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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.

*/

/**

* Helper with all things Timer.

*/

export class Timer {

/**

* @param {!Window} win

*/

constructor(win) {

/** @const {!Window} */

this.win = win;

/** @private @const {!Promise} */

this.resolved_ = Promise.resolve();

this.taskCount_ = 0;

this.canceled_ = {};

}

/**

* Returns the current EPOC time in milliseconds.

* @return {number}

*/

now() {

// TODO(dvoytenko): when can we use Date.now?

return Number(new Date());

}

/**

* Runs the provided callback after the specified delay. This uses a micro

* task for 0 or no specified time. This means that the delay will actually

* be close to 0 and this will NOT yield to the event queue.

*

* Returns the timer ID that can be used to cancel the timer (cancel method).

* @param {!function()} callback

* @param {number=} opt_delay

* @return {number|string}

*/

delay(callback, opt_delay) {

if (!opt_delay) {

// For a delay of zero, schedule a promise based micro task since

// they are predictably fast.

var id = 'p' + this.taskCount_++;

this.resolved_.then(() => {

if (this.canceled_[id]) {

delete this.canceled_[id];

return;

}

callback();

});

return id;

}

return this.win.setTimeout(callback, opt_delay);

}

/**

* Cancels the previously scheduled callback.

* @param {number|string} timeoutId

*/

cancel(timeoutId) {

if (typeof timeoutId == 'string') {

this.canceled_[timeoutId] = true;

return;

}

this.win.clearTimeout(timeoutId);

}

/**

* Returns a promise that will resolve after the delay. Optionally, the

* resolved value can be provided as opt_result argument.

* @param {number=} opt_delay

* @param {RESULT=} opt_result

* @return {!Promise<RESULT>}

* @template RESULT

*/

promise(opt_delay, opt_result) {

var timerKey = null;

return new Promise((resolve, reject) => {

timerKey = this.delay(() => {

timerKey = -1;

resolve(opt_result);

}, opt_delay);

if (timerKey == -1) {

reject(new Error('Failed to schedule timer.'));

}

}).catch((error) => {

// Clear the timer. The most likely reason is "cancel" signal.

if (timerKey != -1) {

this.cancel(timerKey);

}

return Promise.reject(error);

});

}

/**

* Returns a promise that will fail after the specified delay. Optionally,

* this method can take opt_racePromise parameter. In this case, the

* resulting promise will either fail when the specified delay expires or

* will resolve based on the opt_racePromise, whichever happens first.

* @param {number} delay

* @param {!Promise<RESULT>|undefined} opt_racePromise

* @return {!Promise<RESULT>}

* @template RESULT

*/

timeoutPromise(delay, opt_racePromise) {

var timerKey = null;

var delayPromise = new Promise((resolve, reject) => {

timerKey = this.delay(() => {

timerKey = -1;

reject('timeout');

}, delay);

if (timerKey == -1) {

reject(new Error('Failed to schedule timer.'));

}

}).catch((error) => {

// Clear the timer. The most likely reason is "cancel" signal.

if (timerKey != -1) {

this.cancel(timerKey);

}

return Promise.reject(error);

});

if (!opt_racePromise) {

return delayPromise;

}

return Promise.race([delayPromise, opt_racePromise]);

}

}

export const timer = new Timer(window);