(function ($) {

/**

 * Set the client's system time zone as default values of form fields.

 */

Drupal.behaviors.setTimezone = {

  attach: function (context, settings) {

    $('select.timezone-detect', context).once('timezone', function () {

      var dateString = Date();

      // In some client environments, date strings include a time zone

      // abbreviation, between 3 and 5 letters enclosed in parentheses,

      // which can be interpreted by PHP.

      var matches = dateString.match(/\(([A-Z]{3,5})\)/);

      var abbreviation = matches ? matches[1] : 0;

      // For all other client environments, the abbreviation is set to "0"

      // and the current offset from UTC and daylight saving time status are

      // used to guess the time zone.

      var dateNow = new Date();

      var offsetNow = dateNow.getTimezoneOffset() * -60;

      // Use January 1 and July 1 as test dates for determining daylight

      // saving time status by comparing their offsets.

      var dateJan = new Date(dateNow.getFullYear(), 0, 1, 12, 0, 0, 0);

      var dateJul = new Date(dateNow.getFullYear(), 6, 1, 12, 0, 0, 0);

      var offsetJan = dateJan.getTimezoneOffset() * -60;

      var offsetJul = dateJul.getTimezoneOffset() * -60;

      var isDaylightSavingTime;

      // If the offset from UTC is identical on January 1 and July 1,

      // assume daylight saving time is not used in this time zone.

      if (offsetJan == offsetJul) {

        isDaylightSavingTime = '';

      }

      // If the maximum annual offset is equivalent to the current offset,

      // assume daylight saving time is in effect.

      else if (Math.max(offsetJan, offsetJul) == offsetNow) {

        isDaylightSavingTime = 1;

      }

      // Otherwise, assume daylight saving time is not in effect.

      else {

        isDaylightSavingTime = 0;

      }

      // Submit request to the system/timezone callback and set the form field

      // to the response time zone. The client date is passed to the callback

      // for debugging purposes. Submit a synchronous request to avoid database

      // errors associated with concurrent requests during install.

      var path = 'system/timezone/' + abbreviation + '/' + offsetNow + '/' + isDaylightSavingTime;

      var element = this;

      $.ajax({

        async: false,

        url: settings.basePath,

        data: { q: path, date: dateString },

        dataType: 'json',

        success: function (data) {

          if (data) {

            $(element).val(data);

          }

        }

      });

    });

  }

};

})(jQuery);