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// Copyright 2008 The Closure Library Authors. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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//      http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS-IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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/**
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 * @fileoverview Functions for detecting user's time zone.
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 * This work is based on Charlie Luo and Hong Yan's time zone detection work
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 * for CBG.
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 */
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goog.provide('goog.locale.timeZoneDetection');
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goog.require('goog.locale.TimeZoneFingerprint');
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/**
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 * Array of time instances for checking the time zone offset.
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 * @type {Array<number>}
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 * @private
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 */
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goog.locale.timeZoneDetection.TZ_POKE_POINTS_ = [
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  1109635200, 1128902400, 1130657000, 1143333000, 1143806400, 1145000000,
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  1146380000, 1152489600, 1159800000, 1159500000, 1162095000, 1162075000,
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  1162105500
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];
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/**
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 * Calculates time zone fingerprint by poking time zone offsets for 13
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 * preselected time points.
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 * See {@link goog.locale.timeZoneDetection.TZ_POKE_POINTS_}
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 * @param {Date} date Date for calculating the fingerprint.
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 * @return {number} Fingerprint of user's time zone setting.
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 */
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goog.locale.timeZoneDetection.getFingerprint = function(date) {
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  var hash = 0;
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  var stdOffset;
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  var isComplex = false;
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  for (var i = 0; i < goog.locale.timeZoneDetection.TZ_POKE_POINTS_.length;
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       i++) {
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    date.setTime(goog.locale.timeZoneDetection.TZ_POKE_POINTS_[i] * 1000);
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    var offset = date.getTimezoneOffset() / 30 + 48;
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    if (i == 0) {
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      stdOffset = offset;
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    } else if (stdOffset != offset) {
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      isComplex = true;
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    }
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    hash = (hash << 2) ^ offset;
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  }
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  return isComplex ? hash : /** @type {number} */ (stdOffset);
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};
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/**
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 * Detects browser's time zone setting. If user's country is known, a better
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 * time zone choice could be guessed.
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 * @param {string=} opt_country Two-letter ISO 3166 country code.
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 * @param {Date=} opt_date Date for calculating the fingerprint. Defaults to the
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 *     current date.
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 * @return {string} Time zone ID of best guess.
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 */
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goog.locale.timeZoneDetection.detectTimeZone = function(opt_country, opt_date) {
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  var date = opt_date || new Date();
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  var fingerprint = goog.locale.timeZoneDetection.getFingerprint(date);
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  var timeZoneList = goog.locale.TimeZoneFingerprint[fingerprint];
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  // Timezones in goog.locale.TimeZoneDetection.TimeZoneMap are in the format
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  // US-America/Los_Angeles. Country code needs to be stripped before a
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  // timezone is returned.
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  if (timeZoneList) {
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    if (opt_country) {
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      for (var i = 0; i < timeZoneList.length; ++i) {
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        if (timeZoneList[i].indexOf(opt_country) == 0) {
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          return timeZoneList[i].substring(3);
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        }
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      }
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    }
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    return timeZoneList[0].substring(3);
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  }
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  return '';
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};
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/**
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 * Returns an array of time zones that are consistent with user's platform
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 * setting. If user's country is given, only the time zone for that country is
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 * returned.
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 * @param {string=} opt_country 2 letter ISO 3166 country code. Helps in making
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 *     a better guess for user's time zone.
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 * @param {Date=} opt_date Date for retrieving timezone list. Defaults to the
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 *     current date.
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 * @return {!Array<string>} Array of time zone IDs.
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 */
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goog.locale.timeZoneDetection.getTimeZoneList = function(
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    opt_country, opt_date) {
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  var date = opt_date || new Date();
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  var fingerprint = goog.locale.timeZoneDetection.getFingerprint(date);
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  var timeZoneList = goog.locale.TimeZoneFingerprint[fingerprint];
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  if (!timeZoneList) {
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    return [];
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  }
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  var chosenList = [];
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  for (var i = 0; i < timeZoneList.length; i++) {
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    if (!opt_country || timeZoneList[i].indexOf(opt_country) == 0) {
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      chosenList.push(timeZoneList[i].substring(3));
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    }
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  }
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  return chosenList;
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};
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