/********************************************************************************
 *                                                                              *
 * This file is part of IfcOpenShell.                                           *
 *                                                                              *
 * IfcOpenShell is free software: you can redistribute it and/or modify         *
 * it under the terms of the Lesser GNU General Public License as published by  *
 * the Free Software Foundation, either version 3.0 of the License, or          *
 * (at your option) any later version.                                          *
 *                                                                              *
 * IfcOpenShell 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                 *
 * Lesser GNU General Public License for more details.                          *
 *                                                                              *
 * You should have received a copy of the Lesser GNU General Public License     *
 * along with this program. If not, see <http://www.gnu.org/licenses/>.         *
 *                                                                              *
 ********************************************************************************/

#ifndef WGPUMODELGPUDATA_H
#define WGPUMODELGPUDATA_H

#include <webgpu/webgpu.h>

#include <cstddef>
#include <cstdint>
#include <vector>

#include "InstancedGeometry.h"

// Per-model wgpu state. Mirrors the GL backend's ModelGpuData but with
// wgpu handles. Stage 2 only allocates and uploads the four core buffers;
// bind groups, pipelines, BVH and cull scratch land in later stages.
//
// All vertex/index/mesh/instance bytes are uploaded once at load time via
// wgpuQueueWriteBuffer. The vertex storage buffer is read by the vertex
// shader (vertex pulling), not used as a classic vertex buffer — there is
// no input-assembler vertex layout to match.
struct WgpuModelGpuData {
    // Raw VBO bytes at the INSTANCED_VERTEX_STRIDE_BYTES layout (12 B/vertex).
    // Bound as a read-only storage buffer in the vertex shader.
    WGPUBuffer vertex_storage = nullptr;
    // Mesh-local u32 indices. base_vertex applied at draw time so a single
    // index buffer per model is shared across meshes.
    WGPUBuffer index_buffer = nullptr;
    // MeshGpu[] — per-mesh quantization basis (aabb_min/max as vec4 pair).
    // Derived from MeshInfo on upload.
    WGPUBuffer mesh_storage = nullptr;
    // InstanceGpu[] — per-instance transform + ids. Derived from InstanceCpu
    // on upload. Stage 2 stores the cached `transform`; later stages will
    // recompose from placement_transformation when stage matrices change.
    WGPUBuffer instance_storage = nullptr;

    // Cross-mesh vertex pulling: one entry per visible (mesh, lod, instance)
    // tuple, written into a single flat buffer per frame. The vertex shader
    // binary-searches `prefix_sums` to find which entry a given
    // gl_VertexID belongs to, then fetches that entry's mesh slice via the
    // offsets baked here. Pre-sized at applyCachedModel to a generous
    // worst case so the bind group stays valid for the model's lifetime.
    //
    // std430 layout: 16 bytes per entry, naturally aligned.
    struct alignas(16) VisibleDrawGpu {
        uint32_t mesh_id;        // -> meshes[] for quantisation basis
        uint32_t instance_idx;   // -> instances[] for transform + ids
        uint32_t ebo_first_u32;  // start of this entry's slice in indices[]
        uint32_t base_vertex;    // start of this mesh's slice in vertices[]
    };
    static_assert(sizeof(VisibleDrawGpu) == 16, "VisibleDrawGpu must be 16 bytes");

    WGPUBuffer visible_draws_buffer = nullptr;
    size_t     visible_draws_capacity = 0;  // entries (not bytes)

    // prefix_sums[i] = sum of index_counts for visible_draws[0..i-1].
    // Sized to visible_draws_capacity + 1 so prefix_sums[N] = total verts.
    WGPUBuffer prefix_sums_buffer = nullptr;
    size_t     prefix_sums_capacity = 0;  // entries (u32 count)

    // Per-model uniform: (draw_count, total_vertex_count, _pad, _pad).
    // The vertex shader uses draw_count to bound the binary search; CPU
    // uses total_vertex_count as the draw() call's vertex count.
    WGPUBuffer per_model_uniform = nullptr;

    // Bind group binding the storage + uniform buffers above (group=1 in
    // the main pipeline). Built in applyCachedModel.
    WGPUBindGroup bind_group = nullptr;

    // Per-frame, populated by cullModelCpu and consumed by render().
    uint32_t total_visible_vertices = 0;
    uint32_t total_visible_draws    = 0;

    // Scratch reused each frame so per-frame cull doesn't allocate. Sized
    // on first use; never shrunk.
    std::vector<VisibleDrawGpu> visible_draws_scratch;
    std::vector<uint32_t>       prefix_sums_scratch;

    // Size mirrors for stats / range checks.
    size_t   vertex_bytes   = 0;
    uint32_t index_count    = 0;
    uint32_t mesh_count     = 0;
    uint32_t instance_count = 0;

    // CPU side, kept for cull / picking / federation recompose.
    std::vector<MeshInfo>    meshes;
    std::vector<InstanceCpu> instances;

    bool hidden = false;
};

// Release every wgpu handle in `m` and clear its size mirrors. Safe to call
// repeatedly; idempotent on already-released entries.
void releaseWgpuModelGpuData(WgpuModelGpuData& m);

#endif // WGPUMODELGPUDATA_H