package DLList;

public class DLList<T> {

    private DLNode<T> head;
    private DLNode<T> last;
    private int size;

    public DLList() {
        this.head = null;
        this.last = null;
        this.size = 0;
    }

    public boolean isEmpty() {
        return this.head == null;
    }

    public int size() {

        return this.size;
    }

    private DLNode<T> nodeAt(int index) {

        DLNode<T> current;

        if (index < size() / 2) {
            current = this.head;
            for (int i = 0; i < index; i++) {
                current = current.next;

            }
        } else {
            current = this.last;
            for (int i = size()-1; i >= index; i--) {
                current = current.prev;
            }

        }
        return current;
    }

    public T get(int index) {

        return nodeAt(index).value;
    }

    public void add(int index, T e) {

        DLNode<T> newNode = new DLNode<T>(null, e, null);

        if(index == 0 && size() == 0){

            this.head = newNode;
            this.last = newNode;

        } else if (index == 0 && size() > 0) {

            newNode.next = this.head.prev;
            head.prev = newNode;
            head = newNode;


        } else if (index == size()) {
            newNode.prev = this.last.next;
            last.next = newNode;
            last = newNode;

        } else {

            DLNode<T> pred = nodeAt(index-1);

            newNode.next = pred.next;
            pred.next = newNode;

            pred.next.prev = newNode;
            newNode.prev = pred;


        }
        size++;
    }
}