Implement powersink surge (#2452)

Implements suggestion https://forums.aurorastation.org/viewtopic.php?f=21&p=78011 in the following fashion:

Powersinks explode ~18 minutes after being placed on normal SMES setup. Obviously more input from engineering will make this process go faster.
Upon reaching their capacity, they will now cause a larger area power surge. The surge will smash all lights belonging to APCs within close to moderate proximity, and call EMP act on all connected powernet items that are within range (severity depending on distance). All of those items have a small chance to cause a minor explosion as well, primarily because EMP act is fucking whimpy.

code/game/objects/items/devices/powersink.dm

@@ -18,7 +18,7 @@
 	var/apc_drain_rate = 5000 		// Max. amount drained from single APC. In Watts.
 	var/dissipation_rate = 20000	// Passive dissipation of drained power. In Watts.
 	var/power_drained = 0 			// Amount of power drained.
-	var/max_power = 5e9				// Detonation point.
+	var/max_power = 8e8				// Detonation point. Roughly 18 minutes with default setup.
 	var/mode = 0					// 0 = off, 1=clamped (off), 2=operating
 	var/drained_this_tick = 0		// This is unfortunately necessary to ensure we process powersinks BEFORE other machinery such as APCs.
 
@@ -27,7 +27,8 @@
 
 /obj/item/device/powersink/Destroy()
 	STOP_PROCESSING(SSprocessing, src)
-	processing_power_items.Remove(src)
+	processing_power_items -= src
+
 	return ..()
 
 /obj/item/device/powersink/attackby(var/obj/item/I, var/mob/user)
@@ -37,15 +38,15 @@
 			if(isturf(T) && !!T.is_plating())
 				attached = locate() in T
 				if(!attached)
-					user << "No exposed cable here to attach to."
+					to_chat(user, "<span class='warning'>No exposed cable here to attach to.</span>")
 					return
 				else
 					anchored = 1
 					mode = 1
-					src.visible_message("<span class='notice'>[user] attaches [src] to the cable!</span>")
+					visible_message("<span class='notice'>\The [user] attaches \the [src] to the cable!</span>")
 					return
 			else
-				user << "Device must be placed over an exposed cable to attach to it."
+				to_chat(user, "<span class='warning'>\The [src] must be placed over an exposed cable to attach to it.</span>")
 				return
 		else
 			if (mode == 2)
@@ -53,7 +54,7 @@
 				processing_power_items.Remove(src)
 			anchored = 0
 			mode = 0
-			src.visible_message("<span class='notice'>[user] detaches [src] from the cable!</span>")
+			visible_message("<span class='notice'>\The [user] detaches \the [src] from the cable!</span>")
 			set_light(0)
 			icon_state = "powersink0"
 
@@ -69,18 +70,18 @@
 		if(0)
 			..()
 		if(1)
-			src.visible_message("<span class='notice'>[user] activates [src]!</span>")
+			visible_message("<span class='notice'>\The [user] activates \the [src]!</span>")
 			mode = 2
 			icon_state = "powersink1"
 			START_PROCESSING(SSprocessing, src)
-			processing_power_items.Add(src)
+			processing_power_items += src
 		if(2)  //This switch option wasn't originally included. It exists now. --NeoFite
-			src.visible_message("<span class='notice'>[user] deactivates [src]!</span>")
+			visible_message("<span class='notice'>\The [user] deactivates \the [src]!</span>")
 			mode = 1
 			set_light(0)
 			icon_state = "powersink0"
 			STOP_PROCESSING(SSprocessing, src)
-			processing_power_items.Remove(src)
+			processing_power_items -= src
 
 /obj/item/device/powersink/pwr_drain()
 	if(!attached)
@@ -120,13 +121,62 @@
 /obj/item/device/powersink/process()
 	drained_this_tick = 0
 	power_drained -= min(dissipation_rate, power_drained)
-	if(power_drained > max_power * 0.95)
-		playsound(src, 'sound/effects/screech.ogg', 100, 1, 1)
-	if(power_drained >= max_power)
-		explosion(src.loc, 3,6,9,12)
-		qdel(src)
-		return
+
 	if(attached && attached.powernet)
 		PN = attached.powernet
 	else
 		PN = null
+
+	if(power_drained > max_power * 0.98)	// Lower the screeching period. It was pretty long during testing.
+		playsound(src, 'sound/effects/screech.ogg', 100, 1, 1)
+
+	if(power_drained >= max_power)
+		handle_overload()
+		qdel(src)
+		return
+
+/obj/item/device/powersink/proc/handle_overload()
+	if (QDELETED(src))
+		return
+
+	// No attached node, or no powernet.
+	if (!PN)
+		explosion(src.loc, 0, 1, 3, 6)
+		return
+
+	// Propagate the power surge through the powernet nodes.
+	for (var/A in PN.nodes)
+		if (!A || A == src)
+			continue
+
+		var/dist = get_dist(src, A)
+
+		if (dist < 1)
+			dist = 1	// For later calculations.
+		else if (dist > 24)
+			continue	// Out of range.
+
+		// Map it to a range of [3, 1] for severity.
+		dist = round(MAP(dist, 1, 28, 3, 1))
+
+		// Check for terminals and affect their master nodes. Also add a special
+		// case for APCs whereby their lights are popped or flicked.
+		if (istype(A, /obj/machinery/power/terminal))
+			var/obj/machinery/power/terminal/T = A
+			if (istype(T.master, /obj/machinery/power/apc))
+				var/obj/machinery/power/apc/AP = T.master
+				if (dist > 1)
+					AP.overload_lighting(100, TRUE)
+				else
+					AP.flicker_all()
+			else if (T.master)
+				T.master.emp_act(dist)
+
+		var/atom/aa = A
+		aa.emp_act(dist)
+
+		if (prob(15 * dist))
+			explosion(aa.loc, 0, 0, 3, 4)
+
+	// Also destroy the source.
+	explosion(src.loc, 0, 0, 1, 2)