class MetaEventSubscriber

class MetaEventSubscriber implements EventSubscriberInterface {
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        return [
            CollectResourceObjectMetaEvent::class => 'addResourceObjectMeta',
            CollectRelationshipMetaEvent::class => 'addRelationshipMeta',
        ];
    }
    
    /**
     * @param \Drupal\jsonapi\Events\CollectResourceObjectMetaEvent $event
     *   Event to be processed.
     *
     * @return void
     */
    public function addResourceObjectMeta(CollectResourceObjectMetaEvent $event) : void {
        $config = \Drupal::state()->get('jsonapi_test_meta_events.object_meta', [
            'enabled_type' => FALSE,
            'enabled_id' => FALSE,
            'fields' => FALSE,
            'user_is_admin_context' => FALSE,
        ]);
        // Only continue if the recourse type is enabled.
        if ($config['enabled_type'] === FALSE || $config['enabled_type'] !== $event->getResourceObject()
            ->getTypeName()) {
            return;
        }
        // Only apply on the referenced ID of the resource.
        if ($config['enabled_id'] !== FALSE && $config['enabled_id'] !== $event->getResourceObject()
            ->getId()) {
            return;
        }
        if ($config['fields'] === FALSE) {
            return;
        }
        if ($config['user_is_admin_context']) {
            $event->addCacheContexts([
                'user.roles',
            ]);
            $event->setMetaValue('resource_meta_user_has_admin_role', $this->currentUserHasAdminRole());
            $event->setMetaValue('resource_meta_user_id', \Drupal::currentUser()->id());
        }
        // Add the metadata for each field. The field configuration must be an array
        // of field values keyed by the field name.
        foreach ($config['fields'] as $field_name) {
            $event->setMetaValue('resource_meta_' . $field_name, $event->getResourceObject()
                ->getField($field_name)->value);
        }
        $event->addCacheTags([
            'jsonapi_test_meta_events.object_meta',
        ]);
    }
    
    /**
     * @param \Drupal\jsonapi\Events\CollectRelationshipMetaEvent $event
     *   Event to be processed.
     *
     * @return void
     */
    public function addRelationshipMeta(CollectRelationshipMetaEvent $event) : void {
        $config = \Drupal::state()->get('jsonapi_test_meta_events.relationship_meta', [
            'enabled_type' => FALSE,
            'enabled_id' => FALSE,
            'enabled_relation' => FALSE,
            'fields' => FALSE,
            'user_is_admin_context' => FALSE,
        ]);
        // Only continue if the resource type is enabled.
        if ($config['enabled_type'] === FALSE || $config['enabled_type'] !== $event->getResourceObject()
            ->getTypeName()) {
            return;
        }
        // Only apply on the referenced ID of the resource.
        if ($config['enabled_id'] !== FALSE && $config['enabled_id'] !== $event->getResourceObject()
            ->getId()) {
            return;
        }
        // Only continue if this is the correct relation.
        if ($config['enabled_relation'] === FALSE || $config['enabled_relation'] !== $event->getRelationshipFieldName()) {
            return;
        }
        $relationshipFieldName = $event->getRelationshipFieldName();
        $field = $event->getResourceObject()
            ->getField($relationshipFieldName);
        $referencedEntities = [];
        if ($field instanceof EntityReferenceFieldItemListInterface) {
            $referencedEntities = $field->referencedEntities();
            $event->addCacheTags([
                'jsonapi_test_meta_events.relationship_meta',
            ]);
        }
        if ($config['user_is_admin_context'] ?? FALSE) {
            $event->addCacheContexts([
                'user.roles',
            ]);
            $event->setMetaValue('resource_meta_user_has_admin_role', $this->currentUserHasAdminRole());
        }
        // If no fields are specified just add a list of UUIDs to the relations.
        if ($config['fields'] === FALSE) {
            $referencedEntityIds = [];
            foreach ($referencedEntities as $entity) {
                $referencedEntityIds[] = $entity->uuid();
            }
            $event->setMetaValue('relationship_meta_' . $event->getRelationshipFieldName(), $referencedEntityIds);
            return;
        }
        // Add the metadata for each field. The field configuration must be an array
        // of field values keyed by the field name.
        foreach ($config['fields'] as $field_name) {
            $fieldValues = [];
            foreach ($referencedEntities as $entity) {
                $fieldValues[] = $entity->get($field_name)->value;
            }
            $event->setMetaValue('relationship_meta_' . $field_name, $fieldValues);
        }
    }
    
    /**
     * @return string
     * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
     * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
     */
    protected function currentUserHasAdminRole() : string {
        $admin_roles = \Drupal::entityTypeManager()->getStorage('user_role')
            ->loadByProperties([
            'is_admin' => TRUE,
        ]);
        $has_admin_role = 'yes';
        if (count(array_intersect(\Drupal::currentUser()->getRoles(), array_keys($admin_roles))) === 0) {
            $has_admin_role = 'no';
        }
        return $has_admin_role;
    }

}