/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

/**
 * @template T
 */
class Node {
	/**
	 * @param {T} value the value
	 */
	constructor(value) {
		this.value = value;
		/** @type {Node<T> | undefined} */
		this.next = undefined;
	}
}

/**
 * @template T
 */
class Queue {
	constructor() {
		this._head = undefined;
		this._tail = undefined;
		this._size = 0;
	}

	/**
	 * Appends the specified element to this queue.
	 * @param {T} item The element to add.
	 * @returns {void}
	 */
	enqueue(item) {
		const node = new Node(item);

		if (this._head) {
			/** @type {Node<T>} */
			(this._tail).next = node;
			this._tail = node;
		} else {
			this._head = node;
			this._tail = node;
		}

		this._size++;
	}

	/**
	 * Retrieves and removes the head of this queue.
	 * @returns {T | undefined} The head of the queue of `undefined` if this queue is empty.
	 */
	dequeue() {
		const current = this._head;
		if (!current) {
			return;
		}

		this._head = this._head.next;
		this._size--;
		return current.value;
	}

	/**
	 * Returns the number of elements in this queue.
	 * @returns {number} The number of elements in this queue.
	 */
	get length() {
		return this._size;
	}

	*[Symbol.iterator]() {
		let current = this._head;

		while (current) {
			yield current.value;
			current = current.next;
		}
	}
}

module.exports = Queue;