server-nalc/mods/pipeworks/teleport_tube.lua

local filename=minetest.get_worldpath() .. "/teleport_tubes"

local function read_file()
	local f = io.open(filename, "r")
	if f == nil then return {} end
    	local t = f:read("*all")
    	f:close()
	if t == "" or t == nil then return {} end
	return minetest.deserialize(t)
end

local function write_file(tbl)
	local f = io.open(filename, "w")
    	f:write(minetest.serialize(tbl))
    	f:close()
end

local function update_pos_in_file(pos)
	local tbl=read_file()
	for _, val in ipairs(tbl) do
		if val.x == pos.x and val.y == pos.y and val.z == pos.z then
			local meta = minetest.get_meta(val)
			val.channel = meta:get_string("channel")
			val.cr = meta:get_int("can_receive")
		end
	end
	write_file(tbl)
end

local function add_tube_in_file(pos,channel, cr)
	local tbl=read_file()
	for _,val in ipairs(tbl) do
		if val.x==pos.x and val.y==pos.y and val.z==pos.z then
			return
		end
	end
	table.insert(tbl,{x=pos.x,y=pos.y,z=pos.z,channel=channel,cr=cr})
	write_file(tbl)
end

local function remove_tube_in_file(pos)
	local tbl = read_file()
	local newtbl = {}
	for _, val in ipairs(tbl) do
		if val.x ~= pos.x or val.y ~= pos.y or val.z ~= pos.z then
			table.insert(newtbl, val)
		end
	end
	write_file(newtbl)
end

local function read_node_with_vm(pos)
	local vm = VoxelManip()
	local MinEdge, MaxEdge = vm:read_from_map(pos, pos)
	local data = vm:get_data()
	local area = VoxelArea:new({MinEdge = MinEdge, MaxEdge = MaxEdge})
	return minetest.get_name_from_content_id(data[area:index(pos.x, pos.y, pos.z)])
end

local function get_tubes_in_file(pos,channel)
	local tbl = read_file()
	local newtbl = {}
	local changed = false
	for _, val in ipairs(tbl) do
		local meta = minetest.get_meta(val)
		local name = read_node_with_vm(val)
		local is_loaded = (minetest.get_node_or_nil(val) ~= nil)
		local is_teleport_tube = minetest.registered_nodes[name] and minetest.registered_nodes[name].is_teleport_tube
		if is_teleport_tube then
			if is_loaded and (val.channel ~= meta:get_string("channel") or val.cr ~= meta:get_int("can_receive")) then
				val.channel = meta:get_string("channel")
				val.cr = meta:get_int("can_receive")
				changed = true
			end
			if val.cr == 1 and val.channel == channel and (val.x ~= pos.x or val.y ~= pos.y or val.z ~= pos.z) then
				table.insert(newtbl, val)
			end
		else
			val.to_remove = true
			changed = true
		end
	end
	if changed then
		local updated = {}
		for _, val in ipairs(tbl) do
			if not val.to_remove then
				table.insert(updated, val)
			end
		end
		write_file(updated)
	end
	return newtbl
end

local teleport_noctr_textures={"pipeworks_teleport_tube_noctr.png","pipeworks_teleport_tube_noctr.png","pipeworks_teleport_tube_noctr.png",
		"pipeworks_teleport_tube_noctr.png","pipeworks_teleport_tube_noctr.png","pipeworks_teleport_tube_noctr.png"}
local teleport_plain_textures={"pipeworks_teleport_tube_plain.png","pipeworks_teleport_tube_plain.png","pipeworks_teleport_tube_plain.png",
		"pipeworks_teleport_tube_plain.png","pipeworks_teleport_tube_plain.png","pipeworks_teleport_tube_plain.png"}
local teleport_end_textures={"pipeworks_teleport_tube_end.png","pipeworks_teleport_tube_end.png","pipeworks_teleport_tube_end.png",
		"pipeworks_teleport_tube_end.png","pipeworks_teleport_tube_end.png","pipeworks_teleport_tube_end.png"}
local teleport_short_texture="pipeworks_teleport_tube_short.png"
local teleport_inv_texture="pipeworks_teleport_tube_inv.png"

local function set_teleport_tube_formspec(meta)
	local cr = meta:get_int("can_receive") ~= 0
	meta:set_string("formspec","size[10.5,1;]"..
		"field[0,0.5;7,1;channel;Channel:;${channel}]"..
		"button[8,0;2.5,1;"..(cr and "cr0" or "cr1")..";"..
			(cr and "Send and Receive" or "Send only").."]")
end

pipeworks.register_tube("pipeworks:teleport_tube","Teleporting Pneumatic Tube Segment",teleport_plain_textures,
	teleport_noctr_textures,teleport_end_textures,teleport_short_texture,teleport_inv_texture, {
	is_teleport_tube = true,
	tube = {
		can_go = function(pos,node,velocity,stack)
			velocity.x = 0
			velocity.y = 0
			velocity.z = 0
			local meta = minetest.get_meta(pos)
			local channel = meta:get_string("channel")
			local target = get_tubes_in_file(pos,channel)
			if target[1] == nil then return {} end
			local d = math.random(1,#target)
			pos.x = target[d].x
			pos.y = target[d].y
			pos.z = target[d].z
			return pipeworks.meseadjlist
		end
	},
	on_construct = function(pos)
		local meta = minetest.get_meta(pos)
		meta:set_string("channel","")
		meta:set_int("can_receive",1)
		add_tube_in_file(pos,"")
		set_teleport_tube_formspec(meta)
	end,
	on_receive_fields = function(pos,formname,fields,sender)
		local meta = minetest.get_meta(pos)
		
		--check for private channels
		if fields.channel ~= nil then
			local name, mode = fields.channel:match("^([^:;]+)([:;])")
			if name and mode and name ~= sender:get_player_name() then
				
				--channels starting with '[name]:' can only be used by the named player
				if mode == ":" then
					minetest.chat_send_player(sender:get_player_name(), "Sorry, channel '"..fields.channel.."' is reserved for exclusive use by "..name)
					return
				
				--channels starting with '[name];' can be used by other players, but cannot be received from
				elseif mode == ";" and (fields.cr1 or (meta:get_int("can_receive") ~= 0 and not fields.cr0)) then
					minetest.chat_send_player(sender:get_player_name(), "Sorry, receiving from channel '"..fields.channel.."' is reserved for "..name)
					return
				end
			end
		end
		
		if fields.channel==nil then fields.channel=meta:get_string("channel") end
		meta:set_string("channel",fields.channel)
		remove_tube_in_file(pos)
		if fields.cr0 then meta:set_int("can_receive", 0) end
		if fields.cr1 then meta:set_int("can_receive", 1) end
		local cr = meta:get_int("can_receive")
		add_tube_in_file(pos, fields.channel, meta:get_int("can_receive"))
		set_teleport_tube_formspec(meta)
	end,
	on_destruct = function(pos)
		remove_tube_in_file(pos)
	end})

if minetest.get_modpath("mesecons_mvps") ~= nil then
	mesecon.register_on_mvps_move(function(moved_nodes)
		for _, n in ipairs(moved_nodes) do
			if string.find(n.node.name, "pipeworks:teleport_tube") ~= nil then
				update_pos_in_file(n.pos)
			end
		end
	end)
end