[MIRROR] Refactors the Charge wizard spell [MDB IGNORE] (#13424)

* Refactors the Charge wizard spell (#66599)

This PR refactors the "charge" spell to be signal based instead of looping over held items + istype checks.
This was atomized out of my proc holder removal PR. Figured it was small enough to handle on its own.

* Refactors the Charge wizard spell

Co-authored-by: MrMelbert <51863163+MrMelbert@users.noreply.github.com>

code/modules/projectiles/guns/magic.dm

@@ -16,6 +16,8 @@
 	var/charges = 0
 	var/recharge_rate = 8
 	var/charge_timer = 0
+	/// Whether this wand/staff recharges on its own over time.
+	/// (This is not related to the spell "Charge" whatsoever!)
 	var/can_charge = TRUE
 	var/ammo_type
 	var/no_den_usage
@@ -23,6 +25,34 @@
 	trigger_guard = TRIGGER_GUARD_ALLOW_ALL // Has no trigger at all, uses magic instead
 	pin = /obj/item/firing_pin/magic
 
+/obj/item/gun/magic/Initialize(mapload)
+	. = ..()
+	RegisterSignal(src, COMSIG_ITEM_MAGICALLY_CHARGED, .proc/on_magic_charge)
+
+/**
+ * Signal proc for [COMSIG_ITEM_MAGICALLY_CHARGED]
+ *
+ * Adds uses to wands or staffs.
+ */
+/obj/item/gun/magic/proc/on_magic_charge(datum/source, obj/effect/proc_holder/spell/targeted/charge/spell, mob/living/caster)
+	SIGNAL_HANDLER
+
+	. = COMPONENT_ITEM_CHARGED
+
+	// Non-self charging staves and wands can potentially expire
+	if(!can_charge && max_charges && prob(80))
+		max_charges--
+
+	if(max_charges <= 0)
+		max_charges = 0
+		. |= COMPONENT_ITEM_BURNT_OUT
+
+	charges = max_charges
+	update_appearance(UPDATE_ICON_STATE)
+	recharge_newshot()
+
+	return .
+
 /obj/item/gun/magic/process_fire(atom/target, mob/living/user, message, params, zone_override, bonus_spread)
 	if(no_den_usage)
 		var/area/A = get_area(user)