path: root/core/js/jstz.js

/**
 * This script gives you the zone info key representing your device's time zone setting.
 *
 * @name jsTimezoneDetect
 * @version 1.0.5
 * @author Jon Nylander
 * @license MIT License - http://www.opensource.org/licenses/mit-license.php
 *
 * For usage and examples, visit:
 * http://pellepim.bitbucket.org/jstz/
 *
 * Copyright (c) Jon Nylander
 */

/*jslint undef: true */
/*global console, exports*/

(function(root) {
	/**
	 * Namespace to hold all the code for timezone detection.
	 */
	var jstz = (function () {
		'use strict';
		var HEMISPHERE_SOUTH = 's',

			/**
			 * Gets the offset in minutes from UTC for a certain date.
			 * @param {Date} date
			 * @returns {Number}
			 */
			get_date_offset = function (date) {
				var offset = -date.getTimezoneOffset();
				return (offset !== null ? offset : 0);
			},

			get_date = function (year, month, date) {
				var d = new Date();
				if (year !== undefined) {
					d.setFullYear(year);
				}
				d.setMonth(month);
				d.setDate(date);
				return d;
			},

			get_january_offset = function (year) {
				return get_date_offset(get_date(year, 0 ,2));
			},

			get_june_offset = function (year) {
				return get_date_offset(get_date(year, 5, 2));
			},

			/**
			 * Private method.
			 * Checks whether a given date is in daylight saving time.
			 * If the date supplied is after august, we assume that we're checking
			 * for southern hemisphere DST.
			 * @param {Date} date
			 * @returns {Boolean}
			 */
			date_is_dst = function (date) {
				var is_southern = date.getMonth() > 7,
					base_offset = is_southern ? get_june_offset(date.getFullYear()) :
						get_january_offset(date.getFullYear()),
					date_offset = get_date_offset(date),
					is_west = base_offset < 0,
					dst_offset = base_offset - date_offset;

				if (!is_west && !is_southern) {
					return dst_offset < 0;
				}

				return dst_offset !== 0;
			},

			/**
			 * This function does some basic calculations to create information about
			 * the user's timezone. It uses REFERENCE_YEAR as a solid year for which
			 * the script has been tested rather than depend on the year set by the
			 * client device.
			 *
			 * Returns a key that can be used to do lookups in jstz.olson.timezones.
			 * eg: "720,1,2".
			 *
			 * @returns {String}
			 */

			lookup_key = function () {
				var january_offset = get_january_offset(),
					june_offset = get_june_offset(),
					diff = january_offset - june_offset;

				if (diff < 0) {
					return january_offset + ",1";
				} else if (diff > 0) {
					return june_offset + ",1," + HEMISPHERE_SOUTH;
				}

				return january_offset + ",0";
			},

			/**
			 * Uses get_timezone_info() to formulate a key to use in the olson.timezones dictionary.
			 *
			 * Returns a primitive object on the format:
			 * {'timezone': TimeZone, 'key' : 'the key used to find the TimeZone object'}
			 *
			 * @returns Object
			 */
			determine = function () {
				var key = lookup_key();
				return new jstz.TimeZone(jstz.olson.timezones[key]);
			},

			/**
			 * This object contains information on when daylight savings starts for
			 * different timezones.
			 *
			 * The list is short for a reason. Often we do not have to be very specific
			 * to single out the correct timezone. But when we do, this list comes in
			 * handy.
			 *
			 * Each value is a date denoting when daylight savings starts for that timezone.
			 */
			dst_start_for = function (tz_name) {

				var ru_pre_dst_change = new Date(2010, 6, 15, 1, 0, 0, 0), // In 2010 Russia had DST, this allows us to detect Russia :)
					dst_starts = {
						'America/Denver': new Date(2011, 2, 13, 3, 0, 0, 0),
						'America/Mazatlan': new Date(2011, 3, 3, 3, 0, 0, 0),
						'America/Chicago': new Date(2011, 2, 13, 3, 0, 0, 0),
						'America/Mexico_City': new Date(2011, 3, 3, 3, 0, 0, 0),
						'America/Asuncion': new Date(2012, 9, 7, 3, 0, 0, 0),
						'America/Santiago': new Date(2012, 9, 3, 3, 0, 0, 0),
						'America/Campo_Grande': new Date(2012, 9, 21, 5, 0, 0, 0),
						'America/Montevideo': new Date(2011, 9, 2, 3, 0, 0, 0),
						'America/Sao_Paulo': new Date(2011, 9, 16, 5, 0, 0, 0),
						'America/Los_Angeles': new Date(2011, 2, 13, 8, 0, 0, 0),
						'America/Santa_Isabel': new Date(2011, 3, 5, 8, 0, 0, 0),
						'America/Havana': new Date(2012, 2, 10, 2, 0, 0, 0),
						'America/New_York': new Date(2012, 2, 10, 7, 0, 0, 0),
						'Europe/Helsinki': new Date(2013, 2, 31, 5, 0, 0, 0),
						'Pacific/Auckland': new Date(2011, 8, 26, 7, 0, 0, 0),
						'America/Halifax': new Date(2011, 2, 13, 6, 0, 0, 0),
						'America/Goose_Bay': new Date(2011, 2, 13, 2, 1, 0, 0),
						'America/Miquelon': new Date(2011, 2, 13, 5, 0, 0, 0),
						'America/Godthab': new Date(2011, 2, 27, 1, 0, 0, 0),
						'Europe/Moscow': ru_pre_dst_change,
						'Asia/Amman': new Date(2013, 2, 29, 1, 0, 0, 0),
						'Asia/Beirut': new Date(2013, 2, 31, 2, 0, 0, 0),
						'Asia/Damascus': new Date(2013, 3, 6, 2, 0, 0, 0),
						'Asia/Jerusalem': new Date(2013, 2, 29, 5, 0, 0, 0),
						'Asia/Yekaterinburg': ru_pre_dst_change,
						'Asia/Omsk': ru_pre_dst_change,
						'Asia/Krasnoyarsk': ru_pre_dst_change,
						'Asia/Irkutsk': ru_pre_dst_change,
						'Asia/Yakutsk': ru_pre_dst_change,
						'Asia/Vladivostok': ru_pre_dst_change,
						'Asia/Baku': new Date(2013, 2, 31, 4, 0, 0),
						'Asia/Yerevan': new Date(2013, 2, 31, 3, 0, 0),
						'Asia/Kamchatka': ru_pre_dst_change,
						'Asia/Gaza': new Date(2010, 2, 27, 4, 0, 0),
						'Africa/Cairo': new Date(2010, 4, 1, 3, 0, 0),
						'Europe/Minsk': ru_pre_dst_change,
						'Pacific/Apia': new Date(2010, 10, 1, 1, 0, 0, 0),
						'Pacific/Fiji': new Date(2010, 11, 1, 0, 0, 0),
						'Australia/Perth': new Date(2008, 10, 1, 1, 0, 0, 0)
					};

				return dst_starts[tz_name];
			};

		return {
			determine: determine,
			date_is_dst: date_is_dst,
			dst_start_for: dst_start_for
		};
	}());

	/**
	 * Simple object to perform ambiguity check and to return name of time zone.
	 */
	jstz.TimeZone = function (tz_name) {
		'use strict';
		/**
		 * The keys in this object are timezones that we know may be ambiguous after
		 * a preliminary scan through the olson_tz object.
		 *
		 * The array of timezones to compare must be in the order that daylight savings
		 * starts for the regions.
		 */
		var AMBIGUITIES = {
				'America/Denver':       ['America/Denver', 'America/Mazatlan'],
				'America/Chicago':      ['America/Chicago', 'America/Mexico_City'],
				'America/Santiago':     ['America/Santiago', 'America/Asuncion', 'America/Campo_Grande'],
				'America/Montevideo':   ['America/Montevideo', 'America/Sao_Paulo'],
				'Asia/Beirut':          ['Asia/Amman', 'Asia/Jerusalem', 'Asia/Beirut', 'Europe/Helsinki','Asia/Damascus'],
				'Pacific/Auckland':     ['Pacific/Auckland', 'Pacific/Fiji'],
				'America/Los_Angeles':  ['America/Los_Angeles', 'America/Santa_Isabel'],
				'America/New_York':     ['America/Havana', 'America/New_York'],
				'America/Halifax':      ['America/Goose_Bay', 'America/Halifax'],
				'America/Godthab':      ['America/Miquelon', 'America/Godthab'],
				'Asia/Dubai':           ['Europe/Moscow'],
				'Asia/Dhaka':           ['Asia/Yekaterinburg'],
				'Asia/Jakarta':         ['Asia/Omsk'],
				'Asia/Shanghai':        ['Asia/Krasnoyarsk', 'Australia/Perth'],
				'Asia/Tokyo':           ['Asia/Irkutsk'],
				'Australia/Brisbane':   ['Asia/Yakutsk'],
				'Pacific/Noumea':       ['Asia/Vladivostok'],
				'Pacific/Tarawa':       ['Asia/Kamchatka', 'Pacific/Fiji'],
				'Pacific/Tongatapu':    ['Pacific/Apia'],
				'Asia/Baghdad':         ['Europe/Minsk'],
				'Asia/Baku':            ['Asia/Yerevan','Asia/Baku'],
				'Africa/Johannesburg':  ['Asia/Gaza', 'Africa/Cairo']
			},

			timezone_name = tz_name,

			/**
			 * Checks if a timezone has possible ambiguities. I.e timezones that are similar.
			 *
			 * For example, if the preliminary scan determines that we're in America/Denver.
			 * We double check here that we're really there and not in America/Mazatlan.
			 *
			 * This is done by checking known dates for when daylight savings start for different
			 * timezones during 2010 and 2011.
			 */
			ambiguity_check = function () {
				var ambiguity_list = AMBIGUITIES[timezone_name],
					length = ambiguity_list.length,
					i = 0,
					tz = ambiguity_list[0];

				for (; i < length; i += 1) {
					tz = ambiguity_list[i];

					if (jstz.date_is_dst(jstz.dst_start_for(tz))) {
						timezone_name = tz;
						return;
					}
				}
			},

			/**
			 * Checks if it is possible that the timezone is ambiguous.
			 */
			is_ambiguous = function () {
				return typeof (AMBIGUITIES[timezone_name]) !== 'undefined';
			};

		if (is_ambiguous()) {
			ambiguity_check();
		}

		return {
			name: function () {
				return timezone_name;
			}
		};
	};

	jstz.olson = {};

	/*
	 * The keys in this dictionary are comma separated as such:
	 *
	 * First the offset compared to UTC time in minutes.
	 *
	 * Then a flag which is 0 if the timezone does not take daylight savings into account and 1 if it
	 * does.
	 *
	 * Thirdly an optional 's' signifies that the timezone is in the southern hemisphere,
	 * only interesting for timezones with DST.
	 *
	 * The mapped arrays is used for constructing the jstz.TimeZone object from within
	 * jstz.determine_timezone();
	 */
	jstz.olson.timezones = {
		'-720,0'   : 'Pacific/Majuro',
		'-660,0'   : 'Pacific/Pago_Pago',
		'-600,1'   : 'America/Adak',
		'-600,0'   : 'Pacific/Honolulu',
		'-570,0'   : 'Pacific/Marquesas',
		'-540,0'   : 'Pacific/Gambier',
		'-540,1'   : 'America/Anchorage',
		'-480,1'   : 'America/Los_Angeles',
		'-480,0'   : 'Pacific/Pitcairn',
		'-420,0'   : 'America/Phoenix',
		'-420,1'   : 'America/Denver',
		'-360,0'   : 'America/Guatemala',
		'-360,1'   : 'America/Chicago',
		'-360,1,s' : 'Pacific/Easter',
		'-300,0'   : 'America/Bogota',
		'-300,1'   : 'America/New_York',
		'-270,0'   : 'America/Caracas',
		'-240,1'   : 'America/Halifax',
		'-240,0'   : 'America/Santo_Domingo',
		'-240,1,s' : 'America/Santiago',
		'-210,1'   : 'America/St_Johns',
		'-180,1'   : 'America/Godthab',
		'-180,0'   : 'America/Argentina/Buenos_Aires',
		'-180,1,s' : 'America/Montevideo',
		'-120,0'   : 'America/Noronha',
		'-120,1'   : 'America/Noronha',
		'-60,1'    : 'Atlantic/Azores',
		'-60,0'    : 'Atlantic/Cape_Verde',
		'0,0'      : 'UTC',
		'0,1'      : 'Europe/London',
		'60,1'     : 'Europe/Berlin',
		'60,0'     : 'Africa/Lagos',
		'60,1,s'   : 'Africa/Windhoek',
		'120,1'    : 'Asia/Beirut',
		'120,0'    : 'Africa/Johannesburg',
		'180,0'    : 'Asia/Baghdad',
		'180,1'    : 'Europe/Moscow',
		'210,1'    : 'Asia/Tehran',
		'240,0'    : 'Asia/Dubai',
		'240,1'    : 'Asia/Baku',
		'270,0'    : 'Asia/Kabul',
		'300,1'    : 'Asia/Yekaterinburg',
		'300,0'    : 'Asia/Karachi',
		'330,0'    : 'Asia/Kolkata',
		'345,0'    : 'Asia/Kathmandu',
		'360,0'    : 'Asia/Dhaka',
		'360,1'    : 'Asia/Omsk',
		'390,0'    : 'Asia/Rangoon',
		'420,1'    : 'Asia/Krasnoyarsk',
		'420,0'    : 'Asia/Jakarta',
		'480,0'    : 'Asia/Shanghai',
		'480,1'    : 'Asia/Irkutsk',
		'525,0'    : 'Australia/Eucla',
		'525,1,s'  : 'Australia/Eucla',
		'540,1'    : 'Asia/Yakutsk',
		'540,0'    : 'Asia/Tokyo',
		'570,0'    : 'Australia/Darwin',
		'570,1,s'  : 'Australia/Adelaide',
		'600,0'    : 'Australia/Brisbane',
		'600,1'    : 'Asia/Vladivostok',
		'600,1,s'  : 'Australia/Sydney',
		'630,1,s'  : 'Australia/Lord_Howe',
		'660,1'    : 'Asia/Kamchatka',
		'660,0'    : 'Pacific/Noumea',
		'690,0'    : 'Pacific/Norfolk',
		'720,1,s'  : 'Pacific/Auckland',
		'720,0'    : 'Pacific/Tarawa',
		'765,1,s'  : 'Pacific/Chatham',
		'780,0'    : 'Pacific/Tongatapu',
		'780,1,s'  : 'Pacific/Apia',
		'840,0'    : 'Pacific/Kiritimati'
	};

	if (typeof exports !== 'undefined') {
		exports.jstz = jstz;
	} else {
		root.jstz = jstz;
	}
})(this);