/*
 * \brief  Multiplexing one time source amongst different timeouts
 * \author Martin Stein
 * \date   2016-11-04
 *
 * These classes are not meant to be used directly. They merely exist to share
 * the generic parts of timeout-scheduling between the Timer::Connection and the
 * Timer driver. For user-level timeout-scheduling you should use the interface
 * in timer_session/connection.h instead.
 */

/*
 * Copyright (C) 2016-2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

#ifndef _TIMER__TIMEOUT_H_
#define _TIMER__TIMEOUT_H_

/* Genode includes */
#include <util/noncopyable.h>
#include <base/lock.h>
#include <base/log.h>
#include <base/duration.h>

namespace Genode {

	class Time_source;
	class Timeout_scheduler;
	class Timeout;
	class Alarm_timeout_scheduler;
}

namespace Timer
{
	class Connection;
	class Root_component;
}


/**
 * Interface of a time source that can handle one timeout at a time
 */
struct Genode::Time_source : Interface
{
	/**
	 * Interface of a timeout callback
	 */
	struct Timeout_handler : Interface
	{
		virtual void handle_timeout(Duration curr_time) = 0;
	};

	/**
	 * Return the current time of the source
	 */
	virtual Duration curr_time() = 0;

	/**
	 * Return the maximum timeout duration that the source can handle
	 */
	virtual Microseconds max_timeout() const = 0;

	/**
	 * Install a timeout, overrides the last timeout if any
	 *
	 * \param duration  timeout duration
	 * \param handler   timeout callback
	 */
	virtual void schedule_timeout(Microseconds     duration,
	                              Timeout_handler &handler) = 0;

	/**
	 * Tell the time source which scheduler to use for its own timeouts
	 *
	 * This method enables a time source for example to synchronize with an
	 * accurate but expensive timer only on a periodic basis while using a
	 * cheaper interpolation in general.
	 */
	virtual void scheduler(Timeout_scheduler &) { };
};


/**
 * Interface of a time-source multiplexer
 *
 * Beside 'curr_time()', this abstract interface is used by the Timeout
 * implementation only. Users of the timeout framework must schedule and
 * discard timeouts via methods of the timeout.
 */
class Genode::Timeout_scheduler : Interface
{
	private:

		friend Timeout;

		/**
		 * Add a one-shot timeout to the schedule
		 *
		 * \param timeout   timeout callback object
		 * \param duration  timeout trigger delay
		 */
		virtual void _schedule_one_shot(Timeout &timeout, Microseconds duration) = 0;

		/**
		 * Add a periodic timeout to the schedule
		 *
		 * \param timeout   timeout callback object
		 * \param duration  timeout trigger period
		 */
		virtual void _schedule_periodic(Timeout &timeout, Microseconds duration) = 0;

		/**
		 * Remove timeout from the scheduler
		 *
		 * \param timeout  corresponding timeout callback object
		 */
		virtual void _discard(Timeout &timeout) = 0;

	public:

		/**
		 *  Read out the now time of the scheduler
		 */
		virtual Duration curr_time() = 0;
};


/**
 * Timeout callback that can be used for both one-shot and periodic timeouts
 *
 * This class should be used only if it is necessary to use one timeout
 * callback for both periodic and one-shot timeouts. This is the case, for
 * example, in a Timer-session server. If this is not the case, the classes
 * Periodic_timeout and One_shot_timeout are the better choice.
 */
class Genode::Timeout : private Noncopyable
{
	friend class Alarm_timeout_scheduler;

	public:

		/**
		 * Interface of a timeout handler
		 */
		struct Handler : Interface
		{
			virtual void handle_timeout(Duration curr_time) = 0;
		};

	private:

		class Alarm
		{
			friend class Alarm_timeout_scheduler;

			private:

				typedef uint64_t Time;

				struct Raw
				{
					Time deadline;
					bool deadline_period;
					Time period;

					bool is_pending_at(uint64_t time, bool time_period) const;
				};

				Lock                     _dispatch_lock { };
				Raw                      _raw           { };
				int                      _active        { 0 };
				Alarm                   *_next          { nullptr };
				Alarm_timeout_scheduler *_scheduler     { nullptr };

				void _alarm_assign(Time                     period,
				                   Time                     deadline,
				                   bool                     deadline_period,
				                   Alarm_timeout_scheduler *scheduler)
				{
					_raw.period          = period;
					_raw.deadline_period = deadline_period;
					_raw.deadline        = deadline;
					_scheduler           = scheduler;
				}

				void _alarm_reset() { _alarm_assign(0, 0, false, 0), _active = 0, _next = 0; }

				bool _on_alarm(uint64_t);

				Alarm(Alarm const &);
				Alarm &operator = (Alarm const &);

			public:

				Timeout_scheduler &timeout_scheduler;
				Handler           *handler  = nullptr;
				bool               periodic = false;

				Alarm(Timeout_scheduler &timeout_scheduler)
				: timeout_scheduler(timeout_scheduler) { _alarm_reset(); }

				virtual ~Alarm();

		} _alarm;

	public:

		Timeout(Timeout_scheduler &timeout_scheduler)
		: _alarm(timeout_scheduler) { }

		~Timeout() { discard(); }

		void schedule_periodic(Microseconds duration, Handler &handler);

		void schedule_one_shot(Microseconds duration, Handler &handler);

		void discard();

		bool scheduled() { return _alarm.handler != nullptr; }
};


/**
 * Timeout-scheduler implementation using the Alarm framework
 */
class Genode::Alarm_timeout_scheduler : private Noncopyable,
                                        public  Timeout_scheduler,
                                        public  Time_source::Timeout_handler
{
	friend class Timer::Connection;
	friend class Timer::Root_component;
	friend class Timeout::Alarm;

	private:

		using Alarm = Timeout::Alarm;

		Time_source     &_time_source;
		Lock             _lock              { };
		Alarm           *_active_head       { nullptr };
		Alarm           *_pending_head      { nullptr };
		Alarm::Time      _now               { 0UL };
		bool             _now_period        { false };
		Alarm::Raw       _min_handle_period { };

		void _alarm_unsynchronized_enqueue(Alarm *alarm);

		void _alarm_unsynchronized_dequeue(Alarm *alarm);

		Alarm *_alarm_get_pending_alarm();

		void _alarm_setup_alarm(Alarm &alarm, Alarm::Time period, Alarm::Time first_duration);

		void _enable();


		/**********************************
		 ** Time_source::Timeout_handler **
		 **********************************/

		void handle_timeout(Duration curr_time) override;


		/***********************
		 ** Timeout_scheduler **
		 ***********************/

		void _schedule_one_shot(Timeout &timeout, Microseconds duration) override;
		void _schedule_periodic(Timeout &timeout, Microseconds duration) override;

		void _discard(Timeout &timeout) override {
			_alarm_discard(&timeout._alarm); }

		void _alarm_discard(Alarm *alarm);

		void _alarm_schedule_absolute(Alarm *alarm, Alarm::Time duration);

		void _alarm_schedule(Alarm *alarm, Alarm::Time period);

		void _alarm_handle(Alarm::Time now);

		bool _alarm_next_deadline(Alarm::Time *deadline);

		bool _alarm_head_timeout(const Alarm * alarm) { return _active_head == alarm; }

		Alarm_timeout_scheduler(Alarm_timeout_scheduler const &);
		Alarm_timeout_scheduler &operator = (Alarm_timeout_scheduler const &);

	public:

		Alarm_timeout_scheduler(Time_source  &time_source,
		                        Microseconds  min_handle_period = Microseconds(1));

		~Alarm_timeout_scheduler();


		/***********************
		 ** Timeout_scheduler **
		 ***********************/

		Duration curr_time() override { return _time_source.curr_time(); }
};

#endif /* _TIMER__TIMEOUT_H_ */