util.cpp

template<typename Container, typename E>
void replaceEntities(Container &container, const std::vector<E> &newEntities) {
    auto cmp = [](const E &a, const E &b) { return a.name() < b.name(); };

    std::vector<E> new_entities(newEntities);
    ObjectType ot = nix::objectToType<E>::type;
    ndsize_t current = container.entityCount(ot);
    size_t old_count = nix::check::fits_in_size_t(current, "entityCount() failed; count > size_t.");

    std::vector<E> old_entities(old_count);
    for (size_t i = 0; i < old_count; i++) {
        old_entities[i] = container->getEntity(i, ot);
    }

    std::sort(new_entities.begin(), new_entities.end(), cmp);
    std::sort(old_entities.begin(), old_entities.end(), cmp);
    std::vector<E> add;
    std::vector<E> rem;

    std::set_difference(new_entities.begin(), new_entities.end(),
                        old_tags.begin(), old_tags.end(),
                        std::inserter(add, add.begin()), cmp);
    std::set_difference(old_tags.begin(), old_tags.end(),
                        new_entities.begin(), new_entities.end(),
                        std::inserter(rem, rem.begin()), cmp);

    for (const auto &e : add) {
        E entity = container->getEntity<objectToType<E>::backendType>(e);
        if (!entity)
            throw std::runtime_error("One or more entities do not exist in this block!");
        addEntity(e);
    }

    for (const auto &e : rem) {
        removeEntity(e);
    }

}