C_lib/linked_lists/queue.c

/*
* C_lib Copyright (C) 2021 Wael Karram.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 3 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

/* This file contains the function implementations for queues. */
/* Include guards + includes. */
#ifndef QUEUE_C
#define QUEUE_C
#include "queue.h"
#endif /* QUEUE_C */

/* Function implementations. */

/* This function initializes a new empty queue. */
/* Will return a pointer to the queue on success, otherwise will return NULL. */
queue_t *initialize_queue() {
	/* Variables. */
	queue_t *result;

	/* Attempt to allocate. */
	result = (queue_t*) malloc(sizeof(queue_t));

	/* Check if the allocation failed. */
	if (result == NULL)
		return NULL;

	/* Allocate the internal list struct. */
	result->list = (list_t*) malloc(sizeof(list_t));

	/* Check if the allocation failed. */
	if (result->list == NULL) {
		free(result);
		return NULL;
	}

	/* Initialize the internal fields. */
	result->tail = NULL;
	result->list->head = NULL;
	result->list->length = 0;

	/* Return the result. */
	return result;
}

/* This function enqueues a node. */
/* This function attempts to enqueue a given node into the given queue, on success will return SUCCESS_CODE_QUEUE_C, otherwise will return FAILURE_CODE_QUEUE_C. */
/* Note that if either the queue or node pointer are NULL, the function will automatically fail. */
int enqueue(queue_t *queue, node_t *node) {
	/* Input sanity check. */
	if (queue == NULL || queue->list == NULL || node == NULL || ((queue->list->head == NULL && queue->tail != NULL) || (queue->list->head != NULL && queue->tail == NULL)))
		return FAILURE_CODE_QUEUE_C;

	/* Attempt to enqueue the node. */
	/* Check if the queue is empty. */
	if (queue->list->head == NULL) {
		node->next = NULL;
		queue->tail = node;
	} else
		node->next = queue->list->head;
	/* Relink the head. */
	queue->list->head = node;
	/* Increase the length. */
	(queue->list->length)++;

	/* Success. */
	return SUCCESS_CODE_QUEUE_C;
}

/* This function allocates and enqueues a node. */
/* This function attempts to create a node then enqueue it into the given queue, on success will return SUCCESS_CODE_QUEUE_C, otherwise will return FAILURE_CODE_QUEUE_C. */
/* Note that if either the queue pointer is NULL or node allocation fails, the function will automatically fail. */
int enqueue_data(queue_t *queue, void *data) {
	/* Variables. */
	node_t *node;

	/* Input sanity check. */
	if (queue == NULL || queue->list == NULL || ((queue->list->head == NULL && queue->tail != NULL) || (queue->list->head != NULL && queue->tail == NULL)))
		return FAILURE_CODE_QUEUE_C;

	/* Attempt to allocate the node. */
	node = (node_t) malloc(sizeof(node));
	if (node == NULL)
		return FAILURE_CODE_QUEUE_C;

	/* Attempt to enqueue the node. */
	/* Check if the queue is empty. */
	if (queue->list->head == NULL) {
		node->next = NULL;
		queue->tail = node;
	} else
		node->next = queue->list->head;
	/* Relink the head. */
	queue->list->head = node;
	/* Increase the length. */
	(queue->list->length)++;

	/* Success. */
	return SUCCESS_CODE_QUEUE_C;
}

/* This function dequeues a node. */
/* This function attempts to dequeues a node from the given queue, on success will return a pointer to the dequeued node - otherwise returns NULL. */
/* Note that if either the queue or node pointer are NULL, the function will automatically fail. */
node_t *dequeue(queue_t *queue) {
	/* Variables. */
	node_t *result, *replacement, *tmp;
	int i;

	/* Input sanity check. */
	if (queue == NULL || queue->list == NULL || ((queue->list->head == NULL && queue->tail != NULL) || (queue->list->head != NULL && queue->tail == NULL)))
		return NULL;

	/* Attempt to dequeue the node. */
	/* Check if the queue is empty. */
	if (queue->list->head == NULL)
		return NULL;
	else if (queue->list->length == 1) {
		/* A queue that is of length 1. */
		result = queue->list->head;
		queue->list->head = NULL;
		queue->tail = NULL;
	} else {
		/* This is the general case, move the tail and unlink. */
		/* Set the result to be the tail. */
		result = queue->tail;
		/* Attempt to find the new tail. */
		tmp = queue->list->head;
		while (tmp->next != result)
			tmp = tmp->next;
		/* Unlink and set the new tail. */
		tmp->next = NULL;
		queue->tail = tmp;
	}
	/* Decrease the length. */
	(queue->list->length)--;

	/* Success. */
	return SUCCESS_CODE_QUEUE_C;
}

/* This function frees all the nodes of the given queue and the queue itself (setting it to NULL). */
/* Note that it doesn't touch the data stored within the queue's nodes, returns 1 on success and 0 on failure - in the latter case might exhibit undefined behavior. */
int clear_queue(queue_t **queue) {
	/* Sanity check. */
	if (queue == NULL || *queue == NULL)
		return FAILURE_CODE_QUEUE_C;

	/* Delegate to implementation (linked list). */
	if (!clear_single_linked_list(&((*queue)->list)))
		return FAILURE_CODE_QUEUE_C;

	/* Successfully cleared the internal structure, just free the queue struct and set the pointer to NULL. */
	free(*queue);
	*queue = NULL;
	return SUCCESS_CODE_QUEUE_C;
}

/* This function frees all the nodes of the given queue and the queue itself (setting it to NULL).*/
/* Note that it does free the stored data, returns 1 on success and 0 on failure - in the latter case might exhibit undefined behavior. */
/* If free_function is NULL, then it the standard library's free() call is used. */
int clear_queue(queue_t **queue, void (*free_func)()) {
	/* Sanity check. */
	if (queue == NULL || *queue == NULL)
		return FAILURE_CODE_QUEUE_C;

	/* Delegate to implementation (linked list). */
	if (!clear_single_linked_list(&((*queue)->list), free_function))
		return FAILURE_CODE_QUEUE_C;

	/* Successfully cleared the internal structure, just free the queue struct and set the pointer to NULL. */
	free(*queue);
	*queue = NULL;
	return SUCCESS_CODE_QUEUE_C;
}

/* This function serializes the queue. */
/* Note that it'll return NULL on allocation failure or invalid input - in the former case it'll set the correct length in the specified pointer, in the second it will set -1. */
void **serialize_queue(queue_t *queue, int *length) {
	/* Sanity check. */
	if (queue == NULL) {
		*length = -1;
		return NULL;
	}

	/* Delegate. */
	return serialize_list(queue->list, length);
}