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'));
    }

}