bug: sequence wrong

[niccokunzmann]

Describe the bug

In order to use recurring events for editing as described in the readme, the sequence number MUST be set to the highest one in the UID. That should be done automatically.

The way we interpret the events, we interpret them based on the latest SEQUENCE. As such, SEQUENCE should be set to the value of our assumption to mitigate exposing details and problems to users.

To Reproduce

If the sequence number of the edited event is lower than the sequence number of the base (or another event), then it is not treated as an update.

ICS file

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//IDN nextcloud.com//Calendar app 4.7.15//EN
CALSCALE:GREGORIAN
BEGIN:VEVENT
SUMMARY:new event
DTSTART;TZID=Europe/Zurich:20250405T100000
DTEND;TZID=Europe/Zurich:20250405T110000
DTSTAMP:20250309T035107Z
UID:d4a3afdb-10f7-4905-bb66-10a1d11cd0a2
SEQUENCE:5
CREATED:20250309T035051Z
LAST-MODIFIED:20250309T035107Z
STATUS:CONFIRMED
END:VEVENT
BEGIN:VTIMEZONE
TZID:Europe/Zurich
BEGIN:DAYLIGHT
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
TZNAME:CEST
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:CET
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
SUMMARY:new event✓
DTSTART;TZID=Europe/Zurich:20250405T100000
DTEND;TZID=Europe/Zurich:20250405T110000
DTSTAMP:20250309T035107Z
UID:d4a3afdb-10f7-4905-bb66-10a1d11cd0a2
RECURRENCE-ID;TZID=Europe/Zurich:20250405T100000
SEQUENCE:3
CREATED:20250309T035051Z
LAST-MODIFIED:20250309T035107Z
STATUS:TENTATIVE
END:VEVENT
END:VCALENDAR

Expected behavior

I would expect nextcloud to send an invite but it does not.

Console output

Version:

pip list

Additional context

This concerns caldav scheduling

Suggested implementation

• add an ICS file, example:
  

  python-recurring-ical-events/test/calendars/issue-15-duplicated-events.ics

  Line 1 in f4a90b2

  BEGIN:VCALENDAR

• add a test, example:
  

  python-recurring-ical-events/test/test_issue_15.py

  Line 21 in f4a90b2

  def test_sequence_is_not_present(calendars):

• fix the bug and ensure the test code passes