import {
  error,
  log,
} from 'colorful-logging';

// 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 &&
  window.location &&
  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 function registerServiceWorker() {
  if (process.env.NODE_ENV === 'production' &&
      'serviceWorker' in navigator &&
      window)
  {
    // 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

      // accelerator-core uses no routing. We may need to see if the constant
      // publicUrl value affects this but I suspect it will never fail.
      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(() => {
          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: 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.
                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.
                log('Content is cached for offline use.');
              }
            }
          };
        }
      };
    })
    .catch((err) => {
      error('Error during service worker registration:');
      error(err);
    });
}

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(() => {
    log(
      'No internet connection found. App is running in offline mode.'
    );
  });
}

export function unregister() {
  if (navigator && 'serviceWorker' in navigator) {
    navigator.serviceWorker.ready.then(registration => {
      registration.unregister();
    });
  }
}