local link = ""

function forward(num)
  num = num or 1
  for i = 1, num do
    if turtle.forward() then
      if f == 0 then
        z = z - 1
		updatePos()
      elseif f == 1 then
        x = x + 1
		updatePos()
      elseif f == 2 then
        z = z + 1
		updatePos()
      elseif f == 3 then
        x = x - 1
		updatePos()
      end
      checkFuel(returning)
    else
      return false
    end
  end
  return true
end

function back(num)
  num = num or 1
  for i = 1, num do
    if turtle.back() then
      if f == 0 then
        z = z + 1
		updatePos()
      elseif f == 1 then
        x = x - 1
		updatePos()
      elseif f == 2 then
        z = z - 1
		updatePos()
      elseif f == 3 then
        x = x + 1
		updatePos()
      end
      checkFuel(returning)
    else
      return false
    end
  end
  return true
end

function up(num)
  num = num or 1
  for i = 1, num do
    if turtle.up() then
      y = y + 1
	  updatePos()
      checkFuel(returning)
    else
      return false
    end
  end
  return true
end

function down(num)
  num = num or 1
  for i = 1, num do
    if turtle.down() then
      y = y - 1
	  updatePos()
      checkFuel(returning)
    else
      return false
    end
  end
  return true
end

function left(num)
  num = num or 1
  for i = 1, num do
    turtle.turnLeft()
    f = (f+3)%4
	updatePos()
  end
end

function right(num)
  num = num or 1
  for i = 1, num do
    turtle.turnRight()
    f = (f+1)%4
	updatePos()
  end
end

function updatePos()
	local str = fs.open("info","r").readAll()
	str = str:gsub("x%=%d;","x="..x..";")
    str = str:gsub("y%=%d;","y="..y..";")
    str = str:gsub("z%=%d;","z="..z..";")
    str = str:gsub("f%=%d;","f="..f..";")
	local h = fs.open("info","w")
    h.write(str)
	h.close()
end

--     0 (-z)
-- 3 (-x)  1 (+x)
--     2 (+z)

function home()
  returning = true
  while y ~= 0 do
    if y < 0 then
      turtle.digUp()
      up()
    elseif y > 0 then
      turtle.digDown()
      down()
    end
  end
  if z > 0 then
    while f ~= 0 do
      left()
    end
  elseif z < 0 then
    while f ~= 2 do
      left()
    end
  end
  while z ~= 0 do
    forward()
  end
  if x > 0 then
    while f ~= 3 do
      left()
    end
  elseif x < 0 then
    while f ~= 1 do
      left()
    end
  end
  while x ~= 0 do
    forward()
  end
end

shell.run("info")
shell.run("pastebin run " .. link)
home()