middleware.ts

import { match as matchLocale } from "@formatjs/intl-localematcher";
import Negotiator from "negotiator";
import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";
import { DEFAULT_LOCALE, LOCALES } from "./lib/constants";

function getLocale(request: NextRequest): string | undefined {
  const negotiatorHeaders: Record<string, string> = {};
  request.headers.forEach((value, key) => (negotiatorHeaders[key] = value));

  const languages = new Negotiator({ headers: negotiatorHeaders }).languages(
    LOCALES
  );

  const locale = matchLocale(languages, LOCALES, DEFAULT_LOCALE);

  return locale;
}

export function middleware(request: NextRequest) {
  const pathname = request.nextUrl.pathname;

  if (/\.(.*)$/.test(pathname)) {
    return;
  }

  const pathnameIsMissingLocale = LOCALES.every(
    (locale) => !pathname.startsWith(`/${locale}/`) && pathname !== `/${locale}`
  );

  if (pathnameIsMissingLocale) {
    const locale = getLocale(request);

    return NextResponse.redirect(
      new URL(
        `/${locale}${pathname.startsWith("/") ? "" : "/"}${pathname}`,
        request.url
      )
    );
  }
}

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