#ifndef UC_TAILQ_H_
#define UC_TAILQ_H_

#ifdef __GNUC__
//#define UC_INLINE __attribute__((always_inline,flatten))
#define UC_INLINE inline
#else
#define UC_INLINE inline
#endif
/**
 * Doubly Linked List.
 * It is used either as
 * 1) a linked list "head" - a node serving to hold pointer to the 
 *                           first and last node in a list
 * 2) a linked list entry  - a node in the linked list
 *
 * This is  variant of sys/queue.h TAILQ which avoids too many conditionals.
 * The struct TailQ serves both as an entry/node in a linked list,
 * and as head of a linked list.
 * 
 * Note that unlike the sys/queue.h TAILQ, the list does
 * not begin/end with a NULL pointer. For a entry node, the beginning/end
 * is a back pointer to the head node.
 * Traditional linked list            TailQ
 * node->prev == NULL               node->prev == head
 * node->next == NULL               node->next == head
 *
 * Do not ever add an entry that's a NULL pointer.
 *
 */
struct TailQ {
    //pointer to next element, or for a head node,
    //pointer to the first entry
    struct TailQ *next;
    //pointer to previous element, or for a head node,
    //pointer to the last node
    struct TailQ *prev;
};

#define UC_TAILQ_HEAD_INIT(name) {&(name), &(name)}

#define UC_TAILQ_HEAD(name)\
struct TailQ name = UC_TAILQ_HEAD_INIT(name)


static UC_INLINE void uc_tailq_init(struct TailQ *head)
{
    head->prev = head;
    head->next = head;
}

/** Test if the tailq is empty
 */
static UC_INLINE int uc_tailq_empty(const struct TailQ *head)
{
    return head->next == head->prev;
}

/** Insert the entry between prev and next
 */
static UC_INLINE void uc_tailq_insert(struct TailQ *entry, 
                                      struct TailQ *prev,
                                      struct TailQ *next)
{
    entry->prev = prev;
    prev->next  = entry;

    entry->next = next;
    next->prev  = entry;
}

/** Insert entry to the tail(end) of the list
 */
static UC_INLINE void uc_tailq_insert_tail(struct TailQ *head, struct TailQ *entry)
{
    //head becomes entry->next, signalling the end of the list
    uc_tailq_insert(entry, head->prev, head);
}

/** Insert entry to the head(start) of the list
 */
static UC_INLINE void uc_tailq_insert_head(struct TailQ *head, struct TailQ *entry)
{
    //head becomes entry->prev, signalling the end of the list
    uc_tailq_insert(entry, head, head->next);
}

/** Remove the entry from the list it is part of.
 * (It *must* already be part of a list.
 */
static UC_INLINE void uc_tailq_remove(struct TailQ *entry)
{
    entry->prev->next = entry->next;
    entry->next->prev = entry->prev;

//help catch illegal use:
    entry->next = (void*)0x101;
    entry->prev = (void*)0x102;
}

/** Iterate over a tailq. The list cannot be altered while iterating.
 *
 * @param entry a struct TailQ* to which each element is assigned.
 * @param head the struct TailQ* head of the tailq
 */
#define UC_TAILQ_FOREACH(entry, head)\
    for ((entry) = (head)->next; (entry) != (head); (entry) = (entry)->next)

/** Iterate over a tailq in reverse order. The list cannot be altered while 
 *  iterating.
 *
 * @param entry a struct TailQ* to which each element is assigned.
 * @param head the struct TailQ* head of the tailq
 */
#define UC_TAILQ_FOREACH_REVERSE(entry, head)\
    for ((entry) = (head)->prev; (entry) != (head); (entry) = (entry)->prev)

/** Iterate over a tailq. safe to remove the entry when iterating.
 *
 * @param entry a struct TailQ* to which each element is assigned.
 * @param nxt a struct TailQ* needed for temporary storage.
 * @param head the struct TailQ* head of the tailq
 */
#define UC_TAILQ_FOREACH_SAFE(entry, nxt, head)\
    for ((entry) = (head)->next, nxt = (entry)->next; \
         (entry) != (head); \
         (entry) = (nxt), (nxt) = (entry)->next)

/** Iterate over a tailq in reverse order. safe to remove the entry when 
 *  iterating.
 *
 * @param entry a struct TailQ* to which each element is assigned.
 * @param prv a struct TailQ* needed for temporary storage.
 * @param head the struct TailQ* head of the tailq
 */
#define UC_TAILQ_FOREACH_REVERSE_SAFE(entry, prv, head)\
    for ((entry) = (head)->prev, prev = (entry)->prev; \
         (entry) != (head); \
         (entry) = (prv), (prv) = (entry)->prev)

#endif