using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace KFDtool.P25.ThreeWire
{
    /* TIA 102.AACD-A Annex A */
    class CRC16
    {
        private static readonly ushort[] Table = new ushort[]
        {
            0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD,
            0x6536, 0x74BF, 0x8C48, 0x9DC1, 0xAF5A, 0xBED3,
            0xCA6C, 0xDBE5, 0xE97E, 0xF8F7, 0x1081, 0x0108,
            0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E,
            0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64,
            0xF9FF, 0xE876, 0x2102, 0x308B, 0x0210, 0x1399,
            0x6726, 0x76AF, 0x4434, 0x55BD, 0xAD4A, 0xBCC3,
            0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5,
            0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E,
            0x54B5, 0x453C, 0xBDCB, 0xAC42, 0x9ED9, 0x8F50,
            0xFBEF, 0xEA66, 0xD8FD, 0xC974, 0x4204, 0x538D,
            0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB,
            0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1,
            0xAB7A, 0xBAF3, 0x5285, 0x430C, 0x7197, 0x601E,
            0x14A1, 0x0528, 0x37B3, 0x263A, 0xDECD, 0xCF44,
            0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72,
            0x6306, 0x728F, 0x4014, 0x519D, 0x2522, 0x34AB,
            0x0630, 0x17B9, 0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5,
            0xA96A, 0xB8E3, 0x8A78, 0x9BF1, 0x7387, 0x620E,
            0x5095, 0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738,
            0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB, 0xA862,
            0x9AF9, 0x8B70, 0x8408, 0x9581, 0xA71A, 0xB693,
            0xC22C, 0xD3A5, 0xE13E, 0xF0B7, 0x0840, 0x19C9,
            0x2B52, 0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF,
            0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD, 0xC324,
            0xF1BF, 0xE036, 0x18C1, 0x0948, 0x3BD3, 0x2A5A,
            0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E, 0xA50A, 0xB483,
            0x8618, 0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5,
            0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66, 0x7EEF,
            0x4C74, 0x5DFD, 0xB58B, 0xA402, 0x9699, 0x8710,
            0xF3AF, 0xE226, 0xD0BD, 0xC134, 0x39C3, 0x284A,
            0x1AD1, 0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C,
            0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028, 0x91A1,
            0xA33A, 0xB2B3, 0x4A44, 0x5BCD, 0x6956, 0x78DF,
            0x0C60, 0x1DE9, 0x2F72, 0x3EFB, 0xD68D, 0xC704,
            0xF59F, 0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232,
            0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1, 0x0D68,
            0x3FF3, 0x2E7A, 0xE70E, 0xF687, 0xC41C, 0xD595,
            0xA12A, 0xB0A3, 0x8238, 0x93B1, 0x6B46, 0x7ACF,
            0x4854, 0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9,
            0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB, 0xA022,
            0x92B9, 0x8330, 0x7BC7, 0x6A4E, 0x58D5, 0x495C,
            0x3DE3, 0x2C6A, 0x1EF1, 0x0F78
        };

        public static byte[] CalculateCrc(byte[] value)
        {
            ushort crc = 65535;
            for (int i = 0; i < value.Length; i++)
            {
                crc = (ushort)(Table[value[i] ^ (crc & 0xFF)] ^ (crc >> 8));
            }
            byte[] list = new byte[2];
            list[0] = Convert.ToByte(crc & 0xFF);
            list[1] = Convert.ToByte(crc >> 8);
            return list;
        }
    }
}