class FilterUninstallValidator

class FilterUninstallValidator implements ModuleUninstallValidatorInterface {
  use StringTranslationTrait;

  /**
   * The filter plugin manager.
   *
   * @var \Drupal\Component\Plugin\PluginManagerInterface
   */
  protected $filterManager;

  /**
   * The filter entity storage.
   *
   * @var \Drupal\Core\Config\Entity\ConfigEntityStorageInterface
   */
  protected $filterStorage;

  /**
   * Constructs a new FilterUninstallValidator.
   *
   * @param \Drupal\Component\Plugin\PluginManagerInterface $filter_manager
   *   The filter plugin manager.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
   *   The string translation service.
   */
  public function __construct(PluginManagerInterface $filter_manager, EntityTypeManagerInterface $entity_type_manager, TranslationInterface $string_translation) {
    $this->filterManager = $filter_manager;
    $this->filterStorage = $entity_type_manager
      ->getStorage('filter_format');
    $this->stringTranslation = $string_translation;
  }

  /**
   * {@inheritdoc}
   */
  public function validate($module) {
    $reasons = [];

    // Get filter plugins supplied by this module.
    if ($filter_plugins = $this
      ->getFilterDefinitionsByProvider($module)) {
      $used_in = [];

      // Find out if any filter formats have the plugin enabled.
      foreach ($this
        ->getEnabledFilterFormats() as $filter_format) {
        $filters = $filter_format
          ->filters();
        foreach ($filter_plugins as $filter_plugin) {
          if ($filters
            ->has($filter_plugin['id']) && $filters
            ->get($filter_plugin['id'])->status) {
            $used_in[] = $filter_format
              ->label();
            break;
          }
        }
      }
      if (!empty($used_in)) {
        $reasons[] = $this
          ->t('Provides a filter plugin that is in use in the following filter formats: %formats', [
          '%formats' => implode(', ', $used_in),
        ]);
      }
    }
    return $reasons;
  }

  /**
   * Returns all filter definitions that are provided by the specified provider.
   *
   * @param string $provider
   *   The provider of the filters.
   *
   * @return array
   *   The filter definitions for the specified provider.
   */
  protected function getFilterDefinitionsByProvider($provider) {
    return array_filter($this->filterManager
      ->getDefinitions(), function ($definition) use ($provider) {
      return $definition['provider'] == $provider;
    });
  }

  /**
   * Returns all enabled filter formats.
   *
   * @return \Drupal\filter\FilterFormatInterface[]
   */
  protected function getEnabledFilterFormats() {
    return $this->filterStorage
      ->loadByProperties([
      'status' => TRUE,
    ]);
  }

}