export class AppServiceWorker {

  constructor () {
    'ngInject';

    let isLocalhost = Boolean(
      window.location.hostname === 'localhost' ||
      // [::1] is the IPv6 localhost address.
      window.location.hostname === '[::1]' ||
      // 127.0.0.1/8 is considered localhost for IPv4.
      window.location.hostname.match(/^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/)
    );

    if ('serviceWorker' in navigator && (window.location.protocol === 'https:' || isLocalhost)) {
      navigator.serviceWorker.register('service-worker.js')
        .then((registration) => {

          // updatefound is fired if service-worker.js changes.
          registration.onupdatefound = () => {

            // updatefound is also fired the very first time the SW is installed,
            // and there's no need to prompt for a reload at that point.
            // So check here to see if the page is already controlled,
            // i.e. whether there's an existing service worker.
            // if (navigator.serviceWorker.controller) {

            // The updatefound event implies that registration.installing is set:
            // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-container-updatefound-event
            let installingWorker = registration.installing;

            installingWorker.onstatechange = () => {
              switch (installingWorker.state) {
                case 'installed':
                  // At this point, the old content will have been purged and the
                  // fresh content will have been added to the cache.
                  // It's the perfect time to display a "New content is
                  // available; please refresh." message in the page's interface.
                  console.log('Caching complete ! Future visits will work offline');
                  break;

                case 'redundant':
                  throw new Error('The installing service worker became redundant.');

                default:
                // Ignore
              }
            };
            // }
          };
        }).catch((e) => console.error('Error during service worker registration:', e));
    }
  }

}