class NodeTranslationMigrateSubscriber

class NodeTranslationMigrateSubscriber implements EventSubscriberInterface {
    
    /**
     * The key value factory.
     *
     * @var \Drupal\Core\KeyValueStore\KeyValueFactoryInterface
     */
    protected $keyValue;
    
    /**
     * The state service.
     *
     * @var \Drupal\Core\State\StateInterface
     */
    protected $state;
    
    /**
     * Constructs the NodeTranslationMigrateSubscriber.
     *
     * @param \Drupal\Core\KeyValueStore\KeyValueFactoryInterface $key_value
     *   The key value factory.
     * @param \Drupal\Core\State\StateInterface $state
     *   The state service.
     */
    public function __construct(KeyValueFactoryInterface $key_value, StateInterface $state) {
        $this->keyValue = $key_value;
        $this->state = $state;
    }
    
    /**
     * Helper method to check if we are migrating translated nodes.
     *
     * @param \Drupal\migrate\Event\EventBase $event
     *   The migrate event.
     *
     * @return bool
     *   True if we are migrating translated nodes, false otherwise.
     */
    protected function isNodeTranslationsMigration(EventBase $event) {
        $migration = $event->getMigration();
        $source_configuration = $migration->getSourceConfiguration();
        $destination_configuration = $migration->getDestinationConfiguration();
        return !empty($source_configuration['translations']) && $destination_configuration['plugin'] === 'entity:node';
    }
    
    /**
     * Maps the old nid to the new one in the key value collection.
     *
     * @param \Drupal\migrate\Event\MigratePostRowSaveEvent $event
     *   The migrate post row save event.
     */
    public function onPostRowSave(MigratePostRowSaveEvent $event) {
        if ($this->isNodeTranslationsMigration($event)) {
            $row = $event->getRow();
            $source = $row->getSource();
            $destination = $row->getDestination();
            $collection = $this->keyValue
                ->get('node_translation_redirect');
            $collection->set($source['nid'], [
                $destination['nid'],
                $destination['langcode'],
            ]);
        }
    }
    
    /**
     * Set the node_translation_redirect state to enable the redirects.
     *
     * @param \Drupal\migrate\Event\MigrateImportEvent $event
     *   The migrate import event.
     */
    public function onPostImport(MigrateImportEvent $event) {
        if ($this->isNodeTranslationsMigration($event)) {
            $this->state
                ->set('node_translation_redirect', TRUE);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events = [];
        $events[MigrateEvents::POST_ROW_SAVE] = [
            'onPostRowSave',
        ];
        $events[MigrateEvents::POST_IMPORT] = [
            'onPostImport',
        ];
        return $events;
    }

}