/*
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MIT License http://www.opensource.org/licenses/mit-license.php
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Author Tobias Koppers @sokra
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*/
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"use strict";
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/**
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* FIFO queue that keeps items unique by storing them in insertion order inside
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* a `Set`.
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* @template T
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*/
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class Queue {
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/**
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* Seeds the queue with an optional iterable of initial unique items.
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* @param {Iterable<T>=} items The initial elements.
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*/
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constructor(items) {
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/**
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* @private
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* @type {Set<T>}
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*/
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this._set = new Set(items);
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}
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/**
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* Returns the number of unique items currently waiting in the queue.
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* @returns {number} The number of elements in this queue.
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*/
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get length() {
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return this._set.size;
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}
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/**
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* Enqueues an item, moving nothing if that value is already present.
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* @param {T} item The element to add.
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* @returns {void}
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*/
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enqueue(item) {
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this._set.add(item);
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}
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/**
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* Removes and returns the oldest enqueued item.
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* @returns {T | undefined} The head of the queue of `undefined` if this queue is empty.
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*/
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dequeue() {
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const result = this._set[Symbol.iterator]().next();
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if (result.done) return;
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this._set.delete(result.value);
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return result.value;
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}
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}
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module.exports = Queue;
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