//
// MpqHuffman.cs
//
// Authors:
//		Foole (fooleau@gmail.com)
//
// (C) 2006 Foole (fooleau@gmail.com)
// Based on code from StormLib by Ladislav Zezula and ShadowFlare
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
using System;
using System.IO;
using System.Collections;

namespace OpenDiablo2.Common.Models
{
    // A node which is both hierachcical (parent/child) and doubly linked (next/prev)
    internal class LinkedNode
    {
        public int DecompressedValue;
        public int Weight;
        public LinkedNode Parent;
        public LinkedNode Child0;

        public LinkedNode Child1
        { get { return Child0.Prev; } }

        public LinkedNode Next;
        public LinkedNode Prev;

        public LinkedNode(int decompVal, int weight)
        {
            DecompressedValue = decompVal;
            this.Weight = weight;
        }

        // TODO: This would be more efficient as a member of the other class
        // ie avoid the recursion
        public LinkedNode Insert(LinkedNode other)
        {
            // 'Next' should have a lower weight
            // we should return the lower weight
            if (other.Weight <= Weight)
            {
                // insert before
                if (Next != null)
                {
                    Next.Prev = other;
                    other.Next = Next;
                }
                Next = other;
                other.Prev = this;
                return other;
            }
            else
            {
                if (Prev == null)
                {
                    // Insert after
                    other.Prev = null;
                    Prev = other;
                    other.Next = this;
                }
                else
                {
                    Prev.Insert(other);
                }
            }
            return this;
        }
    }

    /// <summary>
    /// A decompressor for MPQ's huffman compression
    /// </summary>
    internal static class MpqHuffman
    {
        private static readonly byte[][] sPrime =
        {
			// Compression type 0
			new byte[]
            {
                0x0A, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02,
            },
			// Compression type 1
			new byte[]
            {
                0x54, 0x16, 0x16, 0x0D, 0x0C, 0x08, 0x06, 0x05, 0x06, 0x05, 0x06, 0x03, 0x04, 0x04, 0x03, 0x05,
                0x0E, 0x0B, 0x14, 0x13, 0x13, 0x09, 0x0B, 0x06, 0x05, 0x04, 0x03, 0x02, 0x03, 0x02, 0x02, 0x02,
                0x0D, 0x07, 0x09, 0x06, 0x06, 0x04, 0x03, 0x02, 0x04, 0x03, 0x03, 0x03, 0x03, 0x03, 0x02, 0x02,
                0x09, 0x06, 0x04, 0x04, 0x04, 0x04, 0x03, 0x02, 0x03, 0x02, 0x02, 0x02, 0x02, 0x03, 0x02, 0x04,
                0x08, 0x03, 0x04, 0x07, 0x09, 0x05, 0x03, 0x03, 0x03, 0x03, 0x02, 0x02, 0x02, 0x03, 0x02, 0x02,
                0x03, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01, 0x02, 0x01, 0x02, 0x02,
                0x06, 0x0A, 0x08, 0x08, 0x06, 0x07, 0x04, 0x03, 0x04, 0x04, 0x02, 0x02, 0x04, 0x02, 0x03, 0x03,
                0x04, 0x03, 0x07, 0x07, 0x09, 0x06, 0x04, 0x03, 0x03, 0x02, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02,
                0x0A, 0x02, 0x02, 0x03, 0x02, 0x02, 0x01, 0x01, 0x02, 0x02, 0x02, 0x06, 0x03, 0x05, 0x02, 0x03,
                0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x03, 0x01, 0x01, 0x01,
                0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x04, 0x04, 0x04, 0x07, 0x09, 0x08, 0x0C, 0x02,
                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x03,
                0x04, 0x01, 0x02, 0x04, 0x05, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01,
                0x04, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
                0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x03, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
                0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x01, 0x01, 0x02, 0x02, 0x02, 0x06, 0x4B,
            },
			// Compression type 2
			new byte[]
            {
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x27, 0x00, 0x00, 0x23, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0xFF, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x01, 0x01, 0x06, 0x0E, 0x10, 0x04,
                0x06, 0x08, 0x05, 0x04, 0x04, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03, 0x01, 0x01, 0x02, 0x01, 0x01,
                0x01, 0x04, 0x02, 0x04, 0x02, 0x02, 0x02, 0x01, 0x01, 0x04, 0x01, 0x01, 0x02, 0x03, 0x03, 0x02,
                0x03, 0x01, 0x03, 0x06, 0x04, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x02, 0x01, 0x01,
                0x01, 0x29, 0x07, 0x16, 0x12, 0x40, 0x0A, 0x0A, 0x11, 0x25, 0x01, 0x03, 0x17, 0x10, 0x26, 0x2A,
                0x10, 0x01, 0x23, 0x23, 0x2F, 0x10, 0x06, 0x07, 0x02, 0x09, 0x01, 0x01, 0x01, 0x01, 0x01
            },
			// Compression type 3
			new byte[]
            {
                0xFF, 0x0B, 0x07, 0x05, 0x0B, 0x02, 0x02, 0x02, 0x06, 0x02, 0x02, 0x01, 0x04, 0x02, 0x01, 0x03,
                0x09, 0x01, 0x01, 0x01, 0x03, 0x04, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01,
                0x05, 0x01, 0x01, 0x01, 0x0D, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
                0x02, 0x01, 0x01, 0x03, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01, 0x01,
                0x0A, 0x04, 0x02, 0x01, 0x06, 0x03, 0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x03, 0x01, 0x01, 0x01,
                0x05, 0x02, 0x03, 0x04, 0x03, 0x03, 0x03, 0x02, 0x01, 0x01, 0x01, 0x02, 0x01, 0x02, 0x03, 0x03,
                0x01, 0x03, 0x01, 0x01, 0x02, 0x05, 0x01, 0x01, 0x04, 0x03, 0x05, 0x01, 0x03, 0x01, 0x03, 0x03,
                0x02, 0x01, 0x04, 0x03, 0x0A, 0x06, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
                0x02, 0x02, 0x01, 0x0A, 0x02, 0x05, 0x01, 0x01, 0x02, 0x07, 0x02, 0x17, 0x01, 0x05, 0x01, 0x01,
                0x0E, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
                0x06, 0x02, 0x01, 0x04, 0x05, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01,
                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x07, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01, 0x01,
                0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x11,
            },
			// Compression type 4
			new byte[]
            {
                0xFF, 0xFB, 0x98, 0x9A, 0x84, 0x85, 0x63, 0x64, 0x3E, 0x3E, 0x22, 0x22, 0x13, 0x13, 0x18, 0x17,
            },
			// Compression type 5
			new byte[]
            {
                0xFF, 0xF1, 0x9D, 0x9E, 0x9A, 0x9B, 0x9A, 0x97, 0x93, 0x93, 0x8C, 0x8E, 0x86, 0x88, 0x80, 0x82,
                0x7C, 0x7C, 0x72, 0x73, 0x69, 0x6B, 0x5F, 0x60, 0x55, 0x56, 0x4A, 0x4B, 0x40, 0x41, 0x37, 0x37,
                0x2F, 0x2F, 0x27, 0x27, 0x21, 0x21, 0x1B, 0x1C, 0x17, 0x17, 0x13, 0x13, 0x10, 0x10, 0x0D, 0x0D,
                0x0B, 0x0B, 0x09, 0x09, 0x08, 0x08, 0x07, 0x07, 0x06, 0x05, 0x05, 0x04, 0x04, 0x04, 0x19, 0x18
            },
			// Compression type 6
			new byte[]
            {
                0xC3, 0xCB, 0xF5, 0x41, 0xFF, 0x7B, 0xF7, 0x21, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0xBF, 0xCC, 0xF2, 0x40, 0xFD, 0x7C, 0xF7, 0x22, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x7A, 0x46
            },
			// Compression type 7
			new byte[]
            {
                0xC3, 0xD9, 0xEF, 0x3D, 0xF9, 0x7C, 0xE9, 0x1E, 0xFD, 0xAB, 0xF1, 0x2C, 0xFC, 0x5B, 0xFE, 0x17,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0xBD, 0xD9, 0xEC, 0x3D, 0xF5, 0x7D, 0xE8, 0x1D, 0xFB, 0xAE, 0xF0, 0x2C, 0xFB, 0x5C, 0xFF, 0x18,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x70, 0x6C
            },
			// Compression type 8
			new byte[]
            {
                0xBA, 0xC5, 0xDA, 0x33, 0xE3, 0x6D, 0xD8, 0x18, 0xE5, 0x94, 0xDA, 0x23, 0xDF, 0x4A, 0xD1, 0x10,
                0xEE, 0xAF, 0xE4, 0x2C, 0xEA, 0x5A, 0xDE, 0x15, 0xF4, 0x87, 0xE9, 0x21, 0xF6, 0x43, 0xFC, 0x12,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0xB0, 0xC7, 0xD8, 0x33, 0xE3, 0x6B, 0xD6, 0x18, 0xE7, 0x95, 0xD8, 0x23, 0xDB, 0x49, 0xD0, 0x11,
                0xE9, 0xB2, 0xE2, 0x2B, 0xE8, 0x5C, 0xDD, 0x15, 0xF1, 0x87, 0xE7, 0x20, 0xF7, 0x44, 0xFF, 0x13,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x5F, 0x9E
            }
        };

        public static MemoryStream Decompress(Stream data)
        {
            int comptype = data.ReadByte();

            if (comptype == 0)
                throw new NotImplementedException("Compression type 0 is not currently supported");

            LinkedNode tail = BuildList(sPrime[comptype]);
            LinkedNode head = BuildTree(tail);

            MemoryStream outputstream = new MemoryStream();
            BitStream bitstream = new BitStream(data);
            int decoded;
            do
            {
                LinkedNode node = Decode(bitstream, head);
                decoded = node.DecompressedValue;
                switch (decoded)
                {
                    case 256:
                        break;
                    case 257:
                        int newvalue = bitstream.ReadBits(8);
                        outputstream.WriteByte((byte)newvalue);
                        tail = InsertNode(tail, newvalue);
                        break;
                    default:
                        outputstream.WriteByte((byte)decoded);
                        break;
                }
            } while (decoded != 256);

            outputstream.Seek(0, SeekOrigin.Begin);
            return outputstream;
        }

        private static LinkedNode Decode(BitStream input, LinkedNode head)
        {
            LinkedNode node = head;

            while (node.Child0 != null)
            {
                int bit = input.ReadBits(1);
                if (bit == -1)
                    throw new Exception("Unexpected end of file");

                node = bit == 0 ? node.Child0 : node.Child1;
            }
            return node;
        }

        private static LinkedNode BuildList(byte[] primeData)
        {
            LinkedNode root;

            root = new LinkedNode(256, 1);
            root = root.Insert(new LinkedNode(257, 1));

            for (int i = 0; i < primeData.Length; i++)
            {
                if (primeData[i] != 0)
                    root = root.Insert(new LinkedNode(i, primeData[i]));
            }
            return root;
        }

        private static LinkedNode BuildTree(LinkedNode tail)
        {
            LinkedNode current = tail;

            while (current != null)
            {
                LinkedNode child0 = current;
                LinkedNode child1 = current.Prev;
                if (child1 == null) break;

                LinkedNode parent = new LinkedNode(0, child0.Weight + child1.Weight);
                parent.Child0 = child0;
                child0.Parent = parent;
                child1.Parent = parent;

                current.Insert(parent);
                current = current.Prev.Prev;
            }
            return current;
        }

        private static LinkedNode InsertNode(LinkedNode tail, int decomp)
        {
            LinkedNode parent = tail;
            LinkedNode result = tail.Prev; // This will be the new tail after the tree is updated

            LinkedNode temp = new LinkedNode(parent.DecompressedValue, parent.Weight);
            temp.Parent = parent;

            LinkedNode newnode = new LinkedNode(decomp, 0);
            newnode.Parent = parent;

            parent.Child0 = newnode;

            tail.Next = temp;
            temp.Prev = tail;
            newnode.Prev = temp;
            temp.Next = newnode;

            AdjustTree(newnode);
            // TODO: For compression type 0, AdjustTree should be called 
            // once for every value written and only once here
            AdjustTree(newnode);
            return result;
        }

        // This increases the weight of the new node and its antecendants
        // and adjusts the tree if needed
        private static void AdjustTree(LinkedNode newNode)
        {
            LinkedNode current = newNode;

            while (current != null)
            {
                current.Weight++;
                LinkedNode insertpoint;
                LinkedNode prev;
                // Go backwards thru the list looking for the insertion point
                insertpoint = current;
                while (true)
                {
                    prev = insertpoint.Prev;
                    if (prev == null) break;
                    if (prev.Weight >= current.Weight) break;
                    insertpoint = prev;
                }

                // No insertion point found
                if (insertpoint == current)
                {
                    current = current.Parent;
                    continue;
                }

                // The following code basicly swaps insertpoint with current

                // remove insert point
                if (insertpoint.Prev != null) insertpoint.Prev.Next = insertpoint.Next;
                insertpoint.Next.Prev = insertpoint.Prev;

                // Insert insertpoint after current
                insertpoint.Next = current.Next;
                insertpoint.Prev = current;
                if (current.Next != null) current.Next.Prev = insertpoint;
                current.Next = insertpoint;

                // remove current
                current.Prev.Next = current.Next;
                current.Next.Prev = current.Prev;

                // insert current after prev
                LinkedNode temp = prev.Next;
                current.Next = temp;
                current.Prev = prev;
                temp.Prev = current;
                prev.Next = current;

                // Set up parent/child links
                LinkedNode currentparent = current.Parent;
                LinkedNode insertparent = insertpoint.Parent;

                if (currentparent.Child0 == current)
                    currentparent.Child0 = insertpoint;

                if (currentparent != insertparent && insertparent.Child0 == insertpoint)
                    insertparent.Child0 = current;

                current.Parent = insertparent;
                insertpoint.Parent = currentparent;

                current = current.Parent;
            }
        }
    }
}