using System;
using System.Linq;

namespace NFC.Crypto
{
    public class CRC32
    {
        public byte[] Calculate(byte[] data)
        {
            UInt32 crc32 = 0xFFFFFFFF;

            crc32 = Calculate(data, crc32);

            return BitConverter.GetBytes(crc32);
        }

        public byte[] Calculate(byte[] cmd, byte[] data)
        {
            UInt32 crc32 = 0xFFFFFFFF;

            crc32 = Calculate(cmd, crc32);
            crc32 = Calculate(data, crc32);

            return BitConverter.GetBytes(crc32);
        }

        public UInt32 Calculate(byte[] data, UInt32 crc32)
        {
            for (int i = 0; i < data.Length; i++)
            {
                crc32 ^= data[i];
                for (int b = 0; b < 8; b++)
                {
                    bool b_Bit = (crc32 & 0x01) > 0;
                    crc32 >>= 1;
                    if (b_Bit)
                    {
                        crc32 ^= 0xEDB88320;
                    }
                }
            }
            return crc32;
        }
    }
}