class DefaultSingleLazyPluginCollection

class DefaultSingleLazyPluginCollection extends LazyPluginCollection {
    use DependencySerializationTrait;
    
    /**
     * The manager used to instantiate the plugins.
     *
     * @var \Drupal\Component\Plugin\PluginManagerInterface
     */
    protected $manager;
    
    /**
     * An array of configuration to instantiate the plugin with.
     *
     * @var array
     */
    protected $configuration;
    
    /**
     * The instance ID used for this plugin collection.
     *
     * @var string
     */
    protected $instanceId;
    
    /**
     * Constructs a new DefaultSingleLazyPluginCollection object.
     *
     * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
     *   The manager to be used for instantiating plugins.
     * @param string $instance_id
     *   The ID of the plugin instance.
     * @param array $configuration
     *   An array of configuration.
     */
    public function __construct(PluginManagerInterface $manager, $instance_id, array $configuration) {
        $this->manager = $manager;
        $this->addInstanceId($instance_id, $configuration);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function initializePlugin($instance_id) {
        $this->set($instance_id, $this->manager
            ->createInstance($instance_id, $this->configuration));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConfiguration() {
        $plugin = $this->get($this->instanceId);
        if (PluginHelper::isConfigurable($plugin)) {
            return $plugin->getConfiguration();
        }
        else {
            return $this->configuration;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function setConfiguration($configuration) {
        $this->configuration = $configuration;
        $plugin = $this->get($this->instanceId);
        if (PluginHelper::isConfigurable($plugin)) {
            $plugin->setConfiguration($configuration);
        }
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addInstanceId($id, $configuration = NULL) {
        $this->instanceId = $id;
        // Reset the list of instance IDs since there can be only one.
        $this->instanceIds = [];
        parent::addInstanceId($id, $configuration);
        if ($configuration !== NULL) {
            $this->setConfiguration($configuration);
        }
    }

}