/*
 * Copyright 2009-present MongoDB, Inc.
 *
 * Licensed 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.
 */


#include <mongoc/mongoc-queue-private.h>

#include <string.h>


void
_mongoc_queue_init(mongoc_queue_t *queue)
{
   BSON_ASSERT(queue);

   memset(queue, 0, sizeof *queue);
}


void
_mongoc_queue_push_head(mongoc_queue_t *queue, void *data)
{
   mongoc_queue_item_t *item;

   BSON_ASSERT(queue);
   BSON_ASSERT(data);

   item = (mongoc_queue_item_t *)bson_malloc0(sizeof *item);
   item->next = queue->head;
   item->data = data;

   queue->head = item;

   if (!queue->tail) {
      queue->tail = item;
   }

   queue->length++;
}


void
_mongoc_queue_push_tail(mongoc_queue_t *queue, void *data)
{
   mongoc_queue_item_t *item;

   BSON_ASSERT(queue);
   BSON_ASSERT(data);

   item = (mongoc_queue_item_t *)bson_malloc0(sizeof *item);
   item->data = data;

   if (queue->tail) {
      queue->tail->next = item;
   } else {
      queue->head = item;
   }

   queue->tail = item;
   queue->length++;
}


void *
_mongoc_queue_pop_head(mongoc_queue_t *queue)
{
   mongoc_queue_item_t *item;
   void *data = NULL;

   BSON_ASSERT(queue);

   if ((item = queue->head)) {
      if (!item->next) {
         queue->tail = NULL;
      }
      queue->head = item->next;
      data = item->data;
      bson_free(item);
      queue->length--;
   }

   return data;
}


void *
_mongoc_queue_pop_tail(mongoc_queue_t *queue)
{
   mongoc_queue_item_t *item;
   void *data = NULL;

   BSON_ASSERT(queue);

   if (queue->length == 0) {
      return NULL;
   }

   data = queue->tail->data;

   if (queue->length == 1) {
      bson_free(queue->tail);
      queue->head = queue->tail = NULL;
   } else {
      /* find item pointing at tail */
      for (item = queue->head; item; item = item->next) {
         if (item->next == queue->tail) {
            item->next = NULL;
            bson_free(queue->tail);
            queue->tail = item;
            break;
         }
      }
   }

   queue->length--;

   return data;
}


uint32_t
_mongoc_queue_get_length(const mongoc_queue_t *queue)
{
   BSON_ASSERT(queue);

   return queue->length;
}
