class ContentUninstallValidator

class ContentUninstallValidator implements ModuleUninstallValidatorInterface {
  use StringTranslationTrait;
  
  /**
   * The entity type manager service.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;
  
  /**
   * Constructs a new ContentUninstallValidator.
   *
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager service.
   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
   *   The string translation service.
   */
  public function __construct(EntityTypeManagerInterface $entity_type_manager, TranslationInterface $string_translation) {
    $this->entityTypeManager = $entity_type_manager;
    $this->stringTranslation = $string_translation;
  }
  
  /**
   * {@inheritdoc}
   */
  public function validate($module) {
    $entity_types = $this->entityTypeManager
      ->getDefinitions();
    $reasons = [];
    foreach ($entity_types as $entity_type) {
      if ($module == $entity_type->getProvider() && $entity_type instanceof ContentEntityTypeInterface && $this->entityTypeManager
        ->getStorage($entity_type->id())
        ->hasData()) {
        $reasons[] = $this->t('There is content for the entity type: @entity_type. <a href=":url">Remove @entity_type_plural</a>.', [
          '@entity_type' => $entity_type->getLabel(),
          '@entity_type_plural' => $entity_type->getPluralLabel(),
          ':url' => Url::fromRoute('system.prepare_modules_entity_uninstall', [
            'entity_type_id' => $entity_type->id(),
          ])
            ->toString(),
        ]);
      }
    }
    return $reasons;
  }

}