using AcDream.App.Rendering.Gpu.Gl;

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

public sealed class GlTextureSlotAllocatorTests
{
    [Fact]
    public void AllocationsBumpSequentiallyFromZero()
    {
        var allocator = new GlTextureSlotAllocator(capacity: 4);
        Assert.Equal(0u, allocator.Allocate());
        Assert.Equal(1u, allocator.Allocate());
        Assert.Equal(2u, allocator.Allocate());
        Assert.Equal(3, allocator.LiveCount);
    }

    [Fact]
    public void ExhaustingCapacityThrows()
    {
        var allocator = new GlTextureSlotAllocator(capacity: 2);
        allocator.Allocate();
        allocator.Allocate();
        Assert.Throws<InvalidOperationException>(() => allocator.Allocate());
    }

    [Fact]
    public void ReleasedSlotsAreReusedBeforeBumpingFurther()
    {
        var allocator = new GlTextureSlotAllocator(capacity: 4);
        uint first = allocator.Allocate();
        allocator.Allocate();

        allocator.Release(first);
        Assert.Equal(1, allocator.LiveCount);

        uint reused = allocator.Allocate();
        Assert.Equal(first, reused);
        Assert.Equal(2, allocator.LiveCount);
    }

    [Fact]
    public void ReleasingAnUnallocatedSlotThrows()
    {
        var allocator = new GlTextureSlotAllocator(capacity: 4);
        allocator.Allocate();
        Assert.Throws<ArgumentOutOfRangeException>(() => allocator.Release(3));
    }

    [Fact]
    public void FreeingThenExhaustingTheBumpRangeStillThrowsPastCapacity()
    {
        var allocator = new GlTextureSlotAllocator(capacity: 2);
        uint first = allocator.Allocate();
        allocator.Allocate();
        allocator.Release(first);
        allocator.Allocate();

        Assert.Throws<InvalidOperationException>(() => allocator.Allocate());
    }
}