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, EntityStorageInterface $date_storage) {
        parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $third_party_settings);
        $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('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;
    }

}