TODO-App-AsyncResult-FB-Login.swift

func loginWithFacebook() -> AsyncResult<Context, String, GenericError> {
    return AsyncResult.unfoldTT{ context, continuation in
        let loginManager = LoginManager()
        loginManager.logIn([ .publicProfile ], viewController: self) { loginResult in
            switch loginResult {
            case .Failed(let error):
                continuation(Result.failure(error))
            case .Cancelled:
                continuation(Result.failure(LoginCancelledError()))
            case .Success(let grantedPermissions, let declinedPermissions, let accessToken):
                continuation(Result.success(accessToken))
            }
        }
    }
}