Anvil-related forging help!

Hello! I am working on a mod that fixes a few things that I think should be added to vanilla minecraft. One of the things I'm making is a custom book called Book of Cleansing. It is a white book only found in end cities. When you apply it to an item via an anvil, it removes all curses currently affecting the item, and destroy the book. I need a little help on how to make it work in the anvil. It is a specific book (not an enchantment) so it won't work that way. I don't know how to get it to check and change slots on an anvil, or even how to check when an anvil is opened. If all else fails, I can use a smithing table instead, but I'd much rather use the anvil. I want the level cost to be the same as the number of curses on the item. Can anyone help?