Amplify Subscription with filters for iOS

SubscriptionWithfilter.swift

import Amplify
import AmplifyPlugins

class SubscriptionManager {
  
  static var subscription: GraphQLSubscriptionOperation<JSONValue>?  
  
  static func createSubscription(courseId: String) {
      subscription = Amplify.API.subscribe (request: GraphQLRequest<JSONValue>.subscribeToCourseNotes(byCourseId: courseId),
          valueListener: { subscriptionEvent in
              switch subscriptionEvent {
              case .connection(let connectionState):
                  print("connection state:", connectionState)
              case .data(let data):
                  switch data {
                  case .success(let json):
                      do {
                          if let noteJSON = json.value(at: "subscribeToCourseNotes") {
                              let noteData = try JSONEncoder().encode(noteJSON)
                              let note = try JSONDecoder().decode(Note.self, from: noteData)
                              updateCourseWithNote(note: note)
                          } else {
                              fallbackRefresh(error: nil, courseId: courseId) // fallback to refresh the entire course
                          }
                      } catch(let error) {
                          fallbackRefresh(error: error, courseId: courseId)
                      }
                  case .failure(let error):
                      fallbackRefresh(error: error, courseId: courseId)
                  }
              }
          },
          completionListener: { result in
              switch result {
              case .success:
                  print("Subscription has been closed successfully")
              case .failure(let error):
                  ErrorHandler.handleError(error: error, showUser: false)
              }
          }
      )
  }
    
  static func cancelSubscription() {
      // Cancel the subscription listener when you're finished with it
      subscription?.cancel();
  }

}

extension GraphQLRequest {
    static func subscribeToCourseNotes(byCourseId courseId: String) -> GraphQLRequest<JSONValue> {
        let document = """
        subscription subscribeToCourseNotes($courseId: ID!) {
          subscribeToCourseNotes(courseId: $courseId) {
            id
            body
            updatedAt
            user {
              id
              name
            }
          }
        }
        """
        return GraphQLRequest<JSONValue>(document: document,
                                         variables: ["courseId": courseId],
                                         responseType: JSONValue.self)
    }
}