protected function getCacheModificationDate($file)
    {
        $storageKey   = $this->getStorageKey() . '.lasmodified';
        $filemtime    = filemtime($file);
        $lastmodified = $this->storage->has($storageKey) ? $this->storage->get($storageKey) : $filemtime - 1;

        return array($filemtime, $lastmodified);
    }