Railroad busterizer

-- -----------------------------
-- Railroad busterizer
-- pastebin get puUKhwXm bust
-- -----------------------------
function checkFuel()
  if turtle.getFuelLevel() < 10 then
    print('Refuel')
    selectItem('fuel')
    while not turtle.refuel(1) do sleep(5) end
  end
end

function clearUp()
  if turtle.detectUp() then
    turtle.select(16)
    while not turtle.digUp() do turtle.attackUp() end
    turtle.drop()
  else
    turtle.attackUp()
  end
end

function clearDown()
  if turtle.detectDown() then
    turtle.select(16)
    while not turtle.digDown() do turtle.attackDown() end
    turtle.drop()
  else
    turtle.attackDown()
  end
end

function clearFront()
  if turtle.detect() then
    turtle.select(16)
    while not turtle.dig() do turtle.attack() end
    turtle.drop()
  else
    turtle.attack()
  end
end

function clearBack()
  turtle.turnRight()
  turtle.turnRight()
  clearFront()
  turtle.turnRight()
  turtle.turnRight()
end

function goForward()
  while not turtle.forward() do clearFront() end
end

function goBack()
  while not turtle.back() do clearBack() end
end

function goUp()
  while not turtle.up() do clearUp() end
end

function goDown()
  while not turtle.down() do clearDown() end
end

function placeBlock(item)
  selectItem( item )
  while not turtle.placeDown() do clearDown() end
end

function placeFrontBlock(item)
  selectItem( item )
  while not turtle.place() do
    clearFront()
    selectItem( item )
  end
end

function placeBooster()
  clearDown()
  goDown()
  selectItem( 'floor' )
  turtle.digDown()
  goDown()
  clearDown()
  goDown()
  clearDown()
  placeBlock('floor')
  placeFrontBlock('floor')
  turtle.turnRight()
  placeFrontBlock('floor')
  turtle.turnRight()
  placeFrontBlock('floor')
  turtle.turnRight()
  placeFrontBlock('floor')
  turtle.turnRight()
  goUp()
  placeBlock('red_torch')
  goUp()
  placeBlock('floor')
  goUp()
  placeBlock('booster')
end

function selectFrom( slots )
  selected = false
  while not selected do
    for _, slot_num in ipairs(slots) do
      if turtle.getItemCount(slot_num) > 1 then
        turtle.select(slot_num)
        selected = true
        return
      end
    end
    if not selected then
      sleep(5)
    end
  end
end

function selectItem( item )
  inventory = {fuel = {1}, floor = {2, 3, 4, 5, 6}, booster = {7, 8}, red_torch = {9, 10}}
  selectFrom(inventory[item])
end

local lenth = 0
term.clear()
term.setCursorPos(1,1)
print("1: fuel, 2, 3, 4, 5, 6: floor material")
print("7, 8: boosters, 9, 10: red torches")

write("How long the road is? ")
lenth = read()
checkFuel()
steps_to_booster = 7
for a = 0, lenth do
  steps_to_booster = steps_to_booster - 1
  checkFuel()
  goForward()
  if steps_to_booster == 0 then
    placeBooster()
    steps_to_booster = 7
  end
end