local pairs = pairs
local tonumber = tonumber

tsm_railcorridors = {}

-- Load node names
dofile(minetest.get_modpath(minetest.get_current_modname()).."/gameconfig.lua")

-- Settings
local setting

-- Probability function
local P = function (float)
	return math.floor(32767 * float)
end

-- Probability for every newly generated mapchunk to get corridors
local probability_railcaves_in_mapchunk = P(0.33333)
setting = tonumber(minetest.settings:get("tsm_railcorridors_probability_railcaves_in_mapchunk"))
-- Extra check to prevent mod griefing in singlenode, mcimported worlds.
local mg_name = minetest.get_mapgen_setting("mg_name")
if mg_name == "singlenode" then
	probability_railcaves_in_mapchunk = P(0)
elseif setting then
	probability_railcaves_in_mapchunk = P(setting)
end

-- Minimal and maximal value of path length (forks don't look up this value)
local way_min = 4
local way_max = 7
setting = tonumber(minetest.settings:get("tsm_railcorridors_way_min"))
if setting then
	way_min = setting
end
setting = tonumber(minetest.settings:get("tsm_railcorridors_way_max"))
if setting then
	way_max = setting
end

-- Probability for every horizontal part of a corridor to be with torches
local probability_torches_in_segment = P(0.5)
setting = tonumber(minetest.settings:get("tsm_railcorridors_probability_torches_in_segment"))
if setting then
	probability_torches_in_segment = P(setting)
end

-- Probability for every part of a corridor to go up or down
local probability_up_or_down = P(0.2)
setting = tonumber(minetest.settings:get("tsm_railcorridors_probability_up_or_down"))
if setting then
	probability_up_or_down = P(setting)
end

-- Probability for every part of a corridor to fork – caution, too high values may cause MT to hang on.
local probability_fork = P(0.04)
setting = tonumber(minetest.settings:get("tsm_railcorridors_probability_fork"))
if setting then
	probability_fork = P(setting)
end

-- Probability for every part of a corridor to contain a chest
local probability_chest = P(0.05)
setting = tonumber(minetest.settings:get("tsm_railcorridors_probability_chest"))
if setting then
	probability_chest = P(setting)
end

-- Probability for every part of a corridor to contain a cart
local probability_cart = P(0.05)
setting = tonumber(minetest.settings:get("tsm_railcorridors_probability_cart"))
if setting then
	probability_cart = P(setting)
end

-- Probability for a rail corridor system to be damaged
local probability_damage = P(0.55)
setting = tonumber(minetest.settings:get("tsm_railcorridors_probability_damage"))
if setting then
	probability_damage = P(setting)
end

-- Enable cobwebs
local place_cobwebs = true
setting = minetest.settings:get_bool("tsm_railcorridors_place_cobwebs")
if setting ~= nil then
	place_cobwebs = setting
end

-- Enable mob spawners
local place_mob_spawners = true
setting = minetest.settings:get_bool("tsm_railcorridors_place_mob_spawners")
if setting ~= nil then
	place_mob_spawners = setting
end

-- Max. and min. heights between rail corridors are generated
local height_min
if mcl_vars.mg_lava then
	height_min = mcl_vars.mg_lava_overworld_max + 2
else
	height_min = mcl_vars.mg_bedrock_overworld_max + 2
end
local height_max = mcl_worlds.layer_to_y(60)

-- Chaos Mode: If enabled, rail corridors don't stop generating when hitting obstacles
local chaos_mode = minetest.settings:get_bool("tsm_railcorridors_chaos") or false

-- End of parameters

if not tsm_railcorridors.nodes.corridor_woods_function then
	local accumulated_chance = 0
	for w=1, #tsm_railcorridors.nodes.corridor_woods do
		accumulated_chance = accumulated_chance + tsm_railcorridors.nodes.corridor_woods[w].chance
	end
	assert(accumulated_chance == 1000, "Rail corridor wood chances add up to "..accumulated_chance.." per mille! (should be 1000 per mille)")
end

-- Random Perlin noise generators
local pr, pr_carts, pr_deco, webperlin_major, webperlin_minor
--local pr_treasures

local function InitRandomizer(seed)
	-- Mostly used for corridor gen.
	pr = PseudoRandom(seed)
	-- Dirt room decorations
	pr_deco = PseudoRandom(seed+25)
	-- Separate randomizer for carts because spawning carts is very timing-dependent
	pr_carts = PseudoRandom(seed-654)
	-- Chest contents randomizer
	--pr_treasures = PseudoRandom(seed+777)
	-- Used for cobweb generation, both noises have to reach a high value for cobwebs to appear
	webperlin_major = PerlinNoise(934, 3, 0.6, 500)
	webperlin_minor = PerlinNoise(834, 3, 0.6, 50)
end

local carts_table = {}

local dirt_room_coords

-- Returns true if pos is inside the dirt room of the current corridor system
local function IsInDirtRoom(pos)
	local min = dirt_room_coords.min
	local max = dirt_room_coords.max
	return pos.x >= min.x and pos.x <= max.x and pos.y >= min.y and pos.y <= max.y and pos.z >= min.z and pos.z <= max.z
end

-- Checks if the mapgen is allowed to carve through this structure and only sets
-- the node if it is allowed. Does never build in liquids.
-- If check_above is true, don't build if the node above is attached (e.g. rail)
-- or a liquid.
local function SetNodeIfCanBuild(pos, node, check_above, can_replace_rail)
	if check_above then
		local abovename = minetest.get_node({x=pos.x,y=pos.y+1,z=pos.z}).name
		local abovedef = minetest.registered_nodes[abovename]
		if (not abovedef) or abovename == "unknown" or abovename == "ignore" or
				(abovedef.groups and abovedef.groups.attached_node) or
				-- This is done because cobwebs are often fake liquids
				(abovedef.liquidtype ~= "none" and abovename ~= tsm_railcorridors.nodes.cobweb) then
			return false
		end
	end
	local name = minetest.get_node(pos).name
	local def = minetest.registered_nodes[name]
	if name ~= "unknown" and name ~= "ignore" and def and
			((def.is_ground_content and def.liquidtype == "none") or
			name == tsm_railcorridors.nodes.cobweb or
			name == tsm_railcorridors.nodes.torch_wall or
			name == tsm_railcorridors.nodes.torch_floor or
			(can_replace_rail and name == tsm_railcorridors.nodes.rail)
			) then
		minetest.set_node(pos, node)
		return true
	else
		return false
	end
end

-- Tries to place a rail, taking the damage chance into account
local function PlaceRail(pos, damage_chance)
	if damage_chance ~= nil and damage_chance > 0 then
		local x = pr:next(0,100)
		if x <= damage_chance then
			return false
		end
	end
	return SetNodeIfCanBuild(pos, {name=tsm_railcorridors.nodes.rail})
end

-- Returns true if the node as point can be considered “ground”, that is, a solid material
-- in which mine shafts can be built into, e.g. stone, but not air or water
local function IsGround(pos)
	local nodename = minetest.get_node(pos).name
	local nodedef = minetest.registered_nodes[nodename]
	return nodename ~= "unknown" and nodename ~= "ignore" and nodedef and nodedef.is_ground_content and nodedef.walkable and nodedef.liquidtype == "none"
end

-- Returns true if rails are allowed to be placed on top of this node
local function IsRailSurface(pos)
	local nodename = minetest.get_node(pos).name
	local nodename_above = minetest.get_node({x=pos.x,y=pos.y+2,z=pos.z}).name
	local nodedef = minetest.registered_nodes[nodename]
	return nodename ~= "unknown" and nodename ~= "ignore" and nodedef and nodedef.walkable and (nodedef.node_box == nil or nodedef.node_box.type == "regular") and nodename_above ~= tsm_railcorridors.nodes.rail
end

-- Checks if the node is empty space which requires to be filled by a platform
local function NeedsPlatform(pos)
	local node = minetest.get_node({x=pos.x,y=pos.y-1,z=pos.z})
	local node2 = minetest.get_node({x=pos.x,y=pos.y-2,z=pos.z})
	local nodedef = minetest.registered_nodes[node.name]
	local falling = minetest.get_item_group(node.name, "falling_node") == 1
	return
		-- Node can be replaced if ground content or rail
		(nodedef and node.name ~= "ignore" and node.name ~= "unknown" and nodedef.is_ground_content) and
		-- Node needs platform if node below is not walkable.
		-- Unless 2 nodes below there is dirt: This is a special case for the starter cube.
		((nodedef.walkable == false and node2.name ~= tsm_railcorridors.nodes.dirt) or
		-- Falling nodes always need to be replaced by a platform, we want a solid and safe ground
		falling),
		-- second return value
		falling
end

-- Create a cube filled with the specified nodes
-- Specialties:
-- * Avoids floating rails
-- * May cut into wood structures of the corridors (alongside with their torches)
-- Arguments:
-- * p: Center position
-- * radius: How many nodes from the center the cube will extend
-- * node: Node to set
-- * replace_air_only: If true, only air can be replaced
-- * wood, post: Wood and post nodes of the railway corridor to cut into (optional)

-- Returns true if all nodes could be set
-- Returns false if setting one or more nodes failed
local function Cube(p, radius, node, replace_air_only, wood, post)
	local y_top = p.y+radius
	local nodedef = minetest.registered_nodes[node.name]
	local solid = nodedef and nodedef.walkable and (nodedef.node_box == nil or nodedef.node_box.type == "regular") and nodedef.liquidtype == "none"
	-- Check if all the nodes could be set
	local built_all = true

	-- If wood has been removed, remod
	local cleanup_torches = {}
	for xi = p.x-radius, p.x+radius do
		for zi = p.z-radius, p.z+radius do
			local column_last_attached = nil
			for yi = y_top, p.y-radius, -1 do
				local ok = false
				local thisnode = minetest.get_node({x=xi,y=yi,z=zi})
				if not solid then
					if yi == y_top then
						local topnode = minetest.get_node({x=xi,y=yi+1,z=zi})
						local topdef = minetest.registered_nodes[topnode.name]
						if topdef and minetest.get_item_group(topnode.name, "attached_node") ~= 1 and topdef.liquidtype == "none" then
							ok = true
						end
					elseif column_last_attached and yi == column_last_attached - 1 then
						ok = false
					else
						ok = true
					end
					if minetest.get_item_group(thisnode.name, "attached_node") == 1 then
						column_last_attached = yi
					end
				else
					ok = true
				end
				local built = false
				if ok then
					if replace_air_only ~= true then
						-- Cut into wood structures (post/wood)
						if post and (xi == p.x or zi == p.z) and thisnode.name == post then
							minetest.set_node({x=xi,y=yi,z=zi}, node)
							built = true
						elseif wood and (xi == p.x or zi == p.z) and thisnode.name == wood then
							local topnode = minetest.get_node({x=xi,y=yi+1,z=zi})
							local topdef = minetest.registered_nodes[topnode.name]
							if topdef and topdef.walkable and topnode.name ~= wood then
								minetest.set_node({x=xi,y=yi,z=zi}, node)
								-- Check for torches around the wood and schedule them
								-- for removal
								if node.name == "air" then
									table.insert(cleanup_torches, {x=xi+1,y=yi,z=zi})
									table.insert(cleanup_torches, {x=xi-1,y=yi,z=zi})
									table.insert(cleanup_torches, {x=xi,y=yi,z=zi+1})
									table.insert(cleanup_torches, {x=xi,y=yi,z=zi-1})
								end
								built = true
							end
						-- Set node normally
						else
							built = SetNodeIfCanBuild({x=xi,y=yi,z=zi}, node)
						end
					else
						if minetest.get_node({x=xi,y=yi,z=zi}).name == "air" then
							built = SetNodeIfCanBuild({x=xi,y=yi,z=zi}, node)
						end
					end
				end
				if not built then
					built_all = false
				end
			end
		end
	end
	-- Remove torches we have detected before
	for c=1, #cleanup_torches do
		local check = minetest.get_node(cleanup_torches[c])
		if check.name == tsm_railcorridors.nodes.torch_wall or check.name == tsm_railcorridors.nodes.torch_floor then
			minetest.set_node(cleanup_torches[c], node)
		end
	end
	return built_all
end

local function DirtRoom(p, radius, height, dirt_mode, decorations_mode)
	local y_bottom = p.y
	local y_top = y_bottom + height + 1
	dirt_room_coords = {
		min = { x = p.x-radius, y = y_bottom, z = p.z-radius },
		max = { x = p.x+radius, y = y_top, z = p.z+radius },
	}
	local built_all = true
	for xi = p.x-radius, p.x+radius do
		for zi = p.z-radius, p.z+radius do
			for yi = y_top, y_bottom, -1 do
				local thisnode = minetest.get_node({x=xi,y=yi,z=zi})
				local built = false
				if xi == p.x-radius or xi == p.x+radius or zi == p.z-radius or zi == p.z+radius or yi == y_bottom or yi == y_top then
					if dirt_mode == 1 or yi == y_bottom then
						built = SetNodeIfCanBuild({x=xi,y=yi,z=zi}, {name=tsm_railcorridors.nodes.dirt})
					elseif (dirt_mode == 2 or dirt_mode == 3) and yi == y_top then
						if minetest.get_item_group(thisnode.name, "falling_node") == 1 then
							built = SetNodeIfCanBuild({x=xi,y=yi,z=zi}, {name=tsm_railcorridors.nodes.dirt})
						end
					end
				else
					if yi == y_bottom + 1 then
						-- crazy rails
						if decorations_mode == 1 then
							local r = pr_deco:next(1,3)
							if r == 2 then
								built = SetNodeIfCanBuild({x=xi,y=yi,z=zi}, {name=tsm_railcorridors.nodes.rail})
							end
						end
					end
					if not built then
						built = SetNodeIfCanBuild({x=xi,y=yi,z=zi}, {name="air"})
					end
				end
				if not built then
					built_all = false
				end
			end
		end
	end
	return built_all
end

local function Platform(p, radius, node, node2)
	-- node2 is secondary platform material for replacing falling nodes
	if not node2 then
		node2 = { name = tsm_railcorridors.nodes.dirt }
	end
	local n1, n2 = {}, {}
	for zi = p.z-radius, p.z+radius do
		for xi = p.x-radius, p.x+radius do
			local np, np2 = NeedsPlatform({x=xi,y=p.y,z=zi})
			if np then
				if np2 then
					--minetest.set_node({x=xi,y=p.y-1,z=zi}, node2)
					table.insert(n1,{x=xi,y=p.y-1,z=zi})
				else
					--minetest.set_node({x=xi,y=p.y-1,z=zi}, node)
					table.insert(n2,{x=xi,y=p.y-1,z=zi})
				end
			end
		end
	end
	minetest.bulk_swap_node(n1,node)
	minetest.bulk_swap_node(n2,node2)
end

-- Chests
local function PlaceChest(pos, param2)
	if SetNodeIfCanBuild(pos, {name=tsm_railcorridors.nodes.chest, param2=param2}) then
		vl_structures.construct_nodes(pos, pos, {tsm_railcorridors.nodes.chest})
		local meta = minetest.get_meta(pos)
		local inv = meta:get_inventory()
		local items = tsm_railcorridors.get_treasures(pr)
		mcl_loot.fill_inventory(inv, "main", items, pr)
	end
end

-- This function checks if a cart has ACTUALLY been spawned.
-- To be calld by minetest.after.
-- This is a workaround thanks to the fact that minetest.add_entity is unreliable as fuck
-- See: https://github.com/minetest/minetest/issues/4759
-- FIXME: Kill this horrible hack with fire as soon you can.
local RecheckCartHack = nil
if not minetest.features.random_state_restore then -- proxy for minetest > 5.9.0, this feature will not be removed
RecheckCartHack = function(params)
	local pos = params[1]
	local cart_id = params[2]
	-- Find cart
	for _, obj in ipairs(minetest.get_objects_inside_radius(pos, 1)) do
		if obj ~= nil and obj:get_luaentity().name == cart_id then
			-- Cart found! We can now safely call the callback func.
			-- (calling it earlier has the danger of failing)
			minetest.log("info", "[tsm_railcorridors] Cart spawn succeeded: "..minetest.pos_to_string(pos))
			tsm_railcorridors.on_construct_cart(pos, obj, pr_carts)
			return
		end
	end
	minetest.log("info", "[tsm_railcorridors] Cart spawn FAILED: "..minetest.pos_to_string(pos))
end
end

-- Try to place a cobweb.
-- pos: Position of cobweb
-- needs_check: If true, checks if any of the nodes above, below or to the side of the cobweb.
-- side_vector: Required if needs_check is true. Unit vector which points towards the side of the cobweb to place.
local function TryPlaceCobweb(pos, needs_check, side_vector)
	local check_passed = false
	if needs_check then
		-- Check for walkable nodes above, below or at the side of the cobweb.
		-- If any of those nodes is walkable, we are fine.
		local check_vectors = {
			side_vector,
			{x=0, y=1, z=0},
			{x=0, y=-1, z=0},
		}

		for c=1, #check_vectors do

			local cpos = vector.add(pos, check_vectors[c])
			local cname = minetest.get_node(cpos).name
			local cdef = minetest.registered_nodes[cname]
			if cname ~= "ignore" and cdef and cdef.walkable then
				check_passed = true
				break
			end
		end

	else
		check_passed = true
	end

	if check_passed then
		return SetNodeIfCanBuild(pos, {name=tsm_railcorridors.nodes.cobweb})
	else
		return false
	end
end

-- 4 wooden pillars around pos at height
local function WoodBulk(pos, height, wood)
	for y=0, height-1 do
		SetNodeIfCanBuild({x=pos.x+1, y=pos.y+y, z=pos.z+1}, {name=wood}, false, true)
		SetNodeIfCanBuild({x=pos.x-1, y=pos.y+y, z=pos.z+1}, {name=wood}, false, true)
		SetNodeIfCanBuild({x=pos.x+1, y=pos.y+y, z=pos.z-1}, {name=wood}, false, true)
		SetNodeIfCanBuild({x=pos.x-1, y=pos.y+y, z=pos.z-1}, {name=wood}, false, true)
	end
end

-- Build a wooden support frame
local function WoodSupport(p, wood, post, torches, dir, torchdir)
	local node_wood = {name=wood}
	local node_fence = {name=post}

	local calc = {
		p.x+dir[1], p.z+dir[2], -- X and Z, added by direction
		p.x-dir[1], p.z-dir[2], -- subtracted
		p.x+dir[2], p.z+dir[1], -- orthogonal
		p.x-dir[2], p.z-dir[1], -- orthogonal, the other way
	}
	--[[ Shape:
		WWW
		P.P
		PrP
		pfp
	W = wood
	P = post (above floor level)
	p = post (in floor level, only placed if no floor)

	From previous generation (for reference):
	f = floor
	r = rail
	. = air
	]]

	-- Don't place those wood structs below open air
	if not (minetest.get_node({x=calc[1], y=p.y+2, z=calc[2]}).name == "air" and
		minetest.get_node({x=calc[3], y=p.y+2, z=calc[4]}).name == "air" and
		minetest.get_node({x=p.x, y=p.y+2, z=p.z}).name == "air") then

		-- Left post and planks
		local left_ok
		left_ok = SetNodeIfCanBuild({x=calc[1], y=p.y-1, z=calc[2]}, node_fence)
		if left_ok then left_ok = SetNodeIfCanBuild({x=calc[1], y=p.y  , z=calc[2]}, node_fence) end
		if left_ok then left_ok = SetNodeIfCanBuild({x=calc[1], y=p.y+1, z=calc[2]}, node_wood, false, true) end

		-- Right post and planks
		local right_ok
		right_ok = SetNodeIfCanBuild({x=calc[3], y=p.y-1, z=calc[4]}, node_fence)
		if right_ok then right_ok = SetNodeIfCanBuild({x=calc[3], y=p.y  , z=calc[4]}, node_fence) end
		if right_ok then right_ok = SetNodeIfCanBuild({x=calc[3], y=p.y+1, z=calc[4]}, node_wood, false, true) end

		-- Middle planks
		local top_planks_ok = false
		if left_ok and right_ok then top_planks_ok = SetNodeIfCanBuild({x=p.x, y=p.y+1, z=p.z}, node_wood) end

		if minetest.get_node({x=p.x,y=p.y-2,z=p.z}).name=="air" then
			if left_ok then SetNodeIfCanBuild({x=calc[1], y=p.y-2, z=calc[2]}, node_fence) end
			if right_ok then SetNodeIfCanBuild({x=calc[3], y=p.y-2, z=calc[4]}, node_fence) end
		end
		-- Torches on the middle planks
		if torches and top_planks_ok then
			-- Place torches at horizontal sides
			SetNodeIfCanBuild({x=calc[5], y=p.y+1, z=calc[6]}, {name=tsm_railcorridors.nodes.torch_wall, param2=torchdir[1]}, true)
			SetNodeIfCanBuild({x=calc[7], y=p.y+1, z=calc[8]}, {name=tsm_railcorridors.nodes.torch_wall, param2=torchdir[2]}, true)
		end
	elseif torches then
		-- Try to build torches instead of the wood structs
		local node = {name=tsm_railcorridors.nodes.torch_floor, param2=minetest.dir_to_wallmounted({x=0,y=-1,z=0})}

		-- Try two different height levels
		local pos1 = {x=calc[1], y=p.y-2, z=calc[2]}
		local pos2 = {x=calc[3], y=p.y-2, z=calc[4]}
		local nodedef1 = minetest.registered_nodes[minetest.get_node(pos1).name]
		local nodedef2 = minetest.registered_nodes[minetest.get_node(pos2).name]

		if nodedef1 and nodedef1.walkable then
			pos1.y = pos1.y + 1
		end
		SetNodeIfCanBuild(pos1, node, true)

		if nodedef2 and nodedef2.walkable then
			pos2.y = pos2.y + 1
		end
		SetNodeIfCanBuild(pos2, node, true)

	end
end

-- Dig out a single corridor section and place wooden structures and torches

-- Returns <success>, <segments>
-- success: true if corridor could be placed entirely
-- segments: Number of segments successfully placed
local function dig_corridor_section(start_point, segment_vector, segment_count, wood, post, up_or_down_prev)
	local p = {x=start_point.x, y=start_point.y, z=start_point.z}
	local torches = pr:next() < probability_torches_in_segment
	local dir = {0, 0}
	local torchdir = {1, 1}
	local node_wood = {name=wood}
	if segment_vector.x == 0 and segment_vector.z ~= 0 then
		dir = {1, 0}
		torchdir = {5, 4}
	elseif segment_vector.x ~= 0 and segment_vector.z == 0 then
		dir = {0, 1}
		torchdir = {3, 2}
	end
	for segmentindex = 0, segment_count-1 do
		local dug
		if segment_vector.y == 0 then
			dug = Cube(p, 1, {name="air"}, false, wood, post)
		else
			dug = Cube(p, 1, {name="air"}, false)
		end
		if not chaos_mode and segmentindex > 0 and not dug then return false, segmentindex end
		-- Add wooden platform, if neccessary. To avoid floating rails
		if segment_vector.y == 0 then
			if segmentindex == 0 and up_or_down_prev then
				-- Thin 1×1 platform directly after going up or down.
				-- This is done to avoid placing too much wood at slopes
				Platform({x=p.x-dir[2], y=p.y-1, z=p.z-dir[1]}, 0, node_wood)
				Platform({x=p.x, y=p.y-1, z=p.z}, 0, node_wood)
				Platform({x=p.x+dir[2], y=p.y-1, z=p.z+dir[1]}, 0, node_wood)
			else
				-- Normal 3×3 platform
				Platform({x=p.x, y=p.y-1, z=p.z}, 1, node_wood)
			end
		else
			-- Sloped bridge
			Platform({x=p.x-dir[1], y=p.y-2, z=p.z-dir[2]}, 0, node_wood)
			Platform({x=p.x, y=p.y-2, z=p.z}, 0, node_wood)
			Platform({x=p.x+dir[1], y=p.y-2, z=p.z+dir[2]}, 0, node_wood)
		end
		if segmentindex % 2 == 1 and segment_vector.y == 0 then
			WoodSupport(p, wood, post, torches, dir, torchdir)
		end

		-- Next way point
		p = vector.add(p, segment_vector)
	end

	-- End of the corridor segment; create the final piece
	local dug
	if segment_vector.y == 0 then
		dug = Cube(p, 1, {name="air"}, false, wood, post)
	else
		dug = Cube(p, 1, {name="air"}, false)
	end
	if not chaos_mode and not dug then return false, segment_count end
	if segment_vector.y == 0 then
		Platform({x=p.x, y=p.y-1, z=p.z}, 1, node_wood)
	end
	return true, segment_count
end

-- Generate a corridor section. Corridor sections are part of a corridor line.
-- This is one short part of a corridor line. It can be one straight section or it goes up or down.
-- It digs out the corridor and places wood structs and torches using the helper function dig_corridor_function,
-- then it places rails, chests, and other goodies.
local function create_corridor_section(waypoint, axis, sign, up_or_down, up_or_down_next, up_or_down_prev, up, wood, post, first_or_final, damage, no_spawner)
	local segamount = 3
	if up_or_down then
		segamount = 1
	end
	if sign then
		segamount = 0-segamount
	end
	local vek = {x=0,y=0,z=0}
	local start = table.copy(waypoint)
	if axis == "x" then
		vek.x=segamount
		if up_or_down and up == false then
			start.x=start.x+segamount
		end
	elseif axis == "z" then
		vek.z=segamount
		if up_or_down and up == false then
			start.z=start.z+segamount
		end
	end
	if up_or_down then
		if up then
			vek.y = 1
		else
			vek.y = -1
		end
	end
	local segcount = pr:next(4,6)
	if up_or_down and up == false then
		Cube(waypoint, 1, {name="air"}, false)
	end
	local corridor_dug, corridor_segments_dug = dig_corridor_section(start, vek, segcount, wood, post, up_or_down_prev)
	local corridor_vek = {x=vek.x*segcount, y=vek.y*segcount, z=vek.z*segcount}

	-- After this: rails
	segamount = 1
	if sign then
		segamount = 0-segamount
	end
	if axis == "x" then
		vek.x=segamount
	elseif axis == "z" then
		vek.z=segamount
	end
	if up_or_down then
		if up then
			vek.y = 1
		else
			vek.y = -1
		end
	end
	-- Calculate chest and cart position
	local chestplace = -1
	local cartplace = -1
	local minseg
	if first_or_final == "first" then
		minseg = 2
	else
		minseg = 1
	end
	if corridor_dug and not up_or_down then
		if pr:next() < probability_chest then
			chestplace = pr:next(minseg, segcount+1)
		end
		if tsm_railcorridors.carts and #tsm_railcorridors.carts > 0 and pr:next() < probability_cart then
			cartplace = pr:next(minseg, segcount+1)
		end
	end
	local railsegcount
	if not chaos_mode and not corridor_dug then
		railsegcount = corridor_segments_dug * 3
	elseif not up_or_down then
		railsegcount = segcount * 3
	else
		railsegcount = segcount
	end
	for i=1,railsegcount do
		local p = {x = waypoint.x + vek.x * i, y = waypoint.y + vek.y * i-1, z = waypoint.z + vek.z * i}

		-- Randomly returns either the left or right side of the main rail.
		-- Also returns offset as second return value.
		local function left_or_right(pos, vek)
			local off
			if pr:next(1, 2) == 1 then
				-- left
				off = {x = -vek.z, y= 0, z = vek.x}
			else
				-- right
				off = {x=vek.z, y= 0, z= -vek.x}
			end
			return vector.add(pos, off), off
		end

		if (minetest.get_node({x=p.x,y=p.y-1,z=p.z}).name=="air" and minetest.get_node({x=p.x,y=p.y-3,z=p.z}).name~=tsm_railcorridors.nodes.rail) then
			p.y = p.y - 1
			if i == chestplace then
				chestplace = chestplace + 1
			end
			if i == cartplace then
				cartplace = cartplace + 1
			end
		end

		-- Chest
		if i == chestplace then
			local cpos, offset = left_or_right(p, vek)
			if minetest.get_node(cpos).name == post or IsInDirtRoom(p) then
				chestplace = chestplace + 1
			else
				PlaceChest(cpos, minetest.dir_to_facedir(offset))
			end
		end

		-- A rail at the side of the track to put a cart on
		if i == cartplace and #tsm_railcorridors.carts > 0 then
			local cpos = left_or_right(p, vek)
			if minetest.get_node(cpos).name == post then
				cartplace = cartplace + 1
			else
				local placed
				if IsRailSurface({x=cpos.x, y=cpos.y-1, z=cpos.z}) then
					placed = PlaceRail(cpos, damage)
				else
					placed = false
				end
				if placed then
					-- We don't put on a cart yet, we put it in the carts table
					-- for later placement
					local cart_type = pr_carts:next(1, #tsm_railcorridors.carts)
					table.insert(carts_table, {pos = cpos, cart_type = cart_type})
				end
			end
		end

		-- Mob spawner (at center)
		if place_mob_spawners and tsm_railcorridors.nodes.spawner and not no_spawner and
				webperlin_major:get_3d(p) > 0.3 and webperlin_minor:get_3d(p) > 0.5 then
			-- Place spawner (if activated in gameconfig),
			-- enclose in cobwebs and setup the spawner node.
			local spawner_placed = SetNodeIfCanBuild(p, {name=tsm_railcorridors.nodes.spawner})
			if spawner_placed then
				local size = 1
				if webperlin_major:get_3d(p) > 0.5 then
					size = 2
				end
				if place_cobwebs then
					Cube(p, size, {name=tsm_railcorridors.nodes.cobweb}, true)
				end
				tsm_railcorridors.on_construct_spawner(p)
				no_spawner = true
			end
		end

		-- Main rail; this places almost all the rails
		if IsRailSurface({x=p.x,y=p.y-1,z=p.z}) then
			PlaceRail(p, damage)
		end

		-- Place cobwebs left and right in the corridor
		if place_cobwebs and tsm_railcorridors.nodes.cobweb then
			-- Helper function to place a cobweb at the side (based on chance an Perlin noise)
			local function cobweb_at_side(basepos, vek)
				if pr:next(1,5) == 1 then
					local h = pr:next(0, 2) -- 3 possible cobweb heights
					local cpos = {x=basepos.x+vek.x, y=basepos.y+h, z=basepos.z+vek.z}
					if webperlin_major:get_3d(cpos) > 0.05 and webperlin_minor:get_3d(cpos) > 0.1 then
						if h == 0 then
							-- No check neccessary at height offset 0 since the cobweb is on the floor
							return TryPlaceCobweb(cpos)
						else
							-- Check nessessary
							return TryPlaceCobweb(cpos, true, vek)
						end
					end
				end
				return false
			end

			-- Right cobweb
			local rvek = {x=-vek.z, y=0, z=vek.x}
			cobweb_at_side(p, rvek)

			-- Left cobweb
			local lvek = {x=vek.z, y=0, z=-vek.x}
			cobweb_at_side(p, lvek)

		end
	end

	local offset = table.copy(corridor_vek)
	local final_point = vector.add(waypoint, offset)
	if up_or_down then
		if up then
			offset.y = offset.y - 1
			final_point = vector.add(waypoint, offset)
		else
			offset[axis] = offset[axis] + segamount
			final_point = vector.add(waypoint, offset)
		end
		-- After going up or down, 1 missing rail piece must be added
		Platform({x=final_point.x,y=final_point.y-1,z=final_point.z}, 0, {name=wood})
		if IsRailSurface({x=final_point.x,y=final_point.y-2,z=final_point.z}) then
			PlaceRail({x=final_point.x,y=final_point.y-1,z=final_point.z}, damage)
		end
	end
	if not corridor_dug then
		return false, no_spawner
	else
		return final_point, no_spawner
	end
end

-- Generate a line of corridors.
-- The corridor can go up/down, take turns and it can branch off, creating more corridor lines.
local function create_corridor_line(waypoint, axis, sign, length, wood, post, damage, no_spawner)
	local wp = waypoint
	local a = axis
	local s = sign
	local ud = false -- Up or down
	local udn = false -- Up or down is next
	local udp = false -- Up or down was previous
	local up = false -- true if going up
	local upp = false -- true if was going up previously
	for i=1,length do
		-- Update previous up/down status
		udp = ud
		-- Can't go up/down if a platform is needed at waypoint
		local needs_platform = NeedsPlatform({x=wp.x,y=wp.y-2,z=wp.z})
		-- Update current up/down status
		if udn and not needs_platform then
			ud = true
			-- Force direction near the height limits
			if wp.y >= height_max - 12 then
				if udp then
					ud = false
				end
				up = false
			elseif wp.y <= height_min + 12 then
				if udp then
					ud = false
				end
				up = true
			else
				-- If previous was up/down, keep the vertical direction
				if udp and not chaos_mode then
					up = upp
				else
					-- Chose random direction
					up = pr:next(1, 2) == 1
				end
			end
			upp = up
		else
			ud = false
		end
		-- Update next up/down status
		if pr:next() < probability_up_or_down and i~=1 and not udn and not needs_platform then
			udn = i < length
		elseif udn and not needs_platform then
			udn = false
		end
		-- Make corridor
		local first_or_final
		if i == length then
			first_or_final = "final"
		elseif i == 1 then
			first_or_final = "first"
		end
		wp, no_spawner = create_corridor_section(wp,a,s, ud, udn, udp, up, wood, post, first_or_final, damage, no_spawner)
		if wp == false then return end
		-- Fork in the road? If so, starts 2-3 new corridor lines and terminates the current one.
		if wp and pr:next() < probability_fork then
			-- 75% chance to fork off in 3 directions (making a crossing)
			-- 25% chance to fork off in 2 directions (making a t-junction)
			local is_crossing = pr:next(0, 3) < 3
			local forks = 2
			if is_crossing then
				forks = 3
			end
			local p = {x=wp.x, y=wp.y, z=wp.z}
			local a2
			if a == "x" then
				a2="z"
			else
				a2="x"
			end
			local fork_dirs = {
				{a2, s}, -- to the side
				{a2, not s}, -- to the other side
				{a, s}, -- straight ahead
			}
			for _= 1, forks do
				local r = pr:next(1, #fork_dirs)
				create_corridor_line(wp, fork_dirs[r][1], fork_dirs[r][2], pr:next(way_min,way_max), wood, post, damage, no_spawner)
				table.remove(fork_dirs, r)
			end
			if is_crossing and not IsInDirtRoom(p) then
				-- 4 large wooden pillars around the center rail
				WoodBulk({x=p.x, y=p.y-1, z=p.z}, 4, wood)
			end
			return
		end
		-- Randomly change sign, toggle axis.
		-- In other words, take a turn.
		if a=="x" then
			a="z"
		elseif a=="z" then
			a="x"
	 	end
		s = pr:next(1, 2) == 1
	end
end

-- Spawns all carts in the carts table and clears the carts table afterwards
local function spawn_carts()
	for c=1, #carts_table do
		local cpos = carts_table[c].pos
		local cart_type = carts_table[c].cart_type
		local node = minetest.get_node(cpos)
		if node.name == tsm_railcorridors.nodes.rail then
			-- FIXME: The cart sometimes fails to spawn
			-- See <https://github.com/minetest/minetest/issues/4759>
			local cart_id = tsm_railcorridors.carts[cart_type]
			minetest.log("info", "[tsm_railcorridors] Cart spawn attempt: "..minetest.pos_to_string(cpos))
			local obj = minetest.add_entity(cpos, cart_id)

			-- This checks if the cart is actually spawned, it's a giant hack!
			-- Note that the callback function is also called there.
			-- TODO: Move callback function to this position when the
			-- minetest.add_entity bug has been fixed (supposedly in 5.9.0?)
			if RecheckCartHack then
				minetest.after(1, RecheckCartHack, {cpos, cart_id})
			else
				tsm_railcorridors.on_construct_cart(cpos, obj, pr_carts)
			end
		end
	end
	carts_table = {}
end

-- Start generation of a rail corridor system
-- main_cave_coords is the center of the floor of the dirt room, from which
-- all corridors expand.
local function create_corridor_system(main_cave_coords)

	-- Dirt room size
	local maxsize = 6
	if chaos_mode then
		maxsize = 9
	end
	local size = pr:next(3, maxsize)

	--[[ Only build if starter coords are in the ground.
	Prevents corridors starting in mid-air or in liquids. ]]
	local check_coords = {
		-- Center of the room, on the floor
		{x=0,y=0,z=0},
		-- Also check near the 4 bottom corners of the dirt room
		{x= size-1, y=0, z=size-1},
		{x=-size+1, y=0, z=size-1},
		{x= size-1, y=0, z=-size+1},
		{x=-size+1, y=0, z=-size+1},
	}
	for c=1, #check_coords do
		if not IsGround(vector.add(main_cave_coords, check_coords[c])) then
			return false
		end
	end

	local center_node = minetest.get_node(main_cave_coords)

	local height = pr:next(4, 7)
	if height > size then
		height = size
	end
	local floor_diff = 1
	if pr:next(0, 100) < 50 then
		floor_diff = 0
	end
	local dirt_mode = pr:next(1,2)
	local rnd = pr:next(1,1000)
	-- Small chance to fill dirt room with random rails
	local decorations_mode = 0
	if rnd == 1000 then
		decorations_mode = 1
	end

	--[[ Starting point: A big hollow dirt cube from which the corridors will extend.
	Corridor generation starts here. ]]
	DirtRoom(main_cave_coords, size, height, dirt_mode, decorations_mode)
	main_cave_coords.y = main_cave_coords.y + 2 + floor_diff

	-- Determine if this corridor system is “damaged” (some rails removed) and to which extent
	local damage = 0
	if pr:next() < probability_damage then
		damage = pr:next(10, 50)
	end

	-- Get wood and fence post types, using gameconfig.

	local wood, post
	if tsm_railcorridors.nodes.corridor_woods_function then
		-- Get wood type by gameconfig function
		wood, post = tsm_railcorridors.nodes.corridor_woods_function(main_cave_coords, center_node)
	else
		-- Select random wood type (found in gameconfig.lua)
		local rnd = pr:next(1,1000)
		local woodtype = 1
		local accumulated_chance = 0

		for w=1, #tsm_railcorridors.nodes.corridor_woods do
			local woodtable = tsm_railcorridors.nodes.corridor_woods[w]
			accumulated_chance = accumulated_chance + woodtable.chance
			if rnd <= accumulated_chance then
				woodtype = w
				break
			end
		end
		wood = tsm_railcorridors.nodes.corridor_woods[woodtype].wood
		post = tsm_railcorridors.nodes.corridor_woods[woodtype].post
	end

	-- Start 2-4 corridors in each direction
	local dirs = {
		{axis="x", axis2="z", sign=false},
		{axis="x", axis2="z", sign=true},
		{axis="z", axis2="x", sign=false},
		{axis="z", axis2="x", sign=true},
	}
	local first_corridor
	local corridors = 2
	for _=1, 2 do
		if pr:next(0,100) < 70 then
			corridors = corridors + 1
		end
	end
	-- Chance for 5th corridor in Chaos Mode
	if chaos_mode and size > 4 then
		if pr:next(0,100) < 50 then
			corridors = corridors + 1
		end
	end
	local centered_crossing = false
	if corridors <= 4 and pr:next(1, 20) >= 11 then
		centered_crossing = true
	end
	-- This moves the start of the corridors in the dirt room back and forth
	local d_max = 3
	if floor_diff == 1 and height <= 4 then
		d_max = d_max + 1
	end
	local from_center_base = size - pr:next(1,d_max)
	for i=1, math.min(4, corridors) do
		local d = pr:next(1, #dirs)
		local dir = dirs[d]
		local side_offset = 0
		if not centered_crossing and size > 3 then
			if i==1 and corridors == 5 then
				side_offset = pr:next(2, size-2)
				if pr:next(1,2) == 1 then
					side_offset = -side_offset
				end
			else
				side_offset = pr:next(-size+2, size-2)
			end
		end
		local from_center = from_center_base
		if dir.sign then
			from_center = -from_center
		end
		if i == 1 then
			first_corridor = {sign=dir.sign, axis=dir.axis, axis2=dir.axis2, side_offset=side_offset, from_center=from_center}
		end
		local coords = vector.add(main_cave_coords, {[dir.axis] = from_center, y=0, [dir.axis2] = side_offset})
		create_corridor_line(coords, dir.axis, dir.sign, pr:next(way_min,way_max), wood, post, damage, false)
		table.remove(dirs, d)
	end
	if corridors == 5 then
		local special_coords = vector.add(main_cave_coords, {[first_corridor.axis2] = -first_corridor.side_offset, y=0, [first_corridor.axis] = first_corridor.from_center})
		create_corridor_line(special_coords, first_corridor.axis, first_corridor.sign, pr:next(way_min,way_max), wood, post, damage, false)
	end

	-- At this point, all corridors were generated and all nodes were set.
	-- We spawn the carts now
	spawn_carts()

	return true
end

vl_structures.register_structure("mineshaft",{
	place_on = {"group:sand","group:grass_block","mcl_core:water_source","group:dirt","mcl_core:dirt_with_grass","mcl_core:gravel","group:material_stone","mcl_core:snow"},
	chunk_probability = 4,
	flags = "place_center_x, place_center_z, force_placement, all_floors",
	y_max = 40,
	y_min = mcl_vars.mg_overworld_min,
	place_func = function(pos,_,pr,blockseed)
		local r = pr:next(-50,-10)
		local p = vector.offset(pos,0,r,0)
		if p.y < mcl_vars.mg_overworld_min + 5 then
			p.y = mcl_vars.mg_overworld_min + 5
		end
		if p.y > -10 then return true end
		InitRandomizer(blockseed)
		create_corridor_system(p)
		return true
	end,

})

--[[ Old Generation code this is VERY slow
-- The rail corridor algorithm starts here
mcl_mapgen_core.register_generator("railcorridors", nil, function(minp, maxp, blockseed, _pr)
	-- We re-init the randomizer for every mapchunk as we start generating in the middle of each mapchunk.
	-- We can't use the mapgen seed as this would make the algorithm depending on the order the mapchunk generate.
	InitRandomizer(blockseed)
	if minp.y < height_max and maxp.y > height_min and pr:next() < probability_railcaves_in_mapchunk then
		-- Keep some distance from the upper/lower mapchunk limits
		local buffer = 5

		-- Do up to 10 tries to start a corridor system
		for t=1,10 do
			-- Get semi-random height in mapchunk
			local y = pr:next(minp.y + buffer, maxp.y - buffer)
			y = math.floor(math.max(height_min + buffer, math.min(height_max - buffer, y)))

			-- Mid point of the mapchunk
			local p = {x=minp.x+math.floor((maxp.x-minp.x)/2), y=y, z=minp.z+math.floor((maxp.z-minp.z)/2)}
			-- Start corridor system at p. Might fail if p is in open air
			minetest.log("verbose", "[tsm_railcorridors] Attempting to start rail corridor system at "..minetest.pos_to_string(p))
			if create_corridor_system(p, pr) then
				minetest.log("info", "[tsm_railcorridors] Generated rail corridor system at "..minetest.pos_to_string(p))
				break
			else
				minetest.log("info", "[tsm_railcorridors] Rail corridor system generation attempt failed at "..minetest.pos_to_string(p).. " (try "..t..")")
			end
		end
	end
end, 10)
--]]