import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";
import { i18n } from "./i18n-config";

function getLocale(request: NextRequest): string {
  const acceptLanguage = request.headers.get("accept-language");
  if (!acceptLanguage) return i18n.defaultLocale;

  // Simple and ultra-robust parsing for accept-language header
  const preferredLocales = acceptLanguage
    .split(",")
    .map((lang) => {
      const [locale, q] = lang.split(";q=");
      return {
        locale: locale.trim().split("-")[0].toLowerCase(), // e.g. "tr", "en"
        priority: q ? parseFloat(q) : 1.0,
      };
    })
    .sort((a, b) => b.priority - a.priority);

  for (const pref of preferredLocales) {
    if (i18n.locales.includes(pref.locale as any)) {
      return pref.locale;
    }
  }

  return i18n.defaultLocale;
}

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

  // Skip static assets, internal paths, and favicon
  if (
    pathname.startsWith("/_next") ||
    pathname.startsWith("/api") ||
    pathname.startsWith("/favicon.ico") ||
    pathname.match(/\.(png|jpg|jpeg|gif|svg|webp|ico|css|js|woff|woff2|ttf|otf|json)$/)
  ) {
    return;
  }

  // Check if pathname already contains a supported locale prefix
  const pathnameIsMissingLocale = i18n.locales.every(
    (locale) => !pathname.startsWith(`/${locale}/`) && pathname !== `/${locale}`
  );

  if (pathnameIsMissingLocale) {
    const locale = getLocale(request);
    
    // Redirect /xxx to /locale/xxx
    return NextResponse.redirect(
      new URL(
        `/${locale}${pathname.startsWith("/") ? "" : "/"}${pathname}`,
        request.url
      )
    );
  }
}

export const config = {
  // Matcher ignoring static items and api routes
  matcher: ["/((?!api|_next/static|_next/image|favicon.ico).*)"],
};