import typing
from hashlib import new as hashlib_new

from redshift_connector import InterfaceError

if typing.TYPE_CHECKING:
    from hashlib import _Hash


class ExtensibleDigest:
    """
    Encodes user/password/salt information in the following way: SHA2(SHA2(password + user) + salt).
    """

    @staticmethod
    def encode(client_nonce: bytes, password: bytes, salt: bytes, algo_name: str, server_nonce: bytes) -> bytes:
        """
        Encodes user/password/salt information in the following way: SHA2(SHA2(password + user) + salt).
        :param client_nonce: The client nonce
        :type client_nonce: bytes
        :param password: The connecting user's password
        :type password: bytes
        :param salt: salt sent by the server
        :type salt: bytes
        :param algo_name: Algorithm name such as "SHA256" etc.
        :type algo_name: str
        :param server_nonce: random number generated by server
        :type server_nonce: bytes
        :return: the digest
        :rtype: bytes
        """
        try:
            hl1: "_Hash" = hashlib_new(name=algo_name)
        except ImportError:
            raise InterfaceError("Unable to encode password with extensible hashing: {}".format(algo_name))
        hl1.update(password)
        hl1.update(salt)
        pass_digest1: bytes = hl1.digest()  # SHA2(user + password)

        hl2: "_Hash" = hashlib_new(name=algo_name)
        hl2.update(pass_digest1)
        hl2.update(server_nonce)
        hl2.update(client_nonce)
        pass_digest2 = hl2.digest()  # SHA2(SHA2(password + user) + salt)

        return pass_digest2