namespace SSPCTester.Devices.Protocol;

public static class ModbusRtuProtocol
{
    public static ushort ComputeCrc(ReadOnlySpan<byte> data)
    {
        ushort crc = 0xFFFF;
        foreach (byte value in data)
        {
            crc ^= value;
            for (int i = 0; i < 8; i++)
                crc = (ushort)((crc & 1) != 0 ? (crc >> 1) ^ 0xA001 : crc >> 1);
        }
        return crc;
    }

    public static byte[] BuildRequest(byte slave, byte function, ushort address, ushort valueOrCount)
    {
        var frame = new byte[8];
        frame[0] = slave;
        frame[1] = function;
        frame[2] = (byte)(address >> 8);
        frame[3] = (byte)address;
        frame[4] = (byte)(valueOrCount >> 8);
        frame[5] = (byte)valueOrCount;
        ushort crc = ComputeCrc(frame.AsSpan(0, 6));
        frame[6] = (byte)crc;
        frame[7] = (byte)(crc >> 8);
        return frame;
    }

    public static void ValidateCrc(ReadOnlySpan<byte> frame)
    {
        if (frame.Length < 5) throw new InvalidDataException("Modbus 响应长度不足。");
        ushort expected = ComputeCrc(frame[..^2]);
        ushort actual = (ushort)(frame[^2] | frame[^1] << 8);
        if (expected != actual)
            throw new InvalidDataException($"Modbus CRC 错误，期望 {expected:X4}，实际 {actual:X4}。");
    }
}

public static class ModbusValueConverter
{
    public static double ConvertRaw(ushort rawBits, bool signed, string formula, double range)
    {
        double raw = signed ? unchecked((short)rawBits) : rawBits;
        return formula switch
        {
            "A" => raw / 10000.0 * range,
            "B" => raw / range,
            _ => throw new InvalidDataException($"不支持换算公式 {formula}")
        };
    }
}