Question: How to make items unbuyable without necessary item

[l)arkSephiroth]

I have recently taken over work on a map and currently I have no way to prevent the map from just sucking up your gold if you accidentally try to don't click me an item for which you do not have the required necessary items already on you ( Item A + Item B = More Powerful Item C ).. like recipes.

The original author didn't bother preventing the gold loss from failed don't click me items.... This is a high priority for improving the map's playability.

I was wondering how you make it so that it (1) Won't take your money or your items if you don't have required items and (2) It will make a message for that player telling them they do not have the necessary items to do the purchase.

Thanks so much.

[Xantan]

event: unit buys item
conditions: item = RECIPE2
conditions: unit does not contain item (boalean or item idk) RECIPE LIST FOR RECIPE2
actions: player, add gold to player, all the gold for recipe2
actions: remove item of type RECIPE2 from triggerint/buying unit