"use strict";

const DoublyLinkedList = require("./DoublyLinkedList");
const DequeIterator = require("./DequeIterator");
/**
 * DoublyLinkedList backed double ended queue
 * implements just enough to keep the Pool
 */
class Deque {
  constructor() {
    this._list = new DoublyLinkedList();
  }

  /**
   * removes and returns the first element from the queue
   * @return {any} [description]
   */
  shift() {
    if (this.length === 0) {
      return undefined;
    }

    const node = this._list.head;
    this._list.remove(node);

    return node.data;
  }

  /**
   * adds one elemts to the beginning of the queue
   * @param  {any} element [description]
   * @return {any}         [description]
   */
  unshift(element) {
    const node = DoublyLinkedList.createNode(element);

    this._list.insertBeginning(node);
  }

  /**
   * adds one to the end of the queue
   * @param  {any} element [description]
   * @return {any}         [description]
   */
  push(element) {
    const node = DoublyLinkedList.createNode(element);

    this._list.insertEnd(node);
  }

  /**
   * removes and returns the last element from the queue
   */
  pop() {
    if (this.length === 0) {
      return undefined;
    }

    const node = this._list.tail;
    this._list.remove(node);

    return node.data;
  }

  [Symbol.iterator]() {
    return new DequeIterator(this._list);
  }

  iterator() {
    return new DequeIterator(this._list);
  }

  reverseIterator() {
    return new DequeIterator(this._list, true);
  }

  /**
   * get a reference to the item at the head of the queue
   * @return {any} [description]
   */
  get head() {
    if (this.length === 0) {
      return undefined;
    }
    const node = this._list.head;
    return node.data;
  }

  /**
   * get a reference to the item at the tail of the queue
   * @return {any} [description]
   */
  get tail() {
    if (this.length === 0) {
      return undefined;
    }
    const node = this._list.tail;
    return node.data;
  }

  get length() {
    return this._list.length;
  }
}

module.exports = Deque;