laag = 0
bezig = true
richting = "down"

function doeLaag()
    for i = 1, 4, 1 do
            succes, data = turtle.inspect()
            if data.name  ~= "minecraft:stone" and data.name ~= "minecraft:dirt" then
                checkInventory()
                turtle.select(3)
                turtle.dig()
            end
            turtle.turnLeft()
    end
end

function volgendeLaag()
	if richting == "down"
		turtle.digDown()
		if turtle.down() then
			laag = laag + 1
			return true
		else
			return false
		end
	else
		turtle.digUp()
		turtle.up()
		laag = laag - 1
		if laag == 0 then
			return false
		else
			return true
		end
	end
end

function checkInventory()
    turtle.select(16)
    if turtle.getItemCount() ~= 0 then
        turtle.select(1)
        turtle.placeUp()
        for i =3, 16, 1 do
            turtle.select(i)
            turtle.dropUp()
        end
        turtle.select(1)
        turtle.digUp()
    end
end

function gaTerug()
    for i = 1, laag, 1 do
        turtle.up()
    end
end

function main()
	checkBrandstof()
    if turtle.volgendeLaag then doeLaag() else
			turtle.dig()
			turtle.forward()
			turtle.dig()
			turtle.forward()
			turtle.turnLeft()
			turtle.dig()
			turtle.forward()
			turtle.turnRight()
			if richting == "down" then richting = "up" else richting = "down" end
end

function checkBrandstof()
    if turtle.getFuelLevel() < 1500 then
        turtle.select(2)
        turtle.refuel(1)
    else
        print("Nog voldoende brandstof")
    end
end

while bezig == true do main() end