/*
Thor Server 2.0 Project - Codenamed "Stockholm"
Copyright 2008 - 2009 Joe Hegarty


This file is part of The Thor Server 2.0 Project - Codenamed "Stockholm".

The Thor Server 2.0 Project - Codenamed "Stockholm" is free software: you can 
redistribute it and/or modify it under the terms of the Microsoft Public License

The Thor Server Project is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
Microsoft Public License for more details.

You should have received a copy of the Microsoft Public License
along with The Thor Server Project.  If not, see 
http://www.opensource.org/licenses/ms-pl.html
*/

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace StockholmLibrary.Net
{
    //------------------------------------
    public static class VL64Encoding
    {
        //**********************************************
        public static byte[] EncodeInt(int inputValue)
        {
            int x = 0;
            return EncodeInt(inputValue, out x);
        }

        //**********************************************
        public static byte[] EncodeInt(int inputValue, out int size)
        {
            byte[] wf = new byte[6];
            int pos = 0;
            int startPos = pos;
            int bytes = 1;
            int negativeMask = inputValue >= 0 ? 0 : 4;
            inputValue = Math.Abs(inputValue);
            wf[pos++] = (byte)(64 + (inputValue & 3));
            for (inputValue >>= 2; inputValue != 0; inputValue >>= 6)
            {
                bytes++;
                wf[pos++] = (byte)(64 + (inputValue & 0x3f));
            }

            wf[startPos] = (byte)(wf[startPos] | bytes << 3 | negativeMask);           
            byte[] result = new byte[pos];
            for (int x = 0; x < pos; ++x)
            {
                result[x] = wf[x];
            }
            size = pos;

            return result;
        }

        //**********************************************
        public static int DecodeInt(byte[] raw)
        {
            int pos = 0;
            int v = 0;
            bool negative = (raw[pos] & 4) == 4;
            int totalBytes = raw[pos] >> 3 & 7;
            v = raw[pos] & 3;
            pos++;
            int shiftAmount = 2;
            for (int b = 1; b < totalBytes; b++)
            {
                v |= (raw[pos] & 0x3f) << shiftAmount;
                shiftAmount = 2 + 6 * b;
                pos++;
            }

            if (negative == true)
            {
                v *= -1;
            }

            return v;
        }
    }
}