<?php
/**
 * @author Joas Schilling <coding@schilljs.com>
 * @author Morris Jobke <hey@morrisjobke.de>
 *
 * @copyright Copyright (c) 2018, ownCloud GmbH
 * @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;


use OCP\IConfig;
use OCP\IDateTimeZone;
use OCP\ISession;

class DateTimeZone implements IDateTimeZone {
	/** @var IConfig */
	protected $config;

	/** @var ISession */
	protected $session;

	/**
	 * Constructor
	 *
	 * @param IConfig $config
	 * @param ISession $session
	 */
	public function __construct(IConfig $config, ISession $session) {
		$this->config = $config;
		$this->session = $session;
	}

	/**
	 * Get the timezone of the current user, based on his session information and config data
	 *
	 * @param bool|int $timestamp
	 * @return \DateTimeZone
	 */
	public function getTimeZone($timestamp = false) {
		$timeZone = $this->config->getUserValue($this->session->get('user_id'), 'core', 'timezone', null);
		if ($timeZone === null) {
			if ($this->session->exists('timezone')) {
				return $this->guessTimeZoneFromOffset($this->session->get('timezone'), $timestamp);
			}
			$timeZone = $this->getDefaultTimeZone();
		}

		try {
			return new \DateTimeZone($timeZone);
		} catch (\Exception $e) {
			\OCP\Util::writeLog('datetimezone', 'Failed to created DateTimeZone "' . $timeZone . "'", \OCP\Util::DEBUG);
			return new \DateTimeZone($this->getDefaultTimeZone());
		}
	}

	/**
	 * Guess the DateTimeZone for a given offset
	 *
	 * We first try to find a Etc/GMT* timezone, if that does not exist,
	 * we try to find it manually, before falling back to UTC.
	 *
	 * @param mixed $offset
	 * @param bool|int $timestamp
	 * @return \DateTimeZone
	 */
	protected function guessTimeZoneFromOffset($offset, $timestamp) {
		try {
			// Note: the timeZone name is the inverse to the offset,
			// so a positive offset means negative timeZone
			// and the other way around.
			if ($offset > 0) {
				$timeZone = 'Etc/GMT-' . $offset;
			} else {
				$timeZone = 'Etc/GMT+' . abs($offset);
			}

			return new \DateTimeZone($timeZone);
		} catch (\Exception $e) {
			// If the offset has no Etc/GMT* timezone,
			// we try to guess one timezone that has the same offset
			foreach (\DateTimeZone::listIdentifiers() as $timeZone) {
				$dtz = new \DateTimeZone($timeZone);
				$dateTime = new \DateTime();

				if ($timestamp !== false) {
					$dateTime->setTimestamp($timestamp);
				}

				$dtOffset = $dtz->getOffset($dateTime);
				if ($dtOffset == 3600 * $offset) {
					return $dtz;
				}
			}

			// No timezone found, fallback to UTC
			\OCP\Util::writeLog('datetimezone', 'Failed to find DateTimeZone for offset "' . $offset . "'", \OCP\Util::DEBUG);
			return new \DateTimeZone($this->getDefaultTimeZone());
		}
	}

	/**
	 * Get the default timezone of the server
	 *
	 * Falls back to UTC if it is not yet set.
	 * 
	 * @return string
	 */
	protected function getDefaultTimeZone() {
		$serverTimeZone = date_default_timezone_get();
		return $serverTimeZone ?: 'UTC';
	}
}
