yeah i was hoping for an event (it happened once already that i missed an event so...) or some system that would check for such an event. Sometimes i write too much, other times almost nothing.
I made a system to merge potions when looted (each looted potion has 5 charges and can have max 50 charges), what i wanted to do is a trigger that checks if a unit moves a potion from a slot to another slot with the same kind of potions then it'll add the charges of the first item to the second, and eventually destroy the second item.
Let's say for example i have 2 potions, one with 50 charges and the other with 5, then i use one of the 50 potions, then move the 5 potions over the 49, at this point i should have 50 potions in one slot and 4 in another.
I've already made the triggers for when the potions are looted, and i'm pretty sure i've seen some maps with something like the one i've just explained (i don't remember which one though...the troll survival one maybe?)