I'm trying to make a stat/ property for weapon, named LifestealRatio, where whenever the weapon module causes damage, the ship gains HP (either immediately or added up to the ship repair per phase) equal to a portion of the damage done. 

I've yet to find any game mechanic triggering this, but the pieces are all available in the Battle Effects and Battle Actions: hit detection, effective damage calculation, health changes (from hit or repair). My idea is that the mod would makes a new property (LifestealRatio) for weapon modules (Idk if ship also needs such property), make a Battle effect that increases HP by Effective damage * LifestealRatio, then make a Battle action that check hit, check weapon module LifestealRatio, track to Core section in the same ship (which handles current ship HP), and apply the Battle effect there. 

However, my attempts were unsuccessful, and I don't understand how to call out things in Battle action to check for stats, and to apply effect. 

Help would be appreciated.