entity.h

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#pragma once

#include <vector>
#include <memory>

namespace yage
{

class Space;
class ComponentGroup;

typedef unsigned int Entity;

class EntityManager
{
public:
    EntityManager() = default;

    EntityManager(Space *space);

    EntityManager(Space *space, std::size_t n);

    Entity createEntity();

    void deleteEntity(Entity entity);

private:
    Entity next_entity_ = 0;

    Space *space_ = nullptr;

    std::vector<Entity> entities_;

    std::vector<std::unique_ptr<ComponentGroup>> components;
};

class BaseComponent {
public:
    typedef unsigned Group;

protected:
    static Group group_id_counter_;
};

template <typename Derived>
class Component : public BaseComponent {
private:
    friend class EntityManager;

    BaseComponent::Group group();
};

class ComponentGroup {
private:
    friend class EntityManager;

    std::vector<BaseComponent *> components_;
};

// Template definitions

template <typename Derived>
BaseComponent::Group Component<Derived>::group()
{
    static Group group_id = group_id_counter_++;
    return group_id;
}

} // namespace yage