class FCMManager {

    var fcmToken: String? { self.fcmClient.fcmToken }
    var apnsToken: Data?

    init() {
        let serviceInfo = FCMServiceInfo(
                BUNDLE_ID:      "< data from GoogleService-Info.plist >",
                PROJECT_ID:     "< data from GoogleService-Info.plist >",
                API_KEY:        "< data from GoogleService-Info.plist >",
                GOOGLE_APP_ID:  "< data from GoogleService-Info.plist >",
                GCM_SENDER_ID:  "< data from GoogleService-Info.plist >")

        self.fcmClient = FCMClient(service: serviceInfo)
        self.fcmClient.delegate = self

        // Ok, lets feed it a bit
        self.fcmClient.info.deviceModel = UIDevice.current.model
        self.fcmClient.info.osVer = UIDevice.current.systemVersion
        if let appVersion = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String {
            self.fcmClient.info.appVer = appVersion
        }

        if let deviceIdStr = UserDefaults.standard.string(forKey: "fcm.checkin.deviceId"),
           let deviceId = UInt64(deviceIdStr),
           let secretTokenStr = UserDefaults.standard.string(forKey: "fcm.checkin.secretToken"),
           let secretToken = UInt64(secretTokenStr),
           let version = UserDefaults.standard.string(forKey: "fcm.checkin.version"),
           let digest = UserDefaults.standard.string(forKey: "fcm.checkin.digest")
        {
            let timestampStr = UserDefaults.standard.string(forKey: "fcm.checkin.timestamp")
            let timestamp = timestampStr != nil ? UInt64(timestampStr!) : nil
            self.fcmClient.checkinData = .init(deviceId: deviceId, secretToken: secretToken, version: version,
                                               digest: digest, timestamp: timestamp)
        }

        if let appInstanceId = UserDefaults.standard.string(forKey: "fcm.install.appInstanceId"),
           let refreshToken = UserDefaults.standard.string(forKey: "fcm.install.refreshToken"),
           let authToken = UserDefaults.standard.string(forKey: "fcm.install.authToken")
        {
            self.fcmClient.installData = FCMInstallData(appInstanceId: appInstanceId,
                                                        refreshToken: refreshToken, authToken: authToken)
        }

        self.fcmClient.fcmToken = UserDefaults.standard.string(forKey: "fcm.fcmToken")
        self.apnsToken = UserDefaults.standard.data(forKey: "fcm.apnsToken")
        NSLog("FCM: Loaded fcmToken: \(self.fcmToken ?? "nil")")
    }
    
    // To call from AppDelegate when receive APNS token.
    func register(apnsToken: Data) {
        if self.apnsToken != apnsToken {
            self.fcmClient.register(apnsToken: apnsToken)
        }
    }

    // Should be called periodically to check if it needs to retry some interrupted stuff.
    // For example when app goes foreground or when internet connection restored.
    func restore() {
        self.fcmClient.restore()
    }

    private let fcmClient: FCMClient
}

extension FCMManager: FCMClientDelegate {

    // Store service registration data somewere (keychain, UserDefaults, etc).
    
    func fcmCheckinDataUpdate(_ checkinData: FCMCheckinData) {
        UserDefaults.standard.set("\(checkinData.deviceId)", forKey: "fcm.checkin.deviceId")
        UserDefaults.standard.set("\(checkinData.secretToken)", forKey: "fcm.checkin.secretToken")
        UserDefaults.standard.set(checkinData.version, forKey: "fcm.checkin.version")
        UserDefaults.standard.set(checkinData.digest, forKey: "fcm.checkin.digest")
        let timestampStr = checkinData.timestamp != nil ? "\(checkinData.timestamp!)" : nil
        UserDefaults.standard.set(timestampStr, forKey: "fcm.checkin.timestamp")
    }

    func fcmInstallDataUpdate(_ installData: FCMInstallData) {
        UserDefaults.standard.set(installData.appInstanceId, forKey: "fcm.install.appInstanceId")
        UserDefaults.standard.set(installData.authToken, forKey: "fcm.install.authToken")
        UserDefaults.standard.set(installData.refreshToken, forKey: "fcm.install.refreshToken")
    }

    func fcmTokenUpdate(fcmToken: String, apnsToken: Data) {
        UserDefaults.standard.set(fcmToken, forKey: "fcm.fcmToken")
        UserDefaults.standard.set(apnsToken, forKey: "fcm.apnsToken")
        self.apnsToken = apnsToken
        NSLog("FCM: Update fcmToken: \(fcmToken)")
    }
}