source: sourcecode/application/libraries/PHPExcel/Shared/TimeZone.php @ 1

<?php

/**
 * PHPExcel
 *
 * Copyright (c) 2006 - 2014 PHPExcel
 *
 * 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   PHPExcel
 * @package     PHPExcel_Shared
 * @copyright  Copyright (c) 2006 - 2014 PHPExcel (http://www.codeplex.com/PHPExcel)
 * @license     http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt   LGPL
 * @version     1.8.0, 2014-03-02
 */


/**
 * PHPExcel_Shared_TimeZone
 *
 * @category   PHPExcel
 * @package     PHPExcel_Shared
 * @copyright  Copyright (c) 2006 - 2014 PHPExcel (http://www.codeplex.com/PHPExcel)
 */
class PHPExcel_Shared_TimeZone
{
        /*
         * Default Timezone used for date/time conversions
         *
         * @private
         * @var string
         */
        protected static $_timezone     = 'UTC';

        /**
         * Validate a Timezone name
         *
         * @param        string         $timezone                       Time zone (e.g. 'Europe/London')
         * @return       boolean                                                Success or failure
         */
        public static function _validateTimeZone($timezone) {
                if (in_array($timezone, DateTimeZone::listIdentifiers())) {
                        return TRUE;
                }
                return FALSE;
        }

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


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


        /**
         *      Return the Timezone transition for the specified timezone and timestamp
         *
         *      @param          DateTimeZone            $objTimezone    The timezone for finding the transitions
         *      @param          integer                         $timestamp              PHP date/time value for finding the current transition
         *      @return         array                           The current transition details
         */
        private static function _getTimezoneTransitions($objTimezone, $timestamp) {
                $allTransitions = $objTimezone->getTransitions();
                $transitions = array();
                foreach($allTransitions as $key => $transition) {
                        if ($transition['ts'] > $timestamp) {
                                $transitions[] = ($key > 0) ? $allTransitions[$key - 1] : $transition;
                                break;
                        }
                        if (empty($transitions)) {
                                $transitions[] = end($allTransitions);
                        }
                }

                return $transitions;
        }

        /**
         *      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          integer                         $timestamp              PHP date/time value
         *      @return         integer                         Number of seconds for timezone adjustment
         *      @throws         PHPExcel_Exception
         */
        public static function getTimeZoneAdjustment($timezone, $timestamp) {
                if ($timezone !== NULL) {
                        if (!self::_validateTimezone($timezone)) {
                                throw new PHPExcel_Exception("Invalid timezone " . $timezone);
                        }
                } else {
                        $timezone = self::$_timezone;
                }

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

                $objTimezone = new DateTimeZone($timezone);
                if (version_compare(PHP_VERSION, '5.3.0') >= 0) {
                        $transitions = $objTimezone->getTransitions($timestamp,$timestamp);
                } else {
                        $transitions = self::_getTimezoneTransitions($objTimezone, $timestamp);
                }

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

}