using System;


namespace SogClient
{

    internal sealed class PackUtils
    {
        internal static uint BE_To_UInt32(byte[] bs, int off)
        {
            return (uint)bs[off] << 24
                | (uint)bs[off + 1] << 16
                | (uint)bs[off + 2] << 8
                | (uint)bs[off + 3];
        }

        internal static void UInt32_To_BE(uint n, byte[] bs, int off)
        {
            bs[off] = (byte)(n >> 24);
            bs[off + 1] = (byte)(n >> 16);
            bs[off + 2] = (byte)(n >> 8);
            bs[off + 3] = (byte)(n);
        }
    }

    public class SogFastXTEAKey
    {
        private const int delta = unchecked((int)0x9E3779B9);

        private uint[] _S = new uint[4];

        public byte[] Key { get; }

        public uint[] Sum0 { get; }
        public uint[] Sum1 { get; }

        public SogFastXTEAKey(byte[] srcKey)
        {
            if(srcKey.Length != 16)
            { 
				TraceLog.Error("SogFastXTEAKey key length must is error {0}", srcKey);
                throw new Exception("SogXTEAKey key length must is 16");
            }

            Key = srcKey;

            Sum0 = new uint[SogFastXTEA.Rounds];
            Sum1 = new uint[SogFastXTEA.Rounds];

            int i, j;
            for (i = j = 0; i < 4; i++, j += 4)
            {
                _S[i] = PackUtils.BE_To_UInt32(srcKey, j);
            }

            for (i = j = 0; i < SogFastXTEA.Rounds; i++)
            {
                Sum0[i] = ((uint)j + _S[j & 3]);
                j += delta;
                Sum1[i] = ((uint)j + _S[j >> 11 & 3]);
            }
        }
    }


    /// <summary>
    /// XTEA加密的变种，小于8个字节不加密，轮数量减少到8，提高效率
    /// </summary>
    public sealed class SogFastXTEA
    {
        public const int Rounds = 8;

        private const int delta = unchecked((int)0x9E3779B9);

        private SogFastXTEA()
        {

        }


        public static void Encrypt(byte[] data, SogFastXTEAKey key)
        {
            int iBlockCount = data.Length / 8;
            int offset = 0;
            for(int block = 0; block < iBlockCount; block++)
            {
                uint v0 = PackUtils.BE_To_UInt32(data, offset);
                uint v1 = PackUtils.BE_To_UInt32(data, offset + 4);

                for (int i = 0; i < Rounds; i++)
                {
                    v0 += ((v1 << 4 ^ v1 >> 5) + v1) ^ key.Sum0[i];
                    v1 += ((v0 << 4 ^ v0 >> 5) + v0) ^ key.Sum1[i];
                }

                PackUtils.UInt32_To_BE(v0, data, offset);
                PackUtils.UInt32_To_BE(v1, data, offset + 4);

                offset += 8;
            }
        }

        public static void Decrypt(byte[] data, SogFastXTEAKey key)
        {
            int iBlockCount = data.Length / 8;
            int offset = 0;
            for (int block = 0; block < iBlockCount; block++)
            {
                uint v0 = PackUtils.BE_To_UInt32(data, offset);
                uint v1 = PackUtils.BE_To_UInt32(data, offset + 4);

                for (int i = Rounds - 1; i >= 0; i--)
                {
                    v1 -= ((v0 << 4 ^ v0 >> 5) + v0) ^ key.Sum1[i];
                    v0 -= ((v1 << 4 ^ v1 >> 5) + v1) ^ key.Sum0[i];
                }

                PackUtils.UInt32_To_BE(v0, data, offset);
                PackUtils.UInt32_To_BE(v1, data, offset + 4);

                offset += 8;
            }
        }

        
    }
}