class CalendarUtils:
  """
  日期工具類
  """

  @staticmethod
  def delta_day(delta=0):
    """
    :param delta:  偏移量 
    :return:    0今天, 1昨天, 2前天, -1明天 ...
    """
    return (datetime.now() + timedelta(days=delta)).strftime('%Y-%m-%d')

  @staticmethod
  def delta_week(delta=0):
    """
    :param delta:  偏移量
    :return:    0本周, -1上周, 1下周 ...
    """
    now = datetime.now()
    week = now.weekday()
    _from = (now - timedelta(days=week - 7 * delta)).strftime('%Y-%m-%d')
    _to = (now + timedelta(days=6 - week + 7 * delta)).strftime('%Y-%m-%d')
    return _from, _to

  @staticmethod
  def delta_month(delta=0):
    """
    :param delta:  偏移量 
    :return:    0本月, -1上月, 1下月, 下下個月...
    """

    def _delta_month(__year, __month, __delta):
      _month = __month + __delta
      if _month < 1:
        delta_year = math.ceil(abs(_month) / 12)
        delta_year = delta_year if delta_year else 1
        __year -= delta_year
        _month = delta_year * 12 + __month + __delta
      elif _month > 12:
        delta_year = math.floor(_month / 12)
        __year += delta_year
        _month %= 12
      return __year, _month

    now = datetime.now()
    _from = datetime(*_delta_month(now.year, now.month, delta), 1)

    _to = datetime(*_delta_month(_from.year, _from.month, 1), 1) - timedelta(days=1)
    return _from.strftime('%Y-%m-%d'), _to.strftime('%Y-%m-%d')

  @staticmethod
  def delta_year(delta=0):
    """
    :param delta:  偏移量
    :return:    0今年, -1去年, 1明年 ...
    """
    now = datetime.now()
    _from = datetime(now.year + delta, 1, 1)
    _to = datetime(_from.year + 1, 1, 1) - timedelta(days=1)
    return _from.strftime('%Y-%m-%d'), _to.strftime('%Y-%m-%d')
    

if __name__ == '__main__':
  print('當前日期: ', datetime.now())
  print('*' * 40)
  print('今天: ', CalendarUtils.delta_day())
  print('昨天: ', CalendarUtils.delta_day(-1))
  print('前天: ', CalendarUtils.delta_day(-2))
  print('明天: ', CalendarUtils.delta_day(1))
  print('后天: ', CalendarUtils.delta_day(2))
  print('*' * 40)
  print('本周: ', CalendarUtils.delta_week())
  print('上周: ', CalendarUtils.delta_week(-1))
  print('下周: ', CalendarUtils.delta_week(1))
  print('*' * 40)
  print('本月: ', CalendarUtils.delta_month())
  print('上月: ', CalendarUtils.delta_month(-1))
  print('下月: ', CalendarUtils.delta_month(1))
  print('*' * 40)
  print('本年: ', CalendarUtils.delta_year())
  print('去年: ', CalendarUtils.delta_year(-1))
  print('明年: ', CalendarUtils.delta_year(1))