/**
* @license
* Copyright The Closure Library Authors.
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @fileoverview Functions for detecting user's time zone.
* This work is based on Charlie Luo and Hong Yan's time zone detection work
* for CBG.
*/
goog.provide('goog.locale.timeZoneDetection');
goog.require('goog.asserts');
goog.require('goog.locale.TimeZoneFingerprint');
/**
* Whether to use the native API for time zone detection (if the runtime
* supports it). You might turn this off if a downstream system can't handle a
* user's timezone as reported by the browser.
* @define {boolean}
*/
goog.locale.timeZoneDetection.USE_NATIVE_TIMEZONE_DETECTION = goog.define(
'goog.locale.timeZoneDetection.USE_NATIVE_TIMEZONE_DETECTION',
goog.FEATURESET_YEAR >= 2021);
/**
* Whether to include the fingerprint algorithm so it can be used as a fallback.
* Without this, the code may be stripped for modern browsers that can be
* assumed to support the native API.
* @define {boolean}
*/
goog.locale.timeZoneDetection.INCLUDE_FINGERPRINT_DETECTION = goog.define(
'goog.locale.timeZoneDetection.INCLUDE_FINGERPRINT_DETECTION',
!goog.locale.timeZoneDetection.USE_NATIVE_TIMEZONE_DETECTION);
/** @private {boolean} */
goog.locale.timeZoneDetection.useNativeTimezoneDetection_ =
goog.locale.timeZoneDetection.USE_NATIVE_TIMEZONE_DETECTION;
/**
* Allows disabling the use of native APIs so that the fingerprinting algorithm
* can be tested.
* @param {boolean} useNative
*/
goog.locale.timeZoneDetection.useNativeTimezoneDetectionForTesting = function(
useNative) {
goog.locale.timeZoneDetection.useNativeTimezoneDetection_ = useNative;
};
/**
* Array of time instances for checking the time zone offset.
* @type {Array<number>}
* @private
*/
goog.locale.timeZoneDetection.TZ_POKE_POINTS_ = [
1109635200, 1128902400, 1130657000, 1143333000, 1143806400, 1145000000,
1146380000, 1152489600, 1159800000, 1159500000, 1162095000, 1162075000,
1162105500
];
/**
* Calculates time zone fingerprint by poking time zone offsets for 13
* preselected time points.
* See {@link goog.locale.timeZoneDetection.TZ_POKE_POINTS_}
* @param {Date} date Date for calculating the fingerprint.
* @return {number} Fingerprint of user's time zone setting.
*/
goog.locale.timeZoneDetection.getFingerprint = function(date) {
'use strict';
var hash = 0;
var stdOffset;
var isComplex = false;
for (var i = 0; i < goog.locale.timeZoneDetection.TZ_POKE_POINTS_.length;
i++) {
date.setTime(goog.locale.timeZoneDetection.TZ_POKE_POINTS_[i] * 1000);
var offset = date.getTimezoneOffset() / 30 + 48;
if (i == 0) {
stdOffset = offset;
} else if (stdOffset != offset) {
isComplex = true;
}
hash = (hash << 2) ^ offset;
}
return isComplex ? hash : /** @type {number} */ (stdOffset);
};
/**
* @return {string?} The local timezone, if the browser supports it and the
* functionality is enabled.
* @private
*/
goog.locale.timeZoneDetection.getNatively_ = function() {
if (!goog.locale.timeZoneDetection.useNativeTimezoneDetection_) {
return null;
}
if (typeof Intl == 'undefined' || typeof Intl.DateTimeFormat == 'undefined') {
return null;
}
const dateTimeFormat = new Intl.DateTimeFormat();
if (typeof dateTimeFormat.resolvedOptions == 'undefined') {
return null;
}
return dateTimeFormat.resolvedOptions().timeZone || null;
};
/**
* Detects browser's time zone setting. If user's country is known, a better
* time zone choice could be guessed. Note that in many browsers this is
* available natively as `new Intl.DateTimeFormat().resolvedOptions().timeZone`.
* @param {string=} opt_country Two-letter ISO 3166 country code.
* @param {Date=} opt_date Date for calculating the fingerprint. Defaults to the
* current date.
* @return {string} Time zone ID of best guess.
*/
goog.locale.timeZoneDetection.detectTimeZone = function(opt_country, opt_date) {
'use strict';
goog.asserts.assert(
goog.locale.timeZoneDetection.USE_NATIVE_TIMEZONE_DETECTION ||
goog.locale.timeZoneDetection.INCLUDE_FINGERPRINT_DETECTION,
'At least one of USE_NATIVE_TIMEZONE_DETECTION or ' +
'INCLUDE_FINGERPRINT_DETECTION must be true');
const nativeResult = goog.locale.timeZoneDetection.getNatively_();
if (nativeResult != null) {
return nativeResult;
}
if (!goog.locale.timeZoneDetection.useNativeTimezoneDetection_ ||
goog.locale.timeZoneDetection.INCLUDE_FINGERPRINT_DETECTION) {
var date = opt_date || new Date();
var fingerprint = goog.locale.timeZoneDetection.getFingerprint(date);
var timeZoneList = goog.locale.TimeZoneFingerprint[fingerprint];
// Timezones in goog.locale.TimeZoneDetection.TimeZoneMap are in the format
// US-America/Los_Angeles. Country code needs to be stripped before a
// timezone is returned.
if (timeZoneList) {
if (opt_country) {
for (var i = 0; i < timeZoneList.length; ++i) {
if (timeZoneList[i].indexOf(opt_country) == 0) {
return timeZoneList[i].substring(3);
}
}
}
return timeZoneList[0].substring(3);
}
}
return '';
};
/**
* Returns an array of time zones that are consistent with user's platform
* setting. If user's country is given, only the time zone for that country is
* returned.
* @param {string=} opt_country 2 letter ISO 3166 country code. Helps in making
* a better guess for user's time zone.
* @param {Date=} opt_date Date for retrieving timezone list. Defaults to the
* current date.
* @return {!Array<string>} Array of time zone IDs.
*/
goog.locale.timeZoneDetection.getTimeZoneList = function(
opt_country, opt_date) {
'use strict';
var date = opt_date || new Date();
var fingerprint = goog.locale.timeZoneDetection.getFingerprint(date);
var timeZoneList = goog.locale.TimeZoneFingerprint[fingerprint];
if (!timeZoneList) {
return [];
}
var chosenList = [];
for (var i = 0; i < timeZoneList.length; i++) {
if (!opt_country || timeZoneList[i].indexOf(opt_country) == 0) {
chosenList.push(timeZoneList[i].substring(3));
}
}
return chosenList;
};
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