cloud-host/frontend/src/middleware.ts

import { NextRequest, NextResponse } from 'next/server';
import { locales, defaultLocale, isLocale, LOCALE_COOKIE, type Locale } from '@/i18n/config';

// Host-based separation between the marketing landing site and the
// authenticated panel. Configured at runtime (server-side) so the same
// frontend image can serve both hosts. When PANEL_HOST is unset (local dev),
// host routing is disabled and everything is served from a single origin.
const PANEL_HOST = process.env.PANEL_HOST?.trim().toLowerCase();
const LANDING_HOST = process.env.LANDING_HOST?.trim().toLowerCase();

// Locale-stripped path prefixes that belong to the authenticated panel.
const PANEL_PATH_PREFIXES = ['/dashboard', '/login', '/register'];

function stripLocale(pathname: string): string {
  for (const l of locales) {
    if (pathname === `/${l}`) return '/';
    if (pathname.startsWith(`/${l}/`)) return pathname.slice(l.length + 1);
  }
  return pathname;
}

function isPanelPath(pathname: string): boolean {
  const p = stripLocale(pathname);
  return PANEL_PATH_PREFIXES.some((pre) => p === pre || p.startsWith(`${pre}/`));
}

function hostOf(request: NextRequest): string {
  return (request.headers.get('host') || '').split(':')[0].toLowerCase();
}

function detectLocale(request: NextRequest): Locale {
  // Honour the user's last explicit choice, persisted in a cookie by the
  // language switcher. On the very first visit (no cookie) we always serve the
  // default locale (fa-IR) rather than guessing from Accept-Language, so the
  // browser's language preference never overrides the default. From then on,
  // the user's last selection is what determines the language.
  const cookieLocale = request.cookies.get(LOCALE_COOKIE)?.value;
  if (isLocale(cookieLocale)) return cookieLocale;

  return defaultLocale;
}

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

  // 1. Ensure a locale prefix (e.g. /login -> /fa-IR/login). On the redirect
  //    the host is preserved, so host routing (below) runs on the next request.
  const pathnameHasLocale = locales.some(
    (locale) => pathname === `/${locale}` || pathname.startsWith(`/${locale}/`),
  );
  if (!pathnameHasLocale) {
    const locale = detectLocale(request);
    request.nextUrl.pathname = `/${locale}${pathname === '/' ? '' : pathname}`;
    const response = NextResponse.redirect(request.nextUrl);
    response.cookies.set(LOCALE_COOKIE, locale, { path: '/', maxAge: 60 * 60 * 24 * 365 });
    return response;
  }

  // 2. Host-based separation between the landing site and the panel.
  //    Disabled entirely unless PANEL_HOST is configured (local dev).
  if (PANEL_HOST) {
    const host = hostOf(request);
    const panelPath = isPanelPath(pathname);

    // Authenticated routes requested on the landing host -> move to the panel.
    if (LANDING_HOST && host === LANDING_HOST && panelPath) {
      return NextResponse.redirect(`https://${PANEL_HOST}${pathname}${search}`, 308);
    }

    // Marketing pages requested on the panel host -> send to the dashboard.
    if (host === PANEL_HOST && !panelPath) {
      const locale = pathname.split('/')[1]; // path is already locale-prefixed
      const target = request.nextUrl.clone();
      target.pathname = `/${locale}/dashboard`;
      return NextResponse.redirect(target);
    }
  }

  return;
}

export const config = {
  // Skip Next internals, the API, and any path containing a dot (static files).
  matcher: ['/((?!_next|api|.*\\..*).*)'],
};