private void Page_Load(object sender, System.EventArgs e)
        {

            if(!IsPostBack)
            {
                //get arraylist from session Create one if there is none
                ArrayList cart = (ArrayList)Session["cart"];
                if(cart==null)
                Session["cart"] = new ArrayList();

                if (Request.QueryString["id"]!=null)
                {
                    //get values from DataList
                    int id = Convert.ToInt32(Request.QueryString["id"]);
                    string name = Request.QueryString["name"];
                    decimal price = Convert.ToDecimal(Request.QueryString["price"]);
                    string stockLeft = Request.QueryString["StockLeft"];

                    //create CartItem object and add to arraylist
                    cart = (ArrayList)Session["cart"];
                    bool found=false;
                    foreach(CartItem item in cart)
                    {
                        if(id==item.ProductID)
                        {
                            item.Quantity++;
                            found = true;
                            break;
                        }
                    }

                    if(!found)
                    {
                        if(stockLeft=="No Stock")
                        {
                            lblStatus.Text = "The product is currently not in stock.";
                        }
                        else 
                        {
                            CartItem item = new CartItem(id,name,price,1,stockLeft);
                            cart.Add(item);
                        }
                    }
                }

                //Calcualte the total amount of all the items in the shopping cart.
                CalculateTotal();

                //Bind arraylist to DataGrid
                dgCart.DataSource=cart;
                dgCart.DataBind();

            }

        }



        private void dgCart_CancelCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs   e)
        {
            dgCart.EditItemIndex = -1;
            dgCart.DataSource=(ArrayList)Session["cart"];
            dgCart.DataBind();
        }

        private void dgCart_DeleteCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs   e)
        {
            //get row selected
            int index = e.Item.ItemIndex;

            //get arraylist from session
            ArrayList cart = (ArrayList)Session["cart"];

            //remove item from arraylist
            cart.RemoveAt(index);

            //Calcualte the total amount of all the items in the shopping cart.
            CalculateTotal();

            //reBind arraylist to DataGrid
            dgCart.DataSource = (ArrayList)Session["cart"];
            dgCart.DataBind();

        }

        private void dgCart_EditCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs   e)
        {

            dgCart.EditItemIndex=e.Item.ItemIndex;
            dgCart.DataSource=(ArrayList)Session["cart"];
            dgCart.DataBind();

        }

        private void dgCart_UpdateCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs   e)
        {
            //get the row selected 
            int index = e.Item.ItemIndex;

            //get the qty from the txt box
            TextBox tb = (TextBox)e.Item.Cells[3].Controls[0];
            int qty = Convert.ToInt32(tb.Text);

            //get arraylist from session
            ArrayList cart = (ArrayList)Session["cart"];

            //update object qty using the index
            CartItem cItem = (CartItem)cart[index];
            cItem.Quantity = qty;

            //Calcualte the total amount of all the items in the shopping cart.
            CalculateTotal();

            //rebind the datagrid
            dgCart.EditItemIndex = -1;
            dgCart.DataSource = (ArrayList)Session["cart"];
            dgCart.DataBind();

        }



        private void btnCheckOut_Click(object sender, System.EventArgs e)
        {
            int Quantity = 1;
            // retrieves cart and checks if it is empty or not exist
            ArrayList cart = (ArrayList)Session["cart"];
            foreach (CartItem item in cart) 
            {
                Quantity = item.Quantity;
                if (Quantity == 0 ){
                    break;
                }
            }

            if (cart == null || cart.Count == 0 || Quantity == 0)
            {    
                lblTotalPrice.Text = "0";
                lblStatus.Text = "Cart is empty! Not allowed to proceed.";
            }
            else {


                Response.Redirect("/shopperH/checkout.aspx");
            }
        }

        private void btnContinueShopping_Click(object sender, System.EventArgs e)
        {
            Server.Transfer("/shopperH/ProductsListing.aspx");
        }

        //This method Calcualtes the total amount of all the items in the shopping cart.
        private void CalculateTotal()
        {
            ArrayList cart = (ArrayList)Session["cart"];
            cart = (ArrayList)Session["cart"];

            decimal totalPrice =0;
            decimal subTotal=0;

            //To Calculate the total price payable from all then items in the cart.
            foreach (CartItem item in cart) 
            {
                subTotal = item.UnitPrice * item.Quantity;
                totalPrice = totalPrice + subTotal;

                Session["OrderTotal"] = totalPrice;
                lblTotalPrice.Text = Convert.ToString(totalPrice);
            }
        }




    }
}