class SearchPageFormBase

abstract class SearchPageFormBase extends EntityForm {
  
  /**
   * The entity being used by this form.
   *
   * @var \Drupal\search\SearchPageInterface
   */
  protected $entity;
  
  /**
   * The search plugin being configured.
   *
   * @var \Drupal\search\Plugin\SearchInterface
   */
  protected $plugin;
  
  /**
   * The search page repository.
   *
   * @var \Drupal\search\SearchPageRepositoryInterface
   */
  protected $searchPageRepository;
  
  /**
   * Constructs a new search form.
   *
   * @param \Drupal\search\SearchPageRepositoryInterface $search_page_repository
   *   The search page repository.
   */
  public function __construct(SearchPageRepositoryInterface $search_page_repository) {
    $this->searchPageRepository = $search_page_repository;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('search.search_page_repository'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function getBaseFormId() {
    return 'search_entity_form';
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $this->plugin = $this->entity
      ->getPlugin();
    return parent::buildForm($form, $form_state);
  }
  
  /**
   * {@inheritdoc}
   */
  public function form(array $form, FormStateInterface $form_state) {
    $form['label'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Label'),
      '#description' => $this->t('The label for this search page.'),
      '#default_value' => $this->entity
        ->label(),
      '#maxlength' => '255',
    ];
    $form['id'] = [
      '#type' => 'machine_name',
      '#default_value' => $this->entity
        ->id(),
      '#disabled' => !$this->entity
        ->isNew(),
      '#maxlength' => 64,
      '#machine_name' => [
        'exists' => [
          $this,
          'exists',
        ],
      ],
    ];
    $form['path'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Path'),
      '#field_prefix' => 'search/',
      '#default_value' => $this->entity
        ->getPath(),
      '#maxlength' => '255',
      '#required' => TRUE,
    ];
    $form['plugin'] = [
      '#type' => 'value',
      '#value' => $this->entity
        ->get('plugin'),
    ];
    if ($this->plugin instanceof PluginFormInterface) {
      $form += $this->plugin
        ->buildConfigurationForm($form, $form_state);
    }
    return parent::form($form, $form_state);
  }
  
  /**
   * Determines if the search page entity already exists.
   *
   * @param string $id
   *   The search configuration ID.
   *
   * @return bool
   *   TRUE if the search configuration exists, FALSE otherwise.
   */
  public function exists($id) {
    $entity = $this->entityTypeManager
      ->getStorage('search_page')
      ->getQuery()
      ->condition('id', $id)
      ->execute();
    return (bool) $entity;
  }
  
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    parent::validateForm($form, $form_state);
    // Ensure each path is unique.
    $path = $this->entityTypeManager
      ->getStorage('search_page')
      ->getQuery()
      ->condition('path', $form_state->getValue('path'))
      ->condition('id', $form_state->getValue('id'), '<>')
      ->execute();
    if ($path) {
      $form_state->setErrorByName('path', $this->t('The search page path must be unique.'));
    }
    if ($this->plugin instanceof PluginFormInterface) {
      $this->plugin
        ->validateConfigurationForm($form, $form_state);
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    parent::submitForm($form, $form_state);
    if ($this->plugin instanceof PluginFormInterface) {
      $this->plugin
        ->submitConfigurationForm($form, $form_state);
    }
    return $this->entity;
  }
  
  /**
   * {@inheritdoc}
   */
  public function save(array $form, FormStateInterface $form_state) {
    $this->entity
      ->save();
    $form_state->setRedirectUrl($this->entity
      ->toUrl('collection'));
  }

}