#include "o3d/mesh.hpp"
#include <vector>
#include <array>
#include <cstdint>
#include <cstddef>
#include <tuple>
#include <unordered_map>
#include "math/vector.hpp"
#include "vulkan_utils.hpp"

using namespace engine::o3d;

template<size_t indices_size>
struct VertexIndicesHasher {
    // taken from boost's container_hash
    std::size_t operator()(const std::array<size_t, indices_size>& vertex_indices) const {
        size_t h = 0;
        for (const auto& idx : vertex_indices)
            h ^= std::hash<size_t>{}(idx) + 0x9e3779b9 + (h << 6) + (h >> 2);
        return h;
    }
};

Mesh Mesh::plane(float width, float height) {
    const float w2 = width / 2,
                h2 = height / 2;
    return {
        {
            { -w2 / 2, 0.f, -h2 / 2 },
            { +w2 / 2, 0.f, -h2 / 2 },
            { +w2 / 2, 0.f, +h2 / 2 },
            { -w2 / 2, 0.f, +h2 / 2 },
        },
        {
            { 0.f, -1.f, 0.f },
            { 0.f, +1.f, 0.f },
        },
        {
            { 0.f, 0.f },
            { 1.f, 0.f },
            { 1.f, 1.f },
            { 0.f, 1.f },
        },
        {
            {{ {{ 0, 0, 0 }}, {{ 1, 0, 1 }}, {{ 2, 0, 2 }} }},
            {{ {{ 2, 0, 2 }}, {{ 3, 0, 3 }}, {{ 0, 0, 0 }} }},
            {{ {{ 0, 1, 0 }}, {{ 3, 1, 3 }}, {{ 2, 1, 2 }} }},
            {{ {{ 2, 1, 2 }}, {{ 1, 1, 1 }}, {{ 0, 1, 0 }} }},
        }
    };
}

std::tuple<std::vector<engine::vk::Vertex>, std::vector<uint16_t>> Mesh::linearize_indices() const & {
    std::unordered_map<std::array<size_t, 3>, size_t, VertexIndicesHasher<3>> unique_vertices;
    std::vector<engine::vk::Vertex> linearized_vertices;
    std::vector<uint16_t> linearized_indices;

    for (const auto& triangle_indices : this->indices) {
        for (const auto& vertex_indices : triangle_indices) {
            auto it = unique_vertices.find(vertex_indices);
            if (it == unique_vertices.end()) {
                linearized_vertices.emplace_back(this->vertices[vertex_indices[0]], this->normals[vertex_indices[1]], this->uvs[vertex_indices[2]]);
                size_t idx = linearized_vertices.size() - 1;
                unique_vertices.emplace(vertex_indices, idx);
                linearized_indices.emplace_back(idx);
            } else {
                linearized_indices.emplace_back((*it).second);
            }
        }
    }

    // TODO: I'm not sure if passing vectors like that makes a copy or not, because they are passed
    // to a structured which is instantly returned. I think that copy-ellision catches that
    return std::tuple { linearized_vertices, linearized_indices };
}