From 5761ecd3dad408f8b06d106d7bf6f99f091be2d3 Mon Sep 17 00:00:00 2001
From: UEDCommander <52104104+UEDCommander@users.noreply.github.com>
Date: Thu, 11 Apr 2024 17:36:06 +0300
Subject: [PATCH] Downstream refactors (#2104)

---
 baystation12.dme                              |   1 +
 code/__defines/dcs/signals/signals_area.dm    |  10 ++
 code/controllers/subsystems/atoms.dm          |  45 +++--
 code/controllers/subsystems/garbage.dm        |   4 +
 code/controllers/subsystems/overlays.dm       | 163 ++++++++++--------
 .../subsystems/processing/icon_updates.dm     |  69 ++++----
 code/game/area/area_power.dm                  |  22 +++
 .../objects/items/devices/radio/intercom.dm   |  68 ++++----
 code/modules/power/apc.dm                     |   6 +-
 9 files changed, 230 insertions(+), 158 deletions(-)
 create mode 100644 code/__defines/dcs/signals/signals_area.dm

diff --git a/baystation12.dme b/baystation12.dme
index f22a037290f3b..f8da9d1219587 100644
--- a/baystation12.dme
+++ b/baystation12.dme
@@ -98,6 +98,7 @@
 #include "code\__defines\zmimic.dm"
 #include "code\__defines\dcs\flags.dm"
 #include "code\__defines\dcs\helpers.dm"
+#include "code\__defines\dcs\signals\signals_area.dm"
 #include "code\__defines\dcs\signals\signals_atom.dm"
 #include "code\__defines\dcs\signals\signals_atom_movable.dm"
 #include "code\__defines\dcs\signals\signals_datum.dm"
diff --git a/code/__defines/dcs/signals/signals_area.dm b/code/__defines/dcs/signals/signals_area.dm
new file mode 100644
index 0000000000000..7e05ef6a0479f
--- /dev/null
+++ b/code/__defines/dcs/signals/signals_area.dm
@@ -0,0 +1,10 @@
+// Main area signals. Format:
+// When the signal is called: (signal arguments)
+// All signals send the source datum of the signal as the first argument
+
+///from base of /area/proc/power_change(): (area/apc_area)
+#define COMSIG_AREA_POWER_CHANGE "area_apc_power_change"
+///from base of /area/proc/set_apc(): (area/apc_area)
+#define COMSIG_AREA_APC_ADDED "area_apc_added"
+///from base of /area/proc/remove_apc(): (area/apc_area)
+#define COMSIG_AREA_APC_REMOVED "area_apc_removed"
diff --git a/code/controllers/subsystems/atoms.dm b/code/controllers/subsystems/atoms.dm
index d7236a00638c9..cc550d2ede5e8 100644
--- a/code/controllers/subsystems/atoms.dm
+++ b/code/controllers/subsystems/atoms.dm
@@ -44,33 +44,32 @@ SUBSYSTEM_DEF(atoms)
 		return
 	atom_init_stage = INITIALIZATION_INNEW_MAPLOAD
 	var/list/mapload_arg = list(TRUE)
-	var/atom/atom
-	var/list/params
 	var/count = 0
 	var/time = Uptime()
-	if (!initialized)
-		for (atom in world)
-			if (!atom || atom.atom_flags & ATOM_FLAG_INITIALIZED)
-				continue
-			InitAtom(atom, mapload_arg)
-			if (++count % 1000)
+	if(!initialized)
+		for(var/atom/atom_to_initialize as anything in world)
+			if(!atom_to_initialize || atom_to_initialize.atom_flags & ATOM_FLAG_INITIALIZED)
 				continue
+			InitAtom(atom_to_initialize, mapload_arg)
+			count++
 			CHECK_TICK
+
 	var/init_queue_length = length(init_queue)
-	if (init_queue_length)
-		for (var/i = 1 to init_queue_length)
-			atom = init_queue[i]
-			if (!atom || atom.atom_flags & ATOM_FLAG_INITIALIZED)
+	if(init_queue_length)
+		for(var/i = 1 to init_queue_length)
+			var/atom/atom_to_initialize = init_queue[i]
+			if (!atom_to_initialize || atom_to_initialize.atom_flags & ATOM_FLAG_INITIALIZED)
 				continue
-			params = init_queue[atom]
+
+			var/list/params = init_queue[atom_to_initialize]
 			if (params)
-				InitAtom(atom, mapload_arg + params)
+				InitAtom(atom_to_initialize, mapload_arg + params)
 			else
-				InitAtom(atom, mapload_arg)
-			if (++count % 500)
-				continue
+				InitAtom(atom_to_initialize, mapload_arg)
+			count++
 			CHECK_TICK
 		init_queue.Cut(1, init_queue_length + 1)
+
 	time = max((Uptime() - time) * 0.1, 0.1)
 	report_progress("Initialized [count] atom\s in [time]s ([floor(count/time)]/s)")
 	atom_init_stage = INITIALIZATION_INNEW_REGULAR
@@ -78,13 +77,13 @@ SUBSYSTEM_DEF(atoms)
 	if (late_queue_length)
 		count = 0
 		time = Uptime()
-		for (var/i = 1 to late_queue_length)
-			atom = late_init_queue[i]
-			if (!atom)
-				continue
-			atom.LateInitialize(arglist(late_init_queue[atom]))
-			if (++count % 250)
+		for(var/i = 1 to late_queue_length)
+			var/atom/atom_to_late_init = late_init_queue[i]
+			if (!atom_to_late_init)
 				continue
+
+			atom_to_late_init.LateInitialize(arglist(late_init_queue[atom_to_late_init]))
+			count++
 			CHECK_TICK
 		late_init_queue.Cut(1, late_queue_length + 1)
 		time = max((Uptime() - time) * 0.1, 0.1)
diff --git a/code/controllers/subsystems/garbage.dm b/code/controllers/subsystems/garbage.dm
index d8cfe79fe21ce..a0a1bbf954cb0 100644
--- a/code/controllers/subsystems/garbage.dm
+++ b/code/controllers/subsystems/garbage.dm
@@ -219,9 +219,13 @@ SUBSYSTEM_DEF(garbage)
 	++details.qdels
 	switch (datum.gc_destroyed)
 		if (null)
+			if(SEND_SIGNAL(datum, COMSIG_PREQDELETED)) // Gives any signal listener a chance to prevent atom qdel
+				return
+
 			datum.gc_destroyed = GC_CURRENTLY_BEING_QDELETED
 			var/start_time = world.time
 			var/start_tick = world.tick_usage
+			SEND_SIGNAL(datum, COMSIG_QDELETING) // Leting signal listeners know, that datum is being qdeleted
 			var/hint = datum.Destroy()
 			if (world.time != start_time)
 				++details.slept_destroy
diff --git a/code/controllers/subsystems/overlays.dm b/code/controllers/subsystems/overlays.dm
index 6090afe02c78e..baf3141f9a0b2 100644
--- a/code/controllers/subsystems/overlays.dm
+++ b/code/controllers/subsystems/overlays.dm
@@ -11,21 +11,17 @@ var/global/const/ATOM_ICON_CACHE_ALL = (ATOM_ICON_CACHE_NORMAL | ATOM_ICON_CACHE
 SUBSYSTEM_DEF(overlays)
 	name = "Overlays"
 	flags = SS_TICKER
-	wait = 1 // ticks
+	wait = 1
 	priority = FIRE_PRIORITY_OVERLAYS
 	init_order = SS_INIT_OVERLAYS
-
 	/// The queue of atoms that need under/overlay updates.
-	var/static/list/atom/queue = list()
-
+	VAR_PRIVATE/static/list/atom/queue = list()
 	/// A list([icon] = list([state] = [appearance], ...), ...) cache of appearances.
-	var/static/list/state_cache = list()
-
+	VAR_PRIVATE/static/list/state_cache = list()
 	/// A list([icon] = [appearance], ...) cache of appearances.
-	var/static/list/icon_cache = list()
-
+	VAR_PRIVATE/static/list/icon_cache = list()
 	/// The number of appearances currently cached.
-	var/static/cache_size = 0
+	VAR_PRIVATE/static/cache_size = 0
 
 
 /datum/controller/subsystem/overlays/Recover()
@@ -33,16 +29,15 @@ SUBSYSTEM_DEF(overlays)
 	LIST_RESIZE(state_cache, 0)
 	LIST_RESIZE(icon_cache, 0)
 	cache_size = 0
-	var/count = 0
-	for (var/atom/atom)
-		atom.atom_flags &= ~ATOM_AWAITING_OVERLAY_UPDATE
-		if (++count % 500)
-			continue
+	for(var/atom/atom as anything in world)
+		if(atom.atom_flags & ATOM_AWAITING_OVERLAY_UPDATE)
+			SSoverlays.queue += atom
+
 		CHECK_TICK
 
 
 /datum/controller/subsystem/overlays/Initialize(start_uptime)
-	fire(FALSE, TRUE)
+	flush_queue()
 
 
 /datum/controller/subsystem/overlays/UpdateStat(time)
@@ -51,73 +46,100 @@ SUBSYSTEM_DEF(overlays)
 	..({"Queued Atoms: [length(queue)], Cache Size: [cache_size]"})
 
 
-/datum/controller/subsystem/overlays/fire(resumed, no_mc_tick)
-	var/queue_length = length(queue)
-	if (queue_length)
-		var/atom/atom
-		for (var/i = 1 to queue_length)
-			atom = queue[i]
-			if (QDELETED(atom))
-				continue
-			if (atom.atom_flags & ATOM_AWAITING_OVERLAY_UPDATE)
-				atom.UpdateOverlays()
-			if (no_mc_tick)
-				if (i % 1000)
-					continue
-				CHECK_TICK
-			else if (MC_TICK_CHECK)
-				queue.Cut(1, i + 1)
-				return
-		queue.Cut(1, queue_length + 1)
+/datum/controller/subsystem/overlays/fire(resumed)
+	var/queue_position = 1
+	while(length(queue) >= queue_position)
+		var/atom/atom_to_update = queue[queue_position]
+		if(!QDELETED(atom_to_update) && atom_to_update.atom_flags & ATOM_AWAITING_OVERLAY_UPDATE)
+			atom_to_update.UpdateOverlays()
+
+		queue_position++
+		if(MC_TICK_CHECK)
+			break
+
+	queue.Cut(1, queue_position)
+
+/datum/controller/subsystem/overlays/proc/flush_queue()
+	var/queue_position = 1
+	while(length(queue) >= queue_position)
+		process_atom_overlays_update(queue[queue_position])
+		queue_position++
+		CHECK_TICK
+
+	LIST_RESIZE(queue, 0)
+
+/datum/controller/subsystem/overlays/proc/process_atom_overlays_update(atom/atom_to_update)
+	if(!QDELETED(atom_to_update) && atom_to_update.atom_flags & ATOM_AWAITING_OVERLAY_UPDATE)
+		atom_to_update.UpdateOverlays()
 
 
 /datum/controller/subsystem/overlays/proc/GetStateAppearance(icon, state)
-	var/list/subcache = state_cache[icon]
-	if (!subcache)
-		subcache = list()
-		state_cache[icon] = subcache
-	if (!subcache[state])
-		var/image/image = image(icon, null, state)
-		subcache[state] = image.appearance
-		++cache_size
-	return subcache[state]
+	var/list/state_to_appearance = state_cache[icon]
+	if(!state_to_appearance)
+		state_to_appearance = list()
+		state_cache[icon] = state_to_appearance
+
+	var/state_appearance = state_to_appearance[state]
+	if(!state_appearance)
+		var/image/state_image = image(icon, null, state)
+		state_appearance = state_image.appearance
+		state_to_appearance[state] = state_appearance
+		cache_size++
+
+	return state_appearance
 
 
 /datum/controller/subsystem/overlays/proc/GetIconAppearance(icon)
-	if (!icon_cache[icon])
-		var/image/image = image(icon)
-		icon_cache[icon] = image.appearance
-		++cache_size
-	return icon_cache[icon]
+	var/icon_appearance = icon_cache[icon]
+	if (!icon_appearance)
+		var/image/icon_image = image(icon)
+		icon_appearance = icon_image.appearance
+		icon_cache[icon] = icon_appearance
+		cache_size++
+
+	return icon_appearance
 
 
-/datum/controller/subsystem/overlays/proc/GetAppearanceList(atom/subject, list/sources)
+/datum/controller/subsystem/overlays/proc/getAppearanceList(atom/subject, list/sources)
 	if (!sources)
 		return list()
+
 	if (!islist(sources))
 		sources = list(sources)
+
 	var/list/result = list()
-	var/icon/icon = subject.icon
-	var/atom/entry
-	for (var/i = 1 to length(sources))
-		entry = sources[i]
-		if (!entry)
+	for (var/atom/source as anything in sources)
+		if(!source)
 			continue
-		else if (istext(entry))
-			result += GetStateAppearance(icon, entry)
-		else if (isicon(entry))
-			result += GetIconAppearance(entry)
+
+		if(istext(source))
+			result += GetStateAppearance(subject.icon, source)
+
+		else if(isicon(source))
+			result += GetIconAppearance(source)
+
 		else
-			if (isloc(entry))
-				if (entry.atom_flags & ATOM_AWAITING_OVERLAY_UPDATE)
-					entry.UpdateOverlays()
-			if (!ispath(entry))
-				result += entry.appearance
+			if(isatom(source) && source.atom_flags & ATOM_AWAITING_OVERLAY_UPDATE)
+				source.UpdateOverlays()
+
+			if(!ispath(source))
+				result += source.appearance
 			else
-				var/image/image = entry
+				var/image/image = source
 				result += image.appearance
+
 	return result
 
+/datum/controller/subsystem/overlays/proc/enque_atom_overlay_update(atom/atom_to_update)
+	if(!atom_to_update)
+		return
+
+	if(atom_to_update.atom_flags & ATOM_AWAITING_OVERLAY_UPDATE)
+		return
+
+	atom_to_update.atom_flags |= ATOM_AWAITING_OVERLAY_UPDATE
+	SSoverlays.queue += atom_to_update
+
 
 /// Immediately runs an overlay update.
 /atom/proc/ImmediateOverlayUpdate()
@@ -147,11 +169,7 @@ SUBSYSTEM_DEF(overlays)
 /// Enqueues the atom for an overlay update if not already queued
 /atom/proc/QueueOverlayUpdate()
 	SHOULD_NOT_OVERRIDE(TRUE)
-	if (atom_flags & ATOM_AWAITING_OVERLAY_UPDATE)
-		return
-	atom_flags |= ATOM_AWAITING_OVERLAY_UPDATE
-	SSoverlays.queue += src
-
+	SSoverlays.enque_atom_overlay_update(src)
 
 /// Builds the atom's overlay state from caches
 /atom/proc/UpdateOverlays()
@@ -160,6 +178,7 @@ SUBSYSTEM_DEF(overlays)
 	if (QDELING(src))
 		LIST_RESIZE(overlays, 0)
 		return
+
 	if (length(atom_protected_overlay_cache))
 		if (length(atom_overlay_cache))
 			overlays = atom_protected_overlay_cache + atom_overlay_cache
@@ -203,7 +222,7 @@ SUBSYSTEM_DEF(overlays)
 	SHOULD_NOT_OVERRIDE(TRUE)
 	if (!sources)
 		return
-	sources = SSoverlays.GetAppearanceList(src, sources)
+	sources = SSoverlays.getAppearanceList(src, sources)
 	if (!length(sources))
 		return
 	if (cache_target & ATOM_ICON_CACHE_PROTECTED)
@@ -228,9 +247,11 @@ SUBSYSTEM_DEF(overlays)
 	SHOULD_NOT_OVERRIDE(TRUE)
 	if (!sources)
 		return
-	sources = SSoverlays.GetAppearanceList(src, sources)
+
+	sources = SSoverlays.getAppearanceList(src, sources)
 	if (!length(sources))
 		return
+
 	var/update
 	if (cache_target & ATOM_ICON_CACHE_PROTECTED)
 		var/outcome = CutCacheBehavior(sources, atom_protected_overlay_cache)
@@ -238,12 +259,14 @@ SUBSYSTEM_DEF(overlays)
 			update = TRUE
 			if (outcome == TRUE)
 				atom_protected_overlay_cache = null
+
 	if (cache_target & ATOM_ICON_CACHE_NORMAL)
 		var/outcome = CutCacheBehavior(sources, atom_overlay_cache)
 		if (!isnull(outcome))
 			update = TRUE
 			if (outcome == TRUE)
 				atom_overlay_cache = null
+
 	if (update)
 		QueueOverlayUpdate()
 
diff --git a/code/controllers/subsystems/processing/icon_updates.dm b/code/controllers/subsystems/processing/icon_updates.dm
index 1d2c918118104..5ce611a23d7f2 100644
--- a/code/controllers/subsystems/processing/icon_updates.dm
+++ b/code/controllers/subsystems/processing/icon_updates.dm
@@ -4,7 +4,7 @@ SUBSYSTEM_DEF(icon_update)
 	flags = SS_TICKER
 	priority = FIRE_PRIORITY_ICON_UPDATE
 	init_order = SS_INIT_ICON_UPDATE
-	var/static/list/queue = list()
+	VAR_PRIVATE/static/list/queue = list()
 
 
 /datum/controller/subsystem/icon_update/Recover()
@@ -19,44 +19,47 @@ SUBSYSTEM_DEF(icon_update)
 
 
 /datum/controller/subsystem/icon_update/Initialize(start_uptime)
-	fire(FALSE, TRUE)
-
-
-/datum/controller/subsystem/icon_update/fire(resumed, no_mc_tick)
-	var/atom/atom
-	var/list/params
-	var/queue_length = length(queue)
-	for (var/i = 1 to queue_length)
-		atom = queue[i]
-		if (QDELETED(atom))
-			continue
-		params = queue[atom]
-		if (islist(params))
-			atom.update_icon(arglist(params))
-		else
-			atom.update_icon()
-		if (no_mc_tick)
-			if (i % 100)
-				continue
-			CHECK_TICK
-		else if (MC_TICK_CHECK)
-			queue.Cut(1, i + 1)
-			return
-	if (queue_length)
-		queue.Cut(1, queue_length + 1)
-	suspend()
+	flush_queue()
 
+/datum/controller/subsystem/icon_update/fire(resumed)
+	var/queue_position = 1
+	while(length(queue) >= queue_position)
+		process_atom_icon_update(queue[queue_position])
+		queue_position++
+		if(MC_TICK_CHECK)
+			break
+
+	queue.Cut(1, queue_position)
+
+/datum/controller/subsystem/icon_update/proc/flush_queue()
+	var/queue_position = 1
+	while(length(queue) >= queue_position)
+		process_atom_icon_update(queue[queue_position])
+		queue_position++
+		CHECK_TICK
+
+	LIST_RESIZE(queue, 0)
+
+/datum/controller/subsystem/icon_update/proc/process_atom_icon_update(atom/atom_to_update)
+	if(QDELETED(atom_to_update))
+		return
+
+	var/list/params = queue[atom_to_update]
+	if (islist(params))
+		atom_to_update.update_icon(arglist(params))
+	else
+		atom_to_update.update_icon()
+
+/datum/controller/subsystem/icon_update/proc/enque_atom_icon_update(atom/atom_to_update, arguments)
+	SSicon_update.queue[atom_to_update] = arguments
 
 /**
  * Adds the atom to the icon_update subsystem to be queued for icon updates. Use this if you're going to be pushing a
  * lot of icon updates at once.
  */
 /atom/proc/queue_icon_update(...)
-	SSicon_update.queue[src] = length(args) ? args : TRUE
-	if (SSicon_update.suspended)
-		SSicon_update.wake()
-
+	SSicon_update.enque_atom_icon_update(src, length(args) ? args : TRUE)
 
-/hook/game_ready/proc/FlushIconUpdateQueue()
-	SSicon_update.fire(FALSE, TRUE)
+/hook/game_ready/proc/flush_icon_update_queue()
+	SSicon_update.flush_queue()
 	return TRUE
diff --git a/code/game/area/area_power.dm b/code/game/area/area_power.dm
index 963a86903be97..f67f32b2b282e 100644
--- a/code/game/area/area_power.dm
+++ b/code/game/area/area_power.dm
@@ -28,9 +28,31 @@
 /area/proc/power_change()
 	for(var/obj/machinery/M as anything in machinery_list)	// for each machine in the area
 		M.power_change()			// reverify power status (to update icons etc.)
+	SEND_SIGNAL(src, COMSIG_AREA_POWER_CHANGE)
 	if (fire || eject || party)
 		update_icon()
 
+/// Sets the apc in area. Sends COMSIG_AREA_APC_ADDED signal
+/area/proc/set_apc(obj/machinery/power/apc/new_apc)
+	if(!istype(new_apc))
+		CRASH("Invalid apc passed [log_info_line(new_apc)]")
+
+	if(apc)
+		stack_trace("Apc set in area when old one is still present")
+		remove_apc()
+
+	apc = new_apc
+	SEND_SIGNAL(src, COMSIG_AREA_APC_ADDED, new_apc)
+
+/// Removes current apc from area, if present. Sends COMSIG_AREA_APC_REMOVED signal
+/area/proc/remove_apc()
+	if(!apc)
+		return
+
+	SEND_SIGNAL(src, COMSIG_AREA_APC_REMOVED, apc)
+	apc = null
+
+
 /// Returns Integer. The total amount of power usage queued for the area from both `used_*` and `oneoff_*` for the given power channel, or all channels if `TOTAL` is passed instead.
 /area/proc/usage(chan)
 	switch(chan)
diff --git a/code/game/objects/items/devices/radio/intercom.dm b/code/game/objects/items/devices/radio/intercom.dm
index d2e549fb6405e..ccbb2f4ac2d85 100644
--- a/code/game/objects/items/devices/radio/intercom.dm
+++ b/code/game/objects/items/devices/radio/intercom.dm
@@ -15,7 +15,7 @@
 	///2 = wired/built, 1 = circuit installed, 0 = frame
 	var/buildstage = 2
 	var/number = 0
-	var/last_tick //used to delay the powercheck
+	var/area/linked_area
 	intercom_handling = TRUE
 
 /obj/item/device/radio/intercom/get_storage_cost()
@@ -93,7 +93,7 @@
 
 /obj/item/device/radio/intercom/Initialize(loc, dir, atom/frame)
 	. = ..()
-	START_PROCESSING(SSobj, src)
+	find_and_set_linked_area()
 
 	if (dir)
 		set_dir(dir)
@@ -148,10 +148,6 @@
 	. = ..()
 	internal_channels[num2text(RAID_FREQ)] = list(access_syndicate)
 
-/obj/item/device/radio/intercom/Destroy()
-	STOP_PROCESSING(SSobj, src)
-	return ..()
-
 /obj/item/device/radio/intercom/attack_ai(mob/user)
 	add_fingerprint(user)
 	if (buildstage == 2)
@@ -322,26 +318,6 @@
 	.["Wirecutters"] += "<p>Used for deconstruction. See deconstruction steps.</p>"
 	.["Wrench"] += "<p>Used for deconstruction. See deconstruction steps.</p>"
 
-/obj/item/device/radio/intercom/Process()
-	if (wiresexposed)
-		on = FALSE
-		return
-	if(((world.timeofday - last_tick) > 30) || ((world.timeofday - last_tick) < 0))
-		last_tick = world.timeofday
-		var/old_on = on
-
-		if(!src.loc)
-			on = FALSE
-		else
-			var/area/A = get_area(src)
-			if(!A)
-				on = FALSE
-			else
-				on = A.powered(EQUIP) // set "on" to the power status
-
-		if (on != old_on)
-			update_icon()
-
 /obj/item/device/radio/intercom/on_update_icon()
 	if (buildstage == 2 && wiresexposed)
 		icon_state = "intercom-b2"
@@ -349,10 +325,11 @@
 		icon_state = "intercom-b1"
 	else if (buildstage == 0)
 		icon_state = "intercom-f"
-	else if (!on)
-		icon_state = "intercom-p"
 	else
-		icon_state = "intercom_[broadcasting][listening]"
+		if(on)
+			icon_state = "intercom_[broadcasting][listening]"
+		else
+			icon_state = "intercom-p"
 
 /obj/item/device/radio/intercom/ToggleBroadcast()
 	..()
@@ -362,6 +339,39 @@
 	..()
 	update_icon()
 
+/obj/item/device/radio/intercom/proc/find_and_set_linked_area()
+	var/area/target_area = get_area(src)
+	if(!target_area.apc)
+		RegisterSignal(target_area, COMSIG_AREA_APC_ADDED, PROC_REF(on_apc_add))
+		return
+
+	on_apc_add(target_area)
+
+/obj/item/device/radio/intercom/proc/on_apc_add(area/apc_area)
+	SIGNAL_HANDLER
+
+	UnregisterSignal(apc_area, COMSIG_AREA_APC_ADDED)
+	linked_area = apc_area
+	RegisterSignal(apc_area, COMSIG_AREA_APC_REMOVED, PROC_REF(on_apc_removal))
+	RegisterSignal(apc_area, COMSIG_AREA_POWER_CHANGE, PROC_REF(change_status))
+
+/obj/item/device/radio/intercom/proc/on_apc_removal(area/apc_area)
+	SIGNAL_HANDLER
+
+	UnregisterSignal(apc_area, COMSIG_AREA_APC_REMOVED)
+	UnregisterSignal(apc_area, COMSIG_AREA_POWER_CHANGE)
+	linked_area = null
+	on = FALSE
+	update_icon()
+
+	RegisterSignal(apc_area, COMSIG_AREA_APC_ADDED, PROC_REF(on_apc_add))
+
+/obj/item/device/radio/intercom/proc/change_status()
+	SIGNAL_HANDLER
+
+	on = linked_area.powered(EQUIP)
+	update_icon()
+
 /obj/item/device/radio/intercom/broadcasting
 	broadcasting = 1
 
diff --git a/code/modules/power/apc.dm b/code/modules/power/apc.dm
index 649e52794e871..01c6ea536ad95 100644
--- a/code/modules/power/apc.dm
+++ b/code/modules/power/apc.dm
@@ -176,7 +176,7 @@
 		area = A
 	if(autoname)
 		SetName("\improper [area.name] APC")
-	area.apc = src
+	area.set_apc(src)
 
 	. = ..()
 
@@ -193,8 +193,8 @@
 	power_change()
 
 /obj/machinery/power/apc/Destroy()
-	src.update()
-	area.apc = null
+	update()
+	area.remove_apc()
 	area.power_light = 0
 	area.power_equip = 0
 	area.power_environ = 0