/* Standard C */
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

/* Project */
#include "util.h"

typedef int T;

struct list_node {
	struct list_node *next;
	T                 data;
};

struct list {
	struct list_node *head, *tail;
};

void
list_init(struct list *list)
{
	list->head = NULL;
}

static struct list_node *
create_node(struct list_node *next, T data)
{
	struct list_node *node = malloc(sizeof *node);

	if ( node != NULL ) {
		node->next = next;
		node->data = data;
	}
	return node;
}

void
list_push_back(struct list *list, T data)
{
	struct list_node *node = create_node(NULL, data);

	if ( node != NULL ) {
		if ( list->head == NULL ) {
			list->head = node;
		}
		else {
			list->tail->next = node;
		}
		list->tail = node;
	}
	else {
		ERROR("out of memory");
	}
}

void
list_push_front(struct list *list, T data)
{
	struct list_node *node = create_node(list->head, data);

	if ( node != NULL ) {
		if ( list->head == NULL ) { // Einfügen in eine leere Liste?
			list->tail = node;
		}
		list->head = node;
	}
	else {
		ERROR("out of memory");
	}
}

bool
list_pop_front(struct list *list, T *data)
{
	if ( list->head != NULL ) {
		struct list_node *next = list->head->next;

		if ( data != NULL ) {
			*data = list->head->data;
		}
		free(list->head);
		list->head = next;

		return true;
	}
	else {
		return false;
	}
}

bool
list_empty(struct list *list)
{
	return list->head == NULL;
}

void
list_free(struct list *list)
{
	struct list_node *item, *next;

	for ( item = list->head; item; item = next ) {
		next = item->next;
		free(item);
	}
}

int
main()
{
	struct list list[1];

	list_init(list);

	for ( int i = 0; i != 10; ++i )
		list_push_front(list, -i);

	for ( int i = 0; i != 10; ++i )
		list_push_back(list, i);

	while ( !list_empty(list) ) {
		int i;
		if ( list_pop_front(list, &i) )
			printf("%d\n", i);
		else
			ERROR("this shouldn't happen!");
	}

	list_free(list);

	return EXIT_SUCCESS;
}