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/**

* Copyright 2015 The AMP HTML Authors. All Rights Reserved.

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS-IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

/**

* @fileoverview Experiments system allows a developer to opt-in to test

* features that are not yet fully tested.

*

* Experiments page: https://cdn.ampproject.org/experiments.html *

*/

import {getCookie, setCookie} from './cookies';

import {parseQueryString} from './url';

/** @const {string} */

const COOKIE_NAME = 'AMP_EXP';

/** @const {number} */

const COOKIE_MAX_AGE_DAYS = 180; // 6 month

/** @const {time} */

const COOKIE_EXPIRATION_INTERVAL = COOKIE_MAX_AGE_DAYS * 24 * 60 * 60 * 1000;

/** @const {string} */

const CANARY_EXPERIMENT_ID = 'dev-channel';

/** @type {Object<string, boolean>|undefined} */

let toggles_;

/**

* A wrapper to avoid a static side-effect.

* @return {!Object<string, boolean>}

*/

function experimentToggles() {

return toggles_ || (toggles_ = Object.create(null));

}

/**

* Whether the scripts come from a dev channel.

* @param {!Window} win

* @return {boolean}

*/

export function isDevChannel(win) {

if (isExperimentOn(win, CANARY_EXPERIMENT_ID)) {

return true;

}

if (isDevChannelVersionDoNotUse_(win)) {

return true;

}

return false;

}

/**

* Whether the version corresponds to the dev-channel binary.

* @param {!Window} win

* @return {boolean}

* @private Visible for testing only!

*/

export function isDevChannelVersionDoNotUse_(win) {

return !!win.AMP_CONFIG && win.AMP_CONFIG.canary;

}

/**

* Whether the specified experiment is on or off.

* @param {!Window} win

* @param {string} experimentId

* @return {boolean}

*/

export function isExperimentOn(win, experimentId) {

const toggles = experimentToggles();

if (experimentId in toggles) {

return toggles[experimentId];

}

return toggles[experimentId] = calcExperimentOn(win, experimentId);

}

/**

* Check whether an experiment is on while allowing viewers to force

* the experiment state via a viewer URL param of the form:

* `e-$experimentId=1` (on) or `e-$experimentId=0` (off).

* NOTE: This should only be used if it is needed and if turning the

* experiment on or off does not have security implications.

* @param {!Window} win

* @param {string} experimentId

* @return {boolean}

*/

export function isExperimentOnAllowUrlOverride(win, experimentId) {

const hash = win.location.originalHash || win.location.hash;

if (hash) {

// Note: If this is used a lot, this should be optimized to only

// parse once per page load.

const param = parseQueryString(hash)['e-' + experimentId];

if (param == '1') {

return true;

}

if (param == '0') {

return false;

}

}

return isExperimentOn(win, experimentId);

}

/**

* Calculate whether the specified experiment is on or off based off of the

* cookieFlag or the global config frequency given.

* @param {!Window} win

* @param {string} experimentId

* @return {boolean}

*/

function calcExperimentOn(win, experimentId) {

const cookieFlag = getExperimentIds(win).indexOf(experimentId) != -1;

if (cookieFlag) {

return true;

}

if (win.AMP_CONFIG && win.AMP_CONFIG.hasOwnProperty(experimentId)) {

const frequency = win.AMP_CONFIG[experimentId];

return Math.random() < frequency;

}

return false;

}

/**

* Toggles the experiment on or off. Returns the actual value of the experiment

* after toggling is done.

* @param {!Window} win

* @param {string} experimentId

* @param {boolean=} opt_on

* @param {boolean=} opt_transientExperiment Whether to toggle the

* experiment state "transiently" (i.e., for this page load only) or

* durably (by saving the experiment IDs to the cookie after toggling).

* Default: false (save durably).

* @return {boolean} New state for experimentId.

*/

export function toggleExperiment(win, experimentId, opt_on,

opt_transientExperiment) {

const toggles = experimentToggles();

const experimentIds = getExperimentIds(win);

const currentlyOn = (experimentIds.indexOf(experimentId) != -1) ||

(experimentId in toggles && toggles[experimentId]);

const on = opt_on !== undefined ? opt_on : !currentlyOn;

if (on != currentlyOn) {

if (on) {

experimentIds.push(experimentId);

toggles[experimentId] = true;

} else {

experimentIds.splice(experimentIds.indexOf(experimentId), 1);

toggles[experimentId] = false;

}

if (!opt_transientExperiment) {

saveExperimentIds(win, experimentIds);

}

}

return on;

}

/**

* Returns a set of experiment IDs currently on.

* @param {!Window} win

* @return {!Array<string>}

*/

function getExperimentIds(win) {

if (win._experimentCookie) {

return win._experimentCookie;

}

const experimentCookie = getCookie(win, COOKIE_NAME);

return win._experimentCookie = (

experimentCookie ? experimentCookie.split(/\s*,\s*/g) : []);

}

/**

* Saves a set of experiment IDs currently on.

* @param {!Window} win

* @param {!Array<string>} experimentIds

*/

function saveExperimentIds(win, experimentIds) {

win._experimentCookie = null;

setCookie(win, COOKIE_NAME, experimentIds.join(','),

Date.now() + COOKIE_EXPIRATION_INTERVAL);

}

/**

* Resets the experimentsToggle cache for testing purposes.

* @visibleForTesting

*/

export function resetExperimentToggles_() {

toggles_ = undefined;

}