--nodedb.lua
--database of all nodes that have 'save_in_at_nodedb' field set to true in node definition


--serialization format:
--(2byte z) (2byte y) (2byte x) (2byte contentid)
--contentid := (14bit nodeid, 2bit param2)

local function int_to_bytes(i)
	local x=i+32768--clip to positive integers
	local cH = math.floor(x /           256) % 256;
	local cL = math.floor(x                ) % 256;
	return(string.char(cH, cL));
end
local function bytes_to_int(bytes)
	local t={string.byte(bytes,1,-1)}
	local n = 
		t[1] *           256 +
		t[2]
    return n-32768
end
local function l2b(x)
	return x%4
end
local function u14b(x)
	return math.floor(x/4)
end
local ndb={}

--local variables for performance
local ndb_nodeids={}
local ndb_nodes={}

local function ndbget(x,y,z)
	local ny=ndb_nodes[y]
	if ny then
		local nx=ny[x]
		if nx then
			return nx[z]
		end
	end
	return nil
end
local function ndbset(x,y,z,v)
	if not ndb_nodes[y] then
		ndb_nodes[y]={}
	end
	if not ndb_nodes[y][x] then
		ndb_nodes[y][x]={}
	end
	ndb_nodes[y][x][z]=v
end


local path=minetest.get_worldpath()..DIR_DELIM.."advtrains_ndb2"
--load
--nodeids get loaded by advtrains init.lua and passed here
function ndb.load_data(data)
	ndb_nodeids = data and data.nodeids or {}
	local file, err = io.open(path, "rb")
	if not file then
		atwarn("Couldn't load the node database: ", err or "Unknown Error")
	else
		local cnt=0
		local hst_z=file:read(2)
		local hst_y=file:read(2)
		local hst_x=file:read(2)
		local cid=file:read(2)
		while hst_z and hst_y and hst_x and cid and #hst_z==2 and #hst_y==2 and #hst_x==2 and #cid==2 do
			ndbset(bytes_to_int(hst_x), bytes_to_int(hst_y), bytes_to_int(hst_z), bytes_to_int(cid))
			cnt=cnt+1
			hst_z=file:read(2)
			hst_y=file:read(2)
			hst_x=file:read(2)
			cid=file:read(2)
		end
		atlog("nodedb: read", cnt, "nodes.")
		file:close()
	end
end

--save
function ndb.save_data()
	local file, err = io.open(path, "wb")
	if not file then
		atwarn("Couldn't save the node database: ", err or "Unknown Error")
	else
		for y, ny in pairs(ndb_nodes) do
			for x, nx in pairs(ny) do
				for z, cid in pairs(nx) do
					file:write(int_to_bytes(z))
					file:write(int_to_bytes(y))
					file:write(int_to_bytes(x))
					file:write(int_to_bytes(cid))
				end
			end
		end
		file:close()
	end
	return {nodeids = ndb_nodeids}
end

--function to get node. track database is not helpful here.
function ndb.get_node_or_nil(pos)
	-- FIX for bug found on linuxworks server:
	-- a loaded node might get read before the LBM has updated its state, resulting in wrongly set signals and switches
	-- -> Using the saved node prioritarily.
	local node = ndb.get_node_raw(pos)
	if node then
		return node
	else
		--try reading the node from the map
		return minetest.get_node_or_nil(pos)
	end
end
function ndb.get_node(pos)
	local n=ndb.get_node_or_nil(pos)
	if not n then
		return {name="ignore", param2=0}
	end
	return n
end
function ndb.get_node_raw(pos)
	local cid=ndbget(pos.x, pos.y, pos.z)
	if cid then
		local nodeid = ndb_nodeids[u14b(cid)]
		if nodeid then
			return {name=nodeid, param2 = l2b(cid)}
		end
	end
	return nil
end


function ndb.swap_node(pos, node, no_inval)
	if minetest.get_node_or_nil(pos) then
		minetest.swap_node(pos, node)
	end
	ndb.update(pos, node)
end

function ndb.update(pos, pnode)
	local node = pnode or minetest.get_node_or_nil(pos)
	if not node or node.name=="ignore" then return end
	if minetest.registered_nodes[node.name] and minetest.registered_nodes[node.name].groups.save_in_at_nodedb then
		local nid
		for tnid, nname in pairs(ndb_nodeids) do
			if nname==node.name then
				nid=tnid
			end
		end
		if not nid then
			nid=#ndb_nodeids+1
			ndb_nodeids[nid]=node.name
		end
		local resid = (nid * 4) + (l2b(node.param2 or 0))
		ndbset(pos.x, pos.y, pos.z, resid )
		--atdebug("nodedb: updating node", pos, "stored nid",nid,"assigned",ndb_nodeids[nid],"resulting cid",resid)
		advtrains.invalidate_all_paths(pos)
	else
		--at this position there is no longer a node that needs to be tracked.
		--atdebug("nodedb: updating node", pos, "cleared")
		ndbset(pos.x, pos.y, pos.z, nil)
	end
end

function ndb.clear(pos)
	ndbset(pos.x, pos.y, pos.z, nil)
end


--get_node with pseudoload. now we only need track data, so we can use the trackdb as second fallback
--nothing new will be saved inside the trackdb.
--returns:
--true, conn1, conn2, rely1, rely2, railheight   in case everything's right.
--false  if it's not a rail or the train does not drive on this rail, but it is loaded or
--nil    if the node is neither loaded nor in trackdb
--the distraction between false and nil will be needed only in special cases.(train initpos)
function advtrains.get_rail_info_at(pos, drives_on)