/*
 * Copyright (c) Carlos Maiolino <carlos@maiolino.me>.
 * All Rights Reserved.
 *
 * 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.
 *
 * This program is distributed in the hope that it would 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, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

 /* This is a simple example of double linked lists I wrote for fun
  * Because I had nothing better to do :)
  */

#include <stdio.h>
#include <stdlib.h>

struct list_item {
	int key;
	struct list_item *prev;
	struct list_item *next;
};

struct list_item *list_add(struct list_item *HEAD, int key)
{
	struct list_item *item = malloc(sizeof(struct list_item));

	if (!item)
		goto err_out;

	item->key = key;
	item->prev = NULL;

	/* list is empty, just asign this item as HEAD */
	if (!HEAD) {
		item->next = NULL;
		HEAD = item;
		return HEAD;
	}

	item->next = HEAD;
	HEAD->prev = item;
	HEAD = item;
	return HEAD;

err_out:
	return NULL;
}

void list_del_by_item(struct list_item **HEAD, int i)
{
	struct list_item *item = *HEAD;

	for (; i > 0; i--) {
		if (item) {
			item = item->next;
		} else {
			printf("Can't free an inexistent item\n");
			return;
		}
	}

	/* if this is the last item, item->next is already NULL */
	if (item->prev)
		item->prev->next = item->next;
	else {
		*HEAD = item->next;
	}

	if (item->next)
		item->next->prev = item->prev;

	free(item);
	return;
}
/*
int list_del_by_key(list, key)
int list_search(list, key)
*/

void print_list(struct list_item *HEAD)
{
	struct list_item *iter = HEAD;

	if (!HEAD) {
		printf("List is empty\n");
		return;
	}

	if (HEAD->prev != NULL) {
		printf("Item is not the head of the list\n");
		return;
	}

	while (iter) {
		printf(" %d", iter->key);
		iter = iter->next;
	}
	printf("\nEND OF LIST\n");
}

void print_node(struct list_item *item)
{
	int *val = &(item->key);
	printf("NODE=  %p \n", item);
	printf("    .prev = %p\n", item->prev);
	printf("    .next = %p\n", item->next);
	printf("    .key  = %p\n", &(item->key));
	printf("    .key  = %d\n", *(&(item->key)));
	printf("    .key  = %d\n", *val);
}

void debug_list(struct list_item *HEAD)
{
	while (HEAD) {
		print_node(HEAD);
		HEAD = HEAD->next;
	}
}

int main(void)
{
	/* Init list head */
	struct list_item *HEAD = NULL;
	int val;
	char cmd;

	while (1) {
		printf("Select option: ");
		scanf(" %c", &cmd);

		switch (cmd) {
			case 'a':
				printf("Add value: ");
				scanf(" %d", &val);
				HEAD = list_add(HEAD, val);
				break;
			case 'd':
				printf("Item to delete (starting on 0): ");
				scanf(" %d", &val);
				if (HEAD)
					list_del_by_item(&HEAD, val);
				else
					printf("List is empty\n");
				break;

			case 'p':
				print_list(HEAD);
				break;
			case 'D':
				debug_list(HEAD);
				break;
			case 'q':
				goto out;
			default:
				printf("a: add to list, d: del item, p: print\n");
				break;
		}
	}

out:
	while (HEAD) {
		struct list_item *next = HEAD->next;
		free(HEAD);
		HEAD = next;
	}

	return 0;
}