# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""
Secret utilities.

.. versionadded:: 3.5
"""

import hmac

import six


try:
    constant_time_compare = hmac.compare_digest
except AttributeError:
    def constant_time_compare(first, second):
        """Returns True if both string inputs are equal, otherwise False.

        This function should take a constant amount of time regardless of
        how many characters in the strings match. This function uses an
        approach designed to prevent timing analysis by avoiding
        content-based short circuiting behaviour, making it appropriate
        for cryptography.
        """
        if isinstance(first, six.string_types):
            first = first.encode('utf-8')
        if isinstance(second, six.string_types):
            second = second.encode('utf-8')
        if len(first) != len(second):
            return False
        result = 0
        for x, y in zip(first, second):
            result |= ord(x) ^ ord(y)
        return result == 0