// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#pragma once
#define HAVE_IRCD_CTX_SHARED_MUTEX_H

namespace ircd::ctx
{
	class shared_mutex;
}

class ircd::ctx::shared_mutex
{
	bool u;
	ssize_t s;
	list q;

	void release();

  public:
	size_t shares() const;
	size_t waiting() const;

	bool try_lock();
	bool try_lock_shared();
	bool try_lock_upgrade();

	template<class time_point> bool try_lock_until(time_point&&);
	template<class time_point> bool try_lock_shared_until(time_point&&);
	template<class time_point> bool try_lock_upgrade_until(time_point&&);

	template<class duration> bool try_lock_for(duration&&);
	template<class duration> bool try_lock_shared_for(duration&&);
	template<class duration> bool try_lock_upgrade_for(duration&&);

	void lock();
	void lock_shared();
	void lock_upgrade();

	bool try_unlock_shared_and_lock();
	bool try_unlock_shared_and_lock_upgrade();
	bool try_unlock_upgrade_and_lock();

	template<class time_point> bool try_unlock_shared_and_lock_until(time_point&&);
	template<class time_point> bool try_unlock_shared_and_lock_upgrade_until(time_point&&);
	template<class time_point> bool try_unlock_upgrade_and_lock_until(time_point&&);

	template<class duration> bool try_unlock_shared_and_lock_for(duration&&);
	template<class duration> bool try_unlock_shared_and_lock_upgrade_for(duration&&);
	template<class duration> bool try_unlock_upgrade_and_lock_for(duration&&);

	void unlock();
	void unlock_shared();
	void unlock_upgrade();
	void unlock_and_lock_shared();
	void unlock_and_lock_upgrade();
	void unlock_upgrade_and_lock();
	void unlock_upgrade_and_lock_shared();

	shared_mutex();
	shared_mutex(shared_mutex &&) noexcept;
	shared_mutex(const shared_mutex &) = delete;
	shared_mutex &operator=(shared_mutex &&) noexcept;
	shared_mutex &operator=(const shared_mutex &) = delete;
	~shared_mutex() noexcept;
};

inline
ircd::ctx::shared_mutex::shared_mutex()
:u{false}
,s{0}
{
}

inline
ircd::ctx::shared_mutex::shared_mutex(shared_mutex &&o)
noexcept
:u{std::move(o.u)}
,s{std::move(o.s)}
{
	o.u = false;
	o.s = 0;
}

inline
ircd::ctx::shared_mutex &
ircd::ctx::shared_mutex::operator=(shared_mutex &&o)
noexcept
{
	this->~shared_mutex();
	std::swap(u, o.u);
	std::swap(s, o.s);
	return *this;
}

inline
ircd::ctx::shared_mutex::~shared_mutex()
noexcept
{
	assert(!u);
	assert(s == 0);
	assert(q.empty());
}

inline void
ircd::ctx::shared_mutex::unlock_upgrade_and_lock_shared()
{
	++s;
	u = false;
	release();
}

inline void
ircd::ctx::shared_mutex::unlock_upgrade_and_lock()
{
	s = std::numeric_limits<decltype(s)>::min();
	u = false;
}

inline void
ircd::ctx::shared_mutex::unlock_and_lock_upgrade()
{
	s = 0;
	u = true;
}

inline void
ircd::ctx::shared_mutex::unlock_and_lock_shared()
{
	s = 1;
	release();
}

inline void
ircd::ctx::shared_mutex::unlock_upgrade()
{
	u = false;
	release();
}

inline void
ircd::ctx::shared_mutex::unlock_shared()
{
	--s;
	release();
}

inline void
ircd::ctx::shared_mutex::unlock()
{
	s = 0;
	release();
}

template<class duration>
bool
ircd::ctx::shared_mutex::try_unlock_upgrade_and_lock_for(duration&& d)
{
	return try_unlock_upgrade_and_lock_until(steady_clock::now() + d);
}

template<class duration>
bool
ircd::ctx::shared_mutex::try_unlock_shared_and_lock_upgrade_for(duration&& d)
{
	return try_unlock_shared_and_lock_upgrade_until(steady_clock::now() + d);
}

template<class duration>
bool
ircd::ctx::shared_mutex::try_unlock_shared_and_lock_for(duration&& d)
{
	return try_unlock_shared_and_lock_until(steady_clock::now() + d);
}

template<class time_point>
bool
ircd::ctx::shared_mutex::try_unlock_upgrade_and_lock_until(time_point&& tp)
{
	assert(0);
	return false;
}

template<class time_point>
bool
ircd::ctx::shared_mutex::try_unlock_shared_and_lock_upgrade_until(time_point&& tp)
{
	assert(0);
	return false;
}

template<class time_point>
bool
ircd::ctx::shared_mutex::try_unlock_shared_and_lock_until(time_point&& tp)
{
	assert(0);
	return false;
}

inline bool
ircd::ctx::shared_mutex::try_unlock_upgrade_and_lock()
{
	if(!try_lock())
		return false;

	u = false;
	return true;
}

inline bool
ircd::ctx::shared_mutex::try_unlock_shared_and_lock_upgrade()
{
	if(!try_lock_upgrade())
		return false;

	--s;
	return true;
}

inline bool
ircd::ctx::shared_mutex::try_unlock_shared_and_lock()
{
	if(s != 1)
		return false;

	s = 1;
	return true;
}

inline void
ircd::ctx::shared_mutex::lock_upgrade()
{
	if(likely(try_lock_upgrade()))
		return;

	assert(current);
	q.push_back(current);
	while(!try_lock_upgrade())
		wait();
}

inline void
ircd::ctx::shared_mutex::lock_shared()
{
	if(likely(try_lock_shared()))
		return;

	assert(current);
	q.push_back(current);
	while(!try_lock_shared())
		wait();
}

inline void
ircd::ctx::shared_mutex::lock()
{
	if(likely(try_lock()))
		return;

	assert(current);
	q.push_back(current);
	while(!try_lock())
		wait();
}

template<class duration>
bool
ircd::ctx::shared_mutex::try_lock_upgrade_for(duration&& d)
{
	return try_lock_upgrade_until(steady_clock::now() + d);
}

template<class duration>
bool
ircd::ctx::shared_mutex::try_lock_shared_for(duration&& d)
{
	return try_lock_shared_until(steady_clock::now() + d);
}

template<class duration>
bool
ircd::ctx::shared_mutex::try_lock_for(duration&& d)
{
	return try_lock_until(steady_clock::now() + d);
}

template<class time_point>
bool
ircd::ctx::shared_mutex::try_lock_upgrade_until(time_point&& d)
{
	assert(0);
	return false;
}

template<class time_point>
bool
ircd::ctx::shared_mutex::try_lock_shared_until(time_point&& d)
{
	assert(0);
	return false;
}

template<class time_point>
bool
ircd::ctx::shared_mutex::try_lock_until(time_point&& tp)
{
	if(likely(try_lock()))
		return true;

	assert(current);
	q.push_back(current);
	while(!try_lock())
	{
		if(unlikely(wait_until<std::nothrow_t>(tp)))
		{
			q.remove(current);
			return false;
		}
	}

	return true;
}

inline bool
ircd::ctx::shared_mutex::try_lock_upgrade()
{
	if(s < 0)
		return false;

	if(u)
		return false;

	u = true;
	return true;
}

inline bool
ircd::ctx::shared_mutex::try_lock_shared()
{
	++s;
	return s >= 0;
}

inline bool
ircd::ctx::shared_mutex::try_lock()
{
	if(s)
		return false;

	s = std::numeric_limits<decltype(s)>::min();
	return true;
}

inline size_t
ircd::ctx::shared_mutex::waiting()
const
{
	return q.size();
}

inline size_t
ircd::ctx::shared_mutex::shares()
const
{
	return std::max(s, ssize_t(0));
}

inline void
ircd::ctx::shared_mutex::release()
{
	release_sequence(q);
}