from datetime import date

from django.conf import settings

from django.utils.http import int_to_base36, base36_to_int

class PasswordResetTokenGenerator(object):

    """

    Stratgy object used to generate and check tokens for the password

    reset mechanism.

    """

    def make_token(self, user):

        """

        Returns a token that can be used once to do a password reset

        for the given user.

        """

        return self._make_token_with_timestamp(user, self._num_days(self._today()))

    def check_token(self, user, token):

        """

        Check that a password reset token is correct for a given user.

        """

        # Parse the tokem

        try:

            ts_b36, hash = token.split("-")

        except ValueError:

            return False

        try:

            ts = base36_to_int(ts_b36)

        except ValueError:

            return False

        # Check that the timestamp/uid has not been tampered with

        if self._make_token_with_timestamp(user, ts) != token:

            return False

        # Check the timestamp is within limit

        if (self._num_days(self._today()) - ts) > settings.PASSWORD_RESET_TIMEOUT_DAYS:

            return False

        return True

    def _make_token_with_timestamp(self, user, timestamp):

        # timestamp is number of days since 2001-1-1.  Converted to

        # base 36, this gives us a 3 digit string until about 2121

        ts_b36 = int_to_base36(timestamp)

        # By hashing on the internal state of the user and using state

        # that is sure to change (the password salt will change as soon as

        # the password is set, at least for current Django auth, and

        # last_login will also change), we produce a hash that will be

        # invalid as soon as it is used.

        # We limit the hash to 20 chars to keep URL short

        from django.utils.hashcompat import sha_constructor

        hash = sha_constructor(settings.SECRET_KEY + unicode(user.id) +

                               user.password + unicode(user.last_login) +

                               unicode(timestamp)).hexdigest()[::2]

        return "%s-%s" % (ts_b36, hash)

    def _num_days(self, dt):

        return (dt - date(2001,1,1)).days

    def _today(self):

        # Used for mocking in tests

        return date.today()

default_token_generator = PasswordResetTokenGenerator()