from typing import Any, Union, Optional

import datetime
import time

from . import utils
from .otp import OTP


class TOTP(OTP):
    """
    Handler for time-based OTP counters.
    """
    def __init__(self, *args: Any, interval: int = 30, **kwargs: Any) -> None:
        """
        :param interval: the time interval in seconds
            for OTP. This defaults to 30.
        """
        self.interval = interval
        super(TOTP, self).__init__(*args, **kwargs)

    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 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) -> 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)

    def timecode(self, for_time: datetime.datetime) -> int:
        i = time.mktime(for_time.timetuple())
        return int(i / self.interval)