public partial class SelectUserViewModel : ViewModelBase
{
    public List<string> _currentUsers;
    public string? _selectedUsername;
    public string? _newUser;

    public SelectUserViewModel()
    {
        CurrentUsers = UserQuery.GetUsernames();

        IObservable<bool> selectedUserOk = this.WhenAnyValue(
            x => x.SelectedUsername,
            x => !string.IsNullOrEmpty(x) && x != "Select One"));

        IObservable<bool> newUserOk = this.WhenAnyValue(
            x => x.NewUser,
            x => !string.IsNullOrEmpty(x));

        IObservable<bool> okSelectedEnabled = selectedUserOk;
        IObservable<bool> okNewUserEnabled = newUserOk;

        Login = ReactiveCommand.Create(
            ReturnSelectedUser,
            okSelectedEnabled);

        CreateUser = ReactiveCommand.Create(
            ReturnNewUser,
            okNewUserEnabled);
    }

    public User ReturnSelectedUser()
    {
        return new User
        {
            UserName = SelectedUsername
        };
    }

    public User ReturnNewUser()
    {
        return new User
        {
            UserName = NewUser
        };
    }

    public List<string> CurrentUsers
    {
        get => _currentUsers;
        set => this.RaiseAndSetIfChanged(ref _currentUsers, value);
    }

    public string? SelectedUsername
    {
        get => _selectedUsername;
        set => this.RaiseAndSetIfChanged(ref _selectedUsername, value);
    }

    public string? NewUser
    {
        get => _newUser;
        set => this.RaiseAndSetIfChanged(ref _newUser, value);
    }

    public ReactiveCommand<Unit, User> Login { get; }
    public ReactiveCommand<Unit, User> CreateUser { get; }
}