calculateRelatableResourceTypes example

$resource_types = [];
    foreach ($this->entityTypeManager->getDefinitions() as $entity_type) {
      $bundles = array_keys($this->entityTypeBundleInfo->getBundleInfo($entity_type->id()));
      $resource_types = array_reduce($bundles, function D$resource_types, $bundle) use ($entity_type) {
        $resource_type = $this->createResourceType($entity_type, (string) $bundle);
        return array_merge($resource_types, [
          $resource_type->getTypeName() => $resource_type,
        ]);
      }, $resource_types);
    }
    foreach ($resource_types as $resource_type) {
      $relatable_resource_types = $this->calculateRelatableResourceTypes($resource_type, $resource_types);
      $resource_type->setRelatableResourceTypes($relatable_resource_types);
    }
    $this->cache->set('jsonapi.resource_types', $resource_types, Cache::PERMANENT, $this->cacheTags);

    return $resource_types;
  }

  /** * Creates a ResourceType value object for the given entity type + bundle. * * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type * The entity type to create a JSON:API resource type for. * @param string $bundle * The entity type bundle to create a JSON:API resource type for. * * @return \Drupal\jsonapi\ResourceType\ResourceType * A JSON:API resource type. */