length = 600
refuel_value = 2

-- If an additional argument is given, it will be used as length for the tunnel
--if #arg > 2 then
--  length = tonumber(arg[2])
--end

function dig_full()
  refuelTurtle()

  for i = 1, length do
    if turtle_is_full() then
      return_to_chest(i)
    else
      dig_forward()
    end
  end
  print('returning to chest')
  print(length)

  -- turn around
  turtle.turnRight()
  turtle.turnRight()

  for i = 1, length do
    refuelTurtle()
    turtle.forward()
  end

  -- make sure that the turtle is in front of a chest
  while not turtle.detect() do
    turtle.forward()
  end

  emptyInventory()
end

function return_to_chest(nr_blocks)
  print('returning to chest')
  print(nr_blocks)

  -- turn around
  turtle.turnRight()
  turtle.turnRight()

  for i = 1, nr_blocks do
    refuelTurtle()
    turtle.forward()
  end

  -- make sure that the turtle is in front of a chest
  while not turtle.detect() do
    turtle.forward()
  end

  emptyInventory()

  -- turn around
  turtle.turnRight()
  turtle.turnRight()

  for i = 1, nr_blocks do
    refuelTurtle()
    turtle.forward()
  end
end

function emptyInventory()
  for i = 2, 16 do
    turtle.select(i)
    turtle.drop()
  end

  turtle.select(1)
end

function turtle_is_full()
  return turtle.getItemCount(16) > 0
end

function dig_small_tunnel()
  dig_forward()
  dig_down()
  dig_up()
end

function dig_up()
  while turtle.detectUp() do
    turtle.digUp()
  end

  turtle.up()
end

function dig_down()
  while turtle.detectDown() do
    turtle.digDown()
  end

  turtle.down()
end

function dig_forward()
  while turtle.detect() do
    turtle.dig()
  end

  while turtle.detectUp() do
    turtle.digUp()
  end

  while turtle.detectDown() do
    turtle.digDown()
  end

  refuelTurtle()
  turtle.forward()
end

function refuelTurtle()
  -- coal has a burn value of 80, below 40 means than only half a coal is left
  if turtle.getFuelLevel() < 40 then
    print('Fuel value below 40, trying to refuel...')
    local success = turtle.refuel(refuel_value)
    if success then
      print('Refueled successfully')
    end
  end
end

print('starting to dig')
dig_full()