Support Calculation of VALARM

[niccokunzmann]

recurring-ical-events should also be able to calculate when alarms take place.

Component: VALARM

RFC 5545:

• single alarm
• repeating alarm
• two alarms at the same time
• absolute alarm
• several alarms for one event
• alarm in TODO
• alarm before event
• alarm after event
• silenced alarm
• icalendar examples
• events modified with RANGE=THISANDFUTURE
• rfc7986 is not affecting alarms
• alarms of day events repeated & modified
• alarms snoozed thunderbird
• alarms snoozed outlook
• alarms snoozed etar/android
• alarms snoozed google
• local timezone alarm
• Google Calendar, X-WR-TIMEZONE - is the modification parameter and such problematic?

RFC 9074:

• UID
• related to
• acknowledged alarm
• snoozed alarm
• access the component the alarm is in

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[niccokunzmann]

The "VALARM" calendar component MUST only appear within either a "VEVENT" or "VTODO" calendar component.

Thus the question is: How should alarms be used?

Proposal

Do we expect e.g. an event to be returned and that has one sub-component which is an alarm?
It could be that we add a Event.subcomponents attribute. This attribute includes all alarms that take place within the requested timespan. Also, the event is included if the alarms are within the timespan.

VEVENT -> event is within timespan
VALARM -> alarm is within timespan
VALARM + VEVENT -> event OR alarm is within timespan

How to deduplicate? Maybe, we merge the events?