# 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.

import hashlib

from cryptography import fernet
from oslo_log import log
import six

from keystone.common import fernet_utils
import keystone.conf
from keystone.credential.providers import core
from keystone import exception
from keystone.i18n import _


CONF = keystone.conf.CONF
LOG = log.getLogger(__name__)

# NOTE(lbragstad): Credential key rotation operates slightly different than
# Fernet key rotation. Each credential holds a hash of the key that encrypted
# it. This is important for credential key rotation because it helps us make
# sure we don't over-rotate credential keys. During a rotation of credential
# keys, if any credential has not been re-encrypted with the current primary
# key, we can abandon the key rotation until all credentials have been migrated
# to the new primary key. If we don't take this step, it is possible that we
# could remove a key used to encrypt credentials, leaving them recoverable.
# This also means that we don't need to expose a `[credential] max_active_keys`
# option through configuration. Instead we will use a global configuration and
# share that across all places that need to use FernetUtils for credential
# encryption.
MAX_ACTIVE_KEYS = 3


def get_multi_fernet_keys():
    key_utils = fernet_utils.FernetUtils(
        CONF.credential.key_repository, MAX_ACTIVE_KEYS)
    keys = key_utils.load_keys()
    fernet_keys = [fernet.Fernet(key) for key in keys]
    crypto = fernet.MultiFernet(fernet_keys)

    return crypto, keys


def primary_key_hash(keys):
    """Calculate a hash of the primary key used for encryption."""
    if isinstance(keys[0], six.text_type):
        keys[0] = keys[0].encode('utf-8')
    return hashlib.sha1(keys[0]).hexdigest()


class Provider(core.Provider):
    def encrypt(self, credential):
        """Attempt to encrypt a plaintext credential.

        :param credential: a plaintext representation of a credential
        :returns: an encrypted credential
        """
        crypto, keys = get_multi_fernet_keys()

        try:
            return (
                crypto.encrypt(credential.encode('utf-8')),
                primary_key_hash(keys))
        except (TypeError, ValueError) as e:
            msg = 'Credential could not be encrypted: %s' % str(e)
            LOG.error(msg)
            raise exception.CredentialEncryptionError(msg)

    def decrypt(self, credential):
        """Attempt to decrypt a credential.

        :param credential: an encrypted credential string
        :returns: a decrypted credential
        """
        key_utils = fernet_utils.FernetUtils(
            CONF.credential.key_repository, MAX_ACTIVE_KEYS)
        keys = key_utils.load_keys()
        fernet_keys = [fernet.Fernet(key) for key in keys]
        crypto = fernet.MultiFernet(fernet_keys)

        try:
            if isinstance(credential, six.text_type):
                credential = credential.encode('utf-8')
            return crypto.decrypt(credential).decode('utf-8')
        except (fernet.InvalidToken, TypeError, ValueError):
            msg = _('Credential could not be decrypted. Please contact the'
                    ' administrator')
            LOG.error(msg)
            raise exception.CredentialEncryptionError(msg)