voice-cat/tests/VoiceCat.Tests/AudioEngineTests.cs

using System.Net;
using System.Net.Sockets;
using VoiceCat.Audio;
using VoiceCat.Codec;
using VoiceCat.Core;
using VoiceCat.Crypto;
using VoiceCat.Protocol;
using VoiceCat.Transport;
using Voicecat.V1;

namespace VoiceCat.Tests;

public class AudioEngineTests
{
    [Fact]
    public void ManagedAudioWorkerUsesDeadlineSchedulingAtRealtimePriority()
    {
        string source = File.ReadAllText(Path.Combine(FindRoot(), "src", "VoiceCat.Audio", "AudioEngine.cs"));

        Assert.Contains("Priority = ThreadPriority.Highest", source);
        Assert.Contains("WaitUntil(deadline);", source);
        Assert.DoesNotContain("Thread.Sleep((int)Math.Ceiling(remaining))", source);
    }

    [Fact]
    public void MediaSenderDoesNotDependOnCoalescedAsyncTimers()
    {
        string source = File.ReadAllText(Path.Combine(FindRoot(), "src", "VoiceCat.Core", "ClientMediaTransport.cs"));

        Assert.Contains("new Thread(Send)", source);
        Assert.Contains("Volatile.Read(ref socket).Send(packet.AsSpan(0, size)", source);
        Assert.DoesNotContain("Task.Delay(5", source);
        Assert.DoesNotContain("SendAsync(packet.AsMemory", source);
    }

    [Fact]
    public void MediaSenderWakesOnQueueSignalInsteadOfTimedPolling()
    {
        string source = File.ReadAllText(Path.Combine(FindRoot(), "src", "VoiceCat.Core", "ClientMediaTransport.cs"));

        Assert.Contains("sendReady.WaitOne(", source);
        Assert.Contains("senderNapping", source);
        Assert.DoesNotContain("Thread.Sleep(1);", source);
    }

    [Fact]
    public async Task MediaSenderDeliversQueuedVoicePromptlyWithoutTimedPolling()
    {
        // A loopback "relay" answers the binding so the sender's own keepalive pass falls back to
        // its five second schedule: only the queue signal can then deliver queued voice promptly,
        // so a lost wake or a polling loop shows up here as a multi-second delay.
        using var relay = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        relay.Bind(new IPEndPoint(IPAddress.Loopback, 0));
        byte[] key = new byte[32]; Random.Shared.NextBytes(key);
        using var crypto = new MediaSessionCrypto(new MediaEncryptor(key), new MediaDecryptor(key));
        await using var transport = new ClientMediaTransport((IPEndPoint)relay.LocalEndPoint!, new byte[16], crypto, CancellationToken.None);

        byte[] datagram = new byte[512];
        using (var startup = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
        {
            SocketReceiveFromResult probe = await relay.ReceiveFromAsync(datagram, SocketFlags.None, new IPEndPoint(IPAddress.Any, 0), startup.Token);
            Assert.Equal(VoiceFrameHeader.Size + 16, probe.ReceivedBytes);
            byte[] keepalive = new byte[VoiceFrameHeader.Size];
            new VoiceFrameHeader(MediaFrameType.Keepalive, 0, 0, 0, 0, 0).Write(keepalive);
            await relay.SendToAsync(keepalive, SocketFlags.None, probe.RemoteEndPoint);
        }
        await transport.Bound.WaitAsync(TimeSpan.FromSeconds(5));

        var stopwatch = System.Diagnostics.Stopwatch.StartNew();
        Assert.True(transport.TrySend(new(MediaFrameType.Voice, VoiceFrameFlags.None, 0, 7, 0, 0), new byte[80]));
        await ReceiveVoiceAsync(relay, datagram, 1, TimeSpan.FromSeconds(2));
        Assert.True(stopwatch.Elapsed < TimeSpan.FromSeconds(2));

        // A burst queued while the sender naps must drain in one wake, not one keepalive pass.
        stopwatch.Restart();
        for (uint i = 1; i <= 30; i++)
            Assert.True(transport.TrySend(new(MediaFrameType.Voice, VoiceFrameFlags.None, 0, 7, 0, i * 960), new byte[80]));
        await ReceiveVoiceAsync(relay, datagram, 30, TimeSpan.FromSeconds(2));
        Assert.True(stopwatch.Elapsed < TimeSpan.FromSeconds(2));
    }

    private static async Task ReceiveVoiceAsync(Socket relay, byte[] datagram, int count, TimeSpan timeout)
    {
        int voice = VoiceFrameHeader.Size + 80 + MediaEncryptor.TagSize;
        using var deadline = new CancellationTokenSource(timeout);
        while (count > 0)
        {
            SocketReceiveFromResult packet = await relay.ReceiveFromAsync(datagram, SocketFlags.None, new IPEndPoint(IPAddress.Any, 0), deadline.Token);
            if (packet.ReceivedBytes == voice) count--;
        }
    }

    [Theory]
    [InlineData(-1000)]
    [InlineData(1000)]
    public void AdaptivePcmBufferAbsorbsIndependentClockDrift(int partsPerMillion)
    {
        var buffer = new AdaptivePcmBuffer(1, 40); short[] input = new short[962], output = new short[960];
        input.AsSpan().Fill(1234); Assert.True(buffer.TryWrite(input.AsSpan(0, 960)));
        Assert.True(buffer.TryWrite(input.AsSpan(0, 960)));
        double produced = 0;
        for (int cycle = 0; cycle < 10_000; cycle++)
        {
            produced += 960 * (1 + partsPerMillion / 1_000_000.0);
            int frames = (int)produced; produced -= frames;
            Assert.True(buffer.TryWrite(input.AsSpan(0, frames)));
            Assert.Equal(output.Length, buffer.Read(output));
        }
        Assert.InRange(buffer.CountFrames, 480, 3840);
        long before = GC.GetAllocatedBytesForCurrentThread();
        for (int i = 0; i < 100; i++) { buffer.TryWrite(input.AsSpan(0, 960)); buffer.Read(output); }
        Assert.Equal(0, GC.GetAllocatedBytesForCurrentThread() - before);
    }

    [Fact]
    public void AdaptivePcmBufferPreservesPartialFrameAcrossCaptureCallbacks()
    {
        var buffer = new AdaptivePcmBuffer(1, 20);
        short[] half = Enumerable.Range(0, 480).Select(value => (short)value).ToArray();
        short[] full = new short[960];

        Assert.True(buffer.TryWrite(half));
        Assert.Equal(0, buffer.Read(full));
        Assert.Equal(480, buffer.CountFrames);

        Assert.True(buffer.TryWrite(half));
        Assert.Equal(960, buffer.Read(full));
        Assert.Equal(0, buffer.CountFrames);
        Assert.Equal(half, full.AsSpan(0, 480).ToArray());
        Assert.Equal(half, full.AsSpan(480, 480).ToArray());
    }

    [Theory]
    [InlineData(20)]
    [InlineData(40)]
    [InlineData(60)]
    public void AdaptivePcmBufferSustainsIosSizedCaptureCallbacks(int bufferMilliseconds)
    {
        var buffer = new AdaptivePcmBuffer(1, bufferMilliseconds);
        short[] callback = new short[1_024], encoded = new short[960];
        long producedFrames = 0;
        int lateStarvation = 0, fullReads = 0;

        // AVAudioEngine commonly delivers 1,024 frames every 21 1/3 ms while the codec owner
        // requests 960 frames every 20 ms. Replay those independent clocks for two minutes.
        for (long consumerFrame = 0; consumerFrame < 48_000L * 120; consumerFrame += 960)
        {
            while (producedFrames <= consumerFrame)
            {
                for (int i = 0; i < callback.Length; i++) callback[i] = (short)(producedFrames + i);
                Assert.True(buffer.TryWrite(callback));
                producedFrames += callback.Length;
            }

            int read = buffer.Read(encoded);
            if (read == encoded.Length) fullReads++;
            // A 20 ms target initially contains one 1,024-frame callback, so the codec's
            // second deadline precedes the next callback by 1.33 ms. Re-priming once during
            // that first second is expected; recurring starvation is the audible defect.
            else if (consumerFrame >= 48_000) lateStarvation++;
        }

        Assert.Equal(0, lateStarvation);
        Assert.True(fullReads > 5_000);
    }

    [Theory]
    [InlineData(-1000)]
    [InlineData(1000)]
    public void AdaptivePcmBufferKeepsBurstingIosCaptureBoundedOverLongCalls(int partsPerMillion)
    {
        var buffer = new AdaptivePcmBuffer(1, 120, 65_536);
        short[] callback = new short[4_800], encoded = new short[960];
        long produced = 0;
        int lateStarvation = 0;
        for (long consumerFrame = 0; consumerFrame < 48_000L * 600; consumerFrame += 960)
        {
            while (produced / (1 + partsPerMillion / 1_000_000.0) <= consumerFrame)
            {
                Assert.True(buffer.TryWrite(callback));
                produced += callback.Length;
            }
            if (buffer.Read(encoded) == 0 && consumerFrame >= 48_000) lateStarvation++;
            Assert.InRange(buffer.CountFrames, 0, 20_000);
        }
        Assert.Equal(0, lateStarvation);
    }

    [Theory]
    [InlineData(20)]
    [InlineData(40)]
    [InlineData(120)]
    public void AdaptivePcmBufferResynchronizeDropsStallBacklogToTheTarget(int bufferMilliseconds)
    {
        var buffer = new AdaptivePcmBuffer(1, bufferMilliseconds, 65_536);
        short[] chunk = new short[960], output = new short[960];
        chunk.AsSpan().Fill(1234);

        // A stalled consumer leaves every chunk queued: feed and drain rates are equal in steady
        // state, so this backlog would otherwise sit at a fixed offset until overflow drops begin.
        for (int i = 0; i < 50; i++) Assert.True(buffer.TryWrite(chunk));
        Assert.Equal(50 * 960, buffer.CountFrames);

        buffer.Resynchronize();
        Assert.Equal(bufferMilliseconds * 48, buffer.CountFrames);
        Assert.Equal(960, buffer.Read(output));
        Assert.All(output, value => Assert.Equal(1234, value));

        // At or below the target the resynchronization drops nothing.
        buffer.Resynchronize();
        Assert.Equal(bufferMilliseconds * 48 - 960, buffer.CountFrames);
    }

    [Fact]
    public void OneCaptureMissDoesNotRestartTalkspurtButSustainedStarvationDoes()
    {
        var sent = new List<(uint Timestamp, VoiceFrameFlags Flags)>();
        using var engine = new AudioEngine((_, timestamp, _, flags) => { sent.Add((timestamp, flags)); return true; }, false)
        { InputMode = AudioInputMode.AlwaysOn, DeviceBufferMilliseconds = 20 };
        engine.AddLocalStream(Stream()); short[] tone = Tone();
        engine.FeedPcm(1, tone, 1); engine.ProcessCycle();
        engine.ProcessCycle();
        engine.FeedPcm(1, tone, 1); engine.ProcessCycle();
        Assert.Equal(2, sent.Count); Assert.True((sent[0].Flags & VoiceFrameFlags.Marker) != 0); Assert.Equal(VoiceFrameFlags.None, sent[1].Flags & VoiceFrameFlags.Marker);
        LocalAudioDiagnostics diagnostic = engine.GetLocalDiagnostics(1);
        Assert.Equal(3, diagnostic.Cycles); Assert.Equal(1, diagnostic.StarvedCycles); Assert.Equal(2, diagnostic.EncodedPackets);
        for (int i = 0; i < 10; i++) engine.ProcessCycle();
        engine.FeedPcm(1, tone, 1); engine.ProcessCycle();
        Assert.True((sent[^1].Flags & VoiceFrameFlags.Marker) != 0);
    }

    [Fact]
    public void AutomaticPacketLossUpdatesOnAudioOwnerAndManualStreamsIgnoreIt()
    {
        StreamInfo automatic = Stream();
        automatic.Audio.PacketLossMode = PacketLossMode.PacketLossAutoBalanced;
        using var engine = new AudioEngine((_, _, _, _) => true, false);
        engine.AddLocalStream(automatic);
        engine.SetExpectedPacketLoss(7);
        Assert.Equal(20, engine.GetAppliedExpectedPacketLoss(1));
        engine.ProcessCycle();
        Assert.Equal(7, engine.GetAppliedExpectedPacketLoss(1));

        engine.RemoveLocalStream(1);
        engine.ProcessCycle();
        engine.AddLocalStream(Stream());
        engine.SetExpectedPacketLoss(4);
        engine.ProcessCycle();
        Assert.Equal(20, engine.GetAppliedExpectedPacketLoss(1));
    }

    [Theory]
    [InlineData(5)] [InlineData(10)] [InlineData(20)] [InlineData(40)] [InlineData(60)]
    public void RecoveryLookaheadTracksChannelFrameDuration(int frameMilliseconds)
    {
        // One frame of standing depth plus one of recovery lookahead. The depth floor keeps a
        // quiet link from playing out with no buffer at all, where reordering alone conceals.
        using var stream = new ReceiveStream(2, Stream(frameMilliseconds));
        Assert.Equal(frameMilliseconds * 96, stream.TargetDepthSamples);

        StreamInfo plain = Stream(frameMilliseconds); plain.Audio.Fec = false;
        using var bare = new ReceiveStream(2, plain);
        Assert.Equal(frameMilliseconds * 48, bare.TargetDepthSamples);
    }

    [Fact]
    public void JitterTargetAdaptsInSampleTimeAndRemainsCapped()
    {
        var clock = new ManualAudioClock(); StreamInfo info = Stream(); info.Audio.Fec = false;
        using var stream = new ReceiveStream(2, info, clock); using var encoder = new OpusEncoder(new() { Bitrate = 32000 });
        byte[] packet = new byte[1275]; int length = encoder.Encode(Tone(), packet);
        for (uint i = 0; i < 40; i++)
        {
            clock.Advance(i % 2 == 0 ? 5 : 35);
            stream.Enqueue(new(MediaFrameType.Voice, 0, 0, 42, i, i * 960), packet.AsSpan(0, length));
        }
        int[] output = new int[1920]; stream.Mix(output, false, null);
        Assert.InRange(stream.TargetDepthSamples, 960, 5760);
    }

    [Fact]
    public void DredUsesTimestampOffsetForConsecutiveMissingShortFrames()
    {
        using var probe = new OpusEncoder();
        if (!probe.SupportsDeepRedundancy) return;
        StreamInfo info = Stream(10, dred: true); using var stream = new ReceiveStream(2, info);
        using var encoder = new OpusEncoder(new() { FrameDurationMilliseconds = 10, DeepRedundancy = true, ExpectedPacketLossPercent = 30, Bitrate = 64000 });
        byte[] packet = new byte[1275]; short[] tone = new short[480]; int[] output = new int[1920];
        for (uint i = 0; i < 50; i++)
        {
            CodecTests.FillTone(tone, 480, 1, 48000, (int)i); int length = encoder.Encode(tone, packet);
            if (i is not (25 or 26)) stream.Enqueue(new(MediaFrameType.Voice, 0, 0, 42, i, i * 480), packet.AsSpan(0, length));
            if (i % 2 == 1) { output.AsSpan().Clear(); stream.Mix(output, false, null); }
        }
        Assert.True(stream.DredFrames >= 2);
    }

    [Theory]
    [InlineData(true)]
    [InlineData(false)]
    public void LostFramesUseDredThenFecBeforeBoundedPlc(bool useDred)
    {
        using var receive = new ReceiveStream(2, Stream(dred: useDred));
        using var encoder = new OpusEncoder(new() { DeepRedundancy = useDred, ForwardErrorCorrection = true, ExpectedPacketLossPercent = 30, Complexity = 10, Bitrate = 64000 });
        byte[] packet = new byte[1275]; short[] tone = Tone(); int[] output = new int[1920];
        for (uint i = 0; i < 40; i++)
        {
            CodecTests.FillTone(tone, 960, 1, 48000, (int)i);
            int size = encoder.Encode(tone, packet);
            if (i != 25 && i != 30 && i != 35) receive.Enqueue(new(MediaFrameType.Voice, 0, 0, 42, i, i * 960), packet.AsSpan(0, size));
            output.AsSpan().Clear(); receive.Mix(output, false, null);
        }
        if (useDred) Assert.True(receive.DredFrames > 0); else Assert.True(receive.FecFrames > 0);
        for (int i = 0; i < 20; i++) { output.AsSpan().Clear(); receive.Mix(output, false, null); }
        Assert.True(receive.ConcealedFrames > 0); Assert.All(output, sample => Assert.Equal(0, sample));
    }

    [Fact]
    public void PcmRingDropsWholeFramesWhenFullAndPreservesOrderAcrossWraps()
    {
        var ring = new PcmRing(8); short[] output = new short[8];
        for (int i = 0; i < 100; i++)
        {
            Assert.True(ring.TryWrite([1, 2, 3, 4, 5, 6])); Assert.False(ring.TryWrite([7, 8, 9]));
            Assert.Equal(4, ring.Read(output.AsSpan(0, 4))); Assert.Equal(new short[] { 1, 2, 3, 4 }, output[..4]);
            Assert.True(ring.TryWrite([7, 8])); Assert.Equal(4, ring.Read(output)); Assert.Equal(new short[] { 5, 6, 7, 8 }, output[..4]); Assert.Equal(0, ring.Count);
        }
    }
    internal static StreamInfo Stream(int frame = 20, bool stereo = false, bool dred = false) => new()
    {
        StreamId = 1, Ssrc = 42, Kind = StreamKind.StreamMic,
        Audio = new() { SampleRate = 48000, BitrateBps = 32000, FrameMs = (uint)frame, Complexity = 5,
            Mode = stereo ? ChannelMode.ModeStereo : ChannelMode.ModeMono, Fec = true, ExpectedPacketLoss = 20, Dred = dred }
    };
    private static short[] Tone(int channels = 1)
    {
        var pcm = new short[960 * channels];
        for (int i = 0; i < 960; i++) for (int c = 0; c < channels; c++) pcm[i * channels + c] = (short)(Math.Sin(i * 2 * Math.PI * (c == 0 ? 440 : 660) / 48000) * 8000);
        return pcm;
    }

    [Theory]
    [InlineData(5, false)] [InlineData(10, false)] [InlineData(20, false)] [InlineData(40, false)] [InlineData(60, false)] [InlineData(20, true)]
    public void ReframedEncodedPcmIsDecodedAndMixedForMonoAndStereo(int frame, bool stereo)
    {
        StreamInfo stream = Stream(frame, stereo);
        using var receive = new AudioEngine((_, _, _, _) => true, false);
        receive.SetRemoteStreams([new() { Id = 2, ChannelId = 1, Streams = { stream } }], 1, 1);
        using var send = new AudioEngine((ssrc, timestamp, payload, flags) => { receive.Receive(new(MediaFrameType.Voice, flags, 0, ssrc, 0, timestamp), payload); return true; }, false);
        send.InputMode = AudioInputMode.AlwaysOn; send.AddLocalStream(stream, stereo ? 2 : 1);
        long energy = 0; int sinkChannels = 0;
        receive.MixedPcm += pcm => { foreach (short sample in pcm) energy += Math.Abs((int)sample); };
        receive.StreamPcm += (_, _, _, channels) => sinkChannels = channels;
        short[] tone = Tone(stereo ? 2 : 1);
        for (int i = 0; i < 30; i++) { Assert.True(send.FeedPcm(1, tone, stereo ? 2 : 1)); send.ProcessCycle(); receive.ProcessCycle(); }
        Assert.True(energy > 100000); Assert.Equal(stereo ? 2 : 1, sinkChannels);
        receive.SetRemotePlayback(2, 1, 1, true, false); energy = 0;
        for (int i = 0; i < 5; i++) { send.FeedPcm(1, tone, stereo ? 2 : 1); send.ProcessCycle(); receive.ProcessCycle(); }
        Assert.Equal(0, energy);
    }

    [Fact]
    public void AudioCyclesAllocateZeroBytesWithEncodeDecodeStereoNoiseReductionAndMixing()
    {
        StreamInfo stream = Stream(20, true);
        using var receive = new AudioEngine((_, _, _, _) => true, false);
        receive.SetRemoteStreams([new() { Id = 2, ChannelId = 1, Streams = { stream } }], 1, 1);
        receive.SetRemotePlayback(2, 1, 0.8f, false, true);
        using var send = new AudioEngine((ssrc, timestamp, payload, flags) => { receive.Receive(new(MediaFrameType.Voice, flags, 0, ssrc, 0, timestamp), payload); return true; }, false);
        send.InputMode = AudioInputMode.AlwaysOn; send.InputNoiseReduction = true; send.AddLocalStream(stream, 2);
        short[] tone = Tone(2);
        for (int i = 0; i < 30; i++) { send.FeedPcm(1, tone, 2); send.ProcessCycle(); receive.ProcessCycle(); }
        long before = GC.GetAllocatedBytesForCurrentThread();
        for (int i = 0; i < 100; i++) { send.FeedPcm(1, tone, 2); send.ProcessCycle(); receive.ProcessCycle(); }
        Assert.Equal(0, GC.GetAllocatedBytesForCurrentThread() - before);
    }

    [Fact]
    public void DeviceClockedRunCyclePacesMixAndCaptureWithNoWorkerThread()
    {
        var sent = new List<(uint Timestamp, VoiceFrameFlags Flags)>(512);
        StreamInfo stream = Stream();
        using var receive = new AudioEngine((_, _, _, _) => true, false);
        receive.SetRemoteStreams([new() { Id = 2, ChannelId = 1, Streams = { stream } }], 1, 1);
        using var send = new AudioEngine((ssrc, timestamp, payload, flags) =>
        {
            sent.Add((timestamp, flags));
            receive.Receive(new(MediaFrameType.Voice, flags, 0, ssrc, 0, timestamp), payload);
            return true;
        }, false) { InputMode = AudioInputMode.AlwaysOn, DeviceBufferMilliseconds = 20 };
        send.AddLocalStream(stream);
        short[] tone = Tone(); long energy = 0;
        receive.MixedPcm += pcm => { foreach (short sample in pcm) energy += Math.Abs((int)sample); };

        // Each iteration is one 20 ms render demand quantum: feed the capture handoff, then pull
        // both mixes, exactly as the iOS render callback drives its device-clocked engine.
        for (int i = 0; i < 30; i++) { Assert.True(send.FeedPcm(1, tone, 1)); send.RunCycle(); receive.RunCycle(); }
        Assert.Equal(30, send.GetLocalDiagnostics(1).Cycles);
        Assert.Equal(0, send.GetLocalDiagnostics(1).StarvedCycles);
        Assert.Equal(30, sent.Count);
        Assert.True(energy > 100000);

        long before = GC.GetAllocatedBytesForCurrentThread();
        for (int i = 0; i < 100; i++) { send.FeedPcm(1, tone, 1); send.RunCycle(); receive.RunCycle(); }
        Assert.Equal(0, GC.GetAllocatedBytesForCurrentThread() - before);
    }

    [Fact]
    public void RunCycleContainsFailuresInsteadOfThrowingIntoRealtimeCallbacks()
    {
        using var engine = new AudioEngine((_, _, _, _) => throw new InvalidOperationException("boom"), false)
            { InputMode = AudioInputMode.AlwaysOn, DeviceBufferMilliseconds = 20 };
        engine.AddLocalStream(Stream());
        Assert.True(engine.FeedPcm(1, Tone(), 1));
        engine.RunCycle();
        Assert.IsType<InvalidOperationException>(engine.Failure);
        engine.RunCycle();
        Assert.Equal(1, engine.GetLocalDiagnostics(1).Cycles);
    }

    [Fact]
    public async Task DeviceClockedClientLeavesMixCadenceToTheAudioCallback()
    {
        string directory = Path.Combine(Path.GetTempPath(), $"voicecat-{Guid.NewGuid():N}");
        Directory.CreateDirectory(directory);
        try
        {
            await using var paced = new VoiceCatClient(tofuStorePath: Path.Combine(directory, "paced.txt"));
            await using var pulled = new VoiceCatClient(tofuStorePath: Path.Combine(directory, "pulled.txt"), deviceClockedAudio: true);
            paced.Audio.AddLocalStream(Stream());
            pulled.Audio.AddLocalStream(Stream());
            await Task.Delay(250);
            Assert.True(paced.Audio.GetLocalDiagnostics(1).Cycles > 0);
            Assert.Equal(0, pulled.Audio.GetLocalDiagnostics(1).Cycles);
            pulled.Audio.RunCycle();
            Assert.Equal(1, pulled.Audio.GetLocalDiagnostics(1).Cycles);
        }
        finally
        {
            try { Directory.Delete(directory, true); }
            catch (IOException) { } catch (UnauthorizedAccessException) { }
        }
    }

    [Fact]
    public void ManagedAudioWorkerResynchronizesProducerBacklogAfterStalls()
    {
        string source = File.ReadAllText(Path.Combine(FindRoot(), "src", "VoiceCat.Audio", "AudioEngine.cs"));
        string buffer = File.ReadAllText(Path.Combine(FindRoot(), "src", "VoiceCat.Audio", "AdaptivePcmBuffer.cs"));

        Assert.Contains("stream.Input.Resynchronize()", source);
        Assert.Contains("public void Resynchronize()", buffer);
    }

    [Fact]
    public void ResynchronizeInputsDropsStalledBacklogToTheBufferTarget()
    {
        using var send = new AudioEngine((_, _, _, _) => true, false);
        send.DeviceBufferMilliseconds = 40; send.AddLocalStream(Stream());
        short[] mono = Tone();
        for (int i = 0; i < 40; i++) send.FeedPcm(1, mono, 1);
        Assert.True(send.GetLocalDiagnostics(1).BufferedFrames > 1920 * 2);

        send.ResynchronizeInputs();

        Assert.Equal(1920, send.GetLocalDiagnostics(1).BufferedFrames);
        send.ProcessCycle();
        Assert.Equal(0, send.GetLocalDiagnostics(1).StarvedCycles);
    }

    [Fact]
    public void RemotePlaybackSettingsAreIndependentForEachUserStream()
    {
        StreamInfo microphone = Stream();
        StreamInfo screen = Stream(); screen.StreamId = 2; screen.Ssrc = 43; screen.Kind = StreamKind.StreamScreenAudio; screen.Label = "Screen audio";
        using var receive = new AudioEngine((_, _, _, _) => true, false);
        receive.SetRemoteStreams([new() { Id = 7, ChannelId = 1, Streams = { microphone, screen } }], 1, 1);

        receive.SetRemotePlayback(7, microphone.StreamId, 0.5f, true, true);
        receive.SetRemotePlayback(7, screen.StreamId, 1.75f, false, false);

        Assert.Equal((0.5f, true, true), receive.GetRemotePlayback(7, microphone.StreamId));
        Assert.Equal((1.75f, false, false), receive.GetRemotePlayback(7, screen.StreamId));
    }

    [Fact]
    public void JitterBacklogIsBoundedAndPlcEventuallyBecomesSilence()
    {
        var info = Stream(); using var stream = new ReceiveStream(2, info); using var encoder = new OpusEncoder(new() { Bitrate = 32000 });
        byte[] packet = new byte[1275]; int length = encoder.Encode(Tone(), packet); int[] output = new int[1920];
        for (uint i = 0; i < 64; i++) stream.Enqueue(new(MediaFrameType.Voice, 0, 0, 42, i, i * 960), packet.AsSpan(0, length));
        stream.Mix(output, false, null); Assert.InRange(stream.Depth, 0, 6);
        for (int i = 0; i < 20; i++) { output.AsSpan().Clear(); stream.Mix(output, false, null); }
        Assert.All(output, value => Assert.Equal(0, value)); Assert.InRange(stream.ConcealedFrames, 1, 16);
    }

    [Fact]
    public void PttResumeAndCaptureChannelChangesKeepTimestampProgressAndAudio()
    {
        var info = Stream(60, true); using var receive = new AudioEngine((_, _, _, _) => true, false);
        receive.SetRemoteStreams([new() { Id = 2, ChannelId = 1, Streams = { info } }], 1, 1);
        using var send = new AudioEngine((ssrc, timestamp, payload, flags) => { receive.Receive(new(MediaFrameType.Voice, flags, 0, ssrc, 0, timestamp), payload); return true; }, false);
        send.InputMode = AudioInputMode.PushToTalk; send.PushToTalk = true; send.AddLocalStream(info);
        short[] mono = Tone(), stereo = Tone(2); long energy = 0;
        receive.MixedPcm += pcm => { foreach (short value in pcm) energy += Math.Abs((int)value); };
        for (int i = 0; i < 15; i++) { send.FeedPcm(1, mono, 1); send.ProcessCycle(); receive.ProcessCycle(); }
        send.PushToTalk = false;
        for (int i = 0; i < 16; i++) { send.FeedPcm(1, mono, 1); send.ProcessCycle(); receive.ProcessCycle(); }
        send.SetCaptureChannels(1, 2); send.PushToTalk = true; energy = 0;
        for (int i = 0; i < 15; i++) { send.FeedPcm(1, stereo, 2); send.ProcessCycle(); receive.ProcessCycle(); }
        Assert.True(energy > 100000);
    }

    private static string FindRoot()
    {
        DirectoryInfo? directory = new(AppContext.BaseDirectory);
        while (directory is not null && !File.Exists(Path.Combine(directory.FullName, "VoiceCat.slnx")))
            directory = directory.Parent;
        return directory?.FullName ?? throw new DirectoryNotFoundException("Repository root not found.");
    }

    private sealed class ManualAudioClock : TimeProvider
    {
        private long milliseconds;
        public override long TimestampFrequency => 1000;
        public override long GetTimestamp() => milliseconds;
        internal void Advance(int value) => milliseconds += value;
    }
}