fix: timezone

src/utils/recurrenceDescription.test.ts

@@ -1,11 +1,12 @@
 import { describe, it, expect } from 'vitest'
 import { describeRecurrence } from './recurrenceDescription'
 
-// Reference: 2026-04-13 local time = Monday, 2nd Monday of April 2026.
-const tuesdayFirstOfMonth = new Date(2026, 3, 7, 18, 30).toISOString() // 2026-04-07 is a Tuesday, 1st of month
-const monday2ndOfMonth = new Date(2026, 3, 13, 18, 30).toISOString() // 2026-04-13
-const sunday13thOfMonth = new Date(2026, 8, 13, 10, 0).toISOString() // 2026-09-13 is a Sunday
-const monday5thOfMonth = new Date(2026, 2, 30, 20, 0).toISOString() // 2026-03-30
+// All test dates fall inside EU DST (Mar 29 – Oct 25, 2026), so Berlin is UTC+2.
+// We spell the UTC instant explicitly so tests are timezone-independent.
+const tuesdayFirstOfMonth = '2026-04-07T16:30:00.000Z' // Tue 2026-04-07 18:30 Berlin
+const monday2ndOfMonth = '2026-04-13T16:30:00.000Z' // Mon 2026-04-13 18:30 Berlin
+const sunday13thOfMonth = '2026-09-13T08:00:00.000Z' // Sun 2026-09-13 10:00 Berlin
+const monday5thOfMonth = '2026-03-30T18:00:00.000Z' // Mon 2026-03-30 20:00 Berlin
 
 describe('describeRecurrence', () => {
   it('returns undefined for none / missing recurrenceType', () => {
@@ -14,7 +15,7 @@ describe('describeRecurrence', () => {
   })
 
   it('describes daily with time from event.date', () => {
-    const dateAt10 = new Date(2026, 3, 13, 10, 0).toISOString()
+    const dateAt10 = '2026-04-13T08:00:00.000Z' // 10:00 Berlin
     expect(describeRecurrence({ recurrenceType: 'daily', date: dateAt10 })).toBe(
       'Täglich um 10:00 Uhr',
     )
@@ -85,7 +86,7 @@ describe('describeRecurrence', () => {
   })
 
   it('pads minutes correctly (08:05, not 8:5)', () => {
-    const dateEarly = new Date(2026, 3, 13, 8, 5).toISOString()
+    const dateEarly = '2026-04-13T06:05:00.000Z' // 08:05 Berlin
     expect(describeRecurrence({ recurrenceType: 'daily', date: dateEarly })).toBe(
       'Täglich um 08:05 Uhr',
     )

src/utils/recurrenceDescription.ts

@@ -28,18 +28,55 @@ const WEEK_OF_MONTH_LABEL: Record<string, string> = {
   last: 'letzten',
 }
 
-// Match the clamp in eventRecurrence.ts so the label on the Event page
-// agrees with the rule the generator actually produces.
-const weekOfMonthN = (d: Date): number => Math.min(Math.ceil(d.getDate() / 7), 4)
+const BERLIN_TZ = 'Europe/Berlin'
 
-const formatTime = (d: Date): string => {
-  const hh = String(d.getHours()).padStart(2, '0')
-  const mm = String(d.getMinutes()).padStart(2, '0')
-  return `${hh}:${mm}`
+const WEEKDAY_EN_TO_INDEX: Record<string, number> = {
+  Sunday: 0,
+  Monday: 1,
+  Tuesday: 2,
+  Wednesday: 3,
+  Thursday: 4,
+  Friday: 5,
+  Saturday: 6,
 }
 
-const withTime = (description: string, d: Date | null): string =>
-  d ? `${description} um ${formatTime(d)} Uhr` : description
+const berlinFormatter = new Intl.DateTimeFormat('en-GB', {
+  timeZone: BERLIN_TZ,
+  hour: '2-digit',
+  minute: '2-digit',
+  day: 'numeric',
+  weekday: 'long',
+  hourCycle: 'h23',
+})
+
+type BerlinParts = {
+  hour: string
+  minute: string
+  day: number
+  weekdayIndex: number
+}
+
+const getBerlinParts = (d: Date): BerlinParts => {
+  const parts = berlinFormatter.formatToParts(d)
+  const get = (type: string) =>
+    parts.find((p) => p.type === type)?.value ?? ''
+  return {
+    hour: get('hour'),
+    minute: get('minute'),
+    day: Number(get('day')),
+    weekdayIndex: WEEKDAY_EN_TO_INDEX[get('weekday')] ?? 0,
+  }
+}
+
+// Match the clamp in eventRecurrence.ts so the label on the Event page
+// agrees with the rule the generator actually produces.
+const weekOfMonthN = (dayOfMonth: number): number =>
+  Math.min(Math.ceil(dayOfMonth / 7), 4)
+
+const formatTime = (p: BerlinParts): string => `${p.hour}:${p.minute}`
+
+const withTime = (description: string, p: BerlinParts | null): string =>
+  p ? `${description} um ${formatTime(p)} Uhr` : description
 
 type RecurrenceRule = NonNullable<Event['recurrenceRules']>[number]
 
@@ -78,33 +115,34 @@ export const describeRecurrence = (
 
   const parsed = event.date ? new Date(event.date) : null
   const d = parsed && !Number.isNaN(parsed.getTime()) ? parsed : null
+  const p = d ? getBerlinParts(d) : null
 
   switch (type) {
     case 'daily':
-      return withTime('Täglich', d)
+      return withTime('Täglich', p)
     case 'weekly':
-      return withTime(d ? `Jeden ${WEEKDAYS_DE[d.getDay()]}` : 'Wöchentlich', d)
+      return withTime(p ? `Jeden ${WEEKDAYS_DE[p.weekdayIndex]}` : 'Wöchentlich', p)
     case 'biweekly':
       return withTime(
-        d ? `Alle 2 Wochen, ${WEEKDAYS_DE[d.getDay()]}` : 'Alle 2 Wochen',
-        d,
+        p ? `Alle 2 Wochen, ${WEEKDAYS_DE[p.weekdayIndex]}` : 'Alle 2 Wochen',
+        p,
       )
     case 'monthlyByDate':
-      return withTime(d ? `Monatlich am ${d.getDate()}.` : 'Monatlich', d)
+      return withTime(p ? `Monatlich am ${p.day}.` : 'Monatlich', p)
     case 'monthlyByWeekday':
       return withTime(
-        d
-          ? `Monatlich am ${weekOfMonthN(d)}. ${WEEKDAYS_DE[d.getDay()]}`
+        p
+          ? `Monatlich am ${weekOfMonthN(p.day)}. ${WEEKDAYS_DE[p.weekdayIndex]}`
           : 'Monatlich',
-        d,
+        p,
       )
     case 'custom': {
       const rules = event.recurrenceRules ?? []
       const parts = rules
         .map(describeCustomRule)
-        .filter((p): p is string => Boolean(p))
-      if (parts.length === 0) return withTime('Benutzerdefiniert', d)
-      return withTime(parts.join(' · '), d)
+        .filter((part): part is string => Boolean(part))
+      if (parts.length === 0) return withTime('Benutzerdefiniert', p)
+      return withTime(parts.join(' · '), p)
     }
     default:
       return undefined