/*
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Queue.js
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A function to represent a queue
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Created by Kate Morley - http://code.iamkate.com/ - and released under the terms
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of the CC0 1.0 Universal legal code:
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http://creativecommons.org/publicdomain/zero/1.0/legalcode
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*/
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var MAX_UNUSED_ARRAY_SIZE = 10000
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/* Creates a new queue. A queue is a first-in-first-out (FIFO) data structure -
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* items are added to the end of the queue and removed from the front.
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*/
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function Queue() {
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// initialise the queue and offset
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var queue = []
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var offset = 0
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// Returns the length of the queue.
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this.getLength = function () {
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return (queue.length - offset)
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}
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/* Enqueues the specified item. The parameter is:
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*
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* item - the item to enqueue
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*/
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this.enqueue = function (item) {
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queue.push(item)
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}
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/* Dequeues an item and returns it. If the queue is empty, the value
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* 'undefined' is returned.
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*/
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this.dequeue = function () {
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// if the queue is empty, return immediately
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if (queue.length === 0) {
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return undefined
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}
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// store the item at the front of the queue
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var item = queue[offset]
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// increment the offset and remove the free space if necessary
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if (++offset > MAX_UNUSED_ARRAY_SIZE) {
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queue = queue.slice(offset)
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offset = 0
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}
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// return the dequeued item
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return item
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}
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}
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module.exports = Queue
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