res_calendar_icalendar: Filter out occurrences superceded by another VEVENT

When we are loading the calendars, we call libical's
icalcomponent_foreach_recurrence method for each VEVENT component that
we have in our calendar.

That method has no knowledge concerning the existence of the other
VEVENT components and will feed our callback with all ocurrences
matching the requested time span.

The occurrences generated by icalcomponent_foreach_recurrence while
expanding a recurring VEVENT's RRULE and RDATE properties can be
superceded by an other VEVENT sharing the same UID.

I use an external iterator (in libical terminology) to avoid messing
with the internal ones from the calling function, and search for
VEVENTS which could supersede the current occurrence.

The event which can invalidate this occurence needs to have:

- the same UID as our recurrent component (comp)
- a RECURRENCE-ID property, which represents the start time of this
  occurrence

If one component is found, just clean and return.

ASTERISK-27296 #close
Reported by: Benoît Dereck-Tricot

Change-Id: I8587ae3eaa765af7cb21eda3b6bf84e8a1c87af8

res/res_calendar_icalendar.c

@@ -177,7 +177,7 @@ static time_t icalfloat_to_timet(icaltimetype time)
 }
 
 /* span->start & span->end may be dates or floating times which have no timezone,
- * which would mean that they should apply to the local timezone for all recepients.
+ * which would mean that they should apply to the local timezone for all recipients.
  * For example, if a meeting was set for 1PM-2PM floating time, people in different time
  * zones would not be scheduled at the same local times.  Dates are often treated as
  * floating times, so all day events will need to be converted--so we can trust the
@@ -249,7 +249,42 @@ static void icalendar_add_event(icalcomponent *comp, struct icaltime_span *span,
 		}
 	}
 
-	/* Get the attendees */
+	/*
+	 * If comp has an RRULE and/or RDATE property, we need to check whether
+	 * another vevent component supercedes this span. Such a component would
+	 * have two characteristics:
+	 *  - its UID is the same as comp
+	 *  - its RECURRENCE-ID property is the same time as span->start
+	 */
+	if (icalcomponent_get_first_property(comp, ICAL_RRULE_PROPERTY)
+	   || icalcomponent_get_first_property(comp, ICAL_RDATE_PROPERTY)) {
+		icalcompiter comp_iter;
+		icaltimetype span_start = icaltime_from_timet_with_zone(
+			event->start, icaltime_is_date(start), icaltime_get_timezone(start));
+
+		icaltime_set_timezone(&span_start, icaltime_get_timezone(start));
+		for (comp_iter = icalcomponent_begin_component(pvt->data, ICAL_VEVENT_COMPONENT);
+			 icalcompiter_deref(&comp_iter);
+			 icalcompiter_next(&comp_iter)) {
+			icalcomponent *vevent = icalcompiter_deref(&comp_iter);
+			icalproperty *uid = icalcomponent_get_first_property(vevent, ICAL_UID_PROPERTY);
+
+			if (uid && !strcmp(icalproperty_get_value_as_string(uid), event->uid)) {
+				icaltimetype recurrence_id = icalcomponent_get_recurrenceid(vevent);
+
+				/* Set the same timezone that we want to compare against */
+				icaltime_set_timezone(&recurrence_id, icaltime_get_timezone(start));
+
+				if (!icaltime_compare(recurrence_id, span_start)
+				   && icaltime_is_date(span_start) == icaltime_is_date(recurrence_id)) {
+					event = ast_calendar_unref_event(event);
+					return;
+				}
+			}
+		}
+	}
+
+    /* Get the attendees */
 	for (prop = icalcomponent_get_first_property(comp, ICAL_ATTENDEE_PROPERTY);
 			prop; prop = icalcomponent_get_next_property(comp, ICAL_ATTENDEE_PROPERTY)) {
 		struct ast_calendar_attendee *attendee;