Seele/src/Engine/Component/Component.h

#pragma once
#include <concepts>
#include <tuple>

namespace Seele {
template <typename... Types> struct Dependencies;
template <> struct Dependencies<> {
    int x;
    template <typename... Right> Dependencies<Right...> operator|(const Dependencies<Right...>&) { return Dependencies<Right...>(); }
};
template <typename This, typename... Rest> struct Dependencies<This, Rest...> : public Dependencies<Rest...> {
    template <typename... Right> Dependencies<This, Rest..., Right...> operator|(const Dependencies<Right...>&) {
        return Dependencies<This, Rest..., Right...>();
    }
    int x;
};

namespace Component {
template <typename Comp> Comp& getComponent();
}

template <typename Comp>
concept has_dependencies = requires(Comp) { Comp::dependencies; };

#define REQUIRE_COMPONENT(x)                                                                                                               \
  private:                                                                                                                                 \
    x& get##x() { return getComponent<x>(); }                                                                                              \
    const x& get##x() const { return getComponent<x>(); }                                                                                  \
                                                                                                                                           \
  public:                                                                                                                                  \
    constexpr static Dependencies<x> dependencies = {};

#define DECLARE_COMPONENT(x)                                                                                                               \
    void accessComponent(x& val);                                                                                                          \
    template <> x& getComponent<x>();

#define DEFINE_COMPONENT(x)                                                                                                                \
    thread_local x* tl_##x = nullptr;                                                                                                      \
    void Seele::Component::accessComponent(x& ref) { tl_##x = &ref; }                                                                      \
    template <> x& Seele::Component::getComponent<x>() { return *tl_##x; }

} // namespace Seele