class ForumUninstallValidator

class ForumUninstallValidator implements ModuleUninstallValidatorInterface {
    use StringTranslationTrait;
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The config factory.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * Constructs a new ForumUninstallValidator.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory.
     * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
     *   The string translation service.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, ConfigFactoryInterface $config_factory, TranslationInterface $string_translation) {
        $this->entityTypeManager = $entity_type_manager;
        $this->configFactory = $config_factory;
        $this->stringTranslation = $string_translation;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate($module) {
        $reasons = [];
        if ($module == 'forum') {
            if ($this->hasForumNodes()) {
                $reasons[] = $this->t('To uninstall Forum, first delete all <em>Forum</em> content');
            }
            $vocabulary = $this->getForumVocabulary();
            if (!empty($vocabulary) && $this->hasTermsForVocabulary($vocabulary)) {
                if ($vocabulary->access('view')) {
                    $reasons[] = $this->t('To uninstall Forum, first delete all <a href=":url">%vocabulary</a> terms', [
                        '%vocabulary' => $vocabulary->label(),
                        ':url' => $vocabulary->toUrl('overview-form')
                            ->toString(),
                    ]);
                }
                else {
                    $reasons[] = $this->t('To uninstall Forum, first delete all %vocabulary terms', [
                        '%vocabulary' => $vocabulary->label(),
                    ]);
                }
            }
        }
        return $reasons;
    }
    
    /**
     * Determines if there are any forum nodes or not.
     *
     * @return bool
     *   TRUE if there are forum nodes, FALSE otherwise.
     */
    protected function hasForumNodes() {
        $nodes = $this->entityTypeManager
            ->getStorage('node')
            ->getQuery()
            ->condition('type', 'forum')
            ->accessCheck(FALSE)
            ->range(0, 1)
            ->execute();
        return !empty($nodes);
    }
    
    /**
     * Determines if there are any taxonomy terms for a specified vocabulary.
     *
     * @param \Drupal\taxonomy\VocabularyInterface $vocabulary
     *   The vocabulary to check for terms.
     *
     * @return bool
     *   TRUE if there are terms for this vocabulary, FALSE otherwise.
     */
    protected function hasTermsForVocabulary(VocabularyInterface $vocabulary) {
        $terms = $this->entityTypeManager
            ->getStorage('taxonomy_term')
            ->getQuery()
            ->condition('vid', $vocabulary->id())
            ->accessCheck(FALSE)
            ->range(0, 1)
            ->execute();
        return !empty($terms);
    }
    
    /**
     * Returns the vocabulary configured for forums.
     *
     * @return \Drupal\taxonomy\VocabularyInterface
     *   The vocabulary entity for forums.
     */
    protected function getForumVocabulary() {
        $vid = $this->configFactory
            ->get('forum.settings')
            ->get('vocabulary');
        if (!empty($vid)) {
            return $this->entityTypeManager
                ->getStorage('taxonomy_vocabulary')
                ->load($vid);
        }
        else {
            return NULL;
        }
    }

}