<?php
/**
 * Pick a database that has pending jobs
 *
 * 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 Maintenance
 */

require_once( __DIR__ . '/Maintenance.php' );

/**
 * Maintenance script that picks a database that has pending jobs.
 *
 * @ingroup Maintenance
 */
class nextJobDB extends Maintenance {
	public function __construct() {
		parent::__construct();
		$this->mDescription = "Pick a database that has pending jobs";
		$this->addOption( 'type', "Search by job type", false, true );
		$this->addOption( 'types', "Space separated list of job types to search for", false, true );
	}

	public function execute() {
		global $wgMemc;

		$type = false; // job type required/picked
		if ( $this->hasOption( 'types' ) ) {
			$types = explode( ' ', $this->getOption( 'types' ) );
		} elseif ( $this->hasOption( 'type' ) ) {
			$types = array( $this->getOption( 'type' ) );
		} else {
			$types = JobQueueGroup::singleton()->getDefaultQueueTypes();
		}

		// Handle any required periodic queue maintenance
		$this->executeReadyPeriodicTasks();

		$memcKey = 'jobqueue:dbs:v3';
		$pendingDbInfo = $wgMemc->get( $memcKey );

		// If the cache entry wasn't present, is stale, or in .1% of cases otherwise,
		// regenerate the cache. Use any available stale cache if another process is
		// currently regenerating the pending DB information.
		if ( !is_array( $pendingDbInfo )
			|| ( time() - $pendingDbInfo['timestamp'] ) > 300 // 5 minutes
			|| mt_rand( 0, 999 ) == 0
		) {
			if ( $wgMemc->add( "$memcKey:rebuild", 1, 1800 ) ) { // lock
				$pendingDbInfo = array(
					'pendingDBs' => $this->getPendingDbs(),
					'timestamp'  => time()
				);
				for ( $attempts=1; $attempts <= 25; ++$attempts ) {
					if ( $wgMemc->add( "$memcKey:lock", 1, 60 ) ) { // lock
						$wgMemc->set( $memcKey, $pendingDbInfo );
						$wgMemc->delete( "$memcKey:lock" ); // unlock
						break;
					}
				}
				$wgMemc->delete( "$memcKey:rebuild" ); // unlock
			}
		}

		if ( !is_array( $pendingDbInfo ) || !$pendingDbInfo['pendingDBs'] ) {
			return; // no DBs with jobs or cache is both empty and locked
		}

		$pendingDBs = $pendingDbInfo['pendingDBs']; // convenience
		do {
			$again = false;

			$candidates = array(); // list of (type, db)
			// Flatten the tree of candidates into a flat list so that a random
			// item can be selected, weighing each queue (type/db tuple) equally.
			foreach ( $pendingDBs as $type => $dbs ) {
				if ( in_array( $type, $types ) ) {
					foreach ( $dbs as $db ) {
						$candidates[] = array( $type, $db );
					}
				}
			}
			if ( !count( $candidates ) ) {
				return; // no jobs for this type
			}

			list( $type, $db ) = $candidates[ mt_rand( 0, count( $candidates ) - 1 ) ];
			if ( !$this->checkJob( $type, $db ) ) { // queue is actually empty?
				$pendingDBs = $this->delistDB( $pendingDBs, $db, $type );
				// Update the cache to remove the outdated information.
				// Make sure that this does not race (especially with full rebuilds).
				if ( $wgMemc->add( "$memcKey:lock", 1, 60 ) ) { // lock
					$curInfo = $wgMemc->get( $memcKey );
					if ( is_array( $curInfo ) ) {
						$curInfo['pendingDBs'] =
							$this->delistDB( $curInfo['pendingDBs'], $db, $type );
						$wgMemc->set( $memcKey, $curInfo );
						// May as well make use of this newer information
						$pendingDBs = $curInfo['pendingDBs'];
					}
					$wgMemc->delete( "$memcKey:lock" ); // unlock
				}
				$again = true;
			}
		} while ( $again );

		if ( $this->hasOption( 'types' ) ) {
			$this->output( $db . " " . $type . "\n" );
		} else {
			$this->output( $db . "\n" );
		}
	}

	/**
	 * Remove a type/DB entry from the list of queues with jobs
	 *
	 * @param $pendingDBs array
	 * @param $db string
	 * @param $type string
	 * @return Array
	 */
	private function delistDB( array $pendingDBs, $db, $type ) {
		$pendingDBs[$type] = array_diff( $pendingDBs[$type], array( $db ) );
		return $pendingDBs;
	}

	/**
	 * Check if the specified database has a job of the specified type in it.
	 * The type may be false to indicate "all".
	 * @param $type string
	 * @param $dbName string
	 * @return bool
	 */
	private function checkJob( $type, $dbName ) {
		return !JobQueueGroup::singleton( $dbName )->get( $type )->isEmpty();
	}

	/**
	 * Get all databases that have a pending job
	 * @return array
	 */
	private function getPendingDbs() {
		global $wgLocalDatabases;

		$pendingDBs = array(); // (job type => (db list))
		foreach ( $wgLocalDatabases as $db ) {
			foreach ( JobQueueGroup::singleton( $db )->getQueuesWithJobs() as $type ) {
				$pendingDBs[$type][] = $db;
			}
		}

		return $pendingDBs;
	}

	/**
	 * Do all ready periodic jobs for all databases every 5 minutes (and .1% of the time)
	 * @return integer
	 */
	private function executeReadyPeriodicTasks() {
		global $wgLocalDatabases, $wgMemc;

		$count = 0;
		$memcKey = 'jobqueue:periodic:lasttime';
		$timestamp = (int)$wgMemc->get( $memcKey ); // UNIX timestamp or 0
		if ( ( time() - $timestamp ) > 300 || mt_rand( 0, 999 ) == 0 ) { // 5 minutes
			if ( $wgMemc->add( "$memcKey:rebuild", 1, 1800 ) ) { // lock
				foreach ( $wgLocalDatabases as $db ) {
					$count += JobQueueGroup::singleton( $db )->executeReadyPeriodicTasks();
				}
				$wgMemc->set( $memcKey, time() );
				$wgMemc->delete( "$memcKey:rebuild" ); // unlock
			}
		}

		return $count;
	}
}

$maintClass = "nextJobDb";
require_once( RUN_MAINTENANCE_IF_MAIN );