class EventSubscriber

class EventSubscriber implements EventSubscriberInterface {
    
    /**
     * The state key value store.
     *
     * @var \Drupal\Core\State\StateInterface
     */
    protected $state;
    
    /**
     * Constructs the Event Subscriber object.
     *
     * @param \Drupal\Core\State\StateInterface $state
     *   The state key value store.
     */
    public function __construct(StateInterface $state) {
        $this->state = $state;
    }
    
    /**
     * Reacts to config event.
     *
     * @param \Drupal\Core\Config\ConfigCrudEvent $event
     *   The configuration event.
     * @param string $event_name
     *   The event name.
     */
    public function configEventRecorder(ConfigCrudEvent $event, $event_name) {
        $config = $event->getConfig();
        $event_info = [
            'event_name' => $event_name,
            'current_config_data' => $config->get(),
            'original_config_data' => $config->getOriginal(),
            'raw_config_data' => $config->getRawData(),
        ];
        $this->state
            ->set('config_events_test.event', $event_info);
        // Record all events that occur.
        $all_events = $this->state
            ->get('config_events_test.all_events', []);
        $config_name = $config->getName();
        $all_events[$event_name][$config_name][] = $event_info;
        $this->state
            ->set('config_events_test.all_events', $all_events);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events[ConfigEvents::SAVE][] = [
            'configEventRecorder',
        ];
        $events[ConfigEvents::DELETE][] = [
            'configEventRecorder',
        ];
        $events[ConfigEvents::RENAME][] = [
            'configEventRecorder',
        ];
        $events[ConfigCollectionEvents::SAVE_IN_COLLECTION][] = [
            'configEventRecorder',
        ];
        $events[ConfigCollectionEvents::DELETE_IN_COLLECTION][] = [
            'configEventRecorder',
        ];
        $events[ConfigCollectionEvents::RENAME_IN_COLLECTION][] = [
            'configEventRecorder',
        ];
        return $events;
    }

}