allow table to reset itself

some don't know how to work the barter table, others block it intentionally.
Having the table expire and reset after certain time, solves that issue.

README.md

@@ -2,3 +2,11 @@ currency
 ========
 
 Repo for Currency Mod
+
+# Settings
+
+Settings with default values:
+```
+# After how much idle-time barter table is reset (seconds)
+barter.chest.expireafter				15 * 60
+```

barter.lua

@@ -5,6 +5,7 @@ local MP = minetest.get_modpath(minetest.get_current_modname())
 local S, NS = dofile(MP.."/intllib.lua")
 
 barter.chest = {}
+barter.chest.expire_after = tonumber(minetest.settings:get('barter.chest.expireafter')) or 15 * 60
 barter.chest.formspec = {
 	main = "size[8,9]"..
 		"list[current_name;pl1;0,0;3,4;]"..
@@ -81,6 +82,8 @@ barter.chest.cancel = function(meta)
 	meta:set_string("pl2","")
 	meta:set_int("pl1step",0)
 	meta:set_int("pl2step",0)
+	meta:set_int("clean",1)
+	meta:set_int("timer",0)
 end
 
 barter.chest.exchange = function(meta)
@@ -90,6 +93,16 @@ barter.chest.exchange = function(meta)
 	meta:set_string("pl2","")
 	meta:set_int("pl1step",0)
 	meta:set_int("pl2step",0)
+	meta:set_int("clean",1)
+	meta:set_int("timer",0)
+end
+
+barter.chest.start_timer = function(pos, meta)
+	meta:set_int("clean",0)
+	meta:set_int("timer",0)
+	local node_timer = minetest.get_node_timer(pos)
+	if node_timer:is_started() then return end
+	node_timer:start(22)
 end
 
 minetest.register_node("currency:barter", {
@@ -118,13 +131,16 @@ minetest.register_node("currency:barter", {
 		meta:set_string("infotext", S("Barter Table"))
 		meta:set_string("pl1","")
 		meta:set_string("pl2","")
+		meta:set_int("clean",1)
+		meta:set_int("timer",0)
 		barter.chest.update_formspec(meta)
 		local inv = meta:get_inventory()
-		inv:set_size("pl1", 3*4)
+		inv:set_size("pl1", 12) -- 3*4
-		inv:set_size("pl2", 3*4)
+		inv:set_size("pl2", 12) -- 3*4
 	end,
 	on_receive_fields = function(pos, formname, fields, sender)
 		local meta = minetest.get_meta(pos)
+		barter.chest.start_timer(pos, meta)
 		pl_receive_fields = function(n)
 			if fields[n.."_start"] and meta:get_string(n) == "" then
 				meta:set_string(n,sender:get_player_name())
@@ -152,18 +168,39 @@ minetest.register_node("currency:barter", {
 	end,
 	allow_metadata_inventory_move = function(pos, from_list, from_index, to_list, to_index, count, player)
 		local meta = minetest.get_meta(pos)
+		barter.chest.start_timer(pos, meta)
 		if not barter.chest.check_privilege(from_list,player:get_player_name(),meta) then return 0 end
 		if not barter.chest.check_privilege(to_list,player:get_player_name(),meta) then return 0 end
 		return count
 	end,
 	allow_metadata_inventory_put = function(pos, listname, index, stack, player)
 		local meta = minetest.get_meta(pos)
+		barter.chest.start_timer(pos, meta)
 		if not barter.chest.check_privilege(listname,player:get_player_name(),meta) then return 0 end
 		return stack:get_count()
 	end,
 	allow_metadata_inventory_take = function(pos, listname, index, stack, player)
 		local meta = minetest.get_meta(pos)
+		barter.chest.start_timer(pos, meta)
 		if not barter.chest.check_privilege(listname,player:get_player_name(),meta) then return 0 end
 		return stack:get_count()
 	end,
+	on_timer = function(pos, dtime)
+		local meta = minetest.get_meta(pos)
+		if 1 == meta:get_int("clean") then return false end
+
+		local timer = meta:get_int("timer")
+		timer = timer + dtime
+		if timer > barter.chest.expire_after then
+			-- attempt to return items to owners
+			barter.chest.cancel(meta)
+			-- also clear out items of offline users
+			local inv = meta:get_inventory()
+			inv:set_list("pl1", {})
+			inv:set_list("pl2", {})
+			return false
+		end
+		meta:set_int("timer",timer)
+		return true
+	end
 })