module Logger::Period

def next_rotate_time(now, shift_age)
  case shift_age
  when 'daily', :daily
    t = Time.mktime(now.year, now.month, now.mday) + SiD
  when 'weekly', :weekly
    t = Time.mktime(now.year, now.month, now.mday) + SiD * (7 - now.wday)
  when 'monthly', :monthly
    t = Time.mktime(now.year, now.month, 1) + SiD * 32
    return Time.mktime(t.year, t.month, 1)
  when 'now', 'everytime', :now, :everytime
    return now
  else
    raise ArgumentError, "invalid :shift_age #{shift_age.inspect}, should be daily, weekly, monthly, or everytime"
  end
  if t.hour.nonzero? or t.min.nonzero? or t.sec.nonzero?
    hour = t.hour
    t = Time.mktime(t.year, t.month, t.mday)
    t += SiD if hour > 12
  end
  t
end