Turtle Tunnel v2.1

--place in bottom left corner

local args = {...}

local width = tonumber(args[1])
local height = tonumber(args[2])
local depth = tonumber(args [3])

if table.getn(args) < 3 then
  print('Usage: ' .. shell.getRunningProgram() .. ' <width> <height> <depth>')
  error()
end

if width == nil or height == nil or depth == nil then
  print('Dimensions must be numbers')
  error()
end

if width ~= math.floor(width) or height ~= math.floor(height) or depth ~= math.floor(depth) then
  print('Dimensions must be whole numbers')
  error()
end

if width < 1 or height < 1 or depth < 1 then
  print('All dimensions must be at least 1')
  error()
end

local x = 0
local y = 0 --in minecraft y is really z but the turtles coords are relative to itself so it doesnt matter
local z = 0
local orient = 1

local xDiff = {0, 1, 0, -1}
local yDiff = {1, 0, -1, 0}

function forward()
  x = x + xDiff[orient + 1]
  y = y + yDiff[orient + 1]

  moved = turtle.forward()

  while not moved do
    if turtle.getFuelLevel() == 0 then
        print('Out of fuel\nWaiting for fuel in slot 1...')
        while turtle.getFuelLevel() == 0 do
           turtle.refuel()
        end
    print('Fuel level is: ' .. turtle.getFuelLevel())
    end
    if turtle.detect() then turtle.dig() end
    moved = turtle.forward()
  end

  if z > -depth + 1 and turtle.detectDown() and z > 0 then turtle.digDown() end
  if turtle.detectUp() then turtle.digUp() end
end

function left()
  orient = orient - 1
  orient = (orient % 4)
  turtle.turnLeft()
end

function right()
  orient = orient + 1
  orient = (orient % 4)
  turtle.turnRight()
end

function up()
  if turtle.detectUp() then turtle.digUp() end
  moved = turtle.up()
  if not moved then
    repeat
        if turtle.detectUp() then turtle.digUp() end
        moved = turtle.up()
    until moved
  end

  z = z + 1
  if turtle.detectUp() and z < height -1 then turtle.digUp() end
end

function down()
  if turtle.detectDown() then turtle.digDown() end
  moved = turtle.down()
  if not moved then
    repeat
        if turtle.detectDown() then turtle.digDown() end
        moved = turtle.down()
    until moved
  end

  z = z - 1
  if turtle.detectDown() and z > 0 then turtle.digDown() end
end

function digRow()
  if width > 1 then
    repeat
        forward()
     until y == width - 1 or y == 0
  end
end

function digLayer(direction)
  if z == 0 and height ~= 1 then up()
  elseif z == height then down() end

  if width > 1 then
    if y ~= 0 then right()
    else left() end
  end


  repeat
    digRow()
    if (width > 3 or height > 3) and height ~= 1 and width ~= 1 then
      left()
      left()
    end

    if height > 1 then
      if direction and z < height - 2 then
        up()
        if z < height - 2 then up() end
        if z < height - 2 then up() end

      elseif z > 1 then
        down()
        if z > 1 then down() end
        if z > 1 then down() end
      end
    end

    until z <= 1 or z >= height -2

    if (width > 3 or height > 3) and height ~= 1 then digRow() end

    while orient ~= 1 do
      if orient == 2 then left()
      else right()
    end
  end
end

function digTunnel()
  for n = 1, depth do
    forward()
    digLayer((n % 2) ~= 0)
  end
end

if width == 1 and height <= 2 then
  for n = 1, depth do
    forward()
    if height == 2 then turtle.digUp() end
  end
else
  digTunnel()
end

while z > 0 do down() end