using AcDream.App.Rendering.Gpu.Gl;

namespace AcDream.App.Tests.Rendering.Gpu.Gl;

public sealed class GlGpuTimerPoolTests
{
    [Fact]
    public void UnsupportedPoolReturnsNoOpScopesAndNeverResolves()
    {
        var pool = new GlGpuTimerPool(new FakeTimerQueryApi(), isSupported: false);

        using (pool.BeginScope("world"))
        {
        }

        Assert.False(pool.TryResolve("world", out _));
    }

    [Fact]
    public void ScopeNamesGetIndependentDoubleBufferedQueries()
    {
        var api = new FakeTimerQueryApi();
        var pool = new GlGpuTimerPool(api, isSupported: true);

        using (pool.BeginScope("world"))
        {
        }
        using (pool.BeginScope("ui"))
        {
        }

        Assert.Equal(4, api.CreatedQueryCount);
    }

    [Fact]
    public void NestingAScopeBeforeDisposingThePreviousOneThrows()
    {
        var pool = new GlGpuTimerPool(new FakeTimerQueryApi(), isSupported: true);
        pool.BeginScope("world");

        Assert.Throws<InvalidOperationException>(() => pool.BeginScope("ui"));
    }

    [Fact]
    public void AResolvedResultIsPromotedTheNextTimeTheSameScopeBegins()
    {
        var api = new FakeTimerQueryApi();
        var pool = new GlGpuTimerPool(api, isSupported: true);

        using (pool.BeginScope("world"))
        {
        }
        // No result available yet — the first slot hasn't been revisited.
        Assert.False(pool.TryResolve("world", out _));

        api.MakeNextResultReady(milliseconds: 1.5);
        using (pool.BeginScope("world"))
        {
        }

        Assert.True(pool.TryResolve("world", out double milliseconds));
        Assert.Equal(1.5, milliseconds);
    }

    [Fact]
    public void DisposeQueriesDeletesEveryCreatedQuery()
    {
        var api = new FakeTimerQueryApi();
        var pool = new GlGpuTimerPool(api, isSupported: true);
        using (pool.BeginScope("world"))
        {
        }

        pool.DisposeQueries();

        Assert.Equal(2, api.DeletedQueryCount);
    }

    private sealed class FakeTimerQueryApi : IGlTimerQueryApi
    {
        private uint _nextQuery = 1;
        private bool _nextResultReady;
        private double _nextResultMilliseconds;

        public int CreatedQueryCount { get; private set; }
        public int DeletedQueryCount { get; private set; }

        public uint CreateQuery()
        {
            CreatedQueryCount++;
            return _nextQuery++;
        }

        public void DeleteQuery(uint query) => DeletedQueryCount++;

        public void Begin(uint query)
        {
        }

        public void End()
        {
        }

        public void MakeNextResultReady(double milliseconds)
        {
            _nextResultReady = true;
            _nextResultMilliseconds = milliseconds;
        }

        public bool TryGetResult(uint query, out double milliseconds)
        {
            if (_nextResultReady)
            {
                milliseconds = _nextResultMilliseconds;
                _nextResultReady = false;
                return true;
            }

            milliseconds = 0;
            return false;
        }
    }
}