-- train_related.lua
-- Occupation of track sections - mainly implementation of train callbacks

--[[
Track section occupation is saved as follows

In train:
train.il_sections = {
	[n] = {ts_id = <...> (origin = <sigd>)}
}
-- "origin" is the TCB (signal describer) the train initially entered this section

In track section
ts.trains = {
	[n] = <train_id>
}

When any inconsistency is detected, we will assume the most restrictive setup.
It will be possible to indicate a section "free" via the GUI.
]]

local ildb = advtrains.interlocking.db

local sigd_equal = advtrains.interlocking.sigd_equal

local function itexist(tbl, com)
	for _,item in ipairs(tbl) do
		if (item==com) then
			return true
		end
	end
	return false
end
local function itkexist(tbl, ikey, com)
	for _,item in ipairs(tbl) do
		if item[ikey] == com then
			return true
		end
	end
	return false
end

local function itremove(tbl, com, once)
	local i=1
	while i <= #tbl do
		if tbl[i] == com then
			table.remove(tbl, i)
			if once then return end
		else
			i = i + 1
		end
	end
end
local function itkremove(tbl, ikey, com, once)
	local i=1
	while i <= #tbl do
		if tbl[i][ikey] == com then
			table.remove(tbl, i)
			if once then return end
		else
			i = i + 1
		end
	end
end

local function setsection(tid, train, ts_id, ts, sigd, only_if_not_exist)
	-- train
	if not train.il_sections then train.il_sections = {} end
	if only_if_not_exist then
		-- called for the back connid on enter, only to ensure that section is blocked if train was so far not registered
		if not itkexist(train.il_sections, "ts_id", ts_id) then
			table.insert(train.il_sections, {ts_id = ts_id, origin = sigd})
		end
	else
		-- insert always, this leads to duplicate entries if the train enters the same section a second time
		table.insert(train.il_sections, {ts_id = ts_id, origin = sigd})
	end
	
	-- ts
	if not ts.trains then ts.trains = {} end
	if only_if_not_exist then
		-- called for the back connid on enter, only to ensure that section is blocked if train was so far not registered
		if not itexist(ts.trains, tid) then
			table.insert(ts.trains, tid)
		end
	else
		table.insert(ts.trains, tid)
	end
	
	-- routes
	local tcbs
	if sigd then
		tcbs = advtrains.interlocking.db.get_tcbs(sigd)
	end
	
	-- route setting - clear route state
	if ts.route then
		--atdebug(tid,"enters",ts_id,"examining Routestate",ts.route)
		if sigd and not sigd_equal(ts.route.entry, sigd) then
			-- Train entered not from the route. Locate origin and cancel route!
			atwarn("Train",tid,"hit route",ts.route.rsn,"!")
			advtrains.interlocking.route.cancel_route_from(ts.route.origin)
			atwarn("Route was cancelled.")
		else
			-- train entered route regularily.
		end
		ts.route = nil
	end
	if tcbs and tcbs.signal then
		-- Reset route and signal
		-- Note that the hit-route case is already handled by cancel_route_from
		-- this code only handles signal at entering tcb and also triggers for non-route ts
		tcbs.route_committed = nil
		tcbs.route_aspect = nil
		tcbs.route_remote = nil
		tcbs.route_origin = nil
		tcbs.route_rsn = nil
		if not tcbs.route_auto then
			tcbs.routeset = nil
		end
		advtrains.interlocking.signal.update_route_aspect(tcbs)
		advtrains.interlocking.route.update_route(sigd, tcbs)
	end
end

local function freesection(tid, train, ts_id, ts, clear_all)
	-- train
	if not train.il_sections then train.il_sections = {} end
	itkremove(train.il_sections, "ts_id", ts_id, not clear_all)
	
	-- ts
	if not ts.trains then ts.trains = {} end
	itremove(ts.trains, tid, not clear_all)
	
	-- route locks
	if ts.route_post then
		advtrains.interlocking.route.free_route_locks(ts_id, ts.route_post.locks)
		if ts.route_post.next then
			--this does nothing when the train went the right way, because
			-- "route" info is already cleared.
			advtrains.interlocking.route.cancel_route_from(ts.route_post.next)
		end
		ts.route_post = nil
	end
	-- This must be delayed, because this code is executed in-between a train step
	-- TODO use luaautomation timers?
	minetest.after(0, advtrains.interlocking.route.update_waiting, "ts", ts_id)
end


-- This is regular operation
-- The train is on a track and drives back and forth

-- This sets the section for both directions, to be failsafe
advtrains.tnc_register_on_enter(function(pos, id, train, index)
	local tcb = ildb.get_tcb(pos)
	if tcb and train.path_cp[index] and train.path_cn[index] then
		-- forward conn
		local connid = train.path_cn[index]
		local ts = tcb[connid].ts_id and ildb.get_ts(tcb[connid].ts_id)
		if ts then
			setsection(id, train, tcb[connid].ts_id, ts, {p=pos, s=connid})
		end
		-- backward conn (safety only)
		connid = train.path_cp[index]
		ts = tcb[connid].ts_id and ildb.get_ts(tcb[connid].ts_id)
		if ts then
			setsection(id, train, tcb[connid].ts_id, ts, {p=pos, s=connid}, true)
		end
	end
end)


-- this time, of course, only clear the backside (cp connid)
advtrains.tnc_register_on_leave(function(pos, id, train, index)
	local tcb = ildb.get_tcb(pos)
	if tcb and train.path_cp[index] then
		-- backward conn
		local connid = train.path_cp[index]
		local ts = tcb[connid].ts_id and ildb.get_ts(tcb[connid].ts_id)
		if ts then
			freesection(id, train, tcb[connid].ts_id, ts)
		end
	end
end)

-- those callbacks are needed to account for created and removed trains (also regarding coupling)

advtrains.te_register_on_create(function(id, train)
	-- let's see what track sections we find here
	local index = atround(train.index)
	local pos = advtrains.path_get(train, index)
	local ts_id = ildb.check_and_repair_ts_at_pos(pos, 1) -- passing connid 1 - that always exists
	if ts_id then
		local ts = ildb.get_ts(ts_id)
		if ts then
			setsection(id, train, ts_id, ts, nil, true)
		else
			atwarn("While placing train, TS didnt exist ",ts_id)
		end
		-- Make train a shunt move
		train.is_shunt = true
	elseif ts_id==nil then
		atlog("Train",id,": Unable to determine whether to block a track section!")
	else
		--atdebug("Train",id,": Outside of interlocked area!")
	end
end)

advtrains.te_register_on_remove(function(id, train)
	if train.il_sections then
		for idx, item in ipairs(train.il_sections) do
			
			local ts = item.ts_id and ildb.get_ts(item.ts_id)
			
			if ts and ts.trains then
				itremove(ts.trains, id)
			end
		end
		train.il_sections = nil
	end
end)