public function children(CategoryHandler $handler, $categoryId) { $parentId = Input::get('id'); if ($parentId === null) { $category = $handler->get($categoryId); $children = $handler->progenitors($category); } else { if (!($parent = $handler->getItem($parentId))) { throw new InvalidArgumentHttpException(); } $children = $handler->children($parent); } return Presenter::makeApi($children); }