Fixing spellcasting and edge cases.

code/datums/elements/spellcasting.dm

@@ -4,6 +4,7 @@
 	var/cast_flags
 	var/cast_slots
 	var/list/users_by_item = list()
+	var/list/stacked_spellcasting_by_user = list()
 
 /datum/element/spellcasting/Attach(datum/target, _flags, _slots)
 	. = ..()
@@ -12,6 +13,7 @@
 		RegisterSignal(target, COMSIG_ITEM_DROPPED, .proc/on_drop)
 	else if(ismob(target))
 		RegisterSignal(target, COMSIG_MOB_SPELL_CAST_CHECK, .proc/on_cast)
+		stacked_spellcasting_by_user[target]++
 	else
 		return ELEMENT_INCOMPATIBLE
 	cast_flags = _flags
@@ -22,16 +24,31 @@
 	UnregisterSignal(target, list(COMSIG_ITEM_EQUIPPED, COMSIG_ITEM_DROPPED, COMSIG_MOB_SPELL_CAST_CHECK))
 	if(users_by_item[target])
 		var/mob/user = users_by_item[target]
-		UnregisterSignal(user, COMSIG_MOB_SPELL_CAST_CHECK)
+		stacked_spellcasting_by_user[user]--
+		if(!stacked_spellcasting_by_user[user])
+			stacked_spellcasting_by_user -= user
+			UnregisterSignal(user, COMSIG_MOB_SPELL_CAST_CHECK)
+	else if(ismob(target))
+		stacked_spellcasting_by_user[target]--
+		if(!stacked_spellcasting_by_user[target])
+			stacked_spellcasting_by_user -= target
 
 /datum/element/spellcasting/proc/on_equip(datum/source, mob/equipper, slot)
-	if(slot in cast_slots)
+	if(!(slot in cast_slots))
+		return
+	users_by_item[source] = equipper
+	if(!stacked_spellcasting_by_user[equipper])
 		RegisterSignal(equipper, COMSIG_MOB_SPELL_CAST_CHECK, .proc/on_cast)
-		users_by_item[source] = equipper
+	stacked_spellcasting_by_user[equipper]++
 
 /datum/element/spellcasting/proc/on_drop(datum/source, mob/user)
-	UnregisterSignal(user, COMSIG_MOB_SPELL_CAST_CHECK)
+	if(!users_by_item[source])
+		return
 	users_by_item -= source
+	stacked_spellcasting_by_user[user]--
+	if(!stacked_spellcasting_by_user[user])
+		stacked_spellcasting_by_user -= user
+		UnregisterSignal(user, COMSIG_MOB_SPELL_CAST_CHECK)
 
 /datum/element/spellcasting/proc/on_cast(mob/caster, obj/effect/proc_holder/spell)
 	return cast_flags