(function(){
 "use strict";

 function Node(element){
  this.element = element;
  this.next = null;
 }

 module.exports = Node;
})();

(function(){
 "use strict";

 var Node = require("./lib/SingleNode");

 function LinkedList(){
  this._head = new Node("This is Head Node.");
  this._size = 0;
 }

 LinkedList.prototype.isEmpty = function(){
  return this._size === 0;
 };

 LinkedList.prototype.size = function(){
  return this._size;
 };

 LinkedList.prototype.getHead = function(){
  return this._head;
 };

 LinkedList.prototype.display = function(){
  var currNode = this.getHead().next;
  while(currNode){
   console.log(currNode.element);
   currNode = currNode.next;
  }
 };

 LinkedList.prototype.remove = function(item){
  if(item) {
   var preNode = this.findPre(item);
   if(preNode == null)
    return ;
   if (preNode.next !== null) {
    preNode.next = preNode.next.next;
    this._size--;
   }
  }
 };

 LinkedList.prototype.add = function(item){
  this.insert(item);
 };

 LinkedList.prototype.insert = function(newElement, item){
  var newNode = new Node(newElement);
  var finder = item ? this.find(item) : null;
  if(!finder){
   var last = this.findLast();
   last.next = newNode;
  }
  else{
   newNode.next = finder.next;
   finder.next = newNode;
  }
  this._size++;
 };

 /*********************** Utility Functions ********************************/

 LinkedList.prototype.findLast = function(){
  var currNode = this.getHead();
  while(currNode.next){
   currNode = currNode.next;
  }
  return currNode;
 };

 LinkedList.prototype.findPre = function(item){
  var currNode = this.getHead();
  while(currNode.next !== null && currNode.next.element !== item){
   currNode = currNode.next;
  }
  return currNode;
 };

 LinkedList.prototype.find = function(item){
  if(item == null)
   return null;
  var currNode = this.getHead();
  while(currNode && currNode.element !== item){
   currNode = currNode.next;
  }
  return currNode;
 };

 module.exports = LinkedList;
})();

(function(){
 "use strict";

 function Node(element){
  this.element = element;
  this.next = null;
  this.previous = null;
 }

 module.exports = Node;
})();

(function(){
 "use strict";
 var Node = require("./lib/DoubleNode");

 function DoubleLinkedList(){
  this._head = new Node("This is Head Node.");
  this._size = 0;
 }

 DoubleLinkedList.prototype.getHead = function(){
  return this._head;
 };

 DoubleLinkedList.prototype.isEmpty = function(){
  return this._size === 0;
 };

 DoubleLinkedList.prototype.size = function(){
  return this._size;
 };

 DoubleLinkedList.prototype.findLast = function(){
  var currNode = this.getHead();
  while(currNode.next){
   currNode = currNode.next;
  }
  return currNode;
 };

 DoubleLinkedList.prototype.add = function(item){
  if(item == null)
   return null;
  this.insert(item);
 };

 DoubleLinkedList.prototype.remove = function(item){
  if(item) {
   var node = this.find(item);
   if(node == null)
    return ;
   if (node.next === null) {
    node.previous.next = null;
    node.previous = null;
   } else{
    node.previous.next = node.next;
    node.next.previous = node.previous;
    node.next = null;
    node.previous = null;
   }
   this._size--;
  }
 };

 DoubleLinkedList.prototype.find = function(item){
  if(item == null)
   return null;
  var currNode = this.getHead();
  while(currNode && currNode.element !== item){
   currNode = currNode.next;
  }
  return currNode;
 };

 DoubleLinkedList.prototype.insert = function(newElement, item){
  var newNode = new Node(newElement);
  var finder = item ? this.find(item) : null;
  if(!finder){
   var last = this.findLast();
   newNode.previous = last;
   last.next = newNode;
  }
  else{
   newNode.next = finder.next;
   newNode.previous = finder;
   finder.next.previous = newNode;
   finder.next = newNode;
  }
  this._size++;
 };

 DoubleLinkedList.prototype.dispReverse = function(){
  var currNode = this.findLast();
  while(currNode != this.getHead()){
   console.log(currNode.element);
   currNode = currNode.previous;
  }
 };

 DoubleLinkedList.prototype.display = function(){
  var currNode = this.getHead().next;
  while(currNode){
   console.log(currNode.element);
   currNode = currNode.next;
  }
 };

 module.exports = DoubleLinkedList;
})();