// SPDX-FileCopyrightText: © 2017 EteSync Authors
// SPDX-License-Identifier: AGPL-3.0-only

// 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();
    });
  }
}