Recurring Events

Recurring events follow the iCalendar RFC 5545 RRULE standard. No backend changes are needed — CalDAV (SabreDAV) handles recurrence natively.

Architecture

RecurrenceEditor (React)
  -> IcsRecurrenceRule (ts-ics)
    -> RRULE string (RFC 5545)
      -> .ics file (CalDAV)
        -> SabreDAV server

RecurrenceEditor Component

Located at src/frontend/apps/calendars/src/features/calendar/components/RecurrenceEditor.tsx

import { RecurrenceEditor } from '@/features/calendar/components/RecurrenceEditor';

const [recurrence, setRecurrence] = useState<IcsRecurrenceRule>();

<RecurrenceEditor value={recurrence} onChange={setRecurrence} />

Include in the event object:

const event: IcsEvent = {
  // ...other fields
  recurrenceRule: recurrence,
};

Supported patterns

Pattern	RRULE
Every day	`FREQ=DAILY`
Every 3 days	`FREQ=DAILY;INTERVAL=3`
Every Monday	`FREQ=WEEKLY;BYDAY=MO`
Mon/Wed/Fri	`FREQ=WEEKLY;BYDAY=MO,WE,FR`
Every 2 weeks on Thu	`FREQ=WEEKLY;INTERVAL=2;BYDAY=TH`
15th of each month	`FREQ=MONTHLY;BYMONTHDAY=15`
March 15 yearly	`FREQ=YEARLY;BYMONTH=3;BYMONTHDAY=15`
10 occurrences	append `;COUNT=10`
Until a date	append `;UNTIL=20251231T235959Z`

Not yet supported

BYSETPOS (e.g. "1st Monday of month", "last Friday")
Edit single instance vs series (needs RECURRENCE-ID UI)
Visual preview of recurrence pattern

Date validation

The component warns about edge cases:

Feb 30/31 — "February has at most 29 days"
Feb 29 — "Only exists in leap years"
Day 31 on 30-day months — shown as warning

Translations

Supported: English, French, Dutch. Keys are in src/frontend/apps/calendars/src/features/i18n/translations.json under calendar.recurrence.*.

IcsRecurrenceRule interface (ts-ics)

interface IcsRecurrenceRule {
  frequency: 'DAILY' | 'WEEKLY' | 'MONTHLY' | 'YEARLY';
  interval?: number;
  count?: number;
  until?: IcsDateObject;
  byDay?: { day: 'MO'|'TU'|'WE'|'TH'|'FR'|'SA'|'SU' }[];
  byMonthDay?: number[];
  byMonth?: number[];
}

How CalDAV handles it

RRULE is stored as a property in the VEVENT inside the .ics file
SabreDAV expands recurring instances when clients query date ranges
Individual instance modifications use RECURRENCE-ID (not yet in UI)

Example .ics:

BEGIN:VEVENT
UID:abc-123
SUMMARY:Weekly Team Meeting
DTSTART:20260125T140000Z
RRULE:FREQ=WEEKLY;BYDAY=MO;UNTIL=20261231T235959Z
END:VEVENT

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