os.loadAPI("/apis/storage")
local db = storage

local pos = {}
for _, k in ipairs({
  "X", "Y", "Z", "F"
}) do
  local v = db.get(k)
  pos[k] = v and v - 0 or 0
end

local function horizontal (s)
  local d = 0 == pos.F % 2 and "Z" or "X"
  local c = 0 == pos.F % 3 and 1 or -1
  pos[d] = pos[d] + c * s
  db.set(d, pos[d])
end

function forward () horizontal(1) end
function back () horizontal(-1) end

local function turn (d)
  pos.F = (pos.F + 4 + d) % 4
  db.set("F", pos.F)
end

function turnRight () turn(1) end
function turnLeft () turn(-1) end

local function vertical (s)
  pos.Y = pos.Y + s
  db.set("Y", pos.Y)
end

function up () vertical(1) end
function down () vertical(-1) end

get = {
  ["X"] = function () return pos.X end,
  ["Y"] = function () return pos.Y end,
  ["Z"] = function () return pos.Z end,
  ["F"] = function () return pos.F end
}

function setHome ()
  for i, d in ipairs({
    "X", "Y", "Z", "F"
  }) do
    pos[d] = 0
    db.set(d, 0)
  end
end

function hook ()
  local t = turtle
  if t.position then return false end
  t.position = {}
  for i, v in ipairs({
    "forward", "back", "up", "down",
    "turnLeft", "turnRight"
  }) do
    t.position[v] = t[v]
    t[v] = function ()
      local ret = t.position[v]()
      if ret then position[v]() end
      return ret
    end
  end
  return true
end