middleware.ts

import { NextRequest, NextResponse } from "next/server";
import { LANGUAGE_STORAGE_KEY, SUPPORTED_LANGUAGES } from "@/src/constants";
import { detectLanguageFromHeader, isRedirectExcludedUrl } from "@/src/hooks/i18n/serverUtils";

/**
 * Middleware to handle server-side language detection and redirection
 * This runs on every request before the page is rendered
 */
export function middleware(request: NextRequest) {
  // Get current URL and pathname
  const url = request.nextUrl.clone();
  const { pathname } = url;

  // Skip redirects for excluded URLs
  if (isRedirectExcludedUrl(pathname)) {
    return NextResponse.next();
  }

  // Check if user has a language preference in cookies
  const cookieLanguage = request.cookies.get(LANGUAGE_STORAGE_KEY)?.value;

  // Check if user's preferred language is already set in cookies
  if (cookieLanguage && SUPPORTED_LANGUAGES.includes(cookieLanguage as any)) {
    // User has a valid language preference, no need to redirect
    return NextResponse.next();
  }

  // Detect preferred language from Accept-Language header
  const detectedLanguage = detectLanguageFromHeader(request);

  // Create response to set cookie with detected language
  const response = NextResponse.next();

  // Set cookie with the detected language
  response.cookies.set(LANGUAGE_STORAGE_KEY, detectedLanguage, {
    maxAge: 60 * 60 * 24 * 365, // 1 year
    path: "/",
  });

  return response;
}

/**
 * Configure the middleware to run on specific paths
 */
export const config = {
  // Match all request paths except for excluded paths
  matcher: [
    /*
     * Match all paths except for:
     * 1. /api routes
     * 2. /_next (Next.js internals)
     * 3. /static (static files)
     * 4. /locales (translation files)
     * 5. all files in the public folder
     */
    "/((?!api|_next|static|locales|favicon.ico|robots.txt).*)",
  ],
};