Fixes #5915

Also allows checking remaining engine charge by examining, and removes
the verb.

code/modules/vehicles/cargo_train.dm

@@ -48,7 +48,7 @@
 	turn_off()	//so engine verbs are correctly set
 
 /obj/vehicle/train/cargo/engine/Move()
-	if(on && cell.charge < power_use)
+	if(on && cell.charge < charge_use)
 		turn_off()
 		update_stats()
 		if(load && is_train_head())
@@ -183,20 +183,7 @@
 	
 	if(get_dist(usr,src) <= 1)
 		usr << "The power light is [on ? "on" : "off"].\nThere are[key ? "" : " no"] keys in the ignition."
-
-/obj/vehicle/train/cargo/engine/verb/check_power()
-	set name = "Check power level"
-	set category = "Object"
-	set src in view(1)
-	
-	if(!istype(usr, /mob/living/carbon/human))
-		return
-
-	if(!cell)
-		usr << "There is no power cell installed in [src]."
-		return
-
-	usr << "The power meter reads [round(cell.percent(), 0.01)]%"
+		usr << "The charge meter reads [cell? round(cell.percent(), 0.01) : 0]%"
 
 /obj/vehicle/train/cargo/engine/verb/start_engine()
 	set name = "Start engine"
@@ -214,7 +201,7 @@
 	if (on)
 		usr << "You start [src]'s engine."
 	else
-		if(cell.charge < power_use)
+		if(cell.charge < charge_use)
 			usr << "[src] is out of power."
 		else
 			usr << "[src]'s engine won't start."
@@ -288,13 +275,22 @@
 // more engines increases this limit by car_limit per
 // engine.
 //-------------------------------------------------------
-/obj/vehicle/train/cargo/engine/update_train_stats()
-	..()
+/obj/vehicle/train/cargo/engine/update_car(var/train_length, var/active_engines)
+	src.train_length = train_length
+	src.active_engines = active_engines
 
-	update_move_delay()
+	//Update move delay
+	if(!is_train_head() || !on)
+		move_delay = initial(move_delay)		//so that engines that have been turned off don't lag behind
+	else
+		move_delay = max(0, (-car_limit * active_engines) + train_length - active_engines)	//limits base overweight so you cant overspeed trains
+		move_delay *= (1 / max(1, active_engines)) * 2 										//overweight penalty (scaled by the number of engines)
+		move_delay += config.run_speed 														//base reference speed
+		move_delay *= 1.1																	//makes cargo trains 10% slower than running when not overweight
 
-/obj/vehicle/train/cargo/trolley/update_train_stats()
-	..()
+/obj/vehicle/train/cargo/trolley/update_car(var/train_length, var/active_engines)
+	src.train_length = train_length
+	src.active_engines = active_engines
 	
 	if(!lead && !tow)
 		anchored = 0
@@ -305,12 +301,3 @@
 	else
 		anchored = 1
 		verbs -= /atom/movable/verb/pull
-
-/obj/vehicle/train/cargo/engine/proc/update_move_delay()
-	if(!is_train_head() || !on)
-		move_delay = initial(move_delay)		//so that engines that have been turned off don't lag behind
-	else
-		move_delay = max(0, (-car_limit * active_engines) + train_length - active_engines)	//limits base overweight so you cant overspeed trains
-		move_delay *= (1 / max(1, active_engines)) * 2 										//overweight penalty (scaled by the number of engines)
-		move_delay += config.run_speed 														//base reference speed
-		move_delay *= 1.1																	//makes cargo trains 10% slower than running when not overweight

code/modules/vehicles/train.dm

@@ -142,6 +142,15 @@
 	if (T.tow)
 		user << "\red [T] is already towing something."
 		return
+	
+	//check for cycles.
+	var/obj/vehicle/train/next_car = T
+	while (next_car)
+		if (next_car == src)
+			user << "\red That seems very silly."
+			return
+		next_car = next_car.lead
+	
 	//latch with src as the follower
 	lead = T
 	T.tow = src
@@ -192,23 +201,28 @@
 // size of the train, to limit super long trains.
 //-------------------------------------------------------
 /obj/vehicle/train/update_stats()
-	if(tow)
-		return tow.update_stats()	//take us to the very end
-	else
-		update_train_stats()		//we're at the end
+	//first, seek to the end of the train
+	var/obj/vehicle/train/T = src
+	while(T.tow)
+		//check for cyclic train.
+		if (T.tow == src)
+			lead.tow = null
+			lead.update_stats()
+			
+			lead = null
+			update_stats()
+			return
+		T = T.tow
 
-/obj/vehicle/train/proc/update_train_stats()
-	if(powered && on)
-		active_engines = 1	//increment active engine count if this is a running engine
-	else
-		active_engines = 0
+	//now walk back to the front.
+	var/active_engines = 0
+	var/train_length = 0
+	while(T)
+		train_length++
+		if (powered && on)
+			active_engines++
+		T.update_car(train_length, active_engines)
+		T = T.lead
 
-	train_length = 1
-
-	if(istype(tow))
-		active_engines += tow.active_engines
-		train_length += tow.train_length
-
-	//update the next section of train ahead of us
-	if(istype(lead))
-		lead.update_train_stats()
+/obj/vehicle/train/proc/update_car(var/train_length, var/active_engines)
+	return

code/modules/vehicles/vehicle.dm

@@ -22,7 +22,7 @@
 	var/movable = 1
 
 	var/obj/item/weapon/cell/cell
-	var/power_use = 5	//set this to adjust the amount of power the vehicle uses per move
+	var/charge_use = 5	//set this to adjust the amount of power the vehicle uses per move
 
 	var/atom/movable/load		//all vehicles can take a load, since they should all be a least drivable
 	var/load_item_visible = 1	//set if the loaded item should be overlayed on the vehicle sprite
@@ -39,7 +39,7 @@
 
 /obj/vehicle/Move()
 	if(world.time > l_move_time + move_delay)
-		if(on && powered && cell.charge < power_use)
+		if(on && powered && cell.charge < charge_use)
 			turn_off()
 
 		var/init_anc = anchored
@@ -51,7 +51,7 @@
 		anchored = init_anc
 
 		if(on && powered)
-			cell.use(power_use)			
+			cell.use(charge_use)
 
 		if(load)
 			load.forceMove(loc)// = loc
@@ -172,7 +172,7 @@
 /obj/vehicle/proc/turn_on()
 	if(stat)
 		return 0
-	if(powered && cell.charge < power_use)
+	if(powered && cell.charge < charge_use)
 		return 0
 	on = 1
 	luminosity = initial(luminosity)
@@ -228,7 +228,7 @@
 		turn_off()
 		return
 
-	if(cell.charge < power_use)
+	if(cell.charge < charge_use)
 		turn_off()
 		return