Creates a disposal pipe that filters items that haven't found a valid…

… sorting pipe (#11375)

* Adds an unsorted sorting pipe

* Only send unsorted things if they need sorting

* Adds the ability to build the unsorted pipe with the RPD

* Fixes pipe sorting

* Update pipe_sorting.dm

* Bug fixes

* Entering a pipe backwards will send you the way that you came

* Update code/modules/recycling/disposal/pipe_sorting.dm

code/game/objects/items/RPD.dm

@@ -56,6 +56,7 @@ GLOBAL_LIST_INIT(disposal_pipe_recipes, list(
 		new /datum/pipe_info/disposal("Y-Junction",		/obj/structure/disposalpipe/junction/yjunction),
 		new /datum/pipe_info/disposal("Sort Junction",	/obj/structure/disposalpipe/sorting/mail, PIPE_TRIN_M),
 		new /datum/pipe_info/disposal("Package Junction",	/obj/structure/disposalpipe/sorting/wrap, PIPE_TRIN_M),
+		new /datum/pipe_info/disposal("Unsorted Mail Junction",	/obj/structure/disposalpipe/sorting/unsorted, PIPE_TRIN_M),
 		new /datum/pipe_info/disposal("Trunk",			/obj/structure/disposalpipe/trunk),
 		new /datum/pipe_info/disposal("Bin",			/obj/machinery/disposal/bin, PIPE_ONEDIR),
 		new /datum/pipe_info/disposal("Outlet",			/obj/structure/disposaloutlet),

code/modules/recycling/disposal/holder.dm

@@ -16,6 +16,7 @@
 	var/destinationTag = NONE	// changes if contains a delivery container
 	var/tomail = FALSE			// contains wrapped package
 	var/hasmob = FALSE			// contains a mob
+	var/unsorted = TRUE			// have we been sorted yet?
 
 /obj/structure/disposalholder/Destroy()
 	QDEL_NULL(gas)

code/modules/recycling/disposal/pipe_sorting.dm

@@ -8,10 +8,17 @@
 
 /obj/structure/disposalpipe/sorting/nextdir(obj/structure/disposalholder/H)
 	var/sortdir = dpdir & ~(dir | turn(dir, 180))
-	if(H.dir != sortdir)		// probably came from the negdir
-		if(check_sorting(H))	// if destination matches filtered type...
-			return sortdir		// exit through sortdirection
-
+	var/input_direction = dir
+	// probably came from the negdir
+	if(H.dir == input_direction)
+		// if destination matches filtered type...
+		if(check_sorting(H))
+			H.unsorted = FALSE
+			// exit through sortdirection
+			return sortdir
+	// If we are entering backwards, continue onwards
+	if (H.dir == turn(input_direction, 180))
+		return H.dir
 	// go with the flow to positive direction
 	return dir
 
@@ -23,7 +30,7 @@
 
 // Mail sorting junction, uses package tags to sort objects.
 /obj/structure/disposalpipe/sorting/mail
-	desc = "An underfloor disposal pipe that sorts wrapped objects based on their destination tags."
+	desc = "An underfloor disposal pipe that sorts wrapped objects based on their destination tags. Objects passing through it become sorted."
 	flip_type = /obj/structure/disposalpipe/sorting/mail/flip
 	var/sortType = 0
 	// sortType is to be set in map editor.
@@ -82,7 +89,7 @@
 // Wrap sorting junction, sorts objects destined for the mail office mail table (tomail = 1)
 /obj/structure/disposalpipe/sorting/wrap
 	name = "package sorting disposal pipe"
-	desc = "An underfloor disposal pipe which sorts wrapped and unwrapped objects."
+	desc = "An underfloor disposal pipe which sorts wrapped and unwrapped objects. Objects passing through it become sorted."
 	flip_type = /obj/structure/disposalpipe/sorting/wrap/flip
 	initialize_dirs = DISP_DIR_RIGHT | DISP_DIR_FLIP
 
@@ -93,3 +100,19 @@
 	icon_state = "pipe-j2s"
 	flip_type = /obj/structure/disposalpipe/sorting/wrap
 	initialize_dirs = DISP_DIR_LEFT | DISP_DIR_FLIP
+
+// Unsorted junction, will divert things based on whether or not they have been sorted.
+/obj/structure/disposalpipe/sorting/unsorted
+	name = "unsorted sorting disposal pipe"
+	desc = "An underfloor disposal pipe which sorts sorted and unsorted objects. Objects passing through it become sorted."
+	flip_type = /obj/structure/disposalpipe/sorting/unsorted/flip
+	initialize_dirs = DISP_DIR_RIGHT | DISP_DIR_FLIP
+
+/obj/structure/disposalpipe/sorting/unsorted/check_sorting(obj/structure/disposalholder/H)
+	return H.unsorted && (H.destinationTag > 1 || H.tomail)
+
+/obj/structure/disposalpipe/sorting/unsorted/flip
+	icon_state = "pipe-j2s"
+	flip_type = /obj/structure/disposalpipe/sorting/unsorted
+	initialize_dirs = DISP_DIR_LEFT | DISP_DIR_FLIP
+