-- ars.lua
-- automatic routesetting

--[[
	The "ARS table" and its effects:
	Every route has (or can have) an associated ARS table:
	ars = {
		[n] = {
			ln = "<line>"			-- either line
			rc = "<routingcode>"  -- or routingcode
			n = true/false -- true = logical not (matches everything that does not have this line/rc)
			conj = { -- and conjunction, optional. This must be true in addition to the main rule
				ln=... / rc=... / n=... -- like toplevel
				conj=... -- can be nested
						-- note that conj cannot have prio, in inherits the prio from main rule
			}
			prio = <num> -- optional, a priority number. If set, enables "multi-ARS" where train can wait for multiple routes at once
			-- or
			c="<a comment>"
		}
		default = true -- Route is the default route for trains
		default_prio -- optional, priority for multi-ars with default route
		default_conj = {...} -- optional, conditions (conjunction) that need to be fulfilled for this to be considered default route
	}
	
	In case a train matches the ARS rules of multiple routes, precedence is as follows:
	1. train matches rules without priority in one or more routes -> first matching route is unconditionally set
	2. train matches rules with priority in one or more routes -> all of the matching routes are set (multi-ars)
			in the order given by priority, first available route is set
	3. route is default=true, default_prio=nil and train matches default_conj (if present) -> first default route is set
	4. one or more routes are default=true, with default_prio set,and train matches default_conj (if present)
			-> all of the matching routes are set (multi-ars) in the order given by priority, first available route is set
	
	For editing, those tables are transformed into lines in a text area:
	{ln=...} -> LN ...
	{rc=...} -> RC ...
	{c=...}  -> #...
	{default=true} -> *
	n -> ! (e.g. ln=..., n=true -> !LN ...)
	prio -> <num> (e.g. ln=..., prio=1 -> 1 LN ...)
	
	conj -> goes on the next line, with an & prepended, e.g.:
		{ln="S1", conj={rc="Left"}} ->
		LN S1
		& RC Left
	
	Example combining everything:
	ars = {
		[1] = {
			ln = "S1"
			n = true
			prio = 4
			conj = {
				rc = "R4"
			}
		}
		default = true
		default_prio = 2
		default_conj = {
			rc = "R5"
			n = true
		}
	} ->
	4 !LN S1
	& RC R4
	2 *
	& !RC R5
	
]]

local il = advtrains.interlocking


local function conj_to_text(conj, txt)
	while conj do
		n = ""
		if conj.n then
			n = "!"
		end
		if conj.ln then
			txt[#txt+1] = "& "..n.."LN "..conj.ln
		elseif conj.rc then
			txt[#txt+1] = "& "..n.."RC "..conj.rc
		end
		conj = conj.conj
	end
end

-- The ARS data are saved in a table format, but are entered in text format. Utility functions to transform between both.
function il.ars_to_text(arstab)
	if not arstab then
		return ""
	end
	
	local txt = {}

	for i, arsent in ipairs(arstab) do
		local prio = ""
		if arsent.prio then
			prio = arsent.prio.." "
		end
		local n = ""
		if arsent.n then
			n = "!"
		end
		if arsent.ln then
			txt[#txt+1] = prio..n.."LN "..arsent.ln
		elseif arsent.rc then
			txt[#txt+1] = prio..n.."RC "..arsent.rc
		elseif arsent.c then
			txt[#txt+1] = "#"..arsent.c
		end
		conj_to_text(arsent.conj, txt)
	end
	
	if arstab.default then
		local prio = ""
		if arstab.default_prio then
			prio = arstab.default_prio.." "
		end
		txt[#txt+1] = prio.."*"
		conj_to_text(arstab.default_conj, txt)
	end
	return table.concat(txt, "\n")
end

local function parse_ruleexp(line)
	local excl, key, val = string.match(line, "^%s*(!?)%s*([RL][CN])%s+(.+)%s*$")
	if key == "RC" then
		return {rc=val, n=(excl=="!")}
	elseif key == "LN" then
		return {ln=val, n=(excl=="!")}
	end