public function listFiles(): array {

        try {
            return array_column(
                array_map(function($key, $archive) {
                    return [ "key" => $key, "files" => $archive->listFiles() ];
                }, array_keys($this->zip_archives), $this->zip_archives),
            "files", "key");
        } catch (ZipException $ze) {
            throw $ze;
        }

    }