/* fiber.c - fiber management and scheduling
 *
 * Copyright (C) 2009 Timo Teräs <timo.teras@iki.fi>
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 or later as
 * published by the Free Software Foundation.
 *
 * See http://www.gnu.org/ for details.
 */

#include <time.h>
#include <errno.h>
#include <unistd.h>
#include <libtf/tf.h>
#include <libtf/heap.h>

struct tf_fiber {
	unsigned int		ref_count;
	struct tf_list_node	queue_node;
	struct tf_heap_node	heap_node;
	char			data[TF_EMPTY_ARRAY];
};

#include TF_UCTX_H

/* FIXME: should be in thread local storage */
struct tf_scheduler *__tf_scheduler;

void *tf_fiber_create(tf_fiber_proc fiber_main, int private_size)
{
	struct tf_scheduler *sched = tf_get_scheduler();
	struct tf_fiber *fiber;

	if (tf_heap_prealloc(&sched->heap, sched->num_fibers + 1) < 0)
		return NULL;

	fiber = tf_uctx_create(fiber_main, private_size);
	if (fiber == NULL)
		return NULL;

	/* The initial references for caller and scheduler */
	*fiber = (struct tf_fiber) {
		.ref_count = 2,
		.queue_node = TF_LIST_INITIALIZER(fiber->queue_node),
	};

	tf_list_add_tail(&fiber->queue_node, &sched->run_q);
	sched->num_fibers++;

	return fiber->data;
}

static void __tf_fiber_destroy(struct tf_fiber *fiber)
{
	tf_heap_delete(&fiber->heap_node, &tf_get_scheduler()->heap);
	tf_uctx_destroy(fiber);
}

void *tf_fiber_get(void *data)
{
	struct tf_fiber *fiber = container_of(data, struct tf_fiber, data);
	tf_atomic_inc(fiber->ref_count);
	return data;
}

void tf_fiber_put(void *data)
{
	struct tf_fiber *fiber = container_of(data, struct tf_fiber, data);
	if (tf_atomic_dec(fiber->ref_count) == 0)
		__tf_fiber_destroy(fiber);
}

static void update_time(struct tf_scheduler *sched)
{
	struct timespec ts;

	clock_gettime(CLOCK_MONOTONIC, &ts);
	sched->scheduler_time = ts.tv_sec * 1000 + ts.tv_nsec / 1000000;
}

static void run_fiber(struct tf_scheduler *sched, struct tf_fiber *f)
{
	struct tf_fiber *schedf = container_of((void*) tf_get_scheduler(), struct tf_fiber, data);

	sched->active_fiber = f;
	switch (tf_uctx_transfer(schedf, f, 1)) {
	case EFAULT: /* Fiber is dead */
		tf_fiber_put(f->data);
		sched->num_fibers--;
		break;
	case EAGAIN: /* Yielded, reshedule */
		tf_list_add_tail(&f->queue_node, &sched->run_q);
		break;
	case EIO: /* Blocked, in sleep */
		tf_list_add_tail(&f->queue_node, &sched->sleep_q);
		break;
	default:
		TF_BUG_ON("bad scheduler call from fiber");
	}
}

static void process_heap(struct tf_scheduler *sched)
{
	struct tf_heap_node *node;
	struct tf_fiber *f;
	tf_mtime_t now = tf_mtime();

	while (!tf_heap_empty(&sched->heap) &&
	       tf_mtime_diff(now, tf_heap_get_value(&sched->heap)) > 0) {
		node = tf_heap_get_node(&sched->heap);
		f = container_of(node, struct tf_fiber, heap_node);
		run_fiber(sched, f);
	}
}

static void process_runq(struct tf_scheduler *sched)
{
	struct tf_fiber *f;

	while (!tf_list_empty(&sched->run_q)) {
		f = tf_list_first(&sched->run_q, struct tf_fiber, queue_node);
		tf_list_del(&f->queue_node);
		run_fiber(sched, f);
	}
}

int tf_main(tf_fiber_proc main_fiber)
{
	struct tf_uctx *ctx = alloca(sizeof(struct tf_uctx) + sizeof(struct tf_scheduler));
	struct tf_scheduler *sched = (struct tf_scheduler*) ctx->fiber.data;
	int stack_guard = STACK_GUARD;

	ctx->stack_guard = &stack_guard;
	*sched = (struct tf_scheduler){
		.run_q = TF_LIST_HEAD_INITIALIZER(sched->run_q),
		.sleep_q = TF_LIST_HEAD_INITIALIZER(sched->sleep_q),
	};
	__tf_scheduler = sched;
	update_time(sched);
	tf_fiber_put(tf_fiber_create(main_fiber, 0));
	do {
		tf_mtime_diff_t timeout;

		update_time(sched);
		if (!tf_list_empty(&sched->run_q)) {
			timeout = 0;
		} else if (!tf_heap_empty(&sched->heap)) {
			timeout = tf_mtime_diff(tf_heap_get_value(&sched->heap),
						sched->scheduler_time);
			if (timeout < 0)
				timeout = 0;
		} else
			timeout = -1;

		if (timeout > 0)
			usleep(timeout * 1000);

		process_heap(sched);
		process_runq(sched);
	} while (likely(sched->num_fibers));
	__tf_scheduler = NULL;

	return 0;
}

int tf_schedule(int err)
{
	struct tf_scheduler *sched = tf_get_scheduler();
	struct tf_fiber *schedf = container_of((void*) sched, struct tf_fiber, data);
	struct tf_fiber *f = sched->active_fiber;
	int r;

	r = tf_uctx_transfer(f, schedf, err);
	if (r == 1)
		return 0;

	return r;
}

int tf_msleep(int milliseconds)
{
	struct tf_scheduler *sched = tf_get_scheduler();
	struct tf_fiber *f = sched->active_fiber;

	tf_heap_change(&f->heap_node, &sched->heap, tf_mtime() + milliseconds);

	return tf_schedule(EIO);
}

void tf_kill(void *fiber)
{
}