GameOverlay.Capture/tests/GameOverlay.Capture.Tests/FrameTimeStatisticsTests.cs

using GameOverlay.Capture;
using Xunit;

namespace GameOverlay.Capture.Tests;

public class FrameTimeStatisticsTests
{
    [Fact]
    public void Empty_ReturnsEmptySummary()
    {
        var stats = new FrameTimeStatistics();
        Assert.Equal(0, stats.Count);
        Assert.Equal(MetricsSummary.Empty, stats.ComputeSummary());
    }

    [Fact]
    public void ConstantFrameTimes_GiveExactFps()
    {
        var stats = new FrameTimeStatistics();
        for (int i = 0; i < 100; i++)
            stats.AddFrameTime(10.0); // 10 ms => 100 fps

        var s = stats.ComputeSummary();
        Assert.Equal(100, s.FrameCount);
        Assert.Equal(100.0, s.AverageFps, 6);
        Assert.Equal(100.0, s.MinFps, 6);
        Assert.Equal(100.0, s.MaxFps, 6);
        Assert.Equal(100.0, s.OnePercentLowFps, 6);
        Assert.Equal(100.0, s.PointOnePercentLowFps, 6);
        Assert.Equal(10.0, s.AverageFrameTimeMs, 6);
        Assert.Equal(1.0, s.DurationSeconds, 6); // 100 * 10ms = 1s
    }

    [Fact]
    public void NonPositiveFrameTimes_AreIgnored()
    {
        var stats = new FrameTimeStatistics();
        stats.AddFrameTime(0);
        stats.AddFrameTime(-5);
        stats.AddFrameTime(double.NaN);
        stats.AddFrameTime(double.PositiveInfinity);
        stats.AddFrameTime(16.6);
        Assert.Equal(1, stats.Count);
    }

    [Fact]
    public void MinMaxFps_DerivedFromExtremeFrameTimes()
    {
        var stats = new FrameTimeStatistics();
        // Mostly fast frames, a couple of slow spikes.
        for (int i = 0; i < 98; i++)
            stats.AddFrameTime(8.0);   // 125 fps
        stats.AddFrameTime(4.0);       // 250 fps  -> fastest frame => MaxFps
        stats.AddFrameTime(50.0);      // 20 fps   -> slowest frame => MinFps

        var s = stats.ComputeSummary();
        Assert.Equal(250.0, s.MaxFps, 6);
        Assert.Equal(20.0, s.MinFps, 6);
    }

    [Fact]
    public void OnePercentLow_UsesNinetyNinthPercentileFrameTime()
    {
        var stats = new FrameTimeStatistics();
        // 99 frames at 10 ms, 1 frame at 100 ms. Nearest-rank P99 of 100 samples = the 99th value.
        for (int i = 0; i < 99; i++)
            stats.AddFrameTime(10.0);
        stats.AddFrameTime(100.0);

        // Sorted ascending: [10 x99, 100]. rank at P99 = ceil(0.99*100)=99 => element#99 = 10ms => 100 fps.
        Assert.Equal(10.0, stats.PercentileFrameTimeMs(99.0), 6);
        // P99.9 = ceil(0.999*100)=100 => element#100 = 100ms => 10 fps.
        Assert.Equal(100.0, stats.PercentileFrameTimeMs(99.9), 6);

        var s = stats.ComputeSummary();
        Assert.Equal(100.0, s.OnePercentLowFps, 6);       // 1000/10
        Assert.Equal(10.0, s.PointOnePercentLowFps, 6);   // 1000/100
    }

    [Fact]
    public void PresentTimestamps_ConvertToFrameTimeDeltas()
    {
        var stats = new FrameTimeStatistics();
        const long tps = 1000; // 1 tick = 1 ms
        stats.AddPresentTimestamp(0, tps);      // baseline, no sample
        stats.AddPresentTimestamp(16, tps);     // 16 ms
        stats.AddPresentTimestamp(32, tps);     // 16 ms
        stats.AddPresentTimestamp(50, tps);     // 18 ms

        Assert.Equal(3, stats.Count);
        var s = stats.ComputeSummary();
        Assert.Equal((16.0 + 16.0 + 18.0) / 3.0, s.AverageFrameTimeMs, 6);
    }

    [Fact]
    public void Percentile_OutOfRange_Throws()
    {
        var stats = new FrameTimeStatistics();
        stats.AddFrameTime(10);
        Assert.Throws<ArgumentOutOfRangeException>(() => stats.PercentileFrameTimeMs(-1));
        Assert.Throws<ArgumentOutOfRangeException>(() => stats.PercentileFrameTimeMs(101));
    }

    [Fact]
    public void Reset_ClearsState()
    {
        var stats = new FrameTimeStatistics();
        stats.AddFrameTime(10);
        stats.AddPresentTimestamp(100, 1000);
        stats.Reset();
        Assert.Equal(0, stats.Count);
        stats.AddPresentTimestamp(200, 1000); // first after reset is a baseline again
        Assert.Equal(0, stats.Count);
    }
}