// Copyright (c) 2020-2021 Drew Lemmy
// This file is part of TenebraWeb 2 under AGPL-3.0.
// Full details: https://github.com/tmpim/TenebraWeb2/blob/master/LICENSE.txt

// This optional code is used to register a service worker.
// register() is not called by default.

// 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 subsequent visits to a page, after all the
// existing tabs open on the page have been closed, since previously cached
// resources are updated in the background.

// To learn more about the benefits of this model and instructions on how to
// opt-in, read https://cra.link/PWA

import { isLocalhost } from "./";

import { criticalError } from "@utils";
import Debug from "debug";
const debug = Debug("tenebraweb:service-worker");

interface Config {
  onSuccess?: (registration: ServiceWorkerRegistration) => void;
  onUpdate?: (registration: ServiceWorkerRegistration) => void;
}

export function register(config?: Config): void {
  debug("SW: %s (%b), %b, %b", process.env.NODE_ENV, process.env.NODE_ENV === "production", "serviceWorker" in navigator, isLocalhost);

  if (process.env.NODE_ENV === "production" && "serviceWorker" in navigator) {
    debug("PUBLIC_URL: %s  origin: %s", process.env.PUBLIC_URL, window.location.origin);

    // The URL constructor is available in all browsers that support SW.
    const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
    debug("publicUrl: %s", publicUrl);

    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/facebook/create-react-app/issues/2374
      debug("PUBLIC_URL is not correct");
      return;
    }

    // REVIEW: The following code was previously wrapped in window's `load`
    //         event listener, but because we register the service worker from
    //         a component, the window is already loaded. Is this still a valid
    //         way to register the service worker?

    /*window.addEventListener("load", () => {
      debug("window load");*/
    const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;

    if (isLocalhost) {
      debug("running as localhost");

      // This is running on localhost. Let's check if a service worker still exists or not.
      checkValidServiceWorker(swUrl, config);

      // 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://cra.link/PWA"
        );
      });
    } else {
      // Is not localhost. Just register service worker
      registerValidSW(swUrl, config);
    }
    /*});*/
  }
}

function registerValidSW(swUrl: string, config?: Config) {
  debug("registering valid SW");

  navigator.serviceWorker
    .register(swUrl)
    .then((registration) => {
      registration.onupdatefound = () => {
        const installingWorker = registration.installing;
        if (installingWorker === null) {
          debug("no installingWorker");
          return;
        }
        installingWorker.onstatechange = () => {
          if (installingWorker.state === "installed") {
            if (navigator.serviceWorker.controller) {
              // At this point, the updated precached content has been fetched,
              // but the previous service worker will still serve the older
              // content until all client tabs are closed.
              console.log(
                "New content is available and will be used when all " +
                  "tabs for this page are closed. See https://cra.link/PWA."
              );

              // Execute callback
              if (config && config.onUpdate) {
                config.onUpdate(registration);
              }
            } else {
              // At this point, everything has been precached.
              // It's the perfect time to display a
              // "Content is cached for offline use." message.
              debug("content is cached for offline use");

              // Execute callback
              if (config && config.onSuccess) {
                config.onSuccess(registration);
              }
            }
          }
        };
      };
    })
    .catch((error) => {
      criticalError("Error during service worker registration:", error);
    });
}

function checkValidServiceWorker(swUrl: string, config?: Config) {
  // Check if the service worker can be found. If it can't reload the page.
  debug("fetching service worker at %s", swUrl);
  fetch(swUrl, {
    headers: { "Service-Worker": "script" },
  })
    .then((response) => {
      // Ensure service worker exists, and that we really are getting a JS file.
      const contentType = response.headers.get("content-type");
      if (
        response.status === 404 ||
        (contentType !== null && contentType.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, config);
      }
    })
    .catch(() => {
      console.log("No internet connection found. App is running in offline mode.");
    });
}

export function unregister(): void {
  debug("unregistering service worker");
  if ("serviceWorker" in navigator) {
    navigator.serviceWorker.ready
      .then((registration) => {
        registration.unregister();
      })
      .catch((error) => {
        criticalError(error.message);
      });
  }
}