laag = 0
bezig = true
richting = "down"
tunnel = 0

function doeLaag()
    for i = 1, 4, 1 do
            succes, data = turtle.inspect()
            if data.name  ~= "minecraft:stone" and data.name ~= "minecraft:dirt" and data.name ~= "minecraft:gravel" 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)
        if richting == "up" then turtle.placeUp() else turtle.placeDown() end
        for i =3, 16, 1 do
            turtle.select(i)
             if richting == "up" then turtle.dropUp() else turlte.dropDown() end
        end
        turtle.select(1)
         if richting == "up" then turtle.digUp() else turtle.digDown() end
    end
end

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

function main()
    checkBrandstof()
    if 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
            tunnel = tunnel + 1

            if tunnel == 4 then bezig = false end
    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