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				|  |  | +/*
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				|  |  | + *
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				|  |  | + * Copyright 2015, Google Inc.
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				|  |  | + * All rights reserved.
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				|  |  | + *
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				|  |  | + * Redistribution and use in source and binary forms, with or without
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				|  |  | + * modification, are permitted provided that the following conditions are
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				|  |  | + * met:
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				|  |  | + *
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				|  |  | + *     * Redistributions of source code must retain the above copyright
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				|  |  | + * notice, this list of conditions and the following disclaimer.
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				|  |  | + *     * Redistributions in binary form must reproduce the above
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				|  |  | + * copyright notice, this list of conditions and the following disclaimer
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				|  |  | + * in the documentation and/or other materials provided with the
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				|  |  | + * distribution.
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				|  |  | + *     * Neither the name of Google Inc. nor the names of its
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				|  |  | + * contributors may be used to endorse or promote products derived from
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				|  |  | + * this software without specific prior written permission.
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				|  |  | + *
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				|  |  | + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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				|  |  | + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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				|  |  | + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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				|  |  | + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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				|  |  | + * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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				|  |  | + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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				|  |  | + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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				|  |  | + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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				|  |  | + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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				|  |  | + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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				|  |  | + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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				|  |  | + *
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				|  |  | + */
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				|  |  | +
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				|  |  | +'use strict';
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				|  |  | +
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				|  |  | +var _ = require('lodash');
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				|  |  | +
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				|  |  | +/**
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				|  |  | + * This class represents a queue of callbacks that must happen sequentially, each
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				|  |  | + * with a specific delay after the previous event.
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				|  |  | + */
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				|  |  | +function AsyncDelayQueue() {
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				|  |  | +  this.queue = [];
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				|  |  | +
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				|  |  | +  this.callback_pending = false;
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				|  |  | +}
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				|  |  | +
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				|  |  | +/**
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				|  |  | + * Run the next callback after its corresponding delay, if there are any
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				|  |  | + * remaining.
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				|  |  | + */
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				|  |  | +AsyncDelayQueue.prototype.runNext = function() {
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				|  |  | +  var next = this.queue.shift();
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				|  |  | +  var continueCallback = _.bind(this.runNext, this);
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				|  |  | +  if (next) {
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				|  |  | +    this.callback_pending = true;
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				|  |  | +    setTimeout(function() {
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				|  |  | +      next.callback(continueCallback);
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				|  |  | +    }, next.delay);
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				|  |  | +  } else {
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				|  |  | +    this.callback_pending = false;
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				|  |  | +  }
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				|  |  | +};
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				|  |  | +
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				|  |  | +/**
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				|  |  | + * Add a callback to be called with a specific delay after now or after the
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				|  |  | + * current last item in the queue or current pending callback, whichever is
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				|  |  | + * latest.
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				|  |  | + * @param {function(function())} callback The callback
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				|  |  | + * @param {Number} The delay to apply, in milliseconds
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				|  |  | + */
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				|  |  | +AsyncDelayQueue.prototype.add = function(callback, delay) {
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				|  |  | +  this.queue.push({callback: callback, delay: delay});
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				|  |  | +  if (!this.callback_pending) {
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				|  |  | +    this.runNext();
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				|  |  | +  }
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				|  |  | +};
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				|  |  | +
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				|  |  | +module.exports = AsyncDelayQueue;
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