function main()
	refuelAnyTo(200)
	print("Fuel Level: " .. turtle.getFuelLevel())
	cube(2,2,10)
	undoAll()
end

function row(n,l,r)
	addGroup()
	l()
	for i = 1,n do
		dig()
		waitfor(forward)
	end
	r()
	dig()
	waitfor(forward)
	r()
	for i = 1,n do
		dig()
		waitfor(forward)
	end
	l()
	replaceGroup({turtle.forward})
end

function rectangle(x_max,y_max)
	addGroup()
	for x = 1,x_max-1 do
		row(y_max,left,right)
		dig()
		waitfor(forward)
	end
	row(y_max,left,right)
	digDown()
	waitfor(down)
	left()
	left()
	for x = 1,x_max-1 do
		row(y_max,right,left)
		dig()
		waitfor(forward)
	end
	row(y_max,right,left)
	digDown()
	waitfor(down)
	left()
	left()
	replaceGroup({turtle.down,turtle.down})
end

function cube(x_max,y_max,z_max)
	for z = 1,z_max-1 do
		rectangle(x_max,y_max)
	end
end

careful = {1,2,3}

path = {}
index = 0

undo_mapping = {}

function track(original)
	return function()
		while #path > index do
			table.remove(path)
		end
		if original() then
			index = index + 1
			table.insert(path,original)
			return true
		end
		return false
	end
end

function inverse(func_a, func_b)
	undo_mapping[func_a] = func_b
	undo_mapping[func_b] = func_a
	return track(func_a), track(func_b)
end

down,up = inverse(turtle.down,turtle.up)
left,right = inverse(turtle.turnLeft,turtle.turnRight)
forward,back = inverse(turtle.forward,turtle.back)

function digDown()
	if careful and not compare(careful, turtle.compareDown) then
		return false
	end
	turtle.digDown()
	return true
end

function dig()
	if careful and not compare(careful, turtle.compare) then
		return false
	end
	turtle.dig()
	return true
end

function checkFull()
		if turtle.getItemCount(9) > 0 then
			undoAll()
			dropMaterials()
			redoAll()
		end
end

function dropMaterials()
	--Done Manually now
	pause()
end

function undoAll()
	while undoGroup() do
	end
end

function undoGroup()
	while index > 0 do
		f = undo_mapping[path[index]]
		index = index - 1
		if not f then
			--print('Group undo '..index)
			return true
		end
		while not f() do
			pause()
		end
	end
	return false
end

function replaceGroup(replacement)
	while index > 0 do
		f = undo_mapping[path[index]]
		index = index - 1
		table.remove(path)
		if not f then
			for i,v in ipairs(replacement) do
				table.insert(path,v)
				index = index + 1
			end
			return true
		end
	end
	return false
end

function redoAll()
	while index < #path do
		index = index + 1
		f = path[index]
		while type(f) == 'function' and not f() do
			pause()
		end
	end
end

function addGroup()
	while #path > index do
		table.remove(path)
	end
	table.insert(path,0)
	index = index + 1
	--print('New group at '..index)
end

function pause()
	print("Press Enter when done")
	read()
end

function waitfor(f)
	while not f() do
		pause()
	end
end

function resetHistory()
	path = {}
	index = 0
end

function refuelAnyTo(fuelLevel)
	for i = 1,16 do
		turtle.select(i)
		if refuelTo(fuelLevel) then
			return true
		end
	end
	return false
end

function refuelTo(fuelLevel)
	while turtle.getFuelLevel() < fuelLevel do
		if not turtle.refuel(1) then
			return false
		end
		print(turtle.getFuelLevel())
	end
	return true
end

function digToBottom()
	repeat
		digDown()
	until not down()
end

function directControl()
	print('Entering Direct Control Mode')
	local mapping={
	[17]=forward,
	[31]=back,
	[30]=turnLeft,
	[32]=turnRight,
	[16]=up,
	[18]=down
	}
	while true do
		e,v=os.pullEvent('key')
		if v == 28 then
			break
		end
		f = mapping[v]
		if f then
			f()
		end
	end
	print('Leaving Direct Control Mode')
end

function compare(slots, compare_function)
	for i,v in ipairs(slots) do
		turtle.select(v)
		if compare_function() then
			return true
		end
	end
	return false
end

status,msg  = pcall(main)
if not status then
	print(msg)
	undoAll()
end