GetOccurences doesn't return correct items when used with RECURRENCE-ID

[ostruk]

Related to #148. I fixed the crash by adding ToList() to the internal selector, but then I found that function is returning incorrect recurrences. Consider an ical of this form:

BEGIN:VCALENDAR
PRODID:-//Google Inc//Google Calendar 70.9054//EN
VERSION:2.0
CALSCALE:GREGORIAN
METHOD:PUBLISH
X-WR-CALNAME:xxxxx
X-WR-TIMEZONE:America/New_York
BEGIN:VTIMEZONE
TZID:America/New_York
X-LIC-LOCATION:America/New_York
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
END:STANDARD
END:VTIMEZONE

BEGIN:VEVENT
DTSTART;TZID=America/New_York:20160914T170000
DTEND;TZID=America/New_York:20160914T180000
RRULE:FREQ=WEEKLY;COUNT=12;BYDAY=WE
DTSTAMP:20161101T174111Z
UID:tnjve0etvt1qii2m9hqvcq8q10@google.com
CREATED:20160830T144912Z
DESCRIPTION:
LAST-MODIFIED:20160830T144912Z
LOCATION:Location A
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:Summary A
TRANSP:OPAQUE
END:VEVENT

BEGIN:VEVENT
DTSTART;TZID=America/New_York:20161012T170000
DTEND;TZID=America/New_York:20161012T180000
DTSTAMP:20161101T174111Z
UID:tnjve0etvt1qii2m9hqvcq8q10@google.com
RECURRENCE-ID;TZID=America/New_York:20161012T170000
CREATED:20160830T144912Z
DESCRIPTION:
LAST-MODIFIED:20160928T142729Z
LOCATION:Location A
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:Summary B
TRANSP:OPAQUE
END:VEVENT

END:VCALENDAR

GetOccurences function runs this code:

occurrences.ExceptWith(
occurrences.Where(o => o.Source is IUniqueComponent)
.Where(o => o.Source.RecurrenceId != null)
.Where(o => o.Source.RecurrenceId.Equals(o.Period.StartTime)).ToList());

Because the time of recurrence did not change, but summary did, function removes the overridden recurrence and returns the original event, which is incorrect (summary should be "Summary B", but it is "Summary A"). We have replaced this bit of code with the following:

foreach (var baseRecurringItem in occurences.Where(o => o.Source is UniqueComponent)
	.GroupBy(o => ((UniqueComponent)o.Source).Uid)
	.SelectMany(@group => @group.Where(o => o.Source.RecurrenceId != null)
	.SelectMany(occurrence => @group.Where(o => o.Source.RecurrenceId == null && occurrence.Source.RecurrenceId.Date.Equals(o.Period.StartTime.Date)))))
{
	occurences.Remove(baseRecurringItem);
} 

It removes the original item while leaving the override in place. Been using this since dday days when it would just return occurrences without attempting to filter them and haven't had any problems with it.

Thanks.

[ghentsch]

Will you be building a new version of ical.net which incorporates this change or should we just work around it using your sample?

[rianjs]

@ghentsch and @ostruk - I just committed the workaround and published 2.2.25 which incorporates it. I added unit tests, too.

5c766b5