Merge "Tweaked WikiPage::clear() comment a bit"

[mediawiki.git] / includes / content / ContentHandler.php

<?php
/**
 * Base class for content handling.
 *
 * 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
 *
 * @since 1.21
 *
 * @file
 * @ingroup Content
 *
 * @author Daniel Kinzler
 */

/**
 * Exception representing a failure to serialize or unserialize a content object.
 *
 * @ingroup Content
 */
class MWContentSerializationException extends MWException {

}

/**
 * A content handler knows how do deal with a specific type of content on a wiki
 * page. Content is stored in the database in a serialized form (using a
 * serialization format a.k.a. MIME type) and is unserialized into its native
 * PHP representation (the content model), which is wrapped in an instance of
 * the appropriate subclass of Content.
 *
 * ContentHandler instances are stateless singletons that serve, among other
 * things, as a factory for Content objects. Generally, there is one subclass
 * of ContentHandler and one subclass of Content for every type of content model.
 *
 * Some content types have a flat model, that is, their native representation
 * is the same as their serialized form. Examples would be JavaScript and CSS
 * code. As of now, this also applies to wikitext (MediaWiki's default content
 * type), but wikitext content may be represented by a DOM or AST structure in
 * the future.
 *
 * @ingroup Content
 */
abstract class ContentHandler {

        /**
         * Switch for enabling deprecation warnings. Used by ContentHandler::deprecated()
         * and ContentHandler::runLegacyHooks().
         *
         * Once the ContentHandler code has settled in a bit, this should be set to true to
         * make extensions etc. show warnings when using deprecated functions and hooks.
         */
        protected static $enableDeprecationWarnings = false;

        /**
         * Convenience function for getting flat text from a Content object. This
         * should only be used in the context of backwards compatibility with code
         * that is not yet able to handle Content objects!
         *
         * If $content is null, this method returns the empty string.
         *
         * If $content is an instance of TextContent, this method returns the flat
         * text as returned by $content->getNativeData().
         *
         * If $content is not a TextContent object, the behavior of this method
         * depends on the global $wgContentHandlerTextFallback:
         * - If $wgContentHandlerTextFallback is 'fail' and $content is not a
         *   TextContent object, an MWException is thrown.
         * - If $wgContentHandlerTextFallback is 'serialize' and $content is not a
         *   TextContent object, $content->serialize() is called to get a string
         *   form of the content.
         * - If $wgContentHandlerTextFallback is 'ignore' and $content is not a
         *   TextContent object, this method returns null.
         * - otherwise, the behavior is undefined.
         *
         * @since 1.21
         *
         * @param $content Content|null
         * @return null|string the textual form of $content, if available
         * @throws MWException if $content is not an instance of TextContent and
         *   $wgContentHandlerTextFallback was set to 'fail'.
         */
        public static function getContentText( Content $content = null ) {
                global $wgContentHandlerTextFallback;

                if ( is_null( $content ) ) {
                        return '';
                }

                if ( $content instanceof TextContent ) {
                        return $content->getNativeData();
                }

                wfDebugLog( 'ContentHandler', 'Accessing ' . $content->getModel() . ' content as text!' );

                if ( $wgContentHandlerTextFallback == 'fail' ) {
                        throw new MWException(
                                "Attempt to get text from Content with model " .
                                $content->getModel()
                        );
                }

                if ( $wgContentHandlerTextFallback == 'serialize' ) {
                        return $content->serialize();
                }

                return null;
        }

        /**
         * Convenience function for creating a Content object from a given textual
         * representation.
         *
         * $text will be deserialized into a Content object of the model specified
         * by $modelId (or, if that is not given, $title->getContentModel()) using
         * the given format.
         *
         * @since 1.21
         *
         * @param string $text the textual representation, will be
         *    unserialized to create the Content object
         * @param $title null|Title the title of the page this text belongs to.
         *    Required if $modelId is not provided.
         * @param $modelId null|string the model to deserialize to. If not provided,
         *    $title->getContentModel() is used.
         * @param $format null|string the format to use for deserialization. If not
         *    given, the model's default format is used.
         *
         * @throws MWException
         * @return Content a Content object representing $text
         *
         * @throws MWException if $model or $format is not supported or if $text can
         *    not be unserialized using $format.
         */
        public static function makeContent( $text, Title $title = null,
                $modelId = null, $format = null )
        {
                if ( is_null( $modelId ) ) {
                        if ( is_null( $title ) ) {
                                throw new MWException( "Must provide a Title object or a content model ID." );
                        }

                        $modelId = $title->getContentModel();
                }

                $handler = ContentHandler::getForModelID( $modelId );
                return $handler->unserializeContent( $text, $format );
        }

        /**
         * Returns the name of the default content model to be used for the page
         * with the given title.
         *
         * Note: There should rarely be need to call this method directly.
         * To determine the actual content model for a given page, use
         * Title::getContentModel().
         *
         * Which model is to be used by default for the page is determined based
         * on several factors:
         * - The global setting $wgNamespaceContentModels specifies a content model
         *   per namespace.
         * - The hook ContentHandlerDefaultModelFor may be used to override the page's default
         *   model.
         * - Pages in NS_MEDIAWIKI and NS_USER default to the CSS or JavaScript
         *   model if they end in .js or .css, respectively.
         * - Pages in NS_MEDIAWIKI default to the wikitext model otherwise.
         * - The hook TitleIsCssOrJsPage may be used to force a page to use the CSS
         *   or JavaScript model. This is a compatibility feature. The ContentHandlerDefaultModelFor
         *   hook should be used instead if possible.
         * - The hook TitleIsWikitextPage may be used to force a page to use the
         *   wikitext model. This is a compatibility feature. The ContentHandlerDefaultModelFor
         *   hook should be used instead if possible.
         *
         * If none of the above applies, the wikitext model is used.
         *
         * Note: this is used by, and may thus not use, Title::getContentModel()
         *
         * @since 1.21
         *
         * @param $title Title
         * @return null|string default model name for the page given by $title
         */
        public static function getDefaultModelFor( Title $title ) {
                // NOTE: this method must not rely on $title->getContentModel() directly or indirectly,
                //       because it is used to initialize the mContentModel member.

                $ns = $title->getNamespace();

                $ext = false;
                $m = null;
                $model = MWNamespace::getNamespaceContentModel( $ns );

                // Hook can determine default model
                if ( !wfRunHooks( 'ContentHandlerDefaultModelFor', array( $title, &$model ) ) ) {
                        if ( !is_null( $model ) ) {
                                return $model;
                        }
                }

                // Could this page contain custom CSS or JavaScript, based on the title?
                $isCssOrJsPage = NS_MEDIAWIKI == $ns && preg_match( '!\.(css|js)$!u', $title->getText(), $m );
                if ( $isCssOrJsPage ) {
                        $ext = $m[1];
                }

                // Hook can force JS/CSS
                wfRunHooks( 'TitleIsCssOrJsPage', array( $title, &$isCssOrJsPage ) );

                // Is this a .css subpage of a user page?
                $isJsCssSubpage = NS_USER == $ns
                        && !$isCssOrJsPage
                        && preg_match( "/\\/.*\\.(js|css)$/", $title->getText(), $m );
                if ( $isJsCssSubpage ) {
                        $ext = $m[1];
                }

                // Is this wikitext, according to $wgNamespaceContentModels or the DefaultModelFor hook?
                $isWikitext = is_null( $model ) || $model == CONTENT_MODEL_WIKITEXT;
                $isWikitext = $isWikitext && !$isCssOrJsPage && !$isJsCssSubpage;

                // Hook can override $isWikitext
                wfRunHooks( 'TitleIsWikitextPage', array( $title, &$isWikitext ) );

                if ( !$isWikitext ) {
                        switch ( $ext ) {
                                case 'js':
                                        return CONTENT_MODEL_JAVASCRIPT;
                                case 'css':
                                        return CONTENT_MODEL_CSS;
                                default:
                                        return is_null( $model ) ? CONTENT_MODEL_TEXT : $model;
                        }
                }

                // We established that it must be wikitext

                return CONTENT_MODEL_WIKITEXT;
        }

        /**
         * Returns the appropriate ContentHandler singleton for the given title.
         *
         * @since 1.21
         *
         * @param $title Title
         * @return ContentHandler
         */
        public static function getForTitle( Title $title ) {
                $modelId = $title->getContentModel();
                return ContentHandler::getForModelID( $modelId );
        }

        /**
         * Returns the appropriate ContentHandler singleton for the given Content
         * object.
         *
         * @since 1.21
         *
         * @param $content Content
         * @return ContentHandler
         */
        public static function getForContent( Content $content ) {
                $modelId = $content->getModel();
                return ContentHandler::getForModelID( $modelId );
        }

        /**
         * @var Array A Cache of ContentHandler instances by model id
         */
        static $handlers;

        /**
         * Returns the ContentHandler singleton for the given model ID. Use the
         * CONTENT_MODEL_XXX constants to identify the desired content model.
         *
         * ContentHandler singletons are taken from the global $wgContentHandlers
         * array. Keys in that array are model names, the values are either
         * ContentHandler singleton objects, or strings specifying the appropriate
         * subclass of ContentHandler.
         *
         * If a class name is encountered when looking up the singleton for a given
         * model name, the class is instantiated and the class name is replaced by
         * the resulting singleton in $wgContentHandlers.
         *
         * If no ContentHandler is defined for the desired $modelId, the
         * ContentHandler may be provided by the ContentHandlerForModelID hook.
         * If no ContentHandler can be determined, an MWException is raised.
         *
         * @since 1.21
         *
         * @param string $modelId The ID of the content model for which to get a
         *    handler. Use CONTENT_MODEL_XXX constants.
         * @return ContentHandler The ContentHandler singleton for handling the
         *    model given by $modelId
         * @throws MWException if no handler is known for $modelId.
         */
        public static function getForModelID( $modelId ) {
                global $wgContentHandlers;

                if ( isset( ContentHandler::$handlers[$modelId] ) ) {
                        return ContentHandler::$handlers[$modelId];
                }

                if ( empty( $wgContentHandlers[$modelId] ) ) {
                        $handler = null;

                        wfRunHooks( 'ContentHandlerForModelID', array( $modelId, &$handler ) );

                        if ( $handler === null ) {
                                throw new MWException( "No handler for model '$modelId' registered in \$wgContentHandlers" );
                        }

                        if ( !( $handler instanceof ContentHandler ) ) {
                                throw new MWException( "ContentHandlerForModelID must supply a ContentHandler instance" );
                        }
                } else {
                        $class = $wgContentHandlers[$modelId];
                        $handler = new $class( $modelId );

                        if ( !( $handler instanceof ContentHandler ) ) {
                                throw new MWException( "$class from \$wgContentHandlers is not compatible with ContentHandler" );
                        }
                }

                wfDebugLog( 'ContentHandler', 'Created handler for ' . $modelId
                                        . ': ' . get_class( $handler ) );

                ContentHandler::$handlers[$modelId] = $handler;
                return ContentHandler::$handlers[$modelId];
        }

        /**
         * Returns the localized name for a given content model.
         *
         * Model names are localized using system messages. Message keys
         * have the form content-model-$name, where $name is getContentModelName( $id ).
         *
         * @param string $name The content model ID, as given by a CONTENT_MODEL_XXX
         *    constant or returned by Revision::getContentModel().
         *
         * @return string The content model's localized name.
         * @throws MWException if the model id isn't known.
         */
        public static function getLocalizedName( $name ) {
                // Messages: content-model-wikitext, content-model-text,
                // content-model-javascript, content-model-css
                $key = "content-model-$name";

                $msg = wfMessage( $key );

                return $msg->exists() ? $msg->plain() : $name;
        }

        public static function getContentModels() {
                global $wgContentHandlers;

                return array_keys( $wgContentHandlers );
        }

        public static function getAllContentFormats() {
                global $wgContentHandlers;

                $formats = array();

                foreach ( $wgContentHandlers as $model => $class ) {
                        $handler = ContentHandler::getForModelID( $model );
                        $formats = array_merge( $formats, $handler->getSupportedFormats() );
                }

                $formats = array_unique( $formats );
                return $formats;
        }

        // ------------------------------------------------------------------------

        protected $mModelID;
        protected $mSupportedFormats;

        /**
         * Constructor, initializing the ContentHandler instance with its model ID
         * and a list of supported formats. Values for the parameters are typically
         * provided as literals by subclass's constructors.
         *
         * @param string $modelId (use CONTENT_MODEL_XXX constants).
         * @param array $formats List for supported serialization formats
         *    (typically as MIME types)
         */
        public function __construct( $modelId, $formats ) {
                $this->mModelID = $modelId;
                $this->mSupportedFormats = $formats;

                $this->mModelName = preg_replace( '/(Content)?Handler$/', '', get_class( $this ) );
                $this->mModelName = preg_replace( '/[_\\\\]/', '', $this->mModelName );
                $this->mModelName = strtolower( $this->mModelName );
        }

        /**
         * Serializes a Content object of the type supported by this ContentHandler.
         *
         * @since 1.21
         *
         * @param $content Content The Content object to serialize
         * @param $format null|String The desired serialization format
         * @return string Serialized form of the content
         */
        abstract public function serializeContent( Content $content, $format = null );

        /**
         * Unserializes a Content object of the type supported by this ContentHandler.
         *
         * @since 1.21
         *
         * @param string $blob serialized form of the content
         * @param $format null|String the format used for serialization
         * @return Content the Content object created by deserializing $blob
         */
        abstract public function unserializeContent( $blob, $format = null );

        /**
         * Creates an empty Content object of the type supported by this
         * ContentHandler.
         *
         * @since 1.21
         *
         * @return Content
         */
        abstract public function makeEmptyContent();

        /**
         * Creates a new Content object that acts as a redirect to the given page,
         * or null of redirects are not supported by this content model.
         *
         * This default implementation always returns null. Subclasses supporting redirects
         * must override this method.
         *
         * Note that subclasses that override this method to return a Content object
         * should also override supportsRedirects() to return true.
         *
         * @since 1.21
         *
         * @param Title $destination the page to redirect to.
         * @param string $text text to include in the redirect, if possible.
         *
         * @return Content
         */
        public function makeRedirectContent( Title $destination, $text = '' ) {
                return null;
        }

        /**
         * Returns the model id that identifies the content model this
         * ContentHandler can handle. Use with the CONTENT_MODEL_XXX constants.
         *
         * @since 1.21
         *
         * @return String The model ID
         */
        public function getModelID() {
                return $this->mModelID;
        }

        /**
         * Throws an MWException if $model_id is not the ID of the content model
         * supported by this ContentHandler.
         *
         * @since 1.21
         *
         * @param string $model_id The model to check
         *
         * @throws MWException
         */
        protected function checkModelID( $model_id ) {
                if ( $model_id !== $this->mModelID ) {
                        throw new MWException( "Bad content model: " .
                                "expected {$this->mModelID} " .
                                "but got $model_id." );
                }
        }

        /**
         * Returns a list of serialization formats supported by the
         * serializeContent() and unserializeContent() methods of this
         * ContentHandler.
         *
         * @since 1.21
         *
         * @return array of serialization formats as MIME type like strings
         */
        public function getSupportedFormats() {
                return $this->mSupportedFormats;
        }

        /**
         * The format used for serialization/deserialization by default by this
         * ContentHandler.
         *
         * This default implementation will return the first element of the array
         * of formats that was passed to the constructor.
         *
         * @since 1.21
         *
         * @return string the name of the default serialization format as a MIME type
         */
        public function getDefaultFormat() {
                return $this->mSupportedFormats[0];
        }

        /**
         * Returns true if $format is a serialization format supported by this
         * ContentHandler, and false otherwise.
         *
         * Note that if $format is null, this method always returns true, because
         * null means "use the default format".
         *
         * @since 1.21
         *
         * @param string $format the serialization format to check
         * @return bool
         */
        public function isSupportedFormat( $format ) {

                if ( !$format ) {
                        return true; // this means "use the default"
                }

                return in_array( $format, $this->mSupportedFormats );
        }

        /**
         * Throws an MWException if isSupportedFormat( $format ) is not true.
         * Convenient for checking whether a format provided as a parameter is
         * actually supported.
         *
         * @param string $format the serialization format to check
         *
         * @throws MWException
         */
        protected function checkFormat( $format ) {
                if ( !$this->isSupportedFormat( $format ) ) {
                        throw new MWException(
                                "Format $format is not supported for content model "
                                . $this->getModelID()
                        );
                }
        }

        /**
         * Returns overrides for action handlers.
         * Classes listed here will be used instead of the default one when
         * (and only when) $wgActions[$action] === true. This allows subclasses
         * to override the default action handlers.
         *
         * @since 1.21
         *
         * @return Array
         */
        public function getActionOverrides() {
                return array();
        }

        /**
         * Factory for creating an appropriate DifferenceEngine for this content model.
         *
         * @since 1.21
         *
         * @param $context IContextSource context to use, anything else will be
         *    ignored
         * @param $old Integer Old ID we want to show and diff with.
         * @param int|string $new String either 'prev' or 'next'.
         * @param $rcid Integer ??? FIXME (default 0)
         * @param $refreshCache boolean If set, refreshes the diff cache
         * @param $unhide boolean If set, allow viewing deleted revs
         *
         * @return DifferenceEngine
         */
        public function createDifferenceEngine( IContextSource $context,
                $old = 0, $new = 0,
                $rcid = 0, # FIXME: use everywhere!
                $refreshCache = false, $unhide = false
        ) {
                $diffEngineClass = $this->getDiffEngineClass();

                return new $diffEngineClass( $context, $old, $new, $rcid, $refreshCache, $unhide );
        }

        /**
         * Get the language in which the content of the given page is written.
         *
         * This default implementation just returns $wgContLang (except for pages in the MediaWiki namespace)
         *
         * Note that the pages language is not cacheable, since it may in some cases depend on user settings.
         *
         * Also note that the page language may or may not depend on the actual content of the page,
         * that is, this method may load the content in order to determine the language.
         *
         * @since 1.21
         *
         * @param Title        $title the page to determine the language for.
         * @param Content|null $content the page's content, if you have it handy, to avoid reloading it.
         *
         * @return Language the page's language
         */
        public function getPageLanguage( Title $title, Content $content = null ) {
                global $wgContLang, $wgLang;
                $pageLang = $wgContLang;

                if ( $title->getNamespace() == NS_MEDIAWIKI ) {
                        // Parse mediawiki messages with correct target language
                        list( /* $unused */, $lang ) = MessageCache::singleton()->figureMessage( $title->getText() );
                        $pageLang = wfGetLangObj( $lang );
                }

                wfRunHooks( 'PageContentLanguage', array( $title, &$pageLang, $wgLang ) );
                return wfGetLangObj( $pageLang );
        }

        /**
         * Get the language in which the content of this page is written when
         * viewed by user. Defaults to $this->getPageLanguage(), but if the user
         * specified a preferred variant, the variant will be used.
         *
         * This default implementation just returns $this->getPageLanguage( $title, $content ) unless
         * the user specified a preferred variant.
         *
         * Note that the pages view language is not cacheable, since it depends on user settings.
         *
         * Also note that the page language may or may not depend on the actual content of the page,
         * that is, this method may load the content in order to determine the language.
         *
         * @since 1.21
         *
         * @param Title        $title the page to determine the language for.
         * @param Content|null $content the page's content, if you have it handy, to avoid reloading it.
         *
         * @return Language the page's language for viewing
         */
        public function getPageViewLanguage( Title $title, Content $content = null ) {
                $pageLang = $this->getPageLanguage( $title, $content );

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

                return $pageLang;
        }

        /**
         * Determines whether the content type handled by this ContentHandler
         * can be used on the given page.
         *
         * This default implementation always returns true.
         * Subclasses may override this to restrict the use of this content model to specific locations,
         * typically based on the namespace or some other aspect of the title, such as a special suffix
         * (e.g. ".svg" for SVG content).
         *
         * @param Title $title the page's title.
         *
         * @return bool true if content of this kind can be used on the given page, false otherwise.
         */
        public function canBeUsedOn( Title $title ) {
                return true;
        }

        /**
         * Returns the name of the diff engine to use.
         *
         * @since 1.21
         *
         * @return string
         */
        protected function getDiffEngineClass() {
                return 'DifferenceEngine';
        }

        /**
         * Attempts to merge differences between three versions.
         * Returns a new Content object for a clean merge and false for failure or
         * a conflict.
         *
         * This default implementation always returns false.
         *
         * @since 1.21
         *
         * @param $oldContent Content|string  String
         * @param $myContent Content|string   String
         * @param $yourContent Content|string String
         *
         * @return Content|Bool
         */
        public function merge3( Content $oldContent, Content $myContent, Content $yourContent ) {
                return false;
        }

        /**
         * Return an applicable auto-summary if one exists for the given edit.
         *
         * @since 1.21
         *
         * @param $oldContent Content|null: the previous text of the page.
         * @param $newContent Content|null: The submitted text of the page.
         * @param int $flags Bit mask: a bit mask of flags submitted for the edit.
         *
         * @return string An appropriate auto-summary, or an empty string.
         */
        public function getAutosummary( Content $oldContent = null, Content $newContent = null, $flags ) {
                // Decide what kind of auto-summary is needed.

                // Redirect auto-summaries

                /**
                 * @var $ot Title
                 * @var $rt Title
                 */

                $ot = !is_null( $oldContent ) ? $oldContent->getRedirectTarget() : null;
                $rt = !is_null( $newContent ) ? $newContent->getRedirectTarget() : null;

                if ( is_object( $rt ) ) {
                        if ( !is_object( $ot )
                                || !$rt->equals( $ot )
                                || $ot->getFragment() != $rt->getFragment() )
                        {
                                $truncatedtext = $newContent->getTextForSummary(
                                        250
                                                - strlen( wfMessage( 'autoredircomment' )->inContentLanguage()->text() )
                                                - strlen( $rt->getFullText() ) );

                                return wfMessage( 'autoredircomment', $rt->getFullText() )
                                                ->rawParams( $truncatedtext )->inContentLanguage()->text();
                        }
                }

                // New page auto-summaries
                if ( $flags & EDIT_NEW && $newContent->getSize() > 0 ) {
                        // If they're making a new article, give its text, truncated, in
                        // the summary.

                        $truncatedtext = $newContent->getTextForSummary(
                                200 - strlen( wfMessage( 'autosumm-new' )->inContentLanguage()->text() ) );

                        return wfMessage( 'autosumm-new' )->rawParams( $truncatedtext )
                                        ->inContentLanguage()->text();
                }

                // Blanking auto-summaries
                if ( !empty( $oldContent ) && $oldContent->getSize() > 0 && $newContent->getSize() == 0 ) {
                        return wfMessage( 'autosumm-blank' )->inContentLanguage()->text();
                } elseif ( !empty( $oldContent )
                        && $oldContent->getSize() > 10 * $newContent->getSize()
                        && $newContent->getSize() < 500 )
                {
                        // Removing more than 90% of the article

                        $truncatedtext = $newContent->getTextForSummary(
                                200 - strlen( wfMessage( 'autosumm-replace' )->inContentLanguage()->text() ) );

                        return wfMessage( 'autosumm-replace' )->rawParams( $truncatedtext )
                                        ->inContentLanguage()->text();
                }

                // If we reach this point, there's no applicable auto-summary for our
                // case, so our auto-summary is empty.
                return '';
        }

        /**
         * Auto-generates a deletion reason
         *
         * @since 1.21
         *
         * @param $title Title: the page's title
         * @param &$hasHistory Boolean: whether the page has a history
         * @return mixed String containing deletion reason or empty string, or
         *    boolean false if no revision occurred
         *
         * @XXX &$hasHistory is extremely ugly, it's here because
         * WikiPage::getAutoDeleteReason() and Article::generateReason()
         * have it / want it.
         */
        public function getAutoDeleteReason( Title $title, &$hasHistory ) {
                $dbw = wfGetDB( DB_MASTER );

                // Get the last revision
                $rev = Revision::newFromTitle( $title );

                if ( is_null( $rev ) ) {
                        return false;
                }

                // Get the article's contents
                $content = $rev->getContent();
                $blank = false;

                // If the page is blank, use the text from the previous revision,
                // which can only be blank if there's a move/import/protect dummy
                // revision involved
                if ( !$content || $content->isEmpty() ) {
                        $prev = $rev->getPrevious();

                        if ( $prev ) {
                                $rev = $prev;
                                $content = $rev->getContent();
                                $blank = true;
                        }
                }

                $this->checkModelID( $rev->getContentModel() );

                // Find out if there was only one contributor
                // Only scan the last 20 revisions
                $res = $dbw->select( 'revision', 'rev_user_text',
                        array(
                                'rev_page' => $title->getArticleID(),
                                $dbw->bitAnd( 'rev_deleted', Revision::DELETED_USER ) . ' = 0'
                        ),
                        __METHOD__,
                        array( 'LIMIT' => 20 )
                );

                if ( $res === false ) {
                        // This page has no revisions, which is very weird
                        return false;
                }

                $hasHistory = ( $res->numRows() > 1 );
                $row = $dbw->fetchObject( $res );

                if ( $row ) { // $row is false if the only contributor is hidden
                        $onlyAuthor = $row->rev_user_text;
                        // Try to find a second contributor
                        foreach ( $res as $row ) {
                                if ( $row->rev_user_text != $onlyAuthor ) { // Bug 22999
                                        $onlyAuthor = false;
                                        break;
                                }
                        }
                } else {
                        $onlyAuthor = false;
                }

                // Generate the summary with a '$1' placeholder
                if ( $blank ) {
                        // The current revision is blank and the one before is also
                        // blank. It's just not our lucky day
                        $reason = wfMessage( 'exbeforeblank', '$1' )->inContentLanguage()->text();
                } else {
                        if ( $onlyAuthor ) {
                                $reason = wfMessage(
                                        'excontentauthor',
                                        '$1',
                                        $onlyAuthor
                                )->inContentLanguage()->text();
                        } else {
                                $reason = wfMessage( 'excontent', '$1' )->inContentLanguage()->text();
                        }
                }

                if ( $reason == '-' ) {
                        // Allow these UI messages to be blanked out cleanly
                        return '';
                }

                // Max content length = max comment length - length of the comment (excl. $1)
                $text = $content ? $content->getTextForSummary( 255 - ( strlen( $reason ) - 2 ) ) : '';

                // Now replace the '$1' placeholder
                $reason = str_replace( '$1', $text, $reason );

                return $reason;
        }

        /**
         * Get the Content object that needs to be saved in order to undo all revisions
         * between $undo and $undoafter. Revisions must belong to the same page,
         * must exist and must not be deleted.
         *
         * @since 1.21
         *
         * @param $current Revision The current text
         * @param $undo Revision The revision to undo
         * @param $undoafter Revision Must be an earlier revision than $undo
         *
         * @return mixed String on success, false on failure
         */
        public function getUndoContent( Revision $current, Revision $undo, Revision $undoafter ) {
                $cur_content = $current->getContent();

                if ( empty( $cur_content ) ) {
                        return false; // no page
                }

                $undo_content = $undo->getContent();
                $undoafter_content = $undoafter->getContent();

                if ( !$undo_content || !$undoafter_content ) {
                        return false; // no content to undo
                }

                $this->checkModelID( $cur_content->getModel() );
                $this->checkModelID( $undo_content->getModel() );
                $this->checkModelID( $undoafter_content->getModel() );

                if ( $cur_content->equals( $undo_content ) ) {
                        // No use doing a merge if it's just a straight revert.
                        return $undoafter_content;
                }

                $undone_content = $this->merge3( $undo_content, $undoafter_content, $cur_content );

                return $undone_content;
        }

        /**
         * Get parser options suitable for rendering the primary article wikitext
         *
         * @param IContextSource|User|string $context One of the following:
         *        - IContextSource: Use the User and the Language of the provided
         *                                            context
         *        - User: Use the provided User object and $wgLang for the language,
         *                                            so use an IContextSource object if possible.
         *        - 'canonical': Canonical options (anonymous user with default
         *                                            preferences and content language).
         *
         * @param IContextSource|User|string $context
         *
         * @throws MWException
         * @return ParserOptions
         */
        public function makeParserOptions( $context ) {
                global $wgContLang, $wgEnableParserLimitReporting;

                if ( $context instanceof IContextSource ) {
                        $options = ParserOptions::newFromContext( $context );
                } elseif ( $context instanceof User ) { // settings per user (even anons)
                        $options = ParserOptions::newFromUser( $context );
                } elseif ( $context === 'canonical' ) { // canonical settings
                        $options = ParserOptions::newFromUserAndLang( new User, $wgContLang );
                } else {
                        throw new MWException( "Bad context for parser options: $context" );
                }

                $options->enableLimitReport( $wgEnableParserLimitReporting ); // show inclusion/loop reports
                $options->setTidy( true ); // fix bad HTML

                return $options;
        }

        /**
         * Returns true for content models that support caching using the
         * ParserCache mechanism. See WikiPage::isParserCacheUsed().
         *
         * @since 1.21
         *
         * @return bool
         */
        public function isParserCacheSupported() {
                return false;
        }

        /**
         * Returns true if this content model supports sections.
         * This default implementation returns false.
         *
         * Content models that return true here should also implement
         * Content::getSection, Content::replaceSection, etc. to handle sections..
         *
         * @return boolean whether sections are supported.
         */
        public function supportsSections() {
                return false;
        }

        /**
         * Returns true if this content model supports redirects.
         * This default implementation returns false.
         *
         * Content models that return true here should also implement
         * ContentHandler::makeRedirectContent to return a Content object.
         *
         * @return boolean whether redirects are supported.
         */
        public function supportsRedirects() {
                return false;
        }

        /**
         * Logs a deprecation warning, visible if $wgDevelopmentWarnings, but only if
         * self::$enableDeprecationWarnings is set to true.
         *
         * @param string      $func The name of the deprecated function
         * @param string      $version The version since the method is deprecated. Usually 1.21
         *                    for ContentHandler related stuff.
         * @param string|bool $component: Component to which the function belongs.
         *                                If false, it is assumed the function is in MediaWiki core.
         *
         * @see ContentHandler::$enableDeprecationWarnings
         * @see wfDeprecated
         */
        public static function deprecated( $func, $version, $component = false ) {
                if ( self::$enableDeprecationWarnings ) {
                        wfDeprecated( $func, $version, $component, 3 );
                }
        }

        /**
         * Call a legacy hook that uses text instead of Content objects.
         * Will log a warning when a matching hook function is registered.
         * If the textual representation of the content is changed by the
         * hook function, a new Content object is constructed from the new
         * text.
         *
         * @param string $event event name
         * @param array $args parameters passed to hook functions
         * @param bool $warn whether to log a warning.
         *                    Default to self::$enableDeprecationWarnings.
         *                    May be set to false for testing.
         *
         * @return Boolean True if no handler aborted the hook
         *
         * @see ContentHandler::$enableDeprecationWarnings
         */
        public static function runLegacyHooks( $event, $args = array(),
                        $warn = null ) {

                if ( $warn === null ) {
                        $warn = self::$enableDeprecationWarnings;
                }

                if ( !Hooks::isRegistered( $event ) ) {
                        return true; // nothing to do here
                }

                if ( $warn ) {
                        // Log information about which handlers are registered for the legacy hook,
                        // so we can find and fix them.

                        $handlers = Hooks::getHandlers( $event );
                        $handlerInfo = array();

                        wfSuppressWarnings();

                        foreach ( $handlers as $handler ) {
                                if ( is_array( $handler ) ) {
                                        if ( is_object( $handler[0] ) ) {
                                                $info = get_class( $handler[0] );
                                        } else {
                                                $info = $handler[0];
                                        }

                                        if ( isset( $handler[1] ) ) {
                                                $info .= '::' . $handler[1];
                                        }
                                } elseif ( is_object( $handler ) ) {
                                        $info = get_class( $handler[0] );
                                        $info .= '::on' . $event;
                                } else {
                                        $info = $handler;
                                }

                                $handlerInfo[] = $info;
                        }

                        wfRestoreWarnings();

                        wfWarn( "Using obsolete hook $event via ContentHandler::runLegacyHooks()! Handlers: " . implode( ', ', $handlerInfo ), 2 );
                }

                // convert Content objects to text
                $contentObjects = array();
                $contentTexts = array();

                foreach ( $args as $k => $v ) {
                        if ( $v instanceof Content ) {
                                /* @var Content $v */

                                $contentObjects[$k] = $v;

                                $v = $v->serialize();
                                $contentTexts[$k] = $v;
                                $args[$k] = $v;
                        }
                }

                // call the hook functions
                $ok = wfRunHooks( $event, $args );

                // see if the hook changed the text
                foreach ( $contentTexts as $k => $orig ) {
                        /* @var Content $content */

                        $modified = $args[$k];
                        $content = $contentObjects[$k];

                        if ( $modified !== $orig ) {
                                // text was changed, create updated Content object
                                $content = $content->getContentHandler()->unserializeContent( $modified );
                        }

                        $args[$k] = $content;
                }

                return $ok;
        }
}