Crate Shelf Tweaks (#3560)

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## About The Pull Request
Mapped crate shelves now start at a height of 2. You can build them to a
max height of 4
Constructed crate shelves start at 1 crate and need to be built up
You can now add shelves to crate shelves (with metal)

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## Why It's Good For The Game
it's not, honestly. i think this change is going to be the death of the
game. for pr after pr i've made nothing but hastily produced shitcode
changes to a game that used to be soulful and thriving, stripping out
the identity of what's made it so interesting to people. this is where
it comes full circle. im sorry for doing this. but it had to be done.
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benefit the game. If you can't justify it in words, it might not be
worth adding. -->

## Changelog

:cl:
add: You can now add shelves to crate racks
/:cl:

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---------

Co-authored-by: Erika Fox <[email protected]>
Co-authored-by: Sun-Soaked <[email protected]>

code/game/objects/structures/crateshelf.dm

@@ -1,4 +1,5 @@
 #define DEFAULT_SHELF_CAPACITY 3 // Default capacity of the shelf
+#define DEFAULT_SHELF_MAX_CAPACITY 4
 #define DEFAULT_SHELF_USE_DELAY 1 SECONDS // Default interaction delay of the shelf
 #define DEFAULT_SHELF_VERTICAL_OFFSET 10 // Vertical pixel offset of shelving-related things. Set to 10 by default due to this leaving more of the crate on-screen to be clicked.
 
@@ -12,9 +13,13 @@
 	max_integrity = 50 // Not hard to break
 
 	var/capacity = DEFAULT_SHELF_CAPACITY
+	var/max_capacity = DEFAULT_SHELF_MAX_CAPACITY
 	var/use_delay = DEFAULT_SHELF_USE_DELAY
 	var/list/shelf_contents
 
+/obj/structure/crate_shelf/built
+	capacity = 1
+
 /obj/structure/crate_shelf/debug
 	capacity = 12
 
@@ -47,12 +52,40 @@
 		for(var/obj/structure/closet/crate/crate in shelf_contents)
 			. += "	[icon2html(crate, user)] [crate]"
 
+/obj/structure/crate_shelf/proc/add_shelf(num)
+	if(capacity + num > max_capacity)
+		return FALSE
+	var/stack_layer // This is used to generate the sprite layering of the shelf pieces.
+	var/stack_offset // This is used to generate the vertical offset of the shelf pieces.
+	var/prev_capacity = capacity
+	capacity += num
+	shelf_contents.len = capacity
+	for(var/i in prev_capacity to (capacity - 1))
+		if(i >= 3) // If we're at or above three, we'll be on the way to going off the tile we're on. This allows mobs to be below the shelf when this happens.
+			stack_layer = ABOVE_MOB_LAYER + (0.02 * i) - 0.01
+		else
+			stack_layer  = BELOW_OBJ_LAYER + (0.02 * i) - 0.01 // Make each shelf piece render above the last, but below the crate that should be on it.
+		stack_offset = DEFAULT_SHELF_VERTICAL_OFFSET * i // Make each shelf piece physically above the last.
+		overlays += image(icon = 'icons/obj/objects.dmi', icon_state = "shelf_stack", layer = stack_layer, pixel_y = stack_offset)
+
 /obj/structure/crate_shelf/attackby(obj/item/item, mob/living/user, params)
 	if (item.tool_behaviour == TOOL_WRENCH && !(flags_1&NODECONSTRUCT_1))
 		item.play_tool_sound(src)
-		if(do_after(user, 3 SECONDS, target = src))
+		if(do_after(user, 3 SECONDS, src))
 			deconstruct(TRUE)
 			return TRUE
+	if(istype(item, /obj/item/stack/sheet/metal))
+		if(capacity < max_capacity)
+			var/obj/item/stack/sheet/metal/our_sheet = item
+			if(our_sheet.get_amount() >= 2)
+				balloon_alert(user, "adding additional shelf to rack")
+				if(do_after(user, 3 SECONDS, src))
+					add_shelf(1)
+					our_sheet.add(-2)
+					return TRUE
+				to_chat(user, span_notice("Adding a shelf to [src] requires more metal."))
+				return FALSE
+		to_chat(user, span_notice("[src] cannot be built any higher!"))
 	return ..()
 
 /obj/structure/crate_shelf/relay_container_resist_act(mob/living/user, obj/structure/closet/crate)
@@ -143,4 +176,4 @@
 /obj/item/rack_parts/shelf
 	name = "crate shelf parts"
 	desc = "Parts of a shelf."
-	construction_type = /obj/structure/crate_shelf
+	construction_type = /obj/structure/crate_shelf/built