#include "list.h"

#include <assert.h>
#include <stdlib.h>

#ifdef NDEBUG
	#define CHECK(x) (void)(x)
#else
	#define CHECK(x) _check(x)
#endif

struct list
{
	list_item *head, *tail;
	void (*elt_dtor)(void *);
	size_t length;
};

static void
_check(const list *l)
{
	assert(l);
	assert( (!l->head && l->length == 0) ||
	        ( l->head && l->length != 0) );
	assert( (!l->head && !l->tail) ||
	        ( l->head &&  l->tail) );
}

list *
l_new(void (*elt_dtor)(void *))
{
	list *l = malloc(sizeof *l);
	if (!l)
		return NULL;
	*l = (list){.elt_dtor = elt_dtor};
	CHECK(l);
	return l;
}

void
l_free(list *l)
{
	if (!l)
		return;
	l_clear(l);
	free(l);
}

size_t
l_length(const list *l)
{
	return l ? l->length : 0;
}

bool
l_is_empty(const list *l)
{
	return !l || !l->head;
}

list_item *
l_first(const list *l)
{
	return l ? l->head : NULL;
}

list_item *
l_last(const list *l)
{
	return l ? l->tail : NULL;
}

bool
l_append(list *l, void *data)
{
	if (!l)
		return false;
	return l_insert_after(l, l->tail, data);
}

bool
l_prepend(list *l, void *data)
{
	if (!l)
		return false;
	return l_insert(l, l->head, data);
}

list_item *
l_remove_first(list *l)
{
	if (!l)
		return NULL;
	list_item *old_head = l->head;
	if (old_head)
	{
		l->head = old_head->next;
		old_head->next = NULL;
		l->head->prev = NULL;
		l->length--;
	}
	return old_head;
}

list_item *
l_remove_last(list *l)
{
	if (!l)
		return NULL;
	list_item *old_tail = l->tail;
	if (old_tail)
	{
		l->tail = old_tail->prev;
		old_tail->prev = NULL;
		l->tail->next = NULL;
		l->length--;
	}
	return old_tail;
}

bool
l_insert(list *l, list_item *pos, void *data)
{
	if (!l)
		return false;
	if (!pos)
		pos = l->head;
	list_item *li = malloc(sizeof *li);
	if (!li)
		return false;
	*li = (list_item){
		.prev = pos->prev,
		.next = pos,
		.data = data
	};
	if (pos->prev)
		pos->prev->next = li;
	pos->prev = li;

	if (!l->head)
		l->head = l->tail = li;
	else if (pos == l->head)
		l->head = li;
	l->length++;

	CHECK(l);
	return true;
}

bool
l_insert_after(list *l, list_item *pos, void *data)
{
	if (!l)
		return false;
	if (!pos)
		pos = l->tail;
	list_item *li = malloc(sizeof *li);
	if (!li)
		return false;
	*li = (list_item){
		.prev = pos,
		.next = pos->next,
		.data = data
	};
	if (pos->next)
		pos->next->prev = li;
	pos->next = li;

	if (!l->tail)
		l->head = l->tail = li;
	else if (pos == l->tail)
		l->tail = li;
	l->length++;

	CHECK(l);
	return true;
}