fix: timezone parsing issues for calendars (#21665)

* fix timezone parsing issues for calendars

* fix: maintain backward compatibility with other timezone specification methods

accepting the cubic-dev-ai as implement backward compatibility with different event ICS event types

Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>

* Update Cubic comment

* Fix timezone handling in ICS feed calendar service

- Fix VTIMEZONE selection to find matching timezone instead of using first one
- Improve TZID parameter extraction from DTSTART property using jCal array
- Fix precedence: DTSTART TZID > standalone TZID > UTC > fallback
- Resolves issue where Europe/Brussels events showed wrong times in Europe/Paris

* remove comments

* remove comments

---------

Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>
Co-authored-by: Anik Dhabal Babu <81948346+anikdhabal@users.noreply.github.com>
Co-authored-by: Kartik Saini <41051387+kart1ka@users.noreply.github.com>

packages/app-store/ics-feedcalendar/lib/CalendarService.ts

@@ -159,11 +159,17 @@ export default class ICSFeedCalendarService implements Calendar {
         // if (vevent?.getFirstPropertyValue("transp") === "TRANSPARENT") return;
 
         const event = new ICAL.Event(vevent);
+        const dtstartProperty = vevent.getFirstProperty("dtstart");
+        const tzidFromDtstart = dtstartProperty ? (dtstartProperty as any).jCal[1].tzid : undefined;
+
         const dtstart: { [key: string]: string } | undefined = vevent?.getFirstPropertyValue("dtstart");
         const timezone = dtstart ? dtstart["timezone"] : undefined;
         // We check if the dtstart timezone is in UTC which is actually represented by Z instead, but not recognized as that in ICAL.js as UTC
         const isUTC = timezone === "Z";
-        const tzid: string | undefined = vevent?.getFirstPropertyValue("tzid") || isUTC ? "UTC" : timezone;
+
+        // Fix precedence: prioritize TZID from DTSTART property, then standalone TZID, then UTC, then fallback
+        const tzid: string | undefined =
+          tzidFromDtstart || vevent?.getFirstPropertyValue("tzid") || (isUTC ? "UTC" : timezone);
         // In case of icalendar, when only tzid is available without vtimezone, we need to add vtimezone explicitly to take care of timezone diff
         if (!vcalendar.getFirstSubcomponent("vtimezone")) {
           const timezoneToUse = tzid || userTimeZone;
@@ -192,7 +198,16 @@ export default class ICSFeedCalendarService implements Calendar {
             console.error("No timezone found");
           }
         }
-        const vtimezone = vcalendar.getFirstSubcomponent("vtimezone");
+        
+        let vtimezone = null;
+        if (tzid) {
+          const allVtimezones = vcalendar.getAllSubcomponents("vtimezone");
+          vtimezone = allVtimezones.find((vtz) => vtz.getFirstPropertyValue("tzid") === tzid);
+        }
+
+        if (!vtimezone) {
+          vtimezone = vcalendar.getFirstSubcomponent("vtimezone");
+        }
 
         // mutate event to consider travel time
         applyTravelDuration(event, getTravelDurationInSeconds(vevent));
@@ -263,9 +278,11 @@ export default class ICSFeedCalendarService implements Calendar {
           event.endDate = event.endDate.convertToZone(zone);
         }
 
+        const finalStartISO = dayjs(event.startDate.toJSDate()).toISOString();
+        const finalEndISO = dayjs(event.endDate.toJSDate()).toISOString();
         return events.push({
-          start: dayjs(event.startDate.toJSDate()).toISOString(),
-          end: dayjs(event.endDate.toJSDate()).toISOString(),
+          start: finalStartISO,
+          end: finalEndISO,
         });
       });
     });

packages/lib/CalendarService.ts

@@ -393,11 +393,16 @@ export default abstract class BaseCalendarService implements Calendar {
         if (vevent?.getFirstPropertyValue("transp") === "TRANSPARENT") return;
 
         const event = new ICAL.Event(vevent);
+        const dtstartProperty = vevent.getFirstProperty("dtstart");
+        const tzidFromDtstart = dtstartProperty ? (dtstartProperty as any).jCal[1].tzid : undefined;
         const dtstart: { [key: string]: string } | undefined = vevent?.getFirstPropertyValue("dtstart");
         const timezone = dtstart ? dtstart["timezone"] : undefined;
         // We check if the dtstart timezone is in UTC which is actually represented by Z instead, but not recognized as that in ICAL.js as UTC
         const isUTC = timezone === "Z";
-        const tzid: string | undefined = vevent?.getFirstPropertyValue("tzid") || isUTC ? "UTC" : timezone;
+
+        // Fix precedence: prioritize TZID from DTSTART property, then standalone TZID, then UTC, then fallback
+        const tzid: string | undefined =
+          tzidFromDtstart || vevent?.getFirstPropertyValue("tzid") || (isUTC ? "UTC" : timezone);
         // In case of icalendar, when only tzid is available without vtimezone, we need to add vtimezone explicitly to take care of timezone diff
         if (!vcalendar.getFirstSubcomponent("vtimezone")) {
           const timezoneToUse = tzid || userTimeZone;
@@ -426,7 +431,16 @@ export default abstract class BaseCalendarService implements Calendar {
             console.error("No timezone found");
           }
         }
-        const vtimezone = vcalendar.getFirstSubcomponent("vtimezone");
+
+        let vtimezone = null;
+        if (tzid) {
+          const allVtimezones = vcalendar.getAllSubcomponents("vtimezone");
+          vtimezone = allVtimezones.find((vtz) => vtz.getFirstPropertyValue("tzid") === tzid);
+        }
+
+        if (!vtimezone) {
+          vtimezone = vcalendar.getFirstSubcomponent("vtimezone");
+        }
 
         // mutate event to consider travel time
         applyTravelDuration(event, getTravelDurationInSeconds(vevent, this.log));
@@ -498,9 +512,11 @@ export default abstract class BaseCalendarService implements Calendar {
           event.endDate = event.endDate.convertToZone(zone);
         }
 
+        const finalStartISO = dayjs(event.startDate.toJSDate()).toISOString();
+        const finalEndISO = dayjs(event.endDate.toJSDate()).toISOString();
         return events.push({
-          start: dayjs(event.startDate.toJSDate()).toISOString(),
-          end: dayjs(event.endDate.toJSDate()).toISOString(),
+          start: finalStartISO,
+          end: finalEndISO,
         });
       });
     });