My day job is writing a calendar product. I'm currently re-writing the entire product as an API. Something as simple as "Create a new event" has taken months of

My day job is writing a calendar product. I'm currently re-writing the entire product as an API. Something as simple as "Create a new event" has taken months of work (when you save an event you have to update recurrences, alarms, attendees, etc.) Our legacy code has an event save method that's a few thousand lines long. It's the one part of the code that we avoid at all costs because a seemingly minor change can break some weird edge case. We also have a CalDav module that works but also has weird edge cases when different calendars handle things in different ways. For example, you have an event that starts on a Monday, set to repeat on Wed and Fri for 10 occurrences. Do you display the Monday occurrence of the original event even though it's not in the recurrence rule? If so, does it count as one of the 10 occurrences or not? In our testing, iCal, Google Calendar, and Outlook all handle this same case in completely different ways.