Google SignIn proxy class that exposes Observables

Google.swift

//
//  Google.swift
//  
//
//  Created by Andrei on 24/05/16.
//  Copyright © 2016 Andrei Popa. All rights reserved.
//


import UIKit
import RxSwift
import Firebase

// add the following to bridging header
// #import <GoogleSignIn/GoogleSignIn.h>



// ============================================================================
// MARK: GoogleError
// ============================================================================
public enum GoogleError: ErrorType, CustomStringConvertible {
    
    case NotAuthenticated
    case AuthenticationError(message: String)
    
    public var description: String {
        switch self {
        case NotAuthenticated:
            return "Not authenticated"
        case AuthenticationError(let message):
            return "Authentication error: \(message)"
        }
    }
}


// ============================================================================
// MARK: Firebase auth with Google
// ============================================================================
extension Firebase {
    
    func setupGoogleAuth() {
        
        // pass firebase clientID to Google
        if let clientID = clientID {
            Google.instance.clientID = clientID
        }
        
        // new user chain
        Google.instance
            .rx_firebaseCredential
            .flatMapLatest { credential in
                Firebase.instance.rx_signInWithCredential(credential)
            }
            .subscribeNext({ user in
                print("--------------- user logged in: \(user.displayName), \(user.uid)")
                if let appDelegate = UIApplication.sharedApplication().delegate as? AppDelegate {
                    appDelegate.loggedIn.onNext()
                }
            })
            .addDisposableTo(Google.instance.disposeBag)
        
        // error chain
        Google.instance
            .rx_error
            .doOnNext({ _ in print("rx_error doOnNext") })
            .filter({ $0 is GoogleError })
            .subscribeNext { error in
                print("--------------- error: \(error)")
                Firebase.instance.signOut()
            }
            .addDisposableTo(Google.instance.disposeBag)
    }
}


// ============================================================================
// MARK: Google
// ============================================================================
class Google : NSObject, GIDSignInDelegate, GIDSignInUIDelegate {
    
    static let instance = Google()
    internal let disposeBag = DisposeBag()
    
    let rx_error = ReplaySubject<ErrorType>.create(bufferSize: 1)
    var rx_firebaseCredential : Observable<FIRAuthCredential> {
        return rx_user
            .doOnNext({ _ in print("--------------- rx_firebaseCredential received") })
            .map({ $0.authentication })
            .map({ authentication in
                FIRGoogleAuthProvider.credentialWithIDToken(authentication.idToken,
                    accessToken: authentication.accessToken)
            })
    }
    
    private let rx_user = ReplaySubject<GIDGoogleUser>.create(bufferSize: 1)
    
    // view controller that presents the auth UIViewController
    var presentingViewController : UIViewController?
    
    
    
    // this prevents others from using the
    // default '()' initializer for this class.
    private override init() {
        super.init()
        GIDSignIn.sharedInstance().delegate = self
        GIDSignIn.sharedInstance().uiDelegate = self
    }
    
    
    func signOut() {
        // let hasAuthInKeychain = GIDSignIn.sharedInstance().hasAuthInKeychain()
        // print("current user: \(GIDSignIn.sharedInstance().currentUser)")
        // print("current user hasAuthInKeychain: \(hasAuthInKeychain)")
        GIDSignIn.sharedInstance().signOut()
    }
    
    
    var clientID : String {
        get {
            return GIDSignIn.sharedInstance().clientID
        }
        set {
            GIDSignIn.sharedInstance().clientID = newValue
        }
    }
    
    
    // MARK: GIDSignInDelegate
    // ============================================================================
    func signIn(signIn: GIDSignIn!, didSignInForUser user: GIDGoogleUser!, withError error: NSError!) {
        // print("didSignInForUser: \(user)")
        if let error = error {
            rx_error.onNext(GoogleError.AuthenticationError(message: error.localizedDescription))
        }
        if let user = user {
            rx_user.onNext(user)
        } else {
            rx_error.onNext(GoogleError.AuthenticationError(message: "empty user"))
        }
    }
    
    func signIn(signIn: GIDSignIn!, didDisconnectWithUser user: GIDGoogleUser!, withError error: NSError!) {
        // print("didDisconnectWithUser: \(user)")
        rx_error.onNext(GoogleError.NotAuthenticated)
    }
    
    
    // MARK: GIDSignInUIDelegate
    // ============================================================================
    func signIn(signIn: GIDSignIn!, presentViewController viewController: UIViewController!) {
        if let presentingViewController = presentingViewController {
            presentingViewController.presentViewController(viewController, animated: true, completion: nil)
        }
    }
    
    func signIn(signIn: GIDSignIn!, dismissViewController viewController: UIViewController!) {
        viewController.dismissViewControllerAnimated(true, completion: nil)
    }
}

in some LoginViewController you can just add a GIDSignInButton & the following:
Google.instance.presentingViewController = self

The Google class will catch all the delegates and forward relevant information on the Observables:

• rx_user
• rx_error
• rx_firebaseCredential

Have fun :]