/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @file  cache_pqueue.h
 * @brief Cache Priority Queue function declarations
 *
 * @defgroup MOD_CACHE_QUEUE Priority Queue
 * @ingroup  MOD_CACHE
 * @{
 */

#ifndef CACHE_PQUEUE_H
#define CACHE_PQUEUE_H

#include <apr.h>
#include <apr_errno.h>

#if APR_HAVE_STDIO_H
#include <stdio.h>
#endif

#ifdef __cplusplus
extern "C" {
#endif

/** the cache priority queue handle */
typedef struct cache_pqueue_t cache_pqueue_t;

/**
 * callback function to assign a priority for a element
 * @param a the element
 * @return  the score (the lower the score the longer it is kept int the queue)
 */
typedef long (*cache_pqueue_set_priority)(long queue_clock, void *a);
typedef long (*cache_pqueue_get_priority)(void *a);

/** callback function to get a position of a element */
typedef apr_ssize_t (*cache_pqueue_getpos)(void *a);

/**
 * callback function to set a position of a element
 * @param a   the element
 * @param pos the position to set it to
 */
typedef void (*cache_pqueue_setpos)(void *a, apr_ssize_t pos);

/** debug callback function to print a entry */
typedef void (*cache_pqueue_print_entry)(FILE *out, void *a);

/**
 * initialize the queue
 *
 * @param n the initial estimate of the number of queue items for which memory
 *          should be preallocated
 * @param pri the callback function to run to assign a score to a element
 * @param get the callback function to get the current element's position
 * @param set the callback function to set the current element's position
 *
 * @Return the handle or NULL for insufficent memory
 */
cache_pqueue_t *cache_pq_init(apr_ssize_t n,
                              cache_pqueue_get_priority pri,
                              cache_pqueue_getpos get,
                              cache_pqueue_setpos set);
/**
 * free all memory used by the queue
 * @param q the queue
 */
void cache_pq_free(cache_pqueue_t *q);
/**
 * return the size of the queue.
 * @param q the queue
 */
apr_ssize_t cache_pq_size(cache_pqueue_t *q);

/**
 * insert an item into the queue.
 * @param q the queue
 * @param d the item
 * @return APR_SUCCESS on success
 */
apr_status_t cache_pq_insert(cache_pqueue_t *q, void *d);

/*
 * move a existing entry to a different priority
 * @param q the queue
 * @param old the old priority
 * @param d the entry
 */
void cache_pq_change_priority(cache_pqueue_t *q,
                              long old_priority,
                              long new_priority,
                              void *d);

/**
 * pop the highest-ranking item from the queue.
 * @param p the queue
 * @param d where to copy the entry to
 * @return NULL on error, otherwise the entry
 */
void *cache_pq_pop(cache_pqueue_t *q);

/**
 * remove an item from the queue.
 * @param p the queue
 * @param d the entry
 * @return APR_SUCCESS on success
 */
apr_status_t cache_pq_remove(cache_pqueue_t *q, void *d);

/**
 * access highest-ranking item without removing it.
 * @param q the queue
 * @param d the entry
 * @return NULL on error, otherwise the entry
 */
void *cache_pq_peek(cache_pqueue_t *q);

/**
 * print the queue
 * @internal
 * DEBUG function only
 * @param q the queue
 * @param out the output handle
 * @param the callback function to print the entry
 */
void cache_pq_print(cache_pqueue_t *q, 
                    FILE *out, 
                    cache_pqueue_print_entry print);

/**
 * dump the queue and it's internal structure
 * @internal
 * debug function only
 * @param q the queue
 * @param out the output handle
 * @param the callback function to print the entry
 */
void cache_pq_dump(cache_pqueue_t *q, 
                   FILE *out,
                   cache_pqueue_print_entry print);

/**
 * checks that the pq is in the right order, etc
 * @internal
 * debug function only
 * @param q the queue
 */
int cache_pq_is_valid(cache_pqueue_t *q);

#ifdef __cplusplus
}
#endif

#endif /* !CACHE_PQUEUE_H */
/** @} */