file object.
    let curFile = templateFile.clone().QueryInterface(Ci.nsIFile);
    let [base, ext] = DownloadPaths.splitBaseNameAndExtension(curFile.leafName);
    // Try other file names, for example "base(1).txt" or "base(1).tar.gz",
    // only if the file name initially set already exists.
    for (let i = 1; i < 10000 && curFile.exists(); i++) {
      curFile.leafName = base + "(" + i + ")" + ext;
    }
    // At this point we hand off control to createUnique, which will create the
    // file with the name we chose, if it is valid. If not, createUnique will
    // attempt to modify it again, for example it will shorten very long names
    // that can't be created on some platforms, and for which a normal call to
    // nsIFile.create would result in NS_ERROR_FILE_NOT_FOUND. This can result
    // very rarely in strange names like "base(9999).tar-1.gz" or "ba-1.gz".
    curFile.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o644);
    return curFile;
  },

  /**
   * Separates the base name from the extension in a file name, recognizing some
   * double extensions like ".tar.gz".
   *
   * @param leafName
   *        The full leaf name to be parsed. Be careful when processing names
   *        containing leading or trailing dots or spaces.
   *
   * @return [base, ext]
   *         The base name of the file, which can be empty, and its extension,
   *         which always includes the leading dot unless it's an empty string.
   *         Concatenating the two items always results in the original name.
   */
  splitBaseNameAndExtension(leafName) {
    // The following regular expression is built from these key parts:
    //  .*?                      Matches the base name non-greedily.
    //  \.[A-Z0-9]{1,3}          Up to three letters or numbers preceding a
    //                           double extension.
    //  \.(?:gz|bz2|Z)           The second part of common double extensions.
    //  \.[^.]*                  Matches any extension or a single trailing dot.
    let [, base, ext] = /(.*?)(\.[A-Z0-9]{1,3}\.(?:gz|bz2|Z)|\.[^.]*)?$/i.exec(
      leafName
    );
    // Return an empty string instead of undefined if no extension is found.
    return [base, ext || ""];
  },
};
PK