class SearchBlock

class SearchBlock extends BlockBase implements ContainerFactoryPluginInterface {
  
  /**
   * The form builder.
   *
   * @var \Drupal\Core\Form\FormBuilderInterface
   */
  protected $formBuilder;
  
  /**
   * The search page repository.
   *
   * @var \Drupal\search\SearchPageRepositoryInterface
   */
  protected $searchPageRepository;
  
  /**
   * Constructs a new SearchLocalTask.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin ID for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Form\FormBuilderInterface $form_builder
   *   The form builder.
   * @param \Drupal\search\SearchPageRepositoryInterface $search_page_repository
   *   The search page repository.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, FormBuilderInterface $form_builder, SearchPageRepositoryInterface $search_page_repository) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->formBuilder = $form_builder;
    $this->searchPageRepository = $search_page_repository;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('form_builder'), $container->get('search.search_page_repository'));
  }
  
  /**
   * {@inheritdoc}
   */
  protected function blockAccess(AccountInterface $account) {
    return AccessResult::allowedIfHasPermission($account, 'search content');
  }
  
  /**
   * {@inheritdoc}
   */
  public function build() {
    $page = $this->configuration['page_id'] ?? NULL;
    return $this->formBuilder
      ->getForm(SearchBlockForm::class, $page);
  }
  
  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'page_id' => '',
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state) {
    // The configuration for this block is which search page to connect the
    // form to. Options are all configured/active search pages.
    $options = [];
    $active_search_pages = $this->searchPageRepository
      ->getActiveSearchPages();
    foreach ($this->searchPageRepository
      ->sortSearchPages($active_search_pages) as $entity_id => $entity) {
      $options[$entity_id] = $entity->label();
    }
    $form['page_id'] = [
      '#type' => 'select',
      '#title' => $this->t('Search page'),
      '#description' => $this->t('The search page that the form submits to, or Default for the default search page.'),
      '#default_value' => $this->configuration['page_id'],
      '#options' => $options,
      '#empty_option' => $this->t('Default'),
      '#empty_value' => '',
    ];
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function blockSubmit($form, FormStateInterface $form_state) {
    $this->configuration['page_id'] = $form_state->getValue('page_id');
  }

}