Recurring Dates - every X weekdays doesnt parse correctly

Jorge

Forum was down so I raised this in slack:
Slack Bug Report

I just encountered a problem in recurring dates that will annoy any student or professor that might want to use moo.do/Legend for scheduling their classes.
Given a class that needs to be scheduled using the block schedule many schools use, like Day A,B,C,D,E,F where Day A will fall on a different day of the week according to the recurrence pattern (Mon Day A, Tue Day B, Wed Day C, Thu Day D, Fri Day E, Mon Day F, Tue Day A.etc..)
The following text patterns is not parsed correctly by moo.do, but they are parsed correctly by the rrule.js library :
“every 3 weekdays” I expect a class that will happen on M,Th, Tu, Fr, We, M, Th, Tu, Fr, We…. but moo.do interpets it as every 3 weeks.
“every 2 days on Monday, Tuesday, Wednesday” I expect a class that will happen on M,W,Tu,M,W,Tu,….

Jorge

Jay already fixed and is coming in the next release to beta, but just posting it for visibilty

Jorge

After the latest release @Jay did, it works much better, but still a few kinks.

It’s working well for
Every weekday

and Every 2 weekdays

However not working for
every 3 weekdays The 16 should have not been selected.

nor every 4 weekdays
Monday 16 should have been selected and the 18th shouldn’t

nor every 5 weekdays
All Tuesdays should have been selected

Nor every 6 weekdays
Mon 16 shouldn’t be selected instead Wed 18 should have been selected

If you ask me the most urgent for me is every 6 weekdays
Analysing the pattern it seems to me that it is scheduling counting calendar days and only not selecting/marking the ones that land in a weekend.
e.g Every 6 days is counting:
Tue (day 1) SELECTED
Wed (day 2)
Thu (day 3)
Fri (day 4)
Sat (day 5)
Sun (day 6)
Mon (day 1) SELECTED
Tue (day 2)
Wed (day 3)
Thu (day 4)
Fri (day 5)
Sat (day 6)
Sun (day 1) SELECTED BUT FILTERED OUT BECAUSE IT’S A WEEKEND

The Pattern should be
Tue (day 1) SELECTED
Wed (day 2)
Thu (day 3)
Fri (day 4)
Sat ignored
Sun ignored
Mon (day 5)
Tue (day 6)
Wed (day 1) SELECTED
Thu (day 2)
Fri (day 3)
Sat ignored
Sun ignored
Mon (day 4)
Tue (day 5)
Wed (day 1) SELECTED

Jorge

Hi @Jay Were you able to take a look at this? Sorry to insist but it’s really important for me. It is a must to open interest for professors and students alike. I’ve been trying to convince some friends of mine and this has been the major stumbling block.

Jay

Jorge I don’t think it’s possible. We have to follow the rrule spec (so that we can enable sync with Google/Outlook calendars) and this is the rrule behavior for the daily frequency. I can’t figure out a way to make rrule work the way you’re describing.

Every 6 weekdays comes out as:
FREQ=DAILY;INTERVAL=6;BYDAY=MO,TU,WE,TH,FR

If you can figure out a way to make rrule work the way you’re describing please let me know! But I can’t see any way that it’s possible 😢.

Jorge

Jay Yes definitely seems that a bug in rrule. It works perfeclty when you select to apply the pattern in only 4 weekdays M,T,W,Th,, but as soon as you add the 5th day it begins miscalculating. So definitely a bug.

Do you raise the bug in their github in this cases?

Jay

I think it’s actually just a funny math coincidence - the recurrence hits weekend days but they’re just not included in the output although it does offset the result. So every 2 weekdays works fine because there’s 2 days on weekends so the result works out the same. And it would be the same for “every 3 weekdays” if you remove Friday because that effectively makes a 3 day weekend so the math works out the same.

Unfortunately it’s far beyond just the rrule.js project. That’s just the javascript implementation of the spec, but the spec is implemented in other places too. So the problem would be that if we hacked in a change to the behavior, syncing the rrule with Google Calendar would then having a different recurrence pattern in Google Calendar.

It’s currently still kind of hypothetical since we don’t have support for syncing recurrences with Google Calendar yet, but that is the reason we used rrule in the first place, and it’s still on our todo list to add that support. You can see on the Google Calendar API for example that the recurrence is defined by an RRULE string: https://developers.google.com/calendar/api/guides/recurringevents

So in order to be able to fully support syncing with Google Calendar (and other calendars) I think we need to stick tightly to the rrule spec. If we make any changes to its behavior that will cause a ton of confusion in the future if we don’t support syncing specific recurrences or if the recurrences behave differently when synced.

Jorge

Jay I see your point, however all the calendars I’ve used, google, microsoft outlook are very limited in their recurrence patterns support. They don’t support all the patterns that the rrule/iCalendar standard support. So whenever you implement full sincronization of recurring events there will be recuring patterns that the rrule supports that those calendars don’t. e.g. every 5 days on Monday, Tuesday, Wednesday is not supported by any of those calendars and therefore will not be able to be synched properly from Legend into those calendars. Rrule is far more general so you will always have cases that won’t sync into external calendars. .