medium_post_05

GoogleSignInService.swift

class GoogleSignInService: NSObject, SignInService, GIDSignInDelegate, GIDSignInUIDelegate {

    // intermediary closure to be called when sign-in finishes
    var signedIn: ((String) -> Void)?

    func setup() { /* (...) */ }

    func signIn(_ completion: @escaping (String) -> Void) {

        // hand own completion block to intermediary closure
        signedIn = { token in
            completion(token)
        }

        GIDSignIn.sharedInstance().signIn()
    }

    func sign(_ signIn: GIDSignIn!, 
              didSignInFor user: GIDGoogleUser!, 
              withError error: Error!) {

        if let error == nil {
            // call intermediary closure with token
            signedIn?(user.authentication.idToken)
        }
    }

    func signOut() { /* (...) */ }
}