fix: recover from microphone disconnects

MeetingAssistant.Tests/AudioMixingTests.cs

@@ -102,6 +102,23 @@ public sealed class AudioMixingTests
         Assert.Equal(2_000, BitConverter.ToInt16(chunks[0].Pcm));
     }
 
+    [Fact]
+    public async Task CompositeAudioSourceKeepsSystemAudioWhileMicrophoneIsRecovering()
+    {
+        var microphone = new WaitingAudioSource();
+        var system = new FixedAudioSource(Pcm16(10_000));
+        var source = CreateSource(microphone, system);
+        using var cancellation = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+        await using var chunks = source
+            .CaptureAsync(new MeetingAssistantOptions(), cancellation.Token)
+            .GetAsyncEnumerator(cancellation.Token);
+
+        Assert.True(await chunks.MoveNextAsync());
+        Assert.Equal(10_000, BitConverter.ToInt16(chunks.Current.Pcm));
+
+        await cancellation.CancelAsync();
+    }
+
     [Fact]
     public void AdaptiveEchoCancellerReducesEchoFromMicrophoneSignal()
     {
@@ -221,6 +238,16 @@ public sealed class AudioMixingTests
         }
     }
 
+    private sealed class WaitingAudioSource : IMeetingAudioSource
+    {
+        public async IAsyncEnumerable<AudioChunk> CaptureAsync(
+            [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
+        {
+            await Task.Delay(Timeout.InfiniteTimeSpan, cancellationToken);
+            yield break;
+        }
+    }
+
     private sealed class OptionsCapturingAudioSource : IMeetingAudioSource
     {
         private readonly AudioChunk chunk;

MeetingAssistant.Tests/MicrophoneAudioSourceTests.cs

@@ -0,0 +1,109 @@
+using MeetingAssistant.Recording;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace MeetingAssistant.Tests;
+
+public sealed class MicrophoneAudioSourceTests
+{
+    [Fact]
+    public async Task CaptureMovesToNewlyResolvedMicrophoneWhenCurrentCaptureFails()
+    {
+        var captureSources = new SequenceMicrophoneCaptureSourceFactory(
+            new FailingAfterChunkAudioSource(Pcm16(1_000)),
+            new ActiveAudioSource(Pcm16(2_000)));
+        var source = new MicrophoneAudioSource(
+            captureSources,
+            NullLogger<MicrophoneAudioSource>.Instance,
+            TimeSpan.Zero);
+        using var cancellation = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+        await using var chunks = source
+            .CaptureAsync(new MeetingAssistantOptions(), cancellation.Token)
+            .GetAsyncEnumerator(cancellation.Token);
+
+        Assert.True(await chunks.MoveNextAsync());
+        Assert.Equal(1_000, BitConverter.ToInt16(chunks.Current.Pcm));
+        Assert.True(await chunks.MoveNextAsync());
+        Assert.Equal(2_000, BitConverter.ToInt16(chunks.Current.Pcm));
+        Assert.Equal(2, captureSources.CaptureCreationCount);
+
+        await cancellation.CancelAsync();
+    }
+
+    [Fact]
+    public async Task CaptureWaitsForMicrophoneToBecomeAvailable()
+    {
+        var captureSources = new InitiallyUnavailableMicrophoneCaptureSourceFactory(
+            new ActiveAudioSource(Pcm16(3_000)));
+        var source = new MicrophoneAudioSource(
+            captureSources,
+            NullLogger<MicrophoneAudioSource>.Instance,
+            TimeSpan.Zero);
+        using var cancellation = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+        await using var chunks = source
+            .CaptureAsync(new MeetingAssistantOptions(), cancellation.Token)
+            .GetAsyncEnumerator(cancellation.Token);
+
+        Assert.True(await chunks.MoveNextAsync());
+        Assert.Equal(3_000, BitConverter.ToInt16(chunks.Current.Pcm));
+        Assert.Equal(2, captureSources.CaptureCreationCount);
+
+        await cancellation.CancelAsync();
+    }
+
+    private static byte[] Pcm16(short sample)
+    {
+        return BitConverter.GetBytes(sample);
+    }
+
+    private sealed class SequenceMicrophoneCaptureSourceFactory(params IMeetingAudioSource[] sources)
+        : IMicrophoneCaptureSourceFactory
+    {
+        private readonly Queue<IMeetingAudioSource> sources = new(sources);
+
+        public int CaptureCreationCount { get; private set; }
+
+        public IMeetingAudioSource CreateCapture(MeetingAssistantOptions options)
+        {
+            CaptureCreationCount++;
+            return sources.Dequeue();
+        }
+    }
+
+    private sealed class InitiallyUnavailableMicrophoneCaptureSourceFactory(IMeetingAudioSource availableSource)
+        : IMicrophoneCaptureSourceFactory
+    {
+        public int CaptureCreationCount { get; private set; }
+
+        public IMeetingAudioSource CreateCapture(MeetingAssistantOptions options)
+        {
+            CaptureCreationCount++;
+            if (CaptureCreationCount == 1)
+            {
+                throw new InvalidOperationException("No microphone is currently available.");
+            }
+
+            return availableSource;
+        }
+    }
+
+    private sealed class FailingAfterChunkAudioSource(byte[] pcm) : IMeetingAudioSource
+    {
+        public async IAsyncEnumerable<AudioChunk> CaptureAsync(
+            [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
+        {
+            await Task.Yield();
+            yield return new AudioChunk(pcm, 16000, 1);
+            throw new InvalidOperationException("The active microphone was disconnected.");
+        }
+    }
+
+    private sealed class ActiveAudioSource(byte[] pcm) : IMeetingAudioSource
+    {
+        public async IAsyncEnumerable<AudioChunk> CaptureAsync(
+            [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
+        {
+            yield return new AudioChunk(pcm, 16000, 1);
+            await Task.Delay(Timeout.InfiniteTimeSpan, cancellationToken);
+        }
+    }
+}

MeetingAssistant.Tests/MicrophoneSelectionTests.cs

@@ -51,4 +51,17 @@ public sealed class MicrophoneSelectionTests
 
         Assert.Equal("runtime-id", selected?.Id);
     }
+
+    [Fact]
+    public void UnavailableDefaultMicrophoneFallsBackToAnotherActiveDevice()
+    {
+        var selection = new MicrophoneDeviceSelection();
+
+        var selected = selection.Resolve(
+            configuredDeviceId: null,
+            new MicrophoneDevice("disconnected-id", "disconnected microphone"),
+            [new MicrophoneDevice("backup-id", "backup microphone")]);
+
+        Assert.Equal("backup-id", selected?.Id);
+    }
 }