web: fix ✨ timezone issues ✨ so midnight ISR happens the right day

web/Dockerfile

@@ -33,6 +33,8 @@ WORKDIR /app
 ENV NODE_ENV production
 # Uncomment the following line in case you want to disable telemetry during runtime.
 ENV NEXT_TELEMETRY_DISABLED 1
+# Date logic is Oslo-aware in code, but keep the process TZ matching anyway
+ENV TZ=Europe/Oslo
 
 RUN addgroup --system --gid 1001 nodejs
 RUN adduser --system --uid 1001 nextjs

web/src/lib/date.test.ts

@@ -10,6 +10,7 @@ import {
   groupConsecutiveDates,
   isConsecutiveDays,
   isTodayOrFuture,
+  startOfTodayInOslo,
   toLocalTime,
 } from "./date.ts";
 
@@ -30,6 +31,21 @@ describe("toLocalTime", () => {
   });
 });
 
+describe("startOfTodayInOslo", () => {
+  it("returns the Oslo date even when the server runs in UTC", () => {
+    const tz = process.env.TZ;
+    process.env.TZ = "UTC";
+    try {
+      vi.setSystemTime(new Date("2026-07-07T22:20:00Z"));
+      const today = startOfTodayInOslo();
+      expect(today.getDate()).toBe(8);
+      expect(today.getHours()).toBe(0);
+    } finally {
+      process.env.TZ = tz;
+    }
+  });
+});
+
 describe("formatDate", () => {
   it("formats in Oslo time with Norwegian locale", () => {
     expect(formatDate("2026-07-07T18:00:00Z", "dd.MM.yyyy 'kl.' HH:mm")).toBe(

web/src/lib/date.ts

@@ -20,6 +20,11 @@ export function toLocalTime(date: Date | string | number) {
   return toZonedTime(date, timeZone);
 }
 
+// Start of the current Oslo day, regardless of the server's TZ
+export function startOfTodayInOslo() {
+  return startOfDay(toLocalTime(new Date()));
+}
+
 export function formatDate(date: Date | string | number, formatStr: string) {
   return format(toLocalTime(date), formatStr, { timeZone, locale: nb });
 }

web/src/lib/event.test.ts

@@ -164,6 +164,25 @@ describe("getFutureOccurrences", () => {
       "2026-07-14T18:00:00Z",
     ]);
   });
+
+  it("rolls over at Oslo midnight when the server runs in UTC", () => {
+    const tz = process.env.TZ;
+    process.env.TZ = "UTC";
+    try {
+      // 22:20 UTC on tirsdag is 00:20 onsdag in Oslo
+      vi.setSystemTime(new Date("2026-07-07T22:20:00Z"));
+      const event = makeEvent("a", [
+        "2026-07-07T18:00:00Z",
+        "2026-07-08T18:00:00Z",
+      ]);
+
+      expect(getFutureOccurrences(event).map((o) => o.start)).toEqual([
+        "2026-07-08T18:00:00Z",
+      ]);
+    } finally {
+      process.env.TZ = tz;
+    }
+  });
 });
 
 describe("getEventPig", () => {

web/src/lib/event.ts

@@ -1,13 +1,17 @@
 import {
   endOfWeek,
-  startOfToday,
   startOfWeek,
   isAfter,
   eachDayOfInterval,
   addWeeks,
   parseISO,
 } from "date-fns";
-import { toLocalTime, formatDate, compareDates } from "./date";
+import {
+  toLocalTime,
+  formatDate,
+  compareDates,
+  startOfTodayInOslo,
+} from "./date";
 import { graphql, unmaskFragment } from "@/gql";
 import {
   type EventCategoryFragment,
@@ -338,7 +342,7 @@ export function organizeEventsByDate<E extends EventListable>(
 export function getFutureOccurrences<E extends EventListable>(
   event: E
 ): E["occurrences"][number][] {
-  const today = startOfToday();
+  const today = startOfTodayInOslo();
   const occurrences = event?.occurrences ?? [];
   const futureOccurrences = occurrences.filter((occurrence) =>
     isAfter(toLocalTime(occurrence.start), today)

web/src/lib/openinghours.test.ts

@@ -161,4 +161,23 @@ describe("getTodaysOpeningHoursForFunction", () => {
     vi.setSystemTime(new Date("2026-07-07T10:00:00Z"));
     expect(getTodaysOpeningHoursForFunction(openingHours, "kafé")).toBe("?");
   });
+
+  it("uses the Oslo weekday when the server runs in UTC", () => {
+    const tz = process.env.TZ;
+    process.env.TZ = "UTC";
+    try {
+      // 22:20 UTC on torsdag is 00:20 fredag in Oslo (CEST)
+      vi.setSystemTime(new Date("2026-07-09T22:20:00Z"));
+      expect(getTodaysOpeningHoursForFunction(openingHours, "bar")).toBe(
+        "15:00—01:00"
+      );
+      // 23:20 UTC on torsdag is 00:20 fredag in Oslo (CET)
+      vi.setSystemTime(new Date("2026-01-08T23:20:00Z"));
+      expect(getTodaysOpeningHoursForFunction(openingHours, "bar")).toBe(
+        "15:00—01:00"
+      );
+    } finally {
+      process.env.TZ = tz;
+    }
+  });
 });

web/src/lib/openinghours.ts

@@ -1,13 +1,7 @@
-import {
+import { compareDesc, getISODay, isAfter, isSameDay, parseISO } from "date-fns";
-  compareDesc,
-  getISODay,
-  isAfter,
-  isSameDay,
-  parseISO,
-  startOfToday,
-} from "date-fns";
 
 import { getClient } from "@/app/client";
+import { startOfTodayInOslo } from "@/lib/date";
 import { cachedUntilOsloMidnight } from "@/lib/revalidation";
 import { graphql, unmaskFragment } from "@/gql";
 import type {
@@ -63,7 +57,7 @@ export async function fetchOpeningHoursSets() {
 }
 
 export async function getOpeningHours() {
-  const today = startOfToday();
+  const today = startOfTodayInOslo();
   const sets = await fetchOpeningHoursSets();
   const validSets = sets
     .filter((set) => {
@@ -213,7 +207,7 @@ export function getTodaysOpeningHoursForFunction(
   if (!week) {
     return "?";
   }
-  const weekdayIndex = getISODay(startOfToday()) - 1;
+  const weekdayIndex = getISODay(startOfTodayInOslo()) - 1;
   const weekday = WEEKDAYS[weekdayIndex];
   const hours = week[weekday];
   if (hours?.timeFrom && hours?.timeTo) {