#nullable enable

using System;
using System.IO.Ports;
using System.Linq;
using System.Threading;

public class SerialManager : IDisposable
{
    private SerialPort? port;
    private DateTime lastResponse = DateTime.UtcNow;

    private const int BaudRate = 115200;
    private const int PingTimeoutMs = 300;
    private const int WatchdogTimeoutMs = 3000;

    public bool IsConnected => port != null && port.IsOpen;

    // ---------------- DEVICE DISCOVERY ----------------

    public void DiscoverDevice()
    {
        DisposePort();

        foreach (string com in SerialPort.GetPortNames().OrderBy(s => s))
        {
            string? response = null;

            try
            {
                using (var testPort = CreatePort(com, PingTimeoutMs))
                {
                    testPort.Open();
                    Thread.Sleep(350); // RP2040 resets on open

                    testPort.DiscardInBuffer();
                    testPort.DiscardOutBuffer();

                    testPort.Write("PING\n");

                    try
                    {
                        if (testPort.BytesToRead > 0)
                            response = testPort.ReadLine();
                    }
                    catch (TimeoutException)
                    {
                        // No response — move to next port
                    }
                }

                if (response != null &&
                    response.StartsWith("Analog_System_Monitor_"))
                {
                    port = CreatePort(com, 500);
                    port.Open();
                    Thread.Sleep(350); // allow RP2040 reboot again

                    lastResponse = DateTime.UtcNow;
                    return;
                }
            }
            catch
            {
                // Silent fail — move to next COM port
            }
        }

        port = null;
    }

    // ---------------- PORT FACTORY ----------------

    private SerialPort CreatePort(string com, int timeout)
    {
        return new SerialPort(com, BaudRate)
        {
            Parity = Parity.None,
            DataBits = 8,
            StopBits = StopBits.One,
            Handshake = Handshake.None,

            NewLine = "\n",
            Encoding = System.Text.Encoding.ASCII,

            ReadTimeout = timeout,
            WriteTimeout = timeout,

            DtrEnable = true,   // REQUIRED for RP2040 USB CDC
            RtsEnable = true
        };
    }

    // ---------------- WATCHDOG ----------------

    public bool WatchdogExpired =>
        (DateTime.UtcNow - lastResponse).TotalMilliseconds > WatchdogTimeoutMs;

    // ---------------- SEND COMMAND ----------------

    public void SendSetAll(string cmd)
    {
        if (!IsConnected)
            return;

        try
        {
            port!.Write(cmd + "\n");

            string? response = null;

            try
            {
                if (port.BytesToRead > 0)
                    response = port.ReadLine();
            }
            catch (TimeoutException)
            {
                // No response this tick — totally fine
            }

            if (response != null &&
                (response.StartsWith("OK") || response.StartsWith("ERROR")))
            {
                lastResponse = DateTime.UtcNow;
            }
        }
        catch
        {
            // Silent fail — watchdog will trigger reconnect
        }
    }

    // ---------------- CLEANUP ----------------

    private void DisposePort()
    {
        try
        {
            if (port != null)
            {
                port.Close();
                port.Dispose();
            }
        }
        catch
        {
            // ignore
        }

        port = null;
    }

    public void Dispose()
    {
        DisposePort();
    }
}