local args = {...}
if #args < 1 then
  print("Required parameter: <size>")
  return
elseif tonumber(args[1]) == nil or tonumber(args[1]) % 2 == 1 then
  print("Size must be an even 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 currentLevel = 0
local SQUARE_SIZE = tonumber(args[1]) -- has to be even

local garbageItems = {'minecraft:cobblestone', 'minecraft:gravel', 'minecraft:dirt'}

-- Lua helpers

table.contains = function(array, value)
    for _, targetColumn in pairs(array) do
        if targetColumn == value then
            return true
        end
    end
    return false
end

-- End of Lua helpers

local function discardGarbageItems()
  for i = 1, 16 do
    local data = turtle.getItemDetail(i)
    if data and data.name and table.contains(garbageItems, data.name) then
      turtle.select(i)
      turtle.drop()
    end
  end
  turtle.select(1)
end

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


local function digCurrentLevel()
  local success = true
  while success do
    if currentDirection == RIGHT and currentPosition.x == 0 and currentPosition.y == 0 then
      turnLeft()
      break
    elseif currentDirection == UP and currentPosition.x == SQUARE_SIZE - 1 then
      turnLeft()
      success = mineAndMoveForward()
      turnLeft()
    elseif currentDirection == DOWN and currentPosition.x == 1 then
      if currentPosition.y == SQUARE_SIZE - 1 then
        success = mineAndMoveForward()
        turnLeft()
      else
        turnRight()
        success = mineAndMoveForward()
        turnRight()
      end
    else
      success = mineAndMoveForward()
    end
  end
  return success
end

local function goDownLevel()
  turtle.digDown()
  turtle.down()
  turtle.digDown()
  turtle.down()
  turtle.digDown()
  turtle.down()
  currentLevel = currentLevel + 1
end

local function goUpLevel()
  turtle.digUp()
  turtle.up()
  turtle.digUp()
  turtle.up()
  turtle.digUp()
  turtle.up()
  currentLevel = currentLevel - 1
end

local function goBackToStartPosition()
  if currentLevel == 0 then
    return
  end

  while currentLevel > 0 do
    goUpLevel()
  end

  while currentDirection ~= DOWN do
    turnLeft()
  end
  success = true
  while currentPosition.x ~= 0 and success do
    success = mineAndMoveForward()
  end

  if success then
    while currentDirection ~= RIGHT do
      turnLeft()
    end
    while currentPosition.y ~= 0 and success do
      success = mineAndMoveForward()
    end
  end

  return success
end

local success = true
while success do
  success = digCurrentLevel()
  if success then
    discardGarbageItems()
    goDownLevel()
  end
end

goBackToStartPosition()