const DEFAULT_DASHBOARD_URL = 'https://dashboard.informatika.untan.ac.id/index.php?penelitian';
const CACHE_TTL_MS = 5 * 60 * 1000;

let dashboardCache = {
  html: '',
  timestamp: 0,
};

function getDashboardUrl() {
  return process.env.DASHBOARD_TARGET_URL || DEFAULT_DASHBOARD_URL;
}

function response(statusCode, body, extraHeaders = {}) {
  return {
    statusCode,
    headers: {
      'Content-Type': 'text/html; charset=utf-8',
      'Cache-Control': 'public, max-age=60, stale-while-revalidate=300',
      ...extraHeaders,
    },
    body,
  };
}

exports.handler = async () => {
  const now = Date.now();

  if (dashboardCache.html && now - dashboardCache.timestamp < CACHE_TTL_MS) {
    return response(200, dashboardCache.html, { 'X-Cache': 'HIT' });
  }

  const controller = new AbortController();
  const timeoutId = setTimeout(() => controller.abort(), 12000);

  try {
    const dashboardResponse = await fetch(getDashboardUrl(), {
      signal: controller.signal,
      headers: {
        'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0 Safari/537.36',
      },
    });

    if (!dashboardResponse.ok) {
      throw new Error(`HTTP_ERROR_${dashboardResponse.status}`);
    }

    const html = await dashboardResponse.text();
    dashboardCache = { html, timestamp: Date.now() };

    return response(200, html, { 'X-Cache': 'MISS' });
  } catch (error) {
    if (dashboardCache.html) {
      return response(200, dashboardCache.html, { 'X-Cache': 'STALE' });
    }

    return {
      statusCode: 502,
      headers: {
        'Content-Type': 'text/plain; charset=utf-8',
      },
      body: error && error.name === 'AbortError'
        ? 'DASHBOARD_FETCH_TIMEOUT'
        : 'DASHBOARD_FETCH_FAILED',
    };
  } finally {
    clearTimeout(timeoutId);
  }
};