Ensure liker is an existing user

backend-services/feed-service/app/models/Daily.scala

@@ -66,14 +66,23 @@ object Daily {
 
     def likeAsync(dailyId: ObjectId, likerId: ObjectId, timeout: Int = 4): Unit = {
         val result: Future[Unit] = for {
-            oDaily: Option[Daily]  <- dailyRepo.getById(dailyId)
-            like: Unit <- {
-                // Check daily with given ID exists
-                val daily = if (oDaily.isEmpty) throw new NotFoundException("No daily with given ID.") else oDaily.get
-                
-                // Check user has not already liked Daily
-                if (daily.usersLiked.contains(likerId)) throw new ConflictException("User has already liked this Daily.")
+            // Fetch Daily from given ID
+            daily: Daily  <- {
+                dailyRepo.getById(dailyId).map((oDaily: Option[Daily]) => {
+                    if (oDaily.isEmpty) 
+                        throw new NotFoundException("No daily with given ID.") 
+                    else 
+                        oDaily.get
+                })
+            }
+
+            // Check user has not already liked the Daily
+            _ = if (daily.usersLiked.contains(likerId)) throw new ConflictException("User has already liked this Daily.")
 
+            // Check user with given ID exists
+            _ <- User.userExists(likerId).map((exists: Boolean) => if (!exists) throw new NotFoundException("No user with given ID."))
+
+            like: Unit <- {
                 val updatedUsersLiked: Seq[ObjectId] = daily.usersLiked :+ likerId
                 val update: Bson = Updates.set("usersLiked", updatedUsersLiked)
 

backend-services/feed-service/app/models/User.scala

@@ -11,4 +11,11 @@ object User {
         val friends: Seq[ObjectId] = Seq(new ObjectId("641128f7e80bcd1ba39d04af"))
         Future.successful(friends)
     }
+
+    def userExists(userId: ObjectId): Future[Boolean] = {
+        // TODO: Fetch user verification from User Service
+        println("Verifying user with ID ", userId.toString(), " exists")
+        val exists: Boolean = true
+        Future.successful(exists)
+    }
 }