using System;
using System.Diagnostics;

namespace SpaceInvaders
{
    public class SLinkMan : List
    {
        //-------------------------------------------------------------------
        //  FIELDS
        //-------------------------------------------------------------------

        public SLinkIterator poIterator;

        public SLink pHead;
        public SLink pTail;


        //-------------------------------------------------------------------
        //  CONSTRUCTION
        //-------------------------------------------------------------------

        public SLinkMan() : base()
        {
            //LTN: owned by slink manager
            this.poIterator = new SLinkIterator();
            Debug.Assert(this.poIterator != null);

            this.pHead = null;
            this.pTail = null;
        }


        //-------------------------------------------------------------------
        //  PUBLIC METHODS
        //-------------------------------------------------------------------

        public override void AddToFront(Node pNode)
        {
            Debug.Assert(pNode != null);

            SLink pLink = (SLink)pNode;
            if (pHead == null)
            {
                //empty list
                this.pHead = this.pTail = pLink;
                pLink.pNext = null;
            }
            else
            {
                //add to front
                pLink.pNext = pHead;
                pHead = pLink;
            }
        }

        public override Node RemoveFromFront()
        {
            Debug.Assert(pHead != null);
            SLink pLink = pHead;

            if(pLink.pNext == null)
            {
                //only node on list
                this.pHead = this.pTail = null;
            }
            else
            {
                //update head ptr
                this.pHead = this.pHead.pNext;
            }

            pLink.Reset();
            return pLink;
        }

        public override void Remove(Node pNode)
        {
            Debug.Assert(pHead != null);
            Debug.Assert(pNode != null);

            SLink pLink = (SLink)pNode;

            //case 1: only node on list
            if (pHead == pLink)
            {
                //pHead = pTail = null;
                pHead = pLink.pNext;
            }
            //case 2/3: middle or last node
            else
            {
                //middle or last node
                SLink pCurr = this.pHead;
                SLink pPrev = null;

                //iterate and find
                while (pCurr != pLink)
                {
                    pPrev = pCurr;
                    pCurr = pCurr.pNext;
                }

                //unattach it
                if (this.pTail == pCurr)
                {
                    this.pTail = pPrev;
                    pPrev.pNext = null;
                }
                else
                {
                    pPrev.pNext = pCurr.pNext;
                    pCurr.pNext = null;
                }
            }

            pLink.Reset();
        }

        public override Iterator GetIterator()
        {
            poIterator.Reset(this.pHead);
            return poIterator;
        }
    }
}