const cacheName = 'blogCache';
const offlineUrl = '/offline/';
const adminPageSlug = '/ghost';

/**
 * The event listener for the service worker installation
 */
self.addEventListener('install', event => {
  event.waitUntil(
    caches.open(cacheName)
    .then(cache => cache.addAll([
      offlineUrl
    ]))
  );
});

/**
 * Is the current request for an HTML page?
 * @param {Object} event
 */
function isHtmlPage(event) {
  return event.request.method === 'GET' && event.request.headers.get('accept').includes('text/html');
}

/**
 * Is the current request for the admin portal resource
 * @param {Object} event
 */
function isAdminPageResource(event) {
  return event.request.url.includes(adminPageSlug);
}

/**
 * Fetch and cache any results as we receive them.
 */
self.addEventListener('fetch', event => {

  event.respondWith(
    caches.match(event.request)
    .then(response => {
      // Only return cache if it's not an HTML page or admin resources
      if (response && !isHtmlPage(event) && !isAdminPageResource(event)) {
        return response;
      }

      return fetch(event.request).then(
        function (response) {
          // Dont cache if not a 200 response
          if (!response || response.status !== 200) {
            return response;
          }

          let responseToCache = response.clone();
          caches.open(cacheName)
          .then(function (cache) {
            cache.put(event.request, responseToCache);
          });

          return response;
        }
      ).catch(error => {
        // Check if the user is offline first and is trying to navigate to a web page
        if (isHtmlPage(event)
        ) {
          return caches.match(offlineUrl);
        }
      });
    })
  )
  ;
});