const { fetch } = require("undici");

const DEFAULT_ACCEPT =
  "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8";
const DEFAULT_ACCEPT_LANGUAGE = "fr-FR,fr;q=0.9,en;q=0.7";
const DEFAULT_ACCEPT_ENCODING = "gzip, deflate, br";
const DEFAULT_CACHE_CONTROL = "no-cache";
const DEFAULT_PRAGMA = "no-cache";
const DEFAULT_TIMEOUT_MS = 5000;
const DEFAULT_MAX_REDIRECTS = 5;
const DEFAULT_USER_AGENTS = [
  "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36",
  "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36",
];

function buildUserAgent(preferred) {
  if (typeof preferred === "string" && preferred.trim()) {
    return preferred.trim();
  }
  const index = Math.floor(Math.random() * DEFAULT_USER_AGENTS.length);
  return DEFAULT_USER_AGENTS[index];
}

function extractChromeVersion(userAgent) {
  if (typeof userAgent !== "string") {
    return null;
  }
  const match = userAgent.match(/Chrome\/(\d+)/i);
  if (match && match[1]) {
    return match[1];
  }
  return null;
}

function isChromeLike(userAgent) {
  if (typeof userAgent !== "string") {
    return false;
  }
  return /Chrome\/\d+/i.test(userAgent);
}

function derivePlatform(userAgent) {
  if (typeof userAgent !== "string") {
    return null;
  }
  if (/Windows NT/i.test(userAgent)) {
    return "Windows";
  }
  if (/Mac OS X/i.test(userAgent)) {
    return "macOS";
  }
  if (/Android/i.test(userAgent)) {
    return "Android";
  }
  if (/iPhone|iPad|iPod/i.test(userAgent)) {
    return "iOS";
  }
  if (/Linux/i.test(userAgent)) {
    return "Linux";
  }
  return null;
}

function isMobileUserAgent(userAgent) {
  if (typeof userAgent !== "string") {
    return false;
  }
  return /Mobile|Android|iPhone|iPad|iPod/i.test(userAgent);
}

function buildSecChUa(userAgent) {
  if (!isChromeLike(userAgent)) {
    return null;
  }
  const version = extractChromeVersion(userAgent) || "122";
  return `"Chromium";v="${version}", "Not A(Brand";v="24", "Google Chrome";v="${version}"`;
}

function buildNavigationHeaders(url, userAgent, extraHeaders = {}) {
  const platform = derivePlatform(userAgent);
  const secChUa = buildSecChUa(userAgent);
  const secChUaMobile = isMobileUserAgent(userAgent) ? "?1" : "?0";
  const secChUaPlatform = platform ? `"${platform}"` : null;

  const baseHeaders = {
    "user-agent": userAgent,
    accept: DEFAULT_ACCEPT,
    "accept-language": DEFAULT_ACCEPT_LANGUAGE,
    "accept-encoding": DEFAULT_ACCEPT_ENCODING,
    "cache-control": DEFAULT_CACHE_CONTROL,
    pragma: DEFAULT_PRAGMA,
    dnt: "1",
    connection: "keep-alive",
    "upgrade-insecure-requests": "1",
    "sec-fetch-site": "none",
    "sec-fetch-mode": "navigate",
    "sec-fetch-user": "?1",
    "sec-fetch-dest": "document",
    ...extraHeaders,
  };

  if (secChUa) {
    baseHeaders["sec-ch-ua"] = secChUa;
  }
  if (secChUaMobile) {
    baseHeaders["sec-ch-ua-mobile"] = secChUaMobile;
  }
  if (secChUaPlatform) {
    baseHeaders["sec-ch-ua-platform"] = secChUaPlatform;
  }

  return baseHeaders;
}

async function fetchWithRedirects(targetUrl, options, maxRedirects) {
  let currentUrl = targetUrl;
  let response = null;
  let redirects = 0;

  while (redirects <= maxRedirects) {
    response = await fetch(currentUrl, { ...options, redirect: "manual" });
    const location = response.headers.get("location");
    if (
      response.status >= 300 &&
      response.status < 400 &&
      location &&
      redirects < maxRedirects
    ) {
      if (response.body && typeof response.body.cancel === "function") {
        try {
          await response.body.cancel();
        } catch (_) {
          // Ignore cancellation errors; we're moving to the next hop.
        }
      }
      currentUrl = new URL(location, currentUrl).toString();
      redirects += 1;
      continue;
    }
    break;
  }

  return response;
}

async function probeUrl(url, options = {}) {
  const method = typeof options.method === "string" ? options.method.toUpperCase() : "GET";
  const timeoutMs = Number.isFinite(options.timeoutMs) ? options.timeoutMs : DEFAULT_TIMEOUT_MS;
  const maxRedirects = Number.isFinite(options.maxRedirects)
    ? options.maxRedirects
    : DEFAULT_MAX_REDIRECTS;
  const userAgent = buildUserAgent(options.userAgent);
  const headers = buildNavigationHeaders(url, userAgent, options.headers || {});

  const controller = new AbortController();
  const timer = setTimeout(() => controller.abort(), timeoutMs);

  try {
    const response = await fetchWithRedirects(
      url,
      {
        method,
        headers,
        signal: controller.signal,
      },
      maxRedirects
    );
    const status = response ? response.status : null;
    const finalUrl = response?.url || url;
    if (response?.body && typeof response.body.cancel === "function") {
      try {
        await response.body.cancel();
      } catch (_) {
        // Ignore cancellation errors; the status is all we needed.
      }
    }
    return {
      status,
      finalUrl,
      method,
      errorType: null,
    };
  } catch (error) {
    if (error.name === "AbortError") {
      return {
        status: null,
        finalUrl: url,
        method,
        errorType: "timeout",
      };
    }
    return {
      status: null,
      finalUrl: url,
      method,
      errorType: "network",
      message: error.message,
    };
  } finally {
    clearTimeout(timer);
  }
}

function shouldRetry(result) {
  if (!result) return true;
  if (result.errorType) return true;
  if (typeof result.status !== "number") return true;
  return result.status >= 400;
}

async function checkUrl(url, options = {}) {
  const firstMethod = options.firstMethod || "GET";
  const retryWithGet =
    typeof options.retryWithGet === "boolean"
      ? options.retryWithGet
      : firstMethod === "HEAD";
  let result = await probeUrl(url, { ...options, method: firstMethod });
  if (retryWithGet && shouldRetry(result)) {
    result = await probeUrl(url, { ...options, method: "GET" });
  }
  return result;
}

module.exports = {
  buildUserAgent,
  checkUrl,
  probeUrl,
  shouldRetry,
};