addEventListener('fetch', event => {
  event.respondWith(handleRequest(event));
});

async function handleRequest(event) {
  const url = new URL(event.request.url);
  const { request } = event;
  const { headers } = request;

  const referer = headers.get('Referer') || '';
  const userAgent = headers.get('User-Agent');
  const refHost = (() => {
    try {
      return new URL(referer).hostname;
    } catch (e) {
      return '';
    }
  })();
  const uuid = getOrCreateUuid(headers);

  event.waitUntil(logAnalyticsData(event, url, uuid, userAgent, referer));

  const response = new Response(null, {
    status: 204,
    statusText: 'No Content',
  });

  if (!headers.get('cookie')?.includes('uuid=')) {
    response.headers.set(
      'Set-Cookie',
      `uuid=${uuid}; Expires=${new Date(Date.now() + 365 * 86400 * 30 * 1000).toUTCString()}; Path='/';`,
    );
  }

  return response;
}

function shouldBlockRequest(refHost, userAgent, url) {
  if (!refHost || !userAgent || !url.search.includes('ga=')) {
    return true;
  }
  return false;
}

function getOrCreateUuid(headers) {
  const cookie = headers.get('cookie') || '';
  const uuidMatch = cookie.match(/uuid=([^;]+)/);
  if (uuidMatch) {
    return uuidMatch[1];
  }
  return crypto.randomUUID();
}

async function logAnalyticsData(event, url, uuid, userAgent, pageUrl) {
  // - This is defined in the workers runtime
  // eslint-disable-next-line no-undef
  const { ANALYTICS_ENGINE } = globalThis;
  const params = url.searchParams;

  const dataPoint = {
    blobs: [
      pageUrl, // Page URL
      userAgent, // User Agent
      params.get('dt') || '', // Page Title
      params.get('de') || '', // Document Encoding
      params.get('dr') || '', // Document Referrer
      params.get('ul') || '', // User Language
      params.get('sd') || '', // Screen Colors
      params.get('sr') || '', // Screen Resolution
      params.get('vp') || '', // Viewport Size
      uuid, // Client ID
    ],
    doubles: [
      parseFloat(params.get('plt') || '0'), // Page Load Time
      parseFloat(params.get('dns') || '0'), // DNS Time
      parseFloat(params.get('pdt') || '0'), // Page Download Time
      parseFloat(params.get('rrt') || '0'), // Redirect Response Time
      parseFloat(params.get('tcp') || '0'), // TCP Connect Time
      parseFloat(params.get('srt') || '0'), // Server Response Time
      parseFloat(params.get('dit') || '0'), // DOM Interactive Time
      parseFloat(params.get('clt') || '0'), // Content Loaded Time
    ],
    indexes: [
      event.request.headers.get('CF-Connecting-IP') || '', // User IP
    ],
  };

  ANALYTICS_ENGINE.writeDataPoint(dataPoint);
}