session-ios/Session/Notifications/PushRegistrationManager.swift

//
//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
//

import Foundation
import PromiseKit
import PushKit
import SignalUtilitiesKit
import SignalUtilitiesKit

public enum PushRegistrationError: Error {
    case assertionError(description: String)
    case pushNotSupported(description: String)
    case timeout
}

/**
 * Singleton used to integrate with push notification services - registration and routing received remote notifications.
 */
@objc public class PushRegistrationManager: NSObject {

    // MARK: - Dependencies

    private var notificationPresenter: NotificationPresenter {
        return AppEnvironment.shared.notificationPresenter
    }

    // MARK: - Singleton class

    @objc
    public static var shared: PushRegistrationManager {
        get {
            return AppEnvironment.shared.pushRegistrationManager
        }
    }

    override init() {
        super.init()

        SwiftSingletons.register(self)
    }

    private var vanillaTokenPromise: Promise<Data>?
    private var vanillaTokenResolver: Resolver<Data>?

    private var voipRegistry: PKPushRegistry?
    private var voipTokenPromise: Promise<Data>?
    private var voipTokenResolver: Resolver<Data>?

    // MARK: Public interface

    public func requestPushTokens() -> Promise<(pushToken: String, voipToken: String)> {
        return firstly {
            self.registerUserNotificationSettings()
        }.then { () -> Promise<(pushToken: String, voipToken: String)> in
            #if targetEnvironment(simulator)
            throw PushRegistrationError.pushNotSupported(description: "Push not supported on simulators")
            #endif

            return self.registerForVanillaPushToken().map { vanillaPushToken -> (pushToken: String, voipToken: String) in
                return (pushToken: vanillaPushToken, voipToken: "")
            }
        }
    }

    // MARK: Vanilla push token

    // Vanilla push token is obtained from the system via AppDelegate
    @objc
    public func didReceiveVanillaPushToken(_ tokenData: Data) {
        guard let vanillaTokenResolver = self.vanillaTokenResolver else {
            owsFailDebug("promise completion in \(#function) unexpectedly nil")
            return
        }

        vanillaTokenResolver.fulfill(tokenData)
    }

    // Vanilla push token is obtained from the system via AppDelegate    
    @objc
    public func didFailToReceiveVanillaPushToken(error: Error) {
        guard let vanillaTokenResolver = self.vanillaTokenResolver else {
            owsFailDebug("promise completion in \(#function) unexpectedly nil")
            return
        }

        vanillaTokenResolver.reject(error)
    }

    // MARK: helpers

    // User notification settings must be registered *before* AppDelegate will
    // return any requested push tokens.
    public func registerUserNotificationSettings() -> Promise<Void> {
        AssertIsOnMainThread()
        return notificationPresenter.registerNotificationSettings()
    }

    /**
     * When users have disabled notifications and background fetch, the system hangs when returning a push token.
     * More specifically, after registering for remote notification, the app delegate calls neither
     * `didFailToRegisterForRemoteNotificationsWithError` nor `didRegisterForRemoteNotificationsWithDeviceToken`
     * This behavior is identical to what you'd see if we hadn't previously registered for user notification settings, though
     * in this case we've verified that we *have* properly registered notification settings.
     */
    private var isSusceptibleToFailedPushRegistration: Bool {

        // Only affects users who have disabled both: background refresh *and* notifications
        guard UIApplication.shared.backgroundRefreshStatus == .denied else {
            return false
        }

        guard let notificationSettings = UIApplication.shared.currentUserNotificationSettings else {
            return false
        }

        guard notificationSettings.types == [] else {
            return false
        }

        return true
    }

    private func registerForVanillaPushToken() -> Promise<String> {
        AssertIsOnMainThread()

        guard self.vanillaTokenPromise == nil else {
            let promise = vanillaTokenPromise!
            assert(promise.isPending)
            return promise.map { $0.hexEncodedString }
        }

        // No pending vanilla token yet; create a new promise
        let (promise, resolver) = Promise<Data>.pending()
        self.vanillaTokenPromise = promise
        self.vanillaTokenResolver = resolver

        UIApplication.shared.registerForRemoteNotifications()

        let kTimeout: TimeInterval = 10
        let timeout: Promise<Data> = after(seconds: kTimeout).map { throw PushRegistrationError.timeout }
        let promiseWithTimeout: Promise<Data> = race(promise, timeout)

        return promiseWithTimeout.recover { error -> Promise<Data> in
            switch error {
            case PushRegistrationError.timeout:
                if self.isSusceptibleToFailedPushRegistration {
                    // If we've timed out on a device known to be susceptible to failures, quit trying
                    // so the user doesn't remain indefinitely hung for no good reason.
                    throw PushRegistrationError.pushNotSupported(description: "Device configuration disallows push notifications")
                } else {
                    // Sometimes registration can just take a while.
                    // If we're not on a device known to be susceptible to push registration failure,
                    // just return the original promise.
                    return promise
                }
            default:
                throw error
            }
        }.map { (pushTokenData: Data) -> String in
            if self.isSusceptibleToFailedPushRegistration {
                // Sentinal in case this bug is fixed
                OWSLogger.debug("Device was unexpectedly able to complete push registration even though it was susceptible to failure.")
            }

            return pushTokenData.hexEncodedString
        }.ensure {
            self.vanillaTokenPromise = nil
        }
    }
}

// We transmit pushToken data as hex encoded string to the server
fileprivate extension Data {
    var hexEncodedString: String {
        return map { String(format: "%02hhx", $0) }.joined()
    }
}