text: import calendar
  import datetime
  import hashlib
  import time
  from socket import AF_INET, SOCK_DGRAM, socket
  import struct
  
  from typing import Any, Union, Optional
  
  from . import utils
  from .otp import OTP
  
  
  class TOTP(OTP):
      """
      Handler for time-based OTP counters.
      """
      def __init__(self, s: str, digits: int = 6, digest: Any = hashlib.sha1, name: Optional[str] = None,
                   issuer: Optional[str] = None, interval: int = 30) -> None:
          """
          :param s: secret in base32 format
          :param interval: the time interval in seconds for OTP. This defaults to 30.
          :param digits: number of integers in the OTP. Some apps expect this to be 6 digits, others support more.
          :param digest: digest function to use in the HMAC (expected to be sha1)
          :param name: account name
          :param issuer: issuer
          """
          self.interval = interval
          super().__init__(s=s, digits=digits, digest=digest, name=name, issuer=issuer)
  
      def at(self, for_time: Union[int, datetime.datetime], counter_offset: int = 0) -> str:
          """
          Accepts either a Unix timestamp integer or a datetime object.
  
          To get the time until the next timecode change (seconds until the current OTP expires), use this instead::
  
              totp = pyotp.TOTP(...)
              time_remaining = totp.interval - datetime.datetime.now().timestamp() % totp.interval
  
          :param for_time: the time to generate an OTP for
          :param counter_offset: the amount of ticks to add to the time counter
          :returns: OTP value
          """
          if not isinstance(for_time, datetime.datetime):
              for_time = datetime.datetime.fromtimestamp(int(for_time))
          return self.generate_otp(self.timecode(for_time) + counter_offset)
  
      def now(self) -> str:
          """
          Generate the current time OTP
  
          :returns: OTP value
          """
          return self.generate_otp(self.timecode(datetime.datetime.now()))
      
      def now_ntp(self) -> str:
          """
          Generate the OTP based on current correct time queried from NTP servers
          :returns: OTP value
          """
          
          def get_ntp_time(host="pool.ntp.org"):
              port = 123
              buf = 1024
              address = (host, port)
              msg = '\x1b' + 47 * '\0'
      
              # reference time (in seconds since 1900-01-01 00:00:00)
              TIME1970 = 2208988800  # 1970-01-01 00:00:00
      
              # connect to server
              client = socket(AF_INET, SOCK_DGRAM)
              client.sendto(msg.encode('utf-8'), address)
              msg, address = client.recvfrom(buf)
              
              client.close()
      
              t = struct.unpack("!12I", msg)[10]
              t -= TIME1970
              return t
          
          return self.at(get_ntp_time())
  
      def verify(self, otp: str, for_time: Optional[datetime.datetime] = None, valid_window: int = 0) -> bool:
          """
          Verifies the OTP passed in against the current time OTP.
  
          :param otp: the OTP to check against
          :param for_time: Time to check OTP at (defaults to now)
          :param valid_window: extends the validity to this many counter ticks before and after the current one
          :returns: True if verification succeeded, False otherwise
          """
          if for_time is None:
              for_time = datetime.datetime.now()
  
          if valid_window:
              for i in range(-valid_window, valid_window + 1):
                  if utils.strings_equal(str(otp), str(self.at(for_time, i))):
                      return True
              return False
  
          return utils.strings_equal(str(otp), str(self.at(for_time)))
  
      def provisioning_uri(self, name: Optional[str] = None, issuer_name: Optional[str] = None,
                           image: Optional[str] = None) -> str:
  
          """
          Returns the provisioning URI for the OTP.  This can then be
          encoded in a QR Code and used to provision an OTP app like
          Google Authenticator.
  
          See also:
              https://github.com/google/google-authenticator/wiki/Key-Uri-Format
  
          """
          return utils.build_uri(self.secret, name if name else self.name,
                                 issuer=issuer_name if issuer_name else self.issuer,
                                 algorithm=self.digest().name,
                                 digits=self.digits, period=self.interval, image=image)
  
      def timecode(self, for_time: datetime.datetime) -> int:
          """
          Accepts either a timezone naive (`for_time.tzinfo is None`) or
          a timezone aware datetime as argument and returns the
          corresponding counter value (timecode).
  
          """
          if for_time.tzinfo:
              return int(calendar.timegm(for_time.utctimetuple()) / self.interval)
          else:
              return int(time.mktime(for_time.timetuple()) / self.interval)
  