ConfigSnapshotSubscriber.php

<?php

namespace Drupal\Core\EventSubscriber;

use Drupal\Core\Config\ConfigEvents;
use Drupal\Core\Config\ConfigManagerInterface;
use Drupal\Core\Config\StorageInterface;
use Drupal\Core\Config\ConfigImporterEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Create a snapshot when config is imported.
 */
class ConfigSnapshotSubscriber implements EventSubscriberInterface {
    
    /**
     * The configuration manager.
     *
     * @var \Drupal\Core\Config\ConfigManagerInterface
     */
    protected $configManager;
    
    /**
     * The source storage used to discover configuration changes.
     *
     * @var \Drupal\Core\Config\StorageInterface
     */
    protected $sourceStorage;
    
    /**
     * The snapshot storage used to write configuration changes.
     *
     * @var \Drupal\Core\Config\StorageInterface
     */
    protected $snapshotStorage;
    
    /**
     * Constructs the ConfigSnapshotSubscriber object.
     *
     * @param \Drupal\Core\Config\StorageInterface $source_storage
     *   The source storage used to discover configuration changes.
     * @param \Drupal\Core\Config\StorageInterface $snapshot_storage
     *   The snapshot storage used to write configuration changes.
     */
    public function __construct(ConfigManagerInterface $config_manager, StorageInterface $source_storage, StorageInterface $snapshot_storage) {
        $this->configManager = $config_manager;
        $this->sourceStorage = $source_storage;
        $this->snapshotStorage = $snapshot_storage;
    }
    
    /**
     * Creates a config snapshot.
     *
     * @param \Drupal\Core\Config\ConfigImporterEvent $event
     *   The Event to process.
     */
    public function onConfigImporterImport(ConfigImporterEvent $event) {
        $this->configManager
            ->createSnapshot($this->sourceStorage, $this->snapshotStorage);
    }
    
    /**
     * Registers the methods in this class that should be listeners.
     *
     * @return array
     *   An array of event listener definitions.
     */
    public static function getSubscribedEvents() {
        $events[ConfigEvents::IMPORT][] = [
            'onConfigImporterImport',
            40,
        ];
        return $events;
    }

}