Componentizes power cells (cmss13-devs#4855)

# About the pull request
Creates a new, flexible component for power cells. Eventually, anything
powered will use a cell component instead of holding a ref to a
`/obj/item/cell` or having a `charge` variable.

Converts NVGs over to the new system as an example, the rest will come
in time.

Minor rework of how `emp_act()` works

# Explain why it's good for the game
Cells are one of the most obvious things to be componentized, and
componentizing them allows cells to be added to new objects in a very
easy manner.

# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Works

</details>

code/__DEFINES/dcs/signals/atom/signals_atom.dm

@@ -51,3 +51,6 @@
 
 /// Called when an atom is mouse dropped on another atom, from /client/MouseDrop: (atom/dropped_onto)
 #define COMSIG_ATOM_DROP_ON "atom_drop_on"
+
+/// Called when an atom has emp_act called on it, from /atom/emp_act: (severity)
+#define COMSIG_ATOM_EMP_ACT "atom_emp_act"

code/__DEFINES/dcs/signals/atom/signals_cell.dm

@@ -0,0 +1,26 @@
+/// (charge_amount)
+#define COMSIG_CELL_USE_CHARGE "cell_use_charge"
+	#define COMPONENT_CELL_NO_USE_CHARGE (1<<0)
+
+/// (charge_amount)
+#define COMSIG_CELL_ADD_CHARGE "cell_add_charge"
+
+#define COMSIG_CELL_START_TICK_DRAIN "cell_start_tick_drain"
+
+#define COMSIG_CELL_STOP_TICK_DRAIN "cell_stop_tick_drain"
+
+/// (mob/living/user)
+#define COMSIG_CELL_TRY_RECHARGING "cell_try_recharging"
+	#define COMPONENT_CELL_NO_RECHARGE (1<<0)
+
+#define COMSIG_CELL_OUT_OF_CHARGE "cell_out_of_charge"
+
+/// (charge_amount)
+#define COMSIG_CELL_CHECK_CHARGE "cell_check_charge"
+	#define COMPONENT_CELL_CHARGE_INSUFFICIENT (1<<0)
+
+#define COMSIG_CELL_TRY_INSERT_CELL "cell_try_insert_cell"
+	#define COMPONENT_CANCEL_CELL_INSERT (1<<0)
+
+/// (mob/living/user)
+#define COMSIG_CELL_REMOVE_CELL "cell_remove_cell"

code/datums/components/cell.dm

@@ -0,0 +1,202 @@
+#define UNLIMITED_CHARGE -1
+#define UNLIMITED_DISTANCE -1
+
+/datum/component/cell
+	dupe_mode = COMPONENT_DUPE_UNIQUE
+	/// Maximum charge of the power cell, set to -1 for infinite charge
+	var/max_charge = 10000
+	/// Initial max charge of the power cell
+	var/initial_max_charge
+	/// Current charge of power cell
+	var/charge = 10000
+	/// If the component can be recharged by hitting its parent with a cell
+	var/hit_charge = FALSE
+	/// The maximum amount that can be recharged per tick when using a cell to recharge this component
+	var/max_recharge_tick = 400
+	/// If draining charge on process(), how much to drain per process call
+	var/charge_drain = 10
+	/// If the parent should show cell charge on examine
+	var/display_charge = TRUE
+	/// From how many tiles at the highest someone can examine the parent to see the charge
+	var/charge_examine_range = 1
+	/// If the component requires a cell to be inserted to work instead of having an integrated one
+	var/cell_insert = FALSE
+	/// Ref to an inserted cell. Should only be null if cell_insert is false
+	var/obj/item/cell/inserted_cell
+
+
+/datum/component/cell/Initialize(
+	max_charge = 10000,
+	hit_charge = FALSE,
+	max_recharge_tick = 400,
+	charge_drain = 10,
+	display_charge = TRUE,
+	charge_examine_range = 1,
+	cell_insert = FALSE,
+	)
+
+	. = ..()
+	if(!isatom(parent))
+		return COMPONENT_INCOMPATIBLE
+
+	src.max_charge = max_charge
+	charge = max_charge
+	src.hit_charge = hit_charge
+	src.max_recharge_tick = max_recharge_tick
+	src.charge_drain = charge_drain
+	src.display_charge = display_charge
+	src.charge_examine_range = charge_examine_range
+	src.cell_insert = cell_insert
+
+/datum/component/cell/Destroy(force, silent)
+	QDEL_NULL(inserted_cell)
+	return ..()
+
+
+/datum/component/cell/RegisterWithParent()
+	..()
+	RegisterSignal(parent, list(COMSIG_PARENT_ATTACKBY, COMSIG_ITEM_ATTACKED), PROC_REF(on_object_hit))
+	RegisterSignal(parent, COMSIG_CELL_ADD_CHARGE, PROC_REF(add_charge))
+	RegisterSignal(parent, COMSIG_CELL_USE_CHARGE, PROC_REF(use_charge))
+	RegisterSignal(parent, COMSIG_CELL_CHECK_CHARGE, PROC_REF(has_charge))
+	RegisterSignal(parent, COMSIG_CELL_START_TICK_DRAIN, PROC_REF(start_drain))
+	RegisterSignal(parent, COMSIG_CELL_STOP_TICK_DRAIN, PROC_REF(stop_drain))
+	RegisterSignal(parent, COMSIG_CELL_REMOVE_CELL, PROC_REF(remove_cell))
+	RegisterSignal(parent, COMSIG_PARENT_EXAMINE, PROC_REF(on_examine))
+	RegisterSignal(parent, COMSIG_ATOM_EMP_ACT, PROC_REF(on_emp))
+
+/datum/component/cell/process()
+	use_charge(null, charge_drain)
+
+/datum/component/cell/proc/on_emp(datum/source, severity)
+	SIGNAL_HANDLER
+
+	use_charge(null, round(max_charge / severity))
+
+/datum/component/cell/proc/start_drain(datum/source)
+	SIGNAL_HANDLER
+
+	START_PROCESSING(SSobj, src)
+
+/datum/component/cell/proc/stop_drain(datum/source)
+	SIGNAL_HANDLER
+
+	STOP_PROCESSING(SSobj, src)
+
+/datum/component/cell/proc/on_examine(datum/source, mob/examiner, list/examine_text)
+	SIGNAL_HANDLER
+
+	if(!display_charge)
+		return
+
+	if((charge_examine_range != UNLIMITED_DISTANCE) && get_dist(examiner, parent) > charge_examine_range)
+		return
+
+	examine_text += "A small gauge in the corner reads \"Power: [round(100 * charge / max_charge)]%\"."
+
+/datum/component/cell/proc/on_object_hit(datum/source, obj/item/cell/attack_obj, mob/living/attacker, params)
+	SIGNAL_HANDLER
+
+	if(!hit_charge || !istype(attack_obj))
+		return
+
+	if(!cell_insert)
+		INVOKE_ASYNC(src, PROC_REF(charge_from_cell), attack_obj, attacker)
+
+	else
+		insert_cell(attack_obj, attacker)
+
+	return COMPONENT_NO_AFTERATTACK|COMPONENT_CANCEL_ITEM_ATTACK
+
+/datum/component/cell/proc/insert_cell(obj/item/cell/power_cell, mob/living/user)
+	if(inserted_cell)
+		to_chat(user, SPAN_WARNING("There's already a power cell in [parent]!"))
+		return
+
+	if(SEND_SIGNAL(parent, COMSIG_CELL_TRY_INSERT_CELL) & COMPONENT_CANCEL_CELL_INSERT)
+		return
+
+	power_cell.drop_to_floor(user)
+	power_cell.forceMove(parent)
+	inserted_cell = power_cell
+	charge = power_cell.charge
+	max_charge = power_cell.maxcharge
+
+/datum/component/cell/proc/remove_cell(mob/living/user)
+	SIGNAL_HANDLER
+
+	user.put_in_hands(inserted_cell, TRUE)
+	to_chat(user, SPAN_NOTICE("You remove [inserted_cell] from [parent]."))
+	inserted_cell = null
+	max_charge = initial_max_charge
+	charge = 0
+
+/datum/component/cell/proc/charge_from_cell(obj/item/cell/power_cell, mob/living/user)
+	if(max_charge == UNLIMITED_CHARGE)
+		to_chat(user, SPAN_WARNING("[parent] doesn't need more power."))
+		return
+
+	while(charge < max_charge)
+		if(SEND_SIGNAL(parent, COMSIG_CELL_TRY_RECHARGING, user) & COMPONENT_CELL_NO_RECHARGE)
+			return
+
+		if(power_cell.charge <= 0)
+			to_chat(user, SPAN_WARNING("[power_cell] is completely dry."))
+			return
+
+		if(!do_after(user, 1 SECONDS, (INTERRUPT_ALL & (~INTERRUPT_MOVED)), BUSY_ICON_BUILD, power_cell, INTERRUPT_DIFF_LOC))
+			to_chat(user, SPAN_WARNING("You were interrupted."))
+			return
+
+		if(power_cell.charge <= 0)
+			return
+
+		var/to_transfer = min(max_recharge_tick, power_cell.charge, (max_charge - charge))
+		if(power_cell.use(to_transfer))
+			add_charge(null, to_transfer)
+			to_chat(user, "You transfer some power between [power_cell] and [parent]. The gauge now reads: [round(100 * charge / max_charge)]%.")
+
+/datum/component/cell/proc/add_charge(datum/source, charge_add = 0)
+	SIGNAL_HANDLER
+
+	if(max_charge == UNLIMITED_CHARGE)
+		return
+
+	if(!charge_add)
+		return
+
+	charge = clamp(charge + charge_add, 0, max_charge)
+
+/datum/component/cell/proc/use_charge(datum/source, charge_use = 0)
+	SIGNAL_HANDLER
+
+	if(max_charge == UNLIMITED_CHARGE)
+		return
+
+	if(!charge_use)
+		return
+
+	if(!charge)
+		return COMPONENT_CELL_NO_USE_CHARGE
+
+	charge = clamp(charge - charge_use, 0, max_charge)
+
+	if(!charge)
+		on_charge_empty()
+		return
+
+/datum/component/cell/proc/has_charge(datum/source, charge_amount = 0)
+	SIGNAL_HANDLER
+
+	if(!charge)
+		return COMPONENT_CELL_CHARGE_INSUFFICIENT
+
+	if(charge < charge_amount)
+		return COMPONENT_CELL_CHARGE_INSUFFICIENT
+
+/datum/component/cell/proc/on_charge_empty()
+	stop_drain()
+	SEND_SIGNAL(parent, COMSIG_CELL_OUT_OF_CHARGE)
+
+#undef UNLIMITED_CHARGE
+#undef UNLIMITED_DISTANCE

code/game/atoms.dm

@@ -205,7 +205,9 @@ directive is properly returned.
 	return
 
 /atom/proc/emp_act(severity)
-	return
+	SHOULD_CALL_PARENT(TRUE)
+
+	SEND_SIGNAL(src, COMSIG_ATOM_EMP_ACT, severity)
 
 /atom/proc/in_contents_of(container)//can take class or object instance as argument
 	if(ispath(container))
@@ -245,8 +247,8 @@ directive is properly returned.
 	if(!examine_strings)
 		log_debug("Attempted to create an examine block with no strings! Atom : [src], user : [user]")
 		return
-	to_chat(user, examine_block(examine_strings.Join("\n")))
 	SEND_SIGNAL(src, COMSIG_PARENT_EXAMINE, user, examine_strings)
+	to_chat(user, examine_block(examine_strings.Join("\n")))
 
 /atom/proc/get_examine_text(mob/user)
 	. = list()

code/game/machinery/atmoalter/scrubber.dm

@@ -18,16 +18,14 @@
 		PF.flags_can_pass_all = PASS_OVER|PASS_AROUND|PASS_UNDER
 
 /obj/structure/machinery/portable_atmospherics/powered/scrubber/emp_act(severity)
+	. = ..()
 	if(inoperable())
-		..(severity)
 		return
 
 	if(prob(50/severity))
 		on = !on
 		update_icon()
 
-	..(severity)
-
 /obj/structure/machinery/portable_atmospherics/powered/scrubber/update_icon()
 	src.overlays = 0
 

code/game/machinery/bots/bots.dm

@@ -114,6 +114,7 @@
 
 
 /obj/structure/machinery/bot/emp_act(severity)
+	. = ..()
 	var/was_on = on
 	stat |= EMPED
 	new /obj/effect/overlay/temp/emp_sparks (loc)

code/game/machinery/bots/mulebot.dm

@@ -916,11 +916,11 @@
 	post_signal_multiple(control_freq, kv)
 
 /obj/structure/machinery/bot/mulebot/emp_act(severity)
+	. = ..()
 	if (cell)
 		cell.emp_act(severity)
 	if(load)
 		load.emp_act(severity)
-	..()
 
 
 /obj/structure/machinery/bot/mulebot/explode()

code/game/machinery/camera/camera.dm

@@ -35,6 +35,9 @@
 
 	var/colony_camera_mapload = TRUE
 
+	/// If this camera should have innate EMP-proofing
+	var/emp_proof = FALSE
+
 /obj/structure/machinery/camera/Initialize(mapload, ...)
 	. = ..()
 	WireColorToFlag = randomCameraWires()
@@ -72,6 +75,7 @@
 		if(WEST) pixel_x = 27
 
 /obj/structure/machinery/camera/emp_act(severity)
+	. = ..()
 	if(!isEmpProof())
 		if(prob(100/severity))
 			icon_state = "[initial(icon_state)]emp"
@@ -89,7 +93,6 @@
 				if(can_use())
 					cameranet.addCamera(src)
 			kick_viewers()
-			..()
 
 
 /obj/structure/machinery/camera/ex_act(severity)

code/game/machinery/camera/presets.dm

@@ -30,15 +30,14 @@
 	network = list(CAMERA_NET_LASER_TARGETS)
 	unslashable = TRUE
 	unacidable = TRUE
+	emp_proof = TRUE
 
 /obj/structure/machinery/camera/laser_cam/Initialize(mapload, laser_name)
 	. = ..()
 	if(!c_tag && laser_name)
 		var/area/A = get_area(src)
 		c_tag = "[laser_name] ([A.name])"
 
-/obj/structure/machinery/camera/laser_cam/emp_act(severity)
-	return //immune to EMPs, just in case
 
 /obj/structure/machinery/camera/laser_cam/ex_act()
 	return
@@ -125,9 +124,7 @@
 	invisibility = 101 //fuck you init()
 
 	colony_camera_mapload = FALSE
-
-/obj/structure/machinery/camera/autoname/lz_camera/emp_act(severity)
-	return //immune to EMPs, just in case
+	emp_proof = TRUE
 
 /obj/structure/machinery/camera/autoname/lz_camera/ex_act()
 	return
@@ -137,7 +134,7 @@
 
 /obj/structure/machinery/camera/proc/isEmpProof()
 	var/O = locate(/obj/item/stack/sheet/mineral/osmium) in assembly.upgrades
-	return O
+	return O || emp_proof
 
 /obj/structure/machinery/camera/proc/isXRay()
 	var/obj/item/stock_parts/scanning_module/O = locate(/obj/item/stock_parts/scanning_module) in assembly.upgrades

code/game/machinery/cell_charger.dm

@@ -80,11 +80,11 @@
 	return
 
 /obj/structure/machinery/cell_charger/emp_act(severity)
+	. = ..()
 	if(inoperable())
 		return
 	if(charging)
 		charging.emp_act(severity)
-	..(severity)
 
 
 /obj/structure/machinery/cell_charger/process()

code/game/machinery/computer/arcade.dm

@@ -165,8 +165,8 @@
 	return
 
 /obj/structure/machinery/computer/arcade/emp_act(severity)
+	. = ..()
 	if(inoperable())
-		..(severity)
 		return
 	var/empprize = null
 	var/num_of_prizes = 0
@@ -178,5 +178,3 @@
 	for(num_of_prizes; num_of_prizes > 0; num_of_prizes--)
 		empprize = pickweight(prizes)
 		new empprize(src.loc)
-
-	..(severity)

code/game/machinery/computer/camera_console.dm

@@ -354,8 +354,8 @@
 	exproof = TRUE
 	colony_camera_mapload = FALSE
 
-/obj/structure/machinery/computer/cameras/mortar/emp_act(severity)
-	return FALSE
+/obj/structure/machinery/computer/cameras/mortar/set_broken()
+	return
 
 /obj/structure/machinery/computer/cameras/dropship
 	name = "abstract dropship camera computer"