export default () => {
  //*** Determine whether or not the PWA has been installed. ***//

  // Step 1: Check local storage
  let pwaInstalled = localStorage.getItem("pwaInstalled") === "yes";

  // Step 2: Check if the display-mode is standalone. (Only permitted for PWAs.)
  if (
    !pwaInstalled &&
    window.matchMedia("(display-mode: standalone)").matches
  ) {
    localStorage.setItem("pwaInstalled", "yes");
    pwaInstalled = true;
  }

  // Step 3: Check if the navigator is in standalone mode. (Again, only permitted for PWAs.)
  if (!pwaInstalled && window.navigator.standalone === true) {
    localStorage.setItem("pwaInstalled", "yes");
    pwaInstalled = true;
  }

  //*** If the PWA has not been installed, show the install PWA prompt.. ***//
  let deferredPrompt = null;
  window.addEventListener("beforeinstallprompt", event => {
    deferredPrompt = event;

    // Show the install button if the prompt appeared.
    if (!pwaInstalled) {
      document.querySelector("#installPWA").style.display = "inline-flex";
    }
  });

  // When the app is installed, remove install prompts.
  window.addEventListener("appinstalled", event => {
    localStorage.setItem("pwaInstalled", "yes");
    pwaInstalled = true;
    document.getElementById("installPWA").style.display = "none";
  });

  // When the app is uninstalled, add the prompts back
  return async () => {
    if (deferredPrompt) {
      deferredPrompt.prompt();
      let outcome = await deferredPrompt.userChoice;

      if (outcome === "accepted") {
        console.log("Postwoman was installed successfully.");
      } else {
        console.log(
          "Postwoman could not be installed. (Installation rejected by user.)"
        );
      }
      deferredPrompt = null;
    }
  };
};