From b3266a242ee33e1a8df850261752ac22eded8e44 Mon Sep 17 00:00:00 2001
From: Ewan Croft <contact@ewancroft.uk>
Date: Sat, 15 Aug 2026 07:43:16 +0100
Subject: [PATCH] fix(blog): derive blog date URLs in Europe/London timezone

---
 src/lib/utils/date.ts                         | 27 +++++++++++++++++++
 src/routes/+page.svelte                       |  6 ++---
 src/routes/blog/+page.server.ts               | 15 ++++++-----
 src/routes/blog/+page.svelte                  | 20 +++++++-------
 src/routes/blog/[rkey]/+page.server.ts        |  8 +++---
 .../[month]/[day]/[slug]/+page.server.ts      |  9 ++-----
 6 files changed, 51 insertions(+), 34 deletions(-)
 create mode 100644 src/lib/utils/date.ts

diff --git a/src/lib/utils/date.ts b/src/lib/utils/date.ts
new file mode 100644
index 0000000..d4b65f7
--- /dev/null
+++ b/src/lib/utils/date.ts
@@ -0,0 +1,27 @@
+/**
+ * Extract the year/month/day components of an ISO timestamp in the site's
+ * canonical timezone (Europe/London).
+ *
+ * Used to derive stable blog URLs (`/blog/YYYY/MM/DD/slug`). Do not round-trip
+ * through `toLocaleString` + `new Date()` — the resulting "dd/mm/yyyy" string
+ * is re-parsed as US format and yields the wrong date.
+ */
+export function blogDateParts(iso: string): {
+  year: string;
+  month: string;
+  day: string;
+} {
+  const parts = new Intl.DateTimeFormat("en-GB", {
+    timeZone: "Europe/London",
+    year: "numeric",
+    month: "2-digit",
+    day: "2-digit",
+  }).formatToParts(new Date(iso));
+
+  const byType = new Map(parts.map((p) => [p.type, p.value]));
+  return {
+    year: byType.get("year") ?? "",
+    month: byType.get("month") ?? "",
+    day: byType.get("day") ?? "",
+  };
+}
diff --git a/src/routes/+page.svelte b/src/routes/+page.svelte
index 446650d..08ca188 100644
--- a/src/routes/+page.svelte
+++ b/src/routes/+page.svelte
@@ -8,6 +8,7 @@
   import Pentacle from '$lib/components/icons/Pentacle.svelte';
   import { ArrowRight, ExternalLink, Music } from '@lucide/svelte';
   import { normalizeSlug } from '$lib/utils/slugify';
+  import { blogDateParts } from '$lib/utils/date';
   import type { ProfileData } from '@ewanc26/atproto';
   import { PUBLIC_LEAFLET_BLOG_PUBLICATION } from '$env/static/public';
 
@@ -51,10 +52,7 @@
   });
 
   function getBlogUrl(post: any) {
-    const date = new Date(post.createdAt);
-    const y = date.getFullYear();
-    const m = (date.getMonth() + 1).toString().padStart(2, '0');
-    const d = date.getDate().toString().padStart(2, '0');
+    const { year: y, month: m, day: d } = blogDateParts(post.createdAt);
     const slug = normalizeSlug(post.title);
     return `/blog/${y}/${m}/${d}/${slug}`;
   }
diff --git a/src/routes/blog/+page.server.ts b/src/routes/blog/+page.server.ts
index cb48aff..5e9f3c5 100644
--- a/src/routes/blog/+page.server.ts
+++ b/src/routes/blog/+page.server.ts
@@ -13,6 +13,7 @@ import {
   PUBLIC_ATPROTO_DID,
   PUBLIC_LEAFLET_BLOG_PUBLICATION,
 } from "$env/static/public";
+import { blogDateParts } from "$lib/utils/date";
 
 const PAGE_SIZE = 20;
 
@@ -43,14 +44,14 @@ export const load: PageServerLoad = async ({ fetch, setHeaders }) => {
   const grouped = new Map<number, Map<number, typeof publicationPosts>>();
 
   for (const post of publicationPosts) {
-    const date = new Date(post.createdAt);
-    const year = date.getFullYear();
-    const month = date.getMonth() + 1;
+    const { year, month } = blogDateParts(post.createdAt);
+    const yearNum = parseInt(year, 10);
+    const monthNum = parseInt(month, 10);
 
-    if (!grouped.has(year)) grouped.set(year, new Map());
-    const yearMap = grouped.get(year)!;
-    if (!yearMap.has(month)) yearMap.set(month, []);
-    yearMap.get(month)!.push(post);
+    if (!grouped.has(yearNum)) grouped.set(yearNum, new Map());
+    const yearMap = grouped.get(yearNum)!;
+    if (!yearMap.has(monthNum)) yearMap.set(monthNum, []);
+    yearMap.get(monthNum)!.push(post);
   }
 
   // Flatten for initial page — take first PAGE_SIZE posts across all groups
diff --git a/src/routes/blog/+page.svelte b/src/routes/blog/+page.svelte
index 4846b8e..9a47ae6 100644
--- a/src/routes/blog/+page.svelte
+++ b/src/routes/blog/+page.svelte
@@ -1,5 +1,6 @@
 <script lang="ts">
     import { normalizeSlug } from '$lib/utils/slugify';
+    import { blogDateParts } from '$lib/utils/date';
     import SiteHead from '$lib/components/SiteHead.svelte';
     import EmptyState from '$lib/components/EmptyState.svelte';
     import LoadingSkeleton from '$lib/components/LoadingSkeleton.svelte';
@@ -24,10 +25,7 @@
     ));
 
     function getPostUrl(post: PostSummary) {
-        const date = new Date(post.createdAt);
-        const y = date.getFullYear();
-        const m = (date.getMonth() + 1).toString().padStart(2, '0');
-        const d = date.getDate().toString().padStart(2, '0');
+        const { year: y, month: m, day: d } = blogDateParts(post.createdAt);
         const slug = normalizeSlug(post.title);
         return `/blog/${y}/${m}/${d}/${slug}`;
     }
@@ -39,13 +37,13 @@
     function groupPosts(posts: PostSummary[]) {
         const grouped = new Map<number, Map<number, PostSummary[]>>();
         for (const post of posts) {
-            const date = new Date(post.createdAt);
-            const year = date.getFullYear();
-            const month = date.getMonth() + 1;
-            if (!grouped.has(year)) grouped.set(year, new Map());
-            const yearMap = grouped.get(year)!;
-            if (!yearMap.has(month)) yearMap.set(month, []);
-            yearMap.get(month)!.push(post);
+            const { year, month } = blogDateParts(post.createdAt);
+            const y = parseInt(year, 10);
+            const m = parseInt(month, 10);
+            if (!grouped.has(y)) grouped.set(y, new Map());
+            const yearMap = grouped.get(y)!;
+            if (!yearMap.has(m)) yearMap.set(m, []);
+            yearMap.get(m)!.push(post);
         }
         return Array.from(grouped.entries()).sort((a, b) => b[0] - a[0]);
     }
diff --git a/src/routes/blog/[rkey]/+page.server.ts b/src/routes/blog/[rkey]/+page.server.ts
index 6853601..8833d3c 100644
--- a/src/routes/blog/[rkey]/+page.server.ts
+++ b/src/routes/blog/[rkey]/+page.server.ts
@@ -3,6 +3,7 @@ import { fetchBlogPosts } from "@ewanc26/atproto";
 import { PUBLIC_ATPROTO_DID } from "$env/static/public";
 import { error, redirect } from "@sveltejs/kit";
 import { normalizeSlug } from "$lib/utils/slugify";
+import { blogDateParts } from "$lib/utils/date";
 
 export const load: PageServerLoad = async ({ params, fetch }) => {
   const { rkey } = params;
@@ -18,11 +19,8 @@ export const load: PageServerLoad = async ({ params, fetch }) => {
     throw error(404, "Post not found");
   }
 
-  const date = new Date(post.createdAt);
-  const y = date.getFullYear();
-  const m = (date.getMonth() + 1).toString().padStart(2, "0");
-  const d = date.getDate().toString().padStart(2, "0");
+  const { year, month, day } = blogDateParts(post.createdAt);
   const slug = normalizeSlug(post.title);
 
-  throw redirect(301, `/blog/${y}/${m}/${d}/${slug}`);
+  throw redirect(301, `/blog/${year}/${month}/${day}/${slug}`);
 };
diff --git a/src/routes/blog/[year]/[month]/[day]/[slug]/+page.server.ts b/src/routes/blog/[year]/[month]/[day]/[slug]/+page.server.ts
index 8b6b516..1f2d8ec 100644
--- a/src/routes/blog/[year]/[month]/[day]/[slug]/+page.server.ts
+++ b/src/routes/blog/[year]/[month]/[day]/[slug]/+page.server.ts
@@ -8,6 +8,7 @@ import {
 } from "$env/static/public";
 import { error } from "@sveltejs/kit";
 import { normalizeSlug } from "$lib/utils/slugify";
+import { blogDateParts } from "$lib/utils/date";
 import { safeResourceUrl } from "$lib/utils/url";
 import { renderMarkdown } from "$lib/utils/markdown";
 import {
@@ -41,13 +42,7 @@ export const load: PageServerLoad = async ({ params, fetch, setHeaders }) => {
   );
 
   const post = publicationDocs.find((d) => {
-    const date = new Date(d.publishedAt);
-    const ukDate = new Date(
-      date.toLocaleString("en-GB", { timeZone: "Europe/London" }),
-    );
-    const y = ukDate.getFullYear().toString();
-    const m = (ukDate.getMonth() + 1).toString().padStart(2, "0");
-    const dStr = ukDate.getDate().toString().padStart(2, "0");
+    const { year: y, month: m, day: dStr } = blogDateParts(d.publishedAt);
     const docSlug = normalizeSlug(d.title);
     return y === year && m === month && dStr === day && docSlug === slug;
   });
-- 
2.51.2