SessionManager: Ignore Session object destruction during global shutdown

[mediawiki.git] / includes / WatchedItemStore.php

<?php

use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface;
use Wikimedia\Assert\Assert;

/**
 * Storage layer class for WatchedItems.
 * Database interaction.
 *
 * @author Addshore
 *
 * @since 1.27
 */
class WatchedItemStore implements StatsdAwareInterface {

        const SORT_DESC = 'DESC';
        const SORT_ASC = 'ASC';

        /**
         * @var LoadBalancer
         */
        private $loadBalancer;

        /**
         * @var HashBagOStuff
         */
        private $cache;

        /**
         * @var array[] Looks like $cacheIndex[Namespace ID][Target DB Key][User Id] => 'key'
         * The index is needed so that on mass changes all relevant items can be un-cached.
         * For example: Clearing a users watchlist of all items or updating notification timestamps
         *              for all users watching a single target.
         */
        private $cacheIndex = [];

        /**
         * @var callable|null
         */
        private $deferredUpdatesAddCallableUpdateCallback;

        /**
         * @var callable|null
         */
        private $revisionGetTimestampFromIdCallback;

        /**
         * @var StatsdDataFactoryInterface
         */
        private $stats;

        /**
         * @var self|null
         */
        private static $instance;

        /**
         * @param LoadBalancer $loadBalancer
         * @param HashBagOStuff $cache
         */
        public function __construct(
                LoadBalancer $loadBalancer,
                HashBagOStuff $cache
        ) {
                $this->loadBalancer = $loadBalancer;
                $this->cache = $cache;
                $this->stats = new NullStatsdDataFactory();
                $this->deferredUpdatesAddCallableUpdateCallback = [ 'DeferredUpdates', 'addCallableUpdate' ];
                $this->revisionGetTimestampFromIdCallback = [ 'Revision', 'getTimestampFromId' ];
        }

        public function setStatsdDataFactory( StatsdDataFactoryInterface $stats ) {
                $this->stats = $stats;
        }

        /**
         * Overrides the DeferredUpdates::addCallableUpdate callback
         * This is intended for use while testing and will fail if MW_PHPUNIT_TEST is not defined.
         *
         * @param callable $callback
         *
         * @see DeferredUpdates::addCallableUpdate for callback signiture
         *
         * @return ScopedCallback to reset the overridden value
         * @throws MWException
         */
        public function overrideDeferredUpdatesAddCallableUpdateCallback( $callback ) {
                if ( !defined( 'MW_PHPUNIT_TEST' ) ) {
                        throw new MWException(
                                'Cannot override DeferredUpdates::addCallableUpdate callback in operation.'
                        );
                }
                Assert::parameterType( 'callable', $callback, '$callback' );

                $previousValue = $this->deferredUpdatesAddCallableUpdateCallback;
                $this->deferredUpdatesAddCallableUpdateCallback = $callback;
                return new ScopedCallback( function() use ( $previousValue ) {
                        $this->deferredUpdatesAddCallableUpdateCallback = $previousValue;
                } );
        }

        /**
         * Overrides the Revision::getTimestampFromId callback
         * This is intended for use while testing and will fail if MW_PHPUNIT_TEST is not defined.
         *
         * @param callable $callback
         * @see Revision::getTimestampFromId for callback signiture
         *
         * @return ScopedCallback to reset the overridden value
         * @throws MWException
         */
        public function overrideRevisionGetTimestampFromIdCallback( $callback ) {
                if ( !defined( 'MW_PHPUNIT_TEST' ) ) {
                        throw new MWException(
                                'Cannot override Revision::getTimestampFromId callback in operation.'
                        );
                }
                Assert::parameterType( 'callable', $callback, '$callback' );

                $previousValue = $this->revisionGetTimestampFromIdCallback;
                $this->revisionGetTimestampFromIdCallback = $callback;
                return new ScopedCallback( function() use ( $previousValue ) {
                        $this->revisionGetTimestampFromIdCallback = $previousValue;
                } );
        }

        /**
         * Overrides the default instance of this class
         * This is intended for use while testing and will fail if MW_PHPUNIT_TEST is not defined.
         *
         * If this method is used it MUST also be called with null after a test to ensure a new
         * default instance is created next time getDefaultInstance is called.
         *
         * @param WatchedItemStore|null $store
         *
         * @return ScopedCallback to reset the overridden value
         * @throws MWException
         */
        public static function overrideDefaultInstance( WatchedItemStore $store = null ) {
                if ( !defined( 'MW_PHPUNIT_TEST' ) ) {
                        throw new MWException(
                                'Cannot override ' . __CLASS__ . 'default instance in operation.'
                        );
                }

                $previousValue = self::$instance;
                self::$instance = $store;
                return new ScopedCallback( function() use ( $previousValue ) {
                        self::$instance = $previousValue;
                } );
        }

        /**
         * @return self
         */
        public static function getDefaultInstance() {
                if ( !self::$instance ) {
                        self::$instance = new self(
                                wfGetLB(),
                                new HashBagOStuff( [ 'maxKeys' => 100 ] )
                        );
                        self::$instance->setStatsdDataFactory( RequestContext::getMain()->getStats() );
                }
                return self::$instance;
        }

        private function getCacheKey( User $user, LinkTarget $target ) {
                return $this->cache->makeKey(
                        (string)$target->getNamespace(),
                        $target->getDBkey(),
                        (string)$user->getId()
                );
        }

        private function cache( WatchedItem $item ) {
                $user = $item->getUser();
                $target = $item->getLinkTarget();
                $key = $this->getCacheKey( $user, $target );
                $this->cache->set( $key, $item );
                $this->cacheIndex[$target->getNamespace()][$target->getDBkey()][$user->getId()] = $key;
                $this->stats->increment( 'WatchedItemStore.cache' );
        }

        private function uncache( User $user, LinkTarget $target ) {
                $this->cache->delete( $this->getCacheKey( $user, $target ) );
                unset( $this->cacheIndex[$target->getNamespace()][$target->getDBkey()][$user->getId()] );
                $this->stats->increment( 'WatchedItemStore.uncache' );
        }

        private function uncacheLinkTarget( LinkTarget $target ) {
                if ( !isset( $this->cacheIndex[$target->getNamespace()][$target->getDBkey()] ) ) {
                        return;
                }
                $this->stats->increment( 'WatchedItemStore.uncacheLinkTarget' );
                foreach ( $this->cacheIndex[$target->getNamespace()][$target->getDBkey()] as $key ) {
                        $this->stats->increment( 'WatchedItemStore.uncacheLinkTarget.items' );
                        $this->cache->delete( $key );
                }
        }

        /**
         * @param User $user
         * @param LinkTarget $target
         *
         * @return WatchedItem|null
         */
        private function getCached( User $user, LinkTarget $target ) {
                return $this->cache->get( $this->getCacheKey( $user, $target ) );
        }

        /**
         * Return an array of conditions to select or update the appropriate database
         * row.
         *
         * @param User $user
         * @param LinkTarget $target
         *
         * @return array
         */
        private function dbCond( User $user, LinkTarget $target ) {
                return [
                        'wl_user' => $user->getId(),
                        'wl_namespace' => $target->getNamespace(),
                        'wl_title' => $target->getDBkey(),
                ];
        }

        /**
         * @param int $slaveOrMaster DB_MASTER or DB_SLAVE
         *
         * @return DatabaseBase
         * @throws MWException
         */
        private function getConnection( $slaveOrMaster ) {
                return $this->loadBalancer->getConnection( $slaveOrMaster, [ 'watchlist' ] );
        }

        /**
         * @param DatabaseBase $connection
         *
         * @throws MWException
         */
        private function reuseConnection( $connection ) {
                $this->loadBalancer->reuseConnection( $connection );
        }

        /**
         * Count the number of individual items that are watched by the user.
         * If a subject and corresponding talk page are watched this will return 2.
         *
         * @param User $user
         *
         * @return int
         */
        public function countWatchedItems( User $user ) {
                $dbr = $this->getConnection( DB_SLAVE );
                $return = (int)$dbr->selectField(
                        'watchlist',
                        'COUNT(*)',
                        [
                                'wl_user' => $user->getId()
                        ],
                        __METHOD__
                );
                $this->reuseConnection( $dbr );

                return $return;
        }

        /**
         * @param LinkTarget $target
         *
         * @return int
         */
        public function countWatchers( LinkTarget $target ) {
                $dbr = $this->getConnection( DB_SLAVE );
                $return = (int)$dbr->selectField(
                        'watchlist',
                        'COUNT(*)',
                        [
                                'wl_namespace' => $target->getNamespace(),
                                'wl_title' => $target->getDBkey(),
                        ],
                        __METHOD__
                );
                $this->reuseConnection( $dbr );

                return $return;
        }

        /**
         * Number of page watchers who also visited a "recent" edit
         *
         * @param LinkTarget $target
         * @param mixed $threshold timestamp accepted by wfTimestamp
         *
         * @return int
         * @throws DBUnexpectedError
         * @throws MWException
         */
        public function countVisitingWatchers( LinkTarget $target, $threshold ) {
                $dbr = $this->getConnection( DB_SLAVE );
                $visitingWatchers = (int)$dbr->selectField(
                        'watchlist',
                        'COUNT(*)',
                        [
                                'wl_namespace' => $target->getNamespace(),
                                'wl_title' => $target->getDBkey(),
                                'wl_notificationtimestamp >= ' .
                                $dbr->addQuotes( $dbr->timestamp( $threshold ) ) .
                                ' OR wl_notificationtimestamp IS NULL'
                        ],
                        __METHOD__
                );
                $this->reuseConnection( $dbr );

                return $visitingWatchers;
        }

        /**
         * @param LinkTarget[] $targets
         * @param array $options Allowed keys:
         *        'minimumWatchers' => int
         *
         * @return array multi dimensional like $return[$namespaceId][$titleString] = int $watchers
         *         All targets will be present in the result. 0 either means no watchers or the number
         *         of watchers was below the minimumWatchers option if passed.
         */
        public function countWatchersMultiple( array $targets, array $options = [] ) {
                $dbOptions = [ 'GROUP BY' => [ 'wl_namespace', 'wl_title' ] ];

                $dbr = $this->getConnection( DB_SLAVE );

                if ( array_key_exists( 'minimumWatchers', $options ) ) {
                        $dbOptions['HAVING'] = 'COUNT(*) >= ' . (int)$options['minimumWatchers'];
                }

                $lb = new LinkBatch( $targets );
                $res = $dbr->select(
                        'watchlist',
                        [ 'wl_title', 'wl_namespace', 'watchers' => 'COUNT(*)' ],
                        [ $lb->constructSet( 'wl', $dbr ) ],
                        __METHOD__,
                        $dbOptions
                );

                $this->reuseConnection( $dbr );

                $watchCounts = [];
                foreach ( $targets as $linkTarget ) {
                        $watchCounts[$linkTarget->getNamespace()][$linkTarget->getDBkey()] = 0;
                }

                foreach ( $res as $row ) {
                        $watchCounts[$row->wl_namespace][$row->wl_title] = (int)$row->watchers;
                }

                return $watchCounts;
        }

        /**
         * Number of watchers of each page who have visited recent edits to that page
         *
         * @param array $targetsWithVisitThresholds array of pairs (LinkTarget $target, mixed $threshold),
         *        $threshold is:
         *        - a timestamp of the recent edit if $target exists (format accepted by wfTimestamp)
         *        - null if $target doesn't exist
         * @param int|null $minimumWatchers
         * @return array multi-dimensional like $return[$namespaceId][$titleString] = $watchers,
         *         where $watchers is an int:
         *         - if the page exists, number of users watching who have visited the page recently
         *         - if the page doesn't exist, number of users that have the page on their watchlist
         *         - 0 means there are no visiting watchers or their number is below the minimumWatchers
         *         option (if passed).
         */
        public function countVisitingWatchersMultiple(
                array $targetsWithVisitThresholds,
                $minimumWatchers = null
        ) {
                $dbr = $this->getConnection( DB_SLAVE );

                $conds = $this->getVisitingWatchersCondition( $dbr, $targetsWithVisitThresholds );

                $dbOptions = [ 'GROUP BY' => [ 'wl_namespace', 'wl_title' ] ];
                if ( $minimumWatchers !== null ) {
                        $dbOptions['HAVING'] = 'COUNT(*) >= ' . (int)$minimumWatchers;
                }
                $res = $dbr->select(
                        'watchlist',
                        [ 'wl_namespace', 'wl_title', 'watchers' => 'COUNT(*)' ],
                        $conds,
                        __METHOD__,
                        $dbOptions
                );

                $this->reuseConnection( $dbr );

                $watcherCounts = [];
                foreach ( $targetsWithVisitThresholds as list( $target ) ) {
                        /* @var LinkTarget $target */
                        $watcherCounts[$target->getNamespace()][$target->getDBkey()] = 0;
                }

                foreach ( $res as $row ) {
                        $watcherCounts[$row->wl_namespace][$row->wl_title] = (int)$row->watchers;
                }

                return $watcherCounts;
        }

        /**
         * Generates condition for the query used in a batch count visiting watchers.
         *
         * @param IDatabase $db
         * @param array $targetsWithVisitThresholds array of pairs (LinkTarget, last visit threshold)
         * @return string
         */
        private function getVisitingWatchersCondition(
                IDatabase $db,
                array $targetsWithVisitThresholds
        ) {
                $missingTargets = [];
                $namespaceConds = [];
                foreach ( $targetsWithVisitThresholds as list( $target, $threshold ) ) {
                        if ( $threshold === null ) {
                                $missingTargets[] = $target;
                                continue;
                        }
                        /* @var LinkTarget $target */
                        $namespaceConds[$target->getNamespace()][] = $db->makeList( [
                                'wl_title = ' . $db->addQuotes( $target->getDBkey() ),
                                $db->makeList( [
                                        'wl_notificationtimestamp >= ' . $db->addQuotes( $db->timestamp( $threshold ) ),
                                        'wl_notificationtimestamp IS NULL'
                                ], LIST_OR )
                        ], LIST_AND );
                }

                $conds = [];
                foreach ( $namespaceConds as $namespace => $pageConds ) {
                        $conds[] = $db->makeList( [
                                'wl_namespace = ' . $namespace,
                                '(' . $db->makeList( $pageConds, LIST_OR ) . ')'
                        ], LIST_AND );
                }

                if ( $missingTargets ) {
                        $lb = new LinkBatch( $missingTargets );
                        $conds[] = $lb->constructSet( 'wl', $db );
                }

                return $db->makeList( $conds, LIST_OR );
        }

        /**
         * Get an item (may be cached)
         *
         * @param User $user
         * @param LinkTarget $target
         *
         * @return WatchedItem|false
         */
        public function getWatchedItem( User $user, LinkTarget $target ) {
                if ( $user->isAnon() ) {
                        return false;
                }

                $cached = $this->getCached( $user, $target );
                if ( $cached ) {
                        $this->stats->increment( 'WatchedItemStore.getWatchedItem.cached' );
                        return $cached;
                }
                $this->stats->increment( 'WatchedItemStore.getWatchedItem.load' );
                return $this->loadWatchedItem( $user, $target );
        }

        /**
         * Loads an item from the db
         *
         * @param User $user
         * @param LinkTarget $target
         *
         * @return WatchedItem|false
         */
        public function loadWatchedItem( User $user, LinkTarget $target ) {
                // Only loggedin user can have a watchlist
                if ( $user->isAnon() ) {
                        return false;
                }

                $dbr = $this->getConnection( DB_SLAVE );
                $row = $dbr->selectRow(
                        'watchlist',
                        'wl_notificationtimestamp',
                        $this->dbCond( $user, $target ),
                        __METHOD__
                );
                $this->reuseConnection( $dbr );

                if ( !$row ) {
                        return false;
                }

                $item = new WatchedItem(
                        $user,
                        $target,
                        $row->wl_notificationtimestamp
                );
                $this->cache( $item );

                return $item;
        }

        /**
         * @param User $user
         * @param array $options Allowed keys:
         *        'forWrite' => bool defaults to false
         *        'sort' => string optional sorting by namespace ID and title
         *                     one of the self::SORT_* constants
         *
         * @return WatchedItem[]
         */
        public function getWatchedItemsForUser( User $user, array $options = [] ) {
                $options += [ 'forWrite' => false ];

                $dbOptions = [];
                if ( array_key_exists( 'sort', $options ) ) {
                        Assert::parameter(
                                ( in_array( $options['sort'], [ self::SORT_ASC, self::SORT_DESC ] ) ),
                                '$options[\'sort\']',
                                'must be SORT_ASC or SORT_DESC'
                        );
                        $dbOptions['ORDER BY'] = [
                                "wl_namespace {$options['sort']}",
                                "wl_title {$options['sort']}"
                        ];
                }
                $db = $this->getConnection( $options['forWrite'] ? DB_MASTER : DB_SLAVE );

                $res = $db->select(
                        'watchlist',
                        [ 'wl_namespace', 'wl_title', 'wl_notificationtimestamp' ],
                        [ 'wl_user' => $user->getId() ],
                        __METHOD__,
                        $dbOptions
                );
                $this->reuseConnection( $db );

                $watchedItems = [];
                foreach ( $res as $row ) {
                        // todo these could all be cached at some point?
                        $watchedItems[] = new WatchedItem(
                                $user,
                                new TitleValue( (int)$row->wl_namespace, $row->wl_title ),
                                $row->wl_notificationtimestamp
                        );
                }

                return $watchedItems;
        }

        /**
         * Must be called separately for Subject & Talk namespaces
         *
         * @param User $user
         * @param LinkTarget $target
         *
         * @return bool
         */
        public function isWatched( User $user, LinkTarget $target ) {
                return (bool)$this->getWatchedItem( $user, $target );
        }

        /**
         * @param User $user
         * @param LinkTarget[] $targets
         *
         * @return array multi-dimensional like $return[$namespaceId][$titleString] = $timestamp,
         *         where $timestamp is:
         *         - string|null value of wl_notificationtimestamp,
         *         - false if $target is not watched by $user.
         */
        public function getNotificationTimestampsBatch( User $user, array $targets ) {
                $timestamps = [];
                foreach ( $targets as $target ) {
                        $timestamps[$target->getNamespace()][$target->getDBkey()] = false;
                }

                if ( $user->isAnon() ) {
                        return $timestamps;
                }

                $targetsToLoad = [];
                foreach ( $targets as $target ) {
                        $cachedItem = $this->getCached( $user, $target );
                        if ( $cachedItem ) {
                                $timestamps[$target->getNamespace()][$target->getDBkey()] =
                                        $cachedItem->getNotificationTimestamp();
                        } else {
                                $targetsToLoad[] = $target;
                        }
                }

                if ( !$targetsToLoad ) {
                        return $timestamps;
                }

                $dbr = $this->getConnection( DB_SLAVE );

                $lb = new LinkBatch( $targetsToLoad );
                $res = $dbr->select(
                        'watchlist',
                        [ 'wl_namespace', 'wl_title', 'wl_notificationtimestamp' ],
                        [
                                $lb->constructSet( 'wl', $dbr ),
                                'wl_user' => $user->getId(),
                        ],
                        __METHOD__
                );
                $this->reuseConnection( $dbr );

                foreach ( $res as $row ) {
                        $timestamps[(int)$row->wl_namespace][$row->wl_title] = $row->wl_notificationtimestamp;
                }

                return $timestamps;
        }

        /**
         * Must be called separately for Subject & Talk namespaces
         *
         * @param User $user
         * @param LinkTarget $target
         */
        public function addWatch( User $user, LinkTarget $target ) {
                $this->addWatchBatchForUser( $user, [ $target ] );
        }

        /**
         * @param User $user
         * @param LinkTarget[] $targets
         *
         * @return bool success
         */
        public function addWatchBatchForUser( User $user, array $targets ) {
                if ( $this->loadBalancer->getReadOnlyReason() !== false ) {
                        return false;
                }
                // Only loggedin user can have a watchlist
                if ( $user->isAnon() ) {
                        return false;
                }

                if ( !$targets ) {
                        return true;
                }

                $rows = [];
                foreach ( $targets as $target ) {
                        $rows[] = [
                                'wl_user' => $user->getId(),
                                'wl_namespace' => $target->getNamespace(),
                                'wl_title' => $target->getDBkey(),
                                'wl_notificationtimestamp' => null,
                        ];
                        $this->uncache( $user, $target );
                }

                $dbw = $this->getConnection( DB_MASTER );
                foreach ( array_chunk( $rows, 100 ) as $toInsert ) {
                        // Use INSERT IGNORE to avoid overwriting the notification timestamp
                        // if there's already an entry for this page
                        $dbw->insert( 'watchlist', $toInsert, __METHOD__, 'IGNORE' );
                }
                $this->reuseConnection( $dbw );

                return true;
        }

        /**
         * Removes the an entry for the User watching the LinkTarget
         * Must be called separately for Subject & Talk namespaces
         *
         * @param User $user
         * @param LinkTarget $target
         *
         * @return bool success
         * @throws DBUnexpectedError
         * @throws MWException
         */
        public function removeWatch( User $user, LinkTarget $target ) {
                // Only logged in user can have a watchlist
                if ( $this->loadBalancer->getReadOnlyReason() !== false || $user->isAnon() ) {
                        return false;
                }

                $this->uncache( $user, $target );

                $dbw = $this->getConnection( DB_MASTER );
                $dbw->delete( 'watchlist',
                        [
                                'wl_user' => $user->getId(),
                                'wl_namespace' => $target->getNamespace(),
                                'wl_title' => $target->getDBkey(),
                        ], __METHOD__
                );
                $success = (bool)$dbw->affectedRows();
                $this->reuseConnection( $dbw );

                return $success;
        }

        /**
         * @param User $editor The editor that triggered the update. Their notification
         *  timestamp will not be updated(they have already seen it)
         * @param LinkTarget $target The target to update timestamps for
         * @param string $timestamp Set the update timestamp to this value
         *
         * @return int[] Array of user IDs the timestamp has been updated for
         */
        public function updateNotificationTimestamp( User $editor, LinkTarget $target, $timestamp ) {
                $dbw = $this->getConnection( DB_MASTER );
                $res = $dbw->select( [ 'watchlist' ],
                        [ 'wl_user' ],
                        [
                                'wl_user != ' . intval( $editor->getId() ),
                                'wl_namespace' => $target->getNamespace(),
                                'wl_title' => $target->getDBkey(),
                                'wl_notificationtimestamp IS NULL',
                        ], __METHOD__
                );

                $watchers = [];
                foreach ( $res as $row ) {
                        $watchers[] = intval( $row->wl_user );
                }

                if ( $watchers ) {
                        // Update wl_notificationtimestamp for all watching users except the editor
                        $fname = __METHOD__;
                        $dbw->onTransactionIdle(
                                function () use ( $dbw, $timestamp, $watchers, $target, $fname ) {
                                        $dbw->update( 'watchlist',
                                                [ /* SET */
                                                        'wl_notificationtimestamp' => $dbw->timestamp( $timestamp )
                                                ], [ /* WHERE */
                                                        'wl_user' => $watchers,
                                                        'wl_namespace' => $target->getNamespace(),
                                                        'wl_title' => $target->getDBkey(),
                                                ], $fname
                                        );
                                        $this->uncacheLinkTarget( $target );
                                }
                        );
                }

                $this->reuseConnection( $dbw );

                return $watchers;
        }

        /**
         * Reset the notification timestamp of this entry
         *
         * @param User $user
         * @param Title $title
         * @param string $force Whether to force the write query to be executed even if the
         *    page is not watched or the notification timestamp is already NULL.
         *    'force' in order to force
         * @param int $oldid The revision id being viewed. If not given or 0, latest revision is assumed.
         *
         * @return bool success
         */
        public function resetNotificationTimestamp( User $user, Title $title, $force = '', $oldid = 0 ) {
                // Only loggedin user can have a watchlist
                if ( $this->loadBalancer->getReadOnlyReason() !== false || $user->isAnon() ) {
                        return false;
                }

                $item = null;
                if ( $force != 'force' ) {
                        $item = $this->loadWatchedItem( $user, $title );
                        if ( !$item || $item->getNotificationTimestamp() === null ) {
                                return false;
                        }
                }

                // If the page is watched by the user (or may be watched), update the timestamp
                $job = new ActivityUpdateJob(
                        $title,
                        [
                                'type'      => 'updateWatchlistNotification',
                                'userid'    => $user->getId(),
                                'notifTime' => $this->getNotificationTimestamp( $user, $title, $item, $force, $oldid ),
                                'curTime'   => time()
                        ]
                );

                // Try to run this post-send
                // Calls DeferredUpdates::addCallableUpdate in normal operation
                call_user_func(
                        $this->deferredUpdatesAddCallableUpdateCallback,
                        function() use ( $job ) {
                                $job->run();
                        }
                );

                $this->uncache( $user, $title );

                return true;
        }

        private function getNotificationTimestamp( User $user, Title $title, $item, $force, $oldid ) {
                if ( !$oldid ) {
                        // No oldid given, assuming latest revision; clear the timestamp.
                        return null;
                }

                if ( !$title->getNextRevisionID( $oldid ) ) {
                        // Oldid given and is the latest revision for this title; clear the timestamp.
                        return null;
                }

                if ( $item === null ) {
                        $item = $this->loadWatchedItem( $user, $title );
                }

                if ( !$item ) {
                        // This can only happen if $force is enabled.
                        return null;
                }

                // Oldid given and isn't the latest; update the timestamp.
                // This will result in no further notification emails being sent!
                // Calls Revision::getTimestampFromId in normal operation
                $notificationTimestamp = call_user_func(
                        $this->revisionGetTimestampFromIdCallback,
                        $title,
                        $oldid
                );

                // We need to go one second to the future because of various strict comparisons
                // throughout the codebase
                $ts = new MWTimestamp( $notificationTimestamp );
                $ts->timestamp->add( new DateInterval( 'PT1S' ) );
                $notificationTimestamp = $ts->getTimestamp( TS_MW );

                if ( $notificationTimestamp < $item->getNotificationTimestamp() ) {
                        if ( $force != 'force' ) {
                                return false;
                        } else {
                                // This is a little silly…
                                return $item->getNotificationTimestamp();
                        }
                }

                return $notificationTimestamp;
        }

        /**
         * @param User $user
         * @param int $unreadLimit
         *
         * @return int|bool The number of unread notifications
         *                  true if greater than or equal to $unreadLimit
         */
        public function countUnreadNotifications( User $user, $unreadLimit = null ) {
                $queryOptions = [];
                if ( $unreadLimit !== null ) {
                        $unreadLimit = (int)$unreadLimit;
                        $queryOptions['LIMIT'] = $unreadLimit;
                }

                $dbr = $this->getConnection( DB_SLAVE );
                $rowCount = $dbr->selectRowCount(
                        'watchlist',
                        '1',
                        [
                                'wl_user' => $user->getId(),
                                'wl_notificationtimestamp IS NOT NULL',
                        ],
                        __METHOD__,
                        $queryOptions
                );
                $this->reuseConnection( $dbr );

                if ( !isset( $unreadLimit ) ) {
                        return $rowCount;
                }

                if ( $rowCount >= $unreadLimit ) {
                        return true;
                }

                return $rowCount;
        }

        /**
         * Check if the given title already is watched by the user, and if so
         * add a watch for the new title.
         *
         * To be used for page renames and such.
         *
         * @param LinkTarget $oldTarget
         * @param LinkTarget $newTarget
         */
        public function duplicateAllAssociatedEntries( LinkTarget $oldTarget, LinkTarget $newTarget ) {
                $oldTarget = Title::newFromLinkTarget( $oldTarget );
                $newTarget = Title::newFromLinkTarget( $newTarget );

                $this->duplicateEntry( $oldTarget->getSubjectPage(), $newTarget->getSubjectPage() );
                $this->duplicateEntry( $oldTarget->getTalkPage(), $newTarget->getTalkPage() );
        }

        /**
         * Check if the given title already is watched by the user, and if so
         * add a watch for the new title.
         *
         * To be used for page renames and such.
         * This must be called separately for Subject and Talk pages
         *
         * @param LinkTarget $oldTarget
         * @param LinkTarget $newTarget
         */
        public function duplicateEntry( LinkTarget $oldTarget, LinkTarget $newTarget ) {
                $dbw = $this->getConnection( DB_MASTER );

                $result = $dbw->select(
                        'watchlist',
                        [ 'wl_user', 'wl_notificationtimestamp' ],
                        [
                                'wl_namespace' => $oldTarget->getNamespace(),
                                'wl_title' => $oldTarget->getDBkey(),
                        ],
                        __METHOD__,
                        [ 'FOR UPDATE' ]
                );

                $newNamespace = $newTarget->getNamespace();
                $newDBkey = $newTarget->getDBkey();

                # Construct array to replace into the watchlist
                $values = [];
                foreach ( $result as $row ) {
                        $values[] = [
                                'wl_user' => $row->wl_user,
                                'wl_namespace' => $newNamespace,
                                'wl_title' => $newDBkey,
                                'wl_notificationtimestamp' => $row->wl_notificationtimestamp,
                        ];
                }

                if ( !empty( $values ) ) {
                        # Perform replace
                        # Note that multi-row replace is very efficient for MySQL but may be inefficient for
                        # some other DBMSes, mostly due to poor simulation by us
                        $dbw->replace(
                                'watchlist',
                                [ [ 'wl_user', 'wl_namespace', 'wl_title' ] ],
                                $values,
                                __METHOD__
                        );
                }

                $this->reuseConnection( $dbw );
        }

}