using System;
using Xunit;
using ytLive.Services.Audio;

namespace ytLive.Tests;

/// <summary>
/// The mix's sample count comes from the clock, not from a tick count — the fix for the 2026-11-12
/// drift (video 9.888 s against audio 10.112 s on a 9.9 s recording: the audio ran 2.1% long and the
/// sound slid ~200 ms behind the lips by the end of a ten-second clip).
/// </summary>
public class AudioClockTests
{
    [Fact]
    public void The_mix_follows_the_wall_clock_even_when_the_tick_runs_short()
    {
        const int rate = 48000;
        const int maxChunk = rate / 5;

        // The measured scheduler: iterations land every 9.8 ms, not the requested 10 ms.
        var tickSeconds = 0.0098;

        long produced = 0;
        long naive = 0;
        var ticks = 0;
        var elapsed = 0.0;
        while (elapsed < 10.0)
        {
            var frames = AudioClock.FramesDue(elapsed, produced, rate, maxChunk);
            produced += frames;
            naive += (int)Math.Round(rate * 0.010);   // what the old "480 per tick" loop wrote
            ticks++;
            elapsed += tickSeconds;
        }

        var expected = (long)Math.Round(elapsed * rate);

        // The old loop drifted by the tick-rate error — about 2% of ten seconds — and kept drifting.
        Assert.True(naive - expected > rate * 0.01,
            $"the fixed-chunk loop should reproduce the drift (naive {naive} vs expected {expected})");

        // Asking the clock keeps the produced count on the clock, within one chunk of payment.
        Assert.True(Math.Abs(produced - expected) <= maxChunk,
            $"clock-driven count must track the clock (produced {produced} vs expected {expected})");

        // And a stalled loop pays its debt off gradually rather than dumping it in one write.
        Assert.Equal(maxChunk, AudioClock.FramesDue(5.0, 0, rate, maxChunk));
        Assert.Equal(0, AudioClock.FramesDue(5.0, rate * 5, rate, maxChunk));

        // Audio that never reached the encoder stays owed. Counting it would shorten the track by the
        // start-up gap — the mirror image of the drift this clock exists to prevent (27 dropped start-up
        // writes made the first clock-driven recording 226 ms short).
        var produced2 = 0L;
        for (var i = 0; i < 27; i++)
            produced2 = AudioClock.Advance(produced2, 480, wrote: false);
        Assert.Equal(0, produced2);
        Assert.Equal(480, AudioClock.Advance(produced2, 480, wrote: true));
    }
}