#include <chaiscript/chaiscript.hpp>

class Entity {
public:
 int width;
 int height;
 int x;
 int y;
 std::string name;

 std::function<void(Entity &)> updater;

 Entity(const int t_width, const int t_height, const int t_x, const int t_y, std::string t_name)
 : width(t_width)
 , height(t_height)
 , x(t_x)
 , y(t_y)
 , name(std::move(t_name)) {
 }
};

class Factory {
public:
 // we may as well pass the parameters for the entity to the factory method, this does the initialization
 // in one step.
 Entity *make_entity(const int width, const int height, const int x, const int y, const std::string &name) {
 auto entity = entities.insert({name, Entity{width, height, x, y, name}});
 return &(entity.first->second);
 }

 Entity *get_entity(const std::string &name) { return &entities.at(name); }

 // loop over all entities and all their updater function (if it exists)
 void update_entities() {
 for (auto &entity : entities) {
 if (entity.second.updater) {
 entity.second.updater(entity.second);
 }
 }
 }

private:
 // we cannot store the entities in a std::vector if we want to return a pointer to them,
 // because a vector automatically resizing itself can invalidate the pointer that was returned.
 // using a map guarantees that the memory assigned to the entity will never change, plus
 // lets us easily look up an entity by name
 std::map<std::string, Entity> entities;
};

int main() {
 chaiscript::ChaiScript chai;

 chai.add(chaiscript::fun(&Entity::width), "width");
 chai.add(chaiscript::fun(&Entity::height), "height");
 chai.add(chaiscript::fun(&Entity::x), "x");
 chai.add(chaiscript::fun(&Entity::y), "y");
 chai.add(chaiscript::fun(&Entity::name), "name");
 chai.add(chaiscript::fun(&Entity::updater), "updater");
 chai.add(chaiscript::user_type<Entity>(), "Entity"); // this isn't strictly necessary but makes error messages nicer

 chai.add(chaiscript::fun(&Factory::make_entity), "make_entity");
 chai.add(chaiscript::fun(&Factory::get_entity), "get_entity");
 chai.add(chaiscript::fun(&Factory::update_entities), "update_entities");
 chai.add(chaiscript::user_type<Factory>(), "Factory"); // this isn't strictly necessary but makes error messages nicer

 Factory f;
 chai.add(chaiscript::var(&f), "f");

 std::string script = R""(
 f.make_entity(10,10,1,1,"entity1").updater = fun(e){ e.x += 1; e.y += 1 };
 f.make_entity(10,10,10,10,"entity2").updater = fun(e){ e.x += 2; e.y += 2 };
 f.make_entity(10,10,20,20,"entity3");

 print(f.get_entity("entity1").x == 1)
 print(f.get_entity("entity2").x == 10)
 print(f.get_entity("entity3").x == 20)

 f.update_entities(); // this runs the function objects we set in the previous lines
 // we should now see the updated values

 print(f.get_entity("entity1").x == 2)
 print(f.get_entity("entity2").x == 12)
 print(f.get_entity("entity3").x == 20) // this one has no updater, so it stays the same
 )"";

 chai.eval(script);
}