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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 Defines a class useful for handling functions that must be
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 * invoked later when some condition holds. Examples include deferred function
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 * calls that return a boolean flag whether it succedeed or not.
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 *
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 * Example:
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 *
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 *  function deferred() {
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 *     var succeeded = false;
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 *     // ... custom code
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 *     return succeeded;
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 *  }
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 *
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 *  var deferredCall = new goog.async.ConditionalDelay(deferred);
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 *  deferredCall.onSuccess = function() {
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 *    alert('Success: The deferred function has been successfully executed.');
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 *  }
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 *  deferredCall.onFailure = function() {
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 *    alert('Failure: Time limit exceeded.');
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 *  }
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 *
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 *  // Call the deferred() every 100 msec until it returns true,
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 *  // or 5 seconds pass.
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 *  deferredCall.start(100, 5000);
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 *
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 *  // Stop the deferred function call (does nothing if it's not active).
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 *  deferredCall.stop();
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 *
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 */
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goog.provide('goog.async.ConditionalDelay');
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goog.require('goog.Disposable');
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goog.require('goog.async.Delay');
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/**
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 * A ConditionalDelay object invokes the associated function after a specified
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 * interval delay and checks its return value. If the function returns
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 * {@code true} the conditional delay is cancelled and {@see #onSuccess}
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 * is called. Otherwise this object keeps to invoke the deferred function until
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 * either it returns {@code true} or the timeout is exceeded. In the latter case
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 * the {@see #onFailure} method will be called.
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 *
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 * The interval duration and timeout can be specified each time the delay is
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 * started. Calling start on an active delay will reset the timer.
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 *
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 * @param {function():boolean} listener Function to call when the delay
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 *     completes. Should return a value that type-converts to {@code true} if
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 *     the call succeeded and this delay should be stopped.
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 * @param {Object=} opt_handler The object scope to invoke the function in.
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 * @constructor
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 * @struct
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 * @extends {goog.Disposable}
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 */
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goog.async.ConditionalDelay = function(listener, opt_handler) {
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  goog.async.ConditionalDelay.base(this, 'constructor');
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  /**
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   * The delay interval in milliseconds to between the calls to the callback.
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   * Note, that the callback may be invoked earlier than this interval if the
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   * timeout is exceeded.
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   * @private {number}
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   */
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  this.interval_ = 0;
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  /**
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   * The timeout timestamp until which the delay is to be executed.
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   * A negative value means no timeout.
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   * @private {number}
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   */
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  this.runUntil_ = 0;
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  /**
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   * True if the listener has been executed, and it returned {@code true}.
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   * @private {boolean}
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   */
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  this.isDone_ = false;
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  /**
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   * The function that will be invoked after a delay.
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   * @private {function():boolean}
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   */
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  this.listener_ = listener;
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  /**
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   * The object context to invoke the callback in.
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   * @private {Object|undefined}
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   */
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  this.handler_ = opt_handler;
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  /**
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   * The underlying goog.async.Delay delegate object.
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   * @private {goog.async.Delay}
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   */
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  this.delay_ = new goog.async.Delay(
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      goog.bind(this.onTick_, this), 0 /*interval*/, this /*scope*/);
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};
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goog.inherits(goog.async.ConditionalDelay, goog.Disposable);
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/** @override */
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goog.async.ConditionalDelay.prototype.disposeInternal = function() {
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  this.delay_.dispose();
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  delete this.listener_;
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  delete this.handler_;
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  goog.async.ConditionalDelay.superClass_.disposeInternal.call(this);
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};
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/**
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 * Starts the delay timer. The provided listener function will be called
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 * repeatedly after the specified interval until the function returns
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 * {@code true} or the timeout is exceeded. Calling start on an active timer
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 * will stop the timer first.
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 * @param {number=} opt_interval The time interval between the function
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 *     invocations (in milliseconds). Default is 0.
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 * @param {number=} opt_timeout The timeout interval (in milliseconds). Takes
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 *     precedence over the {@code opt_interval}, i.e. if the timeout is less
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 *     than the invocation interval, the function will be called when the
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 *     timeout is exceeded. A negative value means no timeout. Default is 0.
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 */
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goog.async.ConditionalDelay.prototype.start = function(
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    opt_interval, opt_timeout) {
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  this.stop();
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  this.isDone_ = false;
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  var timeout = opt_timeout || 0;
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  this.interval_ = Math.max(opt_interval || 0, 0);
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  this.runUntil_ = timeout < 0 ? -1 : (goog.now() + timeout);
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  this.delay_.start(
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      timeout < 0 ? this.interval_ : Math.min(this.interval_, timeout));
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};
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/**
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 * Stops the delay timer if it is active. No action is taken if the timer is not
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 * in use.
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 */
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goog.async.ConditionalDelay.prototype.stop = function() {
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  this.delay_.stop();
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};
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/**
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 * @return {boolean} True if the delay is currently active, false otherwise.
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 */
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goog.async.ConditionalDelay.prototype.isActive = function() {
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  return this.delay_.isActive();
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};
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/**
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 * @return {boolean} True if the listener has been executed and returned
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 *     {@code true} since the last call to {@see #start}.
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 */
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goog.async.ConditionalDelay.prototype.isDone = function() {
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  return this.isDone_;
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};
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/**
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 * Called when the listener has been successfully executed and returned
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 * {@code true}. The {@see #isDone} method should return {@code true} by now.
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 * Designed for inheritance, should be overridden by subclasses or on the
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 * instances if they care.
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 */
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goog.async.ConditionalDelay.prototype.onSuccess = function() {
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  // Do nothing by default.
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};
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/**
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 * Called when this delayed call is cancelled because the timeout has been
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 * exceeded, and the listener has never returned {@code true}.
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 * Designed for inheritance, should be overridden by subclasses or on the
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 * instances if they care.
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 */
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goog.async.ConditionalDelay.prototype.onFailure = function() {
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  // Do nothing by default.
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};
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/**
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 * A callback function for the underlying {@code goog.async.Delay} object. When
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 * executed the listener function is called, and if it returns {@code true}
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 * the delay is stopped and the {@see #onSuccess} method is invoked.
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 * If the timeout is exceeded the delay is stopped and the
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 * {@see #onFailure} method is called.
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 * @private
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 */
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goog.async.ConditionalDelay.prototype.onTick_ = function() {
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  var successful = this.listener_.call(this.handler_);
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  if (successful) {
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    this.isDone_ = true;
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    this.onSuccess();
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  } else {
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    // Try to reschedule the task.
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    if (this.runUntil_ < 0) {
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      // No timeout.
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      this.delay_.start(this.interval_);
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    } else {
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      var timeLeft = this.runUntil_ - goog.now();
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      if (timeLeft <= 0) {
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        this.onFailure();
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      } else {
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        this.delay_.start(Math.min(this.interval_, timeLeft));
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      }
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    }
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  }
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};
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