Quarry Turtle

function refuel()
  if turtle.getFuelLevel() <= 50 then
    for i = 1, 16 do
      turtle.select(i)
      turtle.refuel()
    end
    turtle.select(1)
  end
end

function forward()
  refuel()
  while turtle.detect() do
    turtle.dig()
  end
  turtle.forward()
end

function getnvar(question, limit)
  write(question)
  n = read()
  if tonumber(n) then
    n = tonumber(n)
    if n > limit then
      print("Too big!")
      return getnvar(question, limit)
    else
      return n
    end
  else
    print("That's not a number")
    return getnvar(question, limit)
  end
end

shell.run("clear")
print("Please put a chest behind me.")
width = getnvar("\nHow wide should I dig? ", 32)
depth = getnvar("\n(To dig to the bottom of the world insert my Y coordinate - 6)\nHow deep should I dig? ", 255)
height = 3
for y = 1, depth do
  turtle.digDown()
  turtle.down()
  for x = 1, width do
    for z = 2, width do
      forward()
    end
    for nz = 2, width do
      turtle.back()
    end
    if x ~= width then
      turtle.turnRight()
      forward()
      turtle.turnLeft()
    end
  end
  turtle.turnLeft()
  for nx = 2, width do
    forward()
  end
  turtle.turnLeft()
  for ny = 1, y do
    turtle.up()
  end
  for slot = 1, 16 do
    turtle.select(slot)
    turtle.drop()
  end
  turtle.select(1)
  turtle.turnLeft()
  turtle.turnLeft()
  if y ~= depth then
    for _y = 1, y do
      turtle.down()
    end
  end
end
print("\n\nDone!")