#include "World.hpp"
#include "Generation/ChunkMeshing.hpp"

namespace MC::World {

std::vector<World::ChunkData*> World::get_visible_chunks(Vector<3> position) {
    auto finished_chunks = load_finished_chunks_from_queue();
    auto visible_chunks = get_visible_chunk_indices(position);

    auto updates = visible_chunks;
    for (auto index : m_visible_chunks) {
        updates.erase(index);
    }
    for (auto index : finished_chunks) {
        updates.insert(index);
    }

    if (!updates.empty()) {
        process_chunk_visibility_updates(updates, position);
        m_visible_chunks = visible_chunks;
    }

    std::vector<ChunkData*> chunks{};
    chunks.reserve(visible_chunks.size());
    for (auto index : visible_chunks) {
        auto& data = get(index);
        if (data.status == ChunkStatus::NeedsMesh) {
            try_to_create_mesh_for_chunk(data);
        }
        if (data.status == ChunkStatus::Done) {
            chunks.push_back(&data);
        }
    }

    return chunks;
}

Chunk* World::get_chunk_for_position(Vector<3> position) {
    I32 x = std::round(position.x() / Chunk::Width);
    I32 y = std::round(position.z() / Chunk::Width);
    auto& data = get({x, y});
    if (data.chunk.has_value()) {
        return &data.chunk.value();
    }
    return nullptr;
}

void World::process_chunk_visibility_updates(const std::unordered_set<ChunkIndex>& new_chunks, const Vector<3> player) {
    for (auto new_index: new_chunks) {
        auto& data = get(new_index);
        if (data.status == ChunkStatus::Empty) {
            request_generation(new_index, player.distance(new_index.middle()));
            data.status = ChunkStatus::WaitingForGeneration;
        }
    }
}

std::unordered_set<ChunkIndex> World::get_visible_chunk_indices(const Vector<3> position) const {
    I32 center_x = std::round(position.x() / Chunk::Width);
    I32 center_y = std::round(position.z() / Chunk::Width);

    std::unordered_set<ChunkIndex> indices{};
    indices.reserve(m_view_distance_radius * m_view_distance_radius * 4);
    auto radius = m_view_distance_radius;
    for (I32 x = -radius; x <= radius; x++) {
        I32 height = std::round(std::sqrt(radius * radius - x * x) + 0.5);
        for (I32 y = -height; y <= height; y++) {
            indices.emplace(x + center_x, y + center_y);
        }
    }

    return indices;
}

std::unordered_set<ChunkIndex> World::load_finished_chunks_from_queue() {
    std::unordered_set<ChunkIndex> indices;
    auto results = m_queue.done();
    for (auto& [id, res] : results) {
        get(id) = {id, ChunkStatus::NeedsMesh, {res.chunk}};
        indices.insert(id);

        log_chunk_time(res.generation_duration);
    }

    return indices;
}

void World::request_generation(ChunkIndex index, Real priority) {
    m_queue.add(index, priority, [=]() -> GenerationResult {
        auto start = timestamp();
        auto chunk = m_generator.generate(index.x, index.y);
        return {chunk, timestamp() - start};
    });
}

World::ChunkData& World::get(ChunkIndex index) {
    auto entry = m_chunks.find(index);
    if (entry == m_chunks.end()) {
        ChunkData data{index, ChunkStatus::Empty};

        m_chunks.insert({index, std::move(data)});
        return m_chunks.at(index);
    }

    return entry->second;
}

U64 World::timestamp() {
    auto time = std::chrono::system_clock::now().time_since_epoch();
    auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(time);
    return ms.count();
}

void World::try_to_create_mesh_for_chunk(ChunkData& data) {
    auto index = data.index;

    UInt neighbor_index = 0;
    std::array<Chunk*, 8> neighbors;
    for (I32 x = -1; x <= 1; x++) {
        for (I32 y = -1; y <= 1; y++) {
            if (x == 0 && y == 0) continue;

            auto& neighbor_data = get({index.x + x, index.y + y});
            if (!neighbor_data.chunk.has_value()) return; // All neighbors need to be generated first.

            neighbors[neighbor_index++] = &neighbor_data.chunk.value();
        }
    }

    // Layout of neighboring chunks in `neighbors` array:
    // (-1; -1) > (-1;  0) > (-1; 1) > (0; -1)
    // ( 0;  1) > ( 1; -1) > ( 1; 0) > (1;  1)
    Generation::ChunkMeshing::ChunkNeighbors chunk_neighbors {
        neighbors[3], neighbors[6], neighbors[4], neighbors[1],
        neighbors[5], neighbors[7], neighbors[2], neighbors[0],
    };

    data.mesh_data = create_mesh_for_chunk(data.chunk.value(), chunk_neighbors);
    data.mesh = GFX::Binder::load(data.mesh_data.value());
    data.status = ChunkStatus::Done;
}

void World::log_chunk_time(U64 chunk_time_ms) {
    m_statistics.chunk_time_sample_count++;
    m_statistics.average_chunk_time_ms += ((Real)chunk_time_ms - m_statistics.average_chunk_time_ms) / m_statistics.chunk_time_sample_count;
}

Real World::get_average_chunk_time() const {
    return m_statistics.average_chunk_time_ms;
}

}