$parent] = [];
                                } else {
                                        $nt = Title::newFromText( $parent );
                                        if ( $nt ) {
                                                $stack[$parent] = $nt->getParentCategoryTree( $children + [ $parent => 1 ] );
                                        }
                                }
                        }
                }

                return $stack;
        }

        /**
         * Get an associative array for selecting this title from
         * the "page" table
         *
         * @return array Array suitable for the $where parameter of DB::select()
         */
        public function pageCond() {
                if ( $this->mArticleID > 0 ) {
                        // PK avoids secondary lookups in InnoDB, shouldn't hurt other DBs
                        return [ 'page_id' => $this->mArticleID ];
                } else {
                        return [ 'page_namespace' => $this->mNamespace, 'page_title' => $this->mDbkeyform ];
                }
        }

        /**
         * Get the revision ID of the previous revision
         *
         * @param int $revId Revision ID. Get the revision that was before this one.
         * @param int $flags Title::GAID_FOR_UPDATE
         * @return int|bool Old revision ID, or false if none exists
         */
        public function getPreviousRevisionID( $revId, $flags = 0 ) {
                $db = ( $flags & self::GAID_FOR_UPDATE ) ? wfGetDB( DB_MASTER ) : wfGetDB( DB_REPLICA );
                $revId = $db->selectField( 'revision', 'rev_id',
                        [
                                'rev_page' => $this->getArticleID( $flags ),
                                'rev_id < ' . intval( $revId )
                        ],
                        __METHOD__,
                        [ 'ORDER BY' => 'rev_id DESC' ]
                );

                if ( $revId === false ) {
                        return false;
                } else {
                        return intval( $revId );
                }
        }

        /**
         * Get the revision ID of the next revision
         *
         * @param int $revId Revision ID. Get the revision that was after this one.
         * @param int $flags Title::GAID_FOR_UPDATE
         * @return int|bool Next revision ID, or false if none exists
         */
        public function getNextRevisionID( $revId, $flags = 0 ) {
                $db = ( $flags & self::GAID_FOR_UPDATE ) ? wfGetDB( DB_MASTER ) : wfGetDB( DB_REPLICA );
                $revId = $db->selectField( 'revision', 'rev_id',
                        [
                                'rev_page' => $this->getArticleID( $flags ),
                                'rev_id > ' . intval( $revId )
                        ],
                        __METHOD__,
                        [ 'ORDER BY' => 'rev_id' ]
                );

                if ( $revId === false ) {
                        return false;
                } else {
                        return intval( $revId );
                }
        }

        /**
         * Get the first revision of the page
         *
         * @param int $flags Title::GAID_FOR_UPDATE
         * @return Revision|null If page doesn't exist
         */
        public function getFirstRevision( $flags = 0 ) {
                $pageId = $this->getArticleID( $flags );
                if ( $pageId ) {
                        $db = ( $flags & self::GAID_FOR_UPDATE ) ? wfGetDB( DB_MASTER ) : wfGetDB( DB_REPLICA );
                        $row = $db->selectRow( 'revision', Revision::selectFields(),
                                [ 'rev_page' => $pageId ],
                                __METHOD__,
                                [ 'ORDER BY' => 'rev_timestamp ASC', 'LIMIT' => 1 ]
                        );
                        if ( $row ) {
                                return new Revision( $row );
                        }
                }
                return null;
        }

        /**
         * Get the oldest revision timestamp of this page
         *
         * @param int $flags Title::GAID_FOR_UPDATE
         * @return string MW timestamp
         */
        public function getEarliestRevTime( $flags = 0 ) {
                $rev = $this->getFirstRevision( $flags );
                return $rev ? $rev->getTimestamp() : null;
        }

        /**
         * Check if this is a new page
         *
         * @return bool
         */
        public function isNewPage() {
                $dbr = wfGetDB( DB_REPLICA );
                return (bool)$dbr->selectField( 'page', 'page_is_new', $this->pageCond(), __METHOD__ );
        }

        /**
         * Check whether the number of revisions of this page surpasses $wgDeleteRevisionsLimit
         *
         * @return bool
         */
        public function isBigDeletion() {
                global $wgDeleteRevisionsLimit;

                if ( !$wgDeleteRevisionsLimit ) {
                        return false;
                }

                if ( $this->mIsBigDeletion === null ) {
                        $dbr = wfGetDB( DB_REPLICA );

                        $revCount = $dbr->selectRowCount(
                                'revision',
                                '1',
                                [ 'rev_page' => $this->getArticleID() ],
                                __METHOD__,
                                [ 'LIMIT' => $wgDeleteRevisionsLimit + 1 ]
                        );

                        $this->mIsBigDeletion = $revCount > $wgDeleteRevisionsLimit;
                }

                return $this->mIsBigDeletion;
        }

        /**
         * Get the approximate revision count of this page.
         *
         * @return int
         */
        public function estimateRevisionCount() {
                if ( !$this->exists() ) {
                        return 0;
                }

                if ( $this->mEstimateRevisions === null ) {
                        $dbr = wfGetDB( DB_REPLICA );
                        $this->mEstimateRevisions = $dbr->estimateRowCount( 'revision', '*',
                                [ 'rev_page' => $this->getArticleID() ], __METHOD__ );
                }

                return $this->mEstimateRevisions;
        }

        /**
         * Get the number of revisions between the given revision.
         * Used for diffs and other things that really need it.
         *
         * @param int|Revision $old Old revision or rev ID (first before range)
         * @param int|Revision $new New revision or rev ID (first after range)
         * @param int|null $max Limit of Revisions to count, will be incremented to detect truncations
         * @return int Number of revisions between these revisions.
         */
        public function countRevisionsBetween( $old, $new, $max = null ) {
                if ( !( $old instanceof Revision ) ) {
                        $old = Revision::newFromTitle( $this, (int)$old );
                }
                if ( !( $new instanceof Revision ) ) {
                        $new = Revision::newFromTitle( $this, (int)$new );
                }
                if ( !$old || !$new ) {
                        return 0; // nothing to compare
                }
                $dbr = wfGetDB( DB_REPLICA );
                $conds = [
                        'rev_page' => $this->getArticleID(),
                        'rev_timestamp > ' . $dbr->addQuotes( $dbr->timestamp( $old->getTimestamp() ) ),
                        'rev_timestamp < ' . $dbr->addQuotes( $dbr->timestamp( $new->getTimestamp() ) )
                ];
                if ( $max !== null ) {
                        return $dbr->selectRowCount( 'revision', '1',
                                $conds,
                                __METHOD__,
                                [ 'LIMIT' => $max + 1 ] // extra to detect truncation
                        );
                } else {
                        return (int)$dbr->selectField( 'revision', 'count(*)', $conds, __METHOD__ );
                }
        }

        /**
         * Get the authors between the given revisions or revision IDs.
         * Used for diffs and other things that really need it.
         *
         * @since 1.23
         *
         * @param int|Revision $old Old revision or rev ID (first before range by default)
         * @param int|Revision $new New revision or rev ID (first after range by default)
         * @param int $limit Maximum number of authors
         * @param string|array $options (Optional): Single option, or an array of options:
         *     'include_old' Include $old in the range; $new is excluded.
         *     'include_new' Include $new in the range; $old is excluded.
         *     'include_both' Include both $old and $new in the range.
         *     Unknown option values are ignored.
         * @return array|null Names of revision authors in the range; null if not both revisions exist
         */
        public function getAuthorsBetween( $old, $new, $limit, $options = [] ) {
                if ( !( $old instanceof Revision ) ) {
                        $old = Revision::newFromTitle( $this, (int)$old );
                }
                if ( !( $new instanceof Revision ) ) {
                        $new = Revision::newFromTitle( $this, (int)$new );
                }
                // XXX: what if Revision objects are passed in, but they don't refer to this title?
                // Add $old->getPage() != $new->getPage() || $old->getPage() != $this->getArticleID()
                // in the sanity check below?
                if ( !$old || !$new ) {
                        return null; // nothing to compare
                }
                $authors = [];
                $old_cmp = '>';
                $new_cmp = '<';
                $options = (array)$options;
                if ( in_array( 'include_old', $options ) ) {
                        $old_cmp = '>=';
                }
                if ( in_array( 'include_new', $options ) ) {
                        $new_cmp = '<=';
                }
                if ( in_array( 'include_both', $options ) ) {
                        $old_cmp = '>=';
                        $new_cmp = '<=';
                }
                // No DB query needed if $old and $new are the same or successive revisions:
                if ( $old->getId() === $new->getId() ) {
                        return ( $old_cmp === '>' && $new_cmp === '<' ) ?
                                [] :
                                [ $old->getUserText( Revision::RAW ) ];
                } elseif ( $old->getId() === $new->getParentId() ) {
                        if ( $old_cmp === '>=' && $new_cmp === '<=' ) {
                                $authors[] = $old->getUserText( Revision::RAW );
                                if ( $old->getUserText( Revision::RAW ) != $new->getUserText( Revision::RAW ) ) {
                                        $authors[] = $new->getUserText( Revision::RAW );
                                }
                        } elseif ( $old_cmp === '>=' ) {
                                $authors[] = $old->getUserText( Revision::RAW );
                        } elseif ( $new_cmp === '<=' ) {
                                $authors[] = $new->getUserText( Revision::RAW );
                        }
                        return $authors;
                }
                $dbr = wfGetDB( DB_REPLICA );
                $res = $dbr->select( 'revision', 'DISTINCT rev_user_text',
                        [
                                'rev_page' => $this->getArticleID(),
                                "rev_timestamp $old_cmp " . $dbr->addQuotes( $dbr->timestamp( $old->getTimestamp() ) ),
                                "rev_timestamp $new_cmp " . $dbr->addQuotes( $dbr->timestamp( $new->getTimestamp() ) )
                        ], __METHOD__,
                        [ 'LIMIT' => $limit + 1 ] // add one so caller knows it was truncated
                );
                foreach ( $res as $row ) {
                        $authors[] = $row->rev_user_text;
                }
                return $authors;
        }

        /**
         * Get the number of authors between the given revisions or revision IDs.
         * Used for diffs and other things that really need it.
         *
         * @param int|Revision $old Old revision or rev ID (first before range by default)
         * @param int|Revision $new New revision or rev ID (first after range by default)
         * @param int $limit Maximum number of authors
         * @param string|array $options (Optional): Single option, or an array of options:
         *     'include_old' Include $old in the range; $new is excluded.
         *     'include_new' Include $new in the range; $old is excluded.
         *     'include_both' Include both $old and $new in the range.
         *     Unknown option values are ignored.
         * @return int Number of revision authors in the range; zero if not both revisions exist
         */
        public function countAuthorsBetween( $old, $new, $limit, $options = [] ) {
                $authors = $this->getAuthorsBetween( $old, $new, $limit, $options );
                return $authors ? count( $authors ) : 0;
        }

        /**
         * Compare with another title.
         *
         * @param Title $title
         * @return bool
         */
        public function equals( Title $title ) {
                // Note: === is necessary for proper matching of number-like titles.
                return $this->getInterwiki() === $title->getInterwiki()
                        && $this->getNamespace() == $title->getNamespace()
                        && $this->getDBkey() === $title->getDBkey();
        }

        /**
         * Check if this title is a subpage of another title
         *
         * @param Title $title
         * @return bool
         */
        public function isSubpageOf( Title $title ) {
                return $this->getInterwiki() === $title->getInterwiki()
                        && $this->getNamespace() == $title->getNamespace()
                        && strpos( $this->getDBkey(), $title->getDBkey() . '/' ) === 0;
        }

        /**
         * Check if page exists.  For historical reasons, this function simply
         * checks for the existence of the title in the page table, and will
         * thus return false for interwiki links, special pages and the like.
         * If you want to know if a title can be meaningfully viewed, you should
         * probably call the isKnown() method instead.
         *
         * @param int $flags An optional bit field; may be Title::GAID_FOR_UPDATE to check
         *   from master/for update
         * @return bool
         */
        public function exists( $flags = 0 ) {
                $exists = $this->getArticleID( $flags ) != 0;
                Hooks::run( 'TitleExists', [ $this, &$exists ] );
                return $exists;
        }

        /**
         * Should links to this title be shown as potentially viewable (i.e. as
         * "bluelinks"), even if there's no record by this title in the page
         * table?
         *
         * This function is semi-deprecated for public use, as well as somewhat
         * misleadingly named.  You probably just want to call isKnown(), which
         * calls this function internally.
         *
         * (ISSUE: Most of these checks are cheap, but the file existence check
         * can potentially be quite expensive.  Including it here fixes a lot of
         * existing code, but we might want to add an optional parameter to skip
         * it and any other expensive checks.)
         *
         * @return bool
         */
        public function isAlwaysKnown() {
                $isKnown = null;

                /**
                 * Allows overriding default behavior for determining if a page exists.
                 * If $isKnown is kept as null, regular checks happen. If it's
                 * a boolean, this value is returned by the isKnown method.
                 *
                 * @since 1.20
                 *
                 * @param Title $title
                 * @param bool|null $isKnown
                 */
                Hooks::run( 'TitleIsAlwaysKnown', [ $this, &$isKnown ] );

                if ( !is_null( $isKnown ) ) {
                        return $isKnown;
                }

                if ( $this->isExternal() ) {
                        return true;  // any interwiki link might be viewable, for all we know
                }

                switch ( $this->mNamespace ) {
                        case NS_MEDIA:
                        case NS_FILE:
                                // file exists, possibly in a foreign repo
                                return (bool)wfFindFile( $this );
                        case NS_SPECIAL:
                                // valid special page
                                return SpecialPageFactory::exists( $this->getDBkey() );
                        case NS_MAIN:
                                // selflink, possibly with fragment
                                return $this->mDbkeyform == '';
                        case NS_MEDIAWIKI:
                                // known system message
                                return $this->hasSourceText() !== false;
                        default:
                                return false;
                }
        }

        /**
         * Does this title refer to a page that can (or might) be meaningfully
         * viewed?  In particular, this function may be used to determine if
         * links to the title should be rendered as "bluelinks" (as opposed to
         * "redlinks" to non-existent pages).
         * Adding something else to this function will cause inconsistency
         * since LinkHolderArray calls isAlwaysKnown() and does its own
         * page existence check.
         *
         * @return bool
         */
        public function isKnown() {
                return $this->isAlwaysKnown() || $this->exists();
        }

        /**
         * Does this page have source text?
         *
         * @return bool
         */
        public function hasSourceText() {
                if ( $this->exists() ) {
                        return true;
                }

                if ( $this->mNamespace == NS_MEDIAWIKI ) {
                        // If the page doesn't exist but is a known system message, default
                        // message content will be displayed, same for language subpages-
                        // Use always content language to avoid loading hundreds of languages
                        // to get the link color.
                        global $wgContLang;
                        list( $name, ) = MessageCache::singleton()->figureMessage(
                                $wgContLang->lcfirst( $this->getText() )
                        );
                        $message = wfMessage( $name )->inLanguage( $wgContLang )->useDatabase( false );
                        return $message->exists();
                }

                return false;
        }

        /**
         * Get the default message text or false if the message doesn't exist
         *
         * @return string|bool
         */
        public function getDefaultMessageText() {
                global $wgContLang;

                if ( $this->getNamespace() != NS_MEDIAWIKI ) { // Just in case
                        return false;
                }

                list( $name, $lang ) = MessageCache::singleton()->figureMessage(
                        $wgContLang->lcfirst( $this->getText() )
                );
                $message = wfMessage( $name )->inLanguage( $lang )->useDatabase( false );

                if ( $message->exists() ) {
                        return $message->plain();
                } else {
                        return false;
                }
        }

        /**
         * Updates page_touched for this page; called from LinksUpdate.php
         *
         * @param string $purgeTime [optional] TS_MW timestamp
         * @return bool True if the update succeeded
         */
        public function invalidateCache( $purgeTime = null ) {
                if ( wfReadOnly() ) {
                        return false;
                } elseif ( $this->mArticleID === 0 ) {
                        return true; // avoid gap locking if we know it's not there
                }

                $dbw = wfGetDB( DB_MASTER );
                $dbw->onTransactionPreCommitOrIdle( function () {
                        ResourceLoaderWikiModule::invalidateModuleCache( $this, null, null, wfWikiID() );
                } );

                $conds = $this->pageCond();
                DeferredUpdates::addUpdate(
                        new AutoCommitUpdate(
                                $dbw,
                                __METHOD__,
                                function ( IDatabase $dbw, $fname ) use ( $conds, $purgeTime ) {
                                        $dbTimestamp = $dbw->timestamp( $purgeTime ?: time() );
                                        $dbw->update(
                                                'page',
                                                [ 'page_touched' => $dbTimestamp ],
                                                $conds + [ 'page_touched < ' . $dbw->addQuotes( $dbTimestamp ) ],
                                                $fname
                                        );
                                        MediaWikiServices::getInstance()->getLinkCache()->invalidateTitle( $this );
                                }
                        ),
                        DeferredUpdates::PRESEND
                );

                return true;
        }

        /**
         * Update page_touched timestamps and send CDN purge messages for
         * pages linking to this title. May be sent to the job queue depending
         * on the number of links. Typically called on create and delete.
         */
        public function touchLinks() {
                DeferredUpdates::addUpdate( new HTMLCacheUpdate( $this, 'pagelinks' ) );
                if ( $this->getNamespace() == NS_CATEGORY ) {
                        DeferredUpdates::addUpdate( new HTMLCacheUpdate( $this, 'categorylinks' ) );
                }
        }

        /**
         * Get the last touched timestamp
         *
         * @param IDatabase $db Optional db
         * @return string|false Last-touched timestamp
         */
        public function getTouched( $db = null ) {
                if ( $db === null ) {
                        $db = wfGetDB( DB_REPLICA );
                }
                $touched = $db->selectField( 'page', 'page_touched', $this->pageCond(), __METHOD__ );
                return $touched;
        }

        /**
         * Get the timestamp when this page was updated since the user last saw it.
         *
         * @param User $user
         * @return string|null
         */
        public function getNotificationTimestamp( $user = null ) {
                global $wgUser;

                // Assume current user if none given
                if ( !$user ) {
                        $user = $wgUser;
                }
                // Check cache first
                $uid = $user->getId();
                if ( !$uid ) {
                        return false;
                }
                // avoid isset here, as it'll return false for null entries
                if ( array_key_exists( $uid, $this->mNotificationTimestamp ) ) {
                        return $this->mNotificationTimestamp[$uid];
                }
                // Don't cache too much!
                if ( count( $this->mNotificationTimestamp ) >= self::CACHE_MAX ) {
                        $this->mNotificationTimestamp = [];
                }

                $store = MediaWikiServices::getInstance()->getWatchedItemStore();
                $watchedItem = $store->getWatchedItem( $user, $this );
                if ( $watchedItem ) {
                        $this->mNotificationTimestamp[$uid] = $watchedItem->getNotificationTimestamp();
                } else {
                        $this->mNotificationTimestamp[$uid] = false;
                }

                return $this->mNotificationTimestamp[$uid];
        }

        /**
         * Generate strings used for xml 'id' names in monobook tabs
         *
         * @param string $prepend Defaults to 'nstab-'
         * @return string XML 'id' name
         */
        public function getNamespaceKey( $prepend = 'nstab-' ) {
                global $wgContLang;
                // Gets the subject namespace if this title
                $namespace = MWNamespace::getSubject( $this->getNamespace() );
                // Checks if canonical namespace name exists for namespace
                if ( MWNamespace::exists( $this->getNamespace() ) ) {
                        // Uses canonical namespace name
                        $namespaceKey = MWNamespace::getCanonicalName( $namespace );
                } else {
                        // Uses text of namespace
                        $namespaceKey = $this->getSubjectNsText();
                }
                // Makes namespace key lowercase
                $namespaceKey = $wgContLang->lc( $namespaceKey );
                // Uses main
                if ( $namespaceKey == '' ) {
                        $namespaceKey = 'main';
                }
                // Changes file to image for backwards compatibility
                if ( $namespaceKey == 'file' ) {
                        $namespaceKey = 'image';
                }
                return $prepend . $namespaceKey;
        }

        /**
         * Get all extant redirects to this Title
         *
         * @param int|null $ns Single namespace to consider; null to consider all namespaces
         * @return Title[] Array of Title redirects to this title
         */
        public function getRedirectsHere( $ns = null ) {
                $redirs = [];

                $dbr = wfGetDB( DB_REPLICA );
                $where = [
                        'rd_namespace' => $this->getNamespace(),
                        'rd_title' => $this->getDBkey(),
                        'rd_from = page_id'
                ];
                if ( $this->isExternal() ) {
                        $where['rd_interwiki'] = $this->getInterwiki();
                } else {
                        $where[] = 'rd_interwiki = ' . $dbr->addQuotes( '' ) . ' OR rd_interwiki IS NULL';
                }
                if ( !is_null( $ns ) ) {
                        $where['page_namespace'] = $ns;
                }

                $res = $dbr->select(
                        [ 'redirect', 'page' ],
                        [ 'page_namespace', 'page_title' ],
                        $where,
                        __METHOD__
                );

                foreach ( $res as $row ) {
                        $redirs[] = self::newFromRow( $row );
                }
                return $redirs;
        }

        /**
         * Check if this Title is a valid redirect target
         *
         * @return bool
         */
        public function isValidRedirectTarget() {
                global $wgInvalidRedirectTargets;

                if ( $this->isSpecialPage() ) {
                        // invalid redirect targets are stored in a global array, but explicitly disallow Userlogout here
                        if ( $this->isSpecial( 'Userlogout' ) ) {
                                return false;
                        }

                        foreach ( $wgInvalidRedirectTargets as $target ) {
                                if ( $this->isSpecial( $target ) ) {
                                        return false;
                                }
                        }
                }

                return true;
        }

        /**
         * Get a backlink cache object
         *
         * @return BacklinkCache
         */
        public function getBacklinkCache() {
                return BacklinkCache::get( $this );
        }

        /**
         * Whether the magic words __INDEX__ and __NOINDEX__ function for  this page.
         *
         * @return bool
         */
        public function canUseNoindex() {
                global $wgExemptFromUserRobotsControl;

                $bannedNamespaces = is_null( $wgExemptFromUserRobotsControl )
                        ? MWNamespace::getContentNamespaces()
                        : $wgExemptFromUserRobotsControl;

                return !in_array( $this->mNamespace, $bannedNamespaces );
        }

        /**
         * Returns the raw sort key to be used for categories, with the specified
         * prefix.  This will be fed to Collation::getSortKey() to get a
         * binary sortkey that can be used for actual sorting.
         *
         * @param string $prefix The prefix to be used, specified using
         *   {{defaultsort:}} or like [[Category:Foo|prefix]].  Empty for no
         *   prefix.
         * @return string
         */
        public function getCategorySortkey( $prefix = '' ) {
                $unprefixed = $this->getText();

                // Anything that uses this hook should only depend
                // on the Title object passed in, and should probably
                // tell the users to run updateCollations.php --force
                // in order to re-sort existing category relations.
                Hooks::run( 'GetDefaultSortkey', [ $this, &$unprefixed ] );
                if ( $prefix !== '' ) {
                        # Separate with a line feed, so the unprefixed part is only used as
                        # a tiebreaker when two pages have the exact same prefix.
                        # In UCA, tab is the only character that can sort above LF
                        # so we strip both of them from the original prefix.
                        $prefix = strtr( $prefix, "\n\t", '  ' );
                        return "$prefix\n$unprefixed";
                }
                return $unprefixed;
        }

        /**
         * Returns the page language code saved in the database, if $wgPageLanguageUseDB is set
         * to true in LocalSettings.php, otherwise returns false. If there is no language saved in
         * the db, it will return NULL.
         *
         * @return string|null|bool
         */
        private function getDbPageLanguageCode() {
                global $wgPageLanguageUseDB;

                // check, if the page language could be saved in the database, and if so and
                // the value is not requested already, lookup the page language using LinkCache
                if ( $wgPageLanguageUseDB && $this->mDbPageLanguage === false ) {
                        $linkCache = LinkCache::singleton();
                        $linkCache->addLinkObj( $this );
                        $this->mDbPageLanguage = $linkCache->getGoodLinkFieldObj( $this, 'lang' );
                }

                return $this->mDbPageLanguage;
        }

        /**
         * Get the language in which the content of this page is written in
         * wikitext. Defaults to $wgContLang, but in certain cases it can be
         * e.g. $wgLang (such as special pages, which are in the user language).
         *
         * @since 1.18
         * @return Language
         */
        public function getPageLanguage() {
                global $wgLang, $wgLanguageCode;
                if ( $this->isSpecialPage() ) {
                        // special pages are in the user language
                        return $wgLang;
                }

                // Checking if DB language is set
                $dbPageLanguage = $this->getDbPageLanguageCode();
                if ( $dbPageLanguage ) {
                        return wfGetLangObj( $dbPageLanguage );
                }

                if ( !$this->mPageLanguage || $this->mPageLanguage[1] !== $wgLanguageCode ) {
                        // Note that this may depend on user settings, so the cache should
                        // be only per-request.
                        // NOTE: ContentHandler::getPageLanguage() may need to load the
                        // content to determine the page language!
                        // Checking $wgLanguageCode hasn't changed for the benefit of unit
                        // tests.
                        $contentHandler = ContentHandler::getForTitle( $this );
                        $langObj = $contentHandler->getPageLanguage( $this );
                        $this->mPageLanguage = [ $langObj->getCode(), $wgLanguageCode ];
                } else {
                        $langObj = wfGetLangObj( $this->mPageLanguage[0] );
                }

                return $langObj;
        }

        /**
         * Get the language in which the content of this page is written when
         * viewed by user. Defaults to $wgContLang, but in certain cases it can be
         * e.g. $wgLang (such as special pages, which are in the user language).
         *
         * @since 1.20
         * @return Language
         */
        public function getPageViewLanguage() {
                global $wgLang;

                if ( $this->isSpecialPage() ) {
                        // If the user chooses a variant, the content is actually
                        // in a language whose code is the variant code.
                        $variant = $wgLang->getPreferredVariant();
                        if ( $wgLang->getCode() !== $variant ) {
                                return Language::factory( $variant );
                        }

                        return $wgLang;
                }

                // Checking if DB language is set
                $dbPageLanguage = $this->getDbPageLanguageCode();
                if ( $dbPageLanguage ) {
                        $pageLang = wfGetLangObj( $dbPageLanguage );
                        $variant = $pageLang->getPreferredVariant();
                        if ( $pageLang->getCode() !== $variant ) {
                                $pageLang = Language::factory( $variant );
                        }

                        return $pageLang;
                }

                // @note Can't be cached persistently, depends on user settings.
                // @note ContentHandler::getPageViewLanguage() may need to load the
                //   content to determine the page language!
                $contentHandler = ContentHandler::getForTitle( $this );
                $pageLang = $contentHandler->getPageViewLanguage( $this );
                return $pageLang;
        }

        /**
         * Get a list of rendered edit notices for this page.
         *
         * Array is keyed by the original message key, and values are rendered using parseAsBlock, so
         * they will already be wrapped in paragraphs.
         *
         * @since 1.21
         * @param int $oldid Revision ID that's being edited
         * @return array
         */
        public function getEditNotices( $oldid = 0 ) {
                $notices = [];

                // Optional notice for the entire namespace
                $editnotice_ns = 'editnotice-' . $this->getNamespace();
                $msg = wfMessage( $editnotice_ns );
                if ( $msg->exists() ) {
                        $html = $msg->parseAsBlock();
                        // Edit notices may have complex logic, but output nothing (T91715)
                        if ( trim( $html ) !== '' ) {
                                $notices[$editnotice_ns] = Html::rawElement(
                                        'div',
                                        [ 'class' => [
                                                'mw-editnotice',
                                                'mw-editnotice-namespace',
                                                Sanitizer::escapeClass( "mw-$editnotice_ns" )
                                        ] ],
                                        $html
                                );
                        }
                }

                if ( MWNamespace::hasSubpages( $this->getNamespace() ) ) {
                        // Optional notice for page itself and any parent page
                        $parts = explode( '/', $this->getDBkey() );
                        $editnotice_base = $editnotice_ns;
                        while ( count( $parts ) > 0 ) {
                                $editnotice_base .= '-' . array_shift( $parts );
                                $msg = wfMessage( $editnotice_base );
                                if ( $msg->exists() ) {
                                        $html = $msg->parseAsBlock();
                                        if ( trim( $html ) !== '' ) {
                                                $notices[$editnotice_base] = Html::rawElement(
                                                        'div',
                                                        [ 'class' => [
                                                                'mw-editnotice',
                                                                'mw-editnotice-base',
                                                                Sanitizer::escapeClass( "mw-$editnotice_base" )
                                                        ] ],
                                                        $html
                                                );
                                        }
                                }
                        }
                } else {
                        // Even if there are no subpages in namespace, we still don't want "/" in MediaWiki message keys
                        $editnoticeText = $editnotice_ns . '-' . strtr( $this->getDBkey(), '/', '-' );
                        $msg = wfMessage( $editnoticeText );
                        if ( $msg->exists() ) {
                                $html = $msg->parseAsBlock();
                                if ( trim( $html ) !== '' ) {
                                        $notices[$editnoticeText] = Html::rawElement(
                                                'div',
                                                [ 'class' => [
                                                        'mw-editnotice',
                                                        'mw-editnotice-page',
                                                        Sanitizer::escapeClass( "mw-$editnoticeText" )
                                                ] ],
                                                $html
                                        );
                                }
                        }
                }

                Hooks::run( 'TitleGetEditNotices', [ $this, $oldid, &$notices ] );
                return $notices;
        }

        /**
         * @return array
         */
        public function __sleep() {
                return [
                        'mNamespace',
                        'mDbkeyform',
                        'mFragment',
                        'mInterwiki',
                        'mLocalInterwiki',
                        'mUserCaseDBKey',
                        'mDefaultNamespace',
                ];
        }

        public function __wakeup() {
                $this->mArticleID = ( $this->mNamespace >= 0 ) ? -1 : 0;
                $this->mUrlform = wfUrlencode( $this->mDbkeyform );
                $this->mTextform = strtr( $this->mDbkeyform, '_', ' ' );
        }

}