wikimedia/mediawiki-core

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includes/diff/DifferenceEngine.php

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

use MediaWiki\CommentFormatter\CommentFormatter;
use MediaWiki\Content\IContentHandlerFactory;
use MediaWiki\Context\ContextSource;
use MediaWiki\Context\IContextSource;
use MediaWiki\Diff\TextDiffer\ManifoldTextDiffer;
use MediaWiki\HookContainer\HookRunner;
use MediaWiki\Html\Html;
use MediaWiki\Linker\Linker;
use MediaWiki\Linker\LinkRenderer;
use MediaWiki\MainConfigNames;
use MediaWiki\MediaWikiServices;
use MediaWiki\Page\ParserOutputAccess;
use MediaWiki\Page\WikiPageFactory;
use MediaWiki\Permissions\Authority;
use MediaWiki\Permissions\PermissionStatus;
use MediaWiki\Revision\ArchivedRevisionLookup;
use MediaWiki\Revision\BadRevisionException;
use MediaWiki\Revision\RevisionRecord;
use MediaWiki\Revision\RevisionStore;
use MediaWiki\Revision\SlotRecord;
use MediaWiki\SpecialPage\SpecialPage;
use MediaWiki\Storage\NameTableAccessException;
use MediaWiki\Title\Title;
use MediaWiki\User\Options\UserOptionsLookup;
use MediaWiki\User\UserEditTracker;
use MediaWiki\User\UserGroupManager;
use MediaWiki\User\UserGroupMembership;
use MediaWiki\User\UserIdentity;
use MediaWiki\User\UserIdentityUtils;
use Wikimedia\Rdbms\IConnectionProvider;

/**
 * DifferenceEngine is responsible for rendering the difference between two revisions as HTML.
 * This includes interpreting URL parameters, retrieving revision data, checking access permissions,
 * selecting and invoking the diff generator class for the individual slots, doing post-processing
 * on the generated diff, adding the rest of the HTML (such as headers) and writing the whole thing
 * to OutputPage.
 *
 * DifferenceEngine can be subclassed by extensions, by customizing
 * ContentHandler::createDifferenceEngine; the content handler will be selected based on the
 * content model of the main slot (of the new revision, when the two are different).
 * That might change after PageTypeHandler gets introduced.
 *
 * In the past, the class was also used for slot-level diff generation, and extensions might still
 * subclass it and add such functionality. When that is the case (specifically, when a
 * ContentHandler returns a standard SlotDiffRenderer but a nonstandard DifferenceEngine)
 * DifferenceEngineSlotDiffRenderer will be used to convert the old behavior into the new one.
 *
 * @ingroup DifferenceEngine
 *
 * @todo This class is huge and poorly defined. It should be split into a controller responsible
 * for interpreting query parameters, retrieving data and checking permissions; and a HTML renderer.
 */
class DifferenceEngine extends ContextSource {

    use DeprecationHelper;

    /**
     * Constant to indicate diff cache compatibility.
     * Bump this when changing the diff formatting in a way that
     * fixes important bugs or such to force cached diff views to
     * clear.
     */
    private const DIFF_VERSION = '1.41';

    /**
     * Revision ID for the old revision. 0 for the revision previous to $mNewid, false
     * if the diff does not have an old revision (e.g. 'oldid=<first revision of page>&diff=prev'),
     * or the revision does not exist, null if the revision is unsaved.
     * @var int|false|null
     */
    protected $mOldid;

    /**
     * Revision ID for the new revision. 0 for the last revision of the current page
     * (as defined by the request context), false if the revision does not exist, null
     * if it is unsaved, or an alias such as 'next'.
     * @var int|string|false|null
     */
    protected $mNewid;

    /**
     * Old revision (left pane).
     * Allowed to be an unsaved revision, unlikely that's ever needed though.
     * False when the old revision does not exist; this can happen when using
     * diff=prev on the first revision. Null when the revision should exist but
     * doesn't (e.g. load failure); loadRevisionData() will return false in that
     * case. Also null until lazy-loaded. Ignored completely when isContentOverridden
     * is set.
     * @var RevisionRecord|null|false
     */
    private $mOldRevisionRecord;

    /**
     * New revision (right pane).
     * Note that this might be an unsaved revision (e.g. for edit preview).
     * Null in case of load failure; diff methods will just return an error message in that case,
     * and loadRevisionData() will return false. Also null until lazy-loaded. Ignored completely
     * when isContentOverridden is set.
     * @var RevisionRecord|null
     */
    private $mNewRevisionRecord;

    /**
     * Title of old revision or null if the old revision does not exist or does not belong to a page.
     * @var Title|null
     */
    protected $mOldPage;

    /**
     * Title of new revision or null if the new revision does not exist or does not belong to a page.
     * @var Title|null
     */
    protected $mNewPage;

    /**
     * Change tags of old revision or null if it does not exist / is not saved.
     * @var string|false|null
     */
    private $mOldTags;

    /**
     * Change tags of new revision or null if it does not exist / is not saved.
     * @var string|null
     */
    private $mNewTags;

    /**
     * @var Content|null
     * @deprecated since 1.32, content slots are now handled by the corresponding SlotDiffRenderer.
     *   This property is set to the content of the main slot, but not actually used for the main diff.
     */
    private $mOldContent;

    /**
     * @var Content|null
     * @deprecated since 1.32, content slots are now handled by the corresponding SlotDiffRenderer.
     *   This property is set to the content of the main slot, but not actually used for the main diff.
     */
    private $mNewContent;

    /** @var Language */
    protected $mDiffLang;

    /** @var bool Have the revisions IDs been loaded */
    private $mRevisionsIdsLoaded = false;

    /** @var bool Have the revisions been loaded */
    protected $mRevisionsLoaded = false;

    /** @var int How many text blobs have been loaded, 0, 1 or 2? */
    protected $mTextLoaded = 0;

    /**
     * Was the content overridden via setContent()?
     * If the content was overridden, most internal state (e.g. mOldid or mOldRev) should be ignored
     * and only mOldContent and mNewContent is reliable.
     * (Note that setRevisions() does not set this flag as in that case all properties are
     * overridden and remain consistent with each other, so no special handling is needed.)
     * @var bool
     */
    protected $isContentOverridden = false;

    /** @var bool Was the diff fetched from cache? */
    protected $mCacheHit = false;

    /** @var string|null Cache key if the diff was fetched from cache */
    private $cacheHitKey = null;

    /**
     * Set this to true to add debug info to the HTML output.
     * Warning: this may cause RSS readers to spuriously mark articles as "new"
     * (T22601)
     * @var bool
     */
    public $enableDebugComment = false;

    /** @var bool If true, line X is not displayed when X is 1, for example
     *    to increase readability and conserve space with many small diffs.
     */
    protected $mReducedLineNumbers = false;

    /** @var string Link to action=markpatrolled */
    protected $mMarkPatrolledLink = null;

    /** @var bool Show rev_deleted content if allowed */
    protected $unhide = false;

    /** @var bool Refresh the diff cache */
    protected $mRefreshCache = false;

    /** @var SlotDiffRenderer[]|null DifferenceEngine classes for the slots, keyed by role name. */
    protected $slotDiffRenderers = null;

    /**
     * Temporary hack for B/C while slot diff related methods of DifferenceEngine are being
     * deprecated. When true, we are inside a DifferenceEngineSlotDiffRenderer and
     * $slotDiffRenderers should not be used.
     * @var bool
     */
    protected $isSlotDiffRenderer = false;

    /**
     * A set of options that will be passed to the SlotDiffRenderer upon creation
     * @var array
     */
    private $slotDiffOptions = [];

    /**
     * Extra query parameters to be appended to diff page links
     */
    private $extraQueryParams = [];

    /** @var ManifoldTextDiffer|null */
    private $textDiffer;

    protected LinkRenderer $linkRenderer;
    private IContentHandlerFactory $contentHandlerFactory;
    private RevisionStore $revisionStore;
    private ArchivedRevisionLookup $archivedRevisionLookup;
    private HookRunner $hookRunner;
    private WikiPageFactory $wikiPageFactory;
    private UserOptionsLookup $userOptionsLookup;
    private CommentFormatter $commentFormatter;
    private IConnectionProvider $dbProvider;
    private UserGroupManager $userGroupManager;
    private UserEditTracker $userEditTracker;
    private UserIdentityUtils $userIdentityUtils;

    /** @var Message[] */
    private $revisionLoadErrors = [];

    /**
     * @param IContextSource|null $context Context to use, anything else will be ignored
     * @param int $old Old ID we want to show and diff with.
     * @param string|int $new Either revision ID or 'prev' or 'next'. Default: 0.
     * @param int $rcid Deprecated, no longer used!
     * @param bool $refreshCache If set, refreshes the diff cache
     * @param bool $unhide If set, allow viewing deleted revs
     */
    public function __construct( $context = null, $old = 0, $new = 0, $rcid = 0,
        $refreshCache = false, $unhide = false
    ) {
        if ( $context instanceof IContextSource ) {
            $this->setContext( $context );
        }

        wfDebug( "DifferenceEngine old '$old' new '$new' rcid '$rcid'" );

        $this->mOldid = $old;
        $this->mNewid = $new;
        $this->mRefreshCache = $refreshCache;
        $this->unhide = $unhide;

        $services = MediaWikiServices::getInstance();
        $this->linkRenderer = $services->getLinkRenderer();
        $this->contentHandlerFactory = $services->getContentHandlerFactory();
        $this->revisionStore = $services->getRevisionStore();
        $this->archivedRevisionLookup = $services->getArchivedRevisionLookup();
        $this->hookRunner = new HookRunner( $services->getHookContainer() );
        $this->wikiPageFactory = $services->getWikiPageFactory();
        $this->userOptionsLookup = $services->getUserOptionsLookup();
        $this->commentFormatter = $services->getCommentFormatter();
        $this->dbProvider = $services->getConnectionProvider();
        $this->userGroupManager = $services->getUserGroupManager();
        $this->userEditTracker = $services->getUserEditTracker();
        $this->userIdentityUtils = $services->getUserIdentityUtils();
    }

    /**
     * @return SlotDiffRenderer[] Diff renderers for each slot, keyed by role name.
     *   Includes slots only present in one of the revisions. Does not include slots
     *   for which content is identical in the two revisions.
     */
    protected function getSlotDiffRenderers() {
        if ( $this->isSlotDiffRenderer ) {
            throw new LogicException( __METHOD__ . ' called in slot diff renderer mode' );
        }

        if ( $this->slotDiffRenderers === null ) {
            if ( !$this->loadRevisionData() ) {
                return [];
            }

            $slotContents = $this->getSlotContents();
            $this->slotDiffRenderers = [];
            foreach ( $slotContents as $role => $contents ) {
                if ( $contents['new'] && $contents['old']
                    && $contents['new']->equals( $contents['old'] )
                ) {
                    // Do not produce a diff of identical content
                    continue;
                }
                $handler = ( $contents['new'] ?: $contents['old'] )->getContentHandler();
                $this->slotDiffRenderers[$role] = $handler->getSlotDiffRenderer(
                    $this->getContext(),
                    $this->slotDiffOptions + [
                        'contentLanguage' => $this->getDiffLang()->getCode(),
                        'textDiffer' => $this->getTextDiffer()
                    ]
                );
            }
        }

        return $this->slotDiffRenderers;
    }

    /**
     * Mark this DifferenceEngine as a slot renderer (as opposed to a page renderer).
     * This is used in legacy mode when the DifferenceEngine is wrapped in a
     * DifferenceEngineSlotDiffRenderer.
     * @internal For use by DifferenceEngineSlotDiffRenderer only.
     */
    public function markAsSlotDiffRenderer() {
        $this->isSlotDiffRenderer = true;
    }

    /**
     * Get the old and new content objects for all slots.
     * This method does not do any permission checks.
     * @return (Content|null)[][] [ role => [ 'old' => Content|null, 'new' => Content|null ], ... ]
     */
    protected function getSlotContents() {
        if ( $this->isContentOverridden ) {
            return [
                SlotRecord::MAIN => [ 'old' => $this->mOldContent, 'new' => $this->mNewContent ]
            ];
        } elseif ( !$this->loadRevisionData() ) {
            return [];
        }

        $newSlots = $this->mNewRevisionRecord->getPrimarySlots()->getSlots();
        $oldSlots = $this->mOldRevisionRecord ?
            $this->mOldRevisionRecord->getPrimarySlots()->getSlots() :
            [];
        // The order here will determine the visual order of the diff. The current logic is
        // slots of the new revision first in natural order, then deleted ones. This is ad hoc
        // and should not be relied on - in the future we may want the ordering to depend
        // on the page type.
        $roles = array_keys( array_merge( $newSlots, $oldSlots ) );

        $slots = [];
        foreach ( $roles as $role ) {
            $slots[$role] = [
                'old' => $this->loadSingleSlot(
                    $oldSlots[$role] ?? null,
                    'old'
                ),
                'new' => $this->loadSingleSlot(
                    $newSlots[$role] ?? null,
                    'new'
                )
            ];
        }
        // move main slot to front
        if ( isset( $slots[SlotRecord::MAIN] ) ) {
            $slots = [ SlotRecord::MAIN => $slots[SlotRecord::MAIN] ] + $slots;
        }
        return $slots;
    }

    /**
     * Load the content of a single slot record
     *
     * @param SlotRecord|null $slot
     * @param string $which "new" or "old"
     * @return Content|null
     */
    private function loadSingleSlot( ?SlotRecord $slot, string $which ) {
        if ( !$slot ) {
            return null;
        }
        try {
            return $slot->getContent();
        } catch ( BadRevisionException $e ) {
            $this->addRevisionLoadError( $which );
            return null;
        }
    }

    /**
     * Set a message to show as a notice at the top of the page
     *
     * @param string $which "new" or "old"
     */
    private function addRevisionLoadError( $which ) {
        $this->revisionLoadErrors[] = $this->msg( $which === 'new'
            ? 'difference-bad-new-revision' : 'difference-bad-old-revision'
        );
    }

    /**
     * If errors were encountered while loading the revision contents, this
     * will return an array of Messages describing the errors.
     *
     * @return Message[]
     */
    public function getRevisionLoadErrors() {
        return $this->revisionLoadErrors;
    }

    /**
     * Determine whether there was an error loading the new revision
     * @return bool
     */
    private function hasNewRevisionLoadError() {
        foreach ( $this->revisionLoadErrors as $error ) {
            if ( $error->getKey() === 'difference-bad-new-revision' ) {
                return true;
            }
        }
        return false;
    }

    /** @inheritDoc */
    public function getTitle() {
        // T202454 avoid errors when there is no title
        return parent::getTitle() ?: Title::makeTitle( NS_SPECIAL, 'BadTitle/DifferenceEngine' );
    }

    /**
     * Set reduced line numbers mode.
     * When set, line X is not displayed when X is 1, for example to increase readability and
     * conserve space with many small diffs.
     * @param bool $value
     */
    public function setReducedLineNumbers( $value = true ) {
        $this->mReducedLineNumbers = $value;
    }

    /**
     * Get the language in which the diff text is written
     *
     * @return Language
     */
    public function getDiffLang() {
        # Default language in which the diff text is written.
        $this->mDiffLang ??= $this->getDefaultLanguage();
        return $this->mDiffLang;
    }

    /**
     * Get the language to use if none has been set by setTextLanguage().
     * Wikibase overrides this to use the user language.
     *
     * @return Language
     */
    protected function getDefaultLanguage() {
        return $this->getTitle()->getPageLanguage();
    }

    /**
     * @return bool
     */
    public function wasCacheHit() {
        return $this->mCacheHit;
    }

    /**
     * Get the ID of old revision (left pane) of the diff. 0 for the revision
     * previous to getNewid(), false if the old revision does not exist, null
     * if it's unsaved.
     * To get a real revision ID instead of 0, call loadRevisionData() first.
     * @return int|false|null
     */
    public function getOldid() {
        $this->loadRevisionIds();

        return $this->mOldid;
    }

    /**
     * Get the ID of new revision (right pane) of the diff. 0 for the current revision,
     * false if the new revision does not exist, null if it's unsaved.
     * To get a real revision ID instead of 0, call loadRevisionData() first.
     * @return int|false|null
     */
    public function getNewid() {
        $this->loadRevisionIds();

        return $this->mNewid;
    }

    /**
     * Get the left side of the diff.
     * Could be null when the first revision of the page is diffed to 'prev' (or in the case of
     * load failure).
     * @return RevisionRecord|null
     */
    public function getOldRevision() {
        return $this->mOldRevisionRecord ?: null;
    }

    /**
     * Get the right side of the diff.
     * Should not be null but can still happen in the case of load failure.
     * @return RevisionRecord|null
     */
    public function getNewRevision() {
        return $this->mNewRevisionRecord;
    }

    /**
     * Look up a special:Undelete link to the given deleted revision id,
     * as a workaround for being unable to load deleted diffs in currently.
     *
     * @param int $id Revision ID
     *
     * @return string|bool Link HTML or false
     */
    public function deletedLink( $id ) {
        if ( $this->getAuthority()->isAllowed( 'deletedhistory' ) ) {
            $revRecord = $this->archivedRevisionLookup->getArchivedRevisionRecord( null, $id );
            if ( $revRecord ) {
                $title = Title::newFromPageIdentity( $revRecord->getPage() );

                return SpecialPage::getTitleFor( 'Undelete' )->getFullURL( [
                    'target' => $title->getPrefixedText(),
                    'timestamp' => $revRecord->getTimestamp()
                ] );
            }
        }

        return false;
    }

    /**
     * Build a wikitext link toward a deleted revision, if viewable.
     *
     * @param int $id Revision ID
     *
     * @return string Wikitext fragment
     */
    public function deletedIdMarker( $id ) {
        $link = $this->deletedLink( $id );
        if ( $link ) {
            return "[$link $id]";
        } else {
            return (string)$id;
        }
    }

    private function showMissingRevision() {
        $out = $this->getOutput();

        $missing = [];
        if ( $this->mOldid && ( !$this->mOldRevisionRecord || !$this->mOldContent ) ) {
            $missing[] = $this->deletedIdMarker( $this->mOldid );
        }
        if ( !$this->mNewRevisionRecord || !$this->mNewContent ) {
            $missing[] = $this->deletedIdMarker( $this->mNewid );
        }

        $out->setPageTitleMsg( $this->msg( 'errorpagetitle' ) );
        $msg = $this->msg( 'difference-missing-revision' )
            ->params( $this->getLanguage()->listToText( $missing ) )
            ->numParams( count( $missing ) )
            ->parseAsBlock();
        $out->addHTML( $msg );
    }

    /**
     * Checks whether one of the given Revisions was deleted
     *
     * @return bool
     */
    public function hasDeletedRevision() {
        $this->loadRevisionData();
        return (
                $this->mNewRevisionRecord &&
                $this->mNewRevisionRecord->isDeleted( RevisionRecord::DELETED_TEXT )
            ) ||
            (
                $this->mOldRevisionRecord &&
                $this->mOldRevisionRecord->isDeleted( RevisionRecord::DELETED_TEXT )
            );
    }

    /**
     * Get the permission errors associated with the revisions for the current diff.
     *
     * @param Authority $performer
     * @return array[] Array of arrays of the arguments to wfMessage to explain permissions problems.
     */
    public function getPermissionErrors( Authority $performer ) {
        $this->loadRevisionData();
        $permStatus = PermissionStatus::newEmpty();
        if ( $this->mNewPage ) {
            $performer->authorizeRead( 'read', $this->mNewPage, $permStatus );
        }
        if ( $this->mOldPage ) {
            $performer->authorizeRead( 'read', $this->mOldPage, $permStatus );
        }
        return $permStatus->toLegacyErrorArray();
    }

    /**
     * Checks whether one of the given Revisions was suppressed
     *
     * @return bool
     */
    public function hasSuppressedRevision() {
        return $this->hasDeletedRevision() && (
            ( $this->mOldRevisionRecord &&
                $this->mOldRevisionRecord->isDeleted( RevisionRecord::DELETED_RESTRICTED ) ) ||
            ( $this->mNewRevisionRecord &&
                $this->mNewRevisionRecord->isDeleted( RevisionRecord::DELETED_RESTRICTED ) )
        );
    }

    /**
     * Renders user associated edit count
     *
     * @param UserIdentity $user
     * @return string
     */
    private function getUserEditCount( $user ): string {
        $editCount = $this->userEditTracker->getUserEditCount( $user );
        if ( $editCount === null ) {
            return '';
        }

        return Html::rawElement( 'div', [
            'class' => 'mw-diff-usereditcount',
        ],
            $this->msg(
                'diff-user-edits',
                $this->getLanguage()->formatNum( $editCount )
            )->parse()
        );
    }

    /**
     * Renders user roles
     *
     * @param UserIdentity $user
     * @return string
     */
    private function getUserRoles( UserIdentity $user ) {
        if ( !$this->userIdentityUtils->isNamed( $user ) ) {
            return '';
        }
        $userGroups = $this->userGroupManager->getUserGroups( $user );
        $userGroupLinks = [];
        foreach ( $userGroups as $group ) {
            $userGroupLinks[] = UserGroupMembership::getLinkHTML( $group, $this->getContext() );
        }
        return Html::rawElement( 'div', [
            'class' => 'mw-diff-userroles',
        ], $this->getLanguage()->commaList( $userGroupLinks ) );
    }

    /**
     * Renders user associated meta data
     *
     * @param UserIdentity|null $user
     * @return string
     */
    private function getUserMetaData( ?UserIdentity $user ) {
        if ( !$user ) {
            return '';
        }
        return Html::rawElement( 'div', [
            'class' => 'mw-diff-usermetadata',
        ], $this->getUserRoles( $user ) . $this->getUserEditCount( $user ) );
    }

    /**
     * Checks whether the current user has permission for accessing the revisions of the diff.
     * Note that this does not check whether the user has permission to view the page, it only
     * checks revdelete permissions.
     *
     * It is the caller's responsibility to call
     * $this->getUserPermissionErrors or similar checks.
     *
     * @param Authority $performer
     * @return bool
     */
    public function isUserAllowedToSeeRevisions( Authority $performer ) {
        $this->loadRevisionData();

        if ( $this->mOldRevisionRecord && !$this->mOldRevisionRecord->userCan(
            RevisionRecord::DELETED_TEXT,
            $performer
        ) ) {
            return false;
        }

        // $this->mNewRev will only be falsy if a loading error occurred
        // (in which case the user is allowed to see).
        return !$this->mNewRevisionRecord || $this->mNewRevisionRecord->userCan(
            RevisionRecord::DELETED_TEXT,
            $performer
        );
    }

    /**
     * Checks whether the diff should be hidden from the current user
     * This is based on whether the user is allowed to see it and has specifically asked to see it.
     *
     * @param Authority $performer
     * @return bool
     */
    public function shouldBeHiddenFromUser( Authority $performer ) {
        return $this->hasDeletedRevision() && ( !$this->unhide ||
            !$this->isUserAllowedToSeeRevisions( $performer ) );
    }

    /**
     * @param bool $diffOnly
     */
    public function showDiffPage( $diffOnly = false ) {
        # Allow frames except in certain special cases
        $out = $this->getOutput();
        $out->setPreventClickjacking( false );
        $out->setRobotPolicy( 'noindex,nofollow' );

        // Allow extensions to add any extra output here
        $this->hookRunner->onDifferenceEngineShowDiffPage( $out );

        if ( !$this->loadRevisionData() ) {
            if ( $this->hookRunner->onDifferenceEngineShowDiffPageMaybeShowMissingRevision( $this ) ) {
                $this->showMissingRevision();
            }
            return;
        }

        $user = $this->getUser();
        $permErrors = $this->getPermissionErrors( $this->getAuthority() );
        if ( $permErrors ) {
            throw new PermissionsError( 'read', $permErrors );
        }

        $rollback = '';

        $query = $this->extraQueryParams;
        # Carry over 'diffonly' param via navigation links
        if ( $diffOnly != MediaWikiServices::getInstance()
            ->getUserOptionsLookup()->getBoolOption( $user, 'diffonly' )
        ) {
            $query['diffonly'] = $diffOnly;
        }
        # Cascade unhide param in links for easy deletion browsing
        if ( $this->unhide ) {
            $query['unhide'] = 1;
        }

        # Check if one of the revisions is deleted/suppressed
        $deleted = $this->hasDeletedRevision();
        $suppressed = $this->hasSuppressedRevision();
        $allowed = $this->isUserAllowedToSeeRevisions( $this->getAuthority() );

        $revisionTools = [];
        $breadCrumbs = '';

        # mOldRevisionRecord is false if the difference engine is called with a "vague" query for
        # a diff between a version V and its previous version V' AND the version V
        # is the first version of that article. In that case, V' does not exist.
        if ( $this->mOldRevisionRecord === false ) {
            if ( $this->mNewPage ) {
                $out->setPageTitleMsg(
                    $this->msg( 'difference-title' )->plaintextParams( $this->mNewPage->getPrefixedText() )
                );
            }
            $samePage = true;
            $oldHeader = '';
            // Allow extensions to change the $oldHeader variable
            $this->hookRunner->onDifferenceEngineOldHeaderNoOldRev( $oldHeader );
        } else {
            $this->hookRunner->onDifferenceEngineViewHeader( $this );

            if ( !$this->mOldPage || !$this->mNewPage ) {
                // XXX say something to the user?
                $samePage = false;
            } elseif ( $this->mNewPage->equals( $this->mOldPage ) ) {
                $out->setPageTitleMsg(
                    $this->msg( 'difference-title' )->plaintextParams( $this->mNewPage->getPrefixedText() )
                );
                $samePage = true;
            } else {
                $out->setPageTitleMsg( $this->msg( 'difference-title-multipage' )->plaintextParams(
                    $this->mOldPage->getPrefixedText(), $this->mNewPage->getPrefixedText() ) );
                $out->addSubtitle( $this->msg( 'difference-multipage' ) );
                $samePage = false;
            }

            if ( $samePage && $this->mNewPage &&
                $this->getAuthority()->probablyCan( 'edit', $this->mNewPage )
            ) {
                if ( $this->mNewRevisionRecord->isCurrent() &&
                    $this->getAuthority()->probablyCan( 'rollback', $this->mNewPage )
                ) {
                    $rollbackLink = Linker::generateRollback(
                        $this->mNewRevisionRecord,
                        $this->getContext(),
                        [ 'noBrackets' ]
                    );
                    if ( $rollbackLink ) {
                        $out->setPreventClickjacking( true );
                        $rollback = "\u{00A0}\u{00A0}\u{00A0}" . $rollbackLink;
                    }
                }

                if ( $this->userCanEdit( $this->mOldRevisionRecord ) &&
                    $this->userCanEdit( $this->mNewRevisionRecord )
                ) {
                    $undoLink = $this->linkRenderer->makeKnownLink(
                        $this->mNewPage,
                        $this->msg( 'editundo' )->text(),
                        [ 'title' => Linker::titleAttrib( 'undo' ) ],
                        [
                            'action' => 'edit',
                            'undoafter' => $this->mOldid,
                            'undo' => $this->mNewid
                        ]
                    );
                    $revisionTools['mw-diff-undo'] = $undoLink;
                }
            }
            # Make "previous revision link"
            $hasPrevious = $samePage && $this->mOldPage &&
                $this->revisionStore->getPreviousRevision( $this->mOldRevisionRecord );
            if ( $hasPrevious ) {
                $prevlinkQuery = [ 'diff' => 'prev', 'oldid' => $this->mOldid ] + $query;
                $prevlink = $this->linkRenderer->makeKnownLink(
                    $this->mOldPage,
                    $this->msg( 'previousdiff' )->text(),
                    [ 'id' => 'differences-prevlink' ],
                    $prevlinkQuery
                );
                $breadCrumbs .= $this->linkRenderer->makeKnownLink(
                    $this->mOldPage,
                    $this->msg( 'previousdiff' )->text(),
                    [
                        'class' => 'mw-diff-revision-history-link-previous'
                    ],
                    $prevlinkQuery
                );
            } else {
                $prevlink = "\u{00A0}";
            }

            if ( $this->mOldRevisionRecord->isMinor() ) {
                $oldminor = ChangesList::flag( 'minor' );
            } else {
                $oldminor = '';
            }

            $oldRevRecord = $this->mOldRevisionRecord;

            $ldel = $this->revisionDeleteLink( $oldRevRecord );
            $oldRevisionHeader = $this->getRevisionHeader( $oldRevRecord, 'complete' );
            $oldChangeTags = ChangeTags::formatSummaryRow( $this->mOldTags, 'diff', $this->getContext() );
            $oldRevComment = $this->commentFormatter
                ->formatRevision(
                    $oldRevRecord, $user, !$diffOnly, !$this->unhide, /** disable parentheseses */ false
                );

            if ( $oldRevComment === '' ) {
                $defaultComment = $this->msg( 'changeslist-nocomment' )->escaped();
                $oldRevComment = "<span class=\"comment mw-comment-none\">$defaultComment</span>";
            }

            $oldHeader = '<div id="mw-diff-otitle1"><strong>' . $oldRevisionHeader . '</strong></div>' .
                '<div id="mw-diff-otitle2">' .
                Linker::revUserTools( $oldRevRecord, !$this->unhide ) .
                $this->getUserMetaData( $oldRevRecord->getUser() ) .
                '</div>' .
                '<div id="mw-diff-otitle3">' . $oldminor . $oldRevComment . $ldel . '</div>' .
                '<div id="mw-diff-otitle5">' . $oldChangeTags[0] . '</div>' .
                '<div id="mw-diff-otitle4">' . $prevlink . '</div>';

            // Allow extensions to change the $oldHeader variable
            $this->hookRunner->onDifferenceEngineOldHeader(
                $this, $oldHeader, $prevlink, $oldminor, $diffOnly, $ldel, $this->unhide );
        }

        $out->addJsConfigVars( [
            'wgDiffOldId' => $this->mOldid,
            'wgDiffNewId' => $this->mNewid,
        ] );

        # Make "next revision link"
        # Skip next link on the top revision
        if ( $samePage && $this->mNewPage && !$this->mNewRevisionRecord->isCurrent() ) {
            $nextlinkQuery = [ 'diff' => 'next', 'oldid' => $this->mNewid ] + $query;
            $nextlink = $this->linkRenderer->makeKnownLink(
                $this->mNewPage,
                $this->msg( 'nextdiff' )->text(),
                [ 'id' => 'differences-nextlink' ],
                $nextlinkQuery
            );
            $breadCrumbs .= $this->linkRenderer->makeKnownLink(
                $this->mNewPage,
                $this->msg( 'nextdiff' )->text(),
                [
                    'class' => 'mw-diff-revision-history-link-next'
                ],
                $nextlinkQuery
            );
        } else {
            $nextlink = "\u{00A0}";
        }

        if ( $this->mNewRevisionRecord->isMinor() ) {
            $newminor = ChangesList::flag( 'minor' );
        } else {
            $newminor = '';
        }

        # Handle RevisionDelete links...
        $rdel = $this->revisionDeleteLink( $this->mNewRevisionRecord );

        # Allow extensions to define their own revision tools
        $this->hookRunner->onDiffTools(
            $this->mNewRevisionRecord,
            $revisionTools,
            $this->mOldRevisionRecord ?: null,
            $user
        );

        $formattedRevisionTools = [];
        // Put each one in parentheses (poor man's button)
        foreach ( $revisionTools as $key => $tool ) {
            $toolClass = is_string( $key ) ? $key : 'mw-diff-tool';
            $element = Html::rawElement(
                'span',
                [ 'class' => $toolClass ],
                $tool
            );
            $formattedRevisionTools[] = $element;
        }

        $newRevRecord = $this->mNewRevisionRecord;

        $newRevisionHeader = $this->getRevisionHeader( $newRevRecord, 'complete' ) .
            ' ' . implode( ' ', $formattedRevisionTools );
        $newChangeTags = ChangeTags::formatSummaryRow( $this->mNewTags, 'diff', $this->getContext() );
        $newRevComment = $this->commentFormatter->formatRevision(
            $newRevRecord, $user, !$diffOnly, !$this->unhide, /** disable parentheseses */ false
        );

        if ( $newRevComment === '' ) {
            $defaultComment = $this->msg( 'changeslist-nocomment' )->escaped();
            $newRevComment = "<span class=\"comment mw-comment-none\">$defaultComment</span>";
        }

        $newHeader = '<div id="mw-diff-ntitle1"><strong>' . $newRevisionHeader . '</strong></div>' .
            '<div id="mw-diff-ntitle2">' . Linker::revUserTools( $newRevRecord, !$this->unhide ) .
            $rollback .
            $this->getUserMetaData( $newRevRecord->getUser() ) .
            '</div>' .
            '<div id="mw-diff-ntitle3">' . $newminor . $newRevComment . $rdel . '</div>' .
            '<div id="mw-diff-ntitle5">' . $newChangeTags[0] . '</div>' .
            '<div id="mw-diff-ntitle4">' . $nextlink . $this->markPatrolledLink() . '</div>';

        // Allow extensions to change the $newHeader variable
        $this->hookRunner->onDifferenceEngineNewHeader( $this, $newHeader,
            $formattedRevisionTools, $nextlink, $rollback, $newminor, $diffOnly,
            $rdel, $this->unhide );

        $out->addHTML(
            Html::rawElement( 'div', [
                'class' => 'mw-diff-revision-history-links'
            ], $breadCrumbs )
        );
        # If the diff cannot be shown due to a deleted revision, then output
        # the diff header and links to unhide (if available)...
        if ( $this->shouldBeHiddenFromUser( $this->getAuthority() ) ) {
            $this->showDiffStyle();
            $multi = $this->getMultiNotice();
            $out->addHTML( $this->addHeader( '', $oldHeader, $newHeader, $multi ) );
            if ( !$allowed ) {
                # Give explanation for why revision is not visible
                $msg = [ $suppressed ? 'rev-suppressed-no-diff' : 'rev-deleted-no-diff' ];
            } else {
                # Give explanation and add a link to view the diff...
                $query = $this->getRequest()->appendQueryValue( 'unhide', '1' );
                $msg = [
                    $suppressed ? 'rev-suppressed-unhide-diff' : 'rev-deleted-unhide-diff',
                    $this->getTitle()->getFullURL( $query )
                ];
            }
            $out->addHTML( Html::warningBox( $this->msg( ...$msg )->parse(), 'plainlinks' ) );
        # Otherwise, output a regular diff...
        } else {
            # Add deletion notice if the user is viewing deleted content
            $notice = '';
            if ( $deleted ) {
                $msg = $suppressed ? 'rev-suppressed-diff-view' : 'rev-deleted-diff-view';
                $notice = Html::warningBox( $this->msg( $msg )->parse(), 'plainlinks' );
            }

            # Add an error if the content can't be loaded
            $this->getSlotContents();
            foreach ( $this->getRevisionLoadErrors() as $msg ) {
                $notice .= Html::warningBox( $msg->parse() );
            }

            // Check if inline switcher will be needed
            if ( $this->getTextDiffer()->hasFormat( 'inline' ) ) {
                $out->enableOOUI();
            }

            $this->showTablePrefixes();
            $this->showDiff( $oldHeader, $newHeader, $notice );
            if ( !$diffOnly ) {
                $this->renderNewRevision();
            }

            // Allow extensions to optionally not show the final patrolled link
            if ( $this->hookRunner->onDifferenceEngineRenderRevisionShowFinalPatrolLink() ) {
                # Add redundant patrol link on bottom...
                $out->addHTML( $this->markPatrolledLink() );
            }
        }
    }

    /**
     * Add table prefixes
     */
    private function showTablePrefixes() {
        $parts = [];
        foreach ( $this->getSlotDiffRenderers() as $slotDiffRenderer ) {
            $parts += $slotDiffRenderer->getTablePrefix( $this->getContext(), $this->mNewPage );
        }
        ksort( $parts );
        if ( count( array_filter( $parts ) ) > 0 ) {
            $language = $this->getLanguage();
            $attrs = [
                'class' => 'mw-diff-table-prefix',
                'dir' => $language->getDir(),
                'lang' => $language->getCode(),
            ];
            $this->getOutput()->addHTML(
                Html::rawElement( 'div', $attrs, implode( '', $parts ) ) );
        }
    }

    /**
     * Build a link to mark a change as patrolled.
     *
     * Returns empty string if there's either no revision to patrol or the user is not allowed to.
     *
     * Side effect: When the patrol link is build, this method will call
     * OutputPage::setPreventClickjacking(true) and load a JS module.
     *
     * @return string HTML or empty string
     */
    public function markPatrolledLink() {
        if ( $this->mMarkPatrolledLink === null ) {
            $linkInfo = $this->getMarkPatrolledLinkInfo();
            // If false, there is no patrol link needed/allowed
            if ( !$linkInfo || !$this->mNewPage ) {
                $this->mMarkPatrolledLink = '';
            } else {
                $patrolLinkClass = 'patrollink';
                $this->mMarkPatrolledLink = ' <span class="' . $patrolLinkClass . '" data-mw="interface">[' .
                    $this->linkRenderer->makeKnownLink(
                        $this->mNewPage,
                        $this->msg( 'markaspatrolleddiff' )->text(),
                        [],
                        [
                            'action' => 'markpatrolled',
                            'rcid' => $linkInfo['rcid'],
                        ]
                    ) . ']</span>';
                // Allow extensions to change the markpatrolled link
                $this->hookRunner->onDifferenceEngineMarkPatrolledLink( $this,
                    $this->mMarkPatrolledLink, $linkInfo['rcid'] );
            }
        }
        return $this->mMarkPatrolledLink;
    }

    /**
     * Returns an array of meta data needed to build a "mark as patrolled" link and
     * adds a JS module to the output.
     *
     * @return array|false An array of meta data for a patrol link (rcid only)
     *  or false if no link is needed
     */
    protected function getMarkPatrolledLinkInfo() {
        $user = $this->getUser();
        $config = $this->getConfig();

        // Prepare a change patrol link, if applicable
        if (
            // Is patrolling enabled and the user allowed to?
            $config->get( MainConfigNames::UseRCPatrol ) &&
            $this->mNewPage &&
            $this->getAuthority()->probablyCan( 'patrol', $this->mNewPage ) &&
            // Only do this if the revision isn't more than 6 hours older
            // than the Max RC age (6h because the RC might not be cleaned out regularly)
            RecentChange::isInRCLifespan( $this->mNewRevisionRecord->getTimestamp(), 21600 )
        ) {
            // Look for an unpatrolled change corresponding to this diff
            $change = RecentChange::newFromConds(
                [
                    'rc_this_oldid' => $this->mNewid,
                    'rc_patrolled' => RecentChange::PRC_UNPATROLLED
                ],
                __METHOD__
            );

            if ( $change && !$change->getPerformerIdentity()->equals( $user ) ) {
                $rcid = $change->getAttribute( 'rc_id' );
            } else {
                // None found or the page has been created by the current user.
                // If the user could patrol this it already would be patrolled
                $rcid = 0;
            }

            // Allow extensions to possibly change the rcid here
            // For example the rcid might be set to zero due to the user
            // being the same as the performer of the change but an extension
            // might still want to show it under certain conditions
            $this->hookRunner->onDifferenceEngineMarkPatrolledRCID( $rcid, $this, $change, $user );

            // Build the link
            if ( $rcid ) {
                $this->getOutput()->setPreventClickjacking( true );
                if ( $this->getAuthority()->isAllowed( 'writeapi' ) ) {
                    $this->getOutput()->addModules( 'mediawiki.misc-authed-curate' );
                }

                return [ 'rcid' => $rcid ];
            }
        }

        // No mark as patrolled link applicable
        return false;
    }

    /**
     * @param RevisionRecord $revRecord
     *
     * @return string
     */
    private function revisionDeleteLink( RevisionRecord $revRecord ) {
        $link = Linker::getRevDeleteLink(
            $this->getAuthority(),
            $revRecord,
            $revRecord->getPageAsLinkTarget()
        );
        if ( $link !== '' ) {
            $link = "\u{00A0}\u{00A0}\u{00A0}" . $link . ' ';
        }

        return $link;
    }

    /**
     * Show the new revision of the page.
     *
     * @note Not supported after calling setContent().
     */
    public function renderNewRevision() {
        if ( $this->isContentOverridden ) {
            // The code below only works with a RevisionRecord object. We could construct a
            // fake RevisionRecord (here or in setContent), but since this does not seem
            // needed at the moment, we'll just fail for now.
            throw new LogicException(
                __METHOD__
                . ' is not supported after calling setContent(). Use setRevisions() instead.'
            );
        }

        $out = $this->getOutput();
        $revHeader = $this->getRevisionHeader( $this->mNewRevisionRecord );
        # Add "current version as of X" title
        $out->addHTML( "<hr class='diff-hr' id='mw-oldid' />
        <h2 class='diff-currentversion-title'>{$revHeader}</h2>\n" );
        # Page content may be handled by a hooked call instead...
        if ( $this->hookRunner->onArticleContentOnDiff( $this, $out ) ) {
            $this->loadNewText();
            if ( !$this->mNewPage ) {
                // New revision is unsaved; bail out.
                // TODO in theory rendering the new revision is a meaningful thing to do
                // even if it's unsaved, but a lot of untangling is required to do it safely.
                return;
            }
            if ( $this->hasNewRevisionLoadError() ) {
                // There was an error loading the new revision
                return;
            }

            $out->setRevisionId( $this->mNewid );
            $out->setRevisionIsCurrent( $this->mNewRevisionRecord->isCurrent() );
            $out->setRevisionTimestamp( $this->mNewRevisionRecord->getTimestamp() );
            $out->setArticleFlag( true );

            if ( !$this->hookRunner->onArticleRevisionViewCustom(
                $this->mNewRevisionRecord, $this->mNewPage, $this->mOldid, $out )
            ) {
                // Handled by extension
                // NOTE: sync with hooks called in Article::view()
            } else {
                // Normal page
                if ( $this->getTitle()->equals( $this->mNewPage ) ) {
                    // If the Title stored in the context is the same as the one
                    // of the new revision, we can use its associated WikiPage
                    // object.
                    $wikiPage = $this->getWikiPage();
                } else {
                    // Otherwise we need to create our own WikiPage object
                    $wikiPage = $this->wikiPageFactory->newFromTitle( $this->mNewPage );
                }

                $parserOptions = $wikiPage->makeParserOptions( $this->getContext() );
                $parserOptions->setRenderReason( 'diff-page' );

                $parserOutputAccess = MediaWikiServices::getInstance()->getParserOutputAccess();
                $status = $parserOutputAccess->getParserOutput(
                    $wikiPage,
                    $parserOptions,
                    $this->mNewRevisionRecord,
                    // we already checked
                    ParserOutputAccess::OPT_NO_AUDIENCE_CHECK |
                    // Update cascading protection
                    ParserOutputAccess::OPT_LINKS_UPDATE
                );
                if ( $status->isOK() ) {
                    $parserOutput = $status->getValue();
                    // Allow extensions to change parser output here
                    if ( $this->hookRunner->onDifferenceEngineRenderRevisionAddParserOutput(
                        $this, $out, $parserOutput, $wikiPage )
                    ) {
                        $out->addParserOutput( $parserOutput, [
                            'enableSectionEditLinks' => $this->mNewRevisionRecord->isCurrent()
                                && $this->getAuthority()->probablyCan(
                                    'edit',
                                    $this->mNewRevisionRecord->getPage()
                                ),
                            'absoluteURLs' => $this->slotDiffOptions['expand-url'] ?? false
                        ] );
                    }
                } else {
                    $out->addHTML(
                        Html::errorBox(
                            $out->parseAsInterface(
                                $status->getWikiText( false, false, $this->getLanguage() )
                            )
                        )
                    );
                }
            }
        }
    }

    /**
     * Get the diff text, send it to the OutputPage object
     * Returns false if the diff could not be generated, otherwise returns true
     *
     * @param string|false $otitle Header for old text or false
     * @param string|false $ntitle Header for new text or false
     * @param string $notice HTML between diff header and body
     *
     * @return bool
     */
    public function showDiff( $otitle, $ntitle, $notice = '' ) {
        // Allow extensions to affect the output here
        $this->hookRunner->onDifferenceEngineShowDiff( $this );

        $diff = $this->getDiff( $otitle, $ntitle, $notice );
        if ( $diff === false ) {
            $this->showMissingRevision();
            return false;
        }

        $this->showDiffStyle();
        if ( $this->slotDiffOptions['expand-url'] ?? false ) {
            $diff = Linker::expandLocalLinks( $diff );
        }
        $this->getOutput()->addHTML( $diff );
        return true;
    }

    /**
     * Add style sheets for diff display.
     */
    public function showDiffStyle() {
        if ( !$this->isSlotDiffRenderer ) {
            $this->getOutput()->addModules( 'mediawiki.diff' );
            $this->getOutput()->addModuleStyles( [
                'mediawiki.interface.helpers.styles',
                'mediawiki.diff.styles'
            ] );
            foreach ( $this->getSlotDiffRenderers() as $slotDiffRenderer ) {
                $slotDiffRenderer->addModules( $this->getOutput() );
            }
        }
    }

    /**
     * Get complete diff table, including header
     *
     * @param string|false $otitle Header for old text or false
     * @param string|false $ntitle Header for new text or false
     * @param string $notice HTML between diff header and body
     *
     * @return string|false
     */
    public function getDiff( $otitle, $ntitle, $notice = '' ) {
        $body = $this->getDiffBody();
        if ( $body === false ) {
            return false;
        }

        $multi = $this->getMultiNotice();
        // Display a message when the diff is empty
        if ( $body === '' ) {
            $notice .= '<div class="mw-diff-empty">' .
                $this->msg( 'diff-empty' )->parse() .
                "</div>\n";
        }

        if ( $this->cacheHitKey !== null ) {
            $body .= "\n<!-- diff cache key " . htmlspecialchars( $this->cacheHitKey ) . " -->\n";
        }

        return $this->addHeader( $body, $otitle, $ntitle, $multi, $notice );
    }

    /**
     * Get the diff table body, without header
     *
     * @return string|false
     */
    public function getDiffBody() {
        $this->mCacheHit = true;
        // Check if the diff should be hidden from this user
        if ( !$this->isContentOverridden ) {
            if ( !$this->loadRevisionData() ) {
                return false;
            } elseif ( $this->mOldRevisionRecord &&
                !$this->mOldRevisionRecord->userCan(
                    RevisionRecord::DELETED_TEXT,
                    $this->getAuthority()
                )
            ) {
                return false;
            } elseif ( $this->mNewRevisionRecord &&
                !$this->mNewRevisionRecord->userCan(
                    RevisionRecord::DELETED_TEXT,
                    $this->getAuthority()
                ) ) {
                return false;
            }
            // Short-circuit
            if ( $this->mOldRevisionRecord === false || (
                $this->mOldRevisionRecord &&
                $this->mNewRevisionRecord &&
                $this->mOldRevisionRecord->getId() &&
                $this->mOldRevisionRecord->getId() == $this->mNewRevisionRecord->getId()
            ) ) {
                if ( $this->hookRunner->onDifferenceEngineShowEmptyOldContent( $this ) ) {
                    return '';
                }
            }
        }

        // Cacheable?
        $key = false;
        $services = MediaWikiServices::getInstance();
        $cache = $services->getMainWANObjectCache();
        $stats = $services->getStatsdDataFactory();
        if ( $this->mOldid && $this->mNewid ) {
            $key = $cache->makeKey( ...$this->getDiffBodyCacheKeyParams() );

            // Try cache
            if ( !$this->mRefreshCache ) {
                $difftext = $cache->get( $key );
                if ( is_string( $difftext ) ) {
                    $stats->updateCount( 'diff_cache.hit', 1 );
                    $difftext = $this->localiseDiff( $difftext );
                    $this->cacheHitKey = $key;
                    return $difftext;
                }
            } // don't try to load but save the result
        }
        $this->mCacheHit = false;
        $this->cacheHitKey = null;

        // Loadtext is permission safe, this just clears out the diff
        if ( !$this->loadText() ) {
            return false;
        }

        $difftext = '';
        // We've checked for revdelete at the beginning of this method; it's OK to ignore
        // read permissions here.
        $slotContents = $this->getSlotContents();
        foreach ( $this->getSlotDiffRenderers() as $role => $slotDiffRenderer ) {
            try {
                $slotDiff = $slotDiffRenderer->getDiff( $slotContents[$role]['old'],
                    $slotContents[$role]['new'] );
            } catch ( IncompatibleDiffTypesException $e ) {
                $slotDiff = $this->getSlotError( $e->getMessageObject()->parse() );
            }
            if ( $slotDiff && $role !== SlotRecord::MAIN ) {
                // FIXME: ask SlotRoleHandler::getSlotNameMessage
                $slotTitle = $role;
                $difftext .= $this->getSlotHeader( $slotTitle );
            }
            $difftext .= $slotDiff;
        }

        // Save to cache for 7 days
        if ( !$this->hookRunner->onAbortDiffCache( $this ) ) {
            $stats->updateCount( 'diff_cache.uncacheable', 1 );
        } elseif ( $key !== false ) {
            $stats->updateCount( 'diff_cache.miss', 1 );
            $cache->set( $key, $difftext, 7 * 86400 );
        } else {
            $stats->updateCount( 'diff_cache.uncacheable', 1 );
        }
        // localise line numbers and title attribute text
        $difftext = $this->localiseDiff( $difftext );

        return $difftext;
    }

    /**
     * Get the diff table body for one slot, without header
     *
     * @param string $role
     * @return string|false
     */
    public function getDiffBodyForRole( $role ) {
        $diffRenderers = $this->getSlotDiffRenderers();
        if ( !isset( $diffRenderers[$role] ) ) {
            return false;
        }

        $slotContents = $this->getSlotContents();
        try {
            $slotDiff = $diffRenderers[$role]->getDiff( $slotContents[$role]['old'],
                $slotContents[$role]['new'] );
        } catch ( IncompatibleDiffTypesException $e ) {
            $slotDiff = $this->getSlotError( $e->getMessageObject()->parse() );
        }
        if ( $slotDiff === '' ) {
            return false;
        }

        if ( $role !== SlotRecord::MAIN ) {
            // TODO use human-readable role name at least
            $slotTitle = $role;
            $slotDiff = $this->getSlotHeader( $slotTitle ) . $slotDiff;
        }

        return $this->localiseDiff( $slotDiff );
    }

    /**
     * Get a slot header for inclusion in a diff body (as a table row).
     *
     * @param string $headerText The text of the header
     * @return string
     *
     */
    protected function getSlotHeader( $headerText ) {
        // The old revision is missing on oldid=<first>&diff=prev; only 2 columns in that case.
        $columnCount = $this->mOldRevisionRecord ? 4 : 2;
        $userLang = $this->getLanguage()->getHtmlCode();
        return Html::rawElement( 'tr', [ 'class' => 'mw-diff-slot-header', 'lang' => $userLang ],
            Html::element( 'th', [ 'colspan' => $columnCount ], $headerText ) );
    }

    /**
     * Get an error message for inclusion in a diff body (as a table row).
     *
     * @param string $errorText The HTML of the error
     * @return string
     */
    protected function getSlotError( $errorText ) {
        // The old revision is missing on oldid=<first>&diff=prev; only 2 columns in that case.
        $columnCount = $this->mOldRevisionRecord ? 4 : 2;
        $userLang = $this->getLanguage()->getHtmlCode();
        return Html::rawElement( 'tr', [ 'class' => 'mw-diff-slot-error', 'lang' => $userLang ],
            Html::rawElement( 'td', [ 'colspan' => $columnCount ], $errorText ) );
    }

    /**
     * Get the cache key parameters
     *
     * Subclasses can replace the first element in the array to something
     * more specific to the type of diff (e.g. "inline-diff"), or append
     * if the cache should vary on more things. Overriding entirely should
     * be avoided.
     *
     * @since 1.31
     *
     * @return string[]
     * @phan-return non-empty-array<string>
     */
    protected function getDiffBodyCacheKeyParams() {
        if ( !$this->mOldid || !$this->mNewid ) {
            throw new BadMethodCallException( 'mOldid and mNewid must be set to get diff cache key.' );
        }

        $params = [
            'diff',
            self::DIFF_VERSION,
            "old-{$this->mOldid}",
            "rev-{$this->mNewid}"
        ];

        $extraKeys = [];
        if ( !$this->isSlotDiffRenderer ) {
            foreach ( $this->getSlotDiffRenderers() as $slotDiffRenderer ) {
                $extraKeys = array_merge( $extraKeys, $slotDiffRenderer->getExtraCacheKeys() );
            }
        }
        ksort( $extraKeys );
        return array_merge( $params, array_values( $extraKeys ) );
    }

    /**
     * Implements DifferenceEngineSlotDiffRenderer::getExtraCacheKeys(). Only used when
     * DifferenceEngine is wrapped in DifferenceEngineSlotDiffRenderer.
     * @return string[]
     * @internal for use by DifferenceEngineSlotDiffRenderer only
     * @deprecated
     */
    public function getExtraCacheKeys() {
        // This method is called when the DifferenceEngine is used for a slot diff. We only care
        // about special things, not the revision IDs, which are added to the cache key by the
        // page-level DifferenceEngine, and which might not have a valid value for this object.
        $this->mOldid = 123456789;
        $this->mNewid = 987654321;

        // This will repeat a bunch of unnecessary key fields for each slot. Not nice but harmless.
        $params = $this->getDiffBodyCacheKeyParams();

        // Try to get rid of the standard keys to keep the cache key human-readable:
        // call the getDiffBodyCacheKeyParams implementation of the base class, and if
        // the child class includes the same keys, drop them.
        // Uses an obscure PHP feature where static calls to non-static methods are allowed
        // as long as we are already in a non-static method of the same class, and the call context
        // ($this) will be inherited.
        // phpcs:ignore Squiz.Classes.SelfMemberReference.NotUsed
        $standardParams = DifferenceEngine::getDiffBodyCacheKeyParams();
        if ( array_slice( $params, 0, count( $standardParams ) ) === $standardParams ) {
            $params = array_slice( $params, count( $standardParams ) );
        }

        return $params;
    }

    /**
     * @param array $options for the difference engine. Available options:
     *    - diff-type: The text diff format, e.g. "table" or "inline". If the
     *      specified format is not supported, the option will be ignored, so
     *      the site default format (table) will be used.
     *    - expand-url: If true, put full URLs in href attributes (for action=render)
     *      FIXME: expand-url is not a slot diff option, it is a DifferenceEngine option.
     *    - inline-toggle: If true, and the inline format is supported
     *      a format selector toggle switch will be shown.
     */
    public function setSlotDiffOptions( $options ) {
        $validatedOptions = [];
        if ( isset( $options['diff-type'] )
            && $this->getTextDiffer()->hasFormat( $options['diff-type'] )
        ) {
            $validatedOptions['diff-type'] = $options['diff-type'];
        }
        if ( !empty( $options['expand-url'] ) ) {
            $validatedOptions['expand-url'] = true;
        }
        if ( !empty( $options['inline-toggle'] ) ) {
            $validatedOptions['inline-toggle'] = true;
        }
        $this->slotDiffOptions = $validatedOptions;
    }

    /**
     * Set query parameters to append to diff page links
     *
     * @since 1.41
     *
     * @param array $params
     */
    public function setExtraQueryParams( $params ) {
        $this->extraQueryParams = $params;
    }

    /**
     * Generate a diff, no caching.
     *
     * @since 1.21
     *
     * @param Content $old Old content
     * @param Content $new New content
     *
     * @throws Exception If old or new content is not an instance of TextContent.
     * @return bool|string
     *
     * @deprecated since 1.32, use a SlotDiffRenderer instead.
     */
    public function generateContentDiffBody( Content $old, Content $new ) {
        $slotDiffRenderer = $new->getContentHandler()->getSlotDiffRenderer( $this->getContext() );
        if (
            $slotDiffRenderer instanceof DifferenceEngineSlotDiffRenderer
            && $this->isSlotDiffRenderer
        ) {
            // Oops, we are just about to enter an infinite loop (the slot-level DifferenceEngine
            // called a DifferenceEngineSlotDiffRenderer that wraps the same DifferenceEngine class).
            // This will happen when a content model has no custom slot diff renderer, it does have
            // a custom difference engine, but that does not override this method.
            throw new LogicException( get_class( $this ) . ': could not maintain backwards compatibility. '
                . 'Please use a SlotDiffRenderer.' );
        }
        return $slotDiffRenderer->getDiff( $old, $new ) . $this->getDebugString();
    }

    /**
     * Generate a diff, no caching
     *
     * @param string $otext Old text, must be already segmented
     * @param string $ntext New text, must be already segmented
     *
     * @throws LogicException If content handling for text content is configured in a way
     *   that makes maintaining B/C hard.
     * @return bool|string
     *
     * @deprecated since 1.32, use a TextSlotDiffRenderer instead.
     */
    public function generateTextDiffBody( $otext, $ntext ) {
        $slotDiffRenderer = $this->contentHandlerFactory
            ->getContentHandler( CONTENT_MODEL_TEXT )
            ->getSlotDiffRenderer( $this->getContext() );
        if ( !( $slotDiffRenderer instanceof TextSlotDiffRenderer ) ) {
            // Someone used the GetSlotDiffRenderer hook to replace the renderer.
            // This is too unlikely to happen to bother handling properly.
            throw new LogicException( 'The slot diff renderer for text content should be a '
                . 'TextSlotDiffRenderer subclass' );
        }
        return $slotDiffRenderer->getTextDiff( $otext, $ntext ) . $this->getDebugString();
    }

    /**
     * Process DiffEngine config and get a sensible, usable engine
     *
     * @return string 'wikidiff2', 'php', or path to an executable
     * @internal For use by this class and within Core only.
     */
    public static function getEngine() {
        $differenceEngine = new self;
        $engine = $differenceEngine->getTextDiffer()->getEngineForFormat( 'table' );
        if ( $engine === 'external' ) {
            return MediaWikiServices::getInstance()->getMainConfig()
                ->get( MainConfigNames::ExternalDiffEngine );
        } else {
            return $engine;
        }
    }

    /**
     * Generate a debug comment indicating diff generating time,
     * server node, and generator backend.
     *
     * @param string $generator What diff engine was used
     *
     * @return string
     */
    protected function debug( $generator = "internal" ) {
        if ( !$this->enableDebugComment ) {
            return '';
        }
        $data = [ $generator ];
        if ( $this->getConfig()->get( MainConfigNames::ShowHostnames ) ) {
            $data[] = wfHostname();
        }
        $data[] = wfTimestamp( TS_DB );

        return "<!-- diff generator: " .
            implode( " ", array_map( "htmlspecialchars", $data ) ) .
            " -->\n";
    }

    /**
     * @return string
     */
    private function getDebugString() {
        $engine = self::getEngine();
        if ( $engine === 'wikidiff2' ) {
            return $this->debug( 'wikidiff2' );
        } elseif ( $engine === 'php' ) {
            return $this->debug( 'native PHP' );
        } else {
            return $this->debug( "external $engine" );
        }
    }

    /**
     * Localise diff output
     *
     * @param string $text
     * @return string
     */
    private function localiseDiff( $text ) {
        return $this->getTextDiffer()->localize( $this->getTextDiffFormat(), $text );
    }

    /**
     * Replace a common convention for language-independent line numbers with
     * the text in the user's language.
     *
     * @deprecated since 1.41, use BaseTextDiffer::localizeLineNumbers()
     * @param string $text
     * @return string
     */
    public function localiseLineNumbers( $text ) {
        return preg_replace_callback( '/<!--LINE (\d+)-->/',
            function ( array $matches ) {
                if ( $matches[1] === '1' && $this->mReducedLineNumbers ) {
                    return '';
                }
                return $this->msg( 'lineno' )->numParams( $matches[1] )->escaped();
            }, $text );
    }

    /**
     * If there are revisions between the ones being compared, return a note saying so.
     *
     * @return string
     */
    public function getMultiNotice() {
        // The notice only make sense if we are diffing two saved revisions of the same page.
        if (
            !$this->mOldRevisionRecord || !$this->mNewRevisionRecord
            || !$this->mOldPage || !$this->mNewPage
            || !$this->mOldPage->equals( $this->mNewPage )
            || $this->mOldRevisionRecord->getId() === null
            || $this->mNewRevisionRecord->getId() === null
            // (T237709) Deleted revs might have different page IDs
            || $this->mNewPage->getArticleID() !== $this->mOldRevisionRecord->getPageId()
            || $this->mNewPage->getArticleID() !== $this->mNewRevisionRecord->getPageId()
        ) {
            return '';
        }

        if ( $this->mOldRevisionRecord->getTimestamp() > $this->mNewRevisionRecord->getTimestamp() ) {
            $oldRevRecord = $this->mNewRevisionRecord; // flip
            $newRevRecord = $this->mOldRevisionRecord; // flip
        } else { // normal case
            $oldRevRecord = $this->mOldRevisionRecord;
            $newRevRecord = $this->mNewRevisionRecord;
        }

        // Don't show the notice if too many rows must be scanned
        // @todo show some special message for that case
        $nEdits = 0;
        $revisionIdList = $this->revisionStore->getRevisionIdsBetween(
            $this->mNewPage->getArticleID(),
            $oldRevRecord,
            $newRevRecord,
            1000
        );
        // only count revisions that are visible
        if ( count( $revisionIdList ) > 0 ) {
            foreach ( $revisionIdList as $revisionId ) {
                $revision = $this->revisionStore->getRevisionById( $revisionId );
                if ( $revision->getUser( RevisionRecord::FOR_THIS_USER, $this->getAuthority() ) ) {
                    $nEdits++;
                }
            }
        }
        if ( $nEdits > 0 && $nEdits <= 1000 ) {
            // Use an invalid username to get the wiki's default gender (as fallback)
            $newRevUserForGender = '[HIDDEN]';
            $limit = 100; // use diff-multi-manyusers if too many users
            try {
                $users = $this->revisionStore->getAuthorsBetween(
                    $this->mNewPage->getArticleID(),
                    $oldRevRecord,
                    $newRevRecord,
                    null,
                    $limit
                );
                $numUsers = count( $users );

                $newRevUser = $newRevRecord->getUser( RevisionRecord::RAW );
                $newRevUserText = $newRevUser ? $newRevUser->getName() : '';
                $newRevUserSafe = $newRevRecord->getUser(
                    RevisionRecord::FOR_THIS_USER,
                    $this->getAuthority()
                );
                $newRevUserForGender = $newRevUserSafe ? $newRevUserSafe->getName() : '[HIDDEN]';
                if ( $numUsers == 1 && $users[0]->getName() == $newRevUserText ) {
                    $numUsers = 0; // special case to say "by the same user" instead of "by one other user"
                }
            } catch ( InvalidArgumentException $e ) {
                $numUsers = 0;
            }

            return self::intermediateEditsMsg( $nEdits, $numUsers, $limit, $newRevUserForGender );
        }

        return '';
    }

    /**
     * Get a notice about how many intermediate edits and users there are
     *
     * @param int $numEdits
     * @param int $numUsers
     * @param int $limit
     * @param string $lastUser
     *
     * @return string
     */
    public static function intermediateEditsMsg( $numEdits, $numUsers, $limit, $lastUser = '[HIDDEN]' ) {
        if ( $numUsers === 0 ) {
            $msg = 'diff-multi-sameuser';
            return wfMessage( $msg )
                ->numParams( $numEdits, $numUsers )
                ->params( $lastUser )
                ->parse();
        } elseif ( $numUsers > $limit ) {
            $msg = 'diff-multi-manyusers';
            $numUsers = $limit;
        } else {
            $msg = 'diff-multi-otherusers';
        }

        return wfMessage( $msg )->numParams( $numEdits, $numUsers )->parse();
    }

    /**
     * @param RevisionRecord $revRecord
     * @return bool whether the user can see and edit the revision.
     */
    private function userCanEdit( RevisionRecord $revRecord ) {
        if ( !$revRecord->userCan( RevisionRecord::DELETED_TEXT, $this->getAuthority() ) ) {
            return false;
        }

        return true;
    }

    /**
     * Get a header for a specified revision.
     *
     * @param RevisionRecord $rev
     * @param string $complete 'complete' to get the header wrapped depending
     *        the visibility of the revision and a link to edit the page.
     *
     * @return string HTML fragment
     */
    public function getRevisionHeader( RevisionRecord $rev, $complete = '' ) {
        $lang = $this->getLanguage();
        $user = $this->getUser();
        $revtimestamp = $rev->getTimestamp();
        $timestamp = $lang->userTimeAndDate( $revtimestamp, $user );
        $dateofrev = $lang->userDate( $revtimestamp, $user );
        $timeofrev = $lang->userTime( $revtimestamp, $user );

        $header = $this->msg(
            $rev->isCurrent() ? 'currentrev-asof' : 'revisionasof',
            $timestamp,
            $dateofrev,
            $timeofrev
        );

        if ( $complete !== 'complete' ) {
            return $header->escaped();
        }

        $title = $rev->getPageAsLinkTarget();

        if ( $this->userCanEdit( $rev ) ) {
            $header = $this->linkRenderer->makeKnownLink(
                $title,
                $header->text(),
                [],
                [ 'oldid' => $rev->getId() ]
            );
            $editQuery = [ 'action' => 'edit' ];
            if ( !$rev->isCurrent() ) {
                $editQuery['oldid'] = $rev->getId();
            }

            $key = $this->getAuthority()->probablyCan( 'edit', $rev->getPage() ) ? 'editold' : 'viewsourceold';
            $msg = $this->msg( $key )->text();
            $editLink = $this->linkRenderer->makeKnownLink( $title, $msg, [], $editQuery );
            $header .= ' ' . Html::rawElement(
                'span',
                [ 'class' => 'mw-diff-edit' ],
                $editLink
            );
        } else {
            $header = $header->escaped();
        }

        // Machine readable information
        $header .= Html::element( 'span',
            [
                'class' => 'mw-diff-timestamp',
                'data-timestamp' => wfTimestamp( TS_ISO_8601, $revtimestamp ),
            ], ''
        );

        if ( $rev->isDeleted( RevisionRecord::DELETED_TEXT ) ) {
            return Html::rawElement(
                'span',
                [ 'class' => Linker::getRevisionDeletedClass( $rev ) ],
                $header
            );
        }

        return $header;
    }

    /**
     * Add the header to a diff body
     *
     * @param string $diff Diff body
     * @param string $otitle Old revision header
     * @param string $ntitle New revision header
     * @param string $multi Notice telling user that there are intermediate
     *   revisions between the ones being compared
     * @param string $notice Other notices, e.g. that user is viewing deleted content
     *
     * @return string
     */
    public function addHeader( $diff, $otitle, $ntitle, $multi = '', $notice = '' ) {
        // shared.css sets diff in interface language/dir, but the actual content
        // is often in a different language, mostly the page content language/dir
        $header = Html::openElement( 'table', [
            'class' => [
                'diff',
                // The following classes are used here:
                // * diff-type-table
                // * diff-type-inline
                'diff-type-' . $this->getTextDiffFormat(),
                // The following classes are used here:
                // * diff-contentalign-left
                // * diff-contentalign-right
                'diff-contentalign-' . $this->getDiffLang()->alignStart(),
                // The following classes are used here:
                // * diff-editfont-monospace
                // * diff-editfont-sans-serif
                // * diff-editfont-serif
                'diff-editfont-' . $this->userOptionsLookup->getOption(
                    $this->getUser(),
                    'editfont'
                )
            ],
            'data-mw' => 'interface',
        ] );
        $userLang = htmlspecialchars( $this->getLanguage()->getHtmlCode() );

        if ( !$diff && !$otitle ) {
            $header .= "
            <tr class=\"diff-title\" lang=\"{$userLang}\">
            <td class=\"diff-ntitle\">{$ntitle}</td>
            </tr>";
            $multiColspan = 1;
        } else {
            if ( $diff ) { // Safari/Chrome show broken output if cols not used
                $header .= "
                <col class=\"diff-marker\" />
                <col class=\"diff-content\" />
                <col class=\"diff-marker\" />
                <col class=\"diff-content\" />";
                $colspan = 2;
                $multiColspan = 4;
            } else {
                $colspan = 1;
                $multiColspan = 2;
            }
            if ( $otitle || $ntitle ) {
                // FIXME Hardcoding values from TableDiffFormatter.
                $deletedClass = 'diff-side-deleted';
                $addedClass = 'diff-side-added';
                $header .= "
                <tr class=\"diff-title\" lang=\"{$userLang}\">
                <td colspan=\"$colspan\" class=\"diff-otitle {$deletedClass}\">{$otitle}</td>
                <td colspan=\"$colspan\" class=\"diff-ntitle {$addedClass}\">{$ntitle}</td>
                </tr>";
            }
        }

        if ( $multi != '' ) {
            $header .= "<tr><td colspan=\"{$multiColspan}\" " .
                "class=\"diff-multi\" lang=\"{$userLang}\">{$multi}</td></tr>";
        }
        if ( $notice != '' ) {
            $header .= "<tr><td colspan=\"{$multiColspan}\" " .
                "class=\"diff-notice\" lang=\"{$userLang}\">{$notice}</td></tr>";
        }

        return $header . $diff . "</table>";
    }

    /**
     * Use specified text instead of loading from the database
     * @param Content $oldContent
     * @param Content $newContent
     * @since 1.21
     * @deprecated since 1.32, use setRevisions or ContentHandler::getSlotDiffRenderer.
     */
    public function setContent( Content $oldContent, Content $newContent ) {
        $this->mOldContent = $oldContent;
        $this->mNewContent = $newContent;

        $this->mTextLoaded = 2;
        $this->mRevisionsLoaded = true;
        $this->isContentOverridden = true;
        $this->slotDiffRenderers = null;
    }

    /**
     * Use specified text instead of loading from the database.
     * @param RevisionRecord|null $oldRevision
     * @param RevisionRecord $newRevision
     */
    public function setRevisions(
        ?RevisionRecord $oldRevision, RevisionRecord $newRevision
    ) {
        if ( $oldRevision ) {
            $this->mOldRevisionRecord = $oldRevision;
            $this->mOldid = $oldRevision->getId();
            $this->mOldPage = Title::newFromLinkTarget( $oldRevision->getPageAsLinkTarget() );
            // This method is meant for edit diffs and such so there is no reason to provide a
            // revision that's not readable to the user, but check it just in case.
            $this->mOldContent = $oldRevision->getContent( SlotRecord::MAIN,
                RevisionRecord::FOR_THIS_USER, $this->getAuthority() );
            if ( !$this->mOldContent ) {
                $this->addRevisionLoadError( 'old' );
            }
        } else {
            $this->mOldPage = null;
            $this->mOldRevisionRecord = $this->mOldid = false;
        }
        $this->mNewRevisionRecord = $newRevision;
        $this->mNewid = $newRevision->getId();
        $this->mNewPage = Title::newFromLinkTarget( $newRevision->getPageAsLinkTarget() );
        $this->mNewContent = $newRevision->getContent( SlotRecord::MAIN,
            RevisionRecord::FOR_THIS_USER, $this->getAuthority() );
        if ( !$this->mNewContent ) {
            $this->addRevisionLoadError( 'new' );
        }

        $this->mRevisionsIdsLoaded = $this->mRevisionsLoaded = true;
        $this->mTextLoaded = $oldRevision ? 2 : 1;
        $this->isContentOverridden = false;
        $this->slotDiffRenderers = null;
    }

    /**
     * Set the language in which the diff text is written
     *
     * @param Language $lang
     * @since 1.19
     */
    public function setTextLanguage( Language $lang ) {
        $this->mDiffLang = $lang;
    }

    /**
     * Maps a revision pair definition as accepted by DifferenceEngine constructor
     * to a pair of actual integers representing revision ids.
     *
     * @param int $old Revision id, e.g. from URL parameter 'oldid'
     * @param int|string $new Revision id or strings 'next' or 'prev', e.g. from URL parameter 'diff'
     *
     * @return array List of two revision ids, older first, later second.
     *     Zero signifies invalid argument passed.
     *     false signifies that there is no previous/next revision ($old is the oldest/newest one).
     * @phan-return (int|false)[]
     */
    public function mapDiffPrevNext( $old, $new ) {
        if ( $new === 'prev' ) {
            // Show diff between revision $old and the previous one. Get previous one from DB.
            $newid = intval( $old );
            $oldid = false;
            $newRev = $this->revisionStore->getRevisionById( $newid );
            if ( $newRev ) {
                $oldRev = $this->revisionStore->getPreviousRevision( $newRev );
                if ( $oldRev ) {
                    $oldid = $oldRev->getId();
                }
            }
        } elseif ( $new === 'next' ) {
            // Show diff between revision $old and the next one. Get next one from DB.
            $oldid = intval( $old );
            $newid = false;
            $oldRev = $this->revisionStore->getRevisionById( $oldid );
            if ( $oldRev ) {
                $newRev = $this->revisionStore->getNextRevision( $oldRev );
                if ( $newRev ) {
                    $newid = $newRev->getId();
                }
            }
        } else {
            $oldid = intval( $old );
            $newid = intval( $new );
        }

        // @phan-suppress-next-line PhanTypeMismatchReturn getId does not return null here
        return [ $oldid, $newid ];
    }

    private function loadRevisionIds() {
        if ( $this->mRevisionsIdsLoaded ) {
            return;
        }

        $this->mRevisionsIdsLoaded = true;

        $old = $this->mOldid;
        $new = $this->mNewid;

        [ $this->mOldid, $this->mNewid ] = self::mapDiffPrevNext( $old, $new );
        if ( $new === 'next' && $this->mNewid === false ) {
            # if no result, NewId points to the newest old revision. The only newer
            # revision is cur, which is "0".
            $this->mNewid = 0;
        }

        $this->hookRunner->onNewDifferenceEngine(
            // @phan-suppress-next-line PhanTypeMismatchArgumentNullable False positive
            $this->getTitle(), $this->mOldid, $this->mNewid, $old, $new );
    }

    /**
     * Load revision metadata for the specified revisions. If newid is 0, then compare
     * the old revision in oldid to the current revision of the current page (as defined
     * by the request context); if oldid is 0, then compare the revision in newid to the
     * immediately previous one.
     *
     * If oldid is false, leave the corresponding RevisionRecord object set to false. This can
     * happen with 'diff=prev' pointing to a non-existent revision, and is also used directly
     * by the API.
     *
     * @return bool Whether both revisions were loaded successfully. Setting mOldRevisionRecord
     *   to false counts as successful loading.
     */
    public function loadRevisionData() {
        if ( $this->mRevisionsLoaded ) {
            return $this->isContentOverridden ||
            ( $this->mOldRevisionRecord !== null && $this->mNewRevisionRecord !== null );
        }

        // Whether it succeeds or fails, we don't want to try again
        $this->mRevisionsLoaded = true;

        $this->loadRevisionIds();

        // Load the new RevisionRecord object
        if ( $this->mNewid ) {
            $this->mNewRevisionRecord = $this->revisionStore->getRevisionById( $this->mNewid );
        } else {
            $this->mNewRevisionRecord = $this->revisionStore->getRevisionByTitle( $this->getTitle() );
        }

        if ( !$this->mNewRevisionRecord instanceof RevisionRecord ) {
            return false;
        }

        // Update the new revision ID in case it was 0 (makes life easier doing UI stuff)
        $this->mNewid = $this->mNewRevisionRecord->getId();
        $this->mNewPage = $this->mNewid ?
            Title::newFromLinkTarget( $this->mNewRevisionRecord->getPageAsLinkTarget() ) :
            null;

        // Load the old RevisionRecord object
        $this->mOldRevisionRecord = false;
        if ( $this->mOldid ) {
            $this->mOldRevisionRecord = $this->revisionStore->getRevisionById( $this->mOldid );
        } elseif ( $this->mOldid === 0 ) {
            $revRecord = $this->revisionStore->getPreviousRevision( $this->mNewRevisionRecord );
            // No previous revision; mark to show as first-version only.
            $this->mOldid = $revRecord ? $revRecord->getId() : false;
            $this->mOldRevisionRecord = $revRecord ?? false;
        } /* elseif ( $this->mOldid === false ) leave mOldRevisionRecord false; */

        if ( $this->mOldRevisionRecord === null ) {
            return false;
        }

        if ( $this->mOldRevisionRecord && $this->mOldRevisionRecord->getId() ) {
            $this->mOldPage = Title::newFromLinkTarget(
                $this->mOldRevisionRecord->getPageAsLinkTarget()
            );
        } else {
            $this->mOldPage = null;
        }

        // Load tags information for both revisions
        $dbr = $this->dbProvider->getReplicaDatabase();
        $changeTagDefStore = MediaWikiServices::getInstance()->getChangeTagDefStore();
        if ( $this->mOldid !== false ) {
            $tagIds = $dbr->newSelectQueryBuilder()
                ->select( 'ct_tag_id' )
                ->from( 'change_tag' )
                ->where( [ 'ct_rev_id' => $this->mOldid ] )
                ->caller( __METHOD__ )->fetchFieldValues();
            $tags = [];
            foreach ( $tagIds as $tagId ) {
                try {
                    $tags[] = $changeTagDefStore->getName( (int)$tagId );
                } catch ( NameTableAccessException $exception ) {
                    continue;
                }
            }
            $this->mOldTags = implode( ',', $tags );
        } else {
            $this->mOldTags = false;
        }

        $tagIds = $dbr->newSelectQueryBuilder()
            ->select( 'ct_tag_id' )
            ->from( 'change_tag' )
            ->where( [ 'ct_rev_id' => $this->mNewid ] )
            ->caller( __METHOD__ )->fetchFieldValues();
        $tags = [];
        foreach ( $tagIds as $tagId ) {
            try {
                $tags[] = $changeTagDefStore->getName( (int)$tagId );
            } catch ( NameTableAccessException $exception ) {
                continue;
            }
        }
        $this->mNewTags = implode( ',', $tags );

        return true;
    }

    /**
     * Load the text of the revisions, as well as revision data.
     * When the old revision is missing (mOldRev is false), loading mOldContent is not attempted.
     *
     * @return bool Whether the content of both revisions could be loaded successfully.
     *   (When mOldRev is false, that still counts as a success.)
     *
     */
    public function loadText() {
        if ( $this->mTextLoaded == 2 ) {
            return $this->loadRevisionData() &&
                ( $this->mOldRevisionRecord === false || $this->mOldContent )
                && $this->mNewContent;
        }

        // Whether it succeeds or fails, we don't want to try again
        $this->mTextLoaded = 2;

        if ( !$this->loadRevisionData() ) {
            return false;
        }

        if ( $this->mOldRevisionRecord ) {
            $this->mOldContent = $this->mOldRevisionRecord->getContent(
                SlotRecord::MAIN,
                RevisionRecord::FOR_THIS_USER,
                $this->getAuthority()
            );
            if ( $this->mOldContent === null ) {
                return false;
            }
        }

        $this->mNewContent = $this->mNewRevisionRecord->getContent(
            SlotRecord::MAIN,
            RevisionRecord::FOR_THIS_USER,
            $this->getAuthority()
        );
        $this->hookRunner->onDifferenceEngineLoadTextAfterNewContentIsLoaded( $this );
        if ( $this->mNewContent === null ) {
            return false;
        }

        return true;
    }

    /**
     * Load the text of the new revision, not the old one
     *
     * @return bool Whether the content of the new revision could be loaded successfully.
     */
    public function loadNewText() {
        if ( $this->mTextLoaded >= 1 ) {
            return $this->loadRevisionData();
        }

        $this->mTextLoaded = 1;

        if ( !$this->loadRevisionData() ) {
            return false;
        }

        $this->mNewContent = $this->mNewRevisionRecord->getContent(
            SlotRecord::MAIN,
            RevisionRecord::FOR_THIS_USER,
            $this->getAuthority()
        );

        $this->hookRunner->onDifferenceEngineAfterLoadNewText( $this );

        return true;
    }

    /**
     * Get the TextDiffer which will be used for rendering text
     *
     * @return ManifoldTextDiffer
     */
    protected function getTextDiffer() {
        if ( $this->textDiffer === null ) {
            $this->textDiffer = new ManifoldTextDiffer(
                $this->getContext(),
                $this->getDiffLang(),
                $this->getConfig()->get( MainConfigNames::DiffEngine ),
                $this->getConfig()->get( MainConfigNames::ExternalDiffEngine ),
                $this->getConfig()->get( MainConfigNames::Wikidiff2Options )
            );
        }
        return $this->textDiffer;
    }

    /**
     * Get the list of supported text diff formats
     *
     * @since 1.41
     * @return array|string[]
     */
    public function getSupportedFormats() {
        return $this->getTextDiffer()->getFormats();
    }

    /**
     * Get the selected text diff format
     *
     * @since 1.41
     * @return string
     */
    public function getTextDiffFormat() {
        return $this->slotDiffOptions['diff-type'] ?? 'table';
    }

}