[Remind-Fans] two-way caldav synchronization

[James Cook]

I'm looking for a tool to synchronize changes both ways between a (new)
remind file and my existing CalDAV calendar. (It doesn't have to speak
CalDAV --- I currently use vdirsyncer to sync my calendar with a
directory full of .ics files on disk which is read by khard. So, I'd be
happy with a tool that only works locally.)

I tried Jochen Sprickerhof's dav2rem/rem2dav2 but it doesn't seem to do
what I want. For example:

- If I run "dav2rem -r (...url...) f.rem" twice, events appear twice in
  f.rem.

- If I create f.rem manually, run "rem2dav -r (...url...) f.rem"
  specifying a new test calendar URL, then edit an event in f.rem and
  run rem2dav again, I end up with the old and new events in the CalDAV
  calendar.

I think I understand why that's hapening: dav2rem/rem2dav use simple
logic where on the CalDAV side the event's uid is based on a hash of the
Remind file line.

What I actually want:

- I can make arbitrary changes on either side, including creating or
  deleting events, then run a sync tool, and it will (within reason)
  propagate the changes both way.

I understand this would be somewhat more complicated to implement than
dav2rem/rem2dav (for example, there would have to be some magic to keep
track of which remind lines match which vcalendar events) but wonder if
a tool like this exists.

-- 
James