From e1ebbff23c10213c4bc9f54bff0870810430cf9d Mon Sep 17 00:00:00 2001
From: orwell96 <orwell@bleipb.de>
Date: Thu, 21 Jun 2018 20:34:20 +0200
Subject: Add track section concept and rework TCB design, implement new
 linking behavior

---
 advtrains/init.lua                   |   8 ++
 advtrains_interlocking/database.lua  | 213 +++++++++++++++++++++-------
 advtrains_interlocking/init.lua      |   2 +-
 advtrains_interlocking/tcb.lua       | 180 ------------------------
 advtrains_interlocking/tcb_ts_ui.lua | 265 +++++++++++++++++++++++++++++++++++
 5 files changed, 437 insertions(+), 231 deletions(-)
 delete mode 100644 advtrains_interlocking/tcb.lua
 create mode 100644 advtrains_interlocking/tcb_ts_ui.lua

diff --git a/advtrains/init.lua b/advtrains/init.lua
index de72ea1..e676944 100644
--- a/advtrains/init.lua
+++ b/advtrains/init.lua
@@ -200,6 +200,9 @@ function advtrains.avt_load()
 				advtrains.player_to_train_mapping = tbl.ptmap or {}
 				advtrains.ndb.load_data(tbl.ndb)
 				advtrains.atc.load_data(tbl.atc)
+				if advtrains.interlocking then
+					--advtrains.interlocking.db.load(tbl.interlocking)
+				end
 				--remove wagon_save entries that are not part of a train
 				local todel=advtrains.merge_tables(advtrains.wagon_save)
 				for tid, train in pairs(advtrains.trains) do
@@ -291,12 +294,17 @@ advtrains.avt_save = function(remove_players_from_wagons)
 	
 	--versions:
 	-- 1 - Initial new save format.
+	local il_save
+	if advtrains.interlocking then
+		il_save = advtrains.interlocking.db.save()
+	end
 	local save_tbl={
 		trains = tmp_trains,
 		wagon_save = advtrains.wagons,
 		ptmap = advtrains.player_to_train_mapping,
 		atc = advtrains.atc.save_data(),
 		ndb = advtrains.ndb.save_data(),
+		interlocking = il_save,
 		version = 1,
 	}
 	local datastr = minetest.serialize(save_tbl)
diff --git a/advtrains_interlocking/database.lua b/advtrains_interlocking/database.lua
index e318dd2..b4932ee 100644
--- a/advtrains_interlocking/database.lua
+++ b/advtrains_interlocking/database.lua
@@ -93,13 +93,20 @@ local TRAVERSER_LIMIT = 100
 local ildb = {}
 
 local track_circuit_breaks = {}
+local track_sections = {}
 
 function ildb.load(data)
-
+	if not data then return end
+	if data.tcbs then
+		track_circuit_breaks = data.tcbs
+	end
+	if data.ts then
+		track_sections = data.ts
+	end
 end
 
 function ildb.save()
-	return {}
+	return {tcbs = track_circuit_breaks, ts=track_sections}
 end
 
 --
@@ -107,17 +114,7 @@ end
 TCB data structure
 {
 [1] = { -- Variant: with adjacent TCs.
-	== Synchronized properties == Apply to the whole TC
-	adjacent = { <signal specifier>,... } -- Adjacent TCBs, forms a TC with these
-	conflict = { <signal specifier>,... } -- Conflicting TC's (chosen as a representative TCB member)
-	-- Used e.g. for crossing rails that do not have nodes in common (like it's currently done)
-	incomplete = <boolean> -- Set when the recursion counter hit during traverse. Probably needs to add
-	-- another tcb at some far-away place
-	route = {origin = <signal>, in_dir = <boolean>}
-	-- Set whenever a route has been set through this TC. It saves the origin tcb id and side
-	-- (=the origin signal). in_dir is set when the train will enter the TC from this side
-	
-	== Unsynchronized properties == Apply only to this side of the TC
+	ts_id = <id> -- ID of the assigned track section
 	signal = <pos> -- optional: when set, routes can be set from this tcb/direction and signal
 	-- aspect will be set accordingly.
 	routetar = <signal> -- Route set from this signal. This is the entry that is cleared once
@@ -128,12 +125,25 @@ TCB data structure
 	-- is set true, clearing the signal
 },
 [2] = { -- Variant: end of track-circuited area (initial state of TC)
-	end_of_interlocking = true,
+	ts_id = nil, -- this is the indication for end_of_interlocking
 	section_free = <boolean>, --this can be set by an exit node via mesecons or atlatc, 
 	-- or from the tc formspec.
 }
 }
-Signal specifier (a pair of TCB/Side):
+
+Track section
+[id] = {
+	name = "Some human-readable name"
+	tc_breaks = { <signal specifier>,... } -- Bounding TC's (signal specifiers)
+	-- Can be direct ends (auto-detected), conflicting routes or TCBs that are too far away from each other
+	route = {origin = <signal>, from_tcb = <index>}
+	-- Set whenever a route has been set through this TC. It saves the origin tcb id and side
+	-- (=the origin signal). index is the TCB of the route origin
+	trains = {<id>, ...} -- Set whenever a train (or more) reside in this TC
+}
+
+
+Signal specifier (sigd) (a pair of TCB/Side):
 {p = <pos>, s = <1/2>}
 ]]
 
@@ -141,8 +151,8 @@ Signal specifier (a pair of TCB/Side):
 --
 function ildb.create_tcb(pos)
 	local new_tcb = {
-		[1] = {end_of_interlocking = true},
-		[2] = {end_of_interlocking = true},
+		[1] = {},
+		[2] = {},
 	}
 	local pts = advtrains.roundfloorpts(pos)
 	track_circuit_breaks[pts] = new_tcb
@@ -153,6 +163,48 @@ function ildb.get_tcb(pos)
 	return track_circuit_breaks[pts]
 end
 
+function ildb.get_tcbs(sigd)
+	local tcb = ildb.get_tcb(sigd.p)
+	if not tcb then return nil end
+	return tcb[sigd.s]
+end
+
+
+function ildb.create_ts(sigd)
+	local tcbs = ildb.get_tcbs(sigd)
+	local id = advtrains.random_id()
+	
+	while track_sections[id] do
+		id = advtrains.random_id()
+	end
+	
+	track_sections[id] = {
+		name = "Section "..id,
+		tc_breaks = { sigd }
+	}
+	tcbs.ts_id = id
+end
+
+function ildb.get_ts(id)
+	return track_sections[id]
+end
+
+
+
+-- various helper functions handling sigd's
+local function sigd_equal(sigd, cmp)
+	return vector.equals(sigd.p, cmp.p) and sigd.s==cmp.s
+end
+local function insert_sigd_nodouble(list, sigd)
+	for idx, cmp in pairs(list) do
+		if sigd_equal(sigd, cmp) then
+			return
+		end
+	end
+	table.insert(list, sigd)
+end
+
+
 -- This function will actually handle the node that is in connid direction from the node at pos
 -- so, this needs the conns of the node at pos, since these are already calculated
 local function traverser(found_tcbs, pos, conns, connid, count)
@@ -166,13 +218,14 @@ local function traverser(found_tcbs, pos, conns, connid, count)
 		local tcb = ildb.get_tcb(adj_pos)
 		if tcb then
 			-- done with this branch
-			table.insert(found_tcbs, {p=adj_pos, s=adj_connid})
+			atdebug("Traverser found tcb at",adj_pos, adj_connid)
+			insert_sigd_nodouble(found_tcbs, {p=adj_pos, s=adj_connid})
 			return
 		end
 	end
 	-- recursion abort condition
 	if count > TRAVERSER_LIMIT then
-		atdebug("Traverser hit counter at",adj_pos, adj_connid,"found tcb's:",found_tcbs)
+		atdebug("Traverser hit counter at",adj_pos, adj_connid)
 		return true
 	end
 	-- continue traversing
@@ -185,62 +238,122 @@ local function traverser(found_tcbs, pos, conns, connid, count)
 	return counter_hit
 end
 
-local function sigd_equal(sigd, cmp)
-	return vector.equals(sigd.p, cmp.p) and sigd.s==cmp.s
-end
-
 
 
+-- Merges the TS with merge_id into root_id and then deletes merge_id
+local function merge_ts(root_id, merge_id)
+	local rts = ildb.get_ts(root_id)
+	local mts = ildb.get_ts(merge_id)
+	
+	-- cobble together the list of TCBs
+	for _, msigd in ipairs(mts.tc_breaks) do
+		local tcbs = ildb.get_tcbs(msigd)
+		if tcbs then
+			insert_sigd_nodouble(rts.tc_breaks, msigd)
+			tcbs.ts_id = root_id
+		end
+	end
+	-- done
+	track_sections[merge_id] = nil
+end
 
+-- TODO temporary
+local lntrans = { "A", "B" }
+local function sigd_to_string(sigd)
+	return minetest.pos_to_string(sigd.p).." / "..lntrans[sigd.s]
+end
 
--- Updates the neighbors of this TCB using the traverser function (see comments above)
--- returns true if the traverser hit the counter, which means that there could be another
--- TCB outside of the traversed range.
-function ildb.update_tcb_neighbors(pos, connid)
+-- Check for near TCBs and connect to their TS if they have one, and syncs their data.
+function ildb.sync_tcb_neighbors(pos, connid)
 	local found_tcbs = { {p = pos, s = connid} }
 	local node_ok, conns, rhe = advtrains.get_rail_info_at(pos, advtrains.all_tracktypes)
 	if not node_ok then
 		error("update_tcb_neighbors but node is NOK: "..minetest.pos_to_string(pos))
 	end
 	
+	atdebug("Traversing from ",pos, connid)
 	local counter_hit = traverser(found_tcbs, pos, conns, connid, 0, hit_counter)
 	
+	local ts_id
+	local list_eoi = {}
+	local list_ok = {}
+	local list_mismatch = {}
+	local ts_to_merge = {}
+	
 	for idx, sigd in pairs(found_tcbs) do
-		local tcb = ildb.get_tcb(sigd.p)
-		local tcbs = tcb[sigd.s]
-		
-		tcbs.end_of_interlocking = nil
-		tcbs.incomplete = counter_hit
-		tcbs.adjacent = {}
-		
-		for idx2, other_sigd in pairs(found_tcbs) do
-			if idx~=idx2 then
-				ildb.add_adjacent(tcbs, sigd.p, sigd.s, other_sigd)
+		local tcbs = ildb.get_tcbs(sigd)
+		if not tcbs.ts_id then
+			atdebug("Sync: put",sigd_to_string(sigd),"into list_eoi")
+			table.insert(list_eoi, sigd)
+		elseif not ts_id and tcbs.ts_id then
+			if not ildb.get_ts(tcbs.ts_id) then
+				atwarn("Track section database is inconsistent, there's no TS with ID=",tcbs.ts_id)
+				tcbs.ts_id = nil
+				table.insert(list_eoi, sigd)
+			else
+				atdebug("Sync: put",sigd_to_string(sigd),"into list_ok")
+				ts_id = tcbs.ts_id
+				table.insert(list_ok, sigd)
 			end
+		elseif ts_id and tcbs.ts_id and tcbs.ts_id ~= ts_id then
+			atwarn("Track section database is inconsistent, sections share track!")
+			atwarn("Merging",tcbs.ts_id,"into",ts_id,".")
+			table.insert(list_mismatch, sigd)
+			table.insert(ts_to_merge, tcbs.ts_id)
+		end
+	end
+	if ts_id then
+		local ts = ildb.get_ts(ts_id)
+		for _, sigd in ipairs(list_eoi) do
+			local tcbs = ildb.get_tcbs(sigd)
+			tcbs.ts_id = ts_id
+			table.insert(ts.tc_breaks, sigd)
+		end
+		for _, mts in ipairs(ts_to_merge) do
+			merge_ts(ts_id, mts)
 		end
 	end
-	
-	return hit_counter
 end
 
--- Add the adjacency entry into the tcbs, but without duplicating it
--- and without adding a self-reference
-function ildb.add_adjacent(tcbs, this_pos, this_connid, sigd)
-	if sigd_equal(sigd, {p=this_pos, s=this_connid}) then
+function ildb.link_track_sections(merge_id, root_id)
+	if merge_id == root_id then
 		return
 	end
-	tcbs.end_of_interlocking = nil
-	if not tcbs.adjacent then
-		tcbs.adjacent = {}
-	end
-	for idx, cmp in pairs(tcbs.adjacent) do
-		if sigd_equal(sigd, cmp) then
+	merge_ts(root_id, merge_id)
+end
+
+function ildb.remove_from_interlocking(sigd)
+	local tcbs = ildb.get_tcbs(sigd)
+	if tcbs.ts_id then
+		local tsid = tcbs.ts_id
+		local ts = ildb.get_ts(tsid)
+		if not ts then
+			tcbs.ts_id = nil
 			return
 		end
+		
+		-- remove entry from the list
+		local idx = 1
+		while idx <= #ts.tc_breaks do
+			local cmp = ts.tc_breaks[idx]
+			if sigd_equal(sigd, cmp) then
+				table.remove(ts.tc_breaks, idx)
+			else
+				idx = idx + 1
+			end
+		end
+		tcbs.ts_id = nil
+		
+		ildb.sync_tcb_neighbors(sigd.p, sigd.s)
+		
+		if #ts.tc_breaks == 0 then
+			track_sections[tsid] = nil
+		end
 	end
-	table.insert(tcbs.adjacent, sigd)
 end
 
+
+
 advtrains.interlocking.db = ildb
 
 
diff --git a/advtrains_interlocking/init.lua b/advtrains_interlocking/init.lua
index e3be234..54fdb68 100644
--- a/advtrains_interlocking/init.lua
+++ b/advtrains_interlocking/init.lua
@@ -6,6 +6,6 @@ advtrains.interlocking = {}
 local modpath = minetest.get_modpath(minetest.get_current_modname()) .. DIR_DELIM
 
 dofile(modpath.."database.lua")
-dofile(modpath.."tcb.lua")
+dofile(modpath.."tcb_ts_ui.lua")
 dofile(modpath.."signal_api.lua")
 dofile(modpath.."demosignals.lua")
diff --git a/advtrains_interlocking/tcb.lua b/advtrains_interlocking/tcb.lua
deleted file mode 100644
index 742bb62..0000000
--- a/advtrains_interlocking/tcb.lua
+++ /dev/null
@@ -1,180 +0,0 @@
--- Track Circuit Breaks - Player interaction
-
-local players_assign_tcb = {}
-local players_addfar_tcb = {}
-
-local lntrans = { "A", "B" }
-
-local function sigd_to_string(sigd)
-	return minetest.pos_to_string(sigd.p).." / "..lntrans[sigd.s]
-end
-
-minetest.register_node("advtrains_interlocking:tcb_node", {
-	drawtype = "mesh",
-	paramtype="light",
-	paramtype2="facedir",
-	walkable = true,
-	selection_box = {
-		type = "fixed",
-		fixed = {-1/4, -1/2, -1/4, 1/4, 1/2, 1/4},
-	},
-	mesh = "at_il_tcb_node.obj",
-	tiles = {"at_il_tcb_node.png"},
-	description="Track Circuit Break",
-	sunlight_propagates=true,
-	groups = {
-		cracky=3,
-		not_blocking_trains=1,
-		--save_in_at_nodedb=2,
-	},
-	after_place_node = function(pos, node, player)
-		local meta = minetest.get_meta(pos)
-		meta:set_string("infotext", "Unconfigured Track Circuit Break, right-click to assign.")
-	end,
-	on_rightclick = function(pos, node, player)
-		local meta = minetest.get_meta(pos)
-		local tcbpts = meta:get_string("tcb_pos")
-		local pname = player:get_player_name()
-		if tcbpts ~= "" then
-			local tcbpos = minetest.string_to_pos(tcbpts)
-			advtrains.interlocking.show_tcb_form(tcbpos, pname)
-		else
-			--unconfigured
-			--TODO security
-			minetest.chat_send_player(pname, "Configuring TCB: Please punch the rail you want to assign this TCB to.")
-			
-			players_assign_tcb[pname] = pos
-		end	
-	end,
-	on_punch = function(pos, node, player)
-		local meta = minetest.get_meta(pos)
-		atwarn("Would show tcb marker.")
-			-- TODO TCB-Marker anzeigen
-	end,
-})
-
-minetest.register_on_punchnode(function(pos, node, player, pointed_thing)
-	local pname = player:get_player_name()
-	local tcbnpos = players_assign_tcb[pname]
-	if tcbnpos then
-		if vector.distance(pos, tcbnpos)<=20 then
-			local node_ok, conns, rhe = advtrains.get_rail_info_at(pos, advtrains.all_tracktypes)
-			if node_ok and #conns == 2 then
-				advtrains.interlocking.db.create_tcb(pos)
-				
-				advtrains.interlocking.db.update_tcb_neighbors(pos, 1)
-				advtrains.interlocking.db.update_tcb_neighbors(pos, 2)
-				
-				local meta = minetest.get_meta(tcbnpos)
-				meta:set_string("tcb_pos", minetest.pos_to_string(pos))
-				meta:set_string("infotext", "TCB assigned to "..minetest.pos_to_string(pos))
-				minetest.chat_send_player(pname, "Configuring TCB: Successfully configured TCB")
-			else
-				minetest.chat_send_player(pname, "Configuring TCB: This is not a normal two-connection rail! Aborted.")
-			end
-		else
-			minetest.chat_send_player(pname, "Configuring TCB: Node is too far away. Aborted.")
-		end
-		players_assign_tcb[pname] = nil
-	end
-end)
-
-
-local function mkformspec(tcbs, btnpref, offset, pname)
-	local form = "label[0.5,"..offset..";Side "..btnpref..": "..(tcbs.end_of_interlocking and "End of interlocking" or "Track Circuit").."]"
-	if tcbs.end_of_interlocking then
-		form = form.."button[0.5,"..(offset+1)..";3,1;"..btnpref.."_clearadj;Activate Interlocking]"
-		if tcbs.section_free then
-			form = form.."button[4.5,"..(offset+1)..";3,1;"..btnpref.."_setlocked;Section is free]"
-		else
-			form = form.."button[4.5,"..(offset+1)..";3,1;"..btnpref.."_setfree;Section is blocked]"		
-		end
-	else
-		local strtab = {}
-		for idx, sigd in ipairs(tcbs.adjacent) do
-			strtab[idx] = minetest.formspec_escape(sigd_to_string(sigd))
-		end
-		form = form.."textlist[0.5,"..(offset+1)..";5,3;"..btnpref.."_adjlist;"..table.concat(strtab, ",").."]"
-		if players_addfar_tcb[pname] then
-			local sigd = players_addfar_tcb[pname]
-			form = form.."button[5.5,"..(offset+2)..";2.5,1;"..btnpref.."_addadj;Link TCB to "..sigd_to_string(sigd).."]"
-			form = form.."button[8,"..(offset+2)..";0.5,1;"..btnpref.."_canceladdadj;X]"
-		else
-			form = form.."button[5.5,"..(offset+2)..";3,1;"..btnpref.."_addadj;Add far TCB]"
-		end
-		form = form.."button[5.5,"..(offset+1)..";3,1;"..btnpref.."_clearadj;Clear&Update]"
-		form = form.."button[5.5,"..(offset+3)..";3,1;"..btnpref.."_mknonint;Make non-interlocked]"
-		if tcbs.incomplete then
-			form = form.."label[0.5,"..(offset+0.5)..";Warning: You possibly need to add TCBs manually!]"
-		end
-	end
-	return form
-end
-
-
-
-function advtrains.interlocking.show_tcb_form(pos, pname)
-	local tcb = advtrains.interlocking.db.get_tcb(pos)
-	if not tcb then return end
-	
-	local form = "size[10,10] label[0.5,0.5;Track Circuit Break Configuration]"
-	form = form .. mkformspec(tcb[1], "A", 1, pname)
-	form = form .. mkformspec(tcb[2], "B", 6, pname)
-	
-	minetest.show_formspec(pname, "at_il_tcbconfig_"..minetest.pos_to_string(pos), form)
-end
-
-
-minetest.register_on_player_receive_fields(function(player, formname, fields)
-	local pname = player:get_player_name()
-	local pts = string.match(formname, "^at_il_tcbconfig_(.+)$")
-	local pos
-	if pts then
-		pos = minetest.string_to_pos(pts)
-	end
-	if pos and not fields.quit then
-		local tcb = advtrains.interlocking.db.get_tcb(pos)
-		if not tcb then return end
-		local f_clearadj = {fields.A_clearadj, fields.B_clearadj}
-		local f_addadj = {fields.A_addadj, fields.B_addadj}
-		local f_canceladdadj = {fields.A_canceladdadj, fields.B_canceladdadj}
-		local f_setlocked = {fields.A_setlocked, fields.B_setlocked}
-		local f_setfree = {fields.A_setfree, fields.B_setfree}
-		local f_mknonint = {fields.A_mknonint, fields.B_mknonint}
-		
-		for connid=1,2 do
-			if f_clearadj[connid] then
-				advtrains.interlocking.db.update_tcb_neighbors(pos, connid)
-			end
-			if f_mknonint[connid] then
-				--TODO: remove this from the other tcb's
-				tcb[connid].end_of_interlocking = true
-			end
-			if f_addadj[connid] then
-				if players_addfar_tcb[pname] then
-					local sigd = players_addfar_tcb[pname]
-					advtrains.interlocking.db.add_adjacent(tcb[connid], pos, connid, sigd)
-					players_addfar_tcb[pname] = nil
-				else
-					players_addfar_tcb[pname] = {p = pos, s = connid}
-				end
-			end
-			if f_canceladdadj[connid] then
-				players_addfar_tcb[pname] = nil
-			end
-			if f_setfree[connid] then
-				tcb[connid].section_free = true
-			end
-			if f_setlocked[connid] then
-				tcb[connid].section_free = nil
-			end
-		end
-		advtrains.interlocking.show_tcb_form(pos, pname)
-	end
-
-end)
-
-
-
-
-
diff --git a/advtrains_interlocking/tcb_ts_ui.lua b/advtrains_interlocking/tcb_ts_ui.lua
new file mode 100644
index 0000000..b2f1ef8
--- /dev/null
+++ b/advtrains_interlocking/tcb_ts_ui.lua
@@ -0,0 +1,265 @@
+-- Track Circuit Breaks and Track Sections - Player interaction
+
+local players_assign_tcb = {}
+local players_link_ts = {}
+
+local lntrans = { "A", "B" }
+
+local function sigd_to_string(sigd)
+	return minetest.pos_to_string(sigd.p).." / "..lntrans[sigd.s]
+end
+
+minetest.register_node("advtrains_interlocking:tcb_node", {
+	drawtype = "mesh",
+	paramtype="light",
+	paramtype2="facedir",
+	walkable = true,
+	selection_box = {
+		type = "fixed",
+		fixed = {-1/4, -1/2, -1/4, 1/4, 1/2, 1/4},
+	},
+	mesh = "at_il_tcb_node.obj",
+	tiles = {"at_il_tcb_node.png"},
+	description="Track Circuit Break",
+	sunlight_propagates=true,
+	groups = {
+		cracky=3,
+		not_blocking_trains=1,
+		--save_in_at_nodedb=2,
+	},
+	after_place_node = function(pos, node, player)
+		local meta = minetest.get_meta(pos)
+		meta:set_string("infotext", "Unconfigured Track Circuit Break, right-click to assign.")
+	end,
+	on_rightclick = function(pos, node, player)
+		local meta = minetest.get_meta(pos)
+		local tcbpts = meta:get_string("tcb_pos")
+		local pname = player:get_player_name()
+		if tcbpts ~= "" then
+			local tcbpos = minetest.string_to_pos(tcbpts)
+			advtrains.interlocking.show_tcb_form(tcbpos, pname)
+		else
+			--unconfigured
+			--TODO security
+			minetest.chat_send_player(pname, "Configuring TCB: Please punch the rail you want to assign this TCB to.")
+			
+			players_assign_tcb[pname] = pos
+		end	
+	end,
+	on_punch = function(pos, node, player)
+		local meta = minetest.get_meta(pos)
+		atwarn("Would show tcb marker.")
+			-- TODO TCB-Marker anzeigen
+	end,
+})
+
+minetest.register_on_punchnode(function(pos, node, player, pointed_thing)
+	local pname = player:get_player_name()
+	local tcbnpos = players_assign_tcb[pname]
+	if tcbnpos then
+		if vector.distance(pos, tcbnpos)<=20 then
+			local node_ok, conns, rhe = advtrains.get_rail_info_at(pos, advtrains.all_tracktypes)
+			if node_ok and #conns == 2 then
+				advtrains.interlocking.db.create_tcb(pos)
+				
+				advtrains.interlocking.db.sync_tcb_neighbors(pos, 1)
+				advtrains.interlocking.db.sync_tcb_neighbors(pos, 2)
+				
+				local meta = minetest.get_meta(tcbnpos)
+				meta:set_string("tcb_pos", minetest.pos_to_string(pos))
+				meta:set_string("infotext", "TCB assigned to "..minetest.pos_to_string(pos))
+				minetest.chat_send_player(pname, "Configuring TCB: Successfully configured TCB")
+			else
+				minetest.chat_send_player(pname, "Configuring TCB: This is not a normal two-connection rail! Aborted.")
+			end
+		else
+			minetest.chat_send_player(pname, "Configuring TCB: Node is too far away. Aborted.")
+		end
+		players_assign_tcb[pname] = nil
+	end
+end)
+
+
+-- TCB Form
+
+local function mktcbformspec(tcbs, btnpref, offset, pname)
+	local form = ""
+	local ts
+	if tcbs.ts_id then
+		ts = advtrains.interlocking.db.get_ts(tcbs.ts_id)
+	end
+	if ts then
+		form = form.."label[0.5,"..offset..";Side "..btnpref..": "..ts.name.."]"
+		form = form.."button[0.5,"..(offset+1)..";5,1;"..btnpref.."_gotots;Show track section]"
+		form = form.."button[0.5,"..(offset+2)..";2.5,1;"..btnpref.."_update;Update near TCBs]"
+		form = form.."button[3  ,"..(offset+2)..";2.5,1;"..btnpref.."_remove;Remove from section]"
+	else
+		tcbs.ts_id = nil
+		form = form.."label[0.5,"..offset..";Side "..btnpref..": ".."End of interlocking]"
+		form = form.."button[0.5,"..(offset+1)..";5,1;"..btnpref.."_makeil;Create Interlocked Track Section]"
+		if tcbs.section_free then
+			form = form.."button[0.5,"..(offset+2)..";5,1;"..btnpref.."_setlocked;Section is free]"
+		else
+			form = form.."button[0.5,"..(offset+2)..";5,1;"..btnpref.."_setfree;Section is blocked]"		
+		end
+	end
+	return form
+end
+
+
+function advtrains.interlocking.show_tcb_form(pos, pname)
+	local tcb = advtrains.interlocking.db.get_tcb(pos)
+	if not tcb then return end
+	
+	local form = "size[6,7] label[0.5,0.5;Track Circuit Break Configuration]"
+	form = form .. mktcbformspec(tcb[1], "A", 1, pname)
+	form = form .. mktcbformspec(tcb[2], "B", 4, pname)
+	
+	minetest.show_formspec(pname, "at_il_tcbconfig_"..minetest.pos_to_string(pos), form)
+end
+
+--helper: length of nil table is 0
+local function nlen(t)
+	if not t then return 0 end
+	return #t
+end
+
+
+minetest.register_on_player_receive_fields(function(player, formname, fields)
+	local pname = player:get_player_name()
+	local pts = string.match(formname, "^at_il_tcbconfig_(.+)$")
+	local pos
+	if pts then
+		pos = minetest.string_to_pos(pts)
+	end
+	if pos and not fields.quit then
+		local tcb = advtrains.interlocking.db.get_tcb(pos)
+		if not tcb then return end
+		local f_gotots = {fields.A_gotots, fields.B_gotots}
+		local f_update = {fields.A_update, fields.B_update}
+		local f_remove = {fields.A_remove, fields.B_remove}
+		local f_makeil = {fields.A_makeil, fields.B_makeil}
+		local f_setlocked = {fields.A_setlocked, fields.B_setlocked}
+		local f_setfree = {fields.A_setfree, fields.B_setfree}
+		
+		for connid=1,2 do
+			local tcbs = tcb[connid]
+			if tcbs.ts_id then
+				if f_gotots[connid] then
+					advtrains.interlocking.show_ts_form(tcbs.ts_id, pname)
+					return
+				end
+				if f_update[connid] then
+					advtrains.interlocking.db.sync_tcb_neighbors(pos, connid)
+				end
+				if f_remove[connid] then
+					advtrains.interlocking.db.remove_from_interlocking({p=pos, s=connid})
+				end
+			else
+				if f_makeil[connid] then
+					advtrains.interlocking.db.create_ts({p=pos, s=connid})
+					advtrains.interlocking.db.sync_tcb_neighbors(pos, connid)
+				end
+				-- non-interlocked
+				if f_setfree[connid] then
+					tcbs.section_free = true
+				end
+				if f_setlocked[connid] then
+					tcbs.section_free = nil
+				end
+			end
+		end
+		advtrains.interlocking.show_tcb_form(pos, pname)
+	end
+
+end)
+
+
+
+-- TS Formspec
+
+function advtrains.interlocking.show_ts_form(ts_id, pname, sel_tcb)
+	local ts = advtrains.interlocking.db.get_ts(ts_id)
+	if not ts_id then return end
+	
+	local form = "size[10,10]label[0.5,0.5;Track Section Detail - "..ts_id.."]"
+	form = form.."field[0.8,2;5.2,1;name;Section name;"..ts.name.."]"
+	form = form.."button[5.5,1.7;1,1;setname;Set]"
+	local hint
+	
+	local strtab = {}
+	for idx, sigd in ipairs(ts.tc_breaks) do
+		strtab[#strtab+1] = minetest.formspec_escape(sigd_to_string(sigd))
+	end
+	
+	form = form.."textlist[0.5,3;5,3;tcblist;"..table.concat(strtab, ",").."]"
+	if players_link_ts[pname] then
+		local other_id = players_link_ts[pname]
+		local other_ts = advtrains.interlocking.db.get_ts(other_id)
+		if other_ts then
+			form = form.."button[5.5,3.5;3.5,1;mklink;Join with "..other_ts.name.."]"
+			form = form.."button[9  ,3.5;0.5,1;cancellink;X]"
+		end
+	else
+		form = form.."button[5.5,3.5;4,1;link;Join into other section]"
+		hint = 1
+	end
+	if sel_tcb then
+		form = form.."button[5.5,4.5;4,1;del_tcb;Remove selected TCB]"
+		hint = 2
+	end
+	if hint == 1 then
+		form = form.."label[0.5,0.75;Use the 'Join' button to designate rail crosses and link not listed far-away TCBs]"
+	elseif hint == 2 then
+		form = form.."label[0.5,0.75;Removing a TCB will set it to non-interlocked mode.]"
+		form = form.."label[0.5,1;Trying to remove a TCB directly connected to this track will not work.]"
+	end
+	
+	minetest.show_formspec(pname, "at_il_tsconfig_"..ts_id, form)
+	
+end
+
+
+minetest.register_on_player_receive_fields(function(player, formname, fields)
+	local pname = player:get_player_name()
+	local ts_id = string.match(formname, "^at_il_tsconfig_(.+)$")
+	if ts_id and not fields.quit then
+		local ts = advtrains.interlocking.db.get_ts(ts_id)
+		if not ts then return end
+		
+		local sel_tcb
+		if fields.tcblist then
+			local tev = minetest.explode_textlist_event(fields.tcblist)
+			sel_tcb = tev.index
+		end
+		
+		if players_link_ts[pname] then
+			if fields.cancellink then
+				players_link_ts[pname] = nil
+			elseif fields.mklink then
+				advtrains.interlocking.db.link_track_sections(players_link_ts[pname], ts_id)
+			end
+		end
+		
+		if fields.del_tcb and sel_tcb and sel_tcb > 0 and sel_tcb <= #ts.tc_breaks then
+			advtrains.interlocking.db.remove_from_interlocking(ts.tc_breaks[sel_tcb])
+		end
+		
+		if fields.link then
+			players_link_ts[pname] = ts_id
+		end
+		
+		if fields.setname then
+			ts.name = fields.name
+			if ts.name == "" then
+				ts.name = "Section "..ts_id
+			end
+		end
+		
+		
+		advtrains.interlocking.show_ts_form(ts_id, pname, sel_tcb)
+	end
+
+end)
+
+
-- 
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