frontend/src/proxy.ts

import { NextResponse, type NextRequest } from "next/server";
import { defaultLocale, locales } from "@/i18n/config";

const PUBLIC_FILE = /\.(.*)$/;

function pickLocale(request: NextRequest): string {
  const cookie = request.cookies.get("locale")?.value;
  if (cookie && (locales as readonly string[]).includes(cookie)) return cookie;
  const header = request.headers.get("accept-language") ?? "";
  for (const part of header.split(",")) {
    const code = part.split(";")[0].trim().toLowerCase().split("-")[0];
    if ((locales as readonly string[]).includes(code)) return code;
  }
  return defaultLocale;
}

export function proxy(request: NextRequest) {
  const { pathname } = request.nextUrl;
  if (
    pathname.startsWith("/_next") ||
    pathname.startsWith("/api") ||
    pathname === "/favicon.ico" ||
    PUBLIC_FILE.test(pathname)
  ) {
    return;
  }
  const hasLocale = (locales as readonly string[]).some(
    (l) => pathname === `/${l}` || pathname.startsWith(`/${l}/`)
  );
  if (hasLocale) return;
  const locale = pickLocale(request);
  const url = request.nextUrl.clone();
  url.pathname = `/${locale}${pathname === "/" ? "" : pathname}`;
  return NextResponse.redirect(url);
}

export const config = {
  matcher: ["/((?!_next|api|.*\\..*).*)"],
};