public async Task AddItemToCart(AddCartItemInput input)
{
var userId = GetUserId();
//here we have some global settings
var tenant = await GetCurrentTenantAsync();
// create the cart if not exits otherwise get the current cart
var cart = await _cartManager.CreateCart(new Cart(input.TenantId, tenant.Currency, userId));
// get the product that we'll add to the cart
var productVariant = await _productManager.GetProductVariantAsync(input.ProductVariantId);
var discount = _clientManager.GetClientDiscountByItemGroupCode(input.CardCode, productVariant.ItemGroup);
var cartItem = new CartProductItem(input.TenantId, cart.Id, productVariant.Id, input.Quantity, productVariant.Price, tenant.ISV, discount);
//finally add the item to the cart
await _cartManager.CreateCartProductItem(cartItem);
}