/*
 * Copyright (c) 2009-2017 Richard Braun.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 * Upstream site with license notes :
 * http://git.sceen.net/rbraun/librbraun.git/
 *
 *
 * Doubly-linked list.
 */

#ifndef LIST_H
#define LIST_H

#include <stdbool.h>
#include <stddef.h>

#include "macros.h"

/*
 * Structure used as both head and node.
 *
 * This implementation relies on using the same type for both heads and nodes.
 *
 * It is recommended to encode the use of struct list variables in their names,
 * e.g. struct list free_list or struct list free_objects is a good hint for a
 * list of free objects. A declaration like struct list free_node clearly
 * indicates it is used as part of a node in the free list.
 */
struct list {
    struct list *prev;
    struct list *next;
};

/*
 * Static list initializer.
 */
#define LIST_INITIALIZER(list) { &(list), &(list) }

/*
 * Initialize a list.
 */
static inline void
list_init(struct list *list)
{
    list->prev = list;
    list->next = list;
}

/*
 * Initialize a list node.
 *
 * A node is in no list when its node members point to NULL.
 */
static inline void
list_node_init(struct list *node)
{
    node->prev = NULL;
    node->next = NULL;
}

/*
 * Return true if node is in no list.
 */
static inline bool
list_node_unlinked(const struct list *node)
{
    return node->prev == NULL;
}

/*
 * Return the first node of a list.
 */
static inline struct list *
list_first(const struct list *list)
{
    return list->next;
}

/*
 * Return the last node of a list.
 */
static inline struct list *
list_last(const struct list *list)
{
    return list->prev;
}

/*
 * Return the node next to the given node.
 */
static inline struct list *
list_next(const struct list *node)
{
    return node->next;
}

/*
 * Return the node previous to the given node.
 */
static inline struct list *
list_prev(const struct list *node)
{
    return node->prev;
}

/*
 * Return true if node is invalid and denotes one of the ends of the list.
 */
static inline bool
list_end(const struct list *list, const struct list *node)
{
    return list == node;
}

/*
 * Return true if list is empty.
 */
static inline bool
list_empty(const struct list *list)
{
    return list == list->next;
}

/*
 * Return true if list contains exactly one node.
 */
static inline bool
list_singular(const struct list *list)
{
    return !list_empty(list) && (list->next == list->prev);
}

/*
 * Split list2 by moving its nodes up to, but not including, the given
 * node into list1, which can be in a stale state.
 *
 * If list2 is empty, or node is list2 or list2->next, list1 is merely
 * initialized.
 */
static inline void
list_split(struct list *list1, struct list *list2, struct list *node)
{
    if (list_empty(list2) || (list2->next == node) || list_end(list2, node)) {
        list_init(list1);
        return;
    }

    list1->next = list2->next;
    list1->next->prev = list1;

    list1->prev = node->prev;
    node->prev->next = list1;

    list2->next = node;
    node->prev = list2;
}

/*
 * Append the nodes of list2 at the end of list1.
 *
 * After completion, list2 is stale.
 */
static inline void
list_concat(struct list *list1, const struct list *list2)
{
    struct list *last1, *first2, *last2;

    if (list_empty(list2)) {
        return;
    }

    last1 = list1->prev;
    first2 = list2->next;
    last2 = list2->prev;

    last1->next = first2;
    first2->prev = last1;

    last2->next = list1;
    list1->prev = last2;
}

/*
 * Set the new head of a list.
 *
 * This function is an optimized version of :
 * list_init(&new_list);
 * list_concat(&new_list, &old_list);
 *
 * After completion, old_head is stale.
 */
static inline void
list_set_head(struct list *new_head, const struct list *old_head)
{
    if (list_empty(old_head)) {
        list_init(new_head);
        return;
    }

    *new_head = *old_head;
    new_head->next->prev = new_head;
    new_head->prev->next = new_head;
}

/*
 * Add a node between two nodes.
 *
 * This function is private.
 */
static inline void
list_add(struct list *prev, struct list *next, struct list *node)
{
    next->prev = node;
    node->next = next;

    prev->next = node;
    node->prev = prev;
}

/*
 * Insert a node at the head of a list.
 */
static inline void
list_insert_head(struct list *list, struct list *node)
{
    list_add(list, list->next, node);
}

/*
 * Insert a node at the tail of a list.
 */
static inline void
list_insert_tail(struct list *list, struct list *node)
{
    list_add(list->prev, list, node);
}

/*
 * Insert a node before another node.
 */
static inline void
list_insert_before(struct list *node, struct list *next)
{
    list_add(next->prev, next, node);
}

/*
 * Insert a node after another node.
 */
static inline void
list_insert_after(struct list *node, struct list *prev)
{
    list_add(prev, prev->next, node);
}

/*
 * Remove a node from a list.
 *
 * After completion, the node is stale.
 */
static inline void
list_remove(struct list *node)
{
    node->prev->next = node->next;
    node->next->prev = node->prev;
}

/*
 * Macro that evaluates to the address of the structure containing the
 * given node based on the given type and member.
 */
#define list_entry(node, type, member) structof(node, type, member)

/*
 * Get the first entry of a list.
 */
#define list_first_entry(list, type, member) \
    list_entry(list_first(list), type, member)

/*
 * Get the last entry of a list.
 */
#define list_last_entry(list, type, member) \
    list_entry(list_last(list), type, member)

/*
 * Get the entry next to the given entry.
 */
#define list_next_entry(entry, member) \
    list_entry(list_next(&(entry)->member), typeof(*(entry)), member)

/*
 * Get the entry previous to the given entry.
 */
#define list_prev_entry(entry, member) \
    list_entry(list_prev(&(entry)->member), typeof(*(entry)), member)

/*
 * Forge a loop to process all nodes of a list.
 *
 * The node must not be altered during the loop.
 */
#define list_for_each(list, node)   \
for (node = list_first(list);       \
     !list_end(list, node);         \
     node = list_next(node))

/*
 * Forge a loop to process all nodes of a list.
 */
#define list_for_each_safe(list, node, tmp)             \
for (node = list_first(list), tmp = list_next(node);    \
     !list_end(list, node);                             \
     node = tmp, tmp = list_next(node))

/*
 * Version of list_for_each() that processes nodes backward.
 */
#define list_for_each_reverse(list, node)   \
for (node = list_last(list);                \
     !list_end(list, node);                 \
     node = list_prev(node))

/*
 * Version of list_for_each_safe() that processes nodes backward.
 */
#define list_for_each_reverse_safe(list, node, tmp) \
for (node = list_last(list), tmp = list_prev(node); \
     !list_end(list, node);                         \
     node = tmp, tmp = list_prev(node))

/*
 * Forge a loop to process all entries of a list.
 *
 * The entry node must not be altered during the loop.
 */
#define list_for_each_entry(list, entry, member)                    \
for (entry = list_first_entry(list, typeof(*entry), member);        \
     !list_end(list, &entry->member);                               \
     entry = list_next_entry(entry, member))

/*
 * Forge a loop to process all entries of a list.
 */
#define list_for_each_entry_safe(list, entry, tmp, member)          \
for (entry = list_first_entry(list, typeof(*entry), member),        \
       tmp = list_next_entry(entry, member);                        \
     !list_end(list, &entry->member);                               \
     entry = tmp, tmp = list_next_entry(entry, member))

/*
 * Version of list_for_each_entry() that processes entries backward.
 */
#define list_for_each_entry_reverse(list, entry, member)            \
for (entry = list_last_entry(list, typeof(*entry), member);         \
     !list_end(list, &entry->member);                               \
     entry = list_prev_entry(entry, member))

/*
 * Version of list_for_each_entry_safe() that processes entries backward.
 */
#define list_for_each_entry_reverse_safe(list, entry, tmp, member)  \
for (entry = list_last_entry(list, typeof(*entry), member),         \
       tmp = list_prev_entry(entry, member);                        \
     !list_end(list, &entry->member);                               \
     entry = tmp, tmp = list_prev_entry(entry, member))

/*
 * Lockless variants
 *
 * This is a subset of the main interface that only supports forward traversal.
 * In addition, list_end() is also allowed in read-side critical sections.
 */

/*
 * These macros can be replaced by actual functions in an environment
 * that provides lockless synchronization such as RCU.
 */
#define rcu_store_ptr(ptr, value)       ((ptr) = (value))
#define rcu_load_ptr(ptr)               (ptr)

/*
 * Return the first node of a list.
 */
static inline struct list *
list_rcu_first(const struct list *list)
{
    return rcu_load_ptr(list->next);
}

/*
 * Return the node next to the given node.
 */
static inline struct list *
list_rcu_next(const struct list *node)
{
    return rcu_load_ptr(node->next);
}

/*
 * Add a node between two nodes.
 *
 * This function is private.
 */
static inline void
list_rcu_add(struct list *prev, struct list *next, struct list *node)
{
    node->next = next;
    node->prev = prev;
    rcu_store_ptr(prev->next, node);
    next->prev = node;
}

/*
 * Insert a node at the head of a list.
 */
static inline void
list_rcu_insert_head(struct list *list, struct list *node)
{
    list_rcu_add(list, list->next, node);
}

/*
 * Insert a node at the tail of a list.
 */
static inline void
list_rcu_insert_tail(struct list *list, struct list *node)
{
    list_rcu_add(list->prev, list, node);
}

/*
 * Insert a node before another node.
 */
static inline void
list_rcu_insert_before(struct list *node, struct list *next)
{
    list_rcu_add(next->prev, next, node);
}

/*
 * Insert a node after another node.
 */
static inline void
list_rcu_insert_after(struct list *node, struct list *prev)
{
    list_rcu_add(prev, prev->next, node);
}

/*
 * Remove a node from a list.
 *
 * After completion, the node is stale.
 */
static inline void
list_rcu_remove(struct list *node)
{
    node->next->prev = node->prev;
    rcu_store_ptr(node->prev->next, node->next);
}

/*
 * Macro that evaluates to the address of the structure containing the
 * given node based on the given type and member.
 */
#define list_rcu_entry(node, type, member) \
    structof(rcu_load_ptr(node), type, member)

/*
 * Get the first entry of a list.
 *
 * Unlike list_first_entry(), this macro may evaluate to NULL, because
 * the node pointer can only be read once, preventing the combination
 * of lockless list_empty()/list_first_entry() variants.
 */
#define list_rcu_first_entry(list, type, member)            \
MACRO_BEGIN                                                 \
    struct list *list___;                                   \
    struct list *first___;                                  \
                                                            \
    list___ = (list);                                       \
    first___ = list_rcu_first(list___);                     \
    list_end(list___, first___)                             \
        ? NULL                                              \
        : list_entry(first___, type, member);               \
MACRO_END

/*
 * Get the entry next to the given entry.
 *
 * Unlike list_next_entry(), this macro may evaluate to NULL, because
 * the node pointer can only be read once, preventing the combination
 * of lockless list_empty()/list_next_entry() variants.
 */
#define list_rcu_next_entry(entry, member) \
    list_rcu_first_entry(&entry->member, typeof(*entry), member)

/*
 * Forge a loop to process all nodes of a list.
 *
 * The node must not be altered during the loop.
 */
#define list_rcu_for_each(list, node)       \
for (node = list_rcu_first(list);           \
     !list_end(list, node);                 \
     node = list_rcu_next(node))

/*
 * Forge a loop to process all entries of a list.
 *
 * The entry node must not be altered during the loop.
 */
#define list_rcu_for_each_entry(list, entry, member)        \
for (entry = list_rcu_entry(list_first(list),               \
                               typeof(*entry), member);     \
     !list_end(list, &entry->member);                       \
     entry = list_rcu_entry(list_next(&entry->member),      \
                               typeof(*entry), member))

#endif /* LIST_H */