class DefaultFactory

class DefaultFactory implements FactoryInterface {
    
    /**
     * The object that retrieves the definitions of the plugins that this factory instantiates.
     *
     * The plugin definition includes the plugin class and possibly other
     * information necessary for proper instantiation.
     *
     * @var \Drupal\Component\Plugin\Discovery\DiscoveryInterface
     */
    protected $discovery;
    
    /**
     * Defines an interface each plugin should implement.
     *
     * @var string|null
     */
    protected $interface;
    
    /**
     * Constructs a Drupal\Component\Plugin\Factory\DefaultFactory object.
     *
     * @param \Drupal\Component\Plugin\Discovery\DiscoveryInterface $discovery
     *   The plugin discovery.
     * @param string|null $plugin_interface
     *   (optional) The interface each plugin should implement.
     */
    public function __construct(DiscoveryInterface $discovery, $plugin_interface = NULL) {
        $this->discovery = $discovery;
        $this->interface = $plugin_interface;
    }
    
    /**
     * {@inheritdoc}
     */
    public function createInstance($plugin_id, array $configuration = []) {
        $plugin_definition = $this->discovery
            ->getDefinition($plugin_id);
        $plugin_class = static::getPluginClass($plugin_id, $plugin_definition, $this->interface);
        return new $plugin_class($configuration, $plugin_id, $plugin_definition);
    }
    
    /**
     * Finds the class relevant for a given plugin.
     *
     * @param string $plugin_id
     *   The id of a plugin.
     * @param \Drupal\Component\Plugin\Definition\PluginDefinitionInterface|mixed[] $plugin_definition
     *   The plugin definition associated with the plugin ID.
     * @param string $required_interface
     *   (optional) The required plugin interface.
     *
     * @return string
     *   The appropriate class name.
     *
     * @throws \Drupal\Component\Plugin\Exception\PluginException
     *   Thrown when there is no class specified, the class doesn't exist, or
     *   the class does not implement the specified required interface.
     */
    public static function getPluginClass($plugin_id, $plugin_definition = NULL, $required_interface = NULL) {
        $missing_class_message = sprintf('The plugin (%s) did not specify an instance class.', $plugin_id);
        if (is_array($plugin_definition)) {
            if (empty($plugin_definition['class'])) {
                throw new PluginException($missing_class_message);
            }
            $class = $plugin_definition['class'];
        }
        elseif ($plugin_definition instanceof PluginDefinitionInterface) {
            if (!$plugin_definition->getClass()) {
                throw new PluginException($missing_class_message);
            }
            $class = $plugin_definition->getClass();
        }
        else {
            $plugin_definition_type = is_object($plugin_definition) ? get_class($plugin_definition) : gettype($plugin_definition);
            throw new PluginException(sprintf('%s can only handle plugin definitions that are arrays or that implement %s, but %s given.', __CLASS__, PluginDefinitionInterface::class, $plugin_definition_type));
        }
        if (!class_exists($class)) {
            throw new PluginException(sprintf('Plugin (%s) instance class "%s" does not exist.', $plugin_id, $class));
        }
        if ($required_interface && !is_subclass_of($class, $required_interface)) {
            throw new PluginException(sprintf('Plugin "%s" (%s) must implement interface %s.', $plugin_id, $class, $required_interface));
        }
        return $class;
    }

}