From 98c37108762c6d7c9f1d691b84f49bfa65b81b28 Mon Sep 17 00:00:00 2001
From: "Y. Wang" <yw05@forksworld.de>
Date: Sat, 11 Jun 2022 18:07:00 +0200
Subject: Implement primitive distant signaling

---
 advtrains/formspec.lua                             |  10 ++
 advtrains_interlocking/database.lua                |   4 +
 advtrains_interlocking/demosignals.lua             |   6 +-
 advtrains_interlocking/distant.lua                 | 137 +++++++++++++++++++++
 advtrains_interlocking/distant_ui.lua              |  76 ++++++++++++
 advtrains_interlocking/init.lua                    |   3 +
 advtrains_interlocking/routesetting.lua            |  21 ++++
 advtrains_interlocking/signal_api.lua              |  85 +------------
 advtrains_interlocking/signal_aspect_accessors.lua | 127 +++++++++++++++++++
 advtrains_interlocking/signal_aspect_ui.lua        |   6 +-
 advtrains_interlocking/signal_aspects.lua          |  26 +++-
 advtrains_interlocking/signal_main_ui.lua          |   0
 .../spec/basic_signalling_spec.lua                 |  87 +++++++++++++
 advtrains_interlocking/spec/signal_api_spec.lua    |  49 --------
 advtrains_interlocking/tcb_ts_ui.lua               |   8 +-
 15 files changed, 507 insertions(+), 138 deletions(-)
 create mode 100644 advtrains_interlocking/distant.lua
 create mode 100644 advtrains_interlocking/distant_ui.lua
 create mode 100644 advtrains_interlocking/signal_aspect_accessors.lua
 delete mode 100644 advtrains_interlocking/signal_main_ui.lua
 create mode 100644 advtrains_interlocking/spec/basic_signalling_spec.lua
 delete mode 100644 advtrains_interlocking/spec/signal_api_spec.lua

diff --git a/advtrains/formspec.lua b/advtrains/formspec.lua
index aa5aa69..20dab59 100644
--- a/advtrains/formspec.lua
+++ b/advtrains/formspec.lua
@@ -9,6 +9,14 @@ local function make_list(entries)
 	return table.concat(t, ",")
 end
 
+local function f_button(x, y, w, h, id, text)
+	return sformat("button[%f,%f;%f,%f;%s;%s]", x, y, w, h, id, text)
+end
+
+local function S_button(x, y, w, h, id, ...)
+	return f_button(x, y, w, h, id, attrans(...))
+end
+
 local function f_button_exit(x, y, w, h, id, text)
 	return sformat("button_exit[%f,%f;%f,%f;%s;%s]", x, y, w, h, id, text)
 end
@@ -54,6 +62,8 @@ local function f_tabheader(x, y, w, h, id, entries, sel, transparent, border)
 end
 
 return {
+	button = f_button,
+	S_button = S_button,
 	button_exit = f_button_exit,
 	S_button_exit = S_button_exit,
 	dropdown = f_dropdown,
diff --git a/advtrains_interlocking/database.lua b/advtrains_interlocking/database.lua
index efa5eb8..c5ae906 100644
--- a/advtrains_interlocking/database.lua
+++ b/advtrains_interlocking/database.lua
@@ -134,6 +134,9 @@ function ildb.load(data)
 	if data.supposed_aspects then
 		advtrains.interlocking.load_supposed_aspects(data.supposed_aspects)
 	end
+	if data.distant then
+		advtrains.distant.load(data.distant)
+	end
 	
 	--COMPATIBILITY to Signal aspect format
 	-- TODO remove in time...
@@ -177,6 +180,7 @@ function ildb.save()
 		influence_points = influence_points,
 		npr_rails = advtrains.interlocking.npr_rails,
 		supposed_aspects = advtrains.interlocking.save_supposed_aspects(),
+		distant = advtrains.distant.save(),
 	}
 end
 
diff --git a/advtrains_interlocking/demosignals.lua b/advtrains_interlocking/demosignals.lua
index 1c1b8b2..de6926a 100644
--- a/advtrains_interlocking/demosignals.lua
+++ b/advtrains_interlocking/demosignals.lua
@@ -50,7 +50,7 @@ minetest.register_node("advtrains_interlocking:ds_danger", {
 	},
 	on_rightclick = advtrains.interlocking.signal_rc_handler,
 	can_dig = advtrains.interlocking.signal_can_dig,
-	after_dig_node = advtrains.interlocking.signal_after_dig,
+	after_destruct = advtrains.interlocking.signal_after_dig,
 })
 minetest.register_node("advtrains_interlocking:ds_free", {
 	description = "Demo signal at Free",
@@ -71,7 +71,7 @@ minetest.register_node("advtrains_interlocking:ds_free", {
 	},
 	on_rightclick = advtrains.interlocking.signal_rc_handler,
 	can_dig = advtrains.interlocking.signal_can_dig,
-	after_dig_node = advtrains.interlocking.signal_after_dig,
+	after_destruct = advtrains.interlocking.signal_after_dig,
 })
 minetest.register_node("advtrains_interlocking:ds_slow", {
 	description = "Demo signal at Slow",
@@ -92,6 +92,6 @@ minetest.register_node("advtrains_interlocking:ds_slow", {
 	},
 	on_rightclick = advtrains.interlocking.signal_rc_handler,
 	can_dig = advtrains.interlocking.signal_can_dig,
-	after_dig_node = advtrains.interlocking.signal_after_dig,
+	after_destruct = advtrains.interlocking.signal_after_dig,
 })
 
diff --git a/advtrains_interlocking/distant.lua b/advtrains_interlocking/distant.lua
new file mode 100644
index 0000000..ffa9e08
--- /dev/null
+++ b/advtrains_interlocking/distant.lua
@@ -0,0 +1,137 @@
+local db_distant = {}
+local db_distant_of = {}
+
+local A = advtrains.interlocking.aspects
+local pts = advtrains.encode_pos
+local stp = advtrains.decode_pos
+
+local function db_load(x)
+	if type(x) ~= "table" then
+		return
+	end
+	db_distant = x.distant
+	db_distant_of = x.distant_of
+end
+
+local function db_save()
+	return {
+		distant = db_distant,
+		distant_of = db_distant_of,
+	}
+end
+
+local update_signal, update_main, update_dst
+
+local function unassign_dst(dst, force)
+	local pts_dst = pts(dst)
+	local main = db_distant_of[pts_dst]
+	db_distant_of[pts_dst] = nil
+	if main then
+		local pts_main = main[1]
+		local t = db_distant[pts_main]
+		if t then
+			t[pts_dst] = nil
+		end
+	end
+	if not force then
+		update_dst(dst)
+	end
+end
+
+local function unassign_main(main, force)
+	local pts_main = pts(main)
+	local t = db_distant[pts_main]
+	if not t then
+		return
+	end
+	for pts_dst in pairs(t) do
+		local realmain = db_distant_of[pts_dst]
+		if realmain and realmain[1] == pts_main then
+			db_distant_of[pts_dst] = nil
+			if not force then
+				local dst = stp(pts_dst)
+				update_dst(dst)
+			end
+		end
+	end
+	db_distant[pts_main] = nil
+end
+
+local function unassign_all(pos, force)
+	unassign_main(pos)
+	unassign_dst(pos, force)
+end
+
+local function assign(main, dst, by)
+	local pts_main = pts(main)
+	local pts_dst = pts(dst)
+	local t = db_distant[pts_main]
+	if not t then
+		t = {}
+		db_distant[pts_main] = t
+	end
+	if not by then
+		by = "manual"
+	end
+	unassign_dst(dst, true)
+	t[pts_dst] = by
+	db_distant_of[pts_dst] = {pts_main, by}
+	update_dst(dst)
+end
+
+local function pre_occupy(dst, by)
+	local pts_dst = pts(dst)
+	unassign_dst(dst)
+	db_distant_of[pts_dst] = {nil, by}
+end
+
+local function get_distant(main)
+	local pts_main = pts(main)
+	return db_distant[pts_main] or {}
+end
+
+local function get_main(dst)
+	local pts_dst = pts(dst)
+	local main = db_distant_of[pts_dst]
+	if not main then
+		return
+	end
+	if main[1] then
+		return stp(main[1]), unpack(main, 2)
+	else
+		return unpack(main)
+	end
+end
+
+update_main = function(main)
+	local pts_main = pts(main)
+	local t = get_distant(main)
+	for pts_dst in pairs(t) do
+		local dst = stp(pts_dst)
+		advtrains.interlocking.signal_readjust_aspect(dst)
+	end
+end
+
+update_dst = function(dst)
+	advtrains.interlocking.signal_readjust_aspect(dst)
+end
+
+update_signal = function(pos)
+	update_main(pos)
+	update_dst(pos)
+end
+
+advtrains.distant = {
+	load = db_load,
+	save = db_save,
+	assign = assign,
+	unassign_dst = unassign_dst,
+	unassign_main = unassign_main,
+	unassign_all = unassign_all,
+	get_distant = get_distant,
+	get_dst = get_distant,
+	get_main = get_main,
+	update_main = update_main,
+	update_dst = update_dst,
+	update_signal = update_signal,
+}
diff --git a/advtrains_interlocking/distant_ui.lua b/advtrains_interlocking/distant_ui.lua
new file mode 100644
index 0000000..4ec2255
--- /dev/null
+++ b/advtrains_interlocking/distant_ui.lua
@@ -0,0 +1,76 @@
+local F = advtrains.formspec
+local D = advtrains.distant
+local I = advtrains.interlocking
+
+function advtrains.interlocking.show_distant_signal_form(pos, pname)
+	local form = {"size[7,7]"}
+	form[#form+1] = advtrains.interlocking.make_signal_formspec_tabheader(pname, pos, 7, 3)
+	local main, set_by = D.get_main(pos)
+	if main then
+		local pts_main = minetest.pos_to_string(main)
+		form[#form+1] = F.S_label(0.5, 0.5, "This signal is a distant signal of @1.", pts_main)
+		if set_by == "manual" then
+			form[#form+1] = F.S_label(0.5, 1, "The assignment is made manually.")
+		elseif set_by == "routesetting" then
+			form[#form+1] = F.S_label(0.5, 1, "The assignment is made by the routesetting system.")
+		end
+	else
+		form[#form+1] = F.S_label(0.5, 0.5, "This signal is not assigned to a main signal.")
+		form[#form+1] = F.S_label(0.5, 1, "The distant aspect of the signal is not used.")
+	end
+	if set_by ~= nil then
+		form[#form+1] = F.S_button_exit(0.5, 1.5, 3, 1, "unassign_dst", "Unassign")
+		form[#form+1] = F.S_button_exit(3.5, 1.5, 3, 1, "assign_dst", "Reassign")
+	else
+		form[#form+1] = F.S_button_exit(0.5, 1.5, 6, 1, "assign_dst", "Assign")
+	end
+	minetest.show_formspec(pname, "advtrains:distant_" .. minetest.pos_to_string(pos), table.concat(form))
+end
+
+local signal_pos = {}
+local function init_signal_assignment(pname, pos)
+	if not minetest.check_player_privs(pname, "interlocking") then
+		minetest.chat_send_player(pname, attrans("This operation is not allowed without the @1 privilege.", "interlocking"))
+		return
+	end
+	signal_pos[pname] = pos
+	minetest.chat_send_player(pname, attrans("Please punch the signal to use as the main signal."))
+end
+
+minetest.register_on_punchnode(function(pos, node, player, pointed_thing)
+	local pname = player:get_player_name()
+	if not minetest.check_player_privs(pname, "interlocking") then
+		return
+	end
+	local spos = signal_pos[pname]
+	if not spos then
+		return
+	end
+	signal_pos[pname] = nil
+	local is_signal = minetest.get_item_group(node.name, "advtrains_signal") >= 2
+	if not is_signal then
+		minetest.chat_send_player(pname, attrans("Incompatible signal."))
+		return
+	end
+	minetest.chat_send_player(pname, attrans("Successfully assigned signal."))
+	D.assign(pos, spos, "manual")
+end)
+
+minetest.register_on_player_receive_fields(function(player, formname, fields)
+	local pname = player:get_player_name()
+	local pos = minetest.string_to_pos(string.match(formname, "^advtrains:distant_(.+)$") or "")
+	if not pos then
+		return
+	end
+	if not minetest.check_player_privs(pname, "interlocking") then
+		return
+	end
+	if advtrains.interlocking.handle_signal_formspec_tabheader_fields(pname, fields) then
+		return true
+	end
+	if fields.unassign_dst then
+		D.unassign_dst(pos)
+	elseif fields.assign_dst then
+		init_signal_assignment(pname, pos)
+	end
+end)
diff --git a/advtrains_interlocking/init.lua b/advtrains_interlocking/init.lua
index d0b75a8..908d998 100644
--- a/advtrains_interlocking/init.lua
+++ b/advtrains_interlocking/init.lua
@@ -15,6 +15,9 @@ local modpath = minetest.get_modpath(minetest.get_current_modname()) .. DIR_DELI
 advtrains.interlocking.aspects = dofile(modpath.."signal_aspects.lua")
 
 dofile(modpath.."database.lua")
+dofile(modpath.."distant.lua")
+dofile(modpath.."distant_ui.lua")
+dofile(modpath.."signal_aspect_accessors.lua")
 dofile(modpath.."signal_api.lua")
 dofile(modpath.."signal_aspect_ui.lua")
 dofile(modpath.."demosignals.lua")
diff --git a/advtrains_interlocking/routesetting.lua b/advtrains_interlocking/routesetting.lua
index 67efaea..f1b4455 100644
--- a/advtrains_interlocking/routesetting.lua
+++ b/advtrains_interlocking/routesetting.lua
@@ -45,6 +45,7 @@ function ilrs.set_route(signal, route, try)
 	local rtename = route.name
 	local signalname = ildb.get_tcbs(signal).signal_name
 	local c_tcbs, c_ts_id, c_ts, c_rseg, c_lckp
+	local signals = {}
 	while c_sigd and i<=#route do
 		c_tcbs = ildb.get_tcbs(c_sigd)
 		if not c_tcbs then
@@ -115,6 +116,7 @@ function ilrs.set_route(signal, route, try)
 				c_tcbs.aspect = route.aspect or advtrains.interlocking.GENERIC_FREE
 				c_tcbs.route_origin = signal
 				advtrains.interlocking.update_signal_aspect(c_tcbs)
+				signals[#signals+1] = c_tcbs.signal
 			end
 		end
 		-- advance
@@ -122,6 +124,25 @@ function ilrs.set_route(signal, route, try)
 		c_sigd = c_rseg.next
 		i = i + 1
 	end
+
+	-- Distant signaling
+	local lastsig = nil
+	if c_sigd then
+		local e_tcbs = ildb.get_tcbs(c_sigd)
+		local pos = e_tcbs and e_tcbs.signal
+		if pos then
+			lastsig = pos
+		end
+	end
+	for i = #signals, 1, -1 do
+		if lastsig then
+			local pos = signals[i]
+			local _, assigned_by = advtrains.distant.get_main(pos)
+			if assigned_by ~= "manual" then
+				advtrains.distant.assign(lastsig, signals[i], "routesetting")
+			end
+		end
+	end
 	
 	return true
 end
diff --git a/advtrains_interlocking/signal_api.lua b/advtrains_interlocking/signal_api.lua
index 5b3baf8..1fd4e34 100644
--- a/advtrains_interlocking/signal_api.lua
+++ b/advtrains_interlocking/signal_api.lua
@@ -167,7 +167,6 @@ This function will query get_aspect to retrieve the new aspect.
 
 local DANGER = {
 	main = 0,
-	dst = false,
 	shunt = false,
 }
 advtrains.interlocking.DANGER = DANGER
@@ -178,8 +177,6 @@ advtrains.interlocking.GENERIC_FREE = {
 	dst = false,
 }
 
-local supposed_aspects = {}
-
 local function convert_aspect_if_necessary(asp)
 	if type(asp.main) == "table" then
 		local newasp = {} 
@@ -200,24 +197,7 @@ local function convert_aspect_if_necessary(asp)
 	end
 	return asp
 end
-
-function advtrains.interlocking.load_supposed_aspects(tbl)
-	if tbl then
-		supposed_aspects = tbl
-	end
-end
-
-function advtrains.interlocking.save_supposed_aspects()
-	return supposed_aspects
-end
-
-local function set_supposed_aspect(pos, asp)
-	supposed_aspects[advtrains.roundfloorpts(pos)] = asp
-end
-
-local function get_supposed_aspect(pos)
-	return supposed_aspects[advtrains.roundfloorpts(pos)]
-end
+advtrains.interlocking.signal_convert_aspect_if_necessary = convert_aspect_if_necessary
 
 function advtrains.interlocking.update_signal_aspect(tcbs)
 	if tcbs.signal then
@@ -233,27 +213,8 @@ end
 function advtrains.interlocking.signal_after_dig(pos)
 	-- clear influence point
 	advtrains.interlocking.db.clear_ip_by_signalpos(pos)
-	set_supposed_aspect(pos, nil)
-end
-
-function advtrains.interlocking.signal_set_aspect(pos, asp)
-	asp = convert_aspect_if_necessary(asp)
-	local node=advtrains.ndb.get_node(pos)
-	local ndef=minetest.registered_nodes[node.name]
-	if ndef and ndef.advtrains and ndef.advtrains.set_aspect then
-		local oldasp = advtrains.interlocking.signal_get_aspect(pos) or DANGER
-		local suppasp = advtrains.interlocking.signal_get_supported_aspects(pos) or {}
-		local newasp = asp
-		if suppasp.type == 2 then
-			asp = advtrains.interlocking.aspects.type1_to_type2main(asp, suppasp.group)
-		end
-		set_supposed_aspect(pos, newasp)
-		ndef.advtrains.set_aspect(pos, node, asp)
-		local aspect_changed = advtrains.interlocking.aspects.not_equalp(oldasp, newasp)
-		if aspect_changed then
-			advtrains.interlocking.signal_on_aspect_changed(pos)
-		end
-	end
+	advtrains.interlocking.signal_clear_aspect(pos)
+	advtrains.distant.unassign_all(pos, true)
 end
 
 -- should be called when aspect has changed on this signal.
@@ -312,46 +273,6 @@ function advtrains.interlocking.signal_get_supposed_aspect(pos)
 	return DANGER;
 end
 
--- Returns the actual aspect of the signal at position, as returned by the nodedef.
--- returns nil when there's no signal at the position
-function advtrains.interlocking.signal_get_real_aspect(pos)
-	local node=advtrains.ndb.get_node(pos)
-	local ndef=minetest.registered_nodes[node.name]
-	if ndef and ndef.advtrains and ndef.advtrains.get_aspect then
-		local asp = ndef.advtrains.get_aspect(pos, node)
-		local suppasp = advtrains.interlocking.signal_get_supported_aspects(pos) or {}
-		if suppasp.type == 2 then
-			asp = advtrains.interlocking.aspects.type2main_to_type1(suppasp.group, asp)
-		end
-		if not asp then asp = DANGER end
-		asp = convert_aspect_if_necessary(asp)
-		return asp
-	end
-	return nil
-end
-
--- Returns the signal aspect as reported in the suppasp table.
-function advtrains.interlocking.signal_get_aspect(pos)
-	local asp = get_supposed_aspect(pos)
-	if not asp then
-		asp = advtrains.interlocking.signal_get_real_aspect(pos)
-		set_supposed_aspect(pos, asp)
-	end
-	return asp
-end
-
--- Returns the "supported_aspects" of the signal at position, as returned by the nodedef.
--- returns nil when there's no signal at the position
-function advtrains.interlocking.signal_get_supported_aspects(pos)
-	local node=advtrains.ndb.get_node(pos)
-	local ndef=minetest.registered_nodes[node.name]
-	if ndef and ndef.advtrains and ndef.advtrains.supported_aspects then
-		local asp = ndef.advtrains.supported_aspects
-		return asp
-	end
-	return nil
-end
-
 local players_assign_ip = {}
 
 local function ipmarker(ipos, connid)
diff --git a/advtrains_interlocking/signal_aspect_accessors.lua b/advtrains_interlocking/signal_aspect_accessors.lua
new file mode 100644
index 0000000..02a03ea
--- /dev/null
+++ b/advtrains_interlocking/signal_aspect_accessors.lua
@@ -0,0 +1,127 @@
+local A = advtrains.interlocking.aspects
+local D = advtrains.distant
+local I = advtrains.interlocking
+local N = advtrains.ndb
+local pts = advtrains.roundfloorpts
+
+local get_aspect
+
+local supposed_aspects = {}
+
+function I.load_supposed_aspects(tbl)
+	if tbl then
+		supposed_aspects = tbl
+	end
+end
+
+function I.save_supposed_aspects()
+	return supposed_aspects
+end
+
+local function get_supposed_aspect(pos)
+	return supposed_aspects[pts(pos)]
+end
+
+local function set_supposed_aspect(pos, asp)
+	supposed_aspects[pts(pos)] = asp
+end
+
+local function get_ndef(pos)
+	local node = N.get_node(pos)
+	return minetest.registered_nodes[node.name] or {}
+end
+
+local function get_supported_aspects(pos)
+	local ndef = get_ndef(pos)
+	if ndef.advtrains and ndef.advtrains.supported_aspects then
+		return ndef.advtrains.supported_aspects
+	end
+	return nil
+end
+
+local function adjust_aspect(pos, asp)
+	asp = table.copy(I.signal_convert_aspect_if_necessary(asp))
+
+	local mainpos = D.get_main(pos)
+	local nxtasp
+	if asp.main ~= 0 and mainpos then
+		nxtasp = get_aspect(mainpos)
+		asp.dst = nxtasp.main
+	else
+		asp.dst = nil
+	end
+
+	local suppasp = get_supported_aspects(pos)
+	if not suppasp then
+		return asp, asp
+	end
+	local stype = suppasp.type
+	if stype == 2 then
+		local group = suppasp.group
+		local name
+		if asp.main ~= 0 and nxtasp and nxtasp.type2group == group and nxtasp.type2name then
+			name = A.get_type2_dst(group, nxtasp.type2name)
+		else
+			name = A.type1_to_type2main(asp, group)
+		end
+		asp.type2group = group
+		asp.type2name = name
+		return asp, name
+	end
+	asp.type2name = nil
+	asp.type2group = nil
+	return asp, asp
+end
+
+local function get_real_aspect(pos)
+	local ndef = get_ndef(pos)
+	if ndef.advtrains and ndef.advtrains.get_aspect then
+		local asp = ndef.advtrains.get_aspect(pos, node) or I.DANGER
+		local suppasp = get_supported_aspects(pos)
+		if suppasp.type == 2 then
+			asp = A.type2main_to_type1(suppasp.group, asp)
+		end
+		return adjust_aspect(pos, asp)
+	end
+	return nil
+end
+
+get_aspect = function(pos)
+	local asp = get_supposed_aspect(pos)
+	if not asp then
+		asp = get_real_aspect(pos)
+		set_supposed_aspect(pos, asp)
+	end
+	return asp
+end
+
+local function set_aspect(pos, asp)
+	local node = N.get_node(pos)
+	local ndef = minetest.registered_nodes[node.name]
+	if ndef and ndef.advtrains and ndef.advtrains.set_aspect then
+		local oldasp = I.signal_get_aspect(pos) or DANGER
+		local newasp, aspval = adjust_aspect(pos, asp)
+		set_supposed_aspect(pos, newasp)
+		ndef.advtrains.set_aspect(pos, node, aspval)
+		local aspect_changed = A.not_equalp(oldasp, newasp)
+		if aspect_changed then
+			I.signal_on_aspect_changed(pos)
+			D.update_main(pos)
+		end
+	end
+end
+
+local function clear_aspect(pos)
+	set_supposed_aspect(pos, nil)
+end
+
+local function readjust_aspect(pos)
+	set_aspect(pos, get_aspect(pos))
+end
+
+I.signal_get_supported_aspects = get_supported_aspects
+I.signal_get_real_aspect = get_real_aspect
+I.signal_get_aspect = get_aspect
+I.signal_set_aspect = set_aspect
+I.signal_clear_aspect = clear_aspect
+I.signal_readjust_aspect = readjust_aspect
diff --git a/advtrains_interlocking/signal_aspect_ui.lua b/advtrains_interlocking/signal_aspect_ui.lua
index 4b41187..30b5165 100644
--- a/advtrains_interlocking/signal_aspect_ui.lua
+++ b/advtrains_interlocking/signal_aspect_ui.lua
@@ -43,7 +43,7 @@ local function describe_supported_aspects_t1(suppasp, isasp)
 	local entries = {}
 	local selid = 1
 	for idx, spv in ipairs(suppasp.main) do
-		if isasp and spv == isasp.main then
+		if isasp and spv == (isasp.main or false) then
 			selid = idx
 		end
 		entries[idx] = describe_t1_main_aspect(spv)
@@ -67,7 +67,7 @@ local function describe_supported_aspects_t1(suppasp, isasp)
 	entries = {}
 	selid = 1
 	for idx, spv in ipairs(suppasp.dst) do
-		if isasp and spv == isasp.dst then
+		if isasp and spv == (isasp.dst or false) then
 			selid = idx
 		end
 		entries[idx] = describe_t1_distant_aspect(spv)
@@ -102,6 +102,8 @@ local function handle_signal_formspec_tabheader_fields(pname, fields)
 		advtrains.interlocking.show_signal_form(pos, node, pname)
 	elseif n == 2 then
 		advtrains.interlocking.show_ip_form(pos, pname)
+	elseif n == 3 then
+		advtrains.interlocking.show_distant_signal_form(pos, pname)
 	end
 	return true
 end
diff --git a/advtrains_interlocking/signal_aspects.lua b/advtrains_interlocking/signal_aspects.lua
index eebb4ba..2866ae1 100644
--- a/advtrains_interlocking/signal_aspects.lua
+++ b/advtrains_interlocking/signal_aspects.lua
@@ -44,6 +44,27 @@ local function get_type2_definition(name)
 	return type2defs[name]
 end
 
+local function get_type2_danger(group)
+	local def = type2defs[group]
+	if not def then
+		return nil
+	end
+	local main = def.main
+	return main[#main]
+end
+
+local function get_type2_dst(group, name)
+	local def = type2defs[group]
+	if not def then
+		return nil
+	end
+	local aspidx = name
+	if type(name) ~= "number" then
+		aspidx = def.main[name] or 1
+	end
+	return def.main[math.max(1, aspidx-1)].name
+end
+
 local function type2main_to_type1(name, asp)
 	local def = type2defs[name]
 	if not def then
@@ -53,7 +74,7 @@ local function type2main_to_type1(name, asp)
 	if type(asp) == "number" then
 		aspidx = asp
 	else
-		aspidx = def.main[asp]
+		aspidx = def.main[asp] or 2
 	end
 	local asptbl = def.main[aspidx]
 	if not asptbl then
@@ -62,11 +83,13 @@ local function type2main_to_type1(name, asp)
 	if type(asp) == "number" then
 		asp = asptbl.name
 	end
+	local dst = def.main[math.min(#def.main, aspidx+1)].main
 
 	local t = {
 		main = asptbl.main,
 		type2name = asp,
 		type2group = name,
+		dst = dst,
 	}
 	if aspidx > 1 and aspidx < #asptbl then
 		t.dst = asptbl[aspidx+1].main
@@ -116,6 +139,7 @@ end
 return {
 	register_type2 = register_type2,
 	get_type2_definition = get_type2_definition,
+	get_type2_dst = get_type2_dst,
 	type2main_to_type1 = type2main_to_type1,
 	type1_to_type2main = type1_to_type2main,
 	equalp = equalp,
diff --git a/advtrains_interlocking/signal_main_ui.lua b/advtrains_interlocking/signal_main_ui.lua
deleted file mode 100644
index e69de29..0000000
diff --git a/advtrains_interlocking/spec/basic_signalling_spec.lua b/advtrains_interlocking/spec/basic_signalling_spec.lua
new file mode 100644
index 0000000..0b79972
--- /dev/null
+++ b/advtrains_interlocking/spec/basic_signalling_spec.lua
@@ -0,0 +1,87 @@
+--[[
+This file tests a large part of the signaling system, as a lot of tests for the
+signaling system tend to overlap for various parts of the system.
+]]
+
+require("mineunit")
+mineunit("core")
+
+_G.advtrains = {
+	interlocking = {
+		aspects = fixture("../../signal_aspects"),
+	},
+	ndb = {
+		get_node = minetest.get_node,
+		swap_node = minetest.swap_node,
+	}
+}
+
+fixture("advtrains_helpers")
+fixture("../../database")
+sourcefile("distant")
+sourcefile("signal_api")
+sourcefile("signal_aspect_accessors")
+fixture("../../demosignals")
+
+local D = advtrains.distant
+local I = advtrains.interlocking
+
+local stub_aspect_t1 = {
+	free = {main = -1},
+	slow = {main = 6},
+	danger = {main = 0, shunt = false},
+}
+local stub_pos_t1 = {}
+for i = 1, 3 do
+	stub_pos_t1[i] = {x = 1, y = 0, z = i}
+end
+
+world.layout {
+	{stub_pos_t1[1], "advtrains_interlocking:ds_danger"},
+	{stub_pos_t1[2], "advtrains_interlocking:ds_slow"},
+	{stub_pos_t1[3], "advtrains_interlocking:ds_free"},
+}
+
+describe("API for supposed signal aspects", function()
+	it("should load and save data properly", function()
+		local tbl = {_foo = true}
+		I.load_supposed_aspects(tbl)
+		assert.same(tbl, I.save_supposed_aspects())
+	end)
+	it("should set and get type 1 signals properly", function ()
+		local pos = stub_pos_t1[2]
+		local asp = stub_aspect_t1.slow
+		local newasp = { main = math.random(1,5) }
+		assert.same(asp, I.signal_get_aspect(pos))
+		I.signal_set_aspect(pos, newasp)
+		assert.same(newasp, I.signal_get_aspect(pos))
+		assert.same(asp, I.signal_get_real_aspect(pos))
+		I.signal_set_aspect(pos, asp)
+	end)
+end)
+
+describe("Distant signaling", function()
+	it("should assign distant signals and set the distant aspect correspondingly", function()
+		for i = 1, 2 do
+			D.assign(stub_pos_t1[i], stub_pos_t1[i+1])
+		end
+		assert.same(stub_aspect_t1.danger, I.signal_get_aspect(stub_pos_t1[1]))
+		assert.same({main = 6, dst = 0}, I.signal_get_aspect(stub_pos_t1[2]))
+		assert.same({main = -1, dst = 6}, I.signal_get_aspect(stub_pos_t1[3]))
+	end)
+	it("should report assignments properly", function()
+		assert.same({stub_pos_t1[1], "manual"}, {D.get_main(stub_pos_t1[2])})
+		assert.same({[advtrains.encode_pos(stub_pos_t1[3])] = "manual"}, D.get_dst(stub_pos_t1[2]))
+	end)
+	it("should update distant aspects automatically", function()
+		I.signal_set_aspect(stub_pos_t1[2], {main = 2, dst = -1})
+		assert.same({main = 2, dst = 0}, I.signal_get_aspect(stub_pos_t1[2]))
+		assert.same({main = -1, dst = 2}, I.signal_get_aspect(stub_pos_t1[3]))
+	end)
+	it("should unassign signals when one is removed", function()
+		world.set_node(stub_pos_t1[2], "air")
+		assert.same({}, D.get_dst(stub_pos_t1[1]))
+		assert.same({}, {D.get_main(stub_pos_t1[3])})
+		assert.same(stub_aspect_t1.free, I.signal_get_aspect(stub_pos_t1[3]))
+	end)
+end)
diff --git a/advtrains_interlocking/spec/signal_api_spec.lua b/advtrains_interlocking/spec/signal_api_spec.lua
deleted file mode 100644
index cd7a1d1..0000000
--- a/advtrains_interlocking/spec/signal_api_spec.lua
+++ /dev/null
@@ -1,49 +0,0 @@
-require("mineunit")
-
-mineunit("core")
-
-_G.advtrains = {
-	interlocking = {
-		aspects = fixture("../../signal_aspects"),
-	},
-	ndb = {
-		get_node = minetest.get_node,
-	}
-}
-
-fixture("advtrains_helpers")
-fixture("../../database")
-sourcefile("signal_api")
-
-local stub_aspect_t1 = { main = math.random() }
-local stub_pos_t1 = {x = 1, y = 0, z = 1}
-
-minetest.register_node(":stubsignal_t1", {
-	advtrains = {
-		supported_aspects = {},
-		get_aspect = function () return stub_aspect_t1 end,
-		set_aspect = function () end,
-	},
-	groups = { advtrains_signal = 2 },
-})
-
-world.layout {
-	{stub_pos_t1, "stubsignal_t1"},
-}
-
-describe("API for supposed signal aspects", function()
-	it("should load and save data properly", function()
-		local tbl = {_foo = true}
-		advtrains.interlocking.load_supposed_aspects(tbl)
-		assert.same(tbl, advtrains.interlocking.save_supposed_aspects())
-	end)
-	it("should set and get type 1 signals properly", function ()
-		local pos = stub_pos_t1
-		local asp = stub_aspect_t1
-		local newasp = { dst = math.random() }
-		assert.same(asp, advtrains.interlocking.signal_get_aspect(pos))
-		advtrains.interlocking.signal_set_aspect(pos, newasp)
-		assert.same(newasp, advtrains.interlocking.signal_get_aspect(pos))
-		assert.same(asp, advtrains.interlocking.signal_get_real_aspect(pos))
-	end)
-end)
diff --git a/advtrains_interlocking/tcb_ts_ui.lua b/advtrains_interlocking/tcb_ts_ui.lua
index b3b8221..9f88296 100755
--- a/advtrains_interlocking/tcb_ts_ui.lua
+++ b/advtrains_interlocking/tcb_ts_ui.lua
@@ -14,6 +14,7 @@ local lntrans = { "A", "B" }
 local function sigd_to_string(sigd)
 	return minetest.pos_to_string(sigd.p).." / "..lntrans[sigd.s]
 end
+advtrains.interlocking.sigd_to_string = sigd_to_string
 
 minetest.register_node("advtrains_interlocking:tcb_node", {
 	drawtype = "mesh",
@@ -608,7 +609,7 @@ function advtrains.interlocking.show_signalling_form(sigd, pname, sel_rte, calle
 	if not tcbs.signal_name then tcbs.signal_name = "Signal at "..minetest.pos_to_string(sigd.p) end
 	if not tcbs.routes then tcbs.routes = {} end
 	
-	local form = "size[7,9.75]label[0.5,0.5;Signal at "..minetest.pos_to_string(sigd.p).."]"
+	local form = "size[7,10.25]label[0.5,0.5;Signal at "..minetest.pos_to_string(sigd.p).."]"
 	form = form .. advtrains.interlocking.make_signal_formspec_tabheader(pname, tcbs.signal, 7, 1)
 	form = form.."field[0.8,1.5;5.2,1;name;Signal name;"..minetest.formspec_escape(tcbs.signal_name).."]"
 	form = form.."button[5.5,1.2;1,1;setname;Set]"
@@ -670,6 +671,7 @@ function advtrains.interlocking.show_signalling_form(sigd, pname, sel_rte, calle
 				form = form.."button[0.5,8;2.5,1;newroute;New Route]"
 				form = form.."button[  3,8;2.5,1;unassign;Unassign Signal]"
 				form = form..string.format("checkbox[0.5,8.75;ars;Automatic routesetting;%s]", not tcbs.ars_disabled)
+				form = form..string.format("checkbox[0.5,9.25;dst;Distant signalling;%s]", not tcbs.nodst)
 			end
 		elseif sigd_equal(tcbs.route_origin, sigd) then
 			-- something has gone wrong: tcbs.routeset should have been set...
@@ -796,6 +798,10 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 		if fields.ars then
 			tcbs.ars_disabled = not minetest.is_yes(fields.ars)
 		end
+
+		if fields.dst then
+			tcbs.nodst = not minetest.is_yes(fields.dst)
+		end
 		
 		if fields.auto then
 			tcbs.route_auto = true
-- 
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