Rewrite mine turf overlay adding

Stop adding overlays on adjacent turfs. Just add them on yourself, and push them sideways.

code/modules/mining/mine_turfs.dm

@@ -97,6 +97,25 @@ var/list/mining_overlay_cache = list()
 				attackby(O, R)
 				return
 
+/turf/simulated/mineral/proc/get_cached_border(var/cache_id, var/direction, var/icon_file, var/icon_state, var/offset = 32)
+	//Cache miss
+	if(!mining_overlay_cache["[cache_id]_[direction]"])
+		var/image/new_cached_image = image(icon_state, dir = direction, layer = ABOVE_TURF_LAYER)
+		switch(direction)
+			if(NORTH)
+				new_cached_image.pixel_y = offset
+			if(SOUTH)
+				new_cached_image.pixel_y = -offset
+			if(EAST)
+				new_cached_image.pixel_x = offset
+			if(WEST)
+				new_cached_image.pixel_x = -offset
+		mining_overlay_cache["[cache_id]_[direction]"] = new_cached_image
+		return new_cached_image
+
+	//Cache hit
+	return mining_overlay_cache["[cache_id]_[direction]"]
+
 /turf/simulated/mineral/initialize()
 	. = ..()
 	if(prob(20))
@@ -111,8 +130,9 @@ var/list/mining_overlay_cache = list()
 
 /turf/simulated/mineral/update_icon(var/update_neighbors)
 
-	overlays.Cut()
+	cut_overlays()
 
+	//We are a wall (why does this system work like this??)
 	if(density)
 		if(mineral)
 			name = "[mineral.display_name] deposit"
@@ -122,47 +142,40 @@ var/list/mining_overlay_cache = list()
 		icon = 'icons/turf/walls.dmi'
 		icon_state = "rock"
 
+		//Apply overlays if we should have borders
 		for(var/direction in cardinal)
 			var/turf/T = get_step(src,direction)
 			if(istype(T) && !T.density)
-				var/place_dir = turn(direction, 180)
+				add_overlay(get_cached_border("rock_side",direction,icon,"rock_side"))
-				if(!mining_overlay_cache["rock_side_[place_dir]"])
-					mining_overlay_cache["rock_side_[place_dir]"] = image('icons/turf/walls.dmi', "rock_side", dir = place_dir)
-				T.overlays += mining_overlay_cache["rock_side_[place_dir]"]
 
 			if(archaeo_overlay)
-				overlays += archaeo_overlay
+				add_overlay(archaeo_overlay)
 
 			if(excav_overlay)
-				overlays += excav_overlay
+				add_overlay(excav_overlay)
-	else
 	
+	//We are a sand floor
+	else
 		name = "sand"
 		icon = 'icons/turf/flooring/asteroid.dmi'
 		icon_state = "asteroid"
 
 		if(sand_dug)
-			if(!mining_overlay_cache["dug_overlay"])
+			add_overlay("dug_overlay")
-				mining_overlay_cache["dug_overlay"] = image('icons/turf/flooring/asteroid.dmi', "dug_overlay")
-			overlays += mining_overlay_cache["dug_overlay"]
 
+		//Apply overlays if there's space
 		for(var/direction in cardinal)
 			if(istype(get_step(src, direction), /turf/space) && !istype(get_step(src, direction), /turf/space/cracked_asteroid))
-				if(!mining_overlay_cache["asteroid_edge_[direction]"])
+				add_overlay(get_cached_border("asteroid_edge",direction,icon,"asteroid_edges", 0))
-					mining_overlay_cache["asteroid_edge_[direction]"] = image('icons/turf/flooring/asteroid.dmi', "asteroid_edges", dir = direction)
+			
-				overlays += mining_overlay_cache["asteroid_edge_[direction]"]
+			//Or any time
 			else
 				var/turf/simulated/mineral/M = get_step(src, direction)
 				if(istype(M) && M.density)
-					if(!mining_overlay_cache["rock_side_[direction]"])
+					add_overlay(get_cached_border("rock_side",direction,'icons/turf/walls.dmi',"rock_side"))
-						mining_overlay_cache["rock_side_[direction]"] = image('icons/turf/walls.dmi', "rock_side", dir = direction)
-					overlays += mining_overlay_cache["rock_side_[direction]"]
 
 		if(overlay_detail)
-
+			add_overlay('icons/turf/flooring/decals.dmi',overlay_detail)
-			if(!mining_overlay_cache["decal_[overlay_detail]"])
-				mining_overlay_cache["decal_[overlay_detail]"] = image(icon = 'icons/turf/flooring/decals.dmi', icon_state = overlay_detail)
-			overlays += mining_overlay_cache["decal_[overlay_detail]"]
 
 		if(update_neighbors)
 			for(var/direction in alldirs)
@@ -414,12 +427,13 @@ var/list/mining_overlay_cache = list()
 				if(!archaeo_overlay && finds && finds.len)
 					var/datum/find/F = finds[1]
 					if(F.excavation_required <= excavation_level + F.view_range)
+						cut_overlay(archaeo_overlay)
 						archaeo_overlay = "overlay_archaeo[rand(1,3)]"
-						updateIcon = 1
+						add_overlay(archaeo_overlay)
 
 				else if(archaeo_overlay && (!finds || !finds.len))
+					cut_overlay(archaeo_overlay)
 					archaeo_overlay = null
-					updateIcon = 1
 
 				//there's got to be a better way to do this
 				var/update_excav_overlay = 0
@@ -436,8 +450,9 @@ var/list/mining_overlay_cache = list()
 				//update overlays displaying excavation level
 				if( !(excav_overlay && excavation_level > 0) || update_excav_overlay )
 					var/excav_quadrant = round(excavation_level / 25) + 1
+					cut_overlay(excav_overlay)
 					excav_overlay = "overlay_excv[excav_quadrant]_[rand(1,3)]"
-					updateIcon = 1
+					add_overlay(excav_overlay)
 
 				if(updateIcon)
 					update_icon()