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;
    }

}