fix: recurring event DST time shift and block height overflow

- Use TZID-based local time (instead of UTC 'Z') for DTSTART/DTEND
  when creating recurring CalDAV events, preventing DST-related time
  shifts (e.g. 13:40 CET showing as 14:40 CEST after clock change)
- Send browser timezone from CalendarEventModal to server
- Guard against NaN event duration (missing/invalid endTime) which
  caused event blocks to stretch to end of day

v1.61.1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "my-weekly-todo-list",
-  "version": "1.61.0",
+  "version": "1.61.1",
   "description": "A web-based weekly task management application that organizes to-dos and calendar events in a single, intuitive weekly view",
   "main": "index.js",
   "scripts": {

src/app/api/calendar/events/route.ts

@@ -40,7 +40,7 @@ export async function POST(request: NextRequest) {
 
         const body = await request.json();
         const { calendarId, title, description, start, end, location, allDay, recurrence, recurrenceEndDate, recurrenceCount, recurrenceInterval, recurrenceDays, url,
-                reminders, busyStatus, visibility, attendees, attachments } = body;
+                reminders, busyStatus, visibility, attendees, attachments, timezone } = body;
 
         console.log('[API] Creating event:', { calendarId, title, start, end });
 
@@ -67,6 +67,7 @@ export async function POST(request: NextRequest) {
             recurrenceCount,
             recurrenceInterval,
             recurrenceDays,
+            timezone,
             url,
             reminders,
             busyStatus,

src/components/CalendarEventModal.tsx

@@ -194,6 +194,7 @@ export default function CalendarEventModal({
                 allDay,
                 start: { dateTime: startDate.toISOString() },
                 end: { dateTime: endDate.toISOString() },
+                timezone: Intl.DateTimeFormat().resolvedOptions().timeZone,
                 reminders: activeReminders.length > 0 ? activeReminders : undefined,
                 busyStatus: busyStatus !== 'busy' ? busyStatus : undefined,
                 visibility: visibility !== 'default' ? visibility : undefined,

src/components/WeeklyView.tsx

@@ -3546,6 +3546,11 @@ export default function WeeklyView() {
         const end = new Date(event.endTime);
         const durationMinutes = (end.getTime() - start.getTime()) / (1000 * 60);
 
+        // Guard against NaN or negative durations (missing/invalid end time)
+        if (!isFinite(durationMinutes) || durationMinutes <= 0) {
+            return getSlotHeight(effectiveCellDuration); // Default to one slot height
+        }
+
         // Calculate height based on duration and slot height
         const pixelsPerMinute = getSlotHeight(effectiveCellDuration) / effectiveCellDuration;
         return Math.max(

src/lib/apple-calendar.ts

@@ -394,6 +394,7 @@ export const createEvent = async (
     recurrenceCount?: number;
     recurrenceInterval?: number;
     recurrenceDays?: number[];
+    timezone?: string;
     start: { dateTime?: string; date?: string };
     end: { dateTime?: string; date?: string };
     reminders?: Array<{ method: string; minutes: number }>;
@@ -439,11 +440,29 @@ export const createEvent = async (
       // For all-day events, end date is exclusive, so if they are same, add 1 day
       // But typically UI handles this. Let's assume input is correct.
     } else if (eventData.start.dateTime) {
-      // Timed event
+      // For recurring events, use local time with TZID to avoid DST shifts
-      dtStart = new Date(eventData.start.dateTime).toISOString().replace(/[-:.]/g, '').substring(0, 15) + 'Z';
+      if (eventData.recurrence && eventData.timezone) {
-      dtEnd = eventData.end.dateTime
+        const tz = eventData.timezone;
-        ? new Date(eventData.end.dateTime).toISOString().replace(/[-:.]/g, '').substring(0, 15) + 'Z'
+        const toLocalIcal = (isoStr: string) => {
-        : dtStart;
+          const d = new Date(isoStr);
+          const parts = new Intl.DateTimeFormat('en-CA', {
+            timeZone: tz, year: 'numeric', month: '2-digit', day: '2-digit',
+            hour: '2-digit', minute: '2-digit', second: '2-digit', hour12: false,
+          }).formatToParts(d);
+          const get = (t: string) => parts.find(p => p.type === t)?.value || '00';
+          return `${get('year')}${get('month')}${get('day')}T${get('hour')}${get('minute')}${get('second')}`;
+        };
+        dtStart = toLocalIcal(eventData.start.dateTime);
+        dtEnd = eventData.end.dateTime ? toLocalIcal(eventData.end.dateTime) : dtStart;
+        dtStartParam = `;TZID=${tz}`;
+        dtEndParam = `;TZID=${tz}`;
+      } else {
+        // Timed event (non-recurring or no timezone info)
+        dtStart = new Date(eventData.start.dateTime).toISOString().replace(/[-:.]/g, '').substring(0, 15) + 'Z';
+        dtEnd = eventData.end.dateTime
+          ? new Date(eventData.end.dateTime).toISOString().replace(/[-:.]/g, '').substring(0, 15) + 'Z'
+          : dtStart;
+      }
     }
 
     const description = eventData.description ? `DESCRIPTION:${eventData.description.replace(/\n/g, '\\n')}\r\n` : '';

src/lib/calendar-events.ts

@@ -45,6 +45,7 @@ export interface CalendarEvent {
   recurrenceCount?: number;
   recurrenceInterval?: number;
   recurrenceDays?: number[];
+  timezone?: string;
   recurringEventId?: string;
   isRecurring?: boolean;
   source: 'google' | 'apple' | 'outlook' | 'synology' | 'notion';
@@ -952,6 +953,7 @@ export const createCalendarEvent = async (
         recurrenceCount: event.recurrenceCount,
         recurrenceInterval: event.recurrenceInterval,
         recurrenceDays: event.recurrenceDays,
+        timezone: event.timezone,
         start,
         end,
         reminders: event.reminders,
@@ -992,6 +994,7 @@ export const createCalendarEvent = async (
         recurrenceCount: event.recurrenceCount,
         recurrenceInterval: event.recurrenceInterval,
         recurrenceDays: event.recurrenceDays,
+        timezone: event.timezone,
         start: event.start!,
         end: event.end!,
         reminders: event.reminders,

src/lib/synology-calendar.ts

@@ -404,6 +404,7 @@ export const createEvent = async (
     recurrenceCount?: number;
     recurrenceInterval?: number;
     recurrenceDays?: number[];
+    timezone?: string;
     start: { dateTime?: string; date?: string };
     end: { dateTime?: string; date?: string };
     reminders?: Array<{ method: string; minutes: number }>;
@@ -440,10 +441,28 @@ export const createEvent = async (
       dtStartParam = ';VALUE=DATE';
       dtEndParam = ';VALUE=DATE';
     } else if (eventData.start.dateTime) {
-      dtStart = new Date(eventData.start.dateTime).toISOString().replace(/[-:.]/g, '').substring(0, 15) + 'Z';
+      // For recurring events, use local time with TZID to avoid DST shifts
-      dtEnd = eventData.end.dateTime
+      if (eventData.recurrence && eventData.timezone) {
-        ? new Date(eventData.end.dateTime).toISOString().replace(/[-:.]/g, '').substring(0, 15) + 'Z'
+        const tz = eventData.timezone;
-        : dtStart;
+        const toLocalIcal = (isoStr: string) => {
+          const d = new Date(isoStr);
+          const parts = new Intl.DateTimeFormat('en-CA', {
+            timeZone: tz, year: 'numeric', month: '2-digit', day: '2-digit',
+            hour: '2-digit', minute: '2-digit', second: '2-digit', hour12: false,
+          }).formatToParts(d);
+          const get = (t: string) => parts.find(p => p.type === t)?.value || '00';
+          return `${get('year')}${get('month')}${get('day')}T${get('hour')}${get('minute')}${get('second')}`;
+        };
+        dtStart = toLocalIcal(eventData.start.dateTime);
+        dtEnd = eventData.end.dateTime ? toLocalIcal(eventData.end.dateTime) : dtStart;
+        dtStartParam = `;TZID=${tz}`;
+        dtEndParam = `;TZID=${tz}`;
+      } else {
+        dtStart = new Date(eventData.start.dateTime).toISOString().replace(/[-:.]/g, '').substring(0, 15) + 'Z';
+        dtEnd = eventData.end.dateTime
+          ? new Date(eventData.end.dateTime).toISOString().replace(/[-:.]/g, '').substring(0, 15) + 'Z'
+          : dtStart;
+      }
     }
 
     const description = eventData.description ? `DESCRIPTION:${eventData.description.replace(/\n/g, '\\n')}\r\n` : '';