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

// Parse the Accept-Language header into an ordered list of base language codes.
function parseAcceptLanguage(header: string | null): string[] {
  if (!header) return [];
  return header
    .split(',')
    .map((part) => {
      const [tag, q] = part.trim().split(';q=');
      return { tag: tag.trim().toLowerCase(), q: q ? parseFloat(q) : 1 };
    })
    .sort((a, b) => b.q - a.q)
    .map((x) => x.tag);
}

function detectLocale(request: NextRequest): Locale {
  // 1. Explicit choice via cookie
  const cookieLocale = request.cookies.get(LOCALE_COOKIE)?.value;
  if (isLocale(cookieLocale)) return cookieLocale;

  // 2. Browser preference via Accept-Language
  const accepted = parseAcceptLanguage(request.headers.get('accept-language'));
  for (const tag of accepted) {
    const exact = locales.find((l) => l.toLowerCase() === tag);
    if (exact) return exact;
    const base = locales.find((l) => l.toLowerCase().split('-')[0] === tag.split('-')[0]);
    if (base) return base;
  }

  // 3. Fallback
  return defaultLocale;
}

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

  const pathnameHasLocale = locales.some(
    (locale) => pathname === `/${locale}` || pathname.startsWith(`/${locale}/`),
  );
  if (pathnameHasLocale) return;

  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;
}

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