nelenkov/android-backup-extractor ? reverse-engineered prompt

Build me a small Java command line tool that can unpack and repack Android backup files made with adb backup, and also handle the older Android 4.4 style format. It should take a backup .ab file, extract the contents into a tar file or folder, and then be able to pack that tar back into a valid Android backup that can be restored with adb restore.

If a password is provided, use it for encrypted backups, and if not, leave it unencrypted but still compressed. It should also support reading from standard input and writing to standard output when the filename is -. Please make it easy to build into a single runnable jar, and include clear usage help for the pack and unpack commands. If there are any tricky Android backup rules around tar ordering or restore compatibility, follow them and make the tool work as safely as possible.