roguish/dinkyecs.hpp

#pragma once

#include <functional>
#include <typeindex>
#include <typeinfo>
#include <unordered_map>
#include <any>

namespace DinkyECS {

  typedef unsigned long Entity;

  typedef std::unordered_map<Entity, std::any> EntityMap;

  struct World {
    unsigned long entity_count = 0;
    std::unordered_map<std::type_index, EntityMap> $components;
    std::unordered_map<std::type_index, std::any> $facts;

    Entity entity() {
      return ++entity_count;
    }

    template <typename Comp>
      EntityMap& entity_map_for() {
        return $components[std::type_index(typeid(Comp))];
      }

    template <typename Comp>
      void set(Comp val) {
        $facts[std::type_index(typeid(Comp))] = val;
      }

    template <typename Comp>
      Comp &get() {
        // use .at to get std::out_of_range if fact not set
        std::any &res = $facts.at(std::type_index(typeid(Comp)));
        return std::any_cast<Comp&>(res);
      }

    template <typename Comp>
      void assign(Entity ent, Comp val) {
        EntityMap &map = entity_map_for<Comp>();
        map[ent] = val;
      }

    template <typename Comp>
      Comp &component(Entity ent) {
        EntityMap &map = entity_map_for<Comp>();
        // use .at for bounds checking
        std::any &res = map.at(ent);
        return std::any_cast<Comp&>(res);
      }

    template<typename Comp>
      void system(std::function<void(const Entity&, Comp&)> cb) {
        EntityMap &map = entity_map_for<Comp>();
        for(auto& [entity, any_comp] : map) {
          Comp &res = std::any_cast<Comp&>(any_comp);
          cb(entity, res);
        }
      }

    template<typename Comp>
      void remove(Entity ent) {
        EntityMap &map = entity_map_for<Comp>();
        map.erase(ent);
      }

    template<typename CompA, typename CompB>
      void system(std::function<void(const Entity&, CompA&, CompB&)> cb) {
        EntityMap &map_a = entity_map_for<CompA>();
        EntityMap &map_b = entity_map_for<CompB>();

        for(auto& [entity, any_a] : map_a) {
          if(map_b.contains(entity)) {
            CompA &res_a = std::any_cast<CompA&>(any_a);
            CompB &res_b = component<CompB>(entity);
            cb(entity, res_a, res_b);
          }
        }
      }

    template<typename CompA, typename CompB>
      std::function<void()> runner(std::function<void(const Entity&, CompA&, CompB&)> cb) {
        return [&]{
          system<CompA, CompB>(cb);
        };
      }
  };

}