detect_timezone.js

/*jslint indent: 2, nomen: false, white: false, plusplus: false, regexp: false */
/*global jQuery: false */

/*
 * Original script by Josh Fraser (http://www.onlineaspect.com)
 * Continued by Jon Nylander, (jon at pageloom dot com)
 * According to both of us, you are absolutely free to do whatever 
 * you want with this code.
 * 
 * This code is  maintained at bitbucket.org as jsTimezoneDetect.
 */
(function($) {var HEMISPHERE_SOUTH = 'SOUTH',
      HEMISPHERE_NORTH = 'NORTH',
      HEMISPHERE_UNKNOWN = 'N/A',
      olson = {};

  /**
   * A simple object containing information of utc_offset, which olson timezone key to use,
   * and if the timezone cares about daylight savings or not.
   *
   * @constructor
   * @param {string} offset - for example '-11:00'
   * @param {string} olson_tz - the olson Identifier, such as "America/Denver"
   * @param {boolean} uses_dst - flag for whether the time zone somehow cares about daylight savings.
   */
  function TimeZone(offset, olson_tz, uses_dst) {
    this.utc_offset = offset;
    this.olson_tz = olson_tz;
    this.uses_dst = uses_dst;
  }

  /**
   * Prints out the result.
   * But before it does that, it calls this.ambiguity_check.
   */
  TimeZone.prototype.display = function() {
    this.ambiguity_check();
    var response_text = '<b>UTC-offset</b>: ' + this.utc_offset + '<br/>';
    response_text += '<b>Olson database name</b>: ' + this.olson_tz + '<br/>';
    response_text += '<b>Daylight Savings</b>: ' + (this.uses_dst ? 'yes' : 'no') + '<br/>';

    return response_text;
  };

  /**
   * Gets the offset in minutes from UTC for a certain date.
   *
   * @param date
   * @returns {number}
   */
  function get_date_offset(date) {
    return -date.getTimezoneOffset();
  }

  function get_january_offset() {
    return get_date_offset(new Date(2011, 0, 1, 0, 0, 0, 0));
  }

  function get_june_offset() {
    return get_date_offset(new Date(2011, 5, 1, 0, 0, 0, 0));
  }

  /**
   * Checks whether a given date is in daylight savings time.
   *
   * If the date supplied is after june, we assume that we're checking
   * for southern hemisphere DST.
   *
   * @param {Date} date
   * @returns {boolean}
   */
  function date_is_dst(date) {
    var base_offset = ( (date.getMonth() > 5 ? get_june_offset() : get_january_offset()) ),
        date_offset = get_date_offset(date);

    return (base_offset - date_offset) !== 0;
  }

  /**
   * Checks if a timezone has possible ambiguities. I.e timezones that are similar.
   *
   * 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.
   */
  TimeZone.prototype.ambiguity_check = function() {
    var i,
        local_ambiguity_list = olson.ambiguity_list[this.olson_tz],
        length,
        tz;

    if (typeof(local_ambiguity_list) === 'undefined') {
      return;
    }

    length = local_ambiguity_list.length;

    for (i = 0; i < length; i++) {
      tz = local_ambiguity_list[i];

      if (date_is_dst(olson.dst_start_dates[tz])) {
        this.olson_tz = tz;
        return;
      }
    }
  };

  /**
   * 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 values of the dictionary are TimeZone objects.
   */
  olson.timezones = {
    '-720,0'   : new TimeZone('-12:00', 'Etc/GMT+12', false),
    '-660,0'   : new TimeZone('-11:00', 'Pacific/Pago_Pago', false),
    '-600,1'   : new TimeZone('-11:00', 'America/Adak', true),
    '-660,1,s' : new TimeZone('-11:00', 'Pacific/Apia', true),
    '-600,0'   : new TimeZone('-10:00', 'Pacific/Honolulu', false),
    '-570,0'   : new TimeZone('-10:30', 'Pacific/Marquesas', false),
    '-540,0'   : new TimeZone('-09:00', 'Pacific/Gambier', false),
    '-540,1'   : new TimeZone('-09:00', 'America/Anchorage', true),
    '-480,1'   : new TimeZone('-08:00', 'America/Los_Angeles', true),
    '-480,0'   : new TimeZone('-08:00', 'Pacific/Pitcairn', false),
    '-420,0'   : new TimeZone('-07:00', 'America/Phoenix', false),
    '-420,1'   : new TimeZone('-07:00', 'America/Denver', true),
    '-360,0'   : new TimeZone('-06:00', 'America/Guatemala', false),
    '-360,1'   : new TimeZone('-06:00', 'America/Chicago', true),
    '-360,1,s' : new TimeZone('-06:00', 'Pacific/Easter', true),
    '-300,0'   : new TimeZone('-05:00', 'America/Bogota', false),
    '-300,1'   : new TimeZone('-05:00', 'America/New_York', true),
    '-270,0'   : new TimeZone('-04:30', 'America/Caracas', false),
    '-240,1'   : new TimeZone('-04:00', 'America/Halifax', true),
    '-240,0'   : new TimeZone('-04:00', 'America/Santo_Domingo', false),
    '-240,1,s' : new TimeZone('-04:00', 'America/Asuncion', true),
    '-210,1'   : new TimeZone('-03:30', 'America/St_Johns', true),
    '-180,1'   : new TimeZone('-03:00', 'America/Godthab', true),
    '-180,0'   : new TimeZone('-03:00', 'America/Argentina/Buenos_Aires,', false),
    '-180,1,s' : new TimeZone('-03:00', 'America/Montevideo', true),
    '-120,0'   : new TimeZone('-02:00', 'America/Noronha', false),
    '-120,1'   : new TimeZone('-02:00', 'Etc/GMT+2', true),
    '-60,1'    : new TimeZone('-01:00', 'Atlantic/Azores', true),
    '-60,0'    : new TimeZone('-01:00', 'Atlantic/Cape_Verde', false),
    '0,0'      : new TimeZone('00:00', 'Africa/Casablanca', false),
    '0,1'      : new TimeZone('00:00', 'Europe/London', true),
    '60,1'     : new TimeZone('+01:00', 'Europe/Berlin', true),
    '60,0'     : new TimeZone('+01:00', 'Africa/Lagos', false),
    '60,1,s'   : new TimeZone('+01:00', 'Africa/Windhoek', true),
    '120,1'    : new TimeZone('+02:00', 'Asia/Beirut', true),
    '120,0'    : new TimeZone('+02:00', 'Africa/Johannesburg', false),
    '180,1'    : new TimeZone('+03:00', 'Europe/Moscow', true),
    '180,0'    : new TimeZone('+03:00', 'Asia/Baghdad', false),
    '210,1'    : new TimeZone('+03:30', 'Asia/Tehran', true),
    '240,0'    : new TimeZone('+04:00', 'Asia/Dubai', false),
    '240,1'    : new TimeZone('+04:00', 'Asia/Yerevan', true),
    '270,0'    : new TimeZone('+04:30', 'Asia/Kabul', false),
    '300,1'    : new TimeZone('+05:00', 'Asia/Yekaterinburg', true),
    '300,0'    : new TimeZone('+05:00', 'Asia/Karachi', false),
    '330,0'    : new TimeZone('+05:30', 'Asia/Kolkata', false),
    '345,0'    : new TimeZone('+05:45', 'Asia/Kathmandu', false),
    '360,0'    : new TimeZone('+06:00', 'Asia/Dhaka', false),
    '360,1'    : new TimeZone('+06:00', 'Asia/Omsk', true),
    '390,0'    : new TimeZone('+06:30', 'Asia/Rangoon', false),
    '420,1'    : new TimeZone('+07:00', 'Asia/Krasnoyarsk', true),
    '420,0'    : new TimeZone('+07:00', 'Asia/Jakarta', false),
    '480,0'    : new TimeZone('+08:00', 'Asia/Shanghai', false),
    '480,1'    : new TimeZone('+08:00', 'Asia/Irkutsk', true),
    '525,0'    : new TimeZone('+08:45', 'Australia/Eucla', true),
    '525,1,s'  : new TimeZone('+08:45', 'Australia/Eucla', true),
    '540,1'    : new TimeZone('+09:00', 'Asia/Yakutsk', true),
    '540,0'    : new TimeZone('+09:00', 'Asia/Tokyo', false),
    '570,0'    : new TimeZone('+09:30', 'Australia/Darwin', false),
    '570,1,s'  : new TimeZone('+09:30', 'Australia/Adelaide', true),
    '600,0'    : new TimeZone('+10:00', 'Australia/Brisbane', false),
    '600,1'    : new TimeZone('+10:00', 'Asia/Vladivostok', true),
    '600,1,s'  : new TimeZone('+10:00', 'Australia/Sydney', true),
    '630,1,s'  : new TimeZone('+10:30', 'Australia/Lord_Howe', true),
    '660,1'    : new TimeZone('+11:00', 'Asia/Kamchatka', true),
    '660,0'    : new TimeZone('+11:00', 'Pacific/Noumea', false),
    '690,0'    : new TimeZone('+11:30', 'Pacific/Norfolk', false),
    '720,1,s'  : new TimeZone('+12:00', 'Pacific/Auckland', true),
    '720,0'    : new TimeZone('+12:00', 'Pacific/Tarawa', false),
    '765,1,s'  : new TimeZone('+12:45', 'Pacific/Chatham', true),
    '780,0'    : new TimeZone('+13:00', 'Pacific/Tongatapu', false),
    '840,0'    : new TimeZone('+14:00', 'Pacific/Kiritimati', false)
  };

  /**
   * 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.
   */
  olson.dst_start_dates = {
    '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),
    'Atlantic/Stanley' : new Date(2011, 8, 4, 7, 0, 0, 0),
    'America/Asuncion' : new Date(2011, 9, 2, 3, 0, 0, 0),
    'America/Santiago' : new Date(2011, 9, 9, 3, 0, 0, 0),
    'America/Campo_Grande' : new Date(2011, 9, 16, 5, 0, 0, 0),
    'America/Montevideo' : new Date(2011, 9, 2, 3, 0, 0, 0),
    'America/Sao_Paolo' : 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(2011, 2, 13, 2, 0, 0, 0),
    'America/New_York' : new Date(2011, 2, 13, 7, 0, 0, 0),
    'Asia/Gaza' : new Date(2011, 2, 26, 23, 0, 0, 0),
    'Asia/Beirut' : new Date(2011, 2, 27, 1, 0, 0, 0),
    'Europe/Minsk' : new Date(2011, 2, 27, 3, 0, 0, 0),
    'Europe/Istanbul' : new Date(2011, 2, 27, 7, 0, 0, 0),
    'Asia/Damascus' : new Date(2011, 3, 1, 2, 0, 0, 0),
    'Asia/Jerusalem' : new Date(2011, 3, 1, 6, 0, 0, 0),
    'Africa/Cairo' : new Date(2011, 3, 29, 4, 0, 0, 0),
    'Asia/Yerevan' : new Date(2011, 2, 27, 4, 0, 0, 0),
    'Asia/Baku'    : new Date(2011, 2, 27, 8, 0, 0, 0),
    'Pacific/Auckland' : new Date(2011, 8, 26, 7, 0, 0, 0),
    'Pacific/Fiji' : new Date(2010, 11, 29, 23, 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)
  };

  /**
   * 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.
   */
  olson.ambiguity_list = {
    'America/Denver' : ['America/Denver','America/Mazatlan'],
    'America/Chicago' : ['America/Chicago','America/Mexico_City'],
    'America/Asuncion' : ['Atlantic/Stanley', 'America/Asuncion', 'America/Santiago','America/Campo_Grande'],
    'America/Montevideo' : ['America/Montevideo', 'America/Sao_Paolo'],
    'Asia/Beirut' : ['Asia/Gaza','Asia/Beirut', 'Europe/Minsk', 'Europe/Istanbul', 'Asia/Damascus', 'Asia/Jerusalem','Africa/Cairo'],
    'Asia/Yerevan' : ['Asia/Yerevan', 'Asia/Baku'],
    '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']
  };


  /**
   * This function does some basic calculations to create information about
   * the user's timezone.
   *
   * Returns a primitive object on the format
   * {'utc_offset' : -9, 'dst': 1, hemisphere' : 'north'}
   * where dst is 1 if the region uses daylight savings.
   *
   * @returns {Object}
   */
  function get_timezone_info() {
    var january_offset = get_january_offset(),
        june_offset = get_june_offset(),
        diff = january_offset - june_offset;

    if (diff < 0) {
      return {'utc_offset' : january_offset,
        'dst':  1,
        'hemisphere' : HEMISPHERE_NORTH};
    }
    else if (diff > 0) {
      return {'utc_offset' : june_offset,
        'dst' : 1,
        'hemisphere' : HEMISPHERE_SOUTH};
    }

    return {'utc_offset' : january_offset,
      'dst': 0,
      'hemisphere' : HEMISPHERE_UNKNOWN};
  }

  /**
   * 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
   */
  function determine_timezone() {
    var timezone_key_info = get_timezone_info(),
        hemisphere_suffix = '',
        tz_key;

    if (timezone_key_info.hemisphere === HEMISPHERE_SOUTH) {
      hemisphere_suffix = ',s';
    }

    tz_key = timezone_key_info.utc_offset + ',' + timezone_key_info.dst + hemisphere_suffix;

    return {
      'timezone' : olson.timezones[tz_key],
      'key' : tz_key,
      name: olson.timezones[tz_key].olson_tz
    };
  }

  if ($ && $.extend) {
    $.extend({
      timezone: determine_timezone
    });
  } else {
    jsDetectTimezone = {
      timezone: determine_timezone
    };
  }
}(jQuery));