jstz.main.js

/*global exports, Intl*/
/**
 * This script gives you the zone info key representing your device's time zone setting.
 *
 * @name jsTimezoneDetect
 * @version 1.0.6
 * @author Jon Nylander
 * @license MIT License - https://bitbucket.org/pellepim/jstimezonedetect/src/default/LICENCE.txt
 *
 * For usage and examples, visit:
 * http://pellepim.bitbucket.org/jstz/
 *
 * Copyright (c) Jon Nylander
 */


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

        consts = {
            DAY: 86400000,
            HOUR: 3600000,
            MINUTE: 60000,
            SECOND: 1000,
            BASELINE_YEAR: 2014,
            MAX_SCORE: 864000000, // 10 days
            AMBIGUITIES: {
                'America/Denver':       ['America/Mazatlan'],
                'Europe/London':        ['Africa/Casablanca'],
                'America/Chicago':      ['America/Mexico_City'],
                'America/Asuncion':     ['America/Campo_Grande', 'America/Santiago'],
                'America/Montevideo':   ['America/Sao_Paulo', 'America/Santiago'],
                // Europe/Minsk should not be in this list... but Windows.
                'Asia/Beirut':          ['Asia/Amman', 'Asia/Jerusalem', 'Europe/Helsinki', 'Asia/Damascus', 'Africa/Cairo', 'Asia/Gaza', 'Europe/Minsk'],
                'Pacific/Auckland':     ['Pacific/Fiji'],
                'America/Los_Angeles':  ['America/Santa_Isabel'],
                'America/New_York':     ['America/Havana'],
                'America/Halifax':      ['America/Goose_Bay'],
                'America/Godthab':      ['America/Miquelon'],
                'Asia/Dubai':           ['Asia/Yerevan'],
                'Asia/Jakarta':         ['Asia/Krasnoyarsk'],
                'Asia/Shanghai':        ['Asia/Irkutsk', 'Australia/Perth'],
                'Australia/Sydney':     ['Australia/Lord_Howe'],
                'Asia/Tokyo':           ['Asia/Yakutsk'],
                'Asia/Dhaka':           ['Asia/Omsk'],
                // In the real world Yerevan is not ambigous for Baku... but Windows.
                'Asia/Baku':            ['Asia/Yerevan'],
                'Australia/Brisbane':   ['Asia/Vladivostok'],
                'Pacific/Noumea':       ['Asia/Vladivostok'],
                'Pacific/Majuro':       ['Asia/Kamchatka', 'Pacific/Fiji'],
                'Pacific/Tongatapu':    ['Pacific/Apia'],
                'Asia/Baghdad':         ['Europe/Minsk', 'Europe/Moscow'],
                'Asia/Karachi':         ['Asia/Yekaterinburg'],
                'Africa/Johannesburg':  ['Asia/Gaza', 'Africa/Cairo']
            }
        },

        /**
         * Gets the offset in minutes from UTC for a certain date.
         * @param {Date} date
         * @returns {Number}
         */
        get_date_offset = function get_date_offset(date) {
            var offset = -date.getTimezoneOffset();
            return (offset !== null ? 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 lookup_key() {
            var january_offset = get_date_offset(new Date(consts.BASELINE_YEAR, 0, 2)),
                june_offset = get_date_offset(new Date(consts.BASELINE_YEAR, 5, 2)),
                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";
        },


        /**
         * Tries to get the time zone key directly from the operating system for those
         * environments that support the ECMAScript Internationalization API.
         */
        get_from_internationalization_api = function get_from_internationalization_api() {
            var format, timezone;
            if (typeof Intl === "undefined" || typeof Intl.DateTimeFormat === "undefined") {
                return;
            }
            format = Intl.DateTimeFormat();
            if (typeof format === "undefined" || typeof format.resolvedOptions === "undefined") {
                return;
            }
            timezone = format.resolvedOptions().timeZone;
            if (timezone && (timezone.indexOf("/") > -1 || timezone === 'UTC') && timezone.indexOf("Etc") != 0) {
                return timezone;
            }
        },

        /**
         * Starting point for getting all the DST rules for a specific year
         * for the current timezone (as described by the client system).
         *
         * Returns an object with start and end attributes, or false if no
         * DST rules were found for the year.
         *
         * @param year
         * @returns {Object} || {Boolean}
         */
        dst_dates = function dst_dates(year) {
            var yearstart = new Date(year, 0, 1, 0, 0, 1, 0).getTime();
            var yearend = new Date(year, 12, 31, 23, 59, 59).getTime();
            var current = yearstart;
            var offset = (new Date(current)).getTimezoneOffset();
            var dst_start = null;
            var dst_end = null;

            while (current < yearend - 86400000) {
                var dateToCheck = new Date(current);
                var dateToCheckOffset = dateToCheck.getTimezoneOffset();

                if (dateToCheckOffset !== offset) {
                    if (dateToCheckOffset < offset) {
                        dst_start = dateToCheck;
                    }
                    if (dateToCheckOffset > offset) {
                        dst_end = dateToCheck;
                    }
                    offset = dateToCheckOffset;
                }

                current += 86400000;
            }

            if (dst_start && dst_end) {
                return {
                    s: find_dst_fold(dst_start).getTime(),
                    e: find_dst_fold(dst_end).getTime()
                };
            }

            return false;
        },

        /**
         * Probably completely unnecessary function that recursively finds the
         * exact (to the second) time when a DST rule was changed.
         *
         * @param a_date - The candidate Date.
         * @param padding - integer specifying the padding to allow around the candidate
         *                  date for finding the fold.
         * @param iterator - integer specifying how many milliseconds to iterate while
         *                   searching for the fold.
         *
         * @returns {Date}
         */
        find_dst_fold = function find_dst_fold(a_date, padding, iterator) {
            if (typeof padding === 'undefined') {
                padding = consts.DAY;
                iterator = consts.HOUR;
            }

            var date_start = new Date(a_date.getTime() - padding).getTime();
            var date_end = a_date.getTime() + padding;
            var offset = new Date(date_start).getTimezoneOffset();

            var current = date_start;

            var dst_change = null;
            while (current < date_end - iterator) {
                var dateToCheck = new Date(current);
                var dateToCheckOffset = dateToCheck.getTimezoneOffset();

                if (dateToCheckOffset !== offset) {
                    dst_change = dateToCheck;
                    break;
                }
                current += iterator;
            }

            if (padding === consts.DAY) {
                return find_dst_fold(dst_change, consts.HOUR, consts.MINUTE);
            }

            if (padding === consts.HOUR) {
                return find_dst_fold(dst_change, consts.MINUTE, consts.SECOND);
            }

            return dst_change;
        },

        windows7_adaptations = function windows7_adaptions(rule_list, preliminary_timezone, score, sample) {
            if (score !== 'N/A') {
                return score;
            }
            if (preliminary_timezone === 'Asia/Beirut') {
                if (sample.name === 'Africa/Cairo') {
                    if (rule_list[6].s === 1398376800000 && rule_list[6].e === 1411678800000) {
                        return 0;
                    }
                }
                if (sample.name === 'Asia/Jerusalem') {
                    if (rule_list[6].s === 1395964800000 && rule_list[6].e === 1411858800000) {
                        return 0;
                }
            }
            } else if (preliminary_timezone === 'America/Santiago') {
                if (sample.name === 'America/Asuncion') {
                    if (rule_list[6].s === 1412481600000 && rule_list[6].e === 1397358000000) {
                        return 0;
                    }
                }
                if (sample.name === 'America/Campo_Grande') {
                    if (rule_list[6].s === 1413691200000 && rule_list[6].e === 1392519600000) {
                        return 0;
                    }
                }
            } else if (preliminary_timezone === 'America/Montevideo') {
                if (sample.name === 'America/Sao_Paulo') {
                    if (rule_list[6].s === 1413687600000 && rule_list[6].e === 1392516000000) {
                        return 0;
                    }
                }
            } else if (preliminary_timezone === 'Pacific/Auckland') {
                if (sample.name === 'Pacific/Fiji') {
                    if (rule_list[6].s === 1414245600000 && rule_list[6].e === 1396101600000) {
                        return 0;
                    }
                }
            }

            return score;
        },

        /**
         * Takes the DST rules for the current timezone, and proceeds to find matches
         * in the jstz.olson.dst_rules.zones array.
         *
         * Compares samples to the current timezone on a scoring basis.
         *
         * Candidates are ruled immediately if either the candidate or the current zone
         * has a DST rule where the other does not.
         *
         * Candidates are ruled out immediately if the current zone has a rule that is
         * outside the DST scope of the candidate.
         *
         * Candidates are included for scoring if the current zones rules fall within the
         * span of the samples rules.
         *
         * Low score is best, the score is calculated by summing up the differences in DST
         * rules and if the consts.MAX_SCORE is overreached the candidate is ruled out.
         *
         * Yah follow? :)
         *
         * @param rule_list
         * @param preliminary_timezone
         * @returns {*}
         */
        best_dst_match = function best_dst_match(rule_list, preliminary_timezone) {
            var score_sample = function score_sample(sample) {
                var score = 0;

                for (var j = 0; j < rule_list.length; j++) {

                    // Both sample and current time zone report DST during the year.
                    if (!!sample.rules[j] && !!rule_list[j]) {

                        // The current time zone's DST rules are inside the sample's. Include.
                        if (rule_list[j].s >= sample.rules[j].s && rule_list[j].e <= sample.rules[j].e) {
                            score = 0;
                            score += Math.abs(rule_list[j].s - sample.rules[j].s);
                            score += Math.abs(sample.rules[j].e - rule_list[j].e);

                        // The current time zone's DST rules are outside the sample's. Discard.
                        } else {
                            score = 'N/A';
                            break;
                        }

                        // The max score has been reached. Discard.
                        if (score > consts.MAX_SCORE) {
                            score = 'N/A';
                            break;
                        }
                    }
                }

                score = windows7_adaptations(rule_list, preliminary_timezone, score, sample);

                return score;
            };
            var scoreboard = {};
            var dst_zones = jstz.olson.dst_rules.zones;
            var dst_zones_length = dst_zones.length;
            var ambiguities = consts.AMBIGUITIES[preliminary_timezone];

            for (var i = 0; i < dst_zones_length; i++) {
                var sample = dst_zones[i];
                var score = score_sample(dst_zones[i]);

                if (score !== 'N/A') {
                    scoreboard[sample.name] = score;
                }
            }

            for (var tz in scoreboard) {
                if (scoreboard.hasOwnProperty(tz)) {
                    for (var j = 0; j < ambiguities.length; j++) {
                        if (ambiguities[j] === tz) {
                        return tz;
                        }
                    }
                }
            }

            return preliminary_timezone;
        },

        /**
         * Takes the preliminary_timezone as detected by lookup_key().
         *
         * Builds up the current timezones DST rules for the years defined
         * in the jstz.olson.dst_rules.years array.
         *
         * If there are no DST occurences for those years, immediately returns
         * the preliminary timezone. Otherwise proceeds and tries to solve
         * ambiguities.
         *
         * @param preliminary_timezone
         * @returns {String} timezone_name
         */
        get_by_dst = function get_by_dst(preliminary_timezone) {
            var get_rules = function get_rules() {
                var rule_list = [];
                for (var i = 0; i < jstz.olson.dst_rules.years.length; i++) {
                    var year_rules = dst_dates(jstz.olson.dst_rules.years[i]);
                    rule_list.push(year_rules);
                }
                return rule_list;
            };
            var check_has_dst = function check_has_dst(rules) {
                for (var i = 0; i < rules.length; i++) {
                    if (rules[i] !== false) {
                        return true;
                    }
                }
                return false;
            };
            var rules = get_rules();
            var has_dst = check_has_dst(rules);

            if (has_dst) {
                return best_dst_match(rules, preliminary_timezone);
            }

            return preliminary_timezone;
        },

        /**
         * Uses get_timezone_info() to formulate a key to use in the olson.timezones dictionary.
         *
         * Returns an object with one function ".name()"
         *
         * @returns Object
         */
        determine = function determine() {
            var preliminary_tz = get_from_internationalization_api();

            if (!preliminary_tz) {
                preliminary_tz = jstz.olson.timezones[lookup_key()];

                if (typeof consts.AMBIGUITIES[preliminary_tz] !== 'undefined') {
                    preliminary_tz = get_by_dst(preliminary_tz);
                }
            }

            return {
                name: function () {
                    return preliminary_tz;
                },
                stdTimezoneOffset : function () {
                    // negative to match what (new Date).getTimezoneOffset() will return
                    return -lookup_key().split(',')[0];
                },
                timezoneOffset : function () {
                    // negative to match what (new Date).getTimezoneOffset() will return
                    return -get_date_offset(new Date())
                }
            };
        };

    return {
        determine: determine
    };
}());


jstz.olson = 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();
 */
jstz.olson.timezones = {
    '-720,0': 'Etc/GMT+12',
    '-660,0': 'Pacific/Pago_Pago',
    '-660,1,s': 'Pacific/Apia', // Why? Because windows... cry!
    '-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/Asuncion',
    '-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/Majuro',
    '765,1,s': 'Pacific/Chatham',
    '780,0': 'Pacific/Tongatapu',
    '780,1,s': 'Pacific/Apia',
    '840,0': 'Pacific/Kiritimati'
};