import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";
import { LOCALE, LOCALE_COOKIE_NAME } from "./shared/infrastructure/i18n/config";
import { isValidLocale, determineLocaleFromAcceptLangOrDefault } from "./shared/infrastructure/i18n/utils";

// Exclude static assets and api routes in config
export const config = {
  matcher: [`/((?!api|trpc|_next|_next/image|favicon.ico|_vercel|.*\\..*).*)`],
};

const pathWithoutLocale = ["dashboard"];

// 1. Helper to append locale headers
function createLocaleHeaders({ request, locale }: { request: NextRequest; locale: LOCALE; }) {
  const newHeaders = new Headers(request.headers);
  newHeaders.set(LOCALE_COOKIE_NAME, locale);
  return newHeaders;
}

// 2. Helper to forward request
function createNextResponse({ request, locale }: { request: NextRequest; locale: LOCALE; }) {
  const requestHeaders = createLocaleHeaders({ request, locale });
  const response = NextResponse.next({ request: { headers: requestHeaders } });
  response.cookies.set(LOCALE_COOKIE_NAME, locale, { httpOnly: true, path: "/" });
  return response;
}

// 3. Helper to redirect request
function createLocaleRedirect({ newPath, request, locale }: { newPath: string; request: NextRequest; locale: string; }) {
  const redirectUrl = new URL(newPath, request.url);
  const response = NextResponse.redirect(redirectUrl);
  response.cookies.set(LOCALE_COOKIE_NAME, locale, { httpOnly: true, path: "/" });
  return response;
}

export function proxy(request: NextRequest) {
  const { pathname, search } = request.nextUrl;
  const localeCookie = request.cookies.get(LOCALE_COOKIE_NAME)?.value;
  const segments = pathname.split("/");
  const firstSegment = segments[1];

  const preferredLocale = isValidLocale(localeCookie)
    ? localeCookie
    : determineLocaleFromAcceptLangOrDefault(request.headers.get("accept-language"));

  // Dashboards don't use i18n segments in URL
  if (pathWithoutLocale.includes(firstSegment)) {
    // Add authentication checks here
    return createNextResponse({ request, locale: preferredLocale });
  }

  // Segment matches exactly
  if (isValidLocale(firstSegment)) {
    if (firstSegment === preferredLocale) {
      return createNextResponse({ request, locale: preferredLocale });
    }
    // Redirect to preferred locale if wrong
    const newPath = pathname.replace(`/${firstSegment}`, `/${preferredLocale}`);
    return createLocaleRedirect({ newPath, request, locale: preferredLocale });
  }

  // Missing segment entirely
  const newPath = `/${preferredLocale}${pathname}${search}`;
  return createLocaleRedirect({ newPath, request, locale: preferredLocale });
}