Nonemm/src/Nonemm.Digital/MmttyEngine.cs

using System.Globalization;
using System.Threading.Channels;

namespace Nonemm.Digital;

/// MMTTY or 2Tone, started and driven through the bridge. The startup is
/// N1MM's: the engine is given a title, the PTT port out of Mmtty.INI and a
/// command line, and an engine that fails to initialise is started again up to
/// ten times, which is what N1MM's retry does.
///
/// It holds a buffer of its own and says how much of it is left, so the
/// type-ahead feeds it one character at a time the way N1MM does and paces on
/// the count.
public sealed class MmttyEngine : DigitalEngine, EngineBuffer
{
    private const int StartAttempts = 10;

    private readonly BridgeChannel bridge;
    private readonly MmttyOptions options;
    private readonly Channel<string> lines = Channel.CreateUnbounded<string>();
    private readonly TimeSpan startPatience;
    private TaskCompletionSource<bool>? starting;
    private MmttySettings settings = new();
    private string command = "";
    private int attempts;
    private Task? reading;

    public MmttyEngine(BridgeChannel bridge, MmttyOptions options, TimeSpan? startPatience = null)
    {
        this.bridge = bridge;
        this.options = options;
        this.startPatience = startPatience ?? TimeSpan.FromSeconds(30);
        bridge.LineReceived += (_, line) => lines.Writer.TryWrite(line);
        bridge.Failed += (_, why) => Stopped(why);
    }

    public bool IsConnected { get; private set; }

    public bool IsTransmitting { get; private set; }

    /// The version MMTTY reported when it connected.
    public string Version { get; private set; } = "";

    public int MarkHertz { get; private set; }

    public int SpaceHertz { get; private set; }

    /// MMTTY's AFC, net and reverse bits. Kept here because a toggle is sent as
    /// the whole word, so the current one has to be known.
    public int Switches { get; private set; }

    public event EventHandler<string>? Received;

    public event EventHandler<bool>? TransmitChanged;

    public event EventHandler<bool>? ConnectionChanged;

    /// Anything the bridge says about itself, for the status line.
    public event EventHandler<string>? Reported;

    /// The answer to `AskBufferedAsync`: how many characters the engine still
    /// has to transmit.
    public event EventHandler<int>? Buffered;

    public async Task StartAsync(CancellationToken cancellation = default)
    {
        settings = MmttySettings.Read(options.SettingsPath);
        Switches = settings.Switches;
        await bridge.StartAsync(cancellation).ConfigureAwait(false);
        command = options.CommandLine(
            await bridge.ToWindowsPathAsync(options.EnginePath, cancellation).ConfigureAwait(false));
        starting = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
        attempts = 1;
        reading ??= Task.Run(ReadAsync, CancellationToken.None);
        await OpenAsync(cancellation).ConfigureAwait(false);
        await starting.Task.WaitAsync(startPatience, cancellation).ConfigureAwait(false);
    }

    public Task SendAsync(string text, CancellationToken cancellation = default) =>
        bridge.SendAsync(BridgeLine.Write("send", text), cancellation);

    /// One typed character, which MMTTY transmits as it arrives.
    public Task TypeAsync(char character, CancellationToken cancellation = default) =>
        PostAsync(MmttyMessage.TypeCharacter, character, cancellation);

    /// Asks how many characters the engine still holds. The control has no
    /// event for it, so it is polled; the answer arrives on `Buffered`. A
    /// property name other than `TxBufLen` is only for finding out what the
    /// control answers to.
    public Task AskBufferedAsync(string property = "", CancellationToken cancellation = default) =>
        bridge.SendAsync(BridgeLine.Write("buffer", property), cancellation);

    /// Escape and the RX button: stop now and leave what has not gone out
    /// unsent. N1MM's `AbortXmit`.
    public Task AbortAsync(CancellationToken cancellation = default) =>
        bridge.SendAsync(BridgeLine.Write("ptt", "0"), cancellation);

    /// The control's `PTT` property back to false, which is the key the other
    /// way rather than a stop. N1MM never does this: it keys with the property
    /// and leaves `SetMmttyPTT(1)` to drop the transmitter.
    public Task ReleaseKeyAsync(CancellationToken cancellation = default) =>
        bridge.SendAsync(BridgeLine.Write("key", "0"), cancellation);

    /// N1MM's `{TX}` and `{RX}`. Keying is the control's `PTT` property;
    /// unkeying is `SetMmttyPTT(1)`, which waits for the buffer to empty first,
    /// so a macro that ends with `{RX}` still goes out in full.
    public Task SetPttAsync(bool on, CancellationToken cancellation = default) =>
        bridge.SendAsync(
            on ? BridgeLine.Write("key", "1") : BridgeLine.Write("ptt", "1"),
            cancellation);

    public Task KeyAsync(CancellationToken cancellation = default) =>
        SetPttAsync(true, cancellation);

    public Task ReturnToReceiveAsync(CancellationToken cancellation = default) =>
        SetPttAsync(false, cancellation);

    /// Moves the demodulator, keeping the shift the engine reported.
    public async Task TuneAsync(int markHertz, CancellationToken cancellation = default)
    {
        int shift = SpaceHertz - MarkHertz;
        await PostAsync(MmttyMessage.MarkFrequency, markHertz, cancellation).ConfigureAwait(false);
        await PostAsync(MmttyMessage.SpaceFrequency, markHertz + shift, cancellation)
            .ConfigureAwait(false);
    }

    public Task SetSwitchesAsync(int switches, CancellationToken cancellation = default) =>
        PostAsync(MmttyMessage.Switches, switches, cancellation);

    public Task PostAsync(MmttyMessage message, int parameter, CancellationToken cancellation = default) =>
        bridge.SendAsync(
            BridgeLine.Write("post", ((int)message).ToString(), parameter.ToString()),
            cancellation);

    /// Shuts the engine down and stops the bridge.
    public async Task StopAsync(CancellationToken cancellation = default)
    {
        await bridge.SendAsync(BridgeLine.Write("quit"), cancellation).ConfigureAwait(false);
        if (reading is not null)
        {
            lines.Writer.TryComplete();
            await reading.ConfigureAwait(false);
        }
    }

    public void Dispose()
    {
        lines.Writer.TryComplete();
        bridge.Dispose();
    }

    private Task OpenAsync(CancellationToken cancellation) =>
        bridge.SendAsync(
            BridgeLine.Write("open", options.Title, PttPort(), command),
            cancellation);

    private string PttPort() => options.PttPort ?? settings.PttPort;

    private async Task ReadAsync()
    {
        await foreach (string line in lines.Reader.ReadAllAsync().ConfigureAwait(false))
        {
            (string verb, string[] fields) = BridgeLine.Read(line);
            await ActOnAsync(verb, fields).ConfigureAwait(false);
        }
    }

    private async Task ActOnAsync(string verb, string[] fields)
    {
        switch (verb)
        {
            case "connected":
                Version = Field(fields, 0);
                IsConnected = true;
                starting?.TrySetResult(true);
                ConnectionChanged?.Invoke(this, true);
                break;
            case "disconnected":
                await DisconnectedAsync(Number(fields, 0)).ConfigureAwait(false);
                break;
            case "rx":
                Received?.Invoke(this, ((char)Number(fields, 0)).ToString());
                break;
            case "buffer":
                Buffered?.Invoke(this, Number(fields, 0));
                break;
            case "tx":
                IsTransmitting = Number(fields, 0) == 1;
                TransmitChanged?.Invoke(this, IsTransmitting);
                break;
            case "mark":
                MarkHertz = Number(fields, 0);
                break;
            case "space":
                SpaceHertz = Number(fields, 0);
                break;
            case "switch":
                Switches = Number(fields, 0);
                break;
            case "error":
                Stopped(Field(fields, 0));
                break;
            case "log":
                Reported?.Invoke(this, Field(fields, 0));
                break;
        }
    }

    /// Status 2 is MMTTY failing to come up, which happens often enough that
    /// N1MM starts it again rather than telling the operator.
    private async Task DisconnectedAsync(int status)
    {
        if (status != 2)
        {
            IsConnected = false;
            ConnectionChanged?.Invoke(this, false);
            return;
        }
        if (attempts >= StartAttempts)
        {
            Stopped($"{options.EnginePath} failed to start after {attempts} tries");
            return;
        }
        attempts++;
        Reported?.Invoke(this, $"the engine failed to start, trying again ({attempts})");
        await OpenAsync(CancellationToken.None).ConfigureAwait(false);
    }

    private void Stopped(string why)
    {
        if (starting?.TrySetException(new InvalidOperationException(why)) == true)
        {
            return;
        }
        if (IsConnected)
        {
            IsConnected = false;
            ConnectionChanged?.Invoke(this, false);
        }
        Reported?.Invoke(this, why);
    }

    private static string Field(string[] fields, int index) =>
        index < fields.Length ? fields[index] : "";

    private static int Number(string[] fields, int index) =>
        int.TryParse(Field(fields, index), NumberStyles.Integer, CultureInfo.InvariantCulture, out int value)
            ? value
            : 0;
}