// tslint:disable:no-console
// 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.toString()
    );
    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) {
        // Is not local host.  Just register service worker
        registerValidSW(swUrl);
      } else {
        // This is running on localhost.  Lets check if a service worker still exists or not. 
        checkValidServiceWorker(swUrl);
      }
    });
  }
}

function registerValidSW(swUrl: string) {
  navigator.serviceWorker
    .register(swUrl)
    .then(registration => {
      registration.onupdatefound = () => {
        const installingWorker = registration.installing;
        if (installingWorker) {
          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: string) {
  // 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();
    });
  }
}
