Implement meeting assistant v1

MeetingAssistant.Tests/AudioMixingTests.cs

@@ -0,0 +1,71 @@
+using MeetingAssistant.Recording;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace MeetingAssistant.Tests;
+
+public sealed class AudioMixingTests
+{
+    [Fact]
+    public async Task CompositeAudioSourceMixesMicrophoneAndSystemAudioIntoOnePcmStream()
+    {
+        var microphone = new FixedAudioSource(Pcm16(10_000));
+        var system = new FixedAudioSource(Pcm16(20_000));
+        var source = new CompositeMeetingAudioSource(
+            microphone,
+            system,
+            NullLogger<CompositeMeetingAudioSource>.Instance);
+
+        var chunks = await ReadChunks(source);
+
+        Assert.Single(chunks);
+        Assert.Equal(30_000, BitConverter.ToInt16(chunks[0].Pcm));
+    }
+
+    [Fact]
+    public async Task CompositeAudioSourceClampsMixedSamples()
+    {
+        var microphone = new FixedAudioSource(Pcm16(30_000));
+        var system = new FixedAudioSource(Pcm16(10_000));
+        var source = new CompositeMeetingAudioSource(
+            microphone,
+            system,
+            NullLogger<CompositeMeetingAudioSource>.Instance);
+
+        var chunks = await ReadChunks(source);
+
+        Assert.Equal(short.MaxValue, BitConverter.ToInt16(chunks[0].Pcm));
+    }
+
+    private static async Task<IReadOnlyList<AudioChunk>> ReadChunks(IMeetingAudioSource source)
+    {
+        var chunks = new List<AudioChunk>();
+        await foreach (var chunk in source.CaptureAsync(CancellationToken.None))
+        {
+            chunks.Add(chunk);
+        }
+
+        return chunks;
+    }
+
+    private static byte[] Pcm16(short sample)
+    {
+        return BitConverter.GetBytes(sample);
+    }
+
+    private sealed class FixedAudioSource : IMeetingAudioSource
+    {
+        private readonly AudioChunk chunk;
+
+        public FixedAudioSource(byte[] pcm)
+        {
+            chunk = new AudioChunk(pcm, 16000, 1);
+        }
+
+        public async IAsyncEnumerable<AudioChunk> CaptureAsync(
+            [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
+        {
+            await Task.Yield();
+            yield return chunk;
+        }
+    }
+}