NotificationManager.swift

// https://medium.com/@samermurad555/ios-provisional-notifications-eeb3832836fc

import UserNotifications
import UIKit

typealias GrantCb = (_ didGrant: Bool) -> Void

// Manages Notifications Permissions
class NotificationManager {
  static let instance = NotificationManager()

  private init() {}

  func requestAccess(options: UNAuthorizationOptions, cb: GrantCb?) {
    let center = UNUserNotificationCenter.current()
    // make sure to run on main thread
    DispatchQueue.main.async {
      center.requestAuthorization(options: options) { (didGrant, error) in
        if error != nil {
          print("An error occurred", error ?? "no error")
          cb?(false)
        } else {
          cb?(true)
        }
      }
    }
  }

  // asking for provisional access by adding the .provisional option
  func provisionalAccess(_ cb: GrantCb?) {
    self.requestAccess(options: [.alert, .sound, .badge, .provisional],
                       cb: cb)
  }

  // Explicit access (prompts user for permissions)
  func explicitAccess(_ cb: GrantCb?) {
    self.requestAccess(options: [.alert, .sound, .badge],
                       cb: cb)
  }

  func loacalNotification(message: String,
                          after: TimeInterval = 5,
                          handler: ((_ error: Error?) -> Void)? = nil) {
    self.provisionalAccess { (didGrant) in
      if didGrant {
        DispatchQueue.main.async {
          let notifId = UUID().uuidString
          let content = UNMutableNotificationContent()
          content.body = message
          content.title = "Quick message"
          let trigger = UNTimeIntervalNotificationTrigger(timeInterval: after, repeats: false)
          let req = UNNotificationRequest(identifier: notifId, content: content, trigger: trigger)
          let center = UNUserNotificationCenter.current()
          center.add(req, withCompletionHandler: handler)
        }
      }
    }
  }
}