using System;

namespace NFC.Crypto
{
    public class CRC16
    {
        public byte[] Calculate(byte[] data)
        {
            UInt16 crc16 = 0x6363;

            crc16 = Calculate(data, crc16);

            return BitConverter.GetBytes(crc16);
        }

        public byte[] Calculate(byte[] cmd, byte[] data)
        {
            UInt16 crc16 = 0x6363;

            crc16 = Calculate(cmd, crc16);
            crc16 = Calculate(data, crc16);

            return BitConverter.GetBytes(crc16);
        }

        public UInt16 Calculate(byte[] data, UInt16 crc16)
        {
            for (int i = 0; i < data.Length; i++)
            {
                crc16 ^= data[i];
                for (int b = 0; b < 8; b++)
                {
                    bool b_Bit = (crc16 & 0x01) > 0;
                    crc16 >>= 1;
                    if (b_Bit)
                    {
                        crc16 ^= 0x8408;
                    }
                }
            }
            return crc16;
        }
    }
}