using System;
using System.IO.Ports;
using System.Runtime;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Threading;

namespace Gidrolock_Modbus_Scanner
{
    public static class Modbus
    {

        #region CRC Computation
        static void GetCRC(byte[] message, ref byte[] CRC)
        {
            //Function expects a modbus message of any length as well as a 2 byte CRC array in which to 
            //return the CRC values:

            ushort CRCFull = 0xFFFF;
            byte CRCHigh = 0xFF, CRCLow = 0xFF;
            char CRCLSB;

            for (int i = 0; i < (message.Length) - 2; i++)
            {
                CRCFull = (ushort)(CRCFull ^ message[i]);

                for (int j = 0; j < 8; j++)
                {
                    CRCLSB = (char)(CRCFull & 0x0001);
                    CRCFull = (ushort)((CRCFull >> 1) & 0x7FFF);

                    if (CRCLSB == 1)
                        CRCFull = (ushort)(CRCFull ^ 0xA001);
                }
            }
            CRC[1] = CRCHigh = (byte)((CRCFull >> 8) & 0xFF);
            CRC[0] = CRCLow = (byte)(CRCFull & 0xFF);
        }
        #endregion

        #region Build Message
        static void BuildMessage(byte address, byte type, ushort start, ushort registers, ref byte[] message)
        {
            //Array to receive CRC bytes:
            byte[] CRC = new byte[2];

            message[0] = address;
            message[1] = type;
            message[2] = (byte)(start >> 8);
            message[3] = (byte)start;
            message[4] = (byte)(registers >> 8);
            message[5] = (byte)registers;

            GetCRC(message, ref CRC);
            message[message.Length - 2] = CRC[0];
            message[message.Length - 1] = CRC[1];
            string msg = BitConverter.ToString(message);
            Console.WriteLine("Message: " + msg);
        }
        #endregion

        #region Check Response
        static bool CheckResponse(byte[] response)
        {
            //Perform a basic CRC check:
            byte[] CRC = new byte[2];
            GetCRC(response, ref CRC);
            if (CRC[0] == response[response.Length - 2] && CRC[1] == response[response.Length - 1])
                return true;
            else
                return false;
        }
        #endregion

        #region Get Response
        static void GetResponse(SerialPort port, ref byte[] response)
        {
            Console.WriteLine("Got response from port");
            if (port.BytesToRead == 0)
                return;
            //There is a bug in .Net 2.0 DataReceived Event that prevents people from using this
            //event as an interrupt to handle data (it doesn't fire all of the time).  Therefore
            //we have to use the ReadByte command for a fixed length as it's been shown to be reliable.
            for (int i = 0; i < response.Length; i++)
            {
                response[i] = (byte)(port.ReadByte());
            }
        }
        #endregion

        #region Function 3 - Read Holding Registers
        public static async Task<bool> ReadRegAsync(SerialPort port, byte regType, byte address, ushort start, ushort registers)
        {
            short[] values = new short[8];
            //Ensure port is open:
            if (port.IsOpen)
            {
                //Clear in/out buffers:
                port.DiscardOutBuffer();
                port.DiscardInBuffer();
                //Function 3 request is always 8 bytes:
                byte[] message = new byte[8];
                //Function 3 response buffer:
                byte[] response = new byte[5 + 2 * registers];
                //Build outgoing modbus message:
                BuildMessage(address, (byte)3, start, registers, ref message);
                //Send modbus message to Serial Port:
                try
                {
                    await Task.Run(() => { port.Write(message, 0, message.Length); });
                    return true;
                }
                catch (Exception err)
                {
                    MessageBox.Show(err.Message);
                    port.Close();
                    return false;
                }
            }
            else
            {
                MessageBox.Show("Порт не открыт");
                return false;
            }

        }
        #endregion

    }
}