LlamaCasty/ytLive.Tests/AudioSyncDelayTests.cs

using Xunit;
using ytLive.Services.Audio;

namespace ytLive.Tests;

/// <summary>
/// TASK 22: the global audio-sync delay line. It is a pure fixed positive
/// delay on the interleaved stereo mix — the OBS fix for audio running ahead
/// of video. Positive-only: the line clamps negatives to 0; the NEGATIVE
/// (advance) side — audio running behind video, the OBS "eat the buffer head"
/// case — is covered by <see cref="AudioPipelineTests.StartLive_NegativeOffset_AdvancesAudio_ByDroppingTheStreamHead"/>.
/// </summary>
public class AudioSyncDelayTests
{
    [Fact]
    public void ZeroDelay_PassesThroughUnchanged()
    {
        var delay = new AudioSyncDelay(48000);
        delay.Configure(0);

        var input = new float[16];
        for (var i = 0; i < input.Length; i++)
            input[i] = i - 8;
        var output = new float[16];

        delay.Process(input, output);

        Assert.Equal(input, output);
    }

    [Fact]
    public void ConfigureClampsNegativeToZero_AndBeyond500msTo500ms()
    {
        var delay = new AudioSyncDelay(48000);
        delay.Configure(-50);
        Assert.Equal(0, MarkerShift(delay, 1000));

        // 500 ms at 48 kHz = 24000 frames = 48000 interleaved samples.
        delay.Configure(6000);
        Assert.Equal(48000, MarkerShift(delay, 48000));
    }

    [Fact]
    public void TenMsDelay_EmitsTheSignal960SamplesLater()
    {
        // 10 ms at 48 kHz = 480 frames; interleaved stereo = 960 samples.
        var delay = new AudioSyncDelay(48000);
        Assert.Equal(960, MarkerShift(delay, 480 * 2, configureMs: 10));
    }

    /// <summary>2026-09-12 total-silence regression: <see cref="AudioMixer.FillAndMix"/>
    /// calls <c>Configure(_syncOffsetMs?.Invoke() ?? 0)</c> on EVERY ~10ms tick (it
    /// re-reads the live UI setting each mix, not just on change) — the old
    /// `Configure` unconditionally reallocated and zeroed the delay line and reset
    /// `_writePos` every single call, discarding the buffered marker before the
    /// delay offset could ever read it back. Any persisted non-zero
    /// `Audio.SyncOffsetMs` (this repo's default is 0, but TASK 22 testing/a user
    /// slider left 500 saved) turned the WHOLE recording into digital silence:
    /// mic/loop level meters (sampled upstream of this stage) stayed honest while
    /// the delay line fed the encoder pipe pure zeros forever. This test
    /// reconfigures with the SAME delay before every Process call — exactly the
    /// mixer's calling pattern — and the marker must still survive.</summary>
    [Fact]
    public void RepeatedConfigureWithSameDelay_EveryTick_StillDelivers_TheMarker()
    {
        const int chunkLen = 960; // 10ms of 48kHz interleaved stereo
        var delay = new AudioSyncDelay(48000);
        var chunk = new float[chunkLen];
        var output = new float[chunkLen];
        chunk[0] = 1f; // sole non-zero: left of frame 0

        var foundAt = -1;
        var total = 0;
        for (var c = 0; c < 6 && foundAt < 0; c++)
        {
            delay.Configure(10); // the mixer calls this every tick, not just on change
            delay.Process(chunk, output);
            for (var i = 0; i < chunkLen; i++)
            {
                if (output[i] != 0f) { foundAt = total + i; break; }
            }
            total += chunkLen;
            chunk[0] = 0f; // only the first tick carries the marker
        }

        Assert.Equal(960, foundAt); // same 10ms-delay shift as the single-Configure test
    }

    private static int MarkerShift(AudioSyncDelay delay, int chunkLen, int configureMs = -1)
    {
        if (configureMs >= 0)
            delay.Configure(configureMs);

        var chunk = new float[chunkLen];
        var output = new float[chunkLen];
        chunk[0] = 1f; // sole non-zero: left of frame 0

        var foundAt = -1;
        var total = 0;
        for (var c = 0; c < 4 && foundAt < 0; c++)
        {
            delay.Process(chunk, output);
            for (var i = 0; i < chunkLen; i++)
            {
                if (output[i] != 0f)
                {
                    foundAt = total + i;
                    break;
                }
            }
            total += chunkLen;
        }
        Assert.True(foundAt >= 0, "marker never appeared in the delayed output");
        return foundAt;
    }
}