class EditorLinkDialog

class EditorLinkDialog extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'editor_link_dialog';
    }
    
    /**
     * {@inheritdoc}
     *
     * @param \Drupal\editor\Entity\Editor $editor
     *   The text editor to which this dialog corresponds.
     */
    public function buildForm(array $form, FormStateInterface $form_state, Editor $editor = NULL) {
        // The default values are set directly from \Drupal::request()->request,
        // provided by the editor plugin opening the dialog.
        $user_input = $form_state->getUserInput();
        $input = isset($user_input['editor_object']) ? $user_input['editor_object'] : [];
        $form['#tree'] = TRUE;
        $form['#attached']['library'][] = 'editor/drupal.editor.dialog';
        $form['#prefix'] = '<div id="editor-link-dialog-form">';
        $form['#suffix'] = '</div>';
        // Everything under the "attributes" key is merged directly into the
        // generated link tag's attributes.
        $form['attributes']['href'] = [
            '#title' => $this->t('URL'),
            '#type' => 'textfield',
            '#default_value' => isset($input['href']) ? $input['href'] : '',
            '#maxlength' => 2048,
        ];
        $form['actions'] = [
            '#type' => 'actions',
        ];
        $form['actions']['save_modal'] = [
            '#type' => 'submit',
            '#value' => $this->t('Save'),
            // No regular submit-handler. This form only works via JavaScript.
'#submit' => [],
            '#ajax' => [
                'callback' => '::submitForm',
                'event' => 'click',
            ],
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $response = new AjaxResponse();
        if ($form_state->getErrors()) {
            unset($form['#prefix'], $form['#suffix']);
            $form['status_messages'] = [
                '#type' => 'status_messages',
                '#weight' => -10,
            ];
            $response->addCommand(new HtmlCommand('#editor-link-dialog-form', $form));
        }
        else {
            $response->addCommand(new EditorDialogSave($form_state->getValues()));
            $response->addCommand(new CloseModalDialogCommand());
        }
        return $response;
    }

}