class Node{
  constructor(data, nuxt =null){
    this.data = data;
    this.next = null;
  }
}

class LinkedList{
  constructor(){
    this.head = null;
  }
  //insertFirst
  insertFirst(data){
    this.head = new Node(data);
  }
  //insertLast
  insertLast(data){
    if(this.head === null){
      this.head = new Node(data);
    } else {
      let node = this.head;
      while(node.next){
        node = node.next;
      }
      node.next = new Node(data);
    }
  }

  //size
  size(){
    let node = this.head;
    let counter = 0;
    while(node){
      node = node.next;
      counter++;
    }
    return counter;
  }
  //getFirst
  getFirst(){
    return this.head;
  }
  //getLast
  getLast(){
    let node = this.head;
    while(node){
      if(!node.next){
        return node;
      }
      node = node.next;
    }
  }
  //insertFirst
  insertFirst(item){
    this.head = new _Node(item, this.head);
   }
  //getAt
  getAt(index){
    let node = this.head;
    let counter = 0;
    while(node){
      if(index === counter){
        return node;
      }
      node = node.next;
      counter++;
    }
  }
  //removeAt
  removeAt(index){
    let previous = this.getAt(index-1);
    previous.next = previous.next.next;
  }
  //insertAt
  insertAt(index, data){
    let previous = this.getAt(index-1);
    const node = new Node(data, previous.next);
    previous.next = new Node(data);
  }
  //reverse
  reverse(){
    let curr = this.head;
    let previous = null;
    while(curr){
      let next = curr.next;
       curr.next = previous;
       previous = curr;
       curr = next;
    }
    return previous;
  }

  insertAfter(inList, insertVal){
    let node = this.head;
    while(node){
      if(node.data === inList){
        node.next = new Node(insertVal);
      }
      node = node.next;
    }
  }

  insertBefore(inList, insertVal){
    if(this.head.data === inList){
      this.head = new Node(insertVal);
    }
    let previous = this.head;
    let curr = this.head.next;
    while(curr){
      // console.log('this is curr', curr);
      if(curr.data === inList){
        console.log('this is firing');
        previous.next = new Node(insertVal);
      }
      previous = curr;
      curr = curr.next;
    }
  }
  thirdFromEnd(){
    let countTo = this.size()-3;
    console.log('this is countTo', countTo);
    let counter = 0;
    let node = this.head;
    while(node.nnext){
      if(counter === countTo){
        return node;
      }
      node = node.next;
      counter++;
    }
  }

  Middle(){
    let fast = this.head;
    let slow = this.head;
    while(fast.next && fast.next.next){
      slow = slow.next;
      fast = fast.next.next;
    }
    return slow;
  }

  Cycle(){
    let fast = this.head;
    let slow = this.head;
    while(fast.next && fast.next.next){
      if(slow === fast){
        return true;
      }
      slow = slow.next;
      fast= fast.next.next;
    }
    return false;
  }


}//class end
let pets = new LinkedList();
pets.insertLast('kitten');
pets.insertLast('puppy');
pets.insertLast('parrot');
pets.insertLast('hamster');
pets.insertLast('farrett');
console.log(pets.Middle());