Rework train same-track collision system and deterministic coupling

- Adds a separate collision system for trains sharing a path
- Moved some coupling-related code to couple.lua and refactor it
- Handle coupling in a way that the initiating train always keeps its ID
- As a side effect, engine has its direction reversed after coupling

4 files changed, 478 insertions, 394 deletions

diff --git a/advtrains/couple.lua b/advtrains/couple.lua
index 3dc336f..336a6d4 100644
--- a/advtrains/couple.lua
+++ b/advtrains/couple.lua
@@ -1,14 +1,290 @@
 --couple.lua
---defines couple entities.
+--Handles coupling and discoupling of trains, and defines the coupling entities
+--Rework June 2021 - some functions from trainlogic.lua have been moved here
 
---advtrains:discouple
---set into existing trains to split them when punched.
---they are attached to the wagons.
---[[fields
-wagon
+-- COUPLING --
+-- During coupling rework, the behavior of coupling was changed to make automation easier. It is now as follows:
+-- Coupling is only ever initiated when a train is standing somewhere (not moving) and another train drives onto one of its ends
+-- with a speed greater than 0
+-- "stationary" train is the one standing there - in old code called "train2"
+-- "initiating" train is the one that approached it and bumped into it - typically an engine - in old code called "train1"
+-- When the initiating train has autocouple set, trains are immediately coupled
+-- When not, a couple entity is spawned and coupling commences on click
+-- Coupling MUST preserve the train ID of the initiating train, so it is done like this:
+	-- initiating train is reversed
+	-- stationary train is reversed if required, so that it points towards the initiating train
+	-- do_connect_trains(initiating, stationary)
+-- As a result, the coupled train is reversed in direction. Alternative way of doing things (might be considered later):
+	-- stationary train is reversed if required, so that it points away from the initiating train
+	-- index of initiating train is set so that it matches the front pos of stationary train
+	-- wagons of stationary train are inserted at the beginning of initiating train
+	-- remove stationary train
 
-wagons keep their couple entity minetest-internal id inside the field discouple_id. if it refers to nowhere, they will spawn a new one if player is near
-]]
+-- train.couple_* contain references to ObjectRefs of couple objects, which contain all relevant information
+-- These objectRefs will delete themselves once the couples no longer match (see below)
+local function create_couple_entity(pos, train1, t1_is_front, train2, t2_is_front)
+	local id1 = train1.id
+	local id2 = train2.id
+
+	-- delete previous couple entities
+	if t1_is_front then
+		if train1.cpl_front then train1.cpl_front:remove() end
+	else
+		if train1.cpl_back then train1.cpl_back:remove() end
+	end
+	if t2_is_front then
+		if train2.cpl_front then train2.cpl_front:remove() end
+	else
+		if train2.cpl_back then train2.cpl_back:remove() end
+	end
+	
+	local obj=minetest.add_entity(pos, "advtrains:couple")
+	if not obj then error("Failed creating couple object!") return end
+	local le=obj:get_luaentity()
+	le.train_id_1=id1
+	le.t1_is_front=t1_is_front
+	le.train_id_2=id2
+	le.t2_is_front=t2_is_front
+	--atdebug("created couple between",train1.id,train2.id,t2_is_front)
+	
+	if t1_is_front then
+		train1.cpl_front = obj
+	else
+		train2.cpl_back = obj
+	end
+	if t2_is_front then
+		train2.cpl_front = obj
+	else
+		train2.cpl_back = obj
+	end
+end
+
+-- Old static couple checking. Never used for autocouple, only used for standing trains if train did not approach
+local CPL_CHK_DST = -1
+local CPL_ZONE = 2
+function advtrains.train_check_couples(train)
+	--atdebug("rechecking couples")
+	if train.cpl_front then
+		if not train.cpl_front:get_yaw() then
+			-- objectref is no longer valid. reset.
+			train.cpl_front = nil
+		end
+	end
+	if not train.cpl_front then
+		-- recheck front couple
+		local front_trains, pos = advtrains.occ.get_occupations(train, atround(train.index) + CPL_CHK_DST)
+		if advtrains.is_node_loaded(pos) then -- if the position is loaded...
+			for tid, idx in pairs(front_trains) do
+				local other_train = advtrains.trains[tid]
+				if not advtrains.train_ensure_init(tid, other_train) then
+					atwarn("Train",tid,"is not initialized! Couldn't check couples!")
+					return
+				end
+				--atdebug(train.id,"front: ",idx,"on",tid,atround(other_train.index),atround(other_train.end_index))
+				if other_train.velocity == 0 then
+					if idx>=other_train.index and idx<=other_train.index + CPL_ZONE then
+							create_couple_entity(pos, train, true, other_train, true)
+							break
+					end
+					if idx<=other_train.end_index and idx>=other_train.end_index - CPL_ZONE then
+							create_couple_entity(pos, train, true, other_train, false)
+							break
+					end
+				end
+			end
+		end
+	end
+	if train.cpl_back then
+		if not train.cpl_back:get_yaw() then
+			-- objectref is no longer valid. reset.
+			train.cpl_back = nil
+		end
+	end
+	if not train.cpl_back then
+		-- recheck back couple
+		local back_trains, pos = advtrains.occ.get_occupations(train, atround(train.end_index) - CPL_CHK_DST)
+		if advtrains.is_node_loaded(pos) then -- if the position is loaded...
+			for tid, idx in pairs(back_trains) do
+				local other_train = advtrains.trains[tid]
+				if not advtrains.train_ensure_init(tid, other_train) then
+					atwarn("Train",tid,"is not initialized! Couldn't check couples!")
+					return
+				end
+				--atdebug(train.id,"back: ",idx,"on",tid,atround(other_train.index),atround(other_train.end_index))
+				if other_train.velocity == 0 then
+					if idx>=other_train.index and idx<=other_train.index + CPL_ZONE then
+							create_couple_entity(pos, train, false, other_train, true)
+							break
+					end
+					if idx<=other_train.end_index and idx>=other_train.end_index - CPL_ZONE then
+							create_couple_entity(pos, train, false, other_train, false)
+							break
+					end
+				end
+			end
+		end
+	end
+end
+
+-- Deletes couple entities from the train
+function advtrains.couple_invalidate(train)
+	if train.cpl_back then
+		train.cpl_back:remove()
+		train.cpl_back = nil
+	end
+	if train.cpl_front then
+		train.cpl_front:remove()
+		train.cpl_front = nil
+	end
+	train.couples_up_to_date = nil
+end
+
+-- Called from train_step_b() when the current train (init_train) just stopped at one of the end indices of another train (stat_train)
+-- Depending on autocouple, either couples immediately or spawns a couple entity
+function advtrains.couple_initiate_with(init_train, stat_train, stat_is_front)
+	--atdebug("Initiating couplign between init=",init_train.id,"stat=",stat_train.id,"backside=",stat_is_backside)
+	if init_train.autocouple then
+		advtrains.couple_trains(init_train, true, stat_train, stat_is_front)
+	else
+		local pos = advtrains.path_get_interpolated(init_train, init_train.index)
+		create_couple_entity(pos, init_train, true, stat_train, stat_is_front)
+	end
+	
+end
+
+-- check if the player has permission for the first/last wagon of the train
+local function check_twagon_owner(train, b_first, pname)
+	local wtp = b_first and 1 or #train.trainparts
+	local wid = train.trainparts[wtp]
+	local wdata = advtrains.wagons[wid]
+	if wdata then
+		return advtrains.check_driving_couple_protection(pname, wdata.owner, wdata.whitelist)
+	end
+	return false
+end
+
+-- Perform coupling, but check if the player is authorized to couple
+function advtrains.safe_couple_trains(train1, t1_is_front, train2, t2_is_front, pname)
+
+	if pname and not minetest.check_player_privs(pname, "train_operator") then
+		   minetest.chat_send_player(pname, "Missing train_operator privilege")
+		   return false
+	end
+
+	local wck_t1, wck_t2
+	if pname then
+		   wck_t1 = check_twagon_owner(train1, t1_is_front, pname)
+		   wck_t2 = check_twagon_owner(train2, t2_is_front, pname)
+	end
+	if (wck_t1 or wck_t2) or not pname then
+		advtrains.couple_trains(train1, t1_is_front, train2, t2_is_front)
+	end
+end
+
+-- Actually performs the train coupling. Always retains train ID of train1
+function advtrains.couple_trains(train1, t1_is_front, train2, t2_is_front)
+	--atdebug("Couple trains init=",init_train.id,"stat=",stat_train.id,"statreverse=",stat_must_reverse)
+	-- see comment on top of file
+	if t1_is_front then
+		advtrains.invert_train(train1.id)
+	end
+	if not t2_is_front then
+		advtrains.invert_train(train2.id)
+	end
+
+	advtrains.do_connect_trains(train1, train2)
+end
+
+-- Adds the wagons of first to second and deletes second_id afterwards
+-- Assumes that second_id stands right behind first_id and both trains point to the same direction
+function advtrains.do_connect_trains(first, second)
+	
+	if not advtrains.train_ensure_init(first.id, first) then
+		atwarn("Coupling: first train",first.id,"is not initialized! Operation aborted!")
+		return
+	end
+	if not advtrains.train_ensure_init(second.id, second) then
+		atwarn("Coupling: second train",second.id,"is not initialized! Operation aborted!")
+		return
+	end
+	
+	local first_wagoncnt=#first.trainparts
+	local second_wagoncnt=#second.trainparts
+	
+	for _,v in ipairs(second.trainparts) do
+		table.insert(first.trainparts, v)
+	end
+	
+	advtrains.remove_train(second.id)
+
+	first.velocity = 0
+	
+	advtrains.update_trainpart_properties(first.id)
+	advtrains.couple_invalidate(first)
+	return true
+end
+
+
+
+-- DECOUPLING --
+function advtrains.split_train_at_fc(train, count_empty, length_limit)
+	-- splits train at first different current FC by convention,
+	-- locomotives have empty FC so are ignored
+	-- count_empty is used to split off locomotives
+	-- length_limit limits the length of the first train to length_limit wagons
+	local train_id = train.id
+	local fc = false
+	local ind = 0
+	for i = 1, #train.trainparts do
+		local w_id = train.trainparts[i]
+		local data = advtrains.wagons[w_id]
+		if length_limit and i > length_limit then
+			ind = i
+			break
+		end
+		if data then
+			local wfc = advtrains.get_cur_fc(data)
+			if  wfc ~= "" or count_empty then
+				if  fc then
+					if fc ~= wfc then
+						ind = i
+						break
+					end
+				else
+					fc = wfc
+				end
+			end
+		end
+	end
+	if ind > 0 then
+		return advtrains.split_train_at_index(train, ind), fc
+	end
+	if fc then
+		return nil, fc
+	end
+end
+
+function advtrains.train_step_fc(train)
+	for i=1,#train.trainparts do
+		local w_id = train.trainparts[i]
+		local data = advtrains.wagons[w_id]
+		if data then
+			advtrains.step_fc(data)
+		end
+	end
+end
+
+
+-- split_train_at_index() is in trainlogic.lua because it needs access to two local functions
+
+function advtrains.split_train_at_wagon(wagon_id)
+	--get train
+	local data = advtrains.wagons[wagon_id]
+	advtrains.split_train_at_index(advtrains.trains[data.train_id], data.pos_in_trainparts)
+end
+
+
+-- COUPLE ENTITIES --
 
 local couple_max_dist=3
 
@@ -36,8 +312,6 @@ minetest.register_entity("advtrains:discouple", {
 			if pname and pname~="" and self.wagon then
 				if advtrains.safe_decouple_wagon(self.wagon.id, pname) then
 					self.object:remove()
-				else
-					minetest.add_entity(self.object:getpos(), "advtrains:lockmarker")
 				end
 			end
 	end,
@@ -60,10 +334,6 @@ minetest.register_entity("advtrains:discouple", {
 
 -- advtrains:couple
 -- Couple entity 
-local function lockmarker(obj)
-	minetest.add_entity(obj:get_pos(), "advtrains:lockmarker")
-	obj:remove()
-end
 
 minetest.register_entity("advtrains:couple", {
 	visual="sprite",
@@ -75,107 +345,71 @@ minetest.register_entity("advtrains:couple", {
 	is_couple=true,
 	static_save = false,
 	on_activate=function(self, staticdata)
-			if staticdata=="COUPLE" then
-				--couple entities have no right to exist further...
-				atprint("Couple loaded from staticdata, destroying")
-				self.object:remove()
-				return
-			end
-			self.object:set_armor_groups({immmortal=1})
+		if staticdata=="COUPLE" then
+			--couple entities have no right to exist further...
+			--atdebug("Couple loaded from staticdata, destroying")
+			self.object:remove()
+			return
+		end
+		self.object:set_armor_groups({immmortal=1})
 	end,
 	get_staticdata=function(self) return "COUPLE" end,
 	on_rightclick=function(self, clicker)
-			if not self.train_id_1 or not self.train_id_2 then return end
-			
-			local pname=clicker
-			if type(clicker)~="string" then pname=clicker:get_player_name() end
-			
-			if advtrains.safe_couple_trains(self.train_id_1, self.train_id_2, self.t1_is_front, self.t2_is_front, pname) then
-				self.object:remove()
-			else
-				lockmarker(self.object)
-			end
+		if not self.train_id_1 or not self.train_id_2 then return end
+
+		local pname=clicker
+		if type(clicker)~="string" then pname=clicker:get_player_name() end
+
+		local train1=advtrains.trains[self.train_id_1]
+		local train2=advtrains.trains[self.train_id_2]
+
+		advtrains.safe_couple_trains(train1, self.t1_is_front, train2, self.t2_is_front, pname)
+		self.object:remove()
 	end,
 	on_step=function(self, dtime)
-			if advtrains.wagon_outside_range(self.object:getpos()) then
-				self.object:remove()
-				return
-			end
+		if advtrains.wagon_outside_range(self.object:getpos()) then
+			--atdebug("Couple Removing outside range")
+			self.object:remove()
+			return
+		end
 
-			if not self.train_id_1 or not self.train_id_2 then atprint("Couple: train ids not set!") self.object:remove() return end
-			local train1=advtrains.trains[self.train_id_1]
-			local train2=advtrains.trains[self.train_id_2]
-			if not train1 or not train2 then
-				atprint("Couple: trains missing, destroying")
-				self.object:remove()
-				return
-			end
-			
-			--shh, silence here, this is an on-step callback!
-			if not advtrains.train_ensure_init(self.train_id_1, train1) then
-				--atwarn("Train",self.train_id_1,"is not initialized! Operation aborted!")
-				return
-			end
-			if not advtrains.train_ensure_init(self.train_id_2, train2) then
-				--atwarn("Train",self.train_id_2,"is not initialized! Operation aborted!")
-				return
-			end
-			
-			if train1.velocity>0 or train2.velocity>0 then
-				if not self.position_set then --ensures that train stands a single time before check fires. Using flag below
-					return
-				end
-				atprint("Couple: train is moving, destroying")
-				self.object:remove()
-				return
+		if not self.train_id_1 or not self.train_id_2 then
+			--atdebug("Couple Removing ids missing")
+			self.object:remove()
+			return
+		end
+		local train1=advtrains.trains[self.train_id_1]
+		local train2=advtrains.trains[self.train_id_2]
+		if not train1 or not train2 then
+			--atdebug("Couple Removing trains missing")
+			self.object:remove()
+			return
+		end
+		
+		if self.position_set and train1.velocity>0 or train2.velocity>0 then
+			--atdebug("Couple: train is moving, destroying")
+			self.object:remove()
+			return
+		end
+
+		if not self.position_set then
+			local tp1
+			if self.t1_is_front then
+				tp1=advtrains.path_get_interpolated(train1, train1.index)
+			else
+				tp1=advtrains.path_get_interpolated(train1, train1.end_index)
 			end
-			
-			if not self.position_set then
-				local tp1
-				if self.t1_is_front then
-					tp1=advtrains.path_get_interpolated(train1, train1.index)
-				else
-					tp1=advtrains.path_get_interpolated(train1, train1.end_index)
-				end
-				local tp2
-				if self.t2_is_front then
-					tp2=advtrains.path_get_interpolated(train2, train2.index)
-				else
-					tp2=advtrains.path_get_interpolated(train2, train2.end_index)
-				end
-				local pos_median=advtrains.pos_median(tp1, tp2)
-				if not vector.equals(pos_median, self.object:getpos()) then
-					self.object:set_pos(pos_median)
-				end
-				self.position_set=true
+			local tp2
+			if self.t2_is_front then
+				tp2=advtrains.path_get_interpolated(train2, train2.index)
+			else
+				tp2=advtrains.path_get_interpolated(train2, train2.end_index)
 			end
-			advtrains.atprint_context_tid=nil
-	end,
-})
-minetest.register_entity("advtrains:lockmarker", {
-	visual="sprite",
-	textures = {"advtrains_cpl_lock.png"},
-	collisionbox = {-0.3,-0.3,-0.3, 0.3,0.3,0.3},
-	visual_size = {x=0.7, y=0.7},
-	initial_sprite_basepos = {x=0, y=0},
-	
-	is_lockmarker=true,
-	static_save = false,
-	on_activate=function(self, staticdata)
-			if staticdata=="COUPLE" then
-				--couple entities have no right to exist further...
-				atprint("Couple loaded from staticdata, destroying")
-				self.object:remove()
-				return
+			local pos_median=advtrains.pos_median(tp1, tp2)
+			if not vector.equals(pos_median, self.object:getpos()) then
+				self.object:set_pos(pos_median)
 			end
-			self.object:set_armor_groups({immmortal=1})
-			self.life=5
-	end,
-	get_staticdata=function(self) return "COUPLE" end,
-	on_step=function(self, dtime)
-		self.life=(self.life or 5)-dtime
-		if self.life<0 then
-			self.object:remove()
+			self.position_set=true
 		end
 	end,
-}) 
+})
diff --git a/advtrains/path.lua b/advtrains/path.lua
index 714781a..f2b8a13 100644
--- a/advtrains/path.lua
+++ b/advtrains/path.lua
@@ -417,3 +417,42 @@ function advtrains.path_lookup(train, pos)
 	end
 	return nil
 end
+
+-- Projects the path of "train" onto the path of "onto_train_id", and returns the index on onto_train's path
+-- that corresponds to "index" on "train"'s path, as well as whether both trains face each other
+-- index may be fractional
+-- returns: res_index, trains_facing
+-- returns nil when path can not be projected, either because trains are on different tracks or
+-- node at "index" happens to be on a turnout and it's the wrong direction
+-- Note - duplicate with similar functionality is in train_step_b() - that code combines train detection with projecting
+function advtrains.path_project(train, index, onto_train_id)
+	local base_idx = atfloor(index)
+	local frac_part = index - base_idx
+	local base_pos = advtrains.path_get(train, base_idx)
+	local base_cn =  train.path_cn[base_idx]
+	local otrn = advtrains.trains[onto_train_id]
+	-- query occupation
+	local occ = advtrains.occ.get_trains_over(base_pos)
+	-- is wanted train id contained?
+	local ob_idx = occ[onto_train_id]
+	if not ob_idx then
+		return nil
+	end
+
+	-- retrieve other train's cn and cp
+	local ocn = otrn.path_cn[ob_idx]
+	local ocp = otrn.path_cp[ob_idx]
+
+	if base_cn == ocn then
+		-- same direction
+		return ob_idx + frac_part, false
+	elseif base_cn == ocp then
+		-- facing trains - subtract index frac
+		return ob_idx - frac_part, true
+	else
+		-- same path item but no common connections - deny
+		return nil
+	end
+end
+
+
diff --git a/advtrains/trainlogic.lua b/advtrains/trainlogic.lua
index 0f2a66e..442d6bf 100644
--- a/advtrains/trainlogic.lua
+++ b/advtrains/trainlogic.lua
@@ -139,6 +139,7 @@ minetest.register_on_joinplayer(function(player)
 		advtrains.hhud[player:get_player_name()] = nil
 		--independent of this, cause all wagons of the train which are loaded to reattach their players
 		--needed because already loaded wagons won't call reattach_all()
+		local pname = player:get_player_name()
 		local id=advtrains.player_to_train_mapping[pname]
 		if id then
 			for _,wagon in pairs(minetest.luaentities) do
@@ -394,7 +395,7 @@ function advtrains.train_step_b(id, train, dtime)
 	local back_off_track=train.end_index<train.path_trk_b
 	train.off_track = front_off_track or back_off_track
 	
-	if back_off_track and (not v_cap or v_cap > 1) then
+	if back_off_track and (not sit_v_cap or sit_v_cap > 1) then
 		--atprint("in train_step_b: applying back_off_track")
 		sit_v_cap = 1
 	elseif front_off_track then
@@ -587,12 +588,76 @@ function advtrains.train_step_b(id, train, dtime)
 	else
 		--atprint("in train_step_b: movement calculation reusing from LZB newindex=",new_index_curr_tv)
 	end
-	
+
 	-- if the zeroappr mechanism has hit, go no further than zeroappr index
 	if lzb_next_zero_barrier and new_index_curr_tv > lzb_next_zero_barrier then
 		--atprint("in train_step_b: Zero barrier hit, clipping to newidx_tv=",new_index_curr_tv, "zb_idx=",lzb_next_zero_barrier)
 		new_index_curr_tv = lzb_next_zero_barrier
 	end
+
+	-- New same-track collision system - check for any other trains within the range we're going to move
+	-- do the checks if we either are moving or about to start moving
+	if new_index_curr_tv > train.index or accelerating then -- only if train is actually advancing
+		-- Note: duplicate code from path_project() because of subtle differences: no frac processing and scanning all occupations
+		--[[train.debug = ""
+		local atdebug = function(t, ...)
+			local text=advtrains.print_concat_table({t, ...})
+			train.debug = train.debug..text.."\n"
+		end]]
+		local base_idx = atfloor(new_index_curr_tv + 1)
+		local base_pos = advtrains.path_get(train, base_idx)
+		local base_cn =  train.path_cn[base_idx]
+		--atdebug(id,"Begin Checking for on-track collisions new_idx=",new_index_curr_tv,"base_idx=",base_idx,"base_pos=",base_pos,"base_cn=",base_cn)
+		-- query occupation
+		local occ = advtrains.occ.get_trains_over(base_pos)
+		-- iterate other trains
+		for otid, ob_idx in pairs(occ) do
+			if otid ~= id then
+				--atdebug(id,"Found other train",otid," with matching index ",ob_idx)
+				-- Phase 1 - determine if trains are facing and which is the relefant stpo index
+				local otrn = advtrains.trains[otid]
+
+				-- retrieve other train's cn and cp
+				local ocn = otrn.path_cn[ob_idx]
+				local ocp = otrn.path_cp[ob_idx]
+
+				local target_is_inside, ref_index, facing
+
+				if base_cn == ocn then
+					-- same direction
+					ref_index = otrn.end_index
+					same_dir = true
+					target_is_inside = (ob_idx >= ref_index)
+					--atdebug("Same direction: ref_index",ref_index,"inside=",target_is_inside)
+				elseif base_cn == ocp then
+					-- facing trains - subtract index frac
+					ref_index = otrn.index
+					same_dir = false
+					target_is_inside = (ob_idx <= ref_index)
+					--atdebug("Facing direction: ref_index",ref_index,"inside=",target_is_inside)
+				end
+
+				-- Phase 2 - project ref_index back onto our path and check again (necessary because there might be a turnout on the way and we are driving into the flank
+				if target_is_inside then
+					local our_index = advtrains.path_project(otrn, ref_index, id)
+					--atdebug("Backprojected our_index",our_index)
+					if our_index and our_index <= new_index_curr_tv then
+						-- ON_TRACK COLLISION IS HAPPENING
+						-- the actual collision is handled in train_step_c, so set appropriate signal variables
+						train.ontrack_collision_info = {
+							otid = otid,
+							same_dir = same_dir,
+						}
+						-- clip newindex
+						--atdebug("-- Collision detected!")
+						new_index_curr_tv = our_index
+					end
+				end
+			end
+		end
+	end
+
+	-- ## Movement happens here ##
 	train.index = new_index_curr_tv
 	
 	recalc_end_index(train)
@@ -638,21 +703,39 @@ function advtrains.train_step_c(id, train, dtime)
 		advtrains.spawn_wagons(id)
 		train.check_trainpartload=2
 	end
-	
-	--- 8. check for collisions with other trains and damage players ---
-	
+
 	local train_moves=(train.velocity~=0)
-	
-	--- Check whether this train can be coupled to another, and set couple entities accordingly
-	if not train.was_standing and not train_moves then
-		advtrains.train_check_couples(train)
+
+	--- On-track collision handling - detected in train_step_b, but handled here so all other train movements have already happened.
+	if train.ontrack_collision_info then
+		train.velocity = 0
+		train.acceleration = 0
+		advtrains.atc.train_reset_command(train)
+
+		local otrn = advtrains.trains[train.ontrack_collision_info.otid]
+
+		if otrn.velocity == 0 then -- other train must be standing, else don't initiate coupling
+			advtrains.couple_initiate_with(train, otrn, not train.ontrack_collision_info.same_dir)
+		end
+
+		train.ontrack_collision_info = nil
+		train.couples_up_to_date = true
 	end
-	train.was_standing = not train_moves
-	
+
+	-- handle couples if on_track collision handling did not fire
 	if train_moves then
-		
+		train.couples_up_to_date = nil
+	elseif not train.couples_up_to_date then
+		advtrains.train_check_couples(train) -- no guarantee for train order here
+		train.couples_up_to_date = true
+	end
+
+	--- 8. check for collisions with other trains and damage players ---
+	if train_moves then
+		-- Note: this code handles collisions with trains that are not on the same path as the current train
+		-- The same-track collisions and coupling handling is found in couple.lua and handled from train_step_b() and code 2 blocks above.
 		local collided = false
-		local coll_grace=1
+		local coll_grace=2
 		local collindex = advtrains.path_get_index_by_offset(train, train.index, -coll_grace)
 		local collpos = advtrains.path_get(train, atround(collindex))
 		if collpos then
@@ -666,8 +749,8 @@ function advtrains.train_step_c(id, train, dtime)
 
 						local col_tr = advtrains.occ.check_collision(testpos, id)
 						if col_tr then
-							advtrains.train_check_couples(train)
 							train.velocity = 0
+							train.acceleration = 0
 							advtrains.atc.train_reset_command(train)
 							collided = true
 						end
@@ -899,7 +982,7 @@ function advtrains.remove_train(id)
 	
 	run_callbacks_remove(id, train)
 	
-	advtrains.path_invalidate(train)
+	advtrains.path_invalidate(train, true)
 	advtrains.couple_invalidate(train)
 	
 	local tp = train.trainparts
@@ -1019,53 +1102,6 @@ function advtrains.spawn_wagons(train_id)
 	end
 end
 
-function advtrains.split_train_at_fc(train, count_empty, length_limit)
-	-- splits train at first different current FC by convention,
-	-- locomotives have empty FC so are ignored
-	-- count_empty is used to split off locomotives
-	-- length_limit limits the length of the first train to length_limit wagons
-	local train_id = train.id
-	local fc = false
-	local ind = 0
-	for i = 1, #train.trainparts do
-		local w_id = train.trainparts[i]
-		local data = advtrains.wagons[w_id]
-		if length_limit and i > length_limit then
-			ind = i
-			break
-		end
-		if data then
-			local wfc = advtrains.get_cur_fc(data)
-			if  wfc ~= "" or count_empty then
-				if  fc then
-					if fc ~= wfc then
-						ind = i
-						break
-					end
-				else
-					fc = wfc
-				end
-			end
-		end
-	end
-	if ind > 0 then
-		return advtrains.split_train_at_index(train, ind), fc
-	end
-	if fc then
-		return nil, fc
-	end
-end
-
-function advtrains.train_step_fc(train)
-	for i=1,#train.trainparts do
-		local w_id = train.trainparts[i]
-		local data = advtrains.wagons[w_id]
-		if data then
-			advtrains.step_fc(data)
-		end
-	end
-end
-
 function advtrains.split_train_at_index(train, index)
 	-- this function splits a train at index, creating a new train from the back part of the train.
 
@@ -1121,167 +1157,6 @@ function advtrains.split_train_at_index(train, index)
 
 end
 
-function advtrains.split_train_at_wagon(wagon_id)
-	--get train
-	local data = advtrains.wagons[wagon_id]
-	advtrains.split_train_at_index(advtrains.trains[data.train_id], data.pos_in_trainparts)
-end
-
--- coupling
-local CPL_CHK_DST = -1
-local CPL_ZONE = 2
-
--- train.couple_* contain references to ObjectRefs of couple objects, which contain all relevant information
--- These objectRefs will delete themselves once the couples no longer match
-local function createcouple(pos, train1, t1_is_front, train2, t2_is_front)
-	local id1 = train1.id
-	local id2 = train2.id
-	if train1.autocouple or train2.autocouple then
-		-- couple trains
-		train1.autocouple = nil
-		train2.autocouple = nil		
-		minetest.after(0, advtrains.safe_couple_trains, id1, id2, t1_is_front, t2_is_front, false, false, train1.velocity, train2.velocity)
-		return
-	end
-	
-	local obj=minetest.add_entity(pos, "advtrains:couple")
-	if not obj then error("Failed creating couple object!") return end
-	local le=obj:get_luaentity()
-	le.train_id_1=id1
-	le.train_id_2=id2
-	le.t1_is_front=t1_is_front
-	le.t2_is_front=t2_is_front
-	--atdebug("created couple between",train1.id,t1_is_front,train2.id,t2_is_front)
-	if t1_is_front then
-		train1.cpl_front = obj
-	else
-		train1.cpl_back = obj
-	end
-	if t2_is_front then
-		train2.cpl_front = obj
-	else
-		train2.cpl_back = obj
-	end
-	
-end
-
-function advtrains.train_check_couples(train)
-	--atdebug("rechecking couples")
-	if train.cpl_front then
-		if not train.cpl_front:get_yaw() then
-			-- objectref is no longer valid. reset.
-			train.cpl_front = nil
-		end
-	end
-	if not train.cpl_front then
-		-- recheck front couple
-		local front_trains, pos = advtrains.occ.get_occupations(train, atround(train.index) + CPL_CHK_DST)
-		if advtrains.is_node_loaded(pos) then -- if the position is loaded...
-			for tid, idx in pairs(front_trains) do
-				local other_train = advtrains.trains[tid]
-				if not advtrains.train_ensure_init(tid, other_train) then
-					atwarn("Train",tid,"is not initialized! Couldn't check couples!")
-					return
-				end
-				--atdebug(train.id,"front: ",idx,"on",tid,atround(other_train.index),atround(other_train.end_index))
-				if other_train.velocity == 0 then
-					if idx>=other_train.index and idx<=other_train.index + CPL_ZONE then
-						createcouple(pos, train, true, other_train, true)
-						break
-					end
-					if idx<=other_train.end_index and idx>=other_train.end_index - CPL_ZONE then
-						createcouple(pos, train, true, other_train, false)
-						break
-					end
-				end
-			end
-		end
-	end
-	if train.cpl_back then
-		if not train.cpl_back:get_yaw() then
-			-- objectref is no longer valid. reset.
-			train.cpl_back = nil
-		end
-	end
-	if not train.cpl_back then
-		-- recheck back couple
-		local back_trains, pos = advtrains.occ.get_occupations(train, atround(train.end_index) - CPL_CHK_DST)
-		if advtrains.is_node_loaded(pos) then -- if the position is loaded...
-			for tid, idx in pairs(back_trains) do
-				local other_train = advtrains.trains[tid]
-				if not advtrains.train_ensure_init(tid, other_train) then
-					atwarn("Train",tid,"is not initialized! Couldn't check couples!")
-					return
-				end
-				if other_train.velocity == 0 then
-					if idx>=other_train.index and idx<=other_train.index + CPL_ZONE then
-						createcouple(pos, train, false, other_train, true)
-						break
-					end
-					if idx<=other_train.end_index and idx>=other_train.end_index - CPL_ZONE then
-						createcouple(pos, train, false, other_train, false)
-						break
-					end
-				end
-			end
-		end
-	end
-end
-
-function advtrains.couple_invalidate(train)
-	if train.cpl_back then
-		train.cpl_back:remove()
-		train.cpl_back = nil
-	end
-	if train.cpl_front then
-		train.cpl_front:remove()
-		train.cpl_front = nil
-	end
-	train.was_standing = nil
-end
-
--- relevant code for this comment is in couple.lua
-
---there are 4 cases:
---1/2. F<->R F<->R regular, put second train behind first
---->frontpos of first train will match backpos of second
---3.   F<->R R<->F flip one of these trains, take the other as new train
---->backpos's will match
---4.   R<->F F<->R flip one of these trains and take it as new parent
---->frontpos's will match
-
-
-function advtrains.do_connect_trains(first_id, second_id, vel)
-	local first, second=advtrains.trains[first_id], advtrains.trains[second_id]
-	
-	if not advtrains.train_ensure_init(first_id, first) then
-		atwarn("Train",first_id,"is not initialized! Operation aborted!")
-		return
-	end
-	if not advtrains.train_ensure_init(second_id, second) then
-		atwarn("Train",second_id,"is not initialized! Operation aborted!")
-		return
-	end
-	
-	local first_wagoncnt=#first.trainparts
-	local second_wagoncnt=#second.trainparts
-	
-	for _,v in ipairs(second.trainparts) do
-		table.insert(first.trainparts, v)
-	end
-	
-	advtrains.remove_train(second_id)
-	if vel < 0 then
-		advtrains.invert_train(first_id)
-		vel = -vel
-	end
-	first.velocity= vel or 0
-	
-	advtrains.update_trainpart_properties(first_id)
-	advtrains.couple_invalidate(first)
-	return true
-end
-
 function advtrains.invert_train(train_id)
 	local train=advtrains.trains[train_id]
 	
diff --git a/advtrains/wagons.lua b/advtrains/wagons.lua
index e9b6d7a..4093f06 100644
--- a/advtrains/wagons.lua
+++ b/advtrains/wagons.lua
@@ -1240,70 +1240,6 @@ function wagon:reattach_all()
 	end
 end
 
-local function check_twagon_owner(train, b_first, pname)
-	local wtp = b_first and 1 or #train.trainparts
-	local wid = train.trainparts[wtp]
-	local wdata = advtrains.wagons[wid]
-	if wdata then
-		return advtrains.check_driving_couple_protection(pname, wdata.owner, wdata.whitelist)
-	end
-	return false
-end
-
-function advtrains.safe_couple_trains(id1, id2, t1f, t2f, pname, try_run,v1,v2)
-	
-	if pname and not minetest.check_player_privs(pname, "train_operator") then
-		minetest.chat_send_player(pname, "Missing train_operator privilege")
-		return false
-	end
-	
-	local train1=advtrains.trains[id1]
-	local train2=advtrains.trains[id2]
-	
-	if not advtrains.train_ensure_init(id1, train1)
-		or not advtrains.train_ensure_init(id2, train2) then
-		return false
-	end
-	local wck_t1, wck_t2
-	if pname then
-		wck_t1 = check_twagon_owner(train1, t1f, pname)
-		wck_t2 = check_twagon_owner(train2, t2f, pname)
-	end
-	if (wck_t1 or wck_t2) or not pname then
-		if not v1 then
-			v1 = 0
-		end
-		if not v2 then
-			v2 = 0
-		end
-		if try_run then
-			return true
-		end
-		if t1f then
-			if t2f then
-				v1 = -v1
-				advtrains.invert_train(id1)
-				advtrains.do_connect_trains(id1, id2, v1+v2)
-			else
-				advtrains.do_connect_trains(id2, id1, v1+v2)
-			end
-		else
-			if t2f then
-				advtrains.do_connect_trains(id1, id2, v1+v2)
-			else
-				v2 = -v2
-				advtrains.invert_train(id2)
-				advtrains.do_connect_trains(id1, id2, v1+v2)
-			end
-		end
-		return true
-	else
-		minetest.chat_send_player(pname, "You must be authorized for at least one wagon.")
-		return false
-	end
-end
-
-
 function advtrains.safe_decouple_wagon(w_id, pname, try_run)
 	if not minetest.check_player_privs(pname, "train_operator") then
 		minetest.chat_send_player(pname, "Missing train_operator privilege")