project-swan/libswan/include/swan/Collection.h

#pragma once

#include <vector>
#include <string>
#include <typeindex>
#include <type_traits>

#include "common.h"
#include "log.h"
#include "Entity.h"
#include "SlotVector.h"
#include "SmallOptional.h"

namespace Swan {

class EntityCollection;

class EntityRef {
public:
	EntityRef() = default;
	EntityRef(EntityCollection *coll, size_t index, size_t generation):
		coll_(coll), index_(index), generation_(generation) {}

	template<typename Func>
	EntityRef &then(Func func);

	bool hasValue();
	Entity *get();

private:
	EntityCollection *coll_;
	size_t index_;
	size_t generation_;
};

class EntityCollection {
public:
	struct Factory {
		const std::string name;
		std::unique_ptr<EntityCollection> (*const create)(std::string name);
	};

	template<typename Ent>
	using OptEnt = SmallOptional<
		Ent, SmallOptionalInitialBytesPolicy<Ent, sizeof(void *)>>;
	template<typename Ent>
	using SlotPolicy = SlotVectorDefaultSentinel<SmallNullOpt>;

	virtual ~EntityCollection() = default;

	template<typename Ent, typename... Args>
	EntityRef spawn(Args&&... args);

	virtual const std::string &name() = 0;
	virtual std::type_index type() = 0;

	virtual size_t size() = 0;
	virtual Entity *get(size_t idx) = 0;
	virtual Entity *get(size_t idx, size_t generation) = 0;

	virtual EntityRef spawn(const Context &ctx, const Entity::PackObject &obj) = 0;
	virtual void update(const Context &ctx, float dt) = 0;
	virtual void tick(const Context &ctx, float dt) = 0;
	virtual void draw(const Context &ctx, Win &win) = 0;
	virtual void erase(size_t idx, size_t generation) = 0;

private:
	virtual void *getEntityVector() = 0;
	virtual size_t nextGeneration() = 0;
};

template<typename Ent>
class EntityCollectionImpl: public EntityCollection {
public:
	EntityCollectionImpl(std::string name): name_(std::move(name)) {}

	size_t size() override { return entities_.size(); }
	Entity *get(size_t idx) override { return entities_[idx].get(); }
	Entity *get(size_t idx, size_t generation) override;

	const std::string &name() override { return name_; }
	std::type_index type() override { return typeid(Ent); }

	EntityRef spawn(const Context &ctx, const Entity::PackObject &obj) override;
	void update(const Context &ctx, float dt) override;
	void tick(const Context &ctx, float dt) override;
	void draw(const Context &ctx, Win &win) override;
	void erase(size_t idx, size_t generation) override;

private:
	void *getEntityVector() override { return (void *)&entities_; }
	size_t nextGeneration() override { return generation_++; }

	const std::string name_;
	SlotVector<OptEnt<Ent>, SlotPolicy<Ent>> entities_;
	size_t generation_ = 0;
};

/*
 * EntityRef
 */

template<typename Func>
inline EntityRef &EntityRef::then(Func func) {
	Entity *ent = coll_->get(index_, generation_);
	if (ent != nullptr)
		func(ent);

	return *this;
}

inline Entity *EntityRef::get() {
	return coll_->get(index_, generation_);
}

inline bool EntityRef::hasValue() {
	return coll_->get(index_, generation_) != nullptr;
}

/*
 * EntityCollection
 */

template<typename Ent, typename... Args>
inline EntityRef EntityCollection::spawn(Args&&... args) {
	auto entities = (SlotVector<OptEnt<Ent>, SlotPolicy<Ent>> *)getEntityVector();

	size_t generation = nextGeneration();
	size_t idx = entities->emplace();
	OptEnt<Ent> &ent = (*entities)[idx];
	ent.emplace(std::forward<Args>(args)...);
	ent->index_ = idx;
	ent->generation_ = generation;

	if constexpr (std::is_base_of_v<BodyTrait, Ent>) {
		BodyTrait::Body &body = ent->get(BodyTrait::Tag{});
		body.pos -= body.size / 2;
	}

	return { this, idx, generation };
}

/*
 * EntityCollectionImpl
 */

template<typename Ent>
inline Entity *EntityCollectionImpl<Ent>::get(size_t idx, size_t generation) {
	if (idx >= entities_.size())
		return nullptr;

	auto &e = entities_[idx];
	// We don't even need to check if e.hasValue(), because if it doesn't,
	// its generation will be 0xffff... and the check will fail

	if (e->generation_ != generation)
		return nullptr;

	return e.get();
}

template<typename Ent>
inline EntityRef EntityCollectionImpl<Ent>::spawn(const Context &ctx, const Entity::PackObject &obj) {
	size_t generation = nextGeneration();
	size_t idx = entities_.emplace();
	OptEnt<Ent> &ent = entities_[idx];
	ent.emplace(ctx, obj);
	ent->index_ = idx;
	ent->generation_ = generation;

	return { this, idx, generation };
}

template<typename Ent>
inline void EntityCollectionImpl<Ent>::update(const Context &ctx, float dt) {
	ZoneScopedN(typeid(Ent).name());
	for (auto &ent: entities_) {
		ZoneScopedN("update");
		ent->update(ctx, dt);
	}
}

template<typename Ent>
inline void EntityCollectionImpl<Ent>::tick(const Context &ctx, float dt) {
	ZoneScopedN(typeid(Ent).name());
	for (auto &ent: entities_) {
		ZoneScopedN("tick");
		ent->tick(ctx, dt);
	}
}

template<typename Ent>
inline void EntityCollectionImpl<Ent>::draw(const Context &ctx, Win &win) {
	ZoneScopedN(typeid(Ent).name());
	for (auto &ent: entities_) {
		ZoneScopedN("draw");
		ent->draw(ctx, win);
	}
}

template<typename Ent>
inline void EntityCollectionImpl<Ent>::erase(size_t idx, size_t generation) {
	ZoneScopedN(typeid(Ent).name());
	OptEnt<Ent> &ent = entities_[idx];
	if (!ent.hasValue() || ent->generation_ != generation) {
		warn << "Erasing wrong entity " << typeid(Ent).name() << '[' << idx << "]!";
		return;
	}

	entities_.erase(idx);
}

}