class EntityResource

class EntityResource extends ResourceBase implements DependentPluginInterface {
    use EntityResourceValidationTrait;
    use EntityResourceAccessTrait;
    
    /**
     * The entity type targeted by this resource.
     *
     * @var \Drupal\Core\Entity\EntityTypeInterface
     */
    protected $entityType;
    
    /**
     * The config factory.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * The link relation type manager used to create HTTP header links.
     *
     * @var \Drupal\Component\Plugin\PluginManagerInterface
     */
    protected $linkRelationTypeManager;
    
    /**
     * Constructs a Drupal\rest\Plugin\rest\resource\EntityResource object.
     *
     * @param array $configuration
     *   A configuration array containing information about the plugin instance.
     * @param string $plugin_id
     *   The plugin ID for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager
     * @param array $serializer_formats
     *   The available serialization formats.
     * @param \Psr\Log\LoggerInterface $logger
     *   A logger instance.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory.
     * @param \Drupal\Component\Plugin\PluginManagerInterface $link_relation_type_manager
     *   The link relation type manager.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, $serializer_formats, LoggerInterface $logger, ConfigFactoryInterface $config_factory, PluginManagerInterface $link_relation_type_manager) {
        parent::__construct($configuration, $plugin_id, $plugin_definition, $serializer_formats, $logger);
        $this->entityType = $entity_type_manager->getDefinition($plugin_definition['entity_type']);
        $this->configFactory = $config_factory;
        $this->linkRelationTypeManager = $link_relation_type_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('entity_type.manager'), $container->getParameter('serializer.formats'), $container->get('logger.factory')
            ->get('rest'), $container->get('config.factory'), $container->get('plugin.manager.link_relation_type'));
    }
    
    /**
     * Responds to entity GET requests.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity object.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The incoming request.
     *
     * @return \Drupal\rest\ResourceResponse
     *   The response containing the entity with its accessible fields.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\HttpException
     */
    public function get(EntityInterface $entity, Request $request) {
        $response = new ResourceResponse($entity, 200);
        // @todo Either remove the line below or remove this todo in https://www.drupal.org/project/drupal/issues/2973356
        $response->addCacheableDependency($request->attributes
            ->get(AccessAwareRouterInterface::ACCESS_RESULT));
        $response->addCacheableDependency($entity);
        if ($entity instanceof FieldableEntityInterface) {
            foreach ($entity as $field_name => $field) {
                
                /** @var \Drupal\Core\Field\FieldItemListInterface $field */
                $field_access = $field->access('view', NULL, TRUE);
                $response->addCacheableDependency($field_access);
                if (!$field_access->isAllowed()) {
                    $entity->set($field_name, NULL);
                }
            }
        }
        $this->addLinkHeaders($entity, $response);
        return $response;
    }
    
    /**
     * Responds to entity POST requests and saves the new entity.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity.
     *
     * @return \Drupal\rest\ModifiedResourceResponse
     *   The HTTP response object.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\HttpException
     */
    public function post(?EntityInterface $entity = NULL) {
        if ($entity == NULL) {
            throw new BadRequestHttpException('No entity content received.');
        }
        $entity_access = $entity->access('create', NULL, TRUE);
        if (!$entity_access->isAllowed()) {
            throw new AccessDeniedHttpException($entity_access->getReason() ?: $this->generateFallbackAccessDeniedMessage($entity, 'create'));
        }
        $definition = $this->getPluginDefinition();
        // Verify that the deserialized entity is of the type that we expect to
        // prevent security issues.
        if ($entity->getEntityTypeId() != $definition['entity_type']) {
            throw new BadRequestHttpException('Invalid entity type');
        }
        // POSTed entities must not have an ID set, because we always want to create
        // new entities here.
        if (!$entity->isNew()) {
            throw new BadRequestHttpException('Only new entities can be created');
        }
        $this->checkEditFieldAccess($entity);
        // Validate the received data before saving.
        $this->validate($entity);
        try {
            $entity->save();
            $this->logger
                ->notice('Created entity %type with ID %id.', [
                '%type' => $entity->getEntityTypeId(),
                '%id' => $entity->id(),
            ]);
            // 201 Created responses return the newly created entity in the response
            // body. These responses are not cacheable, so we add no cacheability
            // metadata here.
            $headers = [];
            if (in_array('canonical', $entity->uriRelationships(), TRUE)) {
                $url = $entity->toUrl('canonical', [
                    'absolute' => TRUE,
                ])
                    ->toString(TRUE);
                $headers['Location'] = $url->getGeneratedUrl();
            }
            return new ModifiedResourceResponse($entity, 201, $headers);
        } catch (EntityStorageException $e) {
            throw new HttpException(500, 'Internal Server Error', $e);
        }
    }
    
    /**
     * Responds to entity PATCH requests.
     *
     * @param \Drupal\Core\Entity\EntityInterface $original_entity
     *   The original entity object.
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity.
     *
     * @return \Drupal\rest\ModifiedResourceResponse
     *   The HTTP response object.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\HttpException
     */
    public function patch(EntityInterface $original_entity, ?EntityInterface $entity = NULL) {
        if ($entity == NULL) {
            throw new BadRequestHttpException('No entity content received.');
        }
        $definition = $this->getPluginDefinition();
        if ($entity->getEntityTypeId() != $definition['entity_type']) {
            throw new BadRequestHttpException('Invalid entity type');
        }
        // Overwrite the received fields.
        // @todo Remove $changed_fields in https://www.drupal.org/project/drupal/issues/2862574.
        $changed_fields = [];
        foreach ($entity->_restSubmittedFields as $field_name) {
            $field = $entity->get($field_name);
            // It is not possible to set the language to NULL as it is automatically
            // re-initialized. As it must not be empty, skip it if it is.
            // @todo Remove in https://www.drupal.org/project/drupal/issues/2933408.
            if ($entity->getEntityType()
                ->hasKey('langcode') && $field_name === $entity->getEntityType()
                ->getKey('langcode') && $field->isEmpty()) {
                continue;
            }
            if ($this->checkPatchFieldAccess($original_entity->get($field_name), $field)) {
                $changed_fields[] = $field_name;
                $original_entity->set($field_name, $field->getValue());
            }
        }
        // If no fields are changed, we can send a response immediately!
        if (empty($changed_fields)) {
            return new ModifiedResourceResponse($original_entity, 200);
        }
        // Validate the received data before saving.
        $this->validate($original_entity, $changed_fields);
        try {
            $original_entity->save();
            $this->logger
                ->notice('Updated entity %type with ID %id.', [
                '%type' => $original_entity->getEntityTypeId(),
                '%id' => $original_entity->id(),
            ]);
            // Return the updated entity in the response body.
            return new ModifiedResourceResponse($original_entity, 200);
        } catch (EntityStorageException $e) {
            throw new HttpException(500, 'Internal Server Error', $e);
        }
    }
    
    /**
     * Checks whether the given field should be PATCHed.
     *
     * @param \Drupal\Core\Field\FieldItemListInterface $original_field
     *   The original (stored) value for the field.
     * @param \Drupal\Core\Field\FieldItemListInterface $received_field
     *   The received value for the field.
     *
     * @return bool
     *   Whether the field should be PATCHed or not.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
     *   Thrown when the user sending the request is not allowed to update the
     *   field. Only thrown when the user could not abuse this information to
     *   determine the stored value.
     *
     * @internal
     */
    protected function checkPatchFieldAccess(FieldItemListInterface $original_field, FieldItemListInterface $received_field) {
        // The user might not have access to edit the field, but still needs to
        // submit the current field value as part of the PATCH request. For
        // example, the entity keys required by denormalizers. Therefore, if the
        // received value equals the stored value, return FALSE without throwing an
        // exception. But only for fields that the user has access to view, because
        // the user has no legitimate way of knowing the current value of fields
        // that they are not allowed to view, and we must not make the presence or
        // absence of a 403 response a way to find that out.
        if ($original_field->access('view') && $original_field->equals($received_field)) {
            return FALSE;
        }
        // If the user is allowed to edit the field, it is always safe to set the
        // received value. We may be setting an unchanged value, but that is ok.
        $field_edit_access = $original_field->access('edit', NULL, TRUE);
        if ($field_edit_access->isAllowed()) {
            return TRUE;
        }
        // It's helpful and safe to let the user know when they are not allowed to
        // update a field.
        $field_name = $received_field->getName();
        $error_message = "Access denied on updating field '{$field_name}'.";
        if ($field_edit_access instanceof AccessResultReasonInterface) {
            $reason = $field_edit_access->getReason();
            if ($reason) {
                $error_message .= ' ' . $reason;
            }
        }
        throw new AccessDeniedHttpException($error_message);
    }
    
    /**
     * Responds to entity DELETE requests.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity object.
     *
     * @return \Drupal\rest\ModifiedResourceResponse
     *   The HTTP response object.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\HttpException
     */
    public function delete(EntityInterface $entity) {
        try {
            $entity->delete();
            $this->logger
                ->notice('Deleted entity %type with ID %id.', [
                '%type' => $entity->getEntityTypeId(),
                '%id' => $entity->id(),
            ]);
            // DELETE responses have an empty body.
            return new ModifiedResourceResponse(NULL, 204);
        } catch (EntityStorageException $e) {
            throw new HttpException(500, 'Internal Server Error', $e);
        }
    }
    
    /**
     * Generates a fallback access denied message, when no specific reason is set.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity object.
     * @param string $operation
     *   The disallowed entity operation.
     *
     * @return string
     *   The proper message to display in the AccessDeniedHttpException.
     */
    protected function generateFallbackAccessDeniedMessage(EntityInterface $entity, $operation) {
        $message = "You are not authorized to {$operation} this {$entity->getEntityTypeId()} entity";
        if ($entity->bundle() !== $entity->getEntityTypeId()) {
            $message .= " of bundle {$entity->bundle()}";
        }
        return "{$message}.";
    }
    
    /**
     * {@inheritdoc}
     */
    public function permissions() {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getBaseRoute($canonical_path, $method) {
        $route = parent::getBaseRoute($canonical_path, $method);
        switch ($method) {
            case 'GET':
                $route->setRequirement('_entity_access', $this->entityType
                    ->id() . '.view');
                break;
            case 'POST':
                $route->setRequirement('_entity_create_any_access', $this->entityType
                    ->id());
                $route->setOption('_ignore_create_bundle_access', TRUE);
                break;
            case 'PATCH':
                $route->setRequirement('_entity_access', $this->entityType
                    ->id() . '.update');
                break;
            case 'DELETE':
                $route->setRequirement('_entity_access', $this->entityType
                    ->id() . '.delete');
                break;
        }
        $definition = $this->getPluginDefinition();
        $parameters = $route->getOption('parameters') ?: [];
        $parameters[$definition['entity_type']]['type'] = 'entity:' . $definition['entity_type'];
        $route->setOption('parameters', $parameters);
        return $route;
    }
    
    /**
     * {@inheritdoc}
     */
    public function availableMethods() {
        $methods = parent::availableMethods();
        if ($this->isConfigEntityResource()) {
            // Currently only GET is supported for Config Entities.
            // @todo Remove when supported https://www.drupal.org/node/2300677
            $unsupported_methods = [
                'POST',
                'PUT',
                'DELETE',
                'PATCH',
            ];
            $methods = array_diff($methods, $unsupported_methods);
        }
        return $methods;
    }
    
    /**
     * Checks if this resource is for a Config Entity.
     *
     * @return bool
     *   TRUE if the entity is a Config Entity, FALSE otherwise.
     */
    protected function isConfigEntityResource() {
        return $this->entityType instanceof ConfigEntityType;
    }
    
    /**
     * {@inheritdoc}
     */
    public function calculateDependencies() {
        if (isset($this->entityType)) {
            return [
                'module' => [
                    $this->entityType
                        ->getProvider(),
                ],
            ];
        }
    }
    
    /**
     * Adds link headers to a response.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity.
     * @param \Symfony\Component\HttpFoundation\Response $response
     *   The response.
     *
     * @see https://tools.ietf.org/html/rfc5988#section-5
     */
    protected function addLinkHeaders(EntityInterface $entity, Response $response) {
        foreach ($entity->uriRelationships() as $relation_name) {
            if ($this->linkRelationTypeManager
                ->hasDefinition($relation_name)) {
                
                /** @var \Drupal\Core\Http\LinkRelationTypeInterface $link_relation_type */
                $link_relation_type = $this->linkRelationTypeManager
                    ->createInstance($relation_name);
                $generator_url = $entity->toUrl($relation_name)
                    ->setAbsolute(TRUE)
                    ->toString(TRUE);
                if ($response instanceof CacheableResponseInterface) {
                    $response->addCacheableDependency($generator_url);
                }
                $uri = $generator_url->getGeneratedUrl();
                $relationship = $link_relation_type->isRegistered() ? $link_relation_type->getRegisteredName() : $link_relation_type->getExtensionUri();
                $link_header = '<' . $uri . '>; rel="' . $relationship . '"';
                $response->headers
                    ->set('Link', $link_header, FALSE);
            }
        }
    }

}