Add sslCAFile option to DatabaseMysqli

[mediawiki.git] / includes / deferred / LinksUpdate.php

<?php
/**
 * Updater for link tracking tables after a page edit.
 *
 * 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 Wikimedia\Rdbms\IDatabase;
use MediaWiki\MediaWikiServices;
use Wikimedia\ScopedCallback;

/**
 * Class the manages updates of *_link tables as well as similar extension-managed tables
 *
 * @note: LinksUpdate is managed by DeferredUpdates::execute(). Do not run this in a transaction.
 *
 * See docs/deferred.txt
 */
class LinksUpdate extends DataUpdate implements EnqueueableDataUpdate {
        // @todo make members protected, but make sure extensions don't break

        /** @var int Page ID of the article linked from */
        public $mId;

        /** @var Title Title object of the article linked from */
        public $mTitle;

        /** @var ParserOutput */
        public $mParserOutput;

        /** @var array Map of title strings to IDs for the links in the document */
        public $mLinks;

        /** @var array DB keys of the images used, in the array key only */
        public $mImages;

        /** @var array Map of title strings to IDs for the template references, including broken ones */
        public $mTemplates;

        /** @var array URLs of external links, array key only */
        public $mExternals;

        /** @var array Map of category names to sort keys */
        public $mCategories;

        /** @var array Map of language codes to titles */
        public $mInterlangs;

        /** @var array 2-D map of (prefix => DBK => 1) */
        public $mInterwikis;

        /** @var array Map of arbitrary name to value */
        public $mProperties;

        /** @var bool Whether to queue jobs for recursive updates */
        public $mRecursive;

        /** @var Revision Revision for which this update has been triggered */
        private $mRevision;

        /**
         * @var null|array Added links if calculated.
         */
        private $linkInsertions = null;

        /**
         * @var null|array Deleted links if calculated.
         */
        private $linkDeletions = null;

        /**
         * @var null|array Added properties if calculated.
         */
        private $propertyInsertions = null;

        /**
         * @var null|array Deleted properties if calculated.
         */
        private $propertyDeletions = null;

        /**
         * @var User|null
         */
        private $user;

        /** @var IDatabase */
        private $db;

        /**
         * @param Title $title Title of the page we're updating
         * @param ParserOutput $parserOutput Output from a full parse of this page
         * @param bool $recursive Queue jobs for recursive updates?
         * @throws MWException
         */
        function __construct( Title $title, ParserOutput $parserOutput, $recursive = true ) {
                parent::__construct();

                $this->mTitle = $title;
                $this->mId = $title->getArticleID( Title::GAID_FOR_UPDATE );

                if ( !$this->mId ) {
                        throw new InvalidArgumentException(
                                "The Title object yields no ID. Perhaps the page doesn't exist?"
                        );
                }

                $this->mParserOutput = $parserOutput;

                $this->mLinks = $parserOutput->getLinks();
                $this->mImages = $parserOutput->getImages();
                $this->mTemplates = $parserOutput->getTemplates();
                $this->mExternals = $parserOutput->getExternalLinks();
                $this->mCategories = $parserOutput->getCategories();
                $this->mProperties = $parserOutput->getProperties();
                $this->mInterwikis = $parserOutput->getInterwikiLinks();

                # Convert the format of the interlanguage links
                # I didn't want to change it in the ParserOutput, because that array is passed all
                # the way back to the skin, so either a skin API break would be required, or an
                # inefficient back-conversion.
                $ill = $parserOutput->getLanguageLinks();
                $this->mInterlangs = [];
                foreach ( $ill as $link ) {
                        list( $key, $title ) = explode( ':', $link, 2 );
                        $this->mInterlangs[$key] = $title;
                }

                foreach ( $this->mCategories as &$sortkey ) {
                        # If the sortkey is longer then 255 bytes,
                        # it truncated by DB, and then doesn't get
                        # matched when comparing existing vs current
                        # categories, causing T27254.
                        # Also. substr behaves weird when given "".
                        if ( $sortkey !== '' ) {
                                $sortkey = substr( $sortkey, 0, 255 );
                        }
                }

                $this->mRecursive = $recursive;

                // Avoid PHP 7.1 warning from passing $this by reference
                $linksUpdate = $this;
                Hooks::run( 'LinksUpdateConstructed', [ &$linksUpdate ] );
        }

        /**
         * Update link tables with outgoing links from an updated article
         *
         * @note: this is managed by DeferredUpdates::execute(). Do not run this in a transaction.
         */
        public function doUpdate() {
                if ( $this->ticket ) {
                        // Make sure all links update threads see the changes of each other.
                        // This handles the case when updates have to batched into several COMMITs.
                        $scopedLock = self::acquirePageLock( $this->getDB(), $this->mId );
                }

                // Avoid PHP 7.1 warning from passing $this by reference
                $linksUpdate = $this;
                Hooks::run( 'LinksUpdate', [ &$linksUpdate ] );
                $this->doIncrementalUpdate();

                // Commit and release the lock (if set)
                ScopedCallback::consume( $scopedLock );
                // Run post-commit hooks without DBO_TRX
                $this->getDB()->onTransactionIdle(
                        function () {
                                // Avoid PHP 7.1 warning from passing $this by reference
                                $linksUpdate = $this;
                                Hooks::run( 'LinksUpdateComplete', [ &$linksUpdate, $this->ticket ] );
                        },
                        __METHOD__
                );
        }

        /**
         * Acquire a lock for performing link table updates for a page on a DB
         *
         * @param IDatabase $dbw
         * @param int $pageId
         * @param string $why One of (job, atomicity)
         * @return ScopedCallback
         * @throws RuntimeException
         * @since 1.27
         */
        public static function acquirePageLock( IDatabase $dbw, $pageId, $why = 'atomicity' ) {
                $key = "LinksUpdate:$why:pageid:$pageId";
                $scopedLock = $dbw->getScopedLockAndFlush( $key, __METHOD__, 15 );
                if ( !$scopedLock ) {
                        throw new RuntimeException( "Could not acquire lock '$key'." );
                }

                return $scopedLock;
        }

        protected function doIncrementalUpdate() {
                # Page links
                $existingPL = $this->getExistingLinks();
                $this->linkDeletions = $this->getLinkDeletions( $existingPL );
                $this->linkInsertions = $this->getLinkInsertions( $existingPL );
                $this->incrTableUpdate( 'pagelinks', 'pl', $this->linkDeletions, $this->linkInsertions );

                # Image links
                $existingIL = $this->getExistingImages();
                $imageDeletes = $this->getImageDeletions( $existingIL );
                $this->incrTableUpdate(
                        'imagelinks',
                        'il',
                        $imageDeletes,
                        $this->getImageInsertions( $existingIL ) );

                # Invalidate all image description pages which had links added or removed
                $imageUpdates = $imageDeletes + array_diff_key( $this->mImages, $existingIL );
                $this->invalidateImageDescriptions( $imageUpdates );

                # External links
                $existingEL = $this->getExistingExternals();
                $this->incrTableUpdate(
                        'externallinks',
                        'el',
                        $this->getExternalDeletions( $existingEL ),
                        $this->getExternalInsertions( $existingEL ) );

                # Language links
                $existingLL = $this->getExistingInterlangs();
                $this->incrTableUpdate(
                        'langlinks',
                        'll',
                        $this->getInterlangDeletions( $existingLL ),
                        $this->getInterlangInsertions( $existingLL ) );

                # Inline interwiki links
                $existingIW = $this->getExistingInterwikis();
                $this->incrTableUpdate(
                        'iwlinks',
                        'iwl',
                        $this->getInterwikiDeletions( $existingIW ),
                        $this->getInterwikiInsertions( $existingIW ) );

                # Template links
                $existingTL = $this->getExistingTemplates();
                $this->incrTableUpdate(
                        'templatelinks',
                        'tl',
                        $this->getTemplateDeletions( $existingTL ),
                        $this->getTemplateInsertions( $existingTL ) );

                # Category links
                $existingCL = $this->getExistingCategories();
                $categoryDeletes = $this->getCategoryDeletions( $existingCL );
                $this->incrTableUpdate(
                        'categorylinks',
                        'cl',
                        $categoryDeletes,
                        $this->getCategoryInsertions( $existingCL ) );
                $categoryInserts = array_diff_assoc( $this->mCategories, $existingCL );
                $categoryUpdates = $categoryInserts + $categoryDeletes;

                # Page properties
                $existingPP = $this->getExistingProperties();
                $this->propertyDeletions = $this->getPropertyDeletions( $existingPP );
                $this->incrTableUpdate(
                        'page_props',
                        'pp',
                        $this->propertyDeletions,
                        $this->getPropertyInsertions( $existingPP ) );

                # Invalidate the necessary pages
                $this->propertyInsertions = array_diff_assoc( $this->mProperties, $existingPP );
                $changed = $this->propertyDeletions + $this->propertyInsertions;
                $this->invalidateProperties( $changed );

                # Invalidate all categories which were added, deleted or changed (set symmetric difference)
                $this->invalidateCategories( $categoryUpdates );
                $this->updateCategoryCounts( $categoryInserts, $categoryDeletes );

                # Refresh links of all pages including this page
                # This will be in a separate transaction
                if ( $this->mRecursive ) {
                        $this->queueRecursiveJobs();
                }

                # Update the links table freshness for this title
                $this->updateLinksTimestamp();
        }

        /**
         * Queue recursive jobs for this page
         *
         * Which means do LinksUpdate on all pages that include the current page,
         * using the job queue.
         */
        protected function queueRecursiveJobs() {
                self::queueRecursiveJobsForTable( $this->mTitle, 'templatelinks' );
                if ( $this->mTitle->getNamespace() == NS_FILE ) {
                        // Process imagelinks in case the title is or was a redirect
                        self::queueRecursiveJobsForTable( $this->mTitle, 'imagelinks' );
                }

                $bc = $this->mTitle->getBacklinkCache();
                // Get jobs for cascade-protected backlinks for a high priority queue.
                // If meta-templates change to using a new template, the new template
                // should be implicitly protected as soon as possible, if applicable.
                // These jobs duplicate a subset of the above ones, but can run sooner.
                // Which ever runs first generally no-ops the other one.
                $jobs = [];
                foreach ( $bc->getCascadeProtectedLinks() as $title ) {
                        $jobs[] = RefreshLinksJob::newPrioritized( $title, [] );
                }
                JobQueueGroup::singleton()->push( $jobs );
        }

        /**
         * Queue a RefreshLinks job for any table.
         *
         * @param Title $title Title to do job for
         * @param string $table Table to use (e.g. 'templatelinks')
         */
        public static function queueRecursiveJobsForTable( Title $title, $table ) {
                if ( $title->getBacklinkCache()->hasLinks( $table ) ) {
                        $job = new RefreshLinksJob(
                                $title,
                                [
                                        'table' => $table,
                                        'recursive' => true,
                                ] + Job::newRootJobParams( // "overall" refresh links job info
                                        "refreshlinks:{$table}:{$title->getPrefixedText()}"
                                )
                        );

                        JobQueueGroup::singleton()->push( $job );
                }
        }

        /**
         * @param array $cats
         */
        private function invalidateCategories( $cats ) {
                PurgeJobUtils::invalidatePages( $this->getDB(), NS_CATEGORY, array_keys( $cats ) );
        }

        /**
         * Update all the appropriate counts in the category table.
         * @param array $added Associative array of category name => sort key
         * @param array $deleted Associative array of category name => sort key
         */
        private function updateCategoryCounts( array $added, array $deleted ) {
                global $wgUpdateRowsPerQuery;

                if ( !$added && !$deleted ) {
                        return;
                }

                $wikiId = $this->getDB()->getWikiID();
                $wp = WikiPage::factory( $this->mTitle );
                $lbf = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
                // T163801: try to release any row locks to reduce contention
                $lbf->commitAndWaitForReplication( __METHOD__, $this->ticket, [ 'wiki' => $wikiId ] );

                foreach ( array_chunk( array_keys( $added ), $wgUpdateRowsPerQuery ) as $addBatch ) {
                        $wp->updateCategoryCounts( $addBatch, [], $this->mId );
                        $lbf->commitAndWaitForReplication( __METHOD__, $this->ticket, [ 'wiki' => $wikiId ] );
                }

                foreach ( array_chunk( array_keys( $deleted ), $wgUpdateRowsPerQuery ) as $deleteBatch ) {
                        $wp->updateCategoryCounts( [], $deleteBatch, $this->mId );
                        $lbf->commitAndWaitForReplication( __METHOD__, $this->ticket, [ 'wiki' => $wikiId ] );
                }
        }

        /**
         * @param array $images
         */
        private function invalidateImageDescriptions( $images ) {
                PurgeJobUtils::invalidatePages( $this->getDB(), NS_FILE, array_keys( $images ) );
        }

        /**
         * Update a table by doing a delete query then an insert query
         * @param string $table Table name
         * @param string $prefix Field name prefix
         * @param array $deletions
         * @param array $insertions Rows to insert
         */
        private function incrTableUpdate( $table, $prefix, $deletions, $insertions ) {
                $services = MediaWikiServices::getInstance();
                $bSize = $services->getMainConfig()->get( 'UpdateRowsPerQuery' );
                $lbf = $services->getDBLoadBalancerFactory();

                if ( $table === 'page_props' ) {
                        $fromField = 'pp_page';
                } else {
                        $fromField = "{$prefix}_from";
                }

                $deleteWheres = []; // list of WHERE clause arrays for each DB delete() call
                if ( $table === 'pagelinks' || $table === 'templatelinks' || $table === 'iwlinks' ) {
                        $baseKey = ( $table === 'iwlinks' ) ? 'iwl_prefix' : "{$prefix}_namespace";

                        $curBatchSize = 0;
                        $curDeletionBatch = [];
                        $deletionBatches = [];
                        foreach ( $deletions as $ns => $dbKeys ) {
                                foreach ( $dbKeys as $dbKey => $unused ) {
                                        $curDeletionBatch[$ns][$dbKey] = 1;
                                        if ( ++$curBatchSize >= $bSize ) {
                                                $deletionBatches[] = $curDeletionBatch;
                                                $curDeletionBatch = [];
                                                $curBatchSize = 0;
                                        }
                                }
                        }
                        if ( $curDeletionBatch ) {
                                $deletionBatches[] = $curDeletionBatch;
                        }

                        foreach ( $deletionBatches as $deletionBatch ) {
                                $deleteWheres[] = [
                                        $fromField => $this->mId,
                                        $this->getDB()->makeWhereFrom2d( $deletionBatch, $baseKey, "{$prefix}_title" )
                                ];
                        }
                } else {
                        if ( $table === 'langlinks' ) {
                                $toField = 'll_lang';
                        } elseif ( $table === 'page_props' ) {
                                $toField = 'pp_propname';
                        } else {
                                $toField = $prefix . '_to';
                        }

                        $deletionBatches = array_chunk( array_keys( $deletions ), $bSize );
                        foreach ( $deletionBatches as $deletionBatch ) {
                                $deleteWheres[] = [ $fromField => $this->mId, $toField => $deletionBatch ];
                        }
                }

                foreach ( $deleteWheres as $deleteWhere ) {
                        $this->getDB()->delete( $table, $deleteWhere, __METHOD__ );
                        $lbf->commitAndWaitForReplication(
                                __METHOD__, $this->ticket, [ 'wiki' => $this->getDB()->getWikiID() ]
                        );
                }

                $insertBatches = array_chunk( $insertions, $bSize );
                foreach ( $insertBatches as $insertBatch ) {
                        $this->getDB()->insert( $table, $insertBatch, __METHOD__, 'IGNORE' );
                        $lbf->commitAndWaitForReplication(
                                __METHOD__, $this->ticket, [ 'wiki' => $this->getDB()->getWikiID() ]
                        );
                }

                if ( count( $insertions ) ) {
                        Hooks::run( 'LinksUpdateAfterInsert', [ $this, $table, $insertions ] );
                }
        }

        /**
         * Get an array of pagelinks insertions for passing to the DB
         * Skips the titles specified by the 2-D array $existing
         * @param array $existing
         * @return array
         */
        private function getLinkInsertions( $existing = [] ) {
                $arr = [];
                foreach ( $this->mLinks as $ns => $dbkeys ) {
                        $diffs = isset( $existing[$ns] )
                                ? array_diff_key( $dbkeys, $existing[$ns] )
                                : $dbkeys;
                        foreach ( $diffs as $dbk => $id ) {
                                $arr[] = [
                                        'pl_from' => $this->mId,
                                        'pl_from_namespace' => $this->mTitle->getNamespace(),
                                        'pl_namespace' => $ns,
                                        'pl_title' => $dbk
                                ];
                        }
                }

                return $arr;
        }

        /**
         * Get an array of template insertions. Like getLinkInsertions()
         * @param array $existing
         * @return array
         */
        private function getTemplateInsertions( $existing = [] ) {
                $arr = [];
                foreach ( $this->mTemplates as $ns => $dbkeys ) {
                        $diffs = isset( $existing[$ns] ) ? array_diff_key( $dbkeys, $existing[$ns] ) : $dbkeys;
                        foreach ( $diffs as $dbk => $id ) {
                                $arr[] = [
                                        'tl_from' => $this->mId,
                                        'tl_from_namespace' => $this->mTitle->getNamespace(),
                                        'tl_namespace' => $ns,
                                        'tl_title' => $dbk
                                ];
                        }
                }

                return $arr;
        }

        /**
         * Get an array of image insertions
         * Skips the names specified in $existing
         * @param array $existing
         * @return array
         */
        private function getImageInsertions( $existing = [] ) {
                $arr = [];
                $diffs = array_diff_key( $this->mImages, $existing );
                foreach ( $diffs as $iname => $dummy ) {
                        $arr[] = [
                                'il_from' => $this->mId,
                                'il_from_namespace' => $this->mTitle->getNamespace(),
                                'il_to' => $iname
                        ];
                }

                return $arr;
        }

        /**
         * Get an array of externallinks insertions. Skips the names specified in $existing
         * @param array $existing
         * @return array
         */
        private function getExternalInsertions( $existing = [] ) {
                $arr = [];
                $diffs = array_diff_key( $this->mExternals, $existing );
                foreach ( $diffs as $url => $dummy ) {
                        foreach ( wfMakeUrlIndexes( $url ) as $index ) {
                                $arr[] = [
                                        'el_id' => $this->getDB()->nextSequenceValue( 'externallinks_el_id_seq' ),
                                        'el_from' => $this->mId,
                                        'el_to' => $url,
                                        'el_index' => $index,
                                ];
                        }
                }

                return $arr;
        }

        /**
         * Get an array of category insertions
         *
         * @param array $existing Mapping existing category names to sort keys. If both
         * match a link in $this, the link will be omitted from the output
         *
         * @return array
         */
        private function getCategoryInsertions( $existing = [] ) {
                global $wgContLang, $wgCategoryCollation;
                $diffs = array_diff_assoc( $this->mCategories, $existing );
                $arr = [];
                foreach ( $diffs as $name => $prefix ) {
                        $nt = Title::makeTitleSafe( NS_CATEGORY, $name );
                        $wgContLang->findVariantLink( $name, $nt, true );

                        if ( $this->mTitle->getNamespace() == NS_CATEGORY ) {
                                $type = 'subcat';
                        } elseif ( $this->mTitle->getNamespace() == NS_FILE ) {
                                $type = 'file';
                        } else {
                                $type = 'page';
                        }

                        # Treat custom sortkeys as a prefix, so that if multiple
                        # things are forced to sort as '*' or something, they'll
                        # sort properly in the category rather than in page_id
                        # order or such.
                        $sortkey = Collation::singleton()->getSortKey(
                                $this->mTitle->getCategorySortkey( $prefix ) );

                        $arr[] = [
                                'cl_from' => $this->mId,
                                'cl_to' => $name,
                                'cl_sortkey' => $sortkey,
                                'cl_timestamp' => $this->getDB()->timestamp(),
                                'cl_sortkey_prefix' => $prefix,
                                'cl_collation' => $wgCategoryCollation,
                                'cl_type' => $type,
                        ];
                }

                return $arr;
        }

        /**
         * Get an array of interlanguage link insertions
         *
         * @param array $existing Mapping existing language codes to titles
         *
         * @return array
         */
        private function getInterlangInsertions( $existing = [] ) {
                $diffs = array_diff_assoc( $this->mInterlangs, $existing );
                $arr = [];
                foreach ( $diffs as $lang => $title ) {
                        $arr[] = [
                                'll_from' => $this->mId,
                                'll_lang' => $lang,
                                'll_title' => $title
                        ];
                }

                return $arr;
        }

        /**
         * Get an array of page property insertions
         * @param array $existing
         * @return array
         */
        function getPropertyInsertions( $existing = [] ) {
                $diffs = array_diff_assoc( $this->mProperties, $existing );

                $arr = [];
                foreach ( array_keys( $diffs ) as $name ) {
                        $arr[] = $this->getPagePropRowData( $name );
                }

                return $arr;
        }

        /**
         * Returns an associative array to be used for inserting a row into
         * the page_props table. Besides the given property name, this will
         * include the page id from $this->mId and any property value from
         * $this->mProperties.
         *
         * The array returned will include the pp_sortkey field if this
         * is present in the database (as indicated by $wgPagePropsHaveSortkey).
         * The sortkey value is currently determined by getPropertySortKeyValue().
         *
         * @note this assumes that $this->mProperties[$prop] is defined.
         *
         * @param string $prop The name of the property.
         *
         * @return array
         */
        private function getPagePropRowData( $prop ) {
                global $wgPagePropsHaveSortkey;

                $value = $this->mProperties[$prop];

                $row = [
                        'pp_page' => $this->mId,
                        'pp_propname' => $prop,
                        'pp_value' => $value,
                ];

                if ( $wgPagePropsHaveSortkey ) {
                        $row['pp_sortkey'] = $this->getPropertySortKeyValue( $value );
                }

                return $row;
        }

        /**
         * Determines the sort key for the given property value.
         * This will return $value if it is a float or int,
         * 1 or resp. 0 if it is a bool, and null otherwise.
         *
         * @note In the future, we may allow the sortkey to be specified explicitly
         *       in ParserOutput::setProperty.
         *
         * @param mixed $value
         *
         * @return float|null
         */
        private function getPropertySortKeyValue( $value ) {
                if ( is_int( $value ) || is_float( $value ) || is_bool( $value ) ) {
                        return floatval( $value );
                }

                return null;
        }

        /**
         * Get an array of interwiki insertions for passing to the DB
         * Skips the titles specified by the 2-D array $existing
         * @param array $existing
         * @return array
         */
        private function getInterwikiInsertions( $existing = [] ) {
                $arr = [];
                foreach ( $this->mInterwikis as $prefix => $dbkeys ) {
                        $diffs = isset( $existing[$prefix] )
                                ? array_diff_key( $dbkeys, $existing[$prefix] )
                                : $dbkeys;

                        foreach ( $diffs as $dbk => $id ) {
                                $arr[] = [
                                        'iwl_from' => $this->mId,
                                        'iwl_prefix' => $prefix,
                                        'iwl_title' => $dbk
                                ];
                        }
                }

                return $arr;
        }

        /**
         * Given an array of existing links, returns those links which are not in $this
         * and thus should be deleted.
         * @param array $existing
         * @return array
         */
        private function getLinkDeletions( $existing ) {
                $del = [];
                foreach ( $existing as $ns => $dbkeys ) {
                        if ( isset( $this->mLinks[$ns] ) ) {
                                $del[$ns] = array_diff_key( $existing[$ns], $this->mLinks[$ns] );
                        } else {
                                $del[$ns] = $existing[$ns];
                        }
                }

                return $del;
        }

        /**
         * Given an array of existing templates, returns those templates which are not in $this
         * and thus should be deleted.
         * @param array $existing
         * @return array
         */
        private function getTemplateDeletions( $existing ) {
                $del = [];
                foreach ( $existing as $ns => $dbkeys ) {
                        if ( isset( $this->mTemplates[$ns] ) ) {
                                $del[$ns] = array_diff_key( $existing[$ns], $this->mTemplates[$ns] );
                        } else {
                                $del[$ns] = $existing[$ns];
                        }
                }

                return $del;
        }

        /**
         * Given an array of existing images, returns those images which are not in $this
         * and thus should be deleted.
         * @param array $existing
         * @return array
         */
        private function getImageDeletions( $existing ) {
                return array_diff_key( $existing, $this->mImages );
        }

        /**
         * Given an array of existing external links, returns those links which are not
         * in $this and thus should be deleted.
         * @param array $existing
         * @return array
         */
        private function getExternalDeletions( $existing ) {
                return array_diff_key( $existing, $this->mExternals );
        }

        /**
         * Given an array of existing categories, returns those categories which are not in $this
         * and thus should be deleted.
         * @param array $existing
         * @return array
         */
        private function getCategoryDeletions( $existing ) {
                return array_diff_assoc( $existing, $this->mCategories );
        }

        /**
         * Given an array of existing interlanguage links, returns those links which are not
         * in $this and thus should be deleted.
         * @param array $existing
         * @return array
         */
        private function getInterlangDeletions( $existing ) {
                return array_diff_assoc( $existing, $this->mInterlangs );
        }

        /**
         * Get array of properties which should be deleted.
         * @param array $existing
         * @return array
         */
        function getPropertyDeletions( $existing ) {
                return array_diff_assoc( $existing, $this->mProperties );
        }

        /**
         * Given an array of existing interwiki links, returns those links which are not in $this
         * and thus should be deleted.
         * @param array $existing
         * @return array
         */
        private function getInterwikiDeletions( $existing ) {
                $del = [];
                foreach ( $existing as $prefix => $dbkeys ) {
                        if ( isset( $this->mInterwikis[$prefix] ) ) {
                                $del[$prefix] = array_diff_key( $existing[$prefix], $this->mInterwikis[$prefix] );
                        } else {
                                $del[$prefix] = $existing[$prefix];
                        }
                }

                return $del;
        }

        /**
         * Get an array of existing links, as a 2-D array
         *
         * @return array
         */
        private function getExistingLinks() {
                $res = $this->getDB()->select( 'pagelinks', [ 'pl_namespace', 'pl_title' ],
                        [ 'pl_from' => $this->mId ], __METHOD__ );
                $arr = [];
                foreach ( $res as $row ) {
                        if ( !isset( $arr[$row->pl_namespace] ) ) {
                                $arr[$row->pl_namespace] = [];
                        }
                        $arr[$row->pl_namespace][$row->pl_title] = 1;
                }

                return $arr;
        }

        /**
         * Get an array of existing templates, as a 2-D array
         *
         * @return array
         */
        private function getExistingTemplates() {
                $res = $this->getDB()->select( 'templatelinks', [ 'tl_namespace', 'tl_title' ],
                        [ 'tl_from' => $this->mId ], __METHOD__ );
                $arr = [];
                foreach ( $res as $row ) {
                        if ( !isset( $arr[$row->tl_namespace] ) ) {
                                $arr[$row->tl_namespace] = [];
                        }
                        $arr[$row->tl_namespace][$row->tl_title] = 1;
                }

                return $arr;
        }

        /**
         * Get an array of existing images, image names in the keys
         *
         * @return array
         */
        private function getExistingImages() {
                $res = $this->getDB()->select( 'imagelinks', [ 'il_to' ],
                        [ 'il_from' => $this->mId ], __METHOD__ );
                $arr = [];
                foreach ( $res as $row ) {
                        $arr[$row->il_to] = 1;
                }

                return $arr;
        }

        /**
         * Get an array of existing external links, URLs in the keys
         *
         * @return array
         */
        private function getExistingExternals() {
                $res = $this->getDB()->select( 'externallinks', [ 'el_to' ],
                        [ 'el_from' => $this->mId ], __METHOD__ );
                $arr = [];
                foreach ( $res as $row ) {
                        $arr[$row->el_to] = 1;
                }

                return $arr;
        }

        /**
         * Get an array of existing categories, with the name in the key and sort key in the value.
         *
         * @return array
         */
        private function getExistingCategories() {
                $res = $this->getDB()->select( 'categorylinks', [ 'cl_to', 'cl_sortkey_prefix' ],
                        [ 'cl_from' => $this->mId ], __METHOD__ );
                $arr = [];
                foreach ( $res as $row ) {
                        $arr[$row->cl_to] = $row->cl_sortkey_prefix;
                }

                return $arr;
        }

        /**
         * Get an array of existing interlanguage links, with the language code in the key and the
         * title in the value.
         *
         * @return array
         */
        private function getExistingInterlangs() {
                $res = $this->getDB()->select( 'langlinks', [ 'll_lang', 'll_title' ],
                        [ 'll_from' => $this->mId ], __METHOD__ );
                $arr = [];
                foreach ( $res as $row ) {
                        $arr[$row->ll_lang] = $row->ll_title;
                }

                return $arr;
        }

        /**
         * Get an array of existing inline interwiki links, as a 2-D array
         * @return array (prefix => array(dbkey => 1))
         */
        private function getExistingInterwikis() {
                $res = $this->getDB()->select( 'iwlinks', [ 'iwl_prefix', 'iwl_title' ],
                        [ 'iwl_from' => $this->mId ], __METHOD__ );
                $arr = [];
                foreach ( $res as $row ) {
                        if ( !isset( $arr[$row->iwl_prefix] ) ) {
                                $arr[$row->iwl_prefix] = [];
                        }
                        $arr[$row->iwl_prefix][$row->iwl_title] = 1;
                }

                return $arr;
        }

        /**
         * Get an array of existing categories, with the name in the key and sort key in the value.
         *
         * @return array Array of property names and values
         */
        private function getExistingProperties() {
                $res = $this->getDB()->select( 'page_props', [ 'pp_propname', 'pp_value' ],
                        [ 'pp_page' => $this->mId ], __METHOD__ );
                $arr = [];
                foreach ( $res as $row ) {
                        $arr[$row->pp_propname] = $row->pp_value;
                }

                return $arr;
        }

        /**
         * Return the title object of the page being updated
         * @return Title
         */
        public function getTitle() {
                return $this->mTitle;
        }

        /**
         * Returns parser output
         * @since 1.19
         * @return ParserOutput
         */
        public function getParserOutput() {
                return $this->mParserOutput;
        }

        /**
         * Return the list of images used as generated by the parser
         * @return array
         */
        public function getImages() {
                return $this->mImages;
        }

        /**
         * Set the revision corresponding to this LinksUpdate
         *
         * @since 1.27
         *
         * @param Revision $revision
         */
        public function setRevision( Revision $revision ) {
                $this->mRevision = $revision;
        }

        /**
         * @since 1.28
         * @return null|Revision
         */
        public function getRevision() {
                return $this->mRevision;
        }

        /**
         * Set the User who triggered this LinksUpdate
         *
         * @since 1.27
         * @param User $user
         */
        public function setTriggeringUser( User $user ) {
                $this->user = $user;
        }

        /**
         * @since 1.27
         * @return null|User
         */
        public function getTriggeringUser() {
                return $this->user;
        }

        /**
         * Invalidate any necessary link lists related to page property changes
         * @param array $changed
         */
        private function invalidateProperties( $changed ) {
                global $wgPagePropLinkInvalidations;

                foreach ( $changed as $name => $value ) {
                        if ( isset( $wgPagePropLinkInvalidations[$name] ) ) {
                                $inv = $wgPagePropLinkInvalidations[$name];
                                if ( !is_array( $inv ) ) {
                                        $inv = [ $inv ];
                                }
                                foreach ( $inv as $table ) {
                                        DeferredUpdates::addUpdate( new HTMLCacheUpdate( $this->mTitle, $table ) );
                                }
                        }
                }
        }

        /**
         * Fetch page links added by this LinksUpdate.  Only available after the update is complete.
         * @since 1.22
         * @return null|array Array of Titles
         */
        public function getAddedLinks() {
                if ( $this->linkInsertions === null ) {
                        return null;
                }
                $result = [];
                foreach ( $this->linkInsertions as $insertion ) {
                        $result[] = Title::makeTitle( $insertion['pl_namespace'], $insertion['pl_title'] );
                }

                return $result;
        }

        /**
         * Fetch page links removed by this LinksUpdate.  Only available after the update is complete.
         * @since 1.22
         * @return null|array Array of Titles
         */
        public function getRemovedLinks() {
                if ( $this->linkDeletions === null ) {
                        return null;
                }
                $result = [];
                foreach ( $this->linkDeletions as $ns => $titles ) {
                        foreach ( $titles as $title => $unused ) {
                                $result[] = Title::makeTitle( $ns, $title );
                        }
                }

                return $result;
        }

        /**
         * Fetch page properties added by this LinksUpdate.
         * Only available after the update is complete.
         * @since 1.28
         * @return null|array
         */
        public function getAddedProperties() {
                return $this->propertyInsertions;
        }

        /**
         * Fetch page properties removed by this LinksUpdate.
         * Only available after the update is complete.
         * @since 1.28
         * @return null|array
         */
        public function getRemovedProperties() {
                return $this->propertyDeletions;
        }

        /**
         * Update links table freshness
         */
        private function updateLinksTimestamp() {
                if ( $this->mId ) {
                        // The link updates made here only reflect the freshness of the parser output
                        $timestamp = $this->mParserOutput->getCacheTime();
                        $this->getDB()->update( 'page',
                                [ 'page_links_updated' => $this->getDB()->timestamp( $timestamp ) ],
                                [ 'page_id' => $this->mId ],
                                __METHOD__
                        );
                }
        }

        /**
         * @return IDatabase
         */
        private function getDB() {
                if ( !$this->db ) {
                        $this->db = wfGetDB( DB_MASTER );
                }

                return $this->db;
        }

        public function getAsJobSpecification() {
                if ( $this->user ) {
                        $userInfo = [
                                'userId' => $this->user->getId(),
                                'userName' => $this->user->getName(),
                        ];
                } else {
                        $userInfo = false;
                }

                if ( $this->mRevision ) {
                        $triggeringRevisionId = $this->mRevision->getId();
                } else {
                        $triggeringRevisionId = false;
                }

                return [
                        'wiki' => $this->getDB()->getWikiID(),
                        'job'  => new JobSpecification(
                                'refreshLinksPrioritized',
                                [
                                        // Reuse the parser cache if it was saved
                                        'rootJobTimestamp' => $this->mParserOutput->getCacheTime(),
                                        'useRecursiveLinksUpdate' => $this->mRecursive,
                                        'triggeringUser' => $userInfo,
                                        'triggeringRevisionId' => $triggeringRevisionId,
                                ],
                                [ 'removeDuplicates' => true ],
                                $this->getTitle()
                        )
                ];
        }
}