#include "client/world/chunk.hh"

namespace client {
namespace world {

void chunk::render(const float world_x, const float world_z,
                   const pass& pass) noexcept {
    const auto make_matrix = [&]() -> glm::mat4 {
        const auto& proj = client::render::camera::get_proj();
        const auto& view = client::render::camera::get_view();
        return glm::translate(proj * view, glm::vec3{world_x, 0, world_z});
    };
    static client::render::program program{"res/shaders/face.vs",
                                           "res/shaders/face.fs"};
    static const GLint u_matrix = glGetUniformLocation(program, "_u_matrix");

    const GLuint texture [[maybe_unused]] = client::render::get_texture_atlas();
    glDisable(GL_BLEND);
    glEnable(GL_DEPTH_TEST);
    glUseProgram(program);
    // Our choice of vao depends on which pass we're doing.
    const auto [vao, elements] = [&pass, this]() -> std::pair<GLuint, GLuint> {
        if (pass == pass::solid) {
            return {this->glo->solid_vao, this->glo->solid_elements};
        }
        return {this->glo->water_vao, this->glo->water_elements};
    }();
    glBindVertexArray(vao);

    glUniformMatrix4fv(u_matrix, 1, GL_FALSE, glm::value_ptr(make_matrix()));

    glDrawArrays(GL_TRIANGLES, 0, elements);
}

const chunk* chunk::get_neighbour(const chunks_t& chunks,
                                  shared::math::coords offset) const noexcept {
    const auto find_it = chunks.find(this->pos + offset);
    if (find_it == std::end(chunks) || !find_it->second.has_value()) {
        return nullptr;
    }
    return &((*find_it).second.value());
}

bool chunk::maybe_regenerate_glo(const chunks_t& chunks) noexcept {
    // We need all surrounding chunks to make our vbo, so early out with false
    // if we can't do that yet.
    const auto chunk_forward = this->get_neighbour(chunks, {0, 1});
    const auto chunk_backward = this->get_neighbour(chunks, {0, -1});
    const auto chunk_right = this->get_neighbour(chunks, {1, 0});
    const auto chunk_left = this->get_neighbour(chunks, {-1, 0});
    if (!chunk_forward || !chunk_left || !chunk_backward || !chunk_right) {
        return false;
    }

    // Single-axis-outside-chunk-bounds-allowed block access.
    const auto get_outside_block = [&](const int x, const int y,
                                       const int z) -> shared::world::block {
        if (y < 0 || y >= shared::world::chunk::HEIGHT) {
            return shared::world::block::type::air;
        } else if (x >= shared::world::chunk::WIDTH) {
            return chunk_right->get_block({x - WIDTH, y, z});
        } else if (x < 0) {
            return chunk_left->get_block({x + WIDTH, y, z});
        } else if (z >= shared::world::chunk::WIDTH) {
            return chunk_forward->get_block({x, y, z - WIDTH});
        } else if (z < 0) {
            return chunk_backward->get_block({x, y, z + WIDTH});
        }
        return this->get_block({x, y, z});
    };

    // We fill up two vbos, one for each possible rendering pass.
    std::vector<block::glvert> solid_data;
    std::vector<block::glvert> water_data;

    // For all blocks in the chunk, check if its neighbours are air. If they
    // are, it's possible that we can see the block, so add it to vertices.
    // We need to read into the neighbours chunk occasionally.
    for (auto x = 0; x < WIDTH; ++x) {
        for (auto y = 0; y < HEIGHT; ++y) {
            for (auto z = 0; z < WIDTH; ++z) {
                const auto& block = this->get_block({x, y, z});
                const auto bv = shared::world::block::get_visibility(block);

                if (bv == shared::world::block::visibility::invisible) {
                    continue;
                }

                std::vector<block::glvert> glverts;
                glverts.reserve(6 * 6);

                const auto draw_type = block::get_draw_type(block.type);

                const block::glfaces_t& faces = block::get_glfaces(block.type);
                if (draw_type == block::draw_type::block) {
                    const std::array<shared::world::block, 6> around{
                        get_outside_block(x, y, z + 1),
                        get_outside_block(x + 1, y, z),
                        get_outside_block(x, y, z - 1),
                        get_outside_block(x - 1, y, z),
                        get_outside_block(x, y + 1, z),
                        get_outside_block(x, y - 1, z),
                    };

                    for (auto i = 0ul; i < std::size(faces); ++i) {
                        const auto ov = block::get_visibility(around[i]);
                        if (bv == block::visibility::translucent &&
                            ov == block::visibility::translucent) {
                            continue;
                        }
                        if (ov == block::visibility::solid) {
                            continue;
                        }

                        std::ranges::copy(faces[i],
                                          std::back_inserter(glverts));
                    }
                } else if (draw_type == block::draw_type::custom) {
                    for (const auto& face : faces) {
                        std::ranges::copy(face, std::back_inserter(glverts));
                    }
                }

                // Move the block pos verts to its intended position.
                // Move the block texture verts to fit in the atlas.
                const glm::vec3 offset_vec3{x, y, z};
                const float tex_yoff = static_cast<float>(block.type) - 1.0f;
                const auto fix_face = [&](auto& face) {
                    face.vertice += offset_vec3 + 0.5f; // move to origin too
                    face.texture.z += tex_yoff * 6.0f;
                    return face;
                };

                auto& vbo_dest = block.type == shared::world::block::type::water
                                     ? water_data
                                     : solid_data;
                std::ranges::transform(glverts, std::back_inserter(vbo_dest),
                                       fix_face);
            }
        }
    }

    const auto generate_vbo = [](const auto& data) -> GLuint {
        GLuint vbo = 0;
        glGenBuffers(1, &vbo);
        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        glBufferData(GL_ARRAY_BUFFER, std::size(data) * sizeof(block::glvert),
                     std::data(data), GL_STATIC_DRAW);
        return vbo;
    };
    const auto generate_vao = []() -> GLuint {
        GLuint vao = 0;
        glGenVertexArrays(1, &vao);
        glBindVertexArray(vao);
        // position
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, sizeof(glm::vec3) / sizeof(float), GL_FLOAT,
                              GL_FALSE, sizeof(block::glvert), nullptr);
        // texture
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, sizeof(glm::vec3) / sizeof(float), GL_FLOAT,
                              GL_FALSE, sizeof(block::glvert),
                              reinterpret_cast<void*>(sizeof(glm::vec3)));
        return vao;
    };
    // If we were to emplace glo with these there is no guarantee that each
    // function will be called in order (at least, for g++ it isn't). Therefore
    // we need to call them in order first.
    const auto solid_vbo = generate_vbo(solid_data);
    const auto solid_vao = generate_vao();
    const auto water_vbo = generate_vbo(water_data);
    const auto water_vao = generate_vao();
    this->glo.emplace(std::size(solid_data), solid_vbo, solid_vao,
                      std::size(water_data), water_vbo, water_vao);
    return true;
}

// http://www.lighthouse3d.com/tutorials/view-frustum-culling/geometric-approach-testing-boxes/
static bool box_in_frustum(const std::array<glm::vec3, 8>& points) noexcept {
    const auto& frustum = client::render::camera::get_frustum();

    for (const auto& plane : frustum) {
        bool inside = false;
        bool outside = false;

        for (const auto& point : points) {
            const float distance = plane.x * point.x + plane.y * point.y +
                                   plane.z * point.z + plane.w;
            if (distance < 0.0f) {
                outside = true;
            } else {
                inside = true;
            }

            if (inside && outside) {
                break;
            }
        }

        if (!inside) {
            return false;
        }
    }

    return true;
};

static bool is_chunk_visible(const float world_x,
                             const float world_z) noexcept {
    const std::array<glm::vec3, 8> box_vertices =
        [&world_x, &world_z]() -> std::array<glm::vec3, 8> {
        const float max_world_x = world_x + shared::world::chunk::WIDTH;
        const float max_world_z = world_z + shared::world::chunk::WIDTH;

        return {glm::vec3{world_x, 0.0f, world_z},
                {max_world_x, 0.0f, world_z},
                {world_x, 0.0f, max_world_z},
                {max_world_x, 0.0f, max_world_z},
                {world_x, shared::world::chunk::HEIGHT, world_z},
                {max_world_x, shared::world::chunk::HEIGHT, world_z},
                {world_x, shared::world::chunk::HEIGHT, max_world_z},
                {max_world_x, shared::world::chunk::HEIGHT, max_world_z}};
    }();

    return box_in_frustum(box_vertices);
}

bool chunk::draw(const chunks_t& chunks, const shared::player& lp,
                 const pass& pass, const bool skip_regen) noexcept {
    bool did_regen = false;
    if (!this->glo.has_value() || this->should_regenerate_vbo) {
        if (skip_regen || !maybe_regenerate_glo(chunks)) {
            return false;
        }
        this->should_regenerate_vbo = false;
        did_regen = true;
    }

    const auto [world_x, world_z] = [&lp, this]() -> std::pair<float, float> {
        const float offset_x =
            static_cast<float>(this->pos.x - lp.get_chunk_pos().x);
        const float offset_z =
            static_cast<float>(this->pos.z - lp.get_chunk_pos().z);
        return {offset_x * chunk::WIDTH, offset_z * chunk::WIDTH};
    }();

    if (is_chunk_visible(world_x, world_z)) {
        render(world_x, world_z, pass);
    }

    return did_regen;
}

} // namespace world
} // namespace client