Nonemm/src/Nonemm.Rig/RigctldRadio.cs

using System.Net.Sockets;
using Nonemm.Core;

namespace Nonemm.Rig;

/// Talks to hamlib's `rigctld`, which is started separately for whichever radio
/// is on the desk. The connection is retried on its own, so a radio switched on
/// late or a `rigctld` restarted mid-contest comes back without the operator
/// touching anything.
public sealed class RigctldRadio : Radio
{
    private readonly string host;
    private readonly int port;
    private readonly TimeSpan pollInterval;
    private readonly TimeSpan retryInterval;
    private readonly CancellationTokenSource stopping = new();
    private readonly SemaphoreSlim writing = new(1, 1);
    private TcpClient? client;
    private StreamReader? reader;
    private StreamWriter? writer;
    private Task? loop;

    public RigctldRadio(
        string host = "127.0.0.1",
        int port = 4532,
        int number = 1,
        TimeSpan? pollInterval = null,
        TimeSpan? retryInterval = null)
    {
        this.host = host;
        this.port = port;
        Number = number;
        this.pollInterval = pollInterval ?? TimeSpan.FromMilliseconds(200);
        this.retryInterval = retryInterval ?? TimeSpan.FromSeconds(3);
    }

    public int Number { get; }

    public bool IsConnected { get; private set; }

    public RadioState? State { get; private set; }

    public event EventHandler<RadioState>? Moved;

    public event EventHandler<bool>? ConnectionChanged;

    public void Start() => loop ??= Task.Run(() => RunAsync(stopping.Token));

    public async Task TuneAsync(Frequency frequency, CancellationToken cancellation = default) =>
        await SendAsync($"F {frequency.Hertz}", cancellation).ConfigureAwait(false);

    public async Task SetModeAsync(Mode mode, CancellationToken cancellation = default) =>
        await SendAsync($"M {RigctldMode(mode)} 0", cancellation).ConfigureAwait(false);

    /// The transmit frequency has to be set before split is turned on, or a
    /// radio that was last split somewhere else transmits there.
    public async Task SetSplitAsync(
        Frequency? transmitFrequency,
        CancellationToken cancellation = default)
    {
        if (transmitFrequency is null)
        {
            await SendAsync("S 0 VFOA", cancellation).ConfigureAwait(false);
            return;
        }
        await SendAsync($"I {transmitFrequency.Value.Hertz}", cancellation).ConfigureAwait(false);
        await SendAsync("S 1 VFOB", cancellation).ConfigureAwait(false);
    }

    /// `J` is rigctld's set_rit, in hertz. Zero is the offset turned off,
    /// which is what the radio's own RIT clear button does.
    public async Task ClearRitAsync(CancellationToken cancellation = default) =>
        await SendAsync("J 0", cancellation).ConfigureAwait(false);

    public void Dispose()
    {
        stopping.Cancel();
        client?.Dispose();
        stopping.Dispose();
        writing.Dispose();
    }

    private async Task RunAsync(CancellationToken cancellation)
    {
        while (!cancellation.IsCancellationRequested)
        {
            try
            {
                await ConnectAsync(cancellation).ConfigureAwait(false);
                await PollAsync(cancellation).ConfigureAwait(false);
            }
            catch (OperationCanceledException)
            {
                return;
            }
            catch (Exception e) when (e is IOException or SocketException)
            {
                SetConnected(false);
                await Task.Delay(retryInterval, cancellation).ConfigureAwait(false);
            }
        }
    }

    private async Task ConnectAsync(CancellationToken cancellation)
    {
        client?.Dispose();
        client = new TcpClient();
        await client.ConnectAsync(host, port, cancellation).ConfigureAwait(false);
        NetworkStream stream = client.GetStream();
        reader = new StreamReader(stream);
        writer = new StreamWriter(stream) { AutoFlush = true };
        SetConnected(true);
    }

    private async Task PollAsync(CancellationToken cancellation)
    {
        while (!cancellation.IsCancellationRequested)
        {
            RigctldReply frequency = await AskAsync("f", cancellation).ConfigureAwait(false);
            RigctldReply mode = await AskAsync("m", cancellation).ConfigureAwait(false);
            if (frequency.Number("Frequency") is > 0 and long hertz)
            {
                RadioState state = new(
                    Frequency.FromHertz(hertz),
                    Modes.Parse(mode.Value("Mode") ?? "") ?? State?.Mode ?? Modes.Cw)
                {
                    TransmitFrequency = await TransmitFrequencyAsync(cancellation).ConfigureAwait(false),
                };
                if (state != State)
                {
                    State = state;
                    Moved?.Invoke(this, state);
                }
            }
            await Task.Delay(pollInterval, cancellation).ConfigureAwait(false);
        }
    }

    /// Zero when the radio is not split, and when it cannot tell us.
    private async Task<Frequency> TransmitFrequencyAsync(CancellationToken cancellation)
    {
        RigctldReply split = await AskAsync("s", cancellation).ConfigureAwait(false);
        if (!split.IsOk || split.Number("Split") is not 1)
        {
            return Frequency.Zero;
        }
        RigctldReply transmit = await AskAsync("i", cancellation).ConfigureAwait(false);
        return transmit.Number("TX Frequency") is > 0 and long hertz
            ? Frequency.FromHertz(hertz)
            : Frequency.Zero;
    }

    /// Every command goes out with a `+` in front, which asks rigctld for the
    /// extended answer: named fields ended by an RPRT line. Without the
    /// terminator a client has to know how many lines each command returns, and
    /// one wrong count desynchronises the connection for good.
    private async Task<RigctldReply> AskAsync(string command, CancellationToken cancellation)
    {
        await writing.WaitAsync(cancellation).ConfigureAwait(false);
        try
        {
            if (writer is null || reader is null)
            {
                throw new IOException("the connection to rigctld is not open");
            }
            await writer.WriteAsync("+" + command + "\n").ConfigureAwait(false);
            List<string> lines = [];
            while (true)
            {
                string line = await reader.ReadLineAsync(cancellation).ConfigureAwait(false)
                    ?? throw new IOException($"rigctld closed the connection during '{command}'");
                lines.Add(line);
                if (line.StartsWith("RPRT", StringComparison.Ordinal))
                {
                    return RigctldReply.Parse(lines);
                }
            }
        }
        finally
        {
            writing.Release();
        }
    }

    private async Task SendAsync(string command, CancellationToken cancellation)
    {
        if (!IsConnected)
        {
            return;
        }
        try
        {
            await AskAsync(command, cancellation).ConfigureAwait(false);
        }
        catch (Exception e) when (e is IOException or SocketException)
        {
            SetConnected(false);
        }
    }

    private void SetConnected(bool connected)
    {
        if (IsConnected != connected)
        {
            IsConnected = connected;
            ConnectionChanged?.Invoke(this, connected);
        }
    }

    /// hamlib names the modes CW, USB, LSB, RTTY, FM, AM and PKTUSB.
    private static string RigctldMode(Mode mode) => mode.Name switch
    {
        "CW" => "CW",
        "USB" => "USB",
        "LSB" => "LSB",
        "AM" => "AM",
        "FM" => "FM",
        "RTTY" => "RTTY",
        _ => "PKTUSB",
    };
}