(function(root, factory) {
  if (typeof module === 'object' && module.exports) module.exports = factory;
  else root.createPushNotifications = factory;
})(typeof self !== 'undefined' ? self : this, function createPushNotifications({
  control, status, notification, serviceWorker, fetchJson,
}) {
  let configuration = null;

  function applicationServerKey(value) {
    const padded = value.replace(/-/g, '+').replace(/_/g, '/') + '='.repeat((4 - value.length % 4) % 4);
    if (typeof atob === 'function') {
      return Uint8Array.from(atob(padded), character => character.charCodeAt(0));
    }
    return Uint8Array.from(Buffer.from(padded, 'base64'));
  }

  async function disable() {
    const registration = await serviceWorker.ready;
    const subscription = await registration.pushManager.getSubscription();
    await fetchJson('api/v1/push-subscription', {method:'DELETE'});
    await subscription?.unsubscribe?.();
    control.checked = false;
    status.textContent = 'New update notifications are off for this device.';
  }

  async function enable() {
    const permission = await notification.requestPermission();
    if (permission !== 'granted') {
      control.checked = false;
      status.textContent = 'Notifications are blocked. Allow them in your browser settings to enable updates.';
      return;
    }
    const registration = await serviceWorker.ready;
    let subscription = await registration.pushManager.getSubscription();
    if (!subscription) {
      subscription = await registration.pushManager.subscribe({
        userVisibleOnly: true,
        applicationServerKey: applicationServerKey(configuration.public_key),
      });
    }
    await fetchJson('api/v1/push-subscription', {
      method:'PUT',
      headers:{'Content-Type':'application/json'},
      body:JSON.stringify(subscription.toJSON()),
    });
    control.checked = true;
    status.textContent = 'New update notifications enabled for this device.';
  }

  async function change() {
    control.disabled = true;
    try {
      if (control.checked) await enable();
      else await disable();
    } catch (error) {
      control.checked = !control.checked;
      status.textContent = 'Could not change update notifications. Check your connection and try again.';
    } finally {
      control.disabled = false;
    }
  }

  async function init() {
    if (!control || !notification || !serviceWorker) return;
    control.addEventListener('change', change);
    configuration = await fetchJson('api/v1/push-subscription');
    if (!configuration.available) {
      control.disabled = true;
      status.textContent = 'New update notifications are not available on this server.';
      return;
    }
    control.checked = Boolean(configuration.subscribed);
    status.textContent = configuration.subscribed
      ? 'New update notifications enabled for this device.'
      : 'New update notifications are off for this device.';
  }

  return {init, change};
});