-- ################################
-- Boring by mining turtle
-- version 0.1a
-- http://hevohevo.hatenablog.com/

-- functions
function myRefuel()
  turtle.select(16)  -- fuel item slot is 16
  turtle.refuel()
end

function revolve()
  for i=1, 4 do -- dig four sides
    turtle.dig()
    turtle.turnRight()
  end

  turtle.digDown() -- dig down side

  return turtle.down() -- go down. if failed, return false.
end

function backToHome(n)
  for i=1, n do -- back to home position.
    turtle.up()
  end
end

-- main
myRefuel()

local depth = 0
while revolve() do
  depth = depth +1
end

backToHome(depth)