Localisation updates from https://translatewiki.net.

[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
 */

namespace MediaWiki\Content;

use Action;
use DifferenceEngine;
use DifferenceEngineSlotDiffRenderer;
use InvalidArgumentException;
use LogicException;
use MediaWiki\CommentStore\CommentStore;
use MediaWiki\Content\Renderer\ContentParseParams;
use MediaWiki\Content\Transform\PreloadTransformParams;
use MediaWiki\Content\Transform\PreSaveTransformParams;
use MediaWiki\Context\IContextSource;
use MediaWiki\Context\RequestContext;
use MediaWiki\Deferred\DeferrableUpdate;
use MediaWiki\Diff\TextDiffer\ManifoldTextDiffer;
use MediaWiki\HookContainer\HookRunner;
use MediaWiki\HookContainer\ProtectedHookAccessorTrait;
use MediaWiki\Language\ILanguageConverter;
use MediaWiki\Language\Language;
use MediaWiki\Logger\LoggerFactory;
use MediaWiki\MainConfigNames;
use MediaWiki\MediaWikiServices;
use MediaWiki\Page\ParserOutputAccess;
use MediaWiki\Parser\ParserCache;
use MediaWiki\Parser\ParserOutput;
use MediaWiki\Revision\RevisionRecord;
use MediaWiki\Revision\SlotRecord;
use MediaWiki\Revision\SlotRenderingProvider;
use MediaWiki\Search\ParserOutputSearchDataExtractor;
use MediaWiki\Title\Title;
use MWContentSerializationException;
use MWException;
use MWUnknownContentModelException;
use SearchEngine;
use SearchIndexField;
use SlotDiffRenderer;
use StatusValue;
use TextSlotDiffRenderer;
use UnexpectedValueException;
use Wikimedia\Assert\Assert;
use Wikimedia\Rdbms\IDBAccessObject;
use Wikimedia\ScopedCallback;
use WikiPage;

/**
 * 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.
 *
 * @stable to extend
 *
 * @ingroup Content
 */
abstract class ContentHandler {
        use ProtectedHookAccessorTrait;

        /**
         * 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->getText().
         *
         * If $content is not a TextContent object, this method returns null.
         *
         * @since 1.21
         *
         * @deprecated since 1.37, use Content::getText() for TextContent instances
         * instead. Hard deprecated since 1.43.
         *
         * @param Content|null $content
         * @return string|null Textual form of the content, if available.
         */
        public static function getContentText( ?Content $content = null ) {
                wfDeprecated( __METHOD__, '1.37' );
                if ( $content === null ) {
                        return '';
                }

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

                wfDebugLog( 'ContentHandler', 'Accessing ' . $content->getModel() . ' content as text!' );
                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 string|null $modelId The model to deserialize to. If not provided,
         *    $title->getContentModel() is used.
         * @param string|null $format The format to use for deserialization. If not
         *    given, the model's default format is used.
         *
         * @throws MWContentSerializationException
         * @throws MWUnknownContentModelException
         * @return Content A Content object representing the text.
         */
        public static function makeContent( $text, ?Title $title = null,
                $modelId = null, $format = null ) {
                if ( !$title && !$modelId ) {
                        throw new InvalidArgumentException( "Must provide a Title object or a content model ID." );
                }

                return MediaWikiServices::getInstance()
                        ->getContentHandlerFactory()
                        ->getContentHandler( $modelId ?? $title->getContentModel() )
                        ->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.
         *
         * @since 1.21
         * @deprecated since 1.33, use SlotRoleHandler::getDefaultModel() together with
         *   SlotRoleRegistry::getRoleHandler(). Hard deprecated since 1.43.
         *
         * @param Title $title
         *
         * @return string Default model name for the page given by $title
         */
        public static function getDefaultModelFor( Title $title ) {
                wfDeprecated( __METHOD__, '1.33' );
                $slotRoleregistry = MediaWikiServices::getInstance()->getSlotRoleRegistry();
                $mainSlotHandler = $slotRoleregistry->getRoleHandler( 'main' );
                return $mainSlotHandler->getDefaultModel( $title );
        }

        /**
         * Returns the appropriate ContentHandler singleton for the given Content
         * object.
         *
         * @deprecated since 1.35, instead use
         *   ContentHandlerFactory::getContentHandler( $content->getModel() ).
         *   Hard deprecated since 1.43.
         *
         * @since 1.21
         *
         * @param Content $content
         *
         * @return ContentHandler
         * @throws MWUnknownContentModelException
         */
        public static function getForContent( Content $content ) {
                wfDeprecated( __METHOD__, '1.35' );
                return MediaWikiServices::getInstance()
                        ->getContentHandlerFactory()
                        ->getContentHandler( $content->getModel() );
        }

        /**
         * 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 MWUnknownContentModelException is raised.
         *
         * @since 1.21
         *
         * @deprecated since 1.35, use ContentHandlerFactory::getContentHandler
         *   Hard deprecated since 1.43.
         * @see  ContentHandlerFactory::getContentHandler()
         *
         * @param string $modelId The ID of the content model for which to get a
         *    handler. Use CONTENT_MODEL_XXX constants.
         *
         * @throws MWUnknownContentModelException If no handler is known for the model ID.
         * @return ContentHandler The ContentHandler singleton for handling the model given by the ID.
         */
        public static function getForModelID( $modelId ) {
                wfDeprecated( __METHOD__, '1.35' );
                return MediaWikiServices::getInstance()
                        ->getContentHandlerFactory()
                        ->getContentHandler( $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 Content::getModel() or SlotRecord::getModel().
         * @param Language|null $lang The language to parse the message in (since 1.26)
         *
         * @return string The content model's localized name.
         */
        public static function getLocalizedName( $name, ?Language $lang = null ) {
                // Messages: content-model-wikitext, content-model-text,
                // content-model-javascript, content-model-css
                // Lowercase the name as message keys need to be in lowercase, T358341
                $key = "content-model-" . strtolower( $name ?? '' );

                $msg = wfMessage( $key );
                if ( $lang ) {
                        $msg->inLanguage( $lang );
                }

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

        /**
         * @deprecated since 1.35, use ContentHandlerFactory::getContentModels
         *   Hard deprecated since 1.43.
         * @see ContentHandlerFactory::getContentModels
         *
         * @return string[]
         */
        public static function getContentModels() {
                wfDeprecated( __METHOD__, '1.35' );
                return MediaWikiServices::getInstance()->getContentHandlerFactory()->getContentModels();
        }

        /**
         * @return string[]
         *
         * @deprecated since 1.35, use ContentHandlerFactory::getAllContentFormats
         *   Hard deprecated since 1.43.
         * @see ContentHandlerFactory::getAllContentFormats
         */
        public static function getAllContentFormats() {
                wfDeprecated( __METHOD__, '1.35' );
                return MediaWikiServices::getInstance()->getContentHandlerFactory()->getAllContentFormats();
        }

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

        /**
         * @var string
         */
        protected $mModelID;

        /**
         * @var string[]
         */
        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.
         *
         * @stable to call
         *
         * @param string $modelId (use CONTENT_MODEL_XXX constants).
         * @param string[] $formats List for supported serialization formats
         *    (typically as MIME types)
         */
        public function __construct( $modelId, $formats ) {
                $this->mModelID = $modelId;
                $this->mSupportedFormats = $formats;
        }

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

        /**
         * Applies transformations on export (returns the blob unchanged by default).
         * Subclasses may override this to perform transformations such as conversion
         * of legacy formats or filtering of internal meta-data.
         *
         * @stable to override
         *
         * @param string $blob The blob to be exported
         * @param string|null $format The blob's serialization format
         *
         * @return string
         */
        public function exportTransform( $blob, $format = null ) {
                return $blob;
        }

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

        /**
         * Apply import transformation (by default, returns $blob unchanged).
         * This gives subclasses an opportunity to transform data blobs on import.
         *
         * @stable to override
         * @since 1.24
         *
         * @param string $blob
         * @param string|null $format
         *
         * @return string
         */
        public function importTransform( $blob, $format = null ) {
                return $blob;
        }

        /**
         * Creates an empty Content object of the type supported by this
         * ContentHandler.
         *
         * @stable to override
         * @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 if 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.
         *
         * @stable to override
         * @since 1.21
         *
         * @param Title $destination The page to redirect to.
         * @param string $text Text to include in the redirect, if possible.
         *
         * @return Content|null Always null.
         */
        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;
        }

        /**
         * @since 1.21
         *
         * @param string $model_id The model to check
         *
         * @throws MWException If the model ID is not the ID of the content model supported by this
         * ContentHandler.
         */
        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.
         *
         * @stable to override
         * @since 1.21
         *
         * @return string[] List 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.
         *
         * @stable to override
         * @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".
         *
         * @stable to override
         * @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 );
        }

        /**
         * Convenient for checking whether a format provided as a parameter is actually supported.
         *
         * @param string $format The serialization format to check
         *
         * @throws MWException If the format is not supported by this content handler.
         */
        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.
         *
         * @stable to override
         * @since 1.21
         *
         * @return array<string,class-string|callable|false|Action|array> An array mapping action names
         *  (typically "view", "edit", "history" etc.) to a specification according to
         *  {@see ActionFactory::getActionSpec}. Can be the full qualified class name of an Action
         *  class, a callable taking ( Article $article, IContextSource $context ) as parameters and
         *  returning an Action object, false to disable an action, an actual Action object,
         *  or an ObjectFactory specification array (can have 'class', 'services', etc.).
         *  An empty array in this default implementation.
         *
         * @see Action::factory
         */
        public function getActionOverrides() {
                return [];
        }

        /**
         * Factory for creating an appropriate DifferenceEngine for this content model.
         * Since 1.32, this is only used for page-level diffs; to diff two content objects,
         * use getSlotDiffRenderer.
         *
         * The DifferenceEngine subclass to use is selected in getDiffEngineClass(). The
         * GetDifferenceEngine hook will receive the DifferenceEngine object and can replace or
         * wrap it.
         * (Note that in older versions of MediaWiki the hook documentation instructed extensions
         * to return false from the hook; you should not rely on always being able to decorate
         * the DifferenceEngine instance from the hook. If the owner of the content type wants to
         * decorate the instance, overriding this method is a safer approach.)
         *
         * @todo This is page-level functionality so it should not belong to ContentHandler.
         *   Move it to a better place once one exists (e.g. PageTypeHandler).
         *
         * @since 1.21
         *
         * @param IContextSource $context Context to use, anything else will be ignored.
         * @param int $old Revision ID we want to show and diff with.
         * @param int|string $new Either a revision ID or one of the strings 'cur', 'prev' or 'next'.
         * @param int $rcid FIXME: Deprecated, no longer used. Defaults to 0.
         * @param bool $refreshCache If set, refreshes the diff cache. Defaults to false.
         * @param bool $unhide If set, allow viewing deleted revs. Defaults to false.
         *
         * @return DifferenceEngine
         */
        public function createDifferenceEngine( IContextSource $context, $old = 0, $new = 0,
                $rcid = 0, // FIXME: Deprecated, no longer used
                $refreshCache = false, $unhide = false
        ) {
                $diffEngineClass = $this->getDiffEngineClass();
                $differenceEngine = new $diffEngineClass( $context, $old, $new, $rcid, $refreshCache, $unhide );
                $this->getHookRunner()->onGetDifferenceEngine(
                        $context, $old, $new, $refreshCache, $unhide, $differenceEngine );
                return $differenceEngine;
        }

        /**
         * Get an appropriate SlotDiffRenderer for this content model.
         *
         * @stable to override
         * @since 1.32
         *
         * @param IContextSource $context
         * @param array $options An associative array of options passed to the SlotDiffRenderer:
         *   - diff-type: (string) The text diff format
         *   - contentLanguage: (string) The language code of the content language,
         *     to be passed to the TextDiffer constructor. This is ignored if a
         *     TextDiffer object is provided.
         *   - textDiffer: (TextDiffer) A TextDiffer object to use for text
         *     comparison.
         * @return SlotDiffRenderer
         */
        final public function getSlotDiffRenderer( IContextSource $context, array $options = [] ) {
                $slotDiffRenderer = $this->getSlotDiffRendererWithOptions( $context, $options );
                if ( get_class( $slotDiffRenderer ) === TextSlotDiffRenderer::class ) {
                        // To keep B/C, when SlotDiffRenderer is not overridden for a given content type
                        // but DifferenceEngine is, use that instead.
                        $differenceEngine = $this->createDifferenceEngine( $context );
                        if ( get_class( $differenceEngine ) !== DifferenceEngine::class ) {
                                // TODO turn this into a deprecation warning in a later release
                                LoggerFactory::getInstance( 'diff' )->info(
                                        'Falling back to DifferenceEngineSlotDiffRenderer', [
                                                'modelID' => $this->getModelID(),
                                                'DifferenceEngine' => get_class( $differenceEngine ),
                                        ] );
                                $slotDiffRenderer = new DifferenceEngineSlotDiffRenderer( $differenceEngine );
                        }
                }
                $this->getHookRunner()->onGetSlotDiffRenderer( $this, $slotDiffRenderer, $context );
                return $slotDiffRenderer;
        }

        /**
         * Return the SlotDiffRenderer appropriate for this content handler.
         * @deprecated since 1.35; use getSlotDiffRendererWithOptions instead
         *   Emitting deprecation warnings since 1.41.
         * @param IContextSource $context
         * @return SlotDiffRenderer|null
         */
        protected function getSlotDiffRendererInternal( IContextSource $context ) {
                return null;
        }

        /**
         * Return the SlotDiffRenderer appropriate for this content handler.
         * @stable to override
         *
         * @param IContextSource $context
         * @param array $options See getSlotDiffRenderer()
         *
         * @return SlotDiffRenderer
         */
        protected function getSlotDiffRendererWithOptions( IContextSource $context, $options = [] ) {
                $internalRenderer = $this->getSlotDiffRendererInternal( $context );
                // `getSlotDiffRendererInternal` has been overridden by a class using the deprecated method.
                // Options will not work so exit early!
                if ( $internalRenderer !== null ) {
                        wfDeprecated( 'ContentHandler::getSlotDiffRendererInternal', '1.35' );
                        return $internalRenderer;
                }
                return $this->createTextSlotDiffRenderer( $options );
        }

        /**
         * Create a TextSlotDiffRenderer and inject dependencies
         *
         * @since 1.41
         * @param array $options See getSlotDiffRenderer()
         * @return TextSlotDiffRenderer
         */
        final protected function createTextSlotDiffRenderer( array $options = [] ): TextSlotDiffRenderer {
                $slotDiffRenderer = new TextSlotDiffRenderer();

                $services = MediaWikiServices::getInstance();
                $slotDiffRenderer->setStatsFactory( $services->getStatsFactory() );
                $slotDiffRenderer->setHookContainer( $services->getHookContainer() );
                $slotDiffRenderer->setContentModel( $this->getModelID() );

                if ( isset( $options['textDiffer'] ) ) {
                        $textDiffer = $options['textDiffer'];
                } else {
                        if ( isset( $options['contentLanguage'] ) ) {
                                $language = $services->getLanguageFactory()->getLanguage( $options['contentLanguage'] );
                        } else {
                                $language = $services->getContentLanguage();
                        }
                        $config = $services->getMainConfig();
                        $textDiffer = new ManifoldTextDiffer(
                                RequestContext::getMain(),
                                $language,
                                $config->get( MainConfigNames::DiffEngine ),
                                $config->get( MainConfigNames::ExternalDiffEngine ),
                                $config->get( MainConfigNames::Wikidiff2Options )
                        );
                }
                $format = $options['diff-type'] ?? 'table';
                if ( !$textDiffer->hasFormat( $format ) ) {
                        // Maybe it would be better to throw an exception here, but at
                        // present, the value comes straight from user input without
                        // validation, so we have to fall back.
                        $format = 'table';
                }
                $slotDiffRenderer->setFormat( $format );
                $slotDiffRenderer->setTextDiffer( $textDiffer );
                if ( $options['inline-toggle'] ?? false ) {
                        $slotDiffRenderer->setInlineToggleEnabled();
                }

                return $slotDiffRenderer;
        }

        /**
         * Get the language in which the content of the given page is written.
         *
         * This default implementation just returns the content language (except for pages
         * in the MediaWiki namespace)
         *
         * Note that the page's 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.
         *
         * @stable to override
         * @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
         */
        public function getPageLanguage( Title $title, ?Content $content = null ) {
                $services = MediaWikiServices::getInstance();
                $pageLang = $services->getContentLanguage();

                if ( $title->inNamespace( NS_MEDIAWIKI ) ) {
                        // Parse mediawiki messages with correct target language
                        [ /* $unused */, $lang ] = $services->getMessageCache()->figureMessage( $title->getText() );
                        $pageLang = $services->getLanguageFactory()->getLanguage( $lang );
                }

                // Unused, T299369
                $userLang = null;
                $this->getHookRunner()->onPageContentLanguage( $title, $pageLang, $userLang );

                if ( !$pageLang instanceof Language ) {
                        throw new UnexpectedValueException( 'onPageContentLanguage() hook provided an invalid $pageLang object.' );
                }

                return $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.
         *
         * @stable to override
         * @deprecated since 1.42 Use ParserOutput::getLanguage instead. See also OutputPage::getContLangForJS.
         * @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 = $this->getLanguageConverter( $pageLang )->getPreferredVariant();
                        if ( $pageLang->getCode() !== $variant ) {
                                $pageLang = MediaWikiServices::getInstance()->getLanguageFactory()
                                        ->getLanguage( $variant );
                        }
                }

                return $pageLang;
        }

        /**
         * Determines whether the content type handled by this ContentHandler
         * can be used for the main slot of 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).
         *
         * @note this calls the ContentHandlerCanBeUsedOn hook which may be used to override which
         * content model can be used where.
         *
         * @stable to override
         *
         * @see SlotRoleHandler::isAllowedModel
         *
         * @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 ) {
                $ok = true;

                $this->getHookRunner()->onContentModelCanBeUsedOn( $this->getModelID(), $title, $ok );

                return $ok;
        }

        /**
         * Returns the name of the diff engine to use.
         *
         * @stable to override
         * @since 1.21
         *
         * @return class-string<DifferenceEngine>
         */
        protected function getDiffEngineClass() {
                return DifferenceEngine::class;
        }

        /**
         * 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.
         *
         * @stable to override
         * @since 1.21
         *
         * @param Content $oldContent The page's previous content.
         * @param Content $myContent One of the page's conflicting contents.
         * @param Content $yourContent One of the page's conflicting contents.
         *
         * @return Content|false Always false.
         */
        public function merge3( Content $oldContent, Content $myContent, Content $yourContent ) {
                return false;
        }

        /**
         * Shorthand for getting a Language Converter for specific language
         * @param Language $language Language of converter
         * @return ILanguageConverter
         */
        private function getLanguageConverter( $language ): ILanguageConverter {
                return MediaWikiServices::getInstance()->getLanguageConverterFactory()
                        ->getLanguageConverter( $language );
        }

        /**
         * Return type of change if one exists for the given edit.
         *
         * @stable to override
         * @since 1.31
         *
         * @param Content|null $oldContent The previous text of the page.
         * @param Content|null $newContent The submitted text of the page.
         * @param int $flags Bit mask: a bit mask of flags submitted for the edit.
         *
         * @return string|null String key representing type of change, or null.
         */
        private function getChangeType(
                ?Content $oldContent = null,
                ?Content $newContent = null,
                $flags = 0
        ) {
                $oldTarget = $oldContent !== null ? $oldContent->getRedirectTarget() : null;
                $newTarget = $newContent !== null ? $newContent->getRedirectTarget() : null;

                // We check for the type of change in the given edit, and return string key accordingly

                // Blanking of a page
                if ( $oldContent && $oldContent->getSize() > 0 &&
                        $newContent && $newContent->getSize() === 0
                ) {
                        return 'blank';
                }

                // Redirects
                if ( $newTarget ) {
                        if ( !$oldTarget ) {
                                // New redirect page (by creating new page or by changing content page)
                                return 'new-redirect';
                        } elseif ( !$newTarget->equals( $oldTarget ) ||
                                $oldTarget->getFragment() !== $newTarget->getFragment()
                        ) {
                                // Redirect target changed
                                return 'changed-redirect-target';
                        }
                } elseif ( $oldTarget ) {
                        // Changing an existing redirect into a non-redirect
                        return 'removed-redirect';
                }

                // New page created
                if ( $flags & EDIT_NEW && $newContent ) {
                        if ( $newContent->getSize() === 0 ) {
                                // New blank page
                                return 'newblank';
                        } else {
                                return 'newpage';
                        }
                }

                // Removing more than 90% of the page
                if ( $oldContent && $newContent && $oldContent->getSize() > 10 * $newContent->getSize() ) {
                        return 'replace';
                }

                // Content model changed
                if ( $oldContent && $newContent && $oldContent->getModel() !== $newContent->getModel() ) {
                        return 'contentmodelchange';
                }

                return null;
        }

        /**
         * Return an applicable auto-summary if one exists for the given edit.
         *
         * @stable to override
         * @since 1.21
         *
         * @param Content|null $oldContent The previous text of the page.
         * @param Content|null $newContent 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 = 0
        ) {
                $changeType = $this->getChangeType( $oldContent, $newContent, $flags );

                // There's no applicable auto-summary for our case, so our auto-summary is empty.
                if ( !$changeType ) {
                        return '';
                }

                // Set the maximum auto-summary length to the general maximum summary length
                // T221617
                $summaryLimit = CommentStore::COMMENT_CHARACTER_LIMIT;

                // Decide what kind of auto-summary is needed.
                switch ( $changeType ) {
                        case 'new-redirect':
                                $newTarget = $newContent->getRedirectTarget();
                                $truncatedtext = $newContent->getTextForSummary(
                                        $summaryLimit
                                        - strlen( wfMessage( 'autoredircomment' )->inContentLanguage()->text() )
                                        - strlen( $newTarget->getFullText() )
                                );

                                return wfMessage( 'autoredircomment', $newTarget->getFullText() )
                                        ->plaintextParams( $truncatedtext )->inContentLanguage()->text();
                        case 'changed-redirect-target':
                                $oldTarget = $oldContent->getRedirectTarget();
                                $newTarget = $newContent->getRedirectTarget();

                                $truncatedtext = $newContent->getTextForSummary(
                                        $summaryLimit
                                        - strlen( wfMessage( 'autosumm-changed-redirect-target' )
                                                ->inContentLanguage()->text() )
                                        - strlen( $oldTarget->getFullText() )
                                        - strlen( $newTarget->getFullText() )
                                );

                                return wfMessage( 'autosumm-changed-redirect-target',
                                                $oldTarget->getFullText(),
                                                $newTarget->getFullText() )
                                        ->rawParams( $truncatedtext )->inContentLanguage()->text();
                        case 'removed-redirect':
                                $oldTarget = $oldContent->getRedirectTarget();
                                $truncatedtext = $newContent->getTextForSummary(
                                        $summaryLimit
                                        - strlen( wfMessage( 'autosumm-removed-redirect' )
                                                ->inContentLanguage()->text() )
                                        - strlen( $oldTarget->getFullText() ) );

                                return wfMessage( 'autosumm-removed-redirect', $oldTarget->getFullText() )
                                        ->rawParams( $truncatedtext )->inContentLanguage()->text();
                        case 'newpage':
                                // If they're making a new article, give its text, truncated, in the summary.
                                $truncatedtext = $newContent->getTextForSummary(
                                        $summaryLimit - strlen( wfMessage( 'autosumm-new' )->inContentLanguage()->text() ) );

                                return wfMessage( 'autosumm-new' )->rawParams( $truncatedtext )
                                        ->inContentLanguage()->text();
                        case 'blank':
                                return wfMessage( 'autosumm-blank' )->inContentLanguage()->text();
                        case 'replace':
                                $truncatedtext = $newContent->getTextForSummary(
                                        $summaryLimit - strlen( wfMessage( 'autosumm-replace' )->inContentLanguage()->text() ) );

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

        /**
         * Return an applicable tag if one exists for the given edit or return null.
         *
         * @stable to override
         * @since 1.31
         *
         * @param Content|null $oldContent The previous text of the page.
         * @param Content|null $newContent The submitted text of the page.
         * @param int $flags Bit mask: a bit mask of flags submitted for the edit.
         *
         * @return string|null An appropriate tag, or null.
         */
        public function getChangeTag(
                ?Content $oldContent = null,
                ?Content $newContent = null,
                $flags = 0
        ) {
                $changeType = $this->getChangeType( $oldContent, $newContent, $flags );

                // There's no applicable tag for this change.
                if ( !$changeType ) {
                        return null;
                }

                // Core tags use the same keys as ones returned from $this->getChangeType()
                // but prefixed with pseudo namespace 'mw-', so we add the prefix before checking
                // if this type of change should be tagged
                $tag = 'mw-' . $changeType;

                // Not all change types are tagged, so we check against the list of defined tags.
                if ( in_array( $tag, MediaWikiServices::getInstance()->getChangeTagsStore()->getSoftwareTags() ) ) {
                        return $tag;
                }

                return null;
        }

        /**
         * Auto-generates a deletion reason
         *
         * @stable to override
         * @since 1.21
         *
         * @param Title $title The page's title
         * @param bool &$hasHistory Whether the page has a history
         *
         * @return string|false String containing deletion reason or empty string, or
         *    boolean false if no revision occurred
         */
        public function getAutoDeleteReason( Title $title, &$hasHistory = false ) {
                if ( func_num_args() === 2 ) {
                        wfDeprecated( __METHOD__ . ': $hasHistory parameter', '1.38' );
                }
                $dbr = MediaWikiServices::getInstance()->getConnectionProvider()->getReplicaDatabase();
                $revStore = MediaWikiServices::getInstance()->getRevisionStore();

                // Get the last revision
                $revRecord = $revStore->getRevisionByTitle( $title );

                if ( $revRecord === null ) {
                        return false;
                }

                // Get the article's contents
                $content = $revRecord->getContent( SlotRecord::MAIN );
                $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 = $revStore->getPreviousRevision( $revRecord );

                        if ( $prev ) {
                                $revRecord = $prev;
                                $content = $prev->getContent( SlotRecord::MAIN );
                                $blank = true;
                        }
                }

                $this->checkModelID( $revRecord->getSlot( SlotRecord::MAIN )->getModel() );

                // Find out if there was only one contributor
                // Only scan the last 20 revisions
                $queryBuilder = $revStore->newSelectQueryBuilder( $dbr )
                        ->where( [
                                'rev_page' => $title->getArticleID(),
                                $dbr->bitAnd( 'rev_deleted', RevisionRecord::DELETED_USER ) . ' = 0'
                        ] )
                        ->limit( 20 );
                $res = $queryBuilder->caller( __METHOD__ )->fetchResultSet();

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

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

                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 ) { // T24999
                                        $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)
                $maxLength = CommentStore::COMMENT_CHARACTER_LIMIT - ( strlen( $reason ) - 2 );
                $text = $content ? $content->getTextForSummary( $maxLength ) : '';

                // 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 changes
         * between $undo and $undoafter.
         *
         * @stable to override
         * @since 1.21
         * @since 1.32 accepts Content objects for all parameters instead of Revision objects.
         *  Passing Revision objects is deprecated.
         * @since 1.37 only accepts Content objects
         *
         * @param Content $currentContent The current text
         * @param Content $undoContent The content of the revision to undo
         * @param Content $undoAfterContent Must be from an earlier revision than $undo
         * @param bool $undoIsLatest Set true if $undo is from the current revision (since 1.32)
         *
         * @return Content|false Content on success, false on failure
         */
        public function getUndoContent(
                Content $currentContent,
                Content $undoContent,
                Content $undoAfterContent,
                $undoIsLatest = false
        ) {
                try {
                        $this->checkModelID( $currentContent->getModel() );
                        $this->checkModelID( $undoContent->getModel() );
                        if ( !$undoIsLatest ) {
                                // If we are undoing the most recent revision,
                                // its ok to revert content model changes. However
                                // if we are undoing a revision in the middle, then
                                // doing that will be confusing.
                                $this->checkModelID( $undoAfterContent->getModel() );
                        }
                } catch ( MWException $e ) {
                        // If the revisions have different content models
                        // just return false
                        return false;
                }

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

                $undone_content = $this->merge3( $undoContent, $undoAfterContent, $currentContent );

                return $undone_content;
        }

        /**
         * Returns true for content models that support caching using the
         * ParserCache mechanism. See WikiPage::shouldCheckParserCache().
         *
         * @stable to override
         * @since 1.21
         *
         * @return bool Always false.
         */
        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.
         *
         * @stable to override
         *
         * @return bool Always false.
         */
        public function supportsSections() {
                return false;
        }

        /**
         * Returns true if this content model supports categories.
         * The default implementation returns true.
         *
         * @stable to override
         *
         * @return bool Always true.
         */
        public function supportsCategories() {
                return true;
        }

        /**
         * 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.
         *
         * @stable to override
         *
         * @return bool Always false.
         */
        public function supportsRedirects() {
                return false;
        }

        /**
         * Return true if this content model supports direct editing, such as via EditPage.
         * This should return true for TextContent and its derivatives, and return false
         * for structured data content.
         *
         * @stable to override
         *
         * @return bool Default is false.
         */
        public function supportsDirectEditing() {
                return false;
        }

        /**
         * If a non-existing page can be created with the contents from another (arbitrary) page being
         * preloaded in the editor, see {@see EditPage::getContentObject}. Only makes sense together
         * with {@see supportsDirectEditing}.
         *
         * @stable to override
         * @since 1.39
         *
         * @return bool
         */
        public function supportsPreloadContent(): bool {
                return false;
        }

        /**
         * Whether an edit on the content should trigger an HTML render and ParserCache entry.
         *
         * @stable to override
         * @since 1.37
         *
         * @return bool true if edit should trigger an HTML render false otherwise
         */
        public function generateHTMLOnEdit(): bool {
                return true;
        }

        /**
         * Whether or not this content model supports direct editing via ApiEditPage
         *
         * @stable to override
         *
         * @return bool Default is false, and true for TextContent and derivatives.
         */
        public function supportsDirectApiEditing() {
                return $this->supportsDirectEditing();
        }

        /**
         * Get fields definition for search index
         *
         * @todo Expose title, redirect, namespace, text, source_text, text_bytes
         *       field mappings here. (see T142670 and T143409)
         *
         * @stable to override
         *
         * @param SearchEngine $engine
         * @return SearchIndexField[] List of fields this content handler can provide.
         * @since 1.28
         */
        public function getFieldsForSearchIndex( SearchEngine $engine ) {
                $fields = [];
                $fields['category'] = $engine->makeSearchFieldMapping(
                        'category',
                        SearchIndexField::INDEX_TYPE_TEXT
                );
                $fields['category']->setFlag( SearchIndexField::FLAG_CASEFOLD );

                $fields['external_link'] = $engine->makeSearchFieldMapping(
                        'external_link',
                        SearchIndexField::INDEX_TYPE_KEYWORD
                );

                $fields['outgoing_link'] = $engine->makeSearchFieldMapping(
                        'outgoing_link',
                        SearchIndexField::INDEX_TYPE_KEYWORD
                );

                $fields['template'] = $engine->makeSearchFieldMapping(
                        'template',
                        SearchIndexField::INDEX_TYPE_KEYWORD
                );
                $fields['template']->setFlag( SearchIndexField::FLAG_CASEFOLD );

                $fields['content_model'] = $engine->makeSearchFieldMapping(
                        'content_model',
                        SearchIndexField::INDEX_TYPE_KEYWORD
                );

                return $fields;
        }

        /**
         * Add new field definition to array.
         * @param SearchIndexField[] &$fields
         * @param SearchEngine $engine
         * @param string $name
         * @param string $type
         * @return SearchIndexField[] new field defs
         * @since 1.28
         */
        protected function addSearchField( &$fields, SearchEngine $engine, $name, $type ) {
                $fields[$name] = $engine->makeSearchFieldMapping( $name, $type );
                return $fields;
        }

        /**
         * Return fields to be indexed by search engine
         * as representation of this document.
         * Overriding class should call parent function or take care of calling
         * the SearchDataForIndex hook.
         *
         * The $output must be the result of a call to {@link getParserOutputForIndexing()}
         * on the same content handler. That method may return ParserOutput
         * {@link ParserOutput::hasText() without HTML}; this base implementation
         * does not rely on the HTML being present, so it is safe to call
         * even by subclasses that override {@link getParserOutputForIndexing()}
         * to skip HTML generation. On the other hand,
         * since the default implementation of {@link getParserOutputForIndexing()}
         * does generate HTML, subclasses are free to rely on the HTML here
         * if they do not override {@link getParserOutputForIndexing()}.
         *
         * @stable to override
         * @param WikiPage $page Page to index
         * @param ParserOutput $output
         * @param SearchEngine $engine Search engine for which we are indexing
         * @param RevisionRecord|null $revision Revision content to fetch if provided or use the latest revision
         *                                      from WikiPage::getRevisionRecord() if not
         * @return array Map of name=>value for fields, an empty array is returned if the latest
         *               revision cannot be retrieved.
         * @since 1.28
         */
        public function getDataForSearchIndex(
                WikiPage $page,
                ParserOutput $output,
                SearchEngine $engine,
                ?RevisionRecord $revision = null
        ) {
                $revision ??= $page->getRevisionRecord();
                if ( $revision === null ) {
                        LoggerFactory::getInstance( 'search' )->warning(
                                "Called getDataForSearchIndex on the page {page_id} for which the " .
                                "latest revision cannot be loaded.",
                                [ "page_id" => $page->getId() ]
                        );
                        return [];
                }
                Assert::invariant( $revision->getPageId() === $page->getId(),
                        '$revision and $page must target the same page_id' );

                $fieldData = [];
                $content = $revision->getContent( SlotRecord::MAIN );

                if ( $content ) {
                        $searchDataExtractor = new ParserOutputSearchDataExtractor();

                        $fieldData['category'] = $searchDataExtractor->getCategories( $output );
                        $fieldData['external_link'] = $searchDataExtractor->getExternalLinks( $output );
                        $fieldData['outgoing_link'] = $searchDataExtractor->getOutgoingLinks( $output );
                        $fieldData['template'] = $searchDataExtractor->getTemplates( $output );

                        $text = $content->getTextForSearchIndex();

                        $fieldData['text'] = $text;
                        $fieldData['source_text'] = $text;
                        $fieldData['text_bytes'] = $content->getSize();
                        $fieldData['content_model'] = $content->getModel();
                }

                $this->getHookRunner()->onSearchDataForIndex( $fieldData, $this, $page, $output, $engine );
                $this->getHookRunner()->onSearchDataForIndex2( $fieldData, $this, $page, $output, $engine, $revision );

                return $fieldData;
        }

        /**
         * Produce page output suitable for indexing.
         * Typically used with {@link getDataForSearchIndex()}.
         *
         * Specific content handlers may override it if they need different content handling.
         *
         * The default implementation returns output {@link ParserOutput::hasText() with HTML},
         * but callers should not rely on this, and subclasses may override this method
         * and skip HTML generation if it is not needed for indexing.
         * (In that case, they should not attempt to store the output in the $cache.)
         *
         * @stable to override
         *
         * @param WikiPage $page
         * @param ParserCache|null $cache deprecated since 1.38 and won't have any effect
         * @param RevisionRecord|null $revision
         * @return ParserOutput|null null when the ParserOutput cannot be obtained
         * @see ParserOutputAccess::getParserOutput() for failure modes
         */
        public function getParserOutputForIndexing(
                WikiPage $page,
                ?ParserCache $cache = null,
                ?RevisionRecord $revision = null
        ) {
                // TODO: MCR: ContentHandler should be called per slot, not for the whole page.
                // See T190066.
                $parserOptions = $page->makeParserOptions( 'canonical' );
                $parserOptions->setRenderReason( 'ParserOutputForIndexing' );
                $parserOutputAccess = MediaWikiServices::getInstance()->getParserOutputAccess();
                return $parserOutputAccess->getParserOutput(
                        $page,
                        $parserOptions,
                        $revision,
                        ParserOutputAccess::OPT_NO_UPDATE_CACHE
                )->getValue();
        }

        /**
         * Get the latest revision of the given $page,
         * fetching it from the primary if necessary.
         *
         * @param WikiPage $page
         * @return RevisionRecord
         * @since 1.36 (previously private)
         */
        protected function latestRevision( WikiPage $page ): RevisionRecord {
                $revRecord = $page->getRevisionRecord();
                if ( $revRecord == null ) {
                        // If the content represents a brand new page it's possible
                        // we need to fetch it from the primary.
                        $page->loadPageData( IDBAccessObject::READ_LATEST );
                        $revRecord = $page->getRevisionRecord();
                        if ( $revRecord == null ) {
                                $text = $page->getTitle()->getPrefixedText();
                                throw new MWException(
                                        "No revision could be loaded for page: $text" );
                        }
                }

                return $revRecord;
        }

        /**
         * Returns a list of DeferrableUpdate objects for recording information about the
         * given Content in some secondary data store.
         *
         * Application logic should not call this method directly. Instead, it should call
         * DerivedPageDataUpdater::getSecondaryDataUpdates().
         *
         * @note Implementations must not return a LinksUpdate instance. Instead, a LinksUpdate
         * is created by the calling code in DerivedPageDataUpdater, on the combined ParserOutput
         * of all slots, not for each slot individually. This is in contrast to the old
         * getSecondaryDataUpdates method defined by AbstractContent, which returned a LinksUpdate.
         *
         * @note Implementations should not call $content->getParserOutput, they should call
         * $slotOutput->getSlotRendering( $role, false ) instead if they need to access a ParserOutput
         * of $content. This allows existing ParserOutput objects to be re-used, while avoiding
         * creating a ParserOutput when none is needed.
         *
         * @stable to override
         *
         * @param Title $title The title of the page to supply the updates for
         * @param Content $content The content to generate data updates for.
         * @param string $role The role (slot) in which the content is being used. Which updates
         *        are performed should generally not depend on the role the content has, but the
         *        DeferrableUpdates themselves may need to know the role, to track to which slot the
         *        data refers, and to avoid overwriting data of the same kind from another slot.
         * @param SlotRenderingProvider $slotOutput A provider that can be used to gain access to
         *        a ParserOutput of $content by calling $slotOutput->getSlotParserOutput( $role, false ).
         * @return DeferrableUpdate[] A list of DeferrableUpdate objects for putting information
         *        about this content object somewhere. The default implementation returns an empty
         *        array.
         * @since 1.32
         */
        public function getSecondaryDataUpdates(
                Title $title,
                Content $content,
                $role,
                SlotRenderingProvider $slotOutput
        ) {
                return [];
        }

        /**
         * Returns a list of DeferrableUpdate objects for removing information about content
         * in some secondary data store. This is used when a page is deleted, and also when
         * a slot is removed from a page.
         *
         * Application logic should not call this method directly. Instead, it should call
         * WikiPage::getSecondaryDataUpdates().
         *
         * @note Implementations must not return a LinksDeletionUpdate instance. Instead, a
         * LinksDeletionUpdate is created by the calling code in WikiPage.
         * This is in contrast to the old getDeletionUpdates method defined by AbstractContent,
         * which returned a LinksUpdate.
         *
         * @note Implementations should not rely on the page's current content, but rather the current
         * state of the secondary data store.
         *
         * @stable to override
         *
         * @param Title $title The title of the page to supply the updates for
         * @param string $role The role (slot) in which the content is being used. Which updates
         *        are performed should generally not depend on the role the content has, but the
         *        DeferrableUpdates themselves may need to know the role, to track to which slot the
         *        data refers, and to avoid overwriting data of the same kind from another slot.
         *
         * @return DeferrableUpdate[] A list of DeferrableUpdate objects for putting information
         *        about this content object somewhere. The default implementation returns an empty
         *        array.
         *
         * @since 1.32
         */
        public function getDeletionUpdates( Title $title, $role ) {
                return [];
        }

        /**
         * Returns a $content object with pre-save transformations applied (or the same
         * object if no transformations apply).
         *
         * @note Not stable to call other then from ContentHandler hierarchy.
         * Callers need to use ContentTransformer::preSaveTransform.
         * @stable to override
         * @since 1.37
         *
         * @param Content $content
         * @param PreSaveTransformParams $pstParams
         *
         * @return Content
         */
        public function preSaveTransform(
                Content $content,
                PreSaveTransformParams $pstParams
        ): Content {
                return $content;
        }

        /**
         * Returns a $content object with preload transformations applied (or the same
         * object if no transformations apply).
         *
         * @note Not stable to call other then from ContentHandler hierarchy.
         * Callers need to use ContentTransformer::preLoadTransform.
         * @stable to override
         * @since 1.37
         *
         * @param Content $content
         * @param PreloadTransformParams $pltParams
         *
         * @return Content
         */
        public function preloadTransform(
                Content $content,
                PreloadTransformParams $pltParams
        ): Content {
                return $content;
        }

        /**
         * Validate content for saving it.
         *
         * This may be used to check the content's consistency with global state. This function should
         * NOT write any information to the database.
         *
         * Note that this method will usually be called inside the same transaction
         * bracket that will be used to save the new revision, so the revision passed
         * in is probably unsaved (has no id) and might belong to unsaved page.
         *
         * @since 1.38
         * @stable to override
         *
         * @param Content $content
         * @param ValidationParams $validationParams
         *
         * @return StatusValue A status object indicating if content can be saved in the given revision.
         */
        public function validateSave(
                Content $content,
                ValidationParams $validationParams
        ) {
                if ( $content->isValid() ) {
                        return StatusValue::newGood();
                } else {
                        return StatusValue::newFatal( "invalid-content-data" );
                }
        }

        /**
         * Returns a ParserOutput object containing information derived from this content.
         * Most importantly, unless $cpoParams->getGenerateHtml was false, the return value contains an
         * HTML representation of the content.
         *
         * Subclasses that want to control the parser output may override
         * fillParserOutput() instead.
         *
         *
         *
         * @since 1.38
         *
         * @param Content $content
         * @param ContentParseParams $cpoParams
         * @return ParserOutput Containing information derived from this content.
         */
        public function getParserOutput(
                Content $content,
                ContentParseParams $cpoParams
        ) {
                $services = MediaWikiServices::getInstance();
                $title = $services->getTitleFactory()->newFromPageReference( $cpoParams->getPage() );
                $parserOptions = $cpoParams->getParserOptions();

                if ( $parserOptions->getIsPreview() ) {
                        $scopedCallback = $parserOptions->setupFakeRevision(
                                $title,
                                $content,
                                $parserOptions->getUserIdentity(),
                                $cpoParams->getRevId() ?: 0
                        );
                }

                $hookRunner = new HookRunner( $services->getHookContainer() );

                $po = new ParserOutput();

                // Initialize to the page language
                $po->setLanguage( $title->getPageLanguage() );

                $parserOptions->registerWatcher( [ &$po, 'recordOption' ] );
                if ( $hookRunner->onContentGetParserOutput(
                        // FIXME $cpoParams->getRevId() may be null here?
                        // @phan-suppress-next-line PhanTypeMismatchArgumentNullable
                        $content, $title, $cpoParams->getRevId(), $parserOptions, $cpoParams->getGenerateHtml(), $po )
                ) {
                        // Save and restore the old value, just in case something is reusing
                        // the ParserOptions object in some weird way.
                        $oldRedir = $parserOptions->getRedirectTarget();
                        $parserOptions->setRedirectTarget( $content->getRedirectTarget() );

                        $po->resetParseStartTime();
                        $this->fillParserOutput(
                                $content,
                                $cpoParams,
                                $po
                        );
                        $po->recordTimeProfile();

                        MediaWikiServices::getInstance()->get( '_ParserObserver' )->notifyParse(
                                $title,
                                $cpoParams->getRevId(),
                                $parserOptions,
                                $content,
                                $po
                        );
                        $parserOptions->setRedirectTarget( $oldRedir );
                }

                $hookRunner->onContentAlterParserOutput( $content, $title, $po );
                $parserOptions->registerWatcher( null );
                if ( isset( $scopedCallback ) ) {
                        ScopedCallback::consume( $scopedCallback );
                }

                return $po;
        }

        /**
         * A temporary layer to move AbstractContent::fillParserOutput to ContentHandler::fillParserOutput
         *
         * @internal only core AbstractContent::fillParserOutput implementations need to call this.
         * @since 1.38
         * @param Content $content
         * @param ContentParseParams $cpoParams
         * @param ParserOutput &$output The output object to fill (reference).
         */
        public function fillParserOutputInternal(
                Content $content,
                ContentParseParams $cpoParams,
                ParserOutput &$output
        ) {
                $this->fillParserOutput( $content, $cpoParams, $output );
        }

        /**
         * Fills the provided ParserOutput with information derived from the content.
         * Unless $cpoParams->getGenerateHtml() was false,
         * this includes an HTML representation of the content.
         *
         * If $cpoParams->getGenerateHtml() is false, and you chose not to generate
         * html, the ParserOutput must have a text of null. If the
         * text of the ParserOutput object is anything other than null (even if ''),
         * it is assumed that you don't support not generating html, and that it is
         * safe to reuse the parser output for calls expecting that html was generated.
         *
         * Subclasses are expected to override this method.
         *
         * This placeholder implementation always throws an exception.
         *
         * @stable to override
         *
         * @since 1.38
         * @param Content $content
         * @param ContentParseParams $cpoParams
         * @param ParserOutput &$output The output object to fill (reference).
         * Most implementations should modify the output object passed in here;
         * if you choose to replace it with a fresh object instead,
         * make sure you call {@link ParserOutput::resetParseStartTime()} on it.
         */
        protected function fillParserOutput(
                Content $content,
                ContentParseParams $cpoParams,
                ParserOutput &$output
        ) {
                // Subclasses must override fillParserOutput() to directly don't fail.
                throw new LogicException( 'Subclasses of ContentHandler must override fillParserOutput!' );
        }

}

/** @deprecated class alias since 1.43 */
class_alias( ContentHandler::class, 'ContentHandler' );