fix iOS denied notificationPermissionChange

On iOS `navigator.permissions.query({ name: 'notifications' }`).onchange
does not fire due to a bug with the browser.
To account for this we are calling our
triggerNotificationPermissionChanged event every time the native
notification prompt is answered or dismissed.

This however does create duplicate events so this commit adds logic to
PermissionUtils.triggerNotificationPermissionChanged to prevent this.

Tested event now fire exactly once on iOS 16.5.
Tested both for accepting and declining.
Also confirmed Chrome on macOS still works

Author: jkasten2

src/managers/SubscriptionManager.ts

@@ -334,15 +334,12 @@ export class SubscriptionManager {
       const permission = await SubscriptionManager.requestPresubscribeNotificationPermission();
 
       /*
-        Notification permission changes are already broadcast by the page's
-        notificationpermissionchange handler. This means that allowing or
-        denying the permission prompt will cause double events. However, the
-        native event handler does not broadcast an event for dismissing the
+        The native event handler does not broadcast an event for dismissing the
         prompt, because going from "default" permissions to "default"
         permissions isn't a change. We specifically broadcast "default" to "default" changes.
        */
-      if (permission === NotificationPermission.Default)
-        await PermissionUtils.triggerNotificationPermissionChanged(true);
+      const forcePermissionChangeEvent = permission === NotificationPermission.Default
+      await PermissionUtils.triggerNotificationPermissionChanged(forcePermissionChangeEvent);
 
       // If the user did not grant push permissions, throw and exit
       switch (permission) {

src/utils/PermissionUtils.ts

@@ -2,7 +2,20 @@ import Database from "../services/Database";
 import Event from '../Event';
 
 export class PermissionUtils {
+
+  // This flag prevents firing the NATIVE_PROMPT_PERMISSIONCHANGED event twice
+  // We use multiple APIs:
+  //    1. Notification.requestPermission callback
+  //    2. navigator.permissions.query({ name: 'notifications' }`).onchange
+  // Some browsers support both, while others only support Notification.requestPermission
+  private static executing = false;
+
   public static async triggerNotificationPermissionChanged(updateIfIdentical = false) {
+    if (PermissionUtils.executing) {
+      return;
+    }
+    PermissionUtils.executing = true;
+
     const newPermission = await OneSignal.privateGetNotificationPermission();
     const previousPermission = await Database.get('Options', 'notificationPermission');
 
@@ -13,5 +26,6 @@ export class PermissionUtils {
 
     await Database.put('Options', { key: 'notificationPermission', value: newPermission });
     Event.trigger(OneSignal.EVENTS.NATIVE_PROMPT_PERMISSIONCHANGED, { to: newPermission });
+    PermissionUtils.executing = false;
   }
 }