using System;
using System.Security.Cryptography;

namespace EGFramework{
    public static class EGCrcModbusExtension
    {
        /// CRC calculate is a common device verify algorithm
        /// use 
        // hex = {0x80,0x05};
        // Polynomial = x^16+x^15+x^2+1 = 1 80 05
        public const ushort CRC_16_Modbus_Polynomial = 0x8005;
        // hex = {0xFF,0xFF}
        public const ushort CRC_16_Modbus_Start = 0xFFFF;
        // hex = {0x00,0x00}
        public const ushort CRC_16_Modbus_ResultXOR = 0x0000;
        private static readonly ushort[] Crc_16_Table_Modbus ={
            0x00,0xC0C1,0xC181,0x140,0xC301,0x3C0,0x280,0xC241,0xC601,0x6C0,0x780,0xC741,0x500,0xC5C1,0xC481,0x440,
            0xCC01,0xCC0,0xD80,0xCD41,0xF00,0xCFC1,0xCE81,0xE40,0xA00,0xCAC1,0xCB81,0xB40,0xC901,0x9C0,0x880,0xC841,
            0xD801,0x18C0,0x1980,0xD941,0x1B00,0xDBC1,0xDA81,0x1A40,0x1E00,0xDEC1,0xDF81,0x1F40,0xDD01,0x1DC0,0x1C80,0xDC41,
            0x1400,0xD4C1,0xD581,0x1540,0xD701,0x17C0,0x1680,0xD641,0xD201,0x12C0,0x1380,0xD341,0x1100,0xD1C1,0xD081,0x1040,
            0xF001,0x30C0,0x3180,0xF141,0x3300,0xF3C1,0xF281,0x3240,0x3600,0xF6C1,0xF781,0x3740,0xF501,0x35C0,0x3480,0xF441,
            0x3C00,0xFCC1,0xFD81,0x3D40,0xFF01,0x3FC0,0x3E80,0xFE41,0xFA01,0x3AC0,0x3B80,0xFB41,0x3900,0xF9C1,0xF881,0x3840,
            0x2800,0xE8C1,0xE981,0x2940,0xEB01,0x2BC0,0x2A80,0xEA41,0xEE01,0x2EC0,0x2F80,0xEF41,0x2D00,0xEDC1,0xEC81,0x2C40,
            0xE401,0x24C0,0x2580,0xE541,0x2700,0xE7C1,0xE681,0x2640,0x2200,0xE2C1,0xE381,0x2340,0xE101,0x21C0,0x2080,0xE041,
            0xA001,0x60C0,0x6180,0xA141,0x6300,0xA3C1,0xA281,0x6240,0x6600,0xA6C1,0xA781,0x6740,0xA501,0x65C0,0x6480,0xA441,
            0x6C00,0xACC1,0xAD81,0x6D40,0xAF01,0x6FC0,0x6E80,0xAE41,0xAA01,0x6AC0,0x6B80,0xAB41,0x6900,0xA9C1,0xA881,0x6840,
            0x7800,0xB8C1,0xB981,0x7940,0xBB01,0x7BC0,0x7A80,0xBA41,0xBE01,0x7EC0,0x7F80,0xBF41,0x7D00,0xBDC1,0xBC81,0x7C40,
            0xB401,0x74C0,0x7580,0xB541,0x7700,0xB7C1,0xB681,0x7640,0x7200,0xB2C1,0xB381,0x7340,0xB101,0x71C0,0x7080,0xB041,
            0x5000,0x90C1,0x9181,0x5140,0x9301,0x53C0,0x5280,0x9241,0x9601,0x56C0,0x5780,0x9741,0x5500,0x95C1,0x9481,0x5440,
            0x9C01,0x5CC0,0x5D80,0x9D41,0x5F00,0x9FC1,0x9E81,0x5E40,0x5A00,0x9AC1,0x9B81,0x5B40,0x9901,0x59C0,0x5880,0x9841,
            0x8801,0x48C0,0x4980,0x8941,0x4B00,0x8BC1,0x8A81,0x4A40,0x4E00,0x8EC1,0x8F81,0x4F40,0x8D01,0x4DC0,0x4C80,0x8C41,
            0x4400,0x84C1,0x8581,0x4540,0x8701,0x47C0,0x4680,0x8641,0x8201,0x42C0,0x4380,0x8341,0x4100,0x81C1,0x8081,0x4040,
        };
        public static ushort CalculateCRC16Modbus(this byte[] bytes)
        {
            CRC16 provider = new CRC16(Crc_16_Table_Modbus);
            byte[] hash = provider.ComputeHash(bytes);

            ushort crc16 = BitConverter.ToUInt16(hash, 0);
            
            ushort reversedResult = (ushort)((crc16 >> 8) | (crc16 << 8));
            return reversedResult;
        }

    }
    public static class EGCrcUtility
    {
        //Crc with table
        public static uint CalculateCrc(byte[] data, uint initialValue, uint xorValue, bool inputReverse, bool outputReverse,uint[] CrcTable)
        {
            uint crc = initialValue;

            for (int i = 0; i < data.Length; i++)
            {
                if (inputReverse)
                    data[i] = ReverseBits(data[i]);

                crc ^= (uint)(data[i] << 24);

                for (int j = 0; j < 8; j++)
                {
                    crc = (crc << 8) ^ CrcTable[crc >> 24];
                }
            }

            if (outputReverse)
                crc = ReverseBits(crc);

            return crc ^ xorValue;
        }

        //Crc without table
        public static uint CalculateCrc(byte[] data, uint polynomial, uint initialValue, uint xorValue, bool inputReverse, bool outputReverse)
        {
            uint crc = initialValue;

            for (int i = 0; i < data.Length; i++)
            {
                if (inputReverse)
                    data[i] = ReverseBits(data[i]);

                crc ^= (uint)(data[i] << 24);

                for (int j = 0; j < 8; j++)
                {
                    if ((crc & 0x80000000) != 0)
                    {
                        crc = (crc << 1) ^ polynomial;
                    }
                    else
                    {
                        crc <<= 1;
                    }
                }
            }

            if (outputReverse)
                crc = ReverseBits(crc);

            return crc ^ xorValue;
        }

        private static uint ReverseBits(uint value)
        {
            uint result = 0;
            for (int i = 0; i < 8; i++)
            {
                result = (result << 1) | ((value >> i) & 1);
            }
            return result;
        }

        private static byte ReverseBits(byte value)
        {
            byte result = 0;
            for (int i = 0; i < 8; i++)
            {
                result = (byte)((result << 1) | ((value >> i) & 1));
            }
            return result;
        }
    }
    public class CRC16 : HashAlgorithm
    {
        private const ushort polynomial = 0x8005;
        private ushort[] table = new ushort[256];
        private ushort crc = 0xFFFF;

        public CRC16(ushort[] table)
        {
            HashSizeValue = 16;
            this.table = table;
        }

        protected override void HashCore(byte[] array, int ibStart, int cbSize)
        {
            for (int i = ibStart; i < ibStart + cbSize; i++)
            {
                byte index = (byte)(crc ^ array[i]);
                crc = (ushort)((crc >> 8) ^ table[index]);
            }
        }

        protected override byte[] HashFinal()
        {
            return BitConverter.GetBytes(crc);
        }
        
        public override void Initialize()
        {
            crc = ushort.MaxValue;
        }
    }
}