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: advancing audio needs a video-side delay and is
/// out of the audio layer's scope.
/// </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));
    }

    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;
    }
}