/*****************************************************************************
 * @File    timer.c
 * @Date    10/15/2012
 * @Brief   We use unsorted double linked list to manage timers, Simple and small
 *          for most embedded purposes as we won't have a lot of timers at any
 *          given time. Add:O(1)/Remove:O(1)/Handle:O(N),
 *          1) Optimizing for Timeout timers that don't get called often but
 *             are added/removed often. We optimise for most used path.
 *             This is based on assumption that timers (registered for waking
 *             or notifying timeouts) don't fire that often compared to the
 *             frequency at which timers are added/removed.
 *          2) Periodic timers can be implemented by re-adding timer in callback.
 *             Add:O(N)/Remove:O(1)/Handle:O(1) (sorted list) is bad for this
 *             purpose as periodic timer needs to be resorted giving it Handle:O(N+1)
 *             overhead for each periodic timer in handle instead of Handle:O(2)
 *             using an unsorted list.
 *****************************************************************************/

#include <timer.h>

volatile time_t timer_tick = 0UL; /* DIRTY! */
static   list_t timer_list = LIST_INIT(timer_list);

static inline void timer_insert_internal(timer_t *timer)
{
	if(likely(!list_in_list(&timer->node)))
		list_add(&timer_list, &timer->node);
}

static inline void timer_remove_internal(timer_t *timer)
{
	if(likely(list_in_list(&timer->node)))
		list_delete(&timer->node);
}

void sys_tick(void)
{
	timer_t *tmp;
	timer_t *timer;

	++timer_ticks;

	list_for_every_entry_safe(&timer_list, timer, tmp, timer_t, node)
	{
		if(timer->tick <= timer_ticks)
		{
			if(timer->handle(timer, timer->args) != TIMER_RESCHEDULE)
				list_delete(&timer->node);
		}
	}

	if(unlikely(--curr_thread->quantum <= 0))
		thread_preempt();
}

void timer_cancel(timer_t *timer)
{
	irq_disable();
	timer_remove_internal(timer);
	irq_enable();
}

void timer_reset(timer_t *timer, time_t delay)
{
	timer->tick = cpu_msecs_to_ticks(delay) + timer_ticks;

	irq_disable();
	timer_insert_internal(timer);
	irq_enable();
}

void timer_set(timer_t *timer, time_t delay, timer_handle_t handle, void *args)
{
	timer->args   = args;
	timer->handle = handle;
	timer->tick   = cpu_msecs_to_ticks(delay) + timer_ticks;

	irq_disable();
	timer_insert_internal(timer);
	irq_enable();
}