using AcDream.App.Rendering.Gpu;
using AcDream.App.Rendering.Gpu.Gl;

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

public sealed class GlRenderStateCacheTests
{
    private static GlRenderStateSnapshot Default(uint program = 1) => new(
        program,
        GpuBlendMode.None,
        DepthTest: true,
        DepthWrite: true,
        GpuCompareOp.LessOrEqual,
        GpuCullMode.Back,
        GpuFrontFace.CounterClockwise,
        AlphaToCoverage: false,
        ColorWrite: true,
        // Slice V6l: the stencil dimension. Off is what every pipeline in the
        // tree but the portal depth mask asks for.
        StencilTest: false,
        GpuStencilState.Default);

    [Fact]
    public void FirstApplyReportsEveryDimensionChanged()
    {
        var cache = new GlRenderStateCache();
        GlRenderStateChanges changes = cache.Apply(Default());
        Assert.Equal(GlRenderStateChanges.All, changes);
        Assert.True(changes.AnyChange);
    }

    [Fact]
    public void ReapplyingTheIdenticalSnapshotReportsNoChanges()
    {
        var cache = new GlRenderStateCache();
        GlRenderStateSnapshot snapshot = Default();
        cache.Apply(snapshot);

        GlRenderStateChanges changes = cache.Apply(snapshot);

        Assert.False(changes.AnyChange);
    }

    [Fact]
    public void ChangingOnlyCullModeReportsOnlyThatDimension()
    {
        var cache = new GlRenderStateCache();
        cache.Apply(Default());

        GlRenderStateChanges changes = cache.Apply(Default() with { Cull = GpuCullMode.None });

        Assert.True(changes.Cull);
        Assert.True(changes.AnyChange);
        Assert.False(changes.Program);
        Assert.False(changes.Blend);
        Assert.False(changes.DepthTest);
        Assert.False(changes.DepthWrite);
        Assert.False(changes.DepthCompare);
        Assert.False(changes.FrontFace);
        Assert.False(changes.AlphaToCoverage);
        Assert.False(changes.ColorWrite);
        Assert.False(changes.StencilTest);
        Assert.False(changes.Stencil);
    }

    [Fact]
    public void ChangingOnlyTheStencilValuesReportsOnlyThatDimension()
    {
        // Slice V6l. #117's portal punch changes compare, ops, reference and
        // masks between its mark pass and its punch pass while the test stays
        // enabled, so the two stencil dimensions have to move independently.
        var cache = new GlRenderStateCache();
        cache.Apply(Default() with { StencilTest = true });

        GlRenderStateChanges changes = cache.Apply(Default() with
        {
            StencilTest = true,
            Stencil = GpuStencilState.Default with
            {
                Compare = GpuCompareOp.Equal,
                Pass = GpuStencilOp.Zero,
                Reference = 1,
            },
        });

        Assert.True(changes.Stencil);
        Assert.False(changes.StencilTest);
        Assert.False(changes.DepthTest);
        Assert.False(changes.ColorWrite);
    }

    [Fact]
    public void ChangingTheProgramReportsProgramChangedEvenWhenEveryOtherFieldMatches()
    {
        var cache = new GlRenderStateCache();
        cache.Apply(Default(program: 1));

        GlRenderStateChanges changes = cache.Apply(Default(program: 2));

        Assert.True(changes.Program);
        Assert.False(changes.Blend);
    }

    [Fact]
    public void ResetForcesTheNextApplyToReportEveryDimensionAgain()
    {
        var cache = new GlRenderStateCache();
        GlRenderStateSnapshot snapshot = Default();
        cache.Apply(snapshot);

        cache.Reset();
        GlRenderStateChanges changes = cache.Apply(snapshot);

        Assert.Equal(GlRenderStateChanges.All, changes);
    }

    [Fact]
    public void MultipleDimensionsChangingAreAllReported()
    {
        var cache = new GlRenderStateCache();
        cache.Apply(Default());

        GlRenderStateChanges changes = cache.Apply(Default() with
        {
            Blend = GpuBlendMode.StraightAlpha,
            DepthWrite = false,
            FrontFace = GpuFrontFace.Clockwise,
        });

        Assert.True(changes.Blend);
        Assert.True(changes.DepthWrite);
        Assert.True(changes.FrontFace);
        Assert.False(changes.Cull);
        Assert.False(changes.DepthTest);
        Assert.False(changes.DepthCompare);
        Assert.False(changes.AlphaToCoverage);
        Assert.False(changes.ColorWrite);
        Assert.False(changes.Program);
    }
}