text: // Copyright 2008 The Closure Library 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 Defines a class useful for handling functions that must be
   * invoked later when some condition holds. Examples include deferred function
   * calls that return a boolean flag whether it succedeed or not.
   *
   * Example:
   *
   *  function deferred() {
   *     var succeeded = false;
   *     // ... custom code
   *     return succeeded;
   *  }
   *
   *  var deferredCall = new goog.async.ConditionalDelay(deferred);
   *  deferredCall.onSuccess = function() {
   *    alert('Success: The deferred function has been successfully executed.');
   *  }
   *  deferredCall.onFailure = function() {
   *    alert('Failure: Time limit exceeded.');
   *  }
   *
   *  // Call the deferred() every 100 msec until it returns true,
   *  // or 5 seconds pass.
   *  deferredCall.start(100, 5000);
   *
   *  // Stop the deferred function call (does nothing if it's not active).
   *  deferredCall.stop();
   *
   */
  
  
  goog.provide('goog.async.ConditionalDelay');
  
  goog.require('goog.Disposable');
  goog.require('goog.async.Delay');
  
  
  
  /**
   * A ConditionalDelay object invokes the associated function after a specified
   * interval delay and checks its return value. If the function returns
   * `true` the conditional delay is cancelled and {@see #onSuccess}
   * is called. Otherwise this object keeps to invoke the deferred function until
   * either it returns `true` or the timeout is exceeded. In the latter case
   * the {@see #onFailure} method will be called.
   *
   * The interval duration and timeout can be specified each time the delay is
   * started. Calling start on an active delay will reset the timer.
   *
   * @param {function():boolean} listener Function to call when the delay
   *     completes. Should return a value that type-converts to `true` if
   *     the call succeeded and this delay should be stopped.
   * @param {Object=} opt_handler The object scope to invoke the function in.
   * @constructor
   * @struct
   * @extends {goog.Disposable}
   */
  goog.async.ConditionalDelay = function(listener, opt_handler) {
    goog.async.ConditionalDelay.base(this, 'constructor');
  
    /**
     * The delay interval in milliseconds to between the calls to the callback.
     * Note, that the callback may be invoked earlier than this interval if the
     * timeout is exceeded.
     * @private {number}
     */
    this.interval_ = 0;
  
    /**
     * The timeout timestamp until which the delay is to be executed.
     * A negative value means no timeout.
     * @private {number}
     */
    this.runUntil_ = 0;
  
    /**
     * True if the listener has been executed, and it returned `true`.
     * @private {boolean}
     */
    this.isDone_ = false;
  
    /**
     * The function that will be invoked after a delay.
     * @private {function():boolean}
     */
    this.listener_ = listener;
  
    /**
     * The object context to invoke the callback in.
     * @private {Object|undefined}
     */
    this.handler_ = opt_handler;
  
    /**
     * The underlying goog.async.Delay delegate object.
     * @private {goog.async.Delay}
     */
    this.delay_ = new goog.async.Delay(
        goog.bind(this.onTick_, this), 0 /*interval*/, this /*scope*/);
  };
  goog.inherits(goog.async.ConditionalDelay, goog.Disposable);
  
  
  /** @override */
  goog.async.ConditionalDelay.prototype.disposeInternal = function() {
    this.delay_.dispose();
    delete this.listener_;
    delete this.handler_;
    goog.async.ConditionalDelay.superClass_.disposeInternal.call(this);
  };
  
  
  /**
   * Starts the delay timer. The provided listener function will be called
   * repeatedly after the specified interval until the function returns
   * `true` or the timeout is exceeded. Calling start on an active timer
   * will stop the timer first.
   * @param {number=} opt_interval The time interval between the function
   *     invocations (in milliseconds). Default is 0.
   * @param {number=} opt_timeout The timeout interval (in milliseconds). Takes
   *     precedence over the `opt_interval`, i.e. if the timeout is less
   *     than the invocation interval, the function will be called when the
   *     timeout is exceeded. A negative value means no timeout. Default is 0.
   */
  goog.async.ConditionalDelay.prototype.start = function(
      opt_interval, opt_timeout) {
    this.stop();
    this.isDone_ = false;
  
    var timeout = opt_timeout || 0;
    this.interval_ = Math.max(opt_interval || 0, 0);
    this.runUntil_ = timeout < 0 ? -1 : (goog.now() + timeout);
    this.delay_.start(
        timeout < 0 ? this.interval_ : Math.min(this.interval_, timeout));
  };
  
  
  /**
   * Stops the delay timer if it is active. No action is taken if the timer is not
   * in use.
   */
  goog.async.ConditionalDelay.prototype.stop = function() {
    this.delay_.stop();
  };
  
  
  /**
   * @return {boolean} True if the delay is currently active, false otherwise.
   */
  goog.async.ConditionalDelay.prototype.isActive = function() {
    return this.delay_.isActive();
  };
  
  
  /**
   * @return {boolean} True if the listener has been executed and returned
   *     `true` since the last call to {@see #start}.
   */
  goog.async.ConditionalDelay.prototype.isDone = function() {
    return this.isDone_;
  };
  
  
  /**
   * Called when the listener has been successfully executed and returned
   * `true`. The {@see #isDone} method should return `true` by now.
   * Designed for inheritance, should be overridden by subclasses or on the
   * instances if they care.
   */
  goog.async.ConditionalDelay.prototype.onSuccess = function() {
    // Do nothing by default.
  };
  
  
  /**
   * Called when this delayed call is cancelled because the timeout has been
   * exceeded, and the listener has never returned `true`.
   * Designed for inheritance, should be overridden by subclasses or on the
   * instances if they care.
   */
  goog.async.ConditionalDelay.prototype.onFailure = function() {
    // Do nothing by default.
  };
  
  
  /**
   * A callback function for the underlying `goog.async.Delay` object. When
   * executed the listener function is called, and if it returns `true`
   * the delay is stopped and the {@see #onSuccess} method is invoked.
   * If the timeout is exceeded the delay is stopped and the
   * {@see #onFailure} method is called.
   * @private
   */
  goog.async.ConditionalDelay.prototype.onTick_ = function() {
    var successful = this.listener_.call(this.handler_);
    if (successful) {
      this.isDone_ = true;
      this.onSuccess();
    } else {
      // Try to reschedule the task.
      if (this.runUntil_ < 0) {
        // No timeout.
        this.delay_.start(this.interval_);
      } else {
        var timeLeft = this.runUntil_ - goog.now();
        if (timeLeft <= 0) {
          this.onFailure();
        } else {
          this.delay_.start(Math.min(this.interval_, timeLeft));
        }
      }
    }
  };
  