Приложение MVVM. Диалог добавления/редактирования товара: получение данных, вызов, взаимодействие с VM и прочее

    public partial class Shop : IProductsSource
    {
        public event NotifyListChangedEventHandler<IProduct> ProductChanged = (_, _) => { };
 
        private void RoleVerifyAccess(Rights rights, [CallerMemberName] string methodName = "")
        {
            if (!RoleCheckAccess(rights))
                throw new MethodAccessException($"Доступ к методу "{methodName}" для роли {CurrentUser?.Role.Name ?? "null"} запрещён;");
        }
        public bool RoleCheckAccess(Rights rights)
        {
            return CurrentUser?.Role.Rights is Rights currentRights && (currentRights & rights) == rights;
        }
 
        public void Add(IProduct product)
        {
            RoleVerifyAccess(Rights.Adding);
 
            Product @new = product.Create<Product>();
            @new.Id = 0;

        private bool AddProductCanExecute(IProduct parameter)
        {
            return _shop.RoleCheckAccess(Rights.Adding);
        }
 
        private void AddProductExecute(IProduct product)
        {
            _shop.Add(product);
        }

        public ProductsViewModel(IShop shop)
        {
            _shop = shop;
            _shop.ProductChanged += OnProductChanged;
            _shop.SourcesLoadedChanged += OnSourcesChanged;
            _shop.AuthorizationChanged += OnAuthorizationChanged;
        }
 
        private void OnAuthorizationChanged(object? sender, AuthorizationChangedArgs e)
        {
            AddProduct.RaiseCanExecuteChanged();
        }

public static RoutedEventHandler ContextMenuSetup { get; } = (s, e) =>
{
    var userControl = (UserControl)s!;
    var contextMenu = (ContextMenu)userControl.Resources["contextMenu"];
    var viewModel = (IProductsViewModel)userControl.DataContext;
    if (!viewModel.RemoveProduct.CanExecute(null))
        contextMenu.Items.RemoveAt(2);
    if (!viewModel.AddProduct.CanExecute(null))
        contextMenu.Items.RemoveAt(1);
    if (!viewModel.UpdateProduct.CanExecute(null))
        contextMenu.Items.RemoveAt(0);
    if (contextMenu.Items.Count is 0)
        userControl.Resources.Remove(nameof(contextMenu));
};

public static RoutedEventHandler ContextMenuSetup { get; } = (s, e) =>
{
    var userControl = (UserControl)s;
    var contextMenu = (ContextMenu)userControl.Resources["contextMenu"];
    var viewModel = (IProductsViewModel)userControl.DataContext;
    if (viewModel.CanDelete)
        return;
    if (viewModel.CanUpdate)
    {
        contextMenu.Items.RemoveAt(2);
        contextMenu.Items.RemoveAt(1);
    }
    else if (viewModel.CanAdd)
    {
        contextMenu.Items.RemoveAt(2);
        contextMenu.Items.RemoveAt(0);
    }
    else
        userControl.Resources.Remove("contextMenu");
};

public static RelayCommand<FrameworkElement> Update { get; } = new(UpdateExecute, UpdateCanExecute);
 
private static bool UpdateCanExecute(FrameworkElement element)
{
    var (viewModel, product) = GetData(element);
    return viewModel.UpdateProduct.CanExecute(product);
}
 
private static void UpdateExecute(FrameworkElement element)
{
    var (viewModel, product) = GetData(element);
    AddOrUpdateProductDialog.Update(product, viewModel);
}

canExecute is null ? throw Exceptions.canExecuteException
                  : p => p is T t && canExecute(t)