package  {
	/**
	 * simple circular stack for storing arrays
	 * @author voidSkipper
	 */
	public class Stack{
		private var head:StackElement;
		public var length:uint;

		public function Stack(elements:Array=null) {
			this.head = new StackElement();
			head.next = head;
			head.prev = head;
			head.data = ["This linked list is empty."];
			length = 0;
			if (elements == null) {
				elements = [];
			}
			while (elements.length != 0) {
				pushfront(elements.pop());
			}
		}

		//slowest function in this datatype.
		//o(1), O(n). errynyan else is constant.
		public function dataAt(at:uint):Array {
			if (at >= length) {
				return ["request out of range"];
			}
			var c:StackElement = head.next;
			while (at != 0) {
				c = c.next;
				at--;
			}
			return c.data;
		}

		public function pushback(data:Array):void {
			var oldlast:StackElement = head.prev;
			var newlast:StackElement = new StackElement(data, oldlast, head);
			oldlast.next = newlast;
			head.prev = newlast;
			length++;
		}

		public function pushfront(data:Array):void {
			var oldfirst:StackElement = head.next;
			var newfirst:StackElement = new StackElement(data, head, oldfirst);
			oldfirst.prev = newfirst;
			head.next = newfirst;
			length++;
		}

		public function popback():Array {
			if (length == 0) {
				return head.data;
			}
			var victim:StackElement = head.prev;
			victim.prev.next = head;
			head.prev = victim.prev;
			victim.prev = victim.next = null;
			length--;
			return victim.data;
		}

		public function popfront():Array {
			if (length == 0) {
				return head.data;
			}
			var victim:StackElement = head.next;
			victim.next.prev = head;
			head.next = victim.next;
			victim.prev = victim.next = null;
			length--;
			return victim.data;
		}

		public function toString():String {
			var o:String = "";
			var c:StackElement = head;
			var i:uint = 0;
			while (i < length) {
				c = c.next;
				o = o + "[" + i + "]" + c.data + "\n";
				i++
			}
			return o;
		}
	}

}