/*
 * Copyright (C) 2008-2015 Tobias Brunner
 * Copyright (C) 2005-2006 Martin Willi
 * Copyright (C) 2005 Jan Hutter
 * 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 <stdlib.h>

#include "scheduler.h"

#include <utils/debug.h>
#include <processing/processor.h>
#include <processing/jobs/callback_job.h>
#include <threading/thread.h>
#include <threading/condvar.h>
#include <threading/mutex.h>

/* the initial size of the heap */
#define HEAP_SIZE_DEFAULT 64

typedef struct event_t event_t;

/**
 * Event containing a job and a schedule time
 */
struct event_t {
	/**
	 * Time to fire the event.
	 */
	timeval_t time;

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

/**
 * destroy an event and its job
 */
static void event_destroy(event_t *event)
{
	event->job->destroy(event->job);
	free(event);
}

typedef struct private_scheduler_t private_scheduler_t;

/**
 * Private data of a scheduler_t object.
 */
struct private_scheduler_t {

	/**
	 * Public part of a scheduler_t object.
	 */
	 scheduler_t public;

	/**
	 * The heap in which the events are stored.
	 */
	event_t **heap;

	/**
	 * The size of the heap.
	 */
	u_int heap_size;

	/**
	 * The number of scheduled events.
	 */
	u_int event_count;

	/**
	 * Exclusive access to list
	 */
	mutex_t *mutex;

	/**
	 * Condvar to wait for next job.
	 */
	condvar_t *condvar;
};

/**
 * Comparse two timevals, return >0 if a > b, <0 if a < b and =0 if equal
 */
static int timeval_cmp(timeval_t *a, timeval_t *b)
{
	if (a->tv_sec > b->tv_sec)
	{
		return 1;
	}
	if (a->tv_sec < b->tv_sec)
	{
		return -1;
	}
	if (a->tv_usec > b->tv_usec)
	{
		return 1;
	}
	if (a->tv_usec < b->tv_usec)
	{
		return -1;
	}
	return 0;
}

/**
 * Returns the top event without removing it. Returns NULL if the heap is empty.
 */
static event_t *peek_event(private_scheduler_t *this)
{
	return this->event_count > 0 ? this->heap[1] : NULL;
}

/**
 * Removes the top event from the heap and returns it. Returns NULL if the heap
 * is empty.
 */
static event_t *remove_event(private_scheduler_t *this)
{
	event_t *event, *top;
	if (!this->event_count)
	{
		return NULL;
	}

	/* store the value to return */
	event = this->heap[1];
	/* move the bottom event to the top */
	top = this->heap[1] = this->heap[this->event_count];

	if (--this->event_count > 1)
	{
		/* seep down the top event */
		u_int position = 1;
		while ((position << 1) <= this->event_count)
		{
			u_int child = position << 1;

			if ((child + 1) <= this->event_count &&
				timeval_cmp(&this->heap[child + 1]->time,
							&this->heap[child]->time) < 0)
			{
				/* the "right" child is smaller */
				child++;
			}

			if (timeval_cmp(&top->time, &this->heap[child]->time) <= 0)
			{
				/* the top event fires before the smaller of the two children,
				 * stop */
				break;
			}

			/* swap with the smaller child */
			this->heap[position] = this->heap[child];
			position = child;
		}
		this->heap[position] = top;
	}
	return event;
}

/**
 * Get events from the queue and pass it to the processor
 */
static job_requeue_t schedule(private_scheduler_t * this)
{
	timeval_t now;
	event_t *event;
	bool timed = FALSE, oldstate;

	this->mutex->lock(this->mutex);

	time_monotonic(&now);

	if ((event = peek_event(this)) != NULL)
	{
		if (timeval_cmp(&now, &event->time) >= 0)
		{
			remove_event(this);
			this->mutex->unlock(this->mutex);
			DBG2(DBG_JOB, "got event, queuing job for execution");
			lib->processor->queue_job(lib->processor, event->job);
			free(event);
			return JOB_REQUEUE_DIRECT;
		}
		timersub(&event->time, &now, &now);
		if (now.tv_sec)
		{
			DBG2(DBG_JOB, "next event in %ds %dms, waiting",
				 now.tv_sec, now.tv_usec/1000);
		}
		else
		{
			DBG2(DBG_JOB, "next event in %dms, waiting", now.tv_usec/1000);
		}
		timed = TRUE;
	}
	thread_cleanup_push((thread_cleanup_t)this->mutex->unlock, this->mutex);
	oldstate = thread_cancelability(TRUE);

	if (timed)
	{
		this->condvar->timed_wait_abs(this->condvar, this->mutex, event->time);
	}
	else
	{
		DBG2(DBG_JOB, "no events, waiting");
		this->condvar->wait(this->condvar, this->mutex);
	}
	thread_cancelability(oldstate);
	thread_cleanup_pop(TRUE);
	return JOB_REQUEUE_DIRECT;
}

METHOD(scheduler_t, get_job_load, u_int,
	private_scheduler_t *this)
{
	int count;
	this->mutex->lock(this->mutex);
	count = this->event_count;
	this->mutex->unlock(this->mutex);
	return count;
}

METHOD(scheduler_t, schedule_job_tv, void,
	private_scheduler_t *this, job_t *job, timeval_t tv)
{
	event_t *event;
	u_int position;

	event = malloc_thing(event_t);
	event->job = job;
	event->job->status = JOB_STATUS_QUEUED;
	event->time = tv;

	this->mutex->lock(this->mutex);

	this->event_count++;
	if (this->event_count > this->heap_size)
	{
		/* double the size of the heap */
		this->heap_size <<= 1;
		this->heap = (event_t**)realloc(this->heap,
									(this->heap_size + 1) * sizeof(event_t*));
	}
	/* "put" the event to the bottom */
	position = this->event_count;

	/* then bubble it up */
	while (position > 1 && timeval_cmp(&this->heap[position >> 1]->time,
									   &event->time) > 0)
	{
		/* parent has to be fired after the new event, move up */
		this->heap[position] = this->heap[position >> 1];
		position >>= 1;
	}
	this->heap[position] = event;

	this->condvar->signal(this->condvar);
	this->mutex->unlock(this->mutex);
}

METHOD(scheduler_t, schedule_job, void,
	private_scheduler_t *this, job_t *job, u_int32_t s)
{
	timeval_t tv;

	time_monotonic(&tv);
	tv.tv_sec += s;

	schedule_job_tv(this, job, tv);
}

METHOD(scheduler_t, schedule_job_ms, void,
	private_scheduler_t *this, job_t *job, u_int32_t ms)
{
	timeval_t tv, add;

	time_monotonic(&tv);
	add.tv_sec = ms / 1000;
	add.tv_usec = (ms % 1000) * 1000;

	timeradd(&tv, &add, &tv);

	schedule_job_tv(this, job, tv);
}

METHOD(scheduler_t, flush, void,
	private_scheduler_t *this)
{
	event_t *event;

	this->mutex->lock(this->mutex);
	while ((event = remove_event(this)) != NULL)
	{
		event_destroy(event);
	}
	this->condvar->signal(this->condvar);
	this->mutex->unlock(this->mutex);
}

METHOD(scheduler_t, destroy, void,
	private_scheduler_t *this)
{
	flush(this);
	this->condvar->destroy(this->condvar);
	this->mutex->destroy(this->mutex);
	free(this->heap);
	free(this);
}

/*
 * Described in header.
 */
scheduler_t * scheduler_create()
{
	private_scheduler_t *this;
	callback_job_t *job;

	INIT(this,
		.public = {
			.get_job_load = _get_job_load,
			.schedule_job = _schedule_job,
			.schedule_job_ms = _schedule_job_ms,
			.schedule_job_tv = _schedule_job_tv,
			.flush = _flush,
			.destroy = _destroy,
		},
		.heap_size = HEAP_SIZE_DEFAULT,
		.mutex = mutex_create(MUTEX_TYPE_DEFAULT),
		.condvar = condvar_create(CONDVAR_TYPE_DEFAULT),
	);

	this->heap = (event_t**)calloc(this->heap_size + 1, sizeof(event_t*));

	job = callback_job_create_with_prio((callback_job_cb_t)schedule, this,
										NULL, return_false, JOB_PRIO_CRITICAL);
	lib->processor->queue_job(lib->processor, (job_t*)job);

	return &this->public;
}