meeting-assistant/MeetingAssistant/Recording/MicrophoneAudioSource.cs

using System.Runtime.CompilerServices;

namespace MeetingAssistant.Recording;

public sealed class MicrophoneAudioSource : IMeetingAudioSource
{
    private static readonly TimeSpan DefaultRecoveryDelay = TimeSpan.FromSeconds(1);
    private readonly IMicrophoneCaptureSourceFactory captureSources;
    private readonly ILogger<MicrophoneAudioSource> logger;
    private readonly TimeSpan recoveryDelay;
    private readonly MicrophoneSwitchMonitor? switchMonitor;
    private readonly MicrophoneDeviceSelection? selection;

    public MicrophoneAudioSource(
        IMicrophoneCaptureSourceFactory captureSources,
        ILogger<MicrophoneAudioSource> logger,
        MicrophoneSwitchMonitor? switchMonitor = null,
        MicrophoneDeviceSelection? selection = null)
        : this(captureSources, logger, DefaultRecoveryDelay, switchMonitor, selection)
    {
    }

    internal MicrophoneAudioSource(
        IMicrophoneCaptureSourceFactory captureSources,
        ILogger<MicrophoneAudioSource> logger,
        TimeSpan recoveryDelay,
        MicrophoneSwitchMonitor? switchMonitor = null,
        MicrophoneDeviceSelection? selection = null)
    {
        this.captureSources = captureSources;
        this.logger = logger;
        this.recoveryDelay = recoveryDelay;
        this.switchMonitor = switchMonitor;
        this.selection = selection;
    }

    public IAsyncEnumerable<AudioChunk> CaptureAsync(CancellationToken cancellationToken)
    {
        return CaptureAsync(new MeetingAssistantOptions(), cancellationToken);
    }

    public async IAsyncEnumerable<AudioChunk> CaptureAsync(
        MeetingAssistantOptions options,
        [EnumeratorCancellation] CancellationToken cancellationToken)
    {
        using var session = new CaptureSession(selection, cancellationToken);
        var monitoring = switchMonitor?.RunAsync(session.SwitchTo, session.Token) ?? Task.CompletedTask;
        try
        {
            await foreach (var chunk in CaptureWithRecoveryAsync(options, session, session.Token))
            {
                yield return chunk;
            }
        }
        finally
        {
            session.Stop();
            await monitoring;
        }
    }

    private async IAsyncEnumerable<AudioChunk> CaptureWithRecoveryAsync(
        MeetingAssistantOptions options,
        CaptureSession session,
        [EnumeratorCancellation] CancellationToken cancellationToken)
    {
        var failedAttempts = 0;
        while (!cancellationToken.IsCancellationRequested)
        {
            var captureToken = session.BeginCapture();
            IMeetingAudioSource? captureSource = null;
            IAsyncEnumerator<AudioChunk>? capture = null;
            Exception? failure = null;

            try
            {
                captureSource = captureSources.CreateCapture(options);
                capture = captureSource
                    .CaptureAsync(options, captureToken)
                    .GetAsyncEnumerator(captureToken);
            }
            catch (OperationCanceledException) when (captureToken.IsCancellationRequested)
            {
            }
            catch (Exception exception)
            {
                failure = exception;
            }

            using var captureOwner = captureSource as IDisposable;
            if (cancellationToken.IsCancellationRequested)
            {
                yield break;
            }

            if (capture is not null)
            {
                try
                {
                    while (!captureToken.IsCancellationRequested)
                    {
                        var hasNext = false;
                        try
                        {
                            hasNext = await capture.MoveNextAsync();
                        }
                        catch (OperationCanceledException) when (captureToken.IsCancellationRequested)
                        {
                        }
                        catch (Exception exception)
                        {
                            failure = exception;
                        }

                        if (captureToken.IsCancellationRequested || failure is not null || !hasNext)
                        {
                            break;
                        }

                        if (failedAttempts > 0)
                        {
                            logger.LogInformation(
                                "Microphone capture recovered after {FailedAttemptCount} failed attempt(s)",
                                failedAttempts);
                            failedAttempts = 0;
                        }

                        yield return capture.Current;
                    }
                }
                finally
                {
                    try
                    {
                        await capture.DisposeAsync();
                    }
                    catch (OperationCanceledException) when (captureToken.IsCancellationRequested)
                    {
                    }
                    catch (Exception exception)
                    {
                        failure ??= exception;
                    }
                }
            }

            var switchRequested = captureToken.IsCancellationRequested;
            session.EndCapture();
            if (cancellationToken.IsCancellationRequested)
            {
                yield break;
            }

            if (switchRequested)
            {
                logger.LogInformation("Replacing microphone capture after an accepted device-switch notification");
                continue;
            }

            failedAttempts++;
            logger.LogWarning(
                failure,
                "Microphone capture stopped unexpectedly; re-resolving an available microphone in {RecoveryDelay}",
                recoveryDelay);

            if (!await WaitForRecoveryAsync(cancellationToken))
            {
                yield break;
            }
        }
    }

    private async Task<bool> WaitForRecoveryAsync(CancellationToken cancellationToken)
    {
        try
        {
            await Task.Delay(recoveryDelay, cancellationToken);
            return true;
        }
        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
        {
            return false;
        }
    }

    private sealed class CaptureSession(MicrophoneDeviceSelection? selection, CancellationToken cancellationToken) : IDisposable
    {
        private readonly object gate = new();
        private readonly CancellationTokenSource lifetime = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        private CancellationTokenSource? capture;

        public CancellationToken Token => lifetime.Token;

        public CancellationToken BeginCapture()
        {
            lock (gate)
            {
                capture = CancellationTokenSource.CreateLinkedTokenSource(lifetime.Token);
                return capture.Token;
            }
        }

        public void EndCapture()
        {
            lock (gate)
            {
                capture?.Dispose();
                capture = null;
            }
        }

        public void SwitchTo(MicrophoneDevice device, CancellationToken promptCancellation)
        {
            lock (gate)
            {
                if (lifetime.IsCancellationRequested || promptCancellation.IsCancellationRequested || selection is null) return;
                selection.Select(device.Id);
                capture?.Cancel();
            }
        }

        public void Stop()
        {
            lock (gate) lifetime.Cancel();
        }

        public void Dispose()
        {
            Stop();
            EndCapture();
            lifetime.Dispose();
        }
    }
}