class ResourceObject

class ResourceObject implements CacheableDependencyInterface, ResourceIdentifierInterface {
    use CacheableDependencyTrait;
    use ResourceIdentifierTrait;
    
    /**
     * The resource object's version identifier.
     *
     * @var string|null
     */
    protected $versionIdentifier;
    
    /**
     * The object's fields.
     *
     * This refers to "fields" in the JSON:API sense of the word. Config entities
     * do not have real fields, so in that case, this will be an array of values
     * for config entity attributes.
     *
     * @var \Drupal\Core\Field\FieldItemListInterface[]|mixed[]
     */
    protected $fields;
    
    /**
     * The resource object's links.
     *
     * @var \Drupal\jsonapi\JsonApiResource\LinkCollection
     */
    protected $links;
    
    /**
     * The resource language.
     *
     * @var \Drupal\Core\Language\LanguageInterface
     */
    protected $language;
    
    /**
     * ResourceObject constructor.
     *
     * @param \Drupal\Core\Cache\CacheableDependencyInterface $cacheability
     *   The cacheability for the resource object.
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type of the resource object.
     * @param string $id
     *   The resource object's ID.
     * @param mixed|null $revision_id
     *   The resource object's version identifier. NULL, if the resource object is
     *   not versionable.
     * @param array $fields
     *   An array of the resource object's fields, keyed by public field name.
     * @param \Drupal\jsonapi\JsonApiResource\LinkCollection $links
     *   The links for the resource object.
     * @param \Drupal\Core\Language\LanguageInterface|null $language
     *   (optional) The resource language.
     */
    public function __construct(CacheableDependencyInterface $cacheability, ResourceType $resource_type, $id, $revision_id, array $fields, LinkCollection $links, LanguageInterface $language = NULL) {
        assert(is_null($revision_id) || $resource_type->isVersionable());
        $this->setCacheability($cacheability);
        $this->resourceType = $resource_type;
        $this->resourceIdentifier = new ResourceIdentifier($resource_type, $id);
        $this->versionIdentifier = $revision_id ? 'id:' . $revision_id : NULL;
        $this->fields = $fields;
        $this->links = $links->withContext($this);
        // If the specified language empty it falls back the same way as in the entity system
        // @see \Drupal\Core\Entity\EntityBase::language()
        $this->language = $language ?: new Language([
            'id' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
        ]);
    }
    
    /**
     * Creates a new ResourceObject from an entity.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type of the resource object.
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity to be represented by this resource object.
     * @param \Drupal\jsonapi\JsonApiResource\LinkCollection $links
     *   (optional) Any links for the resource object, if a `self` link is not
     *   provided, one will be automatically added if the resource is locatable
     *   and is not an internal entity.
     *
     * @return static
     *   An instantiated resource object.
     */
    public static function createFromEntity(ResourceType $resource_type, EntityInterface $entity, LinkCollection $links = NULL) {
        return new static($entity, $resource_type, $entity->uuid(), $resource_type->isVersionable() && $entity instanceof RevisionableInterface ? $entity->getRevisionId() : NULL, static::extractFieldsFromEntity($resource_type, $entity), static::buildLinksFromEntity($resource_type, $entity, $links ?: new LinkCollection([])), $entity->language());
    }
    
    /**
     * Whether the resource object has the given field.
     *
     * @param string $public_field_name
     *   A public field name.
     *
     * @return bool
     *   TRUE if the resource object has the given field, FALSE otherwise.
     */
    public function hasField($public_field_name) {
        return isset($this->fields[$public_field_name]);
    }
    
    /**
     * Gets the given field.
     *
     * @param string $public_field_name
     *   A public field name.
     *
     * @return mixed|\Drupal\Core\Field\FieldItemListInterface|null
     *   The field or NULL if the resource object does not have the given field.
     *
     * @see ::extractFields()
     */
    public function getField($public_field_name) {
        return $this->hasField($public_field_name) ? $this->fields[$public_field_name] : NULL;
    }
    
    /**
     * Gets the ResourceObject's fields.
     *
     * @return array
     *   The resource object's fields, keyed by public field name.
     *
     * @see ::extractFields()
     */
    public function getFields() {
        return $this->fields;
    }
    
    /**
     * Gets the ResourceObject's language.
     *
     * @return \Drupal\Core\Language\LanguageInterface
     *   The resource language.
     */
    public function getLanguage() : LanguageInterface {
        return $this->language;
    }
    
    /**
     * Gets the ResourceObject's links.
     *
     * @return \Drupal\jsonapi\JsonApiResource\LinkCollection
     *   The resource object's links.
     */
    public function getLinks() {
        return $this->links;
    }
    
    /**
     * Gets a version identifier for the ResourceObject.
     *
     * @return string
     *   The version identifier of the resource object, if the resource type is
     *   versionable.
     */
    public function getVersionIdentifier() {
        if (!$this->resourceType
            ->isVersionable()) {
            throw new \LogicException('Cannot get a version identifier for a non-versionable resource.');
        }
        return $this->versionIdentifier;
    }
    
    /**
     * Gets a Url for the ResourceObject.
     *
     * @return \Drupal\Core\Url
     *   The URL for the identified resource object.
     *
     * @throws \LogicException
     *   Thrown if the resource object is not locatable.
     *
     * @see \Drupal\jsonapi\ResourceType\ResourceTypeRepository::isLocatableResourceType()
     */
    public function toUrl() {
        foreach ($this->links as $key => $link) {
            if ($key === 'self') {
                $first = reset($link);
                return $first->getUri();
            }
        }
        throw new \LogicException('A Url does not exist for this resource object because its resource type is not locatable.');
    }
    
    /**
     * Extracts the entity's fields.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type of the given entity.
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity from which fields should be extracted.
     *
     * @return mixed|\Drupal\Core\Field\FieldItemListInterface[]
     *   If the resource object represents a content entity, the fields will be
     *   objects satisfying FieldItemListInterface. If it represents a config
     *   entity, the fields will be scalar values or arrays.
     */
    protected static function extractFieldsFromEntity(ResourceType $resource_type, EntityInterface $entity) {
        assert($entity instanceof ContentEntityInterface || $entity instanceof ConfigEntityInterface);
        return $entity instanceof ContentEntityInterface ? static::extractContentEntityFields($resource_type, $entity) : static::extractConfigEntityFields($resource_type, $entity);
    }
    
    /**
     * Builds a LinkCollection for the given entity.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type of the given entity.
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity for which to build links.
     * @param \Drupal\jsonapi\JsonApiResource\LinkCollection $links
     *   (optional) Any extra links for the resource object, if a `self` link is
     *   not provided, one will be automatically added if the resource is
     *   locatable and is not an internal entity.
     *
     * @return \Drupal\jsonapi\JsonApiResource\LinkCollection
     *   The built links.
     */
    protected static function buildLinksFromEntity(ResourceType $resource_type, EntityInterface $entity, LinkCollection $links) {
        if ($resource_type->isLocatable() && !$resource_type->isInternal()) {
            $self_url = Url::fromRoute(Routes::getRouteName($resource_type, 'individual'), [
                'entity' => $entity->uuid(),
            ]);
            if ($resource_type->isVersionable()) {
                assert($entity instanceof RevisionableInterface);
                if (!$links->hasLinkWithKey('self')) {
                    // If the resource is versionable, the `self` link should be the exact
                    // link for the represented version. This helps a client track
                    // revision changes and to disambiguate resource objects with the same
                    // `type` and `id` in a `version-history` collection.
                    $self_with_version_url = $self_url->setOption('query', [
                        JsonApiSpec::VERSION_QUERY_PARAMETER => 'id:' . $entity->getRevisionId(),
                    ]);
                    $links = $links->withLink('self', new Link(new CacheableMetadata(), $self_with_version_url, 'self'));
                }
                if (!$entity->isDefaultRevision()) {
                    $latest_version_url = $self_url->setOption('query', [
                        JsonApiSpec::VERSION_QUERY_PARAMETER => 'rel:' . VersionByRel::LATEST_VERSION,
                    ]);
                    $links = $links->withLink(VersionByRel::LATEST_VERSION, new Link(new CacheableMetadata(), $latest_version_url, VersionByRel::LATEST_VERSION));
                }
                if (!$entity->isLatestRevision()) {
                    $working_copy_url = $self_url->setOption('query', [
                        JsonApiSpec::VERSION_QUERY_PARAMETER => 'rel:' . VersionByRel::WORKING_COPY,
                    ]);
                    $links = $links->withLink(VersionByRel::WORKING_COPY, new Link(new CacheableMetadata(), $working_copy_url, VersionByRel::WORKING_COPY));
                }
            }
            if (!$links->hasLinkWithKey('self')) {
                $links = $links->withLink('self', new Link(new CacheableMetadata(), $self_url, 'self'));
            }
        }
        return $links;
    }
    
    /**
     * Extracts a content entity's fields.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type of the given entity.
     * @param \Drupal\Core\Entity\ContentEntityInterface $entity
     *   The config entity from which fields should be extracted.
     *
     * @return \Drupal\Core\Field\FieldItemListInterface[]
     *   The fields extracted from a content entity.
     */
    protected static function extractContentEntityFields(ResourceType $resource_type, ContentEntityInterface $entity) {
        $output = [];
        $fields = TypedDataInternalPropertiesHelper::getNonInternalProperties($entity->getTypedData());
        // Filter the array based on the field names.
        $enabled_field_names = array_filter(array_keys($fields), [
            $resource_type,
            'isFieldEnabled',
        ]);
        // Special handling for user entities that allows a JSON:API user agent to
        // access the display name of a user. For example, this is useful when
        // displaying the name of a node's author.
        // @todo: eliminate this special casing in https://www.drupal.org/project/drupal/issues/3079254.
        $entity_type = $entity->getEntityType();
        if ($entity_type->id() == 'user' && $resource_type->isFieldEnabled('display_name')) {
            assert($entity instanceof UserInterface);
            $display_name = $resource_type->getPublicName('display_name');
            $output[$display_name] = $entity->getDisplayName();
        }
        // Return a sub-array of $output containing the keys in $enabled_fields.
        $input = array_intersect_key($fields, array_flip($enabled_field_names));
        foreach ($input as $field_name => $field_value) {
            $public_field_name = $resource_type->getPublicName($field_name);
            $output[$public_field_name] = $field_value;
        }
        return $output;
    }
    
    /**
     * Determines the entity type's (internal) label field name.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity from which fields should be extracted.
     *
     * @return string
     *   The label field name.
     */
    protected static function getLabelFieldName(EntityInterface $entity) {
        $label_field_name = $entity->getEntityType()
            ->getKey('label');
        // Special handling for user entities that allows a JSON:API user agent to
        // access the display name of a user. This is useful when displaying the
        // name of a node's author.
        // @see \Drupal\jsonapi\JsonApiResource\ResourceObject::extractContentEntityFields()
        // @todo: eliminate this special casing in https://www.drupal.org/project/drupal/issues/3079254.
        if ($entity->getEntityTypeId() === 'user') {
            $label_field_name = 'display_name';
        }
        return $label_field_name;
    }
    
    /**
     * Extracts a config entity's fields.
     *
     * @param \Drupal\jsonapi\ResourceType\ResourceType $resource_type
     *   The JSON:API resource type of the given entity.
     * @param \Drupal\Core\Config\Entity\ConfigEntityInterface $entity
     *   The config entity from which fields should be extracted.
     *
     * @return array
     *   The fields extracted from a config entity.
     */
    protected static function extractConfigEntityFields(ResourceType $resource_type, ConfigEntityInterface $entity) {
        $enabled_public_fields = [];
        $fields = $entity->toArray();
        // Filter the array based on the field names.
        $enabled_field_names = array_filter(array_keys($fields), function ($internal_field_name) use ($resource_type) {
            // Config entities have "fields" which aren't known to the resource type,
            // these fields should not be excluded because they cannot be enabled or
            // disabled.
            return !$resource_type->hasField($internal_field_name) || $resource_type->isFieldEnabled($internal_field_name);
        });
        // Return a sub-array of $output containing the keys in $enabled_fields.
        $input = array_intersect_key($fields, array_flip($enabled_field_names));
        
        /** @var \Drupal\Core\Config\Entity\ConfigEntityInterface $entity */
        foreach ($input as $field_name => $field_value) {
            $public_field_name = $resource_type->getPublicName($field_name);
            $enabled_public_fields[$public_field_name] = $field_value;
        }
        return $enabled_public_fields;
    }

}