i32 add_entity(entity_t entity, elist_t *list)
{
	assert(list);
	i32 i;
	for (i = 0; i < MAX_ENTITIES; ++i)
		if (!list->nodes[i].id)
			break;
	if (i == MAX_ENTITIES) {
		printf("error: failed to add entity\n");
		return 0;
	}
	++list->count;
	enode_t *node = list->nodes+i;
	node->id = list->count;
	node->entity = entity;
	dllpushback(list->first, list->last, node);
	return node->id;
}

void delete_entity(i32 id, elist_t *list)
{
	assert(list);
	for (enode_t *node = list->first; node; node = node->next) {
		if (node->id == id) {
			dllremove(list->first, list->last, node);
			memzero_struct(node);
			list->count--;
			printf("info: entity %d deleted\n", id);
			return;
		}
	}
	printf("error: entity %d failed to delete\n", id);
}

entity_t *get_entity(elist_t list, i32 id)
{
	for (enode_t *node = list.first; node; node = node->next)
		if (node->id == id)
			return &node->entity;
	return 0;
}

i32 aabb3d(bbox_t a, bbox_t b)
{
	i32 result = ((b.start.x <= a.end.x) && (b.end.x >= a.start.x)) &&
		((b.start.y <= a.end.y) && (b.end.y >= a.start.y)) &&
		((b.start.z <= a.end.z) && (b.end.z >= a.start.z));
	return result;
}

i32 check_collision(entity_t *a, entity_t *b)
{
	if (!(a->flags & ENTITY_COLLIDE) || !(b->flags & ENTITY_COLLIDE))
		return 0;

	bbox_t bboxa = {
		v3_add(a->bbox.start, a->position),
		v3_add(a->bbox.end, a->position)
	};

	bbox_t bboxb = {
		v3_add(b->bbox.start, b->position),
		v3_add(b->bbox.end, b->position)
	};

	i32 result = aabb3d(bboxa, bboxb);

	return result;
}

entity_t move_entity(entity_t old, v3 acceleration, float dt)
{
	entity_t new = old;
	new.position = v3_add(old.position, v3_scalef(old.velocity, dt));
	new.velocity = v3_add(old.velocity, v3_scalef(acceleration, dt*dt));
	new.velocity = v3_sub(new.velocity, v3_scalef(V3_UP, dt));
	return new;
}

/*
void update_entities(elist_t list)
{
	for (enode_t *node = list.first; node; node = node->next) {
		if (node->entity.flags & ENTITY_MOVE)
			move_entity(node->entity, );
		if (node->entity.flags & ENTITY_COLLIDE) {
			for (enode_t *test = list.first; test; test = test->next) {
				if (check_collision(node->entity, test->entity)) {

				}
			}
		}
	}
}
*/