de-duplicate chest code (#123)

* rewrite compat-chests.lua
add pipeworks.override_chest() to make a existing chest connecting to pipeworks

* move pipeworks.override_chest() to a new file
fix crash with after_place_node() there
let mcl_barrels make use of the new function

* some comments

chests.lua

@@ -0,0 +1,90 @@
+pipeworks.chests = {}
+
+-- register a chest to connect with pipeworks tubes.
+-- will autoconnect to tubes and add tube inlets to the textures
+-- it is highly recommended to allow the user to change the "splitstacks" int (1 to enable) in the node meta
+-- but that can't be done by this function
+
+-- @param override: additional overrides, such as stuff to modify the node formspec
+-- @param connect_sides: which directions the chests shall connect to
+function pipeworks.override_chest(chestname, override, connect_sides)
+	local old_def = minetest.registered_nodes[chestname]
+
+	local tube_entry = "^pipeworks_tube_connection_wooden.png"
+	override.tiles = override.tiles or old_def.tiles
+	-- expand the tiles table if it has been shortened
+	if #override.tiles < 6 then
+		for i = #override.tiles, 6 do
+			override.tiles[i] = override.tiles[#override.tiles]
+		end
+	end
+	-- add inlets to the sides that connect to tubes
+	local tile_directions = {"top", "bottom", "right", "left", "back", "front"}
+	for i, direction in ipairs(tile_directions) do
+		if connect_sides[direction] then
+			if type(override.tiles[i]) == "string" then
+				override.tiles[i] = override.tiles[i] .. tube_entry
+			elseif type(override.tiles[i]) == "table" and not override.tiles[i].animation then
+				override.tiles[i].name = override.tiles[i].name .. tube_entry
+			end
+		end
+	end
+
+	local old_after_place_node = override.after_place_node or old_def.after_place_node or function()  end
+	override.after_place_node = function(pos, placer, itemstack, pointed_thing)
+		old_after_place_node(pos, placer, itemstack, pointed_thing)
+		pipeworks.after_place(pos)
+	end
+
+	local old_after_dig = override.after_dig or old_def.after_dig or function()  end
+	override.after_dig_node = function(pos, oldnode, oldmetadata, digger)
+		old_after_dig(pos, oldnode, oldmetadata, digger)
+		pipeworks.after_dig(pos, oldnode, oldmetadata, digger)
+	end
+
+	local old_on_rotate
+	if override.on_rotate ~= nil then
+		old_on_rotate = override.on_rotate
+	elseif old_def.on_rotate ~= nil then
+		old_on_rotate = old_def.on_rotate
+	else
+		old_on_rotate = function()  end
+	end
+	-- on_rotate = false -> rotation disabled, no need to update tubes
+	-- everything else: undefined by the most common screwdriver mods
+	if type(old_on_rotate) == "function" then
+		override.on_rotate = function(pos, node, user, mode, new_param2)
+			if old_on_rotate(pos, node, user, mode, new_param2) ~= false then
+				return pipeworks.on_rotate(pos, node, user, mode, new_param2)
+			else
+				return false
+			end
+		end
+	end
+
+	override.tube = {
+		insert_object = function(pos, node, stack, direction)
+			local meta = minetest.get_meta(pos)
+			local inv = meta:get_inventory()
+			return inv:add_item("main", stack)
+		end,
+		can_insert = function(pos, node, stack, direction)
+			local meta = minetest.get_meta(pos)
+			local inv = meta:get_inventory()
+			if meta:get_int("splitstacks") == 1 then
+				stack = stack:peek_item(1)
+			end
+			return inv:room_for_item("main", stack)
+		end,
+		input_inventory = "main",
+		connect_sides = connect_sides
+	}
+
+	-- Add the extra groups
+	override.groups = override.groups or old_def.groups or {}
+	override.groups.tubedevice = 1
+	override.groups.tubedevice_receiver = 1
+
+	minetest.override_item(chestname, override)
+	pipeworks.chests[chestname] = true
+end