The script asks you for a version of minecraft, you enter it (can be a snapshot), The script copies the TEMPLATE folder and starts the server.jar. If the server.jar does not exist, it will download the correct file from mojangs servers.

Installation / Usage

Download the script
Create a folder called "TEMPLATE" with the lowest version possible (if you use 1.8 - 1.16 inclusive snapshots, create a world in 1.7) with your map (minecraft can upgrade a world, but it cannot downgrade versions, especially not after 1.13). It should contain an eula.txt, your ops.json, your world, and all files you need.
Adjust the javaPath in the file (edit with an editor). If Java 8 is your default JRE, just insert java.
Run the script with python3 server_wrapper.py. You can pass the parameter download-all and it will create an offline cache for all minecraft versions (latest - first)

Assets Properties Generator

A tool to create the assets_properties.json resource. It automatically fetches the minecraft version index and the pixlyzer index. It then combines them, stores all hashes of files that minosoft needs to work. It might also start the minosoft assets properties generator to generate the jar assets hash.