From 57743e6640d23d37ae6c94e725777a9889592e15 Mon Sep 17 00:00:00 2001
From: Jonas Braathen <jonas@ponas.no>
Date: Sat, 5 Sep 2026 18:09:04 +0200
Subject: [PATCH] web: new attempt at fixing revalidation/caching per day

---
 web/src/lib/revalidation.test.ts | 31 ++++++++++++++++++++++++++++++-
 web/src/lib/revalidation.ts      | 10 +++++++---
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/web/src/lib/revalidation.test.ts b/web/src/lib/revalidation.test.ts
index d45ad53..e4523be 100644
--- a/web/src/lib/revalidation.test.ts
+++ b/web/src/lib/revalidation.test.ts
@@ -1,6 +1,9 @@
 import { describe, expect, it } from "vitest";
 
-import { secondsUntilOsloMidnight } from "./revalidation.ts";
+import {
+  cachedUntilOsloMidnight,
+  secondsUntilOsloMidnight,
+} from "./revalidation.ts";
 
 describe("secondsUntilOsloMidnight", () => {
   it("is 12h from midnight at 12:00 CEST on a normal day", () => {
@@ -23,3 +26,29 @@ describe("secondsUntilOsloMidnight", () => {
     expect(secondsUntilOsloMidnight(now)).toBe(23 * 3600);
   });
 });
+
+describe("cachedUntilOsloMidnight", () => {
+  // urql types fetchOptions as RequestInit | () => RequestInit; we always pass an object
+  function fetchOptionsAt(now: Date): RequestInit {
+    const { fetchOptions } = cachedUntilOsloMidnight(now);
+    return typeof fetchOptions === "function" ? fetchOptions() : fetchOptions ?? {};
+  }
+
+  it("keys the fetch cache on the Oslo date, not the UTC date", () => {
+    // 00:30 CEST on Sep 5 is still Sep 4 in UTC
+    const { headers } = fetchOptionsAt(new Date("2026-09-04T22:30:00Z"));
+    expect(headers).toEqual({ "x-oslo-day": "2026-09-05" });
+  });
+
+  it("changes the cache key at Oslo midnight", () => {
+    const before = fetchOptionsAt(new Date("2026-09-04T21:59:59Z"));
+    const after = fetchOptionsAt(new Date("2026-09-04T22:00:00Z"));
+    expect(before.headers).toEqual({ "x-oslo-day": "2026-09-04" });
+    expect(after.headers).toEqual({ "x-oslo-day": "2026-09-05" });
+  });
+
+  it("revalidates at Oslo midnight and tags the entry", () => {
+    const { next } = fetchOptionsAt(new Date("2026-09-05T10:00:00Z"));
+    expect(next).toEqual({ revalidate: 12 * 3600, tags: ["cms"] });
+  });
+});
diff --git a/web/src/lib/revalidation.ts b/web/src/lib/revalidation.ts
index 34e7b24..34bb19f 100644
--- a/web/src/lib/revalidation.ts
+++ b/web/src/lib/revalidation.ts
@@ -1,5 +1,5 @@
 import { addDays, startOfDay } from "date-fns";
-import { fromZonedTime, toZonedTime } from "date-fns-tz";
+import { formatInTimeZone, fromZonedTime, toZonedTime } from "date-fns-tz";
 import type { OperationContext } from "@urql/core";
 
 const timeZone = "Europe/Oslo";
@@ -29,10 +29,14 @@ export const uncached: Partial<OperationContext> = {
 };
 
 // For queries whose results depend on "today" (futureEvents, opening hours)
-export function cachedUntilOsloMidnight(): Partial<OperationContext> {
+export function cachedUntilOsloMidnight(
+  now: Date = new Date()
+): Partial<OperationContext> {
   return {
     fetchOptions: {
-      next: { revalidate: secondsUntilOsloMidnight(), tags: [CMS_CACHE_TAG] },
+      // Part of the fetch cache key, so yesterday's entry is never reused
+      headers: { "x-oslo-day": formatInTimeZone(now, timeZone, "yyyy-MM-dd") },
+      next: { revalidate: secondsUntilOsloMidnight(now), tags: [CMS_CACHE_TAG] },
     },
   };
 }