let visitorCountryPromise = null;
const IP_LOOKUP_TIMEOUT_MS = 3500;

async function fetchWithTimeout(url, options = {}) {
  const controller = new AbortController();
  const timeout = window.setTimeout(() => controller.abort(), IP_LOOKUP_TIMEOUT_MS);
  try {
    return await fetch(url, { ...options, signal: controller.signal });
  } finally {
    window.clearTimeout(timeout);
  }
}

async function countryFromCloudflare() {
  for (const url of ["/cdn-cgi/trace", "https://www.cloudflare.com/cdn-cgi/trace"]) {
    try {
      const response = await fetchWithTimeout(url, { credentials: "omit", headers: { Accept: "text/plain" }, mode: "cors" });
      if (!response.ok) continue;
      const country = String((await response.text()).match(/^loc=([A-Z]{2})$/m)?.[1] || "").toUpperCase();
      if (country) return country;
    } catch {}
  }
  return "";
}

async function countryFromCountryIs() {
  const response = await fetchWithTimeout("https://api.country.is/", { credentials: "omit", mode: "cors" });
  if (!response.ok) return "";
  return String((await response.json())?.country || "").toUpperCase();
}

async function countryFromIpWho() {
  const response = await fetchWithTimeout("https://ipwho.is/?fields=success,country_code", {
    credentials: "omit",
    headers: { Accept: "application/json" },
    mode: "cors",
  });
  if (!response.ok) return "";
  const payload = await response.json();
  return payload?.success ? String(payload.country_code || "").toUpperCase() : "";
}

export function detectVisitorCountry() {
  if (visitorCountryPromise) return visitorCountryPromise;
  if (typeof window === "undefined" || typeof fetch !== "function") return Promise.resolve("");
  visitorCountryPromise = (async () => {
    for (const detector of [countryFromCloudflare, countryFromCountryIs, countryFromIpWho]) {
      try {
        const country = await detector();
        if (/^[A-Z]{2}$/.test(country)) return country;
      } catch (error) {
        console.debug("[家纺跨境情报] IP 区域检测源不可用，继续尝试备用源:", error);
      }
    }
    return "UNKNOWN";
  })();
  return visitorCountryPromise;
}

export function visitorCanUseGoogleFallback() {
  if (typeof navigator === "undefined" || typeof Intl === "undefined") return false;
  const language = String(navigator.languages?.[0] || navigator.language || "").toLowerCase();
  const timeZone = String(Intl.DateTimeFormat().resolvedOptions().timeZone || "");
  const nonChineseLanguage = Boolean(language) && !language.startsWith("zh");
  const outsideChinaTimeZone = Boolean(timeZone) && !["Asia/Shanghai", "Asia/Urumqi"].includes(timeZone);
  return nonChineseLanguage || outsideChinaTimeZone;
}

export function translationProvider(countryCode, googleFallback = visitorCanUseGoogleFallback()) {
  if (countryCode === "CN") return "yandex";
  if (countryCode && countryCode !== "UNKNOWN") return "google";
  if ((!countryCode || countryCode === "UNKNOWN") && googleFallback) return "google";
  return "yandex";
}