class FieldNormalizer

class FieldNormalizer extends SerializationFieldNormalizer {
  
  /**
   * {@inheritdoc}
   */
  protected $format = [
    'hal_json',
  ];
  
  /**
   * {@inheritdoc}
   */
  public function normalize($field_items, $format = NULL, array $context = []) {
    $normalized_field_items = [];
    // Get the field definition.
    $entity = $field_items->getEntity();
    $field_name = $field_items->getName();
    $field_definition = $field_items->getFieldDefinition();
    // If this field is not translatable, it can simply be normalized without
    // separating it into different translations.
    if (!$field_definition->isTranslatable()) {
      $normalized_field_items = $this->normalizeFieldItems($field_items, $format, $context);
    }
    else {
      foreach ($entity->getTranslationLanguages() as $language) {
        $context['langcode'] = $language->getId();
        $translation = $entity->getTranslation($language->getId());
        $translated_field_items = $translation->get($field_name);
        $normalized_field_items = array_merge($normalized_field_items, $this->normalizeFieldItems($translated_field_items, $format, $context));
      }
    }
    // Merge deep so that links set in entity reference normalizers are merged
    // into the links property.
    return NestedArray::mergeDeepArray($normalized_field_items);
  }
  
  /**
   * Helper function to normalize field items.
   *
   * @param \Drupal\Core\Field\FieldItemListInterface $field_items
   *   The field item list object.
   * @param string $format
   *   The format.
   * @param array $context
   *   The context array.
   *
   * @return array
   *   The array of normalized field items.
   */
  protected function normalizeFieldItems($field_items, $format, $context) {
    $normalized_field_items = [];
    if (!$field_items->isEmpty()) {
      foreach ($field_items as $field_item) {
        $normalized_field_items[] = $this->serializer
          ->normalize($field_item, $format, $context);
      }
    }
    return $normalized_field_items;
  }
  
  /**
   * {@inheritdoc}
   */
  public function hasCacheableSupportsMethod() : bool {
    return TRUE;
  }

}