Asp out of stock

I am trying to make it so that the shopping cart we use will not allow the buyer to purchase an item if it is out of stock.

the code that is currently on the page is
<a href="/Cart/ShoppingCart_AddProduct.asp?ProductID=55"

I realize that the code should be something along the lines of

if inventory >1, then
(output) ‘buy it here’ (reroute to the hardcoded link to the shopping cart if buy it here clicked)
(output) ‘we’re sold out’ (do nothing)
(end of asp code)

but have no idea how to add it to the existing code, or write it so that it works. - I do not know asp.

Any help would be appreciated.