class EntityResource

class EntityResource {
    use EntityValidationTrait;
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The field manager.
     *
     * @var \Drupal\Core\Entity\EntityFieldManagerInterface
     */
    protected $fieldManager;
    
    /**
     * The resource type repository.
     *
     * @var \Drupal\jsonapi\ResourceType\ResourceTypeRepositoryInterface
     */
    protected $resourceTypeRepository;
    
    /**
     * The renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * The entity repository.
     *
     * @var \Drupal\Core\Entity\EntityRepositoryInterface
     */
    protected $entityRepository;
    
    /**
     * The include resolver.
     *
     * @var \Drupal\jsonapi\IncludeResolver
     */
    protected $includeResolver;
    
    /**
     * The JSON:API entity access checker.
     *
     * @var \Drupal\jsonapi\Access\EntityAccessChecker
     */
    protected $entityAccessChecker;
    
    /**
     * The JSON:API field resolver.
     *
     * @var \Drupal\jsonapi\Context\FieldResolver
     */
    protected $fieldResolver;
    
    /**
     * The JSON:API serializer.
     *
     * @var \Symfony\Component\Serializer\SerializerInterface|\Symfony\Component\Serializer\Normalizer\DenormalizerInterface
     */
    protected $serializer;
    
    /**
     * The time service.
     *
     * @var \Drupal\Component\Datetime\TimeInterface
     */
    protected $time;
    
    /**
     * The current user account.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $user;
    
    /**
     * Instantiates an EntityResource object.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Entity\EntityFieldManagerInterface $field_manager
     *   The entity type field manager.
     * @param \Drupal\jsonapi\ResourceType\ResourceTypeRepositoryInterface $resource_type_repository
     *   The JSON:API resource type repository.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer.
     * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
     *   The entity repository.
     * @param \Drupal\jsonapi\IncludeResolver $include_resolver
     *   The include resolver.
     * @param \Drupal\jsonapi\Access\EntityAccessChecker $entity_access_checker
     *   The JSON:API entity access checker.
     * @param \Drupal\jsonapi\Context\FieldResolver $field_resolver
     *   The JSON:API field resolver.
     * @param \Symfony\Component\Serializer\SerializerInterface|\Symfony\Component\Serializer\Normalizer\DenormalizerInterface $serializer
     *   The JSON:API serializer.
     * @param \Drupal\Component\Datetime\TimeInterface $time
     *   The time service.
     * @param \Drupal\Core\Session\AccountInterface $user
     *   The current user account.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, EntityFieldManagerInterface $field_manager, ResourceTypeRepositoryInterface $resource_type_repository, RendererInterface $renderer, EntityRepositoryInterface $entity_repository, IncludeResolver $include_resolver, EntityAccessChecker $entity_access_checker, FieldResolver $field_resolver, SerializerInterface $serializer, TimeInterface $time, AccountInterface $user) {
        $this->entityTypeManager = $entity_type_manager;
        $this->fieldManager = $field_manager;
        $this->resourceTypeRepository = $resource_type_repository;
        $this->renderer = $renderer;
        $this->entityRepository = $entity_repository;
        $this->includeResolver = $include_resolver;
        $this->entityAccessChecker = $entity_access_checker;
        $this->fieldResolver = $field_resolver;
        $this->serializer = $serializer;
        $this->time = $time;
        $this->user = $user;
    }
    
    /**
     * Gets the individual entity.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The loaded entity.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     *
     * @throws \Drupal\jsonapi\Exception\EntityAccessDeniedHttpException
     *   Thrown when access to the entity is not allowed.
     */
    public function getIndividual(EntityInterface $entity, Request $request) {
        $resource_object = $this->entityAccessChecker
            ->getAccessCheckedResourceObject($entity);
        if ($resource_object instanceof EntityAccessDeniedHttpException) {
            throw $resource_object;
        }
        $primary_data = new ResourceObjectData([
            $resource_object,
        ], 1);
        $response = $this->buildWrappedResponse($primary_data, $request, $this->getIncludes($request, $primary_data));
        return $response;
    }
    
    /**
     * Creates an individual entity.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type for the request to be served.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\ConflictHttpException
     *   Thrown when the entity already exists.
     * @throws \Drupal\jsonapi\Exception\UnprocessableHttpEntityException
     *   Thrown when the entity does not pass validation.
     */
    public function createIndividual(ResourceType $resource_type, Request $request) {
        $parsed_entity = $this->deserialize($resource_type, $request, JsonApiDocumentTopLevel::class);
        if ($parsed_entity instanceof FieldableEntityInterface) {
            // Only check 'edit' permissions for fields that were actually submitted
            // by the user. Field access makes no distinction between 'create' and
            // 'update', so the 'edit' operation is used here.
            $document = Json::decode($request->getContent());
            $field_mapping = array_map(function (ResourceTypeField $field) {
                return $field->getPublicName();
            }, $resource_type->getFields());
            // User resource objects contain a read-only attribute that is not a
            // real field on the user entity type.
            // @see \Drupal\jsonapi\JsonApiResource\ResourceObject::extractContentEntityFields()
            // @todo: eliminate this special casing in https://www.drupal.org/project/drupal/issues/3079254.
            if ($resource_type->getEntityTypeId() === 'user') {
                $field_mapping = array_diff($field_mapping, [
                    $resource_type->getPublicName('display_name'),
                ]);
            }
            foreach ([
                'attributes',
                'relationships',
            ] as $data_member_name) {
                if (isset($document['data'][$data_member_name])) {
                    foreach (array_intersect_key(array_flip($field_mapping), $document['data'][$data_member_name]) as $internal_field_name) {
                        $field_access = $parsed_entity->get($internal_field_name)
                            ->access('edit', NULL, TRUE);
                        if (!$field_access->isAllowed()) {
                            $public_field_name = $field_mapping[$internal_field_name];
                            throw new EntityAccessDeniedHttpException(NULL, $field_access, "/data/{$data_member_name}/{$public_field_name}", sprintf('The current user is not allowed to POST the selected field (%s).', $public_field_name));
                        }
                    }
                }
            }
        }
        static::validate($parsed_entity);
        // Return a 409 Conflict response in accordance with the JSON:API spec. See
        // http://jsonapi.org/format/#crud-creating-responses-409.
        if ($this->entityExists($parsed_entity)) {
            throw new ConflictHttpException('Conflict: Entity already exists.');
        }
        $parsed_entity->save();
        // Build response object.
        $resource_object = ResourceObject::createFromEntity($resource_type, $parsed_entity);
        $primary_data = new ResourceObjectData([
            $resource_object,
        ], 1);
        $response = $this->buildWrappedResponse($primary_data, $request, $this->getIncludes($request, $primary_data), 201);
        // According to JSON:API specification, when a new entity was created
        // we should send "Location" header to the frontend.
        if ($resource_type->isLocatable()) {
            $url = $resource_object->toUrl()
                ->setAbsolute()
                ->toString(TRUE);
            $response->headers
                ->set('Location', $url->getGeneratedUrl());
        }
        // Return response object with updated headers info.
        return $response;
    }
    
    /**
     * Patches an individual entity.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type for the request to be served.
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The loaded entity.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown when the selected entity does not match the id in th payload.
     * @throws \Drupal\jsonapi\Exception\UnprocessableHttpEntityException
     *   Thrown when the patched entity does not pass validation.
     */
    public function patchIndividual(ResourceType $resource_type, EntityInterface $entity, Request $request) {
        if ($entity instanceof RevisionableInterface && !($entity->isLatestRevision() && $entity->isDefaultRevision())) {
            throw new BadRequestHttpException('Updating a resource object that has a working copy is not yet supported. See https://www.drupal.org/project/drupal/issues/2795279.');
        }
        $parsed_entity = $this->deserialize($resource_type, $request, JsonApiDocumentTopLevel::class);
        $body = Json::decode($request->getContent());
        $data = $body['data'];
        if ($data['id'] != $entity->uuid()) {
            throw new BadRequestHttpException(sprintf('The selected entity (%s) does not match the ID in the payload (%s).', $entity->uuid(), $data['id']));
        }
        $data += [
            'attributes' => [],
            'relationships' => [],
        ];
        $field_names = array_map([
            $resource_type,
            'getInternalName',
        ], array_merge(array_keys($data['attributes']), array_keys($data['relationships'])));
        // User resource objects contain a read-only attribute that is not a real
        // field on the user entity type.
        // @see \Drupal\jsonapi\JsonApiResource\ResourceObject::extractContentEntityFields()
        // @todo: eliminate this special casing in https://www.drupal.org/project/drupal/issues/3079254.
        if ($entity->getEntityTypeId() === 'user') {
            $field_names = array_diff($field_names, [
                $resource_type->getPublicName('display_name'),
            ]);
        }
        array_reduce($field_names, function (EntityInterface $destination, $field_name) use ($resource_type, $parsed_entity) {
            $this->updateEntityField($resource_type, $parsed_entity, $destination, $field_name);
            return $destination;
        }, $entity);
        static::validate($entity, $field_names);
        // Set revision data details for revisionable entities.
        if ($entity->getEntityType()
            ->isRevisionable()) {
            if ($bundle_entity_type = $entity->getEntityType()
                ->getBundleEntityType()) {
                $bundle_entity = $this->entityTypeManager
                    ->getStorage($bundle_entity_type)
                    ->load($entity->bundle());
                if ($bundle_entity instanceof RevisionableEntityBundleInterface) {
                    $entity->setNewRevision($bundle_entity->shouldCreateNewRevision());
                }
            }
            if ($entity instanceof RevisionLogInterface && $entity->isNewRevision()) {
                $entity->setRevisionUserId($this->user
                    ->id());
                $entity->setRevisionCreationTime($this->time
                    ->getRequestTime());
            }
        }
        $entity->save();
        $primary_data = new ResourceObjectData([
            ResourceObject::createFromEntity($resource_type, $entity),
        ], 1);
        return $this->buildWrappedResponse($primary_data, $request, $this->getIncludes($request, $primary_data));
    }
    
    /**
     * Deletes an individual entity.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The loaded entity.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     */
    public function deleteIndividual(EntityInterface $entity) {
        // @todo Replace with entity handlers in: https://www.drupal.org/project/drupal/issues/3230434
        if ($entity->getEntityTypeId() === 'user') {
            $cancel_method = \Drupal::service('config.factory')->get('user.settings')
                ->get('cancel_method');
            // Allow other modules to act.
            user_cancel([], $entity->id(), $cancel_method);
            // Since user_cancel() is not invoked via Form API, batch processing
            // needs to be invoked manually.
            $batch =& batch_get();
            // Mark this batch as non-progressive to bypass the progress bar and
            // redirect.
            $batch['progressive'] = FALSE;
            batch_process();
        }
        else {
            $entity->delete();
        }
        return new ResourceResponse(NULL, 204);
    }
    
    /**
     * Gets the collection of entities.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type for the request to be served.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     *
     * @throws \Drupal\Core\Http\Exception\CacheableBadRequestHttpException
     *   Thrown when filtering on a config entity which does not support it.
     */
    public function getCollection(ResourceType $resource_type, Request $request) {
        // Instantiate the query for the filtering.
        $entity_type_id = $resource_type->getEntityTypeId();
        $params = $this->getJsonApiParams($request, $resource_type);
        $query_cacheability = new CacheableMetadata();
        $query = $this->getCollectionQuery($resource_type, $params, $query_cacheability);
        // If the request is for the latest revision, toggle it on entity query.
        if ($request->get(ResourceVersionRouteEnhancer::WORKING_COPIES_REQUESTED, FALSE)) {
            $query->latestRevision();
        }
        try {
            $results = $this->executeQueryInRenderContext($query, $query_cacheability);
        } catch (\LogicException $e) {
            // Ensure good DX when an entity query involves a config entity type.
            // For example: getting users with a particular role, which is a config
            // entity type: https://www.drupal.org/project/drupal/issues/2959445.
            // @todo Remove the message parsing in https://www.drupal.org/project/drupal/issues/3028967.
            if (strpos($e->getMessage(), 'Getting the base fields is not supported for entity type') === 0) {
                preg_match('/entity type (.*)\\./', $e->getMessage(), $matches);
                $config_entity_type_id = $matches[1];
                $cacheability = (new CacheableMetadata())->addCacheContexts([
                    'url.path',
                    'url.query_args:filter',
                ]);
                throw new CacheableBadRequestHttpException($cacheability, sprintf("Filtering on config entities is not supported by Drupal's entity API. You tried to filter on a %s config entity.", $config_entity_type_id));
            }
            else {
                throw $e;
            }
        }
        $storage = $this->entityTypeManager
            ->getStorage($entity_type_id);
        // We request N+1 items to find out if there is a next page for the pager.
        // We may need to remove that extra item before loading the entities.
        $pager_size = $query->getMetaData('pager_size');
        if ($has_next_page = $pager_size < count($results)) {
            // Drop the last result.
            array_pop($results);
        }
        // Each item of the collection data contains an array with 'entity' and
        // 'access' elements.
        $collection_data = $this->loadEntitiesWithAccess($storage, $results, $request->get(ResourceVersionRouteEnhancer::WORKING_COPIES_REQUESTED, FALSE));
        $primary_data = new ResourceObjectData($collection_data);
        $primary_data->setHasNextPage($has_next_page);
        // Calculate all the results and pass into a JSON:API Data object.
        $count_query_cacheability = new CacheableMetadata();
        if ($resource_type->includeCount()) {
            $count_query = $this->getCollectionCountQuery($resource_type, $params, $count_query_cacheability);
            $total_results = $this->executeQueryInRenderContext($count_query, $count_query_cacheability);
            $primary_data->setTotalCount($total_results);
        }
        $response = $this->respondWithCollection($primary_data, $this->getIncludes($request, $primary_data), $request, $resource_type, $params[OffsetPage::KEY_NAME]);
        $response->addCacheableDependency($query_cacheability);
        $response->addCacheableDependency($count_query_cacheability);
        $response->addCacheableDependency((new CacheableMetadata())->addCacheContexts([
            'url.query_args:filter',
            'url.query_args:sort',
            'url.query_args:page',
        ]));
        if ($resource_type->isVersionable()) {
            $response->addCacheableDependency((new CacheableMetadata())->addCacheContexts([
                ResourceVersionRouteEnhancer::CACHE_CONTEXT,
            ]));
        }
        return $response;
    }
    
    /**
     * Executes the query in a render context, to catch bubbled cacheability.
     *
     * @param \Drupal\Core\Entity\Query\QueryInterface $query
     *   The query to execute to get the return results.
     * @param \Drupal\Core\Cache\CacheableMetadata $query_cacheability
     *   The value object to carry the query cacheability.
     *
     * @return int|array
     *   Returns an integer for count queries or an array of IDs. The values of
     *   the array are always entity IDs. The keys will be revision IDs if the
     *   entity supports revision and entity IDs if not.
     *
     * @see node_query_node_access_alter()
     * @see https://www.drupal.org/project/drupal/issues/2557815
     * @see https://www.drupal.org/project/drupal/issues/2794385
     * @todo Remove this after https://www.drupal.org/project/drupal/issues/3028976 is fixed.
     */
    protected function executeQueryInRenderContext(QueryInterface $query, CacheableMetadata $query_cacheability) {
        $context = new RenderContext();
        $results = $this->renderer
            ->executeInRenderContext($context, function () use ($query) {
            return $query->execute();
        });
        if (!$context->isEmpty()) {
            $query_cacheability->addCacheableDependency($context->pop());
        }
        return $results;
    }
    
    /**
     * Gets the related resource.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type for the request to be served.
     * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
     *   The requested entity.
     * @param string $related
     *   The related field name.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     */
    public function getRelated(ResourceType $resource_type, FieldableEntityInterface $entity, $related, Request $request) {
        
        /** @var \Drupal\Core\Field\EntityReferenceFieldItemListInterface $field_list */
        $resource_relationship = $resource_type->getFieldByPublicName($related);
        $field_list = $entity->get($resource_relationship->getInternalName());
        // Remove the entities pointing to a resource that may be disabled. Even
        // though the normalizer skips disabled references, we can avoid unnecessary
        // work by checking here too.
        
        /** @var \Drupal\Core\Entity\EntityInterface[] $referenced_entities */
        $referenced_entities = array_filter($field_list->referencedEntities(), function (EntityInterface $entity) {
            return (bool) $this->resourceTypeRepository
                ->get($entity->getEntityTypeId(), $entity->bundle());
        });
        $collection_data = [];
        foreach ($referenced_entities as $referenced_entity) {
            $collection_data[] = $this->entityAccessChecker
                ->getAccessCheckedResourceObject($referenced_entity);
        }
        $primary_data = new ResourceObjectData($collection_data, $resource_relationship->hasOne() ? 1 : -1);
        $response = $this->buildWrappedResponse($primary_data, $request, $this->getIncludes($request, $primary_data));
        // $response does not contain the entity list cache tag. We add the
        // cacheable metadata for the finite list of entities in the relationship.
        if ($response instanceof CacheableResponseInterface) {
            $response->addCacheableDependency($entity);
        }
        return $response;
    }
    
    /**
     * Gets the relationship of an entity.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The base JSON:API resource type for the request to be served.
     * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
     *   The requested entity.
     * @param string $related
     *   The related field name.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param int $response_code
     *   The response code. Defaults to 200.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     */
    public function getRelationship(ResourceType $resource_type, FieldableEntityInterface $entity, $related, Request $request, $response_code = 200) {
        
        /** @var \Drupal\Core\Field\EntityReferenceFieldItemListInterface $field_list */
        $field_list = $entity->get($resource_type->getInternalName($related));
        // Access will have already been checked by the RelationshipRouteAccessCheck
        // service, so we don't need to call ::getAccessCheckedResourceObject().
        $resource_object = ResourceObject::createFromEntity($resource_type, $entity);
        $relationship = Relationship::createFromEntityReferenceField($resource_object, $field_list);
        $response = $this->buildWrappedResponse($relationship, $request, $this->getIncludes($request, $resource_object), $response_code);
        // Add the host entity as a cacheable dependency.
        if ($response instanceof CacheableResponseInterface) {
            $response->addCacheableDependency($entity);
        }
        return $response;
    }
    
    /**
     * Adds a relationship to a to-many relationship.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The base JSON:API resource type for the request to be served.
     * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
     *   The requested entity.
     * @param string $related
     *   The related field name.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     *
     * @throws \Drupal\jsonapi\Exception\EntityAccessDeniedHttpException
     *   Thrown when the current user is not allowed to PATCH the selected
     *   field(s).
     * @throws \Symfony\Component\HttpKernel\Exception\ConflictHttpException
     *   Thrown when POSTing to a "to-one" relationship.
     * @throws \Drupal\Core\Entity\EntityStorageException
     *   Thrown when the underlying entity cannot be saved.
     * @throws \Drupal\jsonapi\Exception\UnprocessableHttpEntityException
     *   Thrown when the updated entity does not pass validation.
     */
    public function addToRelationshipData(ResourceType $resource_type, FieldableEntityInterface $entity, $related, Request $request) {
        $resource_identifiers = $this->deserialize($resource_type, $request, ResourceIdentifier::class, $related);
        $internal_relationship_field_name = $resource_type->getInternalName($related);
        // According to the specification, you are only allowed to POST to a
        // relationship if it is a to-many relationship.
        
        /** @var \Drupal\Core\Field\EntityReferenceFieldItemListInterface $field_list */
        $field_list = $entity->{$internal_relationship_field_name};
        
        /** @var \Drupal\field\Entity\FieldConfig $field_definition */
        $field_definition = $field_list->getFieldDefinition();
        $is_multiple = $field_definition->getFieldStorageDefinition()
            ->isMultiple();
        if (!$is_multiple) {
            throw new ConflictHttpException(sprintf('You can only POST to to-many relationships. %s is a to-one relationship.', $related));
        }
        $original_resource_identifiers = ResourceIdentifier::toResourceIdentifiersWithArityRequired($field_list);
        $new_resource_identifiers = array_udiff(ResourceIdentifier::deduplicate(array_merge($original_resource_identifiers, $resource_identifiers)), $original_resource_identifiers, [
            ResourceIdentifier::class,
            'compare',
        ]);
        // There are no relationships that need to be added so we can exit early.
        if (empty($new_resource_identifiers)) {
            $status = static::relationshipResponseRequiresBody($resource_identifiers, $original_resource_identifiers) ? 200 : 204;
            return $this->getRelationship($resource_type, $entity, $related, $request, $status);
        }
        $main_property_name = $field_definition->getItemDefinition()
            ->getMainPropertyName();
        foreach ($new_resource_identifiers as $new_resource_identifier) {
            $new_field_value = [
                $main_property_name => $this->getEntityFromResourceIdentifier($new_resource_identifier)
                    ->id(),
            ];
            // Remove `arity` from the received extra properties, otherwise this
            // will fail field validation.
            $new_field_value += array_diff_key($new_resource_identifier->getMeta(), array_flip([
                ResourceIdentifier::ARITY_KEY,
            ]));
            $field_list->appendItem($new_field_value);
        }
        $this->validate($entity);
        $entity->save();
        $final_resource_identifiers = ResourceIdentifier::toResourceIdentifiersWithArityRequired($field_list);
        $status = static::relationshipResponseRequiresBody($resource_identifiers, $final_resource_identifiers) ? 200 : 204;
        return $this->getRelationship($resource_type, $entity, $related, $request, $status);
    }
    
    /**
     * Updates the relationship of an entity.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The base JSON:API resource type for the request to be served.
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The requested entity.
     * @param string $related
     *   The related field name.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     *
     * @throws \Drupal\Core\Entity\EntityStorageException
     *   Thrown when the underlying entity cannot be saved.
     * @throws \Drupal\jsonapi\Exception\UnprocessableHttpEntityException
     *   Thrown when the updated entity does not pass validation.
     */
    public function replaceRelationshipData(ResourceType $resource_type, EntityInterface $entity, $related, Request $request) {
        
        /** @var \Drupal\Core\Field\EntityReferenceFieldItemListInterface $resource_identifiers */
        $resource_identifiers = $this->deserialize($resource_type, $request, ResourceIdentifier::class, $related);
        $internal_relationship_field_name = $resource_type->getInternalName($related);
        // According to the specification, PATCH works a little bit different if the
        // relationship is to-one or to-many.
        
        /** @var \Drupal\Core\Field\EntityReferenceFieldItemListInterface $field_list */
        $field_list = $entity->{$internal_relationship_field_name};
        $field_definition = $field_list->getFieldDefinition();
        $is_multiple = $field_definition->getFieldStorageDefinition()
            ->isMultiple();
        $method = $is_multiple ? 'doPatchMultipleRelationship' : 'doPatchIndividualRelationship';
        $this->{$method}($entity, $resource_identifiers, $field_definition);
        $this->validate($entity);
        $entity->save();
        $requires_response = static::relationshipResponseRequiresBody($resource_identifiers, ResourceIdentifier::toResourceIdentifiersWithArityRequired($field_list));
        return $this->getRelationship($resource_type, $entity, $related, $request, $requires_response ? 200 : 204);
    }
    
    /**
     * Update a to-one relationship.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The requested entity.
     * @param \Drupal\jsonapi\JsonApiResource\ResourceIdentifier[] $resource_identifiers
     *   The client-sent resource identifiers which should be set on the given
     *   entity. Should be an empty array or an array with a single value.
     * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
     *   The field definition of the entity field to be updated.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown when a "to-one" relationship is not provided.
     */
    protected function doPatchIndividualRelationship(EntityInterface $entity, array $resource_identifiers, FieldDefinitionInterface $field_definition) {
        if (count($resource_identifiers) > 1) {
            throw new BadRequestHttpException(sprintf('Provide a single relationship so to-one relationship fields (%s).', $field_definition->getName()));
        }
        $this->doPatchMultipleRelationship($entity, $resource_identifiers, $field_definition);
    }
    
    /**
     * Update a to-many relationship.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The requested entity.
     * @param \Drupal\jsonapi\JsonApiResource\ResourceIdentifier[] $resource_identifiers
     *   The client-sent resource identifiers which should be set on the given
     *   entity.
     * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
     *   The field definition of the entity field to be updated.
     */
    protected function doPatchMultipleRelationship(EntityInterface $entity, array $resource_identifiers, FieldDefinitionInterface $field_definition) {
        $main_property_name = $field_definition->getItemDefinition()
            ->getMainPropertyName();
        $entity->{$field_definition->getName()} = array_map(function (ResourceIdentifier $resource_identifier) use ($main_property_name) {
            $field_properties = [
                $main_property_name => $this->getEntityFromResourceIdentifier($resource_identifier)
                    ->id(),
            ];
            // Remove `arity` from the received extra properties, otherwise this
            // will fail field validation.
            $field_properties += array_diff_key($resource_identifier->getMeta(), array_flip([
                ResourceIdentifier::ARITY_KEY,
            ]));
            return $field_properties;
        }, $resource_identifiers);
    }
    
    /**
     * Deletes the relationship of an entity.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The base JSON:API resource type for the request to be served.
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The requested entity.
     * @param string $related
     *   The related field name.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown when not body was provided for the DELETE operation.
     * @throws \Symfony\Component\HttpKernel\Exception\ConflictHttpException
     *   Thrown when deleting a "to-one" relationship.
     * @throws \Drupal\Core\Entity\EntityStorageException
     *   Thrown when the underlying entity cannot be saved.
     */
    public function removeFromRelationshipData(ResourceType $resource_type, EntityInterface $entity, $related, Request $request) {
        $resource_identifiers = $this->deserialize($resource_type, $request, ResourceIdentifier::class, $related);
        $internal_relationship_field_name = $resource_type->getInternalName($related);
        
        /** @var \Drupal\Core\Field\EntityReferenceFieldItemListInterface $field_list */
        $field_list = $entity->{$internal_relationship_field_name};
        $is_multiple = $field_list->getFieldDefinition()
            ->getFieldStorageDefinition()
            ->isMultiple();
        if (!$is_multiple) {
            throw new ConflictHttpException(sprintf('You can only DELETE from to-many relationships. %s is a to-one relationship.', $related));
        }
        // Compute the list of current values and remove the ones in the payload.
        $original_resource_identifiers = ResourceIdentifier::toResourceIdentifiersWithArityRequired($field_list);
        $removed_resource_identifiers = array_uintersect($resource_identifiers, $original_resource_identifiers, [
            ResourceIdentifier::class,
            'compare',
        ]);
        $deltas_to_be_removed = [];
        foreach ($removed_resource_identifiers as $removed_resource_identifier) {
            foreach ($original_resource_identifiers as $delta => $existing_resource_identifier) {
                // Identify the field item deltas which should be removed.
                if (ResourceIdentifier::isDuplicate($removed_resource_identifier, $existing_resource_identifier)) {
                    $deltas_to_be_removed[] = $delta;
                }
            }
        }
        // Field item deltas are reset when an item is removed. This removes
        // items in descending order so that the deltas yet to be removed will
        // continue to exist.
        rsort($deltas_to_be_removed);
        foreach ($deltas_to_be_removed as $delta) {
            $field_list->removeItem($delta);
        }
        // Save the entity and return the response object.
        static::validate($entity);
        $entity->save();
        return $this->getRelationship($resource_type, $entity, $related, $request, 204);
    }
    
    /**
     * Deserializes a request body, if any.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type for the current request.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param string $class
     *   The class into which the request data needs to be deserialized.
     * @param string $relationship_field_name
     *   The public relationship field name of the data to be deserialized if the
     *   incoming request is for a relationship update. Not required for non-
     *   relationship requests.
     *
     * @return array
     *   An object normalization.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown if the request body cannot be decoded, or when no request body was
     *   provided with a POST or PATCH request.
     * @throws \Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException
     *   Thrown if the request body cannot be denormalized.
     */
    protected function deserialize(ResourceType $resource_type, Request $request, $class, $relationship_field_name = NULL) {
        assert($class === JsonApiDocumentTopLevel::class || $class === ResourceIdentifier::class && !empty($relationship_field_name) && is_string($relationship_field_name));
        $received = (string) $request->getContent();
        if (!$received) {
            assert($request->isMethod('POST') || $request->isMethod('PATCH') || $request->isMethod('DELETE'));
            if ($request->isMethod('DELETE') && $relationship_field_name) {
                throw new BadRequestHttpException(sprintf('You need to provide a body for DELETE operations on a relationship (%s).', $relationship_field_name));
            }
            else {
                throw new BadRequestHttpException('Empty request body.');
            }
        }
        // First decode the request data. We can then determine if the serialized
        // data was malformed.
        try {
            $decoded = $this->serializer
                ->decode($received, 'api_json');
        } catch (UnexpectedValueException $e) {
            // If an exception was thrown at this stage, there was a problem decoding
            // the data. Throw a 400 HTTP exception.
            throw new BadRequestHttpException($e->getMessage());
        }
        try {
            $context = [
                'resource_type' => $resource_type,
            ];
            if ($relationship_field_name) {
                $context['related'] = $resource_type->getInternalName($relationship_field_name);
            }
            return $this->serializer
                ->denormalize($decoded, $class, 'api_json', $context);
        } catch (UnexpectedValueException $e) {
            throw new UnprocessableEntityHttpException($e->getMessage());
        } catch (InvalidArgumentException $e) {
            throw new UnprocessableEntityHttpException($e->getMessage());
        }
    }
    
    /**
     * Gets a basic query for a collection.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The base JSON:API resource type for the query.
     * @param array $params
     *   The parameters for the query.
     * @param \Drupal\Core\Cache\CacheableMetadata $query_cacheability
     *   Collects cacheability for the query.
     *
     * @return \Drupal\Core\Entity\Query\QueryInterface
     *   A new query.
     */
    protected function getCollectionQuery(ResourceType $resource_type, array $params, CacheableMetadata $query_cacheability) {
        $entity_type = $this->entityTypeManager
            ->getDefinition($resource_type->getEntityTypeId());
        $entity_storage = $this->entityTypeManager
            ->getStorage($resource_type->getEntityTypeId());
        $query = $entity_storage->getQuery();
        // Ensure that access checking is performed on the query.
        $query->accessCheck(TRUE);
        // Compute and apply an entity query condition from the filter parameter.
        if (isset($params[Filter::KEY_NAME]) && ($filter = $params[Filter::KEY_NAME])) {
            $query->condition($filter->queryCondition($query));
            TemporaryQueryGuard::setFieldManager($this->fieldManager);
            TemporaryQueryGuard::setModuleHandler(\Drupal::moduleHandler());
            TemporaryQueryGuard::applyAccessControls($filter, $query, $query_cacheability);
        }
        // Apply any sorts to the entity query.
        if (isset($params[Sort::KEY_NAME]) && ($sort = $params[Sort::KEY_NAME])) {
            foreach ($sort->fields() as $field) {
                $path = $this->fieldResolver
                    ->resolveInternalEntityQueryPath($resource_type, $field[Sort::PATH_KEY]);
                $direction = $field[Sort::DIRECTION_KEY] ?? 'ASC';
                $langcode = $field[Sort::LANGUAGE_KEY] ?? NULL;
                $query->sort($path, $direction, $langcode);
            }
        }
        // Apply any pagination options to the query.
        if (isset($params[OffsetPage::KEY_NAME])) {
            $pagination = $params[OffsetPage::KEY_NAME];
        }
        else {
            $pagination = new OffsetPage(OffsetPage::DEFAULT_OFFSET, OffsetPage::SIZE_MAX);
        }
        // Add one extra element to the page to see if there are more pages needed.
        $query->range($pagination->getOffset(), $pagination->getSize() + 1);
        $query->addMetaData('pager_size', (int) $pagination->getSize());
        // Limit this query to the bundle type for this resource.
        $bundle = $resource_type->getBundle();
        if ($bundle && ($bundle_key = $entity_type->getKey('bundle'))) {
            $query->condition($bundle_key, $bundle);
        }
        return $query;
    }
    
    /**
     * Gets a basic query for a collection count.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The base JSON:API resource type for the query.
     * @param array $params
     *   The parameters for the query.
     * @param \Drupal\Core\Cache\CacheableMetadata $query_cacheability
     *   Collects cacheability for the query.
     *
     * @return \Drupal\Core\Entity\Query\QueryInterface
     *   A new query.
     */
    protected function getCollectionCountQuery(ResourceType $resource_type, array $params, CacheableMetadata $query_cacheability) {
        // Reset the range to get all the available results.
        return $this->getCollectionQuery($resource_type, $params, $query_cacheability)
            ->range()
            ->count();
    }
    
    /**
     * Loads the entity targeted by a resource identifier.
     *
     * @param \Drupal\jsonapi\JsonApiResource\ResourceIdentifier $resource_identifier
     *   A resource identifier.
     *
     * @return \Drupal\Core\Entity\EntityInterface
     *   The entity targeted by a resource identifier.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown if the given resource identifier targets a resource type or
     *   resource which does not exist.
     */
    protected function getEntityFromResourceIdentifier(ResourceIdentifier $resource_identifier) {
        $resource_type_name = $resource_identifier->getTypeName();
        if (!($target_resource_type = $this->resourceTypeRepository
            ->getByTypeName($resource_type_name))) {
            throw new BadRequestHttpException("The resource type `{$resource_type_name}` does not exist.");
        }
        $id = $resource_identifier->getId();
        if (!($targeted_resource = $this->entityRepository
            ->loadEntityByUuid($target_resource_type->getEntityTypeId(), $id))) {
            throw new BadRequestHttpException("The targeted `{$resource_type_name}` resource with ID `{$id}` does not exist.");
        }
        return $targeted_resource;
    }
    
    /**
     * Determines if the client needs to be updated with new relationship data.
     *
     * @param array $received_resource_identifiers
     *   The array of resource identifiers given by the client.
     * @param array $final_resource_identifiers
     *   The final array of resource identifiers after applying the requested
     *   changes.
     *
     * @return bool
     *   Whether the final array of resource identifiers is different than the
     *   client-sent data.
     */
    protected static function relationshipResponseRequiresBody(array $received_resource_identifiers, array $final_resource_identifiers) {
        return !empty(array_udiff($final_resource_identifiers, $received_resource_identifiers, [
            ResourceIdentifier::class,
            'compare',
        ]));
    }
    
    /**
     * Builds a response with the appropriate wrapped document.
     *
     * @param \Drupal\jsonapi\JsonApiResource\TopLevelDataInterface $data
     *   The data to wrap.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param \Drupal\jsonapi\JsonApiResource\IncludedData $includes
     *   The resources to be included in the document. Use NullData if
     *   there should be no included resources in the document.
     * @param int $response_code
     *   The response code.
     * @param array $headers
     *   An array of response headers.
     * @param \Drupal\jsonapi\JsonApiResource\LinkCollection $links
     *   The URLs to which to link. A 'self' link is added automatically.
     * @param array $meta
     *   (optional) The top-level metadata.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     */
    protected function buildWrappedResponse(TopLevelDataInterface $data, Request $request, IncludedData $includes, $response_code = 200, array $headers = [], LinkCollection $links = NULL, array $meta = []) {
        $links = $links ?: new LinkCollection([]);
        if (!$links->hasLinkWithKey('self')) {
            $self_link = new Link(new CacheableMetadata(), self::getRequestLink($request), 'self');
            $links = $links->withLink('self', $self_link);
        }
        $document = new JsonApiDocumentTopLevel($data, $includes, $links, $meta);
        if (!$request->isMethodCacheable()) {
            return new ResourceResponse($document, $response_code, $headers);
        }
        $response = new CacheableResourceResponse($document, $response_code, $headers);
        $cacheability = (new CacheableMetadata())->addCacheContexts([
            // Make sure that different sparse fieldsets are cached differently.
'url.query_args:fields',
            // Make sure that different sets of includes are cached differently.
'url.query_args:include',
        ]);
        $response->addCacheableDependency($cacheability);
        return $response;
    }
    
    /**
     * Respond with an entity collection.
     *
     * @param \Drupal\jsonapi\JsonApiResource\ResourceObjectData $primary_data
     *   The collection of entities.
     * @param \Drupal\jsonapi\JsonApiResource\IncludedData|\Drupal\jsonapi\JsonApiResource\NullIncludedData $includes
     *   The resources to be included in the document.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The base JSON:API resource type for the request to be served.
     * @param \Drupal\jsonapi\Query\OffsetPage $page_param
     *   The pagination parameter for the requested collection.
     *
     * @return \Drupal\jsonapi\ResourceResponse
     *   The response.
     */
    protected function respondWithCollection(ResourceObjectData $primary_data, Data $includes, Request $request, ResourceType $resource_type, OffsetPage $page_param) {
        assert(Inspector::assertAllObjects([
            $includes,
        ], IncludedData::class, NullIncludedData::class));
        $link_context = [
            'has_next_page' => $primary_data->hasNextPage(),
        ];
        $meta = [];
        if ($resource_type->includeCount()) {
            $link_context['total_count'] = $meta['count'] = $primary_data->getTotalCount();
        }
        $collection_links = self::getPagerLinks($request, $page_param, $link_context);
        $response = $this->buildWrappedResponse($primary_data, $request, $includes, 200, [], $collection_links, $meta);
        // When a new change to any entity in the resource happens, we cannot ensure
        // the validity of this cached list. Add the list tag to deal with that.
        $list_tag = $this->entityTypeManager
            ->getDefinition($resource_type->getEntityTypeId())
            ->getListCacheTags();
        $response->getCacheableMetadata()
            ->addCacheTags($list_tag);
        foreach ($primary_data as $entity) {
            $response->addCacheableDependency($entity);
        }
        return $response;
    }
    
    /**
     * Takes a field from the origin entity and puts it to the destination entity.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type of the entity to be updated.
     * @param \Drupal\Core\Entity\EntityInterface $origin
     *   The entity that contains the field values.
     * @param \Drupal\Core\Entity\EntityInterface $destination
     *   The entity that needs to be updated.
     * @param string $field_name
     *   The name of the field to extract and update.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown when the serialized and destination entities are of different
     *   types.
     */
    protected function updateEntityField(ResourceType $resource_type, EntityInterface $origin, EntityInterface $destination, $field_name) {
        // The update is different for configuration entities and content entities.
        if ($origin instanceof ContentEntityInterface && $destination instanceof ContentEntityInterface) {
            // First scenario: both are content entities.
            $field_name = $resource_type->getInternalName($field_name);
            $destination_field_list = $destination->get($field_name);
            $origin_field_list = $origin->get($field_name);
            if ($this->checkPatchFieldAccess($destination_field_list, $origin_field_list)) {
                $destination->set($field_name, $origin_field_list->getValue());
            }
        }
        elseif ($origin instanceof ConfigEntityInterface && $destination instanceof ConfigEntityInterface) {
            // Second scenario: both are config entities.
            $destination->set($field_name, $origin->get($field_name));
        }
        else {
            throw new BadRequestHttpException('The serialized entity and the destination entity are of different types.');
        }
    }
    
    /**
     * Gets includes for the given response data.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param \Drupal\jsonapi\JsonApiResource\ResourceObject|\Drupal\jsonapi\JsonApiResource\ResourceObjectData $data
     *   The response data from which to resolve includes.
     *
     * @return \Drupal\jsonapi\JsonApiResource\Data
     *   A Data object to be included or a NullData object if the request does not
     *   specify any include paths.
     *
     * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
     * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
     */
    public function getIncludes(Request $request, $data) {
        assert($data instanceof ResourceObject || $data instanceof ResourceObjectData);
        return $request->query
            ->has('include') && ($include_parameter = $request->query
            ->get('include')) && !empty($include_parameter) ? $this->includeResolver
            ->resolve($data, $include_parameter) : new NullIncludedData();
    }
    
    /**
     * 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 \Drupal\jsonapi\Exception\EntityAccessDeniedHttpException
     *   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
     *
     * @see \Drupal\rest\Plugin\rest\resource\EntityResource::checkPatchFieldAccess()
     */
    protected function checkPatchFieldAccess(FieldItemListInterface $original_field, FieldItemListInterface $received_field) {
        // 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;
        }
        // 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;
        }
        // It's helpful and safe to let the user know when they are not allowed to
        // update a field.
        $field_name = $received_field->getName();
        throw new EntityAccessDeniedHttpException($original_field->getEntity(), $field_edit_access, '/data/attributes/' . $field_name, sprintf('The current user is not allowed to PATCH the selected field (%s).', $field_name));
    }
    
    /**
     * Build a collection of the entities to respond with and access objects.
     *
     * @param \Drupal\Core\Entity\EntityStorageInterface $storage
     *   The entity storage to load the entities from.
     * @param int[] $ids
     *   An array of entity IDs, keyed by revision ID if the entity type is
     *   revisionable.
     * @param bool $load_latest_revisions
     *   Whether to load the latest revisions instead of the defaults.
     *
     * @return array
     *   An array of loaded entities and/or an access exceptions.
     */
    protected function loadEntitiesWithAccess(EntityStorageInterface $storage, array $ids, $load_latest_revisions) {
        $output = [];
        if ($load_latest_revisions) {
            assert($storage instanceof RevisionableStorageInterface);
            $entities = $storage->loadMultipleRevisions(array_keys($ids));
        }
        else {
            $entities = $storage->loadMultiple($ids);
        }
        foreach ($entities as $entity) {
            $output[$entity->id()] = $this->entityAccessChecker
                ->getAccessCheckedResourceObject($entity);
        }
        return array_values($output);
    }
    
    /**
     * Checks if the given entity exists.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity for which to test existence.
     *
     * @return bool
     *   Whether the entity already has been created.
     */
    protected function entityExists(EntityInterface $entity) {
        $entity_storage = $this->entityTypeManager
            ->getStorage($entity->getEntityTypeId());
        return !empty($entity_storage->loadByProperties([
            'uuid' => $entity->uuid(),
        ]));
    }
    
    /**
     * Extracts JSON:API query parameters from the request.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type.
     *
     * @return array
     *   An array of JSON:API parameters like `sort` and `filter`.
     */
    protected function getJsonApiParams(Request $request, ResourceType $resource_type) {
        if ($request->query
            ->has('filter')) {
            $params[Filter::KEY_NAME] = Filter::createFromQueryParameter($request->query
                ->get('filter'), $resource_type, $this->fieldResolver);
        }
        if ($request->query
            ->has('sort')) {
            $params[Sort::KEY_NAME] = Sort::createFromQueryParameter($request->query
                ->get('sort'));
        }
        if ($request->query
            ->has('page')) {
            $params[OffsetPage::KEY_NAME] = OffsetPage::createFromQueryParameter($request->query
                ->get('page'));
        }
        else {
            $params[OffsetPage::KEY_NAME] = OffsetPage::createFromQueryParameter([
                'page' => [
                    'offset' => OffsetPage::DEFAULT_OFFSET,
                    'limit' => OffsetPage::SIZE_MAX,
                ],
            ]);
        }
        return $params;
    }
    
    /**
     * Get the full URL for a given request object.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param array|null $query
     *   The query parameters to use. Leave it empty to get the query from the
     *   request object.
     *
     * @return \Drupal\Core\Url
     *   The full URL.
     */
    protected static function getRequestLink(Request $request, $query = NULL) {
        if ($query === NULL) {
            return Url::fromUri($request->getUri());
        }
        $uri_without_query_string = $request->getSchemeAndHttpHost() . $request->getBaseUrl() . $request->getPathInfo();
        return Url::fromUri($uri_without_query_string)->setOption('query', $query);
    }
    
    /**
     * Get the pager links for a given request object.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param \Drupal\jsonapi\Query\OffsetPage $page_param
     *   The current pagination parameter for the requested collection.
     * @param array $link_context
     *   An associative array with extra data to build the links.
     *
     * @return \Drupal\jsonapi\JsonApiResource\LinkCollection
     *   A LinkCollection, with:
     *   - a 'next' key if it is not the last page;
     *   - 'prev' and 'first' keys if it's not the first page.
     */
    protected static function getPagerLinks(Request $request, OffsetPage $page_param, array $link_context = []) {
        $pager_links = new LinkCollection([]);
        if (!empty($link_context['total_count']) && !($total = (int) $link_context['total_count'])) {
            return $pager_links;
        }
        $offset = $page_param->getOffset();
        $size = $page_param->getSize();
        if ($size <= 0) {
            $cacheability = (new CacheableMetadata())->addCacheContexts([
                'url.query_args:page',
            ]);
            throw new CacheableBadRequestHttpException($cacheability, sprintf('The page size needs to be a positive integer.'));
        }
        $query = (array) $request->query
            ->getIterator();
        // Check if this is not the last page.
        if ($link_context['has_next_page']) {
            $next_url = static::getRequestLink($request, static::getPagerQueries('next', $offset, $size, $query));
            $pager_links = $pager_links->withLink('next', new Link(new CacheableMetadata(), $next_url, 'next'));
            if (!empty($total)) {
                $last_url = static::getRequestLink($request, static::getPagerQueries('last', $offset, $size, $query, $total));
                $pager_links = $pager_links->withLink('last', new Link(new CacheableMetadata(), $last_url, 'last'));
            }
        }
        // Check if this is not the first page.
        if ($offset > 0) {
            $first_url = static::getRequestLink($request, static::getPagerQueries('first', $offset, $size, $query));
            $pager_links = $pager_links->withLink('first', new Link(new CacheableMetadata(), $first_url, 'first'));
            $prev_url = static::getRequestLink($request, static::getPagerQueries('prev', $offset, $size, $query));
            $pager_links = $pager_links->withLink('prev', new Link(new CacheableMetadata(), $prev_url, 'prev'));
        }
        return $pager_links;
    }
    
    /**
     * Get the query param array.
     *
     * @param string $link_id
     *   The name of the pagination link requested.
     * @param int $offset
     *   The starting index.
     * @param int $size
     *   The pagination page size.
     * @param array $query
     *   The query parameters.
     * @param int $total
     *   The total size of the collection.
     *
     * @return array
     *   The pagination query param array.
     */
    protected static function getPagerQueries($link_id, $offset, $size, array $query = [], $total = 0) {
        $extra_query = [];
        switch ($link_id) {
            case 'next':
                $extra_query = [
                    'page' => [
                        'offset' => $offset + $size,
                        'limit' => $size,
                    ],
                ];
                break;
            case 'first':
                $extra_query = [
                    'page' => [
                        'offset' => 0,
                        'limit' => $size,
                    ],
                ];
                break;
            case 'last':
                if ($total) {
                    $extra_query = [
                        'page' => [
                            'offset' => (ceil($total / $size) - 1) * $size,
                            'limit' => $size,
                        ],
                    ];
                }
                break;
            case 'prev':
                $extra_query = [
                    'page' => [
                        'offset' => max($offset - $size, 0),
                        'limit' => $size,
                    ],
                ];
                break;
        }
        return array_merge($query, $extra_query);
    }

}