This tool started out as a tool for myself to count the number of vacation days I had used from an ownCloud calendar. Since ownCloud didn't have the functionality, I downloaded the ics file, and wrote this tool to extract it myself. Hopefully it can be useful to others as well. https://code.volse.no/icaltool.git/
Beware, this is still extremely primitive, but it solved my need for the day. If anybody else find it useful, it may even evolve to something more polished.