Random mouse placement (#21483)

* Restructured handle_environment()

This creates the environment_is_safe() proc for simple_animals

* Mice are placed at roundstart randomly

Rejoyce as wires are bitten in random locations.

* Removes all mice from the maps

* Code review

* Code review II

code/controllers/subsystem/squeak.dm

@@ -0,0 +1,40 @@
+var/datum/subsystem/squeak/SSsqueak
+
+// The Squeak
+// because this is about placement of mice mobs, and nothing to do with
+// mice - the computer peripheral
+
+/datum/subsystem/squeak
+	name = "Squeak"
+	priority = 40
+	flags = SS_NO_FIRE
+
+	var/list/exposed_wires = list()
+
+/datum/subsystem/squeak/New()
+	NEW_SS_GLOBAL(SSsqueak)
+
+/datum/subsystem/squeak/Initialize(timeofday)
+	find_exposed_wires()
+	var/num_mice = 10
+
+	var/mob/living/simple_animal/mouse/M
+	var/turf/proposed_turf
+
+	while((num_mice > 0) && exposed_wires.len)
+		proposed_turf = pick_n_take(exposed_wires)
+		if(!M)
+			M = new(proposed_turf)
+		else
+			M.forceMove(proposed_turf)
+		if(M.environment_is_safe())
+			num_mice -= 1
+			M = null
+
+/datum/subsystem/squeak/proc/find_exposed_wires()
+	exposed_wires.Cut()
+
+	var/list/all_turfs = block(locate(1,1,1), locate(world.maxx,world.maxy,1))
+	for(var/turf/open/floor/plating/T in all_turfs)
+		if(locate(/obj/structure/cable) in T)
+			exposed_wires += T