public function category()
 {
     $this->buildHeading([trans("ilib::common.statistics"), trans("ilib::common.statistics_category")], 'fa-bar-chart', ['#' => trans("ilib::common.statistics")]);
     /** @var Category[] $categories */
     $categories = CategoryManager::of(Ebook::class)->root()->getDescendants();
     $data = [];
     foreach ($categories as $category) {
         $data[] = ['title' => $category->title, 'depth' => $category->depth, 'count' => Ebook::categorized($category)->count()];
     }
     return view('ilib::backend.statistics.category', compact('data'));
 }