import hashlib
from typing import Any, Optional

from . import utils
from .otp import OTP


class HOTP(OTP):
    """
    Handler for HMAC-based OTP counters.
    """

    def __init__(
        self,
        s: str,
        digits: int = 6,
        digest: Any = None,
        name: Optional[str] = None,
        issuer: Optional[str] = None,
        initial_count: int = 0,
    ) -> None:
        """
        :param s: secret in base32 format
        :param initial_count: starting HMAC counter value, defaults to 0
        :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
        """
        if digest is None:
            digest = hashlib.sha1
        elif digest in [hashlib.md5, hashlib.shake_128]:
            raise ValueError("selected digest function must generate digest size greater than or equals to 18 bytes")

        self.initial_count = initial_count
        super().__init__(s=s, digits=digits, digest=digest, name=name, issuer=issuer)

    def at(self, count: int) -> str:
        """
        Generates the OTP for the given count.

        :param count: the OTP HMAC counter
        :returns: OTP
        """
        return self.generate_otp(self.initial_count + count)

    def verify(self, otp: str, counter: int) -> bool:
        """
        Verifies the OTP passed in against the current counter OTP.

        :param otp: the OTP to check against
        :param counter: the OTP HMAC counter
        """
        return utils.strings_equal(str(otp), str(self.at(counter)))

    def provisioning_uri(
        self,
        name: Optional[str] = None,
        initial_count: Optional[int] = None,
        issuer_name: Optional[str] = None,
        **kwargs,
    ) -> 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

        :param name: name of the user account
        :param initial_count: starting HMAC counter value, defaults to 0
        :param issuer_name: the name of the OTP issuer; this will be the
            organization title of the OTP entry in Authenticator
        :returns: provisioning URI
        """
        return utils.build_uri(
            self.secret,
            name=name if name else self.name,
            initial_count=initial_count if initial_count else self.initial_count,
            issuer=issuer_name if issuer_name else self.issuer,
            algorithm=self.digest().name,
            digits=self.digits,
            **kwargs,
        )
