<?php

use Wikimedia\Rdbms\IDatabase;
use Liuggio\StatsdClient\Factory\StatsdDataFactoryInterface;
use MediaWiki\Linker\LinkTarget;
use Wikimedia\Assert\Assert;
use Wikimedia\ScopedCallback;
use Wikimedia\Rdbms\ILBFactory;
use Wikimedia\Rdbms\LoadBalancer;

/**
 * Storage layer class for WatchedItems.
 * Database interaction & caching
 * TODO caching should be factored out into a CachingWatchedItemStore class
 *
 * @author Addshore
 * @since 1.27
 */
class WatchedItemStore implements WatchedItemStoreInterface, StatsdAwareInterface {

	/**
	 * @var ILBFactory
	 */
	private $lbFactory;

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

	/**
	 * @var JobQueueGroup
	 */
	private $queueGroup;

	/**
	 * @var BagOStuff
	 */
	private $stash;

	/**
	 * @var ReadOnlyMode
	 */
	private $readOnlyMode;

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

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

	/**
	 * @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 int
	 */
	private $updateRowsPerQuery;

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

	/**
	 * @param ILBFactory $lbFactory
	 * @param JobQueueGroup $queueGroup
	 * @param BagOStuff $stash
	 * @param HashBagOStuff $cache
	 * @param ReadOnlyMode $readOnlyMode
	 * @param int $updateRowsPerQuery
	 */
	public function __construct(
		ILBFactory $lbFactory,
		JobQueueGroup $queueGroup,
		BagOStuff $stash,
		HashBagOStuff $cache,
		ReadOnlyMode $readOnlyMode,
		$updateRowsPerQuery
	) {
		$this->lbFactory = $lbFactory;
		$this->loadBalancer = $lbFactory->getMainLB();
		$this->queueGroup = $queueGroup;
		$this->stash = $stash;
		$this->cache = $cache;
		$this->readOnlyMode = $readOnlyMode;
		$this->stats = new NullStatsdDataFactory();
		$this->deferredUpdatesAddCallableUpdateCallback =
			[ DeferredUpdates::class, 'addCallableUpdate' ];
		$this->revisionGetTimestampFromIdCallback =
			[ Revision::class, 'getTimestampFromId' ];
		$this->updateRowsPerQuery = $updateRowsPerQuery;

		$this->latestUpdateCache = new HashBagOStuff( [ 'maxKeys' => 3 ] );
	}

	/**
	 * @param StatsdDataFactoryInterface $stats
	 */
	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( callable $callback ) {
		if ( !defined( 'MW_PHPUNIT_TEST' ) ) {
			throw new MWException(
				'Cannot override DeferredUpdates::addCallableUpdate callback in operation.'
			);
		}
		$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( callable $callback ) {
		if ( !defined( 'MW_PHPUNIT_TEST' ) ) {
			throw new MWException(
				'Cannot override Revision::getTimestampFromId callback in operation.'
			);
		}
		$previousValue = $this->revisionGetTimestampFromIdCallback;
		$this->revisionGetTimestampFromIdCallback = $callback;
		return new ScopedCallback( function () use ( $previousValue ) {
			$this->revisionGetTimestampFromIdCallback = $previousValue;
		} );
	}

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

	private function uncacheUser( User $user ) {
		$this->stats->increment( 'WatchedItemStore.uncacheUser' );
		foreach ( $this->cacheIndex as $ns => $dbKeyArray ) {
			foreach ( $dbKeyArray as $dbKey => $userArray ) {
				if ( isset( $userArray[$user->getId()] ) ) {
					$this->stats->increment( 'WatchedItemStore.uncacheUser.items' );
					$this->cache->delete( $userArray[$user->getId()] );
				}
			}
		}

		$pageSeenKey = $this->getPageSeenTimestampsKey( $user );
		$this->latestUpdateCache->delete( $pageSeenKey );
		$this->stash->delete( $pageSeenKey );
	}

	/**
	 * @param User $user
	 * @param LinkTarget $target
	 *
	 * @return WatchedItem|false
	 */
	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 $dbIndex DB_MASTER or DB_REPLICA
	 *
	 * @return IDatabase
	 * @throws MWException
	 */
	private function getConnectionRef( $dbIndex ) {
		return $this->loadBalancer->getConnectionRef( $dbIndex, [ 'watchlist' ] );
	}

	/**
	 * Deletes ALL watched items for the given user when under
	 * $updateRowsPerQuery entries exist.
	 *
	 * @since 1.30
	 *
	 * @param User $user
	 *
	 * @return bool true on success, false when too many items are watched
	 */
	public function clearUserWatchedItems( User $user ) {
		if ( $this->countWatchedItems( $user ) > $this->updateRowsPerQuery ) {
			return false;
		}

		$dbw = $this->loadBalancer->getConnectionRef( DB_MASTER );
		$dbw->delete(
			'watchlist',
			[ 'wl_user' => $user->getId() ],
			__METHOD__
		);
		$this->uncacheAllItemsForUser( $user );

		return true;
	}

	private function uncacheAllItemsForUser( User $user ) {
		$userId = $user->getId();
		foreach ( $this->cacheIndex as $ns => $dbKeyIndex ) {
			foreach ( $dbKeyIndex as $dbKey => $userIndex ) {
				if ( array_key_exists( $userId, $userIndex ) ) {
					$this->cache->delete( $userIndex[$userId] );
					unset( $this->cacheIndex[$ns][$dbKey][$userId] );
				}
			}
		}

		// Cleanup empty cache keys
		foreach ( $this->cacheIndex as $ns => $dbKeyIndex ) {
			foreach ( $dbKeyIndex as $dbKey => $userIndex ) {
				if ( empty( $this->cacheIndex[$ns][$dbKey] ) ) {
					unset( $this->cacheIndex[$ns][$dbKey] );
				}
			}
			if ( empty( $this->cacheIndex[$ns] ) ) {
				unset( $this->cacheIndex[$ns] );
			}
		}
	}

	/**
	 * Queues a job that will clear the users watchlist using the Job Queue.
	 *
	 * @since 1.31
	 *
	 * @param User $user
	 */
	public function clearUserWatchedItemsUsingJobQueue( User $user ) {
		$job = ClearUserWatchlistJob::newForUser( $user, $this->getMaxId() );
		$this->queueGroup->push( $job );
	}

	/**
	 * @since 1.31
	 * @return int The maximum current wl_id
	 */
	public function getMaxId() {
		$dbr = $this->getConnectionRef( DB_REPLICA );
		return (int)$dbr->selectField(
			'watchlist',
			'MAX(wl_id)',
			'',
			__METHOD__
		);
	}

	/**
	 * @since 1.31
	 * @param User $user
	 * @return int
	 */
	public function countWatchedItems( User $user ) {
		$dbr = $this->getConnectionRef( DB_REPLICA );
		$return = (int)$dbr->selectField(
			'watchlist',
			'COUNT(*)',
			[
				'wl_user' => $user->getId()
			],
			__METHOD__
		);

		return $return;
	}

	/**
	 * @since 1.27
	 * @param LinkTarget $target
	 * @return int
	 */
	public function countWatchers( LinkTarget $target ) {
		$dbr = $this->getConnectionRef( DB_REPLICA );
		$return = (int)$dbr->selectField(
			'watchlist',
			'COUNT(*)',
			[
				'wl_namespace' => $target->getNamespace(),
				'wl_title' => $target->getDBkey(),
			],
			__METHOD__
		);

		return $return;
	}

	/**
	 * @since 1.27
	 * @param LinkTarget $target
	 * @param string|int $threshold
	 * @return int
	 */
	public function countVisitingWatchers( LinkTarget $target, $threshold ) {
		$dbr = $this->getConnectionRef( DB_REPLICA );
		$visitingWatchers = (int)$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__
		);

		return $visitingWatchers;
	}

	/**
	 * @param User $user
	 * @param TitleValue[] $titles
	 * @return bool
	 * @throws MWException
	 */
	public function removeWatchBatchForUser( User $user, array $titles ) {
		if ( $this->readOnlyMode->isReadOnly() ) {
			return false;
		}
		if ( $user->isAnon() ) {
			return false;
		}
		if ( !$titles ) {
			return true;
		}

		$rows = $this->getTitleDbKeysGroupedByNamespace( $titles );
		$this->uncacheTitlesForUser( $user, $titles );

		$dbw = $this->getConnectionRef( DB_MASTER );
		$ticket = count( $titles ) > $this->updateRowsPerQuery ?
			$this->lbFactory->getEmptyTransactionTicket( __METHOD__ ) : null;
		$affectedRows = 0;

		// Batch delete items per namespace.
		foreach ( $rows as $namespace => $namespaceTitles ) {
			$rowBatches = array_chunk( $namespaceTitles, $this->updateRowsPerQuery );
			foreach ( $rowBatches as $toDelete ) {
				$dbw->delete( 'watchlist', [
					'wl_user' => $user->getId(),
					'wl_namespace' => $namespace,
					'wl_title' => $toDelete
				], __METHOD__ );
				$affectedRows += $dbw->affectedRows();
				if ( $ticket ) {
					$this->lbFactory->commitAndWaitForReplication( __METHOD__, $ticket );
				}
			}
		}

		return (bool)$affectedRows;
	}

	/**
	 * @since 1.27
	 * @param LinkTarget[] $targets
	 * @param array $options
	 * @return array
	 */
	public function countWatchersMultiple( array $targets, array $options = [] ) {
		$dbOptions = [ 'GROUP BY' => [ 'wl_namespace', 'wl_title' ] ];

		$dbr = $this->getConnectionRef( DB_REPLICA );

		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
		);

		$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;
	}

	/**
	 * @since 1.27
	 * @param array $targetsWithVisitThresholds
	 * @param int|null $minimumWatchers
	 * @return array
	 */
	public function countVisitingWatchersMultiple(
		array $targetsWithVisitThresholds,
		$minimumWatchers = null
	) {
		if ( $targetsWithVisitThresholds === [] ) {
			// No titles requested => no results returned
			return [];
		}

		$dbr = $this->getConnectionRef( DB_REPLICA );

		$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
		);

		$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 );
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param LinkTarget $target
	 * @return bool
	 */
	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 );
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param LinkTarget $target
	 * @return WatchedItem|bool
	 */
	public function loadWatchedItem( User $user, LinkTarget $target ) {
		// Only loggedin user can have a watchlist
		if ( $user->isAnon() ) {
			return false;
		}

		$dbr = $this->getConnectionRef( DB_REPLICA );

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

		if ( !$row ) {
			return false;
		}

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

		return $item;
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param array $options
	 * @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->getConnectionRef( $options['forWrite'] ? DB_MASTER : DB_REPLICA );

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

		$watchedItems = [];
		foreach ( $res as $row ) {
			$target = new TitleValue( (int)$row->wl_namespace, $row->wl_title );
			// @todo: Should we add these to the process cache?
			$watchedItems[] = new WatchedItem(
				$user,
				new TitleValue( (int)$row->wl_namespace, $row->wl_title ),
				$this->getLatestNotificationTimestamp(
					$row->wl_notificationtimestamp, $user, $target )
			);
		}

		return $watchedItems;
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param LinkTarget $target
	 * @return bool
	 */
	public function isWatched( User $user, LinkTarget $target ) {
		return (bool)$this->getWatchedItem( $user, $target );
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param LinkTarget[] $targets
	 * @return array
	 */
	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->getConnectionRef( DB_REPLICA );

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

		foreach ( $res as $row ) {
			$target = new TitleValue( (int)$row->wl_namespace, $row->wl_title );
			$timestamps[$row->wl_namespace][$row->wl_title] =
				$this->getLatestNotificationTimestamp(
					$row->wl_notificationtimestamp, $user, $target );
		}

		return $timestamps;
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param LinkTarget $target
	 * @throws MWException
	 */
	public function addWatch( User $user, LinkTarget $target ) {
		$this->addWatchBatchForUser( $user, [ $target ] );
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param LinkTarget[] $targets
	 * @return bool
	 * @throws MWException
	 */
	public function addWatchBatchForUser( User $user, array $targets ) {
		if ( $this->readOnlyMode->isReadOnly() ) {
			return false;
		}
		// Only logged-in user can have a watchlist
		if ( $user->isAnon() ) {
			return false;
		}

		if ( !$targets ) {
			return true;
		}

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

		$dbw = $this->getConnectionRef( DB_MASTER );
		$ticket = count( $targets ) > $this->updateRowsPerQuery ?
			$this->lbFactory->getEmptyTransactionTicket( __METHOD__ ) : null;
		$affectedRows = 0;
		$rowBatches = array_chunk( $rows, $this->updateRowsPerQuery );
		foreach ( $rowBatches 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' );
			$affectedRows += $dbw->affectedRows();
			if ( $ticket ) {
				$this->lbFactory->commitAndWaitForReplication( __METHOD__, $ticket );
			}
		}
		// Update process cache to ensure skin doesn't claim that the current
		// page is unwatched in the response of action=watch itself (T28292).
		// This would otherwise be re-queried from a replica by isWatched().
		foreach ( $items as $item ) {
			$this->cache( $item );
		}

		return (bool)$affectedRows;
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param LinkTarget $target
	 * @return bool
	 * @throws MWException
	 */
	public function removeWatch( User $user, LinkTarget $target ) {
		return $this->removeWatchBatchForUser( $user, [ $target ] );
	}

	/**
	 * Set the "last viewed" timestamps for certain titles on a user's watchlist.
	 *
	 * If the $targets parameter is omitted or set to [], this method simply wraps
	 * resetAllNotificationTimestampsForUser(), and in that case you should instead call that method
	 * directly; support for omitting $targets is for backwards compatibility.
	 *
	 * If $targets is omitted or set to [], timestamps will be updated for every title on the user's
	 * watchlist, and this will be done through a DeferredUpdate. If $targets is a non-empty array,
	 * only the specified titles will be updated, and this will be done immediately (not deferred).
	 *
	 * @since 1.27
	 * @param User $user
	 * @param string|int $timestamp Value to set the "last viewed" timestamp to (null to clear)
	 * @param LinkTarget[] $targets Titles to set the timestamp for; [] means the entire watchlist
	 * @return bool
	 */
	public function setNotificationTimestampsForUser( User $user, $timestamp, array $targets = [] ) {
		// Only loggedin user can have a watchlist
		if ( $user->isAnon() || $this->readOnlyMode->isReadOnly() ) {
			return false;
		}

		if ( !$targets ) {
			// Backwards compatibility
			$this->resetAllNotificationTimestampsForUser( $user, $timestamp );
			return true;
		}

		$rows = $this->getTitleDbKeysGroupedByNamespace( $targets );

		$dbw = $this->getConnectionRef( DB_MASTER );
		if ( $timestamp !== null ) {
			$timestamp = $dbw->timestamp( $timestamp );
		}
		$ticket = $this->lbFactory->getEmptyTransactionTicket( __METHOD__ );
		$affectedSinceWait = 0;

		// Batch update items per namespace
		foreach ( $rows as $namespace => $namespaceTitles ) {
			$rowBatches = array_chunk( $namespaceTitles, $this->updateRowsPerQuery );
			foreach ( $rowBatches as $toUpdate ) {
				$dbw->update(
					'watchlist',
					[ 'wl_notificationtimestamp' => $timestamp ],
					[
						'wl_user' => $user->getId(),
						'wl_namespace' => $namespace,
						'wl_title' => $toUpdate
					]
				);
				$affectedSinceWait += $dbw->affectedRows();
				// Wait for replication every time we've touched updateRowsPerQuery rows
				if ( $affectedSinceWait >= $this->updateRowsPerQuery ) {
					$this->lbFactory->commitAndWaitForReplication( __METHOD__, $ticket );
					$affectedSinceWait = 0;
				}
			}
		}

		$this->uncacheUser( $user );

		return true;
	}

	public function getLatestNotificationTimestamp( $timestamp, User $user, LinkTarget $target ) {
		$timestamp = wfTimestampOrNull( TS_MW, $timestamp );
		if ( $timestamp === null ) {
			return null; // no notification
		}

		$seenTimestamps = $this->getPageSeenTimestamps( $user );
		if (
			$seenTimestamps &&
			$seenTimestamps->get( $this->getPageSeenKey( $target ) ) >= $timestamp
		) {
			// If a reset job did not yet run, then the "seen" timestamp will be higher
			return null;
		}

		return $timestamp;
	}

	/**
	 * Schedule a DeferredUpdate that sets all of the "last viewed" timestamps for a given user
	 * to the same value.
	 * @param User $user
	 * @param string|int|null $timestamp Value to set all timestamps to, null to clear them
	 */
	public function resetAllNotificationTimestampsForUser( User $user, $timestamp = null ) {
		// Only loggedin user can have a watchlist
		if ( $user->isAnon() ) {
			return;
		}

		// If the page is watched by the user (or may be watched), update the timestamp
		$job = new ClearWatchlistNotificationsJob( [
			'userId'  => $user->getId(), 'timestamp' => $timestamp, 'casTime' => time()
		] );

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

	/**
	 * @since 1.27
	 * @param User $editor
	 * @param LinkTarget $target
	 * @param string|int $timestamp
	 * @return int[]
	 */
	public function updateNotificationTimestamp( User $editor, LinkTarget $target, $timestamp ) {
		$dbw = $this->getConnectionRef( DB_MASTER );
		$uids = $dbw->selectFieldValues(
			'watchlist',
			'wl_user',
			[
				'wl_user != ' . intval( $editor->getId() ),
				'wl_namespace' => $target->getNamespace(),
				'wl_title' => $target->getDBkey(),
				'wl_notificationtimestamp IS NULL',
			],
			__METHOD__
		);

		$watchers = array_map( 'intval', $uids );
		if ( $watchers ) {
			// Update wl_notificationtimestamp for all watching users except the editor
			$fname = __METHOD__;
			DeferredUpdates::addCallableUpdate(
				function () use ( $timestamp, $watchers, $target, $fname ) {
					$dbw = $this->getConnectionRef( DB_MASTER );
					$ticket = $this->lbFactory->getEmptyTransactionTicket( $fname );

					$watchersChunks = array_chunk( $watchers, $this->updateRowsPerQuery );
					foreach ( $watchersChunks as $watchersChunk ) {
						$dbw->update( 'watchlist',
							[ /* SET */
								'wl_notificationtimestamp' => $dbw->timestamp( $timestamp )
							], [ /* WHERE - TODO Use wl_id T130067 */
								'wl_user' => $watchersChunk,
								'wl_namespace' => $target->getNamespace(),
								'wl_title' => $target->getDBkey(),
							], $fname
						);
						if ( count( $watchersChunks ) > 1 ) {
							$this->lbFactory->commitAndWaitForReplication(
								$fname, $ticket, [ 'domain' => $dbw->getDomainID() ]
							);
						}
					}
					$this->uncacheLinkTarget( $target );
				},
				DeferredUpdates::POSTSEND,
				$dbw
			);
		}

		return $watchers;
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param Title $title
	 * @param string $force
	 * @param int $oldid
	 * @return bool
	 */
	public function resetNotificationTimestamp( User $user, Title $title, $force = '', $oldid = 0 ) {
		$time = time();

		// Only loggedin user can have a watchlist
		if ( $this->readOnlyMode->isReadOnly() || $user->isAnon() ) {
			return false;
		}

		if ( !Hooks::run( 'BeforeResetNotificationTimestamp', [ &$user, &$title, $force, &$oldid ] ) ) {
			return false;
		}

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

		// Get the timestamp (TS_MW) of this revision to track the latest one seen
		$seenTime = call_user_func(
			$this->revisionGetTimestampFromIdCallback,
			$title,
			$oldid ?: $title->getLatestRevID()
		);

		// Mark the item as read immediately in lightweight storage
		$this->stash->merge(
			$this->getPageSeenTimestampsKey( $user ),
			function ( $cache, $key, $current ) use ( $title, $seenTime ) {
				$value = $current ?: new MapCacheLRU( 300 );
				$subKey = $this->getPageSeenKey( $title );

				if ( $seenTime > $value->get( $subKey ) ) {
					// Revision is newer than the last one seen
					$value->set( $subKey, $seenTime );
					$this->latestUpdateCache->set( $key, $value, IExpiringStore::TTL_PROC_LONG );
				} elseif ( $seenTime === false ) {
					// Revision does not exist
					$value->set( $subKey, wfTimestamp( TS_MW ) );
					$this->latestUpdateCache->set( $key, $value, IExpiringStore::TTL_PROC_LONG );
				} else {
					return false; // nothing to update
				}

				return $value;
			},
			IExpiringStore::TTL_HOUR
		);

		// 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 enqueue this post-send
		$this->queueGroup->lazyPush( $job );

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

		return true;
	}

	/**
	 * @param User $user
	 * @return MapCacheLRU|null The map contains prefixed title keys and TS_MW values
	 */
	private function getPageSeenTimestamps( User $user ) {
		$key = $this->getPageSeenTimestampsKey( $user );

		return $this->latestUpdateCache->getWithSetCallback(
			$key,
			IExpiringStore::TTL_PROC_LONG,
			function () use ( $key ) {
				return $this->stash->get( $key ) ?: null;
			}
		);
	}

	/**
	 * @param User $user
	 * @return string
	 */
	private function getPageSeenTimestampsKey( User $user ) {
		return $this->stash->makeGlobalKey(
			'watchlist-recent-updates',
			$this->lbFactory->getLocalDomainID(),
			$user->getId()
		);
	}

	/**
	 * @param LinkTarget $target
	 * @return string
	 */
	private function getPageSeenKey( LinkTarget $target ) {
		return "{$target->getNamespace()}:{$target->getDBkey()}";
	}

	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;
	}

	/**
	 * @since 1.27
	 * @param User $user
	 * @param int|null $unreadLimit
	 * @return int|bool
	 */
	public function countUnreadNotifications( User $user, $unreadLimit = null ) {
		$dbr = $this->getConnectionRef( DB_REPLICA );

		$queryOptions = [];
		if ( $unreadLimit !== null ) {
			$unreadLimit = (int)$unreadLimit;
			$queryOptions['LIMIT'] = $unreadLimit;
		}

		$conds = [
			'wl_user' => $user->getId(),
			'wl_notificationtimestamp IS NOT NULL'
		];

		$rowCount = $dbr->selectRowCount( 'watchlist', '1', $conds, __METHOD__, $queryOptions );

		if ( $unreadLimit === null ) {
			return $rowCount;
		}

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

		return $rowCount;
	}

	/**
	 * @since 1.27
	 * @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() );
	}

	/**
	 * @since 1.27
	 * @param LinkTarget $oldTarget
	 * @param LinkTarget $newTarget
	 */
	public function duplicateEntry( LinkTarget $oldTarget, LinkTarget $newTarget ) {
		$dbw = $this->getConnectionRef( 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__
			);
		}
	}

	/**
	 * @param LinkTarget[] $titles
	 * @return array
	 */
	private function getTitleDbKeysGroupedByNamespace( array $titles ) {
		$rows = [];
		foreach ( $titles as $title ) {
			// Group titles by namespace.
			$rows[ $title->getNamespace() ][] = $title->getDBkey();
		}
		return $rows;
	}

	/**
	 * @param User $user
	 * @param Title[] $titles
	 */
	private function uncacheTitlesForUser( User $user, array $titles ) {
		foreach ( $titles as $title ) {
			$this->uncache( $user, $title );
		}
	}

}