fix(front-end): redirect

frontend/src/server.ts

@@ -5,6 +5,10 @@ import { dirname, join, resolve } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import bootstrap from './main.server';
 import { resolveRequestOrigin } from './core/request-origin';
+import {
+  parseAcceptLanguage,
+  resolveInitialLanguage,
+} from './app/core/i18n/language-resolution';
 import { resolvePublicRedirectTarget } from './server-routing';
 
 const serverDistFolder = dirname(fileURLToPath(import.meta.url));
@@ -37,6 +41,25 @@ app.get(
   }),
 );
 
+app.get('/', (req, res) => {
+  const userAgent = req.get('user-agent');
+  const preferredLanguages = parseAcceptLanguage(req.get('accept-language'));
+  const lang = resolveInitialLanguage({
+    preferredLanguages,
+  });
+  const stableRedirect = shouldUseStableRootRedirect(
+    userAgent,
+    preferredLanguages,
+  );
+
+  res.setHeader('Vary', 'Accept-Language, User-Agent');
+  res.setHeader('Cache-Control', 'private, no-store');
+  res.redirect(
+    stableRedirect ? 308 : 302,
+    `/${stableRedirect ? 'it' : lang}${querySuffix(req.originalUrl)}`,
+  );
+});
+
 app.get('**', (req, res, next) => {
   const targetPath = resolvePublicRedirectTarget(req.path);
   if (!targetPath) {
@@ -83,3 +106,21 @@ function querySuffix(url: string): string {
   const queryIndex = String(url ?? '').indexOf('?');
   return queryIndex >= 0 ? String(url).slice(queryIndex) : '';
 }
+
+function shouldUseStableRootRedirect(
+  userAgent: string | undefined,
+  preferredLanguages: readonly string[],
+): boolean {
+  return preferredLanguages.length === 0 || isLikelyCrawler(userAgent);
+}
+
+function isLikelyCrawler(userAgent: string | undefined): boolean {
+  const normalized = String(userAgent ?? '').toLowerCase();
+  if (!normalized) {
+    return false;
+  }
+
+  return /(bot|crawler|spider|slurp|bingpreview|google-read-aloud)/.test(
+    normalized,
+  );
+}