progress = 0

function dig_until_forward()
	repeat
		turtle.dig()
	until turtle.forward()
end

function dig_sides()
	turtle.turnLeft()
	for i=1,4 do
		dig_until_forward()
		digDown()
	end
	turtle.turnLeft()
	turtle.turnLeft()
	for i=1,4 do
		turtle.forward()
	end
	for i=1,4 do
		dig_until_forward()
		digDown()
	end
	turtle.turnLeft()
	turtle.turnLeft()
	for i=1,4 do
		turtle.forward()
	end
	turtle.turnRight()
end

repeat
	turtle.select(4)
	dig_until_forward()
	turtle.digDown()

	progress = progress + 1

	if progress % 3 == 0 then
		dig_sides()
	end

	if progress % 8 == 0 then
		if turtle.getItemCount(1) == 0 then
			print("No torches in slot 1")
			os.shutdown()
		end
		turtle.select(1)
		turtle.placeDown()
	end

	if turtle.getFuelLevel() == "unlimited" or turtle.getFuelLevel() > 200 then
		print("No refuel required")
	else
		if turtle.getItemCount(3) == 0 then
			print("No fuel in slot 3")
			os.shutdown()
		end
		turtle.select(3)
		turtle.refuel(2)
	end

	if turtle.getItemCount(16) > 0 then
		if turtle.getItemCount(2) == 0 then
			print("No chests in slot 2")
			os.shutdown()
		end
		turtle.select(2)
		turtle.down()
		turtle.digDown()
		turtle.placeDown()
		for i=4,16 do
			turtle.select(i)
			turtle.dropDown()
			sleep(1)
		end
		turtle.select(4)
	end

until true