protected function getCacheDir($user, $imageIdentifier) {
        $userPath = str_pad($user, 3, '0', STR_PAD_LEFT);
        return sprintf(
            '%s/%s/%s/%s/%s/%s/%s/%s/%s',
            $this->getPath(),
            $userPath[0],
            $userPath[1],
            $userPath[2],
            $user,
            $imageIdentifier[0],
            $imageIdentifier[1],
            $imageIdentifier[2],
            $imageIdentifier
        );
    }