package queue;
import java.util.*;

public class FifoQueue<E> extends AbstractQueue<E> implements Queue<E> {
	private QueueNode<E> last;
	private int size=0;
	private FifoQueue<E> queue;

	public FifoQueue() {
		queue = new FifoQueue<E>();
	}

	/**
	 * Returns an iterator over the elements in this queue
	 * @return an iterator over the elements in this queue
	 */
	public Iterator<E> iterator() {
		return queue.iterator();
	}

	/**
	 * Returns the number of elements in this queue
	 * @return the number of elements in this queue
	 */
	public int size() {
		return size;
	}

	/**
	 * Inserts the specified element into this queue, if possible
	 * post:	The specified element is added to the rear of this queue
	 * @param	x the element to insert
	 * @return	true if it was possible to add the element
	 * 			to this queue, else false
	 */
	public boolean offer(E x) {
		if(queue.add(x)){
		size++;
		return true;
		} else  {
			return false;
		}
	}

	/**
	 * Retrieves and removes the head of this queue,
	 * or null if this queue is empty.
	 * post:	the head of the queue is removed if it was not empty
	 * @return 	the head of this queue, or null if the queue is empty
	 */
	public E poll() {
		if(queue.size() > 0) {
			size=size-1;
		}
		return queue.poll();
	}

	/**
	 * Retrieves, but does not remove, the head of this queue,
	 * returning null if this queue is empty
	 * @return 	the head element of this queue, or null
	 * 			if this queue is empty
	 */
	public E peek() {
		return queue.peek();
	}


	private static class QueueNode<E> {
		E element;
		QueueNode<E> next;

		private QueueNode(E x) {
			element = x;
			next = null;
		}

	}

}