/**
 * @file event_queue.c
 *
 * @brief Event-Queue based on class linked_list_t
 *
 */

/*
 * Copyright (C) 2005 Jan Hutter, Martin Willi
 * Hochschule fuer Technik Rapperswil
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 */

#include <pthread.h>
#include <stdlib.h>

#include "event_queue.h"

#include "../types.h"
#include "../utils/allocator.h"
#include "../utils/linked_list.h"



/**
 * @brief Represents an event as it is stored in the event queue.
 *
 * A event consists of a event time and an assigned job object.
 *
 */
typedef struct event_s event_t;

struct event_s{
	/**
	 * Time to fire the event.
	 */
	timeval_t time;

	/**
	 * Every event has its assigned job.
	 */
	job_t * job;

	/**
	 * @brief Destroys a event_t object.
	 *
	 * @param event_t 	calling object
	 * @returns 			always SUCCESS
	 */
	status_t (*destroy) (event_t *event);
};


/**
 * @brief implements function destroy of event_t
 */
static status_t event_destroy(event_t *event)
{
	allocator_free(event);
	return SUCCESS;
}

/**
 * @brief Creates a event for a specific time
 *
 * @param time	absolute time to fire the event
 * @param job 	job to add to job-queue at specific time
 *
 * @returns
 * 				- created event_t object 
 * 				- NULL if memory allocation failed
 */
static event_t *event_create(timeval_t time, job_t *job)
{
	event_t *this = allocator_alloc_thing(event_t);
	if (this == NULL)
	{
		return this;
	}

	this->destroy = event_destroy;
	this->time = time;
	this->job = job;

	return this;
}


/**
 * @brief Private Variables and Functions of event_queue_t class.
 *
 */
typedef struct private_event_queue_s private_event_queue_t;


struct private_event_queue_s {
	/**
	 * Public part.
	 */
 	event_queue_t public;

	/**
	 * The events are stored in a linked list of type linked_list_t.
	 */
	linked_list_t *list;

	/**
	 * Access to linked_list is locked through this mutex.
	 */
	pthread_mutex_t mutex;

	/**
	 * If the queue is empty or an event has not to be fired
	 * a thread has to wait.
	 * 
	 * This condvar is used to wake up such a thread.
	 */
	pthread_cond_t condvar;
};

/**
 * Returns the difference of to timeval structs in microseconds
 *
 * @param end_time 		end time
 * @param start_time 	start time
 *
 * @warning this function is also defined in the tester class
 * 			In later improvements, this function can be added to a general
 *          class type!
 *
 * @return 	difference in microseconds (end time - start time)
 */
static long time_difference(struct timeval *end_time, struct timeval *start_time)
{
	long seconds, microseconds;

	seconds = (end_time->tv_sec - start_time->tv_sec);
	microseconds = (end_time->tv_usec - start_time->tv_usec);
	return ((seconds * 1000000) + microseconds);
}


/**
 * Implements function get_count of event_queue_t.
 * See #event_queue_s.get_count for description.
 */
static int get_count (private_event_queue_t *this)
{
	int count;
	pthread_mutex_lock(&(this->mutex));
	count = this->list->get_count(this->list);
	pthread_mutex_unlock(&(this->mutex));
	return count;
}

/**
 * Implements function get of event_queue_t.
 * See #event_queue_s.get for description.
 */
static status_t get(private_event_queue_t *this, job_t **job)
{
	timespec_t timeout;
	timeval_t current_time;
	event_t * next_event;
	int oldstate;

	pthread_mutex_lock(&(this->mutex));

	while (1)
	{
		while(this->list->get_count(this->list) == 0)
		{
			/* add mutex unlock handler for cancellation, enable cancellation */
			pthread_cleanup_push((void(*)(void*))pthread_mutex_unlock, (void*)&(this->mutex));
			pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &oldstate);

			pthread_cond_wait( &(this->condvar), &(this->mutex));

			/* reset cancellation, remove mutex-unlock handler (without executing) */
			pthread_setcancelstate(oldstate, NULL);
			pthread_cleanup_pop(0);
		}

		this->list->get_first(this->list,(void **) &next_event);

		gettimeofday(&current_time,NULL);
		long difference = time_difference(&current_time,&(next_event->time));
		if (difference <= 0)
		{
			timeout.tv_sec = next_event->time.tv_sec;
            timeout.tv_nsec = next_event->time.tv_usec * 1000;

			pthread_cond_timedwait( &(this->condvar), &(this->mutex),&timeout);
		}
		else
		{
			/* event available */
			this->list->remove_first(this->list,(void **) &next_event);

			*job = next_event->job;

			next_event->destroy(next_event);
			break;
		}

	}
	pthread_cond_signal( &(this->condvar));

	pthread_mutex_unlock(&(this->mutex));

	return SUCCESS;
}

/**
 * Implements function add_absolute of event_queue_t.
 * See #event_queue_s.add_absolute for description.
 */
static status_t add_absolute(private_event_queue_t *this, job_t *job, timeval_t time)
{
	event_t *event = event_create(time,job);
	event_t *current_event;
	status_t status;

	if (event == NULL)
	{
		return FAILED;
	}
	pthread_mutex_lock(&(this->mutex));

	/* while just used to break out */
	while(1)
	{
		if (this->list->get_count(this->list) == 0)
		{
			status = this->list->insert_first(this->list,event);
			break;
		}

		/* check last entry */
		this->list->get_last(this->list,(void **) &current_event);

		if (time_difference(&(event->time), &(current_event->time)) >= 0)
		{
			/* my event has to be fired after the last event in list */
			status = this->list->insert_last(this->list,event);
			break;
		}

		/* check first entry */
		this->list->get_first(this->list,(void **) &current_event);

		if (time_difference(&(event->time), &(current_event->time)) < 0)
		{
			/* my event has to be fired before the first event in list */
			status = this->list->insert_first(this->list,event);
			break;
		}

		linked_list_iterator_t * iterator;

		status = this->list->create_iterator(this->list,&iterator,TRUE);
		if (status != SUCCESS)
		{
			break;
		}


		iterator->has_next(iterator);
		/* first element has not to be checked (already done) */

		while(iterator->has_next(iterator))
		{
			status = iterator->current(iterator,(void **) &current_event);

			if (time_difference(&(event->time), &(current_event->time)) <= 0)
			{
				/* my event has to be fired before the current event in list */
				status = iterator->insert_before(iterator,event);
				break;
			}
		}
		iterator->destroy(iterator);
		break;
	}

	pthread_cond_signal( &(this->condvar));
	pthread_mutex_unlock(&(this->mutex));

	if (status != SUCCESS)
	{
		event->destroy(event);
	}
	return status;
}

/**
 * Implements function add_relative of event_queue_t.
 * See #event_queue_s.add_relative for description.
 */
static status_t add_relative(event_queue_t *this, job_t *job, u_int32_t ms)
{
	timeval_t current_time;
	timeval_t time;
	int micros = ms * 1000;

	gettimeofday(&current_time, NULL);

	time.tv_usec = ((current_time.tv_usec + micros) % 1000000);
	time.tv_sec = current_time.tv_sec + ((current_time.tv_usec + micros)/ 1000000);

	return this->add_absolute(this, job, time);
}


/**
 * Implements function destroy of event_queue_t.
 * See #event_queue_s.destroy for description.
 */
static status_t event_queue_destroy(private_event_queue_t *this)
{
	while (this->list->get_count(this->list) > 0)
	{
		event_t *event;

		if (this->list->remove_first(this->list,(void *) &event) != SUCCESS)
		{
			this->list->destroy(this->list);
			break;
		}
		event->job->destroy_all(event->job);
		event->destroy(event);
	}
	this->list->destroy(this->list);

	pthread_mutex_destroy(&(this->mutex));

	pthread_cond_destroy(&(this->condvar));

	allocator_free(this);
	return SUCCESS;
}

/*
 * Documented in header
 */
event_queue_t *event_queue_create()
{
	linked_list_t *linked_list = linked_list_create();
	if (linked_list == NULL)
	{
		return NULL;
	}

	private_event_queue_t *this = allocator_alloc_thing(private_event_queue_t);
	if (this == NULL)
	{
		linked_list->destroy(linked_list);
		return NULL;
	}

	this->public.get_count = (int (*) (event_queue_t *event_queue)) get_count;
	this->public.get = (status_t (*) (event_queue_t *event_queue, job_t **job)) get;
	this->public.add_absolute = (status_t (*) (event_queue_t *event_queue, job_t *job, timeval_t time)) add_absolute;
	this->public.add_relative = (status_t (*) (event_queue_t *event_queue, job_t *job, u_int32_t ms)) add_relative;
	this->public.destroy = (status_t (*) (event_queue_t *event_queue)) event_queue_destroy;

	this->list = linked_list;
	pthread_mutex_init(&(this->mutex), NULL);
	pthread_cond_init(&(this->condvar), NULL);

	return (&this->public);
}