<?php

namespace PhpOffice\PhpSpreadsheet\Shared;

/**
 * Copyright (c) 2006 - 2016 PhpSpreadsheet.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * @category   PhpSpreadsheet
 *
 * @copyright  Copyright (c) 2006 - 2016 PhpSpreadsheet (https://github.com/PHPOffice/PhpSpreadsheet)
 * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt    LGPL
 */
class TimeZone
{
    /*
     * Default Timezone used for date/time conversions
     *
     * @private
     * @var string
     */
    protected static $timezone = 'UTC';

    /**
     * Validate a Timezone name.
     *
     * @param string $timezone Time zone (e.g. 'Europe/London')
     *
     * @return bool Success or failure
     */
    private static function validateTimeZone($timezone)
    {
        if (in_array($timezone, \DateTimeZone::listIdentifiers())) {
            return true;
        }

        return false;
    }

    /**
     * Set the Default Timezone used for date/time conversions.
     *
     * @param string $timezone Time zone (e.g. 'Europe/London')
     *
     * @return bool Success or failure
     */
    public static function setTimeZone($timezone)
    {
        if (self::validateTimezone($timezone)) {
            self::$timezone = $timezone;

            return true;
        }

        return false;
    }

    /**
     * Return the Default Timezone used for date/time conversions.
     *
     * @return string Timezone (e.g. 'Europe/London')
     */
    public static function getTimeZone()
    {
        return self::$timezone;
    }

    /**
     *    Return the Timezone offset used for date/time conversions to/from UST
     * This requires both the timezone and the calculated date/time to allow for local DST.
     *
     * @param string $timezone The timezone for finding the adjustment to UST
     * @param int $timestamp PHP date/time value
     *
     * @throws \PhpOffice\PhpSpreadsheet\Exception
     *
     * @return int Number of seconds for timezone adjustment
     */
    public static function getTimeZoneAdjustment($timezone, $timestamp)
    {
        if ($timezone !== null) {
            if (!self::validateTimezone($timezone)) {
                throw new \PhpOffice\PhpSpreadsheet\Exception('Invalid timezone ' . $timezone);
            }
        } else {
            $timezone = self::$timezone;
        }

        if ($timezone == 'UST') {
            return 0;
        }

        $objTimezone = new \DateTimeZone($timezone);
        $transitions = $objTimezone->getTransitions($timestamp, $timestamp);

        return (count($transitions) > 0) ? $transitions[0]['offset'] : 0;
    }
}
