using System.IO.Ports;
using System.Text;

namespace Nonemm.Keying;

/// Sends CW through a WinKeyer on a serial port. The keyer is opened in host
/// mode, which is the state where it takes text rather than following a paddle
/// alone.
public sealed class WinkeyerSender : MessageSender
{
    private const byte AdminCommand = 0x00;
    private const byte HostOpen = 0x02;
    private const byte HostClose = 0x03;
    private const byte SetSpeed = 0x02;
    private const byte ClearBuffer = 0x0A;

    private readonly SerialPort port;
    private readonly WinkeyerStatus status = new();

    public WinkeyerSender(string portName, int baudRate = 1200)
    {
        port = new SerialPort(portName, baudRate, Parity.None, 8, StopBits.Two);
        port.DataReceived += (_, _) => ReadStatus();
    }

    public bool IsReady => port.IsOpen;

    /// The keyer sends a status byte of its own accord whenever it starts or
    /// stops sending, so nothing has to be asked for.
    public bool ReportsCompletion => true;

    public event EventHandler? Finished;

    /// Opens the port and puts the keyer in host mode. The keyer answers with
    /// its firmware version, which is read and thrown away.
    public void Open()
    {
        port.Open();
        port.Write([AdminCommand, HostOpen], 0, 2);
        Thread.Sleep(100);
        port.DiscardInBuffer();
    }

    public Task SendAsync(string text, CancellationToken cancellation = default)
    {
        Write(Encoding.ASCII.GetBytes(text.ToUpperInvariant()));
        return Task.CompletedTask;
    }

    public Task AbortAsync(CancellationToken cancellation = default)
    {
        Write([ClearBuffer]);
        return Task.CompletedTask;
    }

    public Task SetSpeedAsync(int wordsPerMinute, CancellationToken cancellation = default)
    {
        Write([SetSpeed, (byte)Math.Clamp(wordsPerMinute, 5, 99)]);
        return Task.CompletedTask;
    }

    public void Dispose()
    {
        if (port.IsOpen)
        {
            port.Write([AdminCommand, HostClose], 0, 2);
            port.Close();
        }
        port.Dispose();
    }

    /// Runs on the serial port's own thread.
    private void ReadStatus()
    {
        int waiting = port.BytesToRead;
        for (int at = 0; at < waiting; at++)
        {
            if (status.Read((byte)port.ReadByte()))
            {
                Finished?.Invoke(this, EventArgs.Empty);
            }
        }
    }

    private void Write(byte[] message)
    {
        if (!port.IsOpen)
        {
            throw new InvalidOperationException($"the keyer on {port.PortName} is not open");
        }
        port.Write(message, 0, message.Length);
    }
}