Swiftgram/NotificationService/NotificationService.swift

import UserNotifications

class NotificationService: UNNotificationServiceExtension {
    var contentHandler: ((UNNotificationContent) -> Void)?
    var bestAttemptContent: UNMutableNotificationContent?
    
    override init() {
        super.init()
    }

    override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        self.contentHandler = contentHandler
        self.bestAttemptContent = request.content.mutableCopy() as? UNMutableNotificationContent
        
        if let bestAttemptContent = self.bestAttemptContent {
            bestAttemptContent.title = "\(bestAttemptContent.title) [modified]"
            contentHandler(bestAttemptContent)
        }
    }
    
    override func serviceExtensionTimeWillExpire() {
        if let contentHandler = self.contentHandler, let bestAttemptContent =  self.bestAttemptContent {
            contentHandler(bestAttemptContent)
        }
    }
}