/* See the end of this file for copyright and license terms. */

#include <arch/interrupt.h>
#include <arch/sched.h>

#include <gay/clist.h>
#include <gay/sched.h>
#include <gay/types.h>

struct task kernel_task = {
	.parent = nil,
	.pid = 0,
	.state = TASK_READY,
};

struct task *current = &kernel_task;

/*
 * Two run queues, one active and one inactive.  The scheduler takes tasks out
 * of the active queue, runs them if possible, and then puts them into the
 * inactive queue if they aren't dead.  When the active queue gets empty, the
 * queues are switched and everything starts over again.
 * The `current` task is always in neither queue.
 */
static struct clist _run_queues[2];
static struct clist *active_queue = &_run_queues[0];
static struct clist *inactive_queue = &_run_queues[1];

int sched_init(void)
{
	clist_init(active_queue);
	clist_init(inactive_queue);
	return 0;
}

void schedule(void)
{
	struct task *old = current;
	struct task *new = nil;

	clist_add(inactive_queue, &old->run_queue);

/* Dijkstra would be so mad if he saw this */
try_again:
	if (clist_is_empty(active_queue)) {
		struct clist *tmp = active_queue;
		active_queue = inactive_queue;
		inactive_queue = tmp;
	}

	struct task *cursor, *tmp;
	clist_foreach_entry_safe(active_queue, cursor, tmp, run_queue) {
		clist_del(&cursor->run_queue);
		if (cursor->state == TASK_READY) {
			new = cursor;
			break;
		} else if (cursor->state == TASK_BLOCKED) {
			clist_add(inactive_queue, &cursor->run_queue);
		}
	}

	/*
	 * This should really make the CPU go idle rather than constantly
	 * looping around until some event occurs, but i have no idea how to do
	 * that (yet)
	 */
	if (new == nil)
		goto try_again;

	if (new != old)
		switch_to(new, old);
}

void switch_to(struct task *new, struct task *old)
{
	disable_intr();
	set_current(new);
	arch_switch_to(&new->tcb, &old->tcb);
	set_current(old);
	enable_intr();
}

/*
 * This file is part of GayBSD.
 * Copyright (c) 2021 fef <owo@fef.moe>.
 *
 * GayBSD is nonviolent software: you may only use, redistribute, and/or
 * modify it under the terms of the Cooperative Nonviolent Public License
 * (CNPL) as found in the LICENSE file in the source code root directory
 * or at <https://git.pixie.town/thufie/npl-builder>; either version 7
 * of the license, or (at your option) any later version.
 *
 * GayBSD comes with ABSOLUTELY NO WARRANTY, to the extent
 * permitted by applicable law.  See the CNPL for details.
 */