mattermost-mobile/ios/NotificationService/NotificationService.swift

import UserNotifications
import UploadAttachments

class NotificationService: UNNotificationServiceExtension {
  
  var contentHandler: ((UNNotificationContent) -> Void)?
  var bestAttemptContent: UNMutableNotificationContent?
  
  override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
    self.contentHandler = contentHandler
    bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
    
    if let bestAttemptContent = bestAttemptContent {
      UploadSession.shared.notificationReceipt(
        notificationId: bestAttemptContent.userInfo["ack_id"],
        receivedAt: Date().millisencondsSince1970,
        type: bestAttemptContent.userInfo["type"]
      )
      
      contentHandler(bestAttemptContent)
    }
  }
  
  override func serviceExtensionTimeWillExpire() {
    // Called just before the extension will be terminated by the system.
    // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
    if let contentHandler = contentHandler, let bestAttemptContent =  bestAttemptContent {
      contentHandler(bestAttemptContent)
    }
  }
  
}

extension Date {
  var millisencondsSince1970: Int {
    return Int((self.timeIntervalSince1970 * 1000.0).rounded())
  }
  
  init(milliseconds: Int) {
    self = Date(timeIntervalSince1970: TimeInterval(milliseconds) / 1000)
  }
}