public function onPostPackageInstall(PackageEvent $event)
    {
        $op = $event->getOperation();
        if ($op instanceof InstallOperation) {
            $package = $op->getPackage()->getName();
            if ($package === self::PACKAGE_NAME) {
                $this->logger->info('composer-merge-plugin installed');
                $this->state->setFirstInstall(true);
                $this->state->setLocked(
                    $event->getComposer()->getLocker()->isLocked()
                );
            }
        }
    }