using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using AcDream.App.Rendering.Gpu;

namespace AcDream.App.Tests.Rendering.Gpu;

/// <summary>
/// Campaign V slice V0 — the pinned RHI contract.
///
/// These are not behaviour tests; they are the tripwires that stop the contract
/// drifting out from under the shaders and the two backends. Every constant
/// asserted here also appears in a GLSL source file or in a backend's binding
/// setup, so a change that lands in only one place fails here rather than as a
/// corrupted frame.
/// </summary>
public sealed class GpuContractTests
{
    [Fact]
    public void PushConstantBlockMatchesThePinnedLayout()
    {
        Assert.Equal(GpuBindingModel.PushConstantBytes, Unsafe.SizeOf<GpuPushConstants>());
        Assert.True(GpuBindingModel.PushConstantBytes <= GpuBindingModel.MaxPushConstantBytes);

        Assert.Equal(0, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.ViewProjection)));
        Assert.Equal(64, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.DrawIdOffset)));
        Assert.Equal(68, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.LightingMode)));
        Assert.Equal(72, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.RenderPass)));
        Assert.Equal(76, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.LightDebug)));
        Assert.Equal(80, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.TextureIndexA)));
        Assert.Equal(84, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.TextureIndexB)));
        Assert.Equal(88, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.ParamA)));
        Assert.Equal(92, (int)Marshal.OffsetOf<GpuPushConstants>(nameof(GpuPushConstants.ParamB)));
    }

    [Fact]
    public void StorageBindingsMatchTheShaderSources()
    {
        // mesh_modern.vert declares std430 bindings 0..8 in exactly this order;
        // binding 9 is the GL-only texture handle table added by slice V2.
        Assert.Equal(0u, GpuBindingModel.StorageInstances);
        Assert.Equal(1u, GpuBindingModel.StorageBatches);
        Assert.Equal(2u, GpuBindingModel.StorageClipRegions);
        Assert.Equal(3u, GpuBindingModel.StorageClipSlots);
        Assert.Equal(4u, GpuBindingModel.StorageGlobalLights);
        Assert.Equal(5u, GpuBindingModel.StorageInstanceLightSets);
        Assert.Equal(6u, GpuBindingModel.StorageInstanceIndoor);
        Assert.Equal(7u, GpuBindingModel.StorageInstanceAlpha);
        Assert.Equal(8u, GpuBindingModel.StorageInstanceSelectionLighting);
        Assert.Equal(9u, GpuBindingModel.StorageTextureTable);
        Assert.Equal(10u, GpuBindingModel.StorageBindingCount);
    }

    [Fact]
    public void UniformAndTextureTableLiveInSeparateSets()
    {
        // The SceneLighting UBO keeps binding=1 even though the BatchBuffer SSBO
        // also uses binding=1. GL tolerates that because its SSBO and UBO binding
        // tables are separate; Vulkan does not, so the set index disambiguates.
        Assert.Equal(GpuBindingModel.StorageBatches, GpuBindingModel.UniformSceneLighting);
        Assert.NotEqual(0u, GpuBindingModel.UniformSet);
        Assert.NotEqual(GpuBindingModel.UniformSet, GpuBindingModel.TextureTableSet);
    }

    [Fact]
    public void ClipRegionStrideMatchesTheUploadedLayout()
    {
        // ClipFrame lays these bytes out on the CPU; ClipFrameLayoutTests pins the
        // producer side, this pins the contract side. 16 B header + 8 x vec4.
        Assert.Equal(8, GpuBindingModel.ClipPlanesPerSlot);
        Assert.Equal(144, GpuBindingModel.ClipRegionStrideBytes);
    }

    [Fact]
    public void UnassignedTextureSlotIsNeverAValidIndex()
    {
        Assert.False(GpuTextureSlot.Unassigned.IsAssigned);
        Assert.True(new GpuTextureSlot(0).IsAssigned);
        Assert.Equal("slot#unassigned", GpuTextureSlot.Unassigned.ToString());
        Assert.Equal("slot#7", new GpuTextureSlot(7).ToString());
    }

    [Fact]
    public void WorldMeshVertexLayoutMatchesTheMeshShaderInputs()
    {
        GpuVertexLayout layout = GpuVertexLayout.WorldMesh;

        Assert.Equal(32u, layout.StrideBytes);
        Assert.Equal(3, layout.Attributes.Length);
        Assert.Equal(new GpuVertexAttribute(0, GpuVertexFormat.Float3, 0), layout.Attributes[0]);
        Assert.Equal(new GpuVertexAttribute(1, GpuVertexFormat.Float3, 12), layout.Attributes[1]);
        Assert.Equal(new GpuVertexAttribute(2, GpuVertexFormat.Float2, 24), layout.Attributes[2]);
    }

    [Fact]
    public void MultisampledBackbufferPassResolvesWhileDepthIsDiscarded()
    {
        GpuPassDescription multisampled = GpuPassDescription.BackbufferClear("world", Vector4.Zero, sampleCount: 4);
        Assert.Equal(GpuStoreOp.Resolve, multisampled.Color.Store);
        Assert.Null(multisampled.Color.Target);
        Assert.Equal(GpuStoreOp.DontCare, multisampled.Depth!.Value.Store);
        Assert.Equal(1f, multisampled.Depth!.Value.ClearDepth);

        GpuPassDescription single = GpuPassDescription.BackbufferClear("world", Vector4.Zero, sampleCount: 1);
        Assert.Equal(GpuStoreOp.Store, single.Color.Store);
    }

    [Fact]
    public void CapabilityRecordAcceptsADeviceThatMeetsEveryRequirement()
    {
        GpuCapabilityRecord record = SupportedRecord();

        Assert.Empty(record.SupportFailures);
        Assert.True(record.IsSupported);
    }

    [Fact]
    public void CapabilityRecordNamesEveryMissingRequirement()
    {
        GpuCapabilityRecord record = SupportedRecord() with
        {
            SupportsMultiDrawIndirect = false,
            SupportsDrawParameters = false,
            SupportsTextureCompressionBc = false,
            MaxTextureTableSlots = 16,
            MaxStorageBufferBindings = 4,
            MaxPushConstantBytes = 32,
            MaxClipDistances = 0,
        };

        Assert.False(record.IsSupported);
        Assert.Equal(7, record.SupportFailures.Count);
        Assert.Contains(record.SupportFailures, failure => failure.Contains("Multi-draw-indirect", StringComparison.Ordinal));
        Assert.Contains(record.SupportFailures, failure => failure.Contains("gl_DrawID", StringComparison.Ordinal));
        Assert.Contains(record.SupportFailures, failure => failure.Contains("BC (DXT)", StringComparison.Ordinal));
        Assert.Contains(record.SupportFailures, failure => failure.Contains("clip distances", StringComparison.Ordinal));
    }

    [Fact]
    public void TimestampSupportIsOptional()
    {
        // Losing GPU timing degrades profiling; it must never refuse to start.
        GpuCapabilityRecord record = SupportedRecord() with { SupportsTimestampQueries = false };
        Assert.True(record.IsSupported);
    }

    private static GpuCapabilityRecord SupportedRecord() => new()
    {
        Backend = GpuBackendKind.Vulkan,
        DeviceName = "test-adapter",
        DriverInfo = "test-driver",
        ApiVersion = "Vulkan 1.3.0",
        MaxTextureTableSlots = GpuBindingModel.TextureTableCapacity,
        MaxStorageBufferBindings = GpuBindingModel.StorageBindingCount,
        MaxPushConstantBytes = GpuBindingModel.MaxPushConstantBytes,
        MinStorageBufferOffsetAlignment = 64,
        MinUniformBufferOffsetAlignment = 256,
        MaxClipDistances = GpuBindingModel.ClipPlanesPerSlot,
        MaxSampleCount = 8,
        SupportsMultiDrawIndirect = true,
        SupportsDrawParameters = true,
        SupportsTextureCompressionBc = true,
        SupportsTimestampQueries = true,
        SupportsPersistentlyMappedRings = true,
    };
}