public function onLoad(LoadResourceEvent $event)
    {
        /** @var Lesson $lesson */
        $lesson = $event->getResource();
        $firstChapter = $this->chapterRepository->getFirstChapter($lesson);
        $root = $this->chapterRepository->findOneBy(['lesson' => $lesson, 'level' => 0, 'parent' => null]);

        $event->setData([
            'exportPdfEnabled' => $this->config->getParameter('is_pdf_export_active'),
            'lesson' => $this->serializer->serialize($lesson),
            'tree' => $this->chapterManager->serializeChapterTree($lesson),
            'chapter' => $firstChapter ? $this->serializer->serialize($firstChapter) : null,
            'root' => $root ? $this->serializer->serialize($root) : null,
        ]);

        $event->stopPropagation();
    }