View source  
  <?php
namespace Drupal\persian_date\Plugin\Field\FieldWidget;
use Drupal\Core\Entity\EntityStorageInterface;
use Drupal\Core\Field\FieldDefinitionInterface;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
use Symfony\Component\DependencyInjection\ContainerInterface;
class PersianDateTimeDefaultWidget extends DateTimeWidgetBase implements ContainerFactoryPluginInterface {
  
  protected $dateStorage;
  
  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;
  }
  
  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.manager')
      ->getStorage('date_format'));
  }
  
  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    $element = parent::formElement($items, $delta, $element, $form, $form_state);
    
    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';
    }
    
    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;
    }
    $date_type = 'text';
    $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;
  }
}