public override string ToString()
{
var header = "List of items in basket:\n";
var itemsMsg = Items.Aggregate(header,
(x, y) => $"{x}{y.Product.Name}: {y.Num}, price: {y.GetPrice()} ({y.Product.Price} per unit)\n");
var msg = Discounts.Aggregate("", (x, y) => $"{x}{y.GetDescription()}\n");
var total = $"Total amount: {Total}\n";
return(Discounts.Any() ? $"{itemsMsg}\n{msg}\n{total}" : total);
}