class FieldItemNormalizer

class FieldItemNormalizer extends NormalizerBase implements DenormalizerInterface {
    use SerializedColumnNormalizerTrait;
    
    /**
     * The interface or class that this Normalizer supports.
     *
     * @var string
     */
    protected $supportedInterfaceOrClass = FieldItemInterface::class;
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * FieldItemNormalizer constructor.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager) {
        $this->entityTypeManager = $entity_type_manager;
    }
    
    /**
     * {@inheritdoc}
     *
     * This normalizer leaves JSON:API normalizer land and enters the land of
     * Drupal core's serialization system. That system was never designed with
     * cacheability in mind, and hence bubbles cacheability out of band. This must
     * catch it, and pass it to the value object that JSON:API uses.
     */
    public function normalize($field_item, $format = NULL, array $context = []) {
        
        /** @var \Drupal\Core\TypedData\TypedDataInterface $property */
        $values = [];
        $context[CacheableNormalizerInterface::SERIALIZATION_CONTEXT_CACHEABILITY] = new CacheableMetadata();
        if (!empty($field_item->getProperties(TRUE))) {
            // We normalize each individual value, so each can do their own casting,
            // if needed.
            $field_properties = TypedDataInternalPropertiesHelper::getNonInternalProperties($field_item);
            foreach ($field_properties as $property_name => $property) {
                $values[$property_name] = $this->serializer
                    ->normalize($property, $format, $context);
            }
            // Flatten if there is only a single property to normalize.
            $values = static::rasterizeValueRecursive(count($field_properties) == 1 ? reset($values) : $values);
        }
        else {
            $values = $field_item->getValue();
        }
        $normalization = new CacheableNormalization($context[CacheableNormalizerInterface::SERIALIZATION_CONTEXT_CACHEABILITY], $values);
        unset($context[CacheableNormalizerInterface::SERIALIZATION_CONTEXT_CACHEABILITY]);
        return $normalization;
    }
    
    /**
     * {@inheritdoc}
     */
    public function denormalize($data, $class, $format = NULL, array $context = []) {
        $item_definition = $context['field_definition']->getItemDefinition();
        assert($item_definition instanceof FieldItemDataDefinitionInterface);
        $field_item = $this->getFieldItemInstance($context['resource_type'], $item_definition);
        $this->checkForSerializedStrings($data, $class, $field_item);
        $property_definitions = $item_definition->getPropertyDefinitions();
        $serialized_property_names = $this->getCustomSerializedPropertyNames($field_item);
        $denormalize_property = function ($property_name, $property_value, $property_value_class, $format, $context) use ($serialized_property_names) {
            if ($this->serializer
                ->supportsDenormalization($property_value, $property_value_class, $format, $context)) {
                return $this->serializer
                    ->denormalize($property_value, $property_value_class, $format, $context);
            }
            else {
                if (in_array($property_name, $serialized_property_names, TRUE)) {
                    $property_value = serialize($property_value);
                }
                return $property_value;
            }
        };
        // Because e.g. the 'bundle' entity key field requires field values to not
        // be expanded to an array of all properties, we special-case single-value
        // properties.
        if (!is_array($data)) {
            // The NULL normalization means there is no value, hence we can return
            // early. Note that this is not just an optimization but a necessity for
            // field types without main properties (such as the "map" field type).
            if ($data === NULL) {
                return $data;
            }
            $property_value = $data;
            $property_name = $item_definition->getMainPropertyName();
            $property_value_class = $property_definitions[$property_name]->getClass();
            return $denormalize_property($property_name, $property_value, $property_value_class, $format, $context);
        }
        $data_internal = [];
        if (!empty($property_definitions)) {
            foreach ($data as $property_name => $property_value) {
                $property_value_class = $property_definitions[$property_name]->getClass();
                $data_internal[$property_name] = $denormalize_property($property_name, $property_value, $property_value_class, $format, $context);
            }
        }
        else {
            $data_internal = $data;
        }
        return $data_internal;
    }
    
    /**
     * Gets a field item instance for use with SerializedColumnNormalizerTrait.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type of the entity being denormalized.
     * @param \Drupal\Core\Field\TypedData\FieldItemDataDefinitionInterface $item_definition
     *   The field item definition of the instance to get.
     *
     * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
     * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
     */
    protected function getFieldItemInstance(ResourceType $resource_type, FieldItemDataDefinitionInterface $item_definition) {
        if ($bundle_key = $this->entityTypeManager
            ->getDefinition($resource_type->getEntityTypeId())
            ->getKey('bundle')) {
            $create_values = [
                $bundle_key => $resource_type->getBundle(),
            ];
        }
        else {
            $create_values = [];
        }
        $entity = $this->entityTypeManager
            ->getStorage($resource_type->getEntityTypeId())
            ->create($create_values);
        $field = $entity->get($item_definition->getFieldDefinition()
            ->getName());
        assert($field instanceof FieldItemListInterface);
        $field_item = $field->appendItem();
        assert($field_item instanceof FieldItemInterface);
        return $field_item;
    }

}