Enhancement: better handle recurring events poorly handled by ical library (#4807)

src/widgets/calendar/integrations/ical.jsx

@@ -51,9 +51,10 @@ export default function Integration({ config, params, setEvents, hideErrors, tim
         title = `${config.name}: ${title}`;
       }
 
-      const eventToAdd = (date, i, type) => {
       // 'dtend' is null for all-day events
       const { dtstart, dtend = { value: 0 } } = event;
+
+      const eventToAdd = (date, i, type) => {
         const days = dtend.value === 0 ? 1 : (dtend.value - dtstart.value) / (1000 * 60 * 60 * 24);
         const eventDate = timezone ? DateTime.fromJSDate(date, { zone: timezone }) : DateTime.fromJSDate(date);
 
@@ -72,7 +73,13 @@ export default function Integration({ config, params, setEvents, hideErrors, tim
         }
       };
 
-      const recurrenceOptions = event?.recurrenceRule?.origOptions;
+      let recurrenceOptions = event?.recurrenceRule?.origOptions;
+      // RRuleSet does not have dtstart, add it manually
+      if (event?.recurrenceRule && event.recurrenceRule.rrules && event.recurrenceRule.rrules()?.[0]?.origOptions) {
+        recurrenceOptions = event.recurrenceRule.rrules()[0].origOptions;
+        recurrenceOptions.dtstart = dtstart.value;
+      }
+
       if (recurrenceOptions && Object.keys(recurrenceOptions).length !== 0) {
         try {
           const rule = new RRule(recurrenceOptions);