// In production, we register a service worker to serve assets from local cache.
 
 // This lets the app load faster on subsequent visits in production, and gives
 // it offline capabilities. However, it also means that developers (and users)
 // will only see deployed updates on the "N+1" visit to a page, since previously
 // cached resources are updated in the background.
 
 // To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
 // This link also includes instructions on opting out of this behavior.
 
 const 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}$/
     )
 );
 
 export default function register() {
   if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
     // The URL constructor is available in all browsers that support SW.
     const publicUrl = new URL(process.env.PUBLIC_URL, window.location);
     if (publicUrl.origin !== window.location.origin) {
       // Our service worker won't work if PUBLIC_URL is on a different origin
       // from what our page is served on. This might happen if a CDN is used to
       // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374
       return;
     }
 
     window.addEventListener('load', () => {
       const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
 
       if (isLocalhost) {
         // This is running on localhost. Lets check if a service worker still exists or not.
         checkValidServiceWorker(swUrl);
 
         // Add some additional logging to localhost, pointing developers to the
         // service worker/PWA documentation.
         navigator.serviceWorker.ready.then(() => {
           console.log(
             'This web app is being served cache-first by a service ' +
               'worker. To learn more, visit https://goo.gl/SC7cgQ'
           );
         });
       } else {
         // Is not local host. Just register service worker
         registerValidSW(swUrl);
       }
     });
   }
 }
 
 function registerValidSW(swUrl) {
   navigator.serviceWorker
     .register(swUrl)
     .then(registration => {
       registration.onupdatefound = () => {
         const installingWorker = registration.installing;
         installingWorker.onstatechange = () => {
           if (installingWorker.state === 'installed') {
             if (navigator.serviceWorker.controller) {
               // 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 your web app.
               console.log('New content is available; please refresh.');
             } else {
               // At this point, everything has been precached.
               // It's the perfect time to display a
               // "Content is cached for offline use." message.
               console.log('Content is cached for offline use.');
             }
           }
         };
       };
     })
     .catch(error => {
       console.error('Error during service worker registration:', error);
     });
 }
 
 function checkValidServiceWorker(swUrl) {
   // Check if the service worker can be found. If it can't reload the page.
   fetch(swUrl)
     .then(response => {
       // Ensure service worker exists, and that we really are getting a JS file.
       if (
         response.status === 404 ||
         response.headers.get('content-type').indexOf('javascript') === -1
       ) {
         // No service worker found. Probably a different app. Reload the page.
         navigator.serviceWorker.ready.then(registration => {
           registration.unregister().then(() => {
             window.location.reload();
           });
         });
       } else {
         // Service worker found. Proceed as normal.
         registerValidSW(swUrl);
       }
     })
     .catch(() => {
       console.log(
         'No internet connection found. App is running in offline mode.'
       );
     });
 }
 
 export function unregister() {
   if ('serviceWorker' in navigator) {
     navigator.serviceWorker.ready.then(registration => {
       registration.unregister();
     });
   }
 }