trait DateRangeAllDayTrait in Date all day 8

trait DateRangeAllDayTrait {

  /**
   * {@inheritdoc}
   *
   * @see Drupal\date_all_day\DateRangeAllDayTrait
   */
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];
    $separator = $this
      ->getSetting('separator');
    foreach ($items as $delta => $item) {
      if (!empty($item->start_date)) {

        /** @var \Drupal\Core\Datetime\DrupalDateTime $start_date */
        $start_date = $item->start_date;

        /** @var \Drupal\Core\Datetime\DrupalDateTime $end_date */
        $end_date = $item->end_date;
        $item_value = $item
          ->getValue();
        $is_all_day = DateRangeAllDayHelper::isAllDay($item);
        if ($end_date !== NULL && $start_date
          ->getTimestamp() !== $end_date
          ->getTimestamp()) {
          $elements[$delta] = [
            'start_date' => $this
              ->buildDateWithIsoAttribute($start_date, $is_all_day),
            'separator' => [
              '#plain_text' => ' ' . $separator . ' ',
            ],
            'end_date' => $this
              ->buildDateWithIsoAttribute($end_date, $is_all_day),
          ];
        }
        else {
          $elements[$delta] = $this
            ->buildDateWithIsoAttribute($start_date, $is_all_day);
          if (!empty($item->_attributes)) {
            $elements[$delta]['#attributes'] += $item->_attributes;

            // Unset field item attributes since they have been included in the
            // formatter output and should not be rendered in the field template.
            unset($item->_attributes);
          }
        }
      }
    }
    return $elements;
  }

  /**
   * {@inheritdoc}
   */
  protected function buildDate(DrupalDateTime $date, $all_day = FALSE) {
    $this
      ->setTimeZone($date);
    $build = [
      '#markup' => $this
        ->formatDate($date, $all_day),
      '#cache' => [
        'contexts' => [
          'timezone',
        ],
      ],
    ];
    return $build;
  }

  /**
   * {@inheritdoc}
   */
  protected function buildDateWithIsoAttribute(DrupalDateTime $date, $all_day = FALSE) {

    // Create the ISO date in Universal Time.
    $iso_date = $date
      ->format("Y-m-d\\TH:i:s") . 'Z';
    $this
      ->setTimeZone($date);
    $build = [
      '#theme' => 'time',
      '#text' => $this
        ->formatDate($date, $all_day),
      '#html' => FALSE,
      '#attributes' => [
        'datetime' => $iso_date,
      ],
      '#cache' => [
        'contexts' => [
          'timezone',
        ],
      ],
    ];
    return $build;
  }

  /**
   * {@inheritdoc}
   */
  public function settingsSummary() {
    $summary = parent::settingsSummary();
    if ($date_only_format = $this
      ->getSetting('date_only_format')) {
      $date = new DrupalDateTime();
      $this
        ->setTimeZone($date);
      $formatted_date = $this->dateFormatter
        ->format($date
        ->getTimestamp(), $date_only_format);
      $summary[] = $this
        ->t('Date only format: %date', [
        '%date' => $formatted_date,
      ]);
    }
    return $summary;
  }

}