import { NextResponse } from "next/server";

const LOCALE_COOKIE = "rs_locale";
const SUPPORTED_LOCALES = new Set(["en", "pt"]);
const PUBLIC_FILE = /\.(?:ico|png|jpg|jpeg|svg|webp|avif|gif|txt|xml|json|webmanifest|css|js|map|woff2?)$/i;
const RESERVED_PREFIXES = [
  "/_next",
  "/_a2a",
  "/.well-known",
  "/api",
  "/auth",
  "/invoke",
  "/mcp",
  "/message:send",
  "/message:stream",
  "/tasks",
  "/answers",
  "/input-requests",
  "/scope-grants",
  "/scope-denials",
];

function isReservedPath(pathname) {
  if (PUBLIC_FILE.test(pathname)) {
    return true;
  }
  return RESERVED_PREFIXES.some(
    (prefix) => pathname === prefix || pathname.startsWith(`${prefix}/`),
  );
}

function normalizeLocale(value) {
  const locale = String(value || "").trim().toLowerCase();
  if (SUPPORTED_LOCALES.has(locale)) {
    return locale;
  }
  return null;
}

function localeFromCountry(request) {
  const country = (
    request.headers.get("x-vercel-ip-country")
    || request.headers.get("cf-ipcountry")
    || request.headers.get("x-country-code")
    || ""
  ).trim().toUpperCase();
  if (country === "BR" || country === "PT") {
    return "pt";
  }
  return null;
}

function localeFromAcceptLanguage(request) {
  const header = request.headers.get("accept-language") || "";
  const ranked = header
    .split(",")
    .map((part) => {
      const [tag, ...params] = part.trim().split(";");
      const q = params
        .map((param) => param.trim())
        .find((param) => param.startsWith("q="));
      const weight = q ? Number.parseFloat(q.slice(2)) : 1;
      return {
        language: tag.toLowerCase().split("-")[0],
        weight: Number.isFinite(weight) ? weight : 1,
      };
    })
    .filter((item) => SUPPORTED_LOCALES.has(item.language))
    .sort((a, b) => b.weight - a.weight);
  return ranked[0]?.language || null;
}

function preferredLocale(request) {
  return (
    normalizeLocale(request.cookies.get(LOCALE_COOKIE)?.value)
    || localeFromAcceptLanguage(request)
    || localeFromCountry(request)
    || "en"
  );
}

function withLocaleCookie(response, locale) {
  response.cookies.set(LOCALE_COOKIE, locale, {
    path: "/",
    maxAge: 60 * 60 * 24 * 365,
    sameSite: "lax",
  });
  return response;
}

export function middleware(request) {
  const url = request.nextUrl;
  const { pathname, searchParams } = url;

  if (isReservedPath(pathname)) {
    return NextResponse.next();
  }

  const requestedLocale = normalizeLocale(searchParams.get("lang"));
  if (requestedLocale) {
    const cleanUrl = url.clone();
    cleanUrl.searchParams.delete("lang");
    const response =
      cleanUrl.toString() === url.toString()
        ? NextResponse.next()
        : NextResponse.redirect(cleanUrl);
    return withLocaleCookie(response, requestedLocale);
  }

  if (pathname === "/") {
    const locale = preferredLocale(request);
    if (locale === "pt") {
      const redirectUrl = url.clone();
      redirectUrl.pathname = "/pt/";
      return NextResponse.redirect(redirectUrl);
    }
  }

  return NextResponse.next();
}

export const config = {
  matcher: ["/:path*"],
};