<?php
/**
 * Delete links table entries which refer to a nonexisting page.
 *
 * 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
 * @author Rob Church <robchur@gmail.com>
 * @author Kunal Mehta <legoktm@debian.org>
 */

require_once __DIR__ . '/Maintenance.php';

use MediaWiki\MediaWikiServices;

/**
 * Maintenance script that deletes revisions which refer to a nonexisting page.
 *
 * @ingroup Maintenance
 */
class PurgeOrphanedLinks extends Maintenance {
	public function __construct() {
		parent::__construct();
		$this->addDescription(
			'Maintenance script to delete links entries which refer to a nonexisting page' );
		$this->addOption( 'dry-run', 'Dry-run' );
		$this->setBatchSize( 500 );
	}

	public function execute() {
		$dbw = $this->getDB( DB_PRIMARY );
		do {
			list( $page, $links ) = $dbw->tableNamesN( 'page', 'categorylinks' );
			$sql = "SELECT cl_from FROM {$links} LEFT JOIN {$page} ON cl_from = page_id "
			. "WHERE page_id IS NULL LIMIT {$this->mBatchSize}";
			# Find all the orphaned links
			$res = $dbw->query( $sql, 'purgeOrphanedLinks' );
			# Stash 'em all up for deletion (if needed)
			$toDelete = [];
			foreach ( $res as $row ) {
				$toDelete[] = $row->cl_from;
			}
			if ( !$toDelete ) {
				break;
			}
			$count = count( $toDelete );
			$this->output( "deleting {$count}..." );
			if ( !$this->hasOption('dry-run' ) ) {
				$dbw->delete( 'categorylinks', [ 'cl_from' => $toDelete ], __METHOD__ );
			}
			$this->output( "done. Sleeping\n" );
			MediaWikiServices::getInstance()->getDBLoadBalancerFactory()->waitForReplication()
		} while ( $dbw->affectedRows() );
		$this->output("Done done!\n" );
	}
}

$maintClass = PurgeOrphanedLinks::class;
require_once RUN_MAINTENANCE_IF_MAIN;