Google Calendar does not play nice with ICS files exported from IBM Lotus Notes, which is a pain if you like to keep your personal calendar in sync with your work calendar. This simple utility uses a parser generated with ANTLR to process the (often huge) ICS file, unroll repeating events and perform some restructuring so that the result can be imported correctly in Google Calendar.

The ICAL grammar is taken from this Github repository.

So far, it seems the following actions make the file possible to import into Google Calendar:

• Remove all calendar properties.
• Remove all VEVENT properties except DTSTART, DTEND, DESCRIPTION, SUMMARY and LOCATION.
• If a calendar entry contains a RDATE property, "unroll" the repetitions into separate VEVENT entries.
• Sort the events in ascending order according to start date.