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

class linkedList {
  constructor(head = null, tail = null) {
    this.head = head;
    this.tail = tail;
    this.size = 0;
  }

  appendAtlast(data) {
    let node = new Node(data);
    if (this.head === null) {
      this.head = node;
      this.tail = node;
    } else {
      this.tail.next = node;
      node.previous = this.tail;
      this.tail = node;
    }
    this.size++;
  }

  addAtFirst(data) {
    let node = new Node(data);
    if (this.head === null) {
      this.head = node;
    } else {
      this.head.previous = node;
      node.next = this.head;
      this.head = node;
    }
    this.size++;
  }

  addAtIndex(data, index) {
    let node = new Node(data);

    if (index === 0) {
      this.addAtFirst(data);
      return;
    }
    if (index >= this.size) {
      return;
    }

    let count = 0;
    let current;
    while (count < index) {
      current = current.next;
      count++;
    }
    const previousNode = current.previous;
    previousNode.next = node;
    node.next = current;
    node.previous = previousNode;
    current.previous = node;
    this.size++;
  }

  remove() {
    if (this.tail) {
      this.size--;
      this.tail = this.tail.previous;
      if (this.tail) {
        this.tail.next = null;
      } else {
        this.head = null;
      }
    } else {
      this.head = null;
    }
  }

  removeAtIndex(index) {
    if (!Number.isInteger(index) || index < 0 || index > this.sixe) {
      console.log(`Invalid index. Current length is ${this.size}.`);
      return this;
    }

    if (index === 0) {
      this.head = this.head.next;
      this.head.previous = null;
      this.size--;
      return;
    }

    if (index === this.size - 1) {
      this.tail = this.tail.previous;
      this.tail.next = null;
      this.size--;
      return;
    }
    let count = 0;
    let current = this.head;
    while (count < index) {
      current = current.next;
      count++;
    }
    const previousNode = current.previous;
    const nextNode = current.next;
    previousNode.next = nextNode;
    nextNode.previous = previousNode;
    this.size--;
  }

  print() {
    let current = this.head;
    console.log("Size", this.size);
    while (current) {
      console.log(` ${current.data}`);
      current = current.next;
    }
  }
}

let ll = new linkedList();

ll.appendAtlast(100);
ll.appendAtlast(200);
ll.addAtFirst(99);
ll.appendAtlast(300);
ll.removeAtIndex(3);
ll.appendAtlast(300);
ll.remove();

ll.print();