mattermost-mobile/ios/NotificationService/NotificationService.swift

import Gekidou
import UserNotifications

class NotificationService: UNNotificationServiceExtension {
  let preferences = Gekidou.Preferences.default
  let fibonacciBackoffsInSeconds = [1.0, 2.0, 3.0, 5.0, 8.0]
  var contentHandler: ((UNNotificationContent) -> Void)?
  var bestAttemptContent: UNMutableNotificationContent?

  var retryIndex = 0
  
  override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
    self.contentHandler = contentHandler

    bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
    if let bestAttemptContent = bestAttemptContent,
       let jsonData = try? JSONSerialization.data(withJSONObject: bestAttemptContent.userInfo),
       let ackNotification = try? JSONDecoder().decode(AckNotification.self, from: jsonData) {
      fetchReceipt(ackNotification)
    } else {
      contentHandler(request.content)
    }
  }

  func processResponse(serverUrl: String, data: Data, bestAttemptContent: UNMutableNotificationContent, contentHandler: ((UNNotificationContent) -> Void)?) {
    bestAttemptContent.userInfo["server_url"] = serverUrl
    
    let json = try? JSONSerialization.jsonObject(with: data) as! [String: Any]
    if let json = json {
      if let message = json["message"] as? String {
        bestAttemptContent.body = message
      }
      if let channelName = json["channel_name"] as? String {
        bestAttemptContent.title = channelName
      }

      let userInfoKeys = ["channel_name", "team_id", "sender_id", "root_id", "override_username", "override_icon_url", "from_webhook", "message"]
      for key in userInfoKeys {
        if let value = json[key] as? String {
          bestAttemptContent.userInfo[key] = value
        }
      }
    }

    if (preferences.object(forKey: "ApplicationIsForeground") as? String != "true") {
      Network.default.fetchAndStoreDataForPushNotification(bestAttemptContent, withContentHandler: contentHandler)
    } else if let contentHandler = contentHandler {
      bestAttemptContent.badge = Gekidou.Database.default.getTotalMentions() as NSNumber
      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)
    }
  }
  
  func fetchReceipt(_ ackNotification: AckNotification) -> Void {
    if (self.retryIndex >= self.fibonacciBackoffsInSeconds.count) {
      self.contentHandler?(self.bestAttemptContent!)
      return
    }

    Network.default.postNotificationReceipt(ackNotification) { data, response, error in
        if let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode != 200 {
          self.contentHandler?(self.bestAttemptContent!)
          return
        }

        guard let data = data, error == nil else {
          if (ackNotification.isIdLoaded) {
            // Receipt retrieval failed. Kick off retries.
            let backoffInSeconds = self.fibonacciBackoffsInSeconds[self.retryIndex]

            DispatchQueue.main.asyncAfter(deadline: .now() + backoffInSeconds, execute: {
              self.fetchReceipt(ackNotification)
            })

            self.retryIndex += 1
          }
          return
        }
      
      self.processResponse(serverUrl: ackNotification.serverUrl, data: data, bestAttemptContent: self.bestAttemptContent!, contentHandler: self.contentHandler)
      }
  }

}

extension Date {
  var millisecondsSince1970: Int {
    return Int((self.timeIntervalSince1970 * 1000.0).rounded())
  }
  
  init(milliseconds: Int) {
    self = Date(timeIntervalSince1970: TimeInterval(milliseconds) / 1000)
  }
}