Remove duplicate Create User requests

* If multiple create user requests are enqueued for the same external ID, only keep the most recent one, and remove the previous.
* These requests should all have the same identity model since they share external IDs, so only keeping the latest is adequate.
* This prevents multiple Create User requests with the same external ID from being executed simultaneously, which is possible when JWT is on, as we allow future logins to be sent before past user's login succeeds.
* An example of this is login(a) > login(b) > login(a) > login(b) but user A has an expired token. Once the token is updated for userA, potentially both logins could be executed if we don't prevent duplicates.

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalUser/Source/Executors/OSUserExecutor.swift

@@ -181,6 +181,26 @@ class OSUserExecutor {
         OneSignalUserManagerImpl.sharedInstance.addIdentityModelToRepo(model)
     }
 
+    /// Checks if two requests are creating the same user by external ID
+    private func isDuplicateCreateUser(_ request: OSRequestCreateUser, _ other: OSUserRequest) -> Bool {
+        guard let other = other as? OSRequestCreateUser,
+              request.identityModel.externalId != nil,
+              other.identityModel.externalId != nil
+        else {
+            return false
+        }
+        return request.identityModel.externalId == other.identityModel.externalId
+    }
+
+    /// Before enqueueing a Create User request, check for duplicates and remove previous matching duplicates
+    private func appendCreateUserToQueue(_ request: OSRequestCreateUser) {
+        self.dispatchQueue.async {
+            self.userRequestQueue.removeAll(where: { self.isDuplicateCreateUser(request, $0) })
+            self.userRequestQueue.append(request)
+            OneSignalUserDefaults.initShared().saveCodeableData(forKey: OS_USER_EXECUTOR_USER_REQUEST_QUEUE_KEY, withValue: self.userRequestQueue)
+        }
+    }
+
     func appendToQueue(_ request: OSUserRequest) {
         self.dispatchQueue.async {
             self.userRequestQueue.append(request)
@@ -286,8 +306,7 @@ extension OSUserExecutor {
         let originalPushToken = user.pushSubscriptionModel.address
         let request = OSRequestCreateUser(identityModel: user.identityModel, propertiesModel: user.propertiesModel, pushSubscriptionModel: user.pushSubscriptionModel, originalPushToken: originalPushToken)
 
-        appendToQueue(request)
-
+        appendCreateUserToQueue(request)
         executePendingRequests()
     }
 
@@ -296,7 +315,7 @@ extension OSUserExecutor {
      */
     func createUser(aliasLabel: String, aliasId: String, identityModel: OSIdentityModel) {
         let request = OSRequestCreateUser(aliasLabel: aliasLabel, aliasId: aliasId, identityModel: identityModel)
-        appendToQueue(request)
+        appendCreateUserToQueue(request)
         executePendingRequests()
     }