/*
Crafter®.Graphics
Copyright (C) 2026 Catcrafts®
catcrafts.net

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License version 3.0 as published by the Free Software Foundation;

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
*/

module;
#ifndef CRAFTER_GRAPHICS_WINDOW_DOM
#include "vulkan/vulkan.h"
#endif // !CRAFTER_GRAPHICS_WINDOW_DOM
export module Crafter.Graphics:RenderingElement3D;
#ifndef CRAFTER_GRAPHICS_WINDOW_DOM
import std;
import :Mesh;
import :VulkanBuffer;
import Crafter.Math;
import :Window;

export namespace Crafter {
    struct TlasWithBuffer {
        VkDeviceAddress address = 0;
        VulkanBuffer<char, false> buffer;
        VkAccelerationStructureKHR accelerationStructure = VK_NULL_HANDLE;
        VulkanBuffer<VkAccelerationStructureInstanceKHR, true> instanceBuffer;
        VulkanBuffer<char, false> scratchBuffer;
        // Parallel to instanceBuffer, indexed by TLAS instance ID. Filled
        // from each element's userMetadata during BuildTLAS. Consumers
        // (e.g. ray-query collision) bind this in the descriptor heap and
        // look up via rayQueryGetIntersectionInstanceIdEXT to recover
        // application-side per-instance data without touching the
        // Vulkan-mandated instanceCustomIndex (which renderers may already
        // use for their own encoding).
        VulkanBuffer<std::uint32_t, true> metadataBuffer;
        // Last instance count this TLAS was built (not refit) for. When
        // elements.size() matches this, BuildTLAS does an in-place refit
        // (UPDATE mode) which is dramatically cheaper than a full rebuild
        // — refit walks the existing BVH and updates AABBs, while rebuild
        // reconstructs the topology from scratch. A change in count forces
        // a fresh rebuild because the AS is sized for that primitive count.
        std::uint32_t builtInstanceCount = 0;
    };

   class RenderingElement3D {
        public:
        VkAccelerationStructureInstanceKHR instance;
        // Position in `elements`, maintained by Add/Remove for O(1) swap-and-pop.
        // Sentinel value = not currently registered.
        std::uint32_t indexInElements = std::numeric_limits<std::uint32_t>::max();
        // Application-defined per-instance tag, copied verbatim into
        // tlases[*].metadataBuffer at this element's TLAS instance ID
        // every BuildTLAS. Crafter doesn't interpret it.
        std::uint32_t userMetadata = 0;
        // When true, BuildTLAS skips copying instance.transform into the
        // TLAS instance buffer — the application's compute shader writes
        // the transform field directly into instanceBuffer at this
        // element's TLAS instance ID. Other instance fields (mask,
        // customIndex, SBT offset, BLAS reference) are still copied from
        // the CPU instance struct.
        //
        // Used to take per-frame transform updates off the CPU for bodies
        // whose transforms derive from GPU-side state (physics nodes that
        // already live on the GPU).
        bool transformOwnedByGpu = false;

        static std::vector<RenderingElement3D*> elements;
        inline static TlasWithBuffer tlases[Window::numFrames];
        static void BuildTLAS(VkCommandBuffer cmd, std::uint32_t index);

        // Register / unregister with `elements`. Use these instead of touching
        // the vector directly: linear find+erase is O(n) and pathological at
        // the body counts physics targets (millions of braces).
        static void Add(RenderingElement3D* e);
        static void Remove(RenderingElement3D* e);
   };
}
#endif // !CRAFTER_GRAPHICS_WINDOW_DOM