Add backgroundcleanup job

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

lib/private/Preview/BackgroundCleanupJob.php

+<?php
+declare(strict_types=1);
+/**
+ * @copyright Copyright (c) 2018, Roeland Jago Douma <roeland@famdouma.nl>
+ *
+ * @author Roeland Jago Douma <roeland@famdouma.nl>
+ *
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OC\Preview;
+
+use OC\BackgroundJob\TimedJob;
+use OC\Files\AppData\Factory;
+use OCP\Files\NotFoundException;
+use OCP\Files\NotPermittedException;
+use OCP\IDBConnection;
+
+class BackgroundCleanupJob extends TimedJob {
+
+	/** @var IDBConnection */
+	private $connection;
+
+	/** @var Factory */
+	private $appDataFactory;
+
+	/** @var bool */
+	private $isCLI;
+
+	public function __construct(IDBConnection $connection,
+								Factory $appDataFactory,
+								bool $isCLI) {
+		// Run at most once an hour
+		$this->setInterval(3600);
+
+		$this->connection = $connection;
+		$this->appDataFactory = $appDataFactory;
+		$this->isCLI = $isCLI;
+	}
+
+	public function run($argument) {
+		$previews = $this->appDataFactory->get('preview');
+
+		$previewFodlerId = $previews->getId();
+
+		$qb2 = $this->connection->getQueryBuilder();
+		$qb2->select('fileid')
+			->from('filecache');
+
+		$qb = $this->connection->getQueryBuilder();
+		$qb->select('name')
+			->from('filecache')
+			->where(
+				$qb->expr()->eq('parent', $qb->createNamedParameter($previewFodlerId))
+			)->andWhere(
+				$qb->expr()->notIn('name', $qb->createFunction($qb2->getSQL()))
+			);
+
+		if (!$this->isCLI) {
+			$qb->setMaxResults(10);
+		}
+
+		$cursor = $qb->execute();
+
+		while ($row = $cursor->fetch()) {
+			try {
+				$preview = $previews->getFolder($row['name']);
+				$preview->delete();
+			} catch (NotFoundException $e) {
+				// continue
+			} catch (NotPermittedException $e) {
+				// continue
+			}
+		}
+
+		$cursor->closeCursor();
+	}
+}