class ResourceVersionRouteEnhancer

final class ResourceVersionRouteEnhancer implements EnhancerInterface {
    
    /**
     * The route default parameter name.
     *
     * @var string
     */
    const REVISION_ID_KEY = 'revision_id';
    
    /**
     * The query parameter for providing a version (revision) value.
     *
     * @var string
     */
    const RESOURCE_VERSION_QUERY_PARAMETER = 'resourceVersion';
    
    /**
     * A route parameter key which indicates that working copies were requested.
     *
     * @var string
     */
    const WORKING_COPIES_REQUESTED = 'working_copies_requested';
    
    /**
     * The cache context by which vary the loaded entity revision.
     *
     * @var string
     *
     * @todo When D8 requires PHP >=5.6, convert to expression using the RESOURCE_VERSION_QUERY_PARAMETER constant.
     */
    const CACHE_CONTEXT = 'url.query_args:resourceVersion';
    
    /**
     * Resource version validation regex.
     *
     * @var string
     *
     * @todo When D8 requires PHP >=5.6, convert to expression using the VersionNegotiator::SEPARATOR constant.
     */
    const VERSION_IDENTIFIER_VALIDATOR = '/^[a-z]+[a-z_]*[a-z]+:[a-zA-Z0-9\\-]+(:[a-zA-Z0-9\\-]+)*$/';
    
    /**
     * The revision ID negotiator.
     *
     * @var \Drupal\jsonapi\Revisions\VersionNegotiator
     */
    protected $versionNegotiator;
    
    /**
     * ResourceVersionRouteEnhancer constructor.
     *
     * @param \Drupal\jsonapi\Revisions\VersionNegotiator $version_negotiator_manager
     *   The version negotiator.
     */
    public function __construct(VersionNegotiator $version_negotiator_manager) {
        $this->versionNegotiator = $version_negotiator_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public function enhance(array $defaults, Request $request) {
        if (!Routes::isJsonApiRequest($defaults) || !($resource_type = Routes::getResourceTypeNameFromParameters($defaults))) {
            return $defaults;
        }
        $has_version_param = $request->query
            ->has(static::RESOURCE_VERSION_QUERY_PARAMETER);
        // If the resource type is not versionable, then nothing needs to be
        // enhanced.
        if (!$resource_type->isVersionable()) {
            // If the query parameter was provided but the resource type is not
            // versionable, provide a helpful error.
            if ($has_version_param) {
                $cacheability = (new CacheableMetadata())->addCacheContexts([
                    'url.path',
                    static::CACHE_CONTEXT,
                ]);
                throw new CacheableHttpException($cacheability, 501, 'Resource versioning is not yet supported for this resource type.');
            }
            return $defaults;
        }
        // Since the resource type is versionable, responses must always vary by the
        // requested version, without regard for whether a version query parameter
        // was provided or not.
        if (isset($defaults['entity'])) {
            assert($defaults['entity'] instanceof EntityInterface);
            $defaults['entity']->addCacheContexts([
                static::CACHE_CONTEXT,
            ]);
        }
        // If no version was specified, nothing is left to enhance.
        if (!$has_version_param) {
            return $defaults;
        }
        // Provide a helpful error when a version is specified with an unsafe
        // method.
        if (!$request->isMethodCacheable()) {
            throw new BadRequestHttpException(sprintf('%s requests with a `%s` query parameter are not supported.', $request->getMethod(), static::RESOURCE_VERSION_QUERY_PARAMETER));
        }
        $resource_version_identifier = $request->query
            ->get(static::RESOURCE_VERSION_QUERY_PARAMETER);
        if (!static::isValidVersionIdentifier($resource_version_identifier)) {
            $cacheability = (new CacheableMetadata())->addCacheContexts([
                static::CACHE_CONTEXT,
            ]);
            $message = sprintf('A resource version identifier was provided in an invalid format: `%s`', $resource_version_identifier);
            throw new CacheableBadRequestHttpException($cacheability, $message);
        }
        // Determine if the request is for a collection resource.
        if ($defaults[RouteObjectInterface::CONTROLLER_NAME] === Routes::CONTROLLER_SERVICE_NAME . ':getCollection') {
            $latest_version_identifier = 'rel' . VersionNegotiator::SEPARATOR . 'latest-version';
            $working_copy_identifier = 'rel' . VersionNegotiator::SEPARATOR . 'working-copy';
            // Until Drupal core has a revision access API that works on entity
            // queries, filtering is not permitted on non-default revisions.
            if ($request->query
                ->has('filter') && $resource_version_identifier !== $latest_version_identifier) {
                $cache_contexts = [
                    'url.path',
                    static::CACHE_CONTEXT,
                    'url.query_args:filter',
                ];
                $cacheability = (new CacheableMetadata())->addCacheContexts($cache_contexts);
                $message = 'JSON:API does not support filtering on revisions other than the latest version because a secure Drupal core API does not yet exist to do so.';
                throw new CacheableHttpException($cacheability, 501, $message);
            }
            // 'latest-version' and 'working-copy' are the only acceptable version
            // identifiers for a collection resource.
            if (!in_array($resource_version_identifier, [
                $latest_version_identifier,
                $working_copy_identifier,
            ])) {
                $cacheability = (new CacheableMetadata())->addCacheContexts([
                    'url.path',
                    static::CACHE_CONTEXT,
                ]);
                $message = sprintf('Collection resources only support the following resource version identifiers: %s', implode(', ', [
                    $latest_version_identifier,
                    $working_copy_identifier,
                ]));
                throw new CacheableBadRequestHttpException($cacheability, $message);
            }
            // Whether the collection to be loaded should include only working copies.
            $defaults[static::WORKING_COPIES_REQUESTED] = $resource_version_identifier === $working_copy_identifier;
            return $defaults;
        }
        
        /** @var \Drupal\Core\Entity\EntityInterface $entity */
        $entity = $defaults['entity'];
        
        /** @var \Drupal\jsonapi\Revisions\VersionNegotiatorInterface $negotiator */
        $resolved_revision = $this->versionNegotiator
            ->getRevision($entity, $resource_version_identifier);
        // Ensure none of the original entity cacheability is lost, especially the
        // query argument's cache context.
        $resolved_revision->addCacheableDependency($entity);
        return [
            'entity' => $resolved_revision,
        ] + $defaults;
    }
    
    /**
     * Validates the user input.
     *
     * @param string $resource_version
     *   The requested resource version identifier.
     *
     * @return bool
     *   TRUE if the received resource version value is valid, FALSE otherwise.
     */
    protected static function isValidVersionIdentifier($resource_version) {
        return preg_match(static::VERSION_IDENTIFIER_VALIDATOR, $resource_version) === 1;
    }

}