class DateTimeDefaultWidget

class DateTimeDefaultWidget extends DateTimeWidgetBase {
  
  /**
   * The date format storage.
   *
   * @var \Drupal\Core\Entity\EntityStorageInterface
   */
  protected $dateStorage;
  
  /**
   * {@inheritdoc}
   */
  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, array $third_party_settings, ElementInfoManagerInterface $elementInfoManager, EntityStorageInterface $date_storage) {
    parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $third_party_settings, $elementInfoManager);
    $this->dateStorage = $date_storage;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($plugin_id, $plugin_definition, $configuration['field_definition'], $configuration['settings'], $configuration['third_party_settings'], $container->get('plugin.manager.element_info'), $container->get('entity_type.manager')
      ->getStorage('date_format'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    $element = parent::formElement($items, $delta, $element, $form, $form_state);
    // If the field is date-only, make sure the title is displayed. Otherwise,
    // wrap everything in a fieldset, and the title will be shown in the legend.
    if ($this->getFieldSetting('datetime_type') === DateTimeItem::DATETIME_TYPE_DATE) {
      $element['value']['#title'] = $this->fieldDefinition
        ->getLabel();
      $element['value']['#description'] = $this->fieldDefinition
        ->getDescription();
    }
    else {
      $element['#theme_wrappers'][] = 'fieldset';
    }
    // Identify the type of date and time elements to use.
    switch ($this->getFieldSetting('datetime_type')) {
      case DateTimeItem::DATETIME_TYPE_DATE:
        $date_type = 'date';
        $time_type = 'none';
        $date_format = $this->dateStorage
          ->load('html_date')
          ->getPattern();
        $time_format = '';
        break;

      default:
        $date_type = 'date';
        $time_type = 'time';
        $date_format = $this->dateStorage
          ->load('html_date')
          ->getPattern();
        $time_format = $this->dateStorage
          ->load('html_time')
          ->getPattern();
        break;

    }
    $element['value'] += [
      '#date_date_format' => $date_format,
      '#date_date_element' => $date_type,
      '#date_date_callbacks' => [],
      '#date_time_format' => $time_format,
      '#date_time_element' => $time_type,
      '#date_time_callbacks' => [],
    ];
    return $element;
  }

}