How to detect an items damage?

So I tried to make a sword that leeches health

and the amount of healing the player gets when he hits a mob scales with the items attack damage

but i cant find any block that detects the item's attack damage

i figured if theres a block which detects the players health then it should have a block that is labelled as "damage of (source enitity) or some other thing

pls help

EDIT: i tried to add in the variable "amount" but it said theres compatibility issues.. the error message keeps popping out