#include "ChunkMeshing.hpp"

namespace MC::World::Generation {

std::array<Vector<2, F32>, 4> face_tex_coords(BlockType type, BlockSide side) {
    U8 atlas_width = 4;
    U8 atlas_height = 4;

    Real width_step = 1.0f / atlas_width;
    Real height_step = 1.0f / atlas_height;

    auto block_coords = [=](U8 x, U8 y) {
        auto t = y * height_step;
        auto l = x * width_step;
        auto b = t + height_step;
        auto r = l + width_step;

        return std::array<Vector<2, F32>, 4>{{
            {l, b}, {r, b}, {r, t}, {l, t},
        }};
    };

    switch (type) {
        case BlockType::Dirt:
            return block_coords(1, 0);
        case BlockType::Grass:
            switch (side) {
                case BlockSide::Front:
                case BlockSide::Back:
                case BlockSide::Left:
                case BlockSide::Right:
                    return block_coords(2, 0);
                case BlockSide::Bottom:
                    return block_coords(1, 0);
                case BlockSide::Top:
                    return block_coords(0, 0);
            }
        case BlockType::Stone:
            return block_coords(3, 0);
        case BlockType::Sand:
            return block_coords(1, 1);
        case BlockType::Water:
            return block_coords(0, 1);
        case BlockType::Snow:
            switch (side) {
                case BlockSide::Front:
                case BlockSide::Back:
                case BlockSide::Left:
                case BlockSide::Right:
                    return block_coords(3, 1);
                case BlockSide::Bottom:
                    return block_coords(1, 0);
                case BlockSide::Top:
                    return block_coords(2, 1);
            }
        case BlockType::Wood:
            switch (side) {
                case BlockSide::Front:
                case BlockSide::Back:
                case BlockSide::Right:
                case BlockSide::Left:
                    return block_coords(0, 2);
                case BlockSide::Bottom:
                case BlockSide::Top:
                    return block_coords(1, 2);
            }
        case BlockType::Leaves:
            return block_coords(2, 2);
        case BlockType::Air:
            return {};
    }
}

std::array<Vector<3, F32>, 4> face_normals(BlockSide side) {
    auto is_side = [=](BlockSide s) -> Real { return s == side; };

    Vector<3, F32> normal = {
        is_side(BlockSide::Right) - is_side(BlockSide::Left),
        is_side(BlockSide::Top) - is_side(BlockSide::Bottom),
        is_side(BlockSide::Front) - is_side(BlockSide::Back),
    };

    return {normal, normal, normal, normal};
}

Bool is_face_visible(Chunk& chunk, const ChunkMeshing::ChunkNeighbors& neighbors, U32 x, U32 y, U32 z, BlockSide side) {
    Vector<3, I32> offset{};
    switch (side) {
        case BlockSide::Front:
            offset[2] = 1;
            break;
        case BlockSide::Back:
            offset[2] = -1;
            break;
        case BlockSide::Top:
            offset[1] = 1;
            break;
        case BlockSide::Bottom:
            offset[1] = -1;
            break;
        case BlockSide::Left:
            offset[0] = -1;
            break;
        case BlockSide::Right:
            offset[0] = 1;
            break;
    }

    Vector<3, I32> neighbor_pos{
        (I32)x + offset.x(), (I32)y + offset.y(), (I32)z + offset.z(),
    };

    Chunk* chunk_to_ask;

    if (neighbor_pos.z() < 0) {
        chunk_to_ask = &neighbors.north;
        neighbor_pos.z() += Chunk::Width;
    } else if (neighbor_pos.x() >= (I32)Chunk::Width) {
        chunk_to_ask = &neighbors.east;
        neighbor_pos.x() -= Chunk::Width;
    } else if (neighbor_pos.z() >= (I32)Chunk::Width) {
        chunk_to_ask = &neighbors.south;
        neighbor_pos.z() -= Chunk::Width;
    } else if (neighbor_pos.x() < 0) {
        chunk_to_ask = &neighbors.west;
        neighbor_pos.x() += Chunk::Width;
    } else {
        chunk_to_ask = &chunk;
    }

    auto [neighbor] = chunk_to_ask->get(neighbor_pos.x(), neighbor_pos.y(), neighbor_pos.z());
    return neighbor.is_transparent();
}

GFX::Mesh ChunkMeshing::create_mesh_for_chunk(Chunk& chunk, const ChunkNeighbors& neighbors) {
    std::vector<Vector<3, F32>> positions{};
    std::vector<Vector<3, F32>> normals{};
    std::vector<Vector<2, F32>> tex_coords{};
    std::vector<U32> indices{};

    for (Int x = 0; x < Chunk::Width; x++) {
        for (Int y = 0; y < Chunk::Height; y++) {
            for (Int z = 0; z < Chunk::Width; z++) {
                auto type = chunk.get(x, y, z).type;
                if (type == BlockType::Air) {
                    continue;
                }

                for (auto side: BlockSide::all()) {
                    if (!is_face_visible(chunk, neighbors, x, y, z, side)) {
                        continue;
                    }

                    auto side_positions = side.face();
                    auto side_normals = face_normals(side);
                    auto side_tex_coords = face_tex_coords(type, side);

                    for (auto& position : side_positions) {
                        position = position + Vector<3, F32>{x, y, z};
                    }

                    U32 s = positions.size();

                    positions.insert(positions.end(), side_positions.begin(), side_positions.end());
                    normals.insert(normals.end(), side_normals.begin(), side_normals.end());
                    tex_coords.insert(tex_coords.end(), side_tex_coords.begin(), side_tex_coords.end());
                    indices.insert(indices.end(), {s, s + 1, s + 3, s + 1, s + 2, s + 3});
                }
            }
        }
    }

    return {
        {positions, normals, tex_coords},
        indices,
    };
}

}