class IncrementalForm

class IncrementalForm extends MigrateUpgradeFormBase {
    
    /**
     * The date formatter service.
     *
     * @var \Drupal\Core\Datetime\DateFormatterInterface
     */
    protected $dateFormatter;
    
    /**
     * IncrementalForm constructor.
     *
     * @param \Drupal\Core\State\StateInterface $state
     *   The state service.
     * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
     *   The date formatter service.
     * @param \Drupal\Core\TempStore\PrivateTempStoreFactory $tempstore_private
     *   The private tempstore factory service.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory service.
     * @param \Drupal\migrate\Plugin\MigrationPluginManagerInterface $migration_plugin_manager
     *   The migration plugin manager service.
     */
    public function __construct(StateInterface $state, DateFormatterInterface $date_formatter, PrivateTempStoreFactory $tempstore_private, ConfigFactoryInterface $config_factory, MigrationPluginManagerInterface $migration_plugin_manager) {
        parent::__construct($config_factory, $migration_plugin_manager, $state, $tempstore_private);
        $this->dateFormatter = $date_formatter;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('state'), $container->get('date.formatter'), $container->get('tempstore.private'), $container->get('config.factory'), $container->get('plugin.manager.migration'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'migrate_drupal_ui_incremental_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        // Get all the data needed for this form.
        $date_performed = $this->state
            ->get('migrate_drupal_ui.performed');
        // If data is missing or this is the wrong step, start over.
        if (!$date_performed || $this->store
            ->get('step') != 'incremental') {
            return $this->restartUpgradeForm();
        }
        $form = parent::buildForm($form, $form_state);
        $form['#title'] = $this->t('Upgrade');
        // @todo Add back support for rollbacks.
        //   https://www.drupal.org/node/2687849
        $form['upgrade_option_item'] = [
            '#type' => 'item',
            '#prefix' => $this->t('An upgrade has already been performed on this site. To perform a new migration, create a clean and empty new install of Drupal @version. Rollbacks are not yet supported through the user interface. For more information, see the <a href=":url">upgrading handbook</a>.', [
                '@version' => $this->destinationSiteVersion,
                ':url' => 'https://www.drupal.org/upgrade/migrate',
            ]),
            '#description' => $this->t('Last upgrade: @date', [
                '@date' => $this->dateFormatter
                    ->format($date_performed),
            ]),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->store
            ->set('step', 'credential');
        $form_state->setRedirect('migrate_drupal_ui.upgrade_credential');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConfirmText() {
        return $this->t('Import new configuration and content from old site');
    }

}