addEventListener('fetch', event => {
  // NOTE: can’t use fetch here, as we’re not in an async scope yet
  event.respondWith(eventHandler(event));
});

async function eventHandler(event) {
  const { headers } = event.request;
  const contentType = headers.get('content-type') || '';

  if (event.request.method === 'POST' && contentType.indexOf('application/activity+json') >= 0) {
    const json = await event.request.clone().json();
    if (json.type !== 'Follow') {
      return new Response('{}', {
        headers: {
          'content-type': 'application/activity+json',
        },
      });
    }
  }

  if (event.request.method === 'GET') {
    // use the cache!
    const cacheUrl = new URL(event.request.url);
    const cacheKey = new Request(cacheUrl.toString(), event.request);
    const cache = caches.default;

    let response = await cache.match(cacheKey);
    if (!response) {
      response = await fetch(event.request, { cf: { resolveOverride: 'realorigin.gervas.io' } });
      response = new Response(response.body, response);
      response.headers.append('Cache-Control', 's-maxage=600');
      event.waitUntil(cache.put(cacheKey, response.clone()));
    }
    return response;
  } else {
    return fetch(event.request, { cf: { resolveOverride: 'realorigin.gervas.io' } });
  }
}