/**
 * 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);
