/*
 * Copyright 2017 Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#ifndef _SYS_ILIST_H
#define _SYS_ILIST_H

/*
 * Generic circular doubly-linked list with a sentinel node.
 *
 * The entire implementation is here as C99 static inline functions.  We
 * hide them if we are not using a C99 compiler to expose the list_node
 * struct for list.h's benefit.
 *
 * Here's the summary of differences:
 *
 * (1) both ilist.h and list.h use the same struct list_node
 * (1) ilist.h uses static inlines while list.h uses normal functions
 * (2) list.h uses struct list to keep track of offsets into objects for the
 *     struct list_node
 * (3) ilist.h uses struct list_head as a sentinel node and has no idea
 *     about the structures containing each of the list entries
 */

#ifdef	__cplusplus
extern "C" {
#endif

struct list_node {
	struct list_node *list_next;
	struct list_node *list_prev;
};

#ifdef _STDC_C99

#include <sys/null.h>

static inline void ilist_init(struct list_node *node)
{
	node->list_next = node;
	node->list_prev = node;
}

static inline int ilist_is_empty(struct list_node *list)
{
	return list->list_next == list;
}

static int ilist_link_active(struct list_node *node)
{
	return node->list_next != NULL;
}

static inline struct list_node *ilist_head(struct list_node *list)
{
	if (ilist_is_empty(list))
		return NULL;

	return list->list_next;
}

static inline struct list_node *ilist_tail(struct list_node *list)
{
	if (ilist_is_empty(list))
		return NULL;

	return list->list_prev;
}

static inline struct list_node *ilist_next(struct list_node *list,
					   struct list_node *cur)
{
	if (cur->list_next == list)
		return NULL;

	return cur->list_next;
}

static inline struct list_node *ilist_prev(struct list_node *list,
					   struct list_node *cur)
{
	if (cur->list_prev == list)
		return NULL;

	return cur->list_prev;
}

static inline void __ilist_insert(struct list_node *before,
				  struct list_node *after,
				  struct list_node *newnode)
{
	before->list_next = newnode;
	newnode->list_prev = before;
	newnode->list_next = after;
	after->list_prev = newnode;
}

static inline void ilist_insert_after(struct list_node *reference,
				      struct list_node *newnode)
{
	__ilist_insert(reference, reference->list_next, newnode);
}

static inline void ilist_insert_before(struct list_node *reference,
				       struct list_node *newnode)
{
	__ilist_insert(reference->list_prev, reference, newnode);
}

#define ilist_insert_head(list, newnode) ilist_insert_after((list), (newnode))
#define ilist_insert_tail(list, newnode) ilist_insert_before((list), (newnode))

static inline void ilist_remove(struct list_node *node)
{
	node->list_prev->list_next = node->list_next;
	node->list_next->list_prev = node->list_prev;

	node->list_prev = NULL;
	node->list_next = NULL;
}

static inline struct list_node *__ilist_remove(struct list_node *list,
					       struct list_node *node)
{
	if (ilist_is_empty(list))
		return NULL;

	ilist_remove(node);
	return node;
}

static inline struct list_node *ilist_remove_head(struct list_node *list)
{
	return __ilist_remove(list, list->list_next);
}

static inline struct list_node *ilist_remove_tail(struct list_node *list)
{
	return __ilist_remove(list, list->list_prev);
}

#endif

#ifdef	__cplusplus
}
#endif

#endif	/* _SYS_ILIST_H */