package Queue

public class Queue<T>
	private SEntry<T> dummy
	private SEntry<T> front
	private SEntry<T> back
	private int size = 0

	construct()
		dummy = new SEntry<T>(null, null)
		front = dummy
		back = dummy

	function peek() returns T
		return front.elem

	// add an element
	function enqueue(T elem)
		if front == dummy
			front = new SEntry(elem, dummy)
			back = front
			front.next = dummy
		else
			back.next = new SEntry(elem, dummy)
			back = back.next
		size++

	// get & remove the top element
	function dequeue() returns T
		let tmp = front
		front = front.next
		size--
		return tmp.elem


	// add all elements from elems to this queue
	function addAll(Queue<T> elems)
		for T elem in elems
			enqueue(elem)


	// gets the size of the queue
	function getSize() returns int
		return size

	// get an iterator for this queue
	function iterator() returns SIterator<T>
		return new SIterator(dummy, front)

	ondestroy
		SEntry<T> current = front
		while current != dummy
			let temp = current
			current = current.next
			destroy temp
		destroy dummy

class SEntry<S>
	S elem
	SEntry<S> next

	construct(S elem, SEntry<S> next)
		this.elem = elem
		this.next = next

class SIterator<Q>
	SEntry<Q> dummy
	SEntry<Q> current

	construct(SEntry<Q> dummy, SEntry<Q> front)
		this.dummy = dummy
		this.current = front

	// remove the current element from the queue
	function remove()
		if current != dummy
			let cp = current.next
			destroy current
			current = cp


	function hasNext() returns boolean
		return current != dummy

	function next() returns Q
		let tmp = current
		current = current.next
		return tmp.elem

	function close()
		destroy this