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

namespace shadowsocks_csharp
{
    class Encryptor
    {
        public byte[] encryptTable = new byte[256];
        public byte[] decryptTable = new byte[256];

        private Int64 compare(byte x, byte y, UInt64 a, int i) {
            return (Int64)(a % (UInt64)(x + i)) - (Int64)(a % (UInt64)(y + i));
        }

        private byte[] mergeSort(byte[] array, UInt64 a, int j)
        {
            if (array.Length == 1)
                return array;
            int middle = array.Length / 2;
            byte[] left = new byte[middle];
            for (int i = 0; i < middle; i++)
            {
                left[i] = array[i];
            }
            byte[] right = new byte[array.Length - middle];
            for (int i = 0; i < array.Length - middle; i++)
            {
                right[i] = array[i + middle];
            }
            left = mergeSort(left, a, j);
            right = mergeSort(right, a, j);

            int leftptr = 0;
            int rightptr = 0;

            byte[] sorted = new byte[array.Length];
            for (int k = 0; k < array.Length; k++)
            {
                if (rightptr == right.Length || ((leftptr < left.Length) && (compare(left[leftptr], right[rightptr], a, j) <= 0)))
                {
                    sorted[k] = left[leftptr];
                    leftptr++;
                }
                else if (leftptr == left.Length || ((rightptr < right.Length) && (compare(right[rightptr], left[leftptr], a, j)) <= 0))
                {
                    sorted[k] = right[rightptr];
                    rightptr++;
                }
            }
            return sorted;
        }

        public Encryptor(string password)
        {
            MD5 md5 = System.Security.Cryptography.MD5.Create();
            byte[] inputBytes = System.Text.Encoding.UTF8.GetBytes(password);
            byte[] hash = md5.ComputeHash(inputBytes);

            // TODO endian
            var a = BitConverter.ToUInt64(hash, 0);
            for (int i = 0; i < 256; i++)
            {
                encryptTable[i] = (byte)i;
            }
            for (int i = 1; i < 1024; i++)
            {
                encryptTable = mergeSort(encryptTable, a, i);
            }
            for (int i = 0; i < 256; i++)
            {
                decryptTable[encryptTable[i]] = (byte)i;
            }
        }

        public void Encrypt(byte[] buf)
        {
            for (int i = 0; i < buf.Length; i++)
            {
                buf[i] = encryptTable[buf[i]];
            }
        }
        public void Decrypt(byte[] buf)
        {
            for (int i = 0; i < buf.Length; i++)
            {
                buf[i] = decryptTable[buf[i]];
            }
        }


    }
}