Complete public brief locale switching

frontend/app/methodology/[slug]/page.tsx

@@ -1,16 +1,37 @@
 import type { Metadata } from "next";
+import { cookies, headers } from "next/headers";
 import { notFound } from "next/navigation";
 import { MethodologyDetailPageView } from "@/components/public-content/PublicContentPages";
+import {
+  LANDING_LOCALE_COOKIE,
+  LANDING_LOCALE_QUERY_PARAM,
+  pickLandingLocale,
+  type LandingLocale,
+} from "@/components/landing/landingLocale";
 import {
   METHODOLOGY_PAGES,
   absolutePublicUrl,
   getMethodologyPage,
+  localizeMethodologyPage,
   methodologyPath,
 } from "@/content/public-content";
 
 type MethodologyPageParams = {
   slug: string;
 };
+type MethodologySearchParams = Promise<Record<string, string | string[] | undefined>>;
+
+async function resolvePublicContentLocale(searchParams: MethodologySearchParams): Promise<LandingLocale> {
+  const params = await searchParams;
+  const rawLocale = params[LANDING_LOCALE_QUERY_PARAM];
+  const queryLocale = Array.isArray(rawLocale) ? rawLocale[0] : rawLocale;
+  const [cookieStore, headerStore] = await Promise.all([cookies(), headers()]);
+  return pickLandingLocale(
+    queryLocale,
+    cookieStore.get(LANDING_LOCALE_COOKIE)?.value,
+    headerStore.get("accept-language"),
+  );
+}
 
 export function generateStaticParams() {
   return METHODOLOGY_PAGES.map((page) => ({ slug: page.slug }));
@@ -18,10 +39,15 @@ export function generateStaticParams() {
 
 export async function generateMetadata({
   params,
+  searchParams,
 }: {
   params: Promise<MethodologyPageParams>;
+  searchParams: MethodologySearchParams;
 }): Promise<Metadata> {
-  const { slug } = await params;
+  const [{ slug }, locale] = await Promise.all([
+    params,
+    resolvePublicContentLocale(searchParams),
+  ]);
   const page = getMethodologyPage(slug);
 
   if (!page) {
@@ -29,17 +55,18 @@ export async function generateMetadata({
       title: "Methodology not found",
     };
   }
+  const localizedPage = localizeMethodologyPage(page, locale);
 
   return {
-    title: page.title,
-    description: page.description,
+    title: localizedPage.title,
+    description: localizedPage.description,
     alternates: {
       canonical: methodologyPath(page),
     },
     openGraph: {
       type: "article",
-      title: page.title,
-      description: page.description,
+      title: localizedPage.title,
+      description: localizedPage.description,
       url: methodologyPath(page),
       modifiedTime: page.updatedAt,
     },
@@ -48,22 +75,28 @@ export async function generateMetadata({
 
 export default async function MethodologyDetailPage({
   params,
+  searchParams,
 }: {
   params: Promise<MethodologyPageParams>;
+  searchParams: MethodologySearchParams;
 }) {
-  const { slug } = await params;
+  const [{ slug }, locale] = await Promise.all([
+    params,
+    resolvePublicContentLocale(searchParams),
+  ]);
   const page = getMethodologyPage(slug);
 
   if (!page) {
     notFound();
   }
 
+  const localizedPage = localizeMethodologyPage(page, locale);
   const pathname = methodologyPath(page);
   const jsonLd = {
     "@context": "https://schema.org",
     "@type": "TechArticle",
-    headline: page.title,
-    description: page.description,
+    headline: localizedPage.title,
+    description: localizedPage.description,
     dateModified: page.updatedAt,
     mainEntityOfPage: absolutePublicUrl(pathname),
     author: {
@@ -79,7 +112,7 @@ export default async function MethodologyDetailPage({
         type="application/ld+json"
         dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
       />
-      <MethodologyDetailPageView page={page} />
+      <MethodologyDetailPageView page={page} locale={locale} />
     </>
   );
 }