#ifndef SRC_CALLBACK_QUEUE_H_

#define SRC_CALLBACK_QUEUE_H_

#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

#include <atomic>

namespace node {

namespace CallbackFlags {

enum Flags {

kUnrefed = 0,

kRefed = 1,

};

}

// A queue of C++ functions that take Args... as arguments and return R

// (this is similar to the signature of std::function).

// New entries are added using `CreateCallback()`/`Push()`, and removed using

// `Shift()`.

// The `refed` flag is left for easier use in situations in which some of these

// should be run even if nothing else is keeping the event loop alive.

template <typename R, typename... Args>

class CallbackQueue {

public:

class Callback {

public:

explicit inline Callback(CallbackFlags::Flags flags);

virtual ~Callback() = default;

virtual R Call(Args... args) = 0;

inline CallbackFlags::Flags flags() const;

private:

inline std::unique_ptr<Callback> get_next();

inline void set_next(std::unique_ptr<Callback> next);

CallbackFlags::Flags flags_;

std::unique_ptr<Callback> next_;

friend class CallbackQueue;

};

template <typename Fn>

inline std::unique_ptr<Callback> CreateCallback(

Fn&& fn, CallbackFlags::Flags);

inline std::unique_ptr<Callback> Shift();

inline void Push(std::unique_ptr<Callback> cb);

// ConcatMove adds elements from 'other' to the end of this list, and clears

// 'other' afterwards.

inline void ConcatMove(CallbackQueue&& other);

// size() is atomic and may be called from any thread.

inline size_t size() const;

private:

template <typename Fn>

class CallbackImpl final : public Callback {

public:

CallbackImpl(Fn&& callback, CallbackFlags::Flags flags);

R Call(Args... args) override;

private:

Fn callback_;

};

std::atomic<size_t> size_ {0};

std::unique_ptr<Callback> head_;

Callback* tail_ = nullptr;

};

} // namespace node

#endif // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

#endif // SRC_CALLBACK_QUEUE_H_