lists_iterator.hpp

#pragma once
 
template <typename T, typename... Types>
class ComponentIterator {
 public:
  ComponentIterator(T& main, Types&... list)
      : lists_(std::make_tuple(&list...)),
        main_list_(&main),
        main_it_(main.begin()) {}
 
  bool next() {
    auto all_exist = [this](auto&... lists) -> bool {
      return (true && ... && lists->at(main_it_.pos()).valid());
    };
    auto it_end = main_list_->end();
    while (main_it_ != it_end) {
      if (main_it_.valid()) {
        if (std::apply(all_exist, lists_)) {
          return true;
        }
      }
      ++main_it_;
    }
    return false;
  }
 
  auto get() {
    auto res = std::apply(
        [this](auto&... lists) {
          return std::make_tuple(
              std::ref(main_it_.component()),
              std::ref(lists->at(main_it_.pos()).component())...);
        },
        lists_);
    ++main_it_;
    return res;
  }
 
  Entity getEntity() {
    auto t = main_it_;
    --t;
    Entity e = Entity(t.pos());
    return e;
  }
  
  void reset() { main_it_ = main_list_->begin(); }
 
 private:
  std::tuple<Types*...> lists_;
  T* main_list_;
  typename T::Iterator main_it_;
};