local args = {...}
if #args < 1 then
  print("Required parameter: <size>")
  return
elseif tonumber(args[1]) == nil then
  print("Size must be a number")
  return
end

local UP = 1
local LEFT = 2
local DOWN = 3
local RIGHT = 4

local DIRECTIONS = {
  [UP] = {x = 1, y = 0}, -- up
  [LEFT] = {x = 0, y = 1}, -- left
  [DOWN] = {x = -1, y = 0}, -- down
  [RIGHT] = {x = 0, y = -1}, -- right
}
local currentDirection = UP
local currentPosition = {x = 0, y = 0}
local TUNNEL_SIZE = tonumber(args[1])
local lastMiningDirection = LEFT

local function mineAndMoveForward()
  turtle.dig()
  success = turtle.forward()
  if success then
    if currentLevel ~= 0 then
      turtle.digUp()
    end
    turtle.digDown()
    currentPosition.x = currentPosition.x + DIRECTIONS[currentDirection].x
    currentPosition.y = currentPosition.y + DIRECTIONS[currentDirection].y
    return true
  end
  return false
end

local function turnLeft()
  turtle.turnLeft()
  currentDirection = currentDirection % 4 + 1
end

local function turnRight()
  turtle.turnRight()
  currentDirection = (currentDirection - 2) % 4 + 1
end

while turtle.getFuelLevel() > 0 do
  if currentDirection == UP then
    mineAndMoveForward()
    if lastMiningDirection == LEFT then
      turnRight()
    else
      turnLeft()
    end
    for i = 1, TUNNEL_SIZE do
      mineAndMoveForward()
    end
    if lastMiningDirection == LEFT then
      turnLeft()
      lastMiningDirection = RIGHT
    else
      turnRight()
      lastMiningDirection = LEFT
    end
    local coalCount = turtle.getItemCount()
    if coalCount > 1 then
      turtle.refuel(coalCount - 1)
    end
  end
end