using System;
using System.Diagnostics;


namespace SpaceInvaders
{
    public class ReverseIterator : TreeIterator
    {
        //-------------------------------------------------------------------
        //  FIELDS
        //-------------------------------------------------------------------

        private Component pRoot;
        private Component pCurr;
        private Component pPrev;

        //-------------------------------------------------------------------
        //  CLASS METHODS
        //-------------------------------------------------------------------

        public ReverseIterator(Component pStart)
        {
            //check component exist & is correct type
            Debug.Assert(pStart != null);
            Debug.Assert(pStart.type == Component.Type.Composite);

            //TODO: fix Keenan's hack...?
            ForwardIterator pForward = new ForwardIterator(pStart);

            this.pRoot = pStart;
            this.pCurr = this.pRoot;
            this.pPrev = null;

            Component pPrevNode = this.pRoot;

            //reverse pointer
            Component pNode = pForward.First();

            while (!pForward.IsDone())
            {
                //keep ref
                pPrevNode = pNode;  

                //get next
                pNode = pForward.Next();
                if (pNode != null)
                {
                    pNode.pReverse = pPrevNode;
                }
            }

            pRoot.pReverse = pPrevNode;
        }

        //-------------------------------------------------------------------
        //  OVERRIDDEN METHODS
        //-------------------------------------------------------------------

        public override Component First()
        {
            Debug.Assert(this.pRoot != null);
            this.pCurr = this.pRoot.pReverse;

            return this.pCurr;
        }

        public override Component Curr()
        {
            return this.pCurr;
        }

        public override Component Next()
        {
            Debug.Assert(this.pCurr != null);
            this.pPrev = this.pCurr;
            this.pCurr = this.pCurr.pReverse;

            return this.pCurr;
        }

        public override bool IsDone()
        {
            return (this.pPrev == this.pRoot);
        }
    }
}