# 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.

""" Module defining the Django auth backend class for the Keystone API. """

import datetime
import logging

import pytz

from django.conf import settings
from django.utils.module_loading import import_string
from django.utils.translation import ugettext_lazy as _

from openstack_auth import exceptions
from openstack_auth import user as auth_user
from openstack_auth import utils


LOG = logging.getLogger(__name__)


KEYSTONE_CLIENT_ATTR = "_keystoneclient"


# TODO(stephenfin): Subclass 'django.contrib.auth.backends.BaseBackend' once we
# (only) support Django 3.0
class KeystoneBackend(object):
    """Django authentication backend for use with ``django.contrib.auth``."""

    def __init__(self):
        self._auth_plugins = None

    @property
    def auth_plugins(self):
        if self._auth_plugins is None:
            plugins = settings.AUTHENTICATION_PLUGINS
            self._auth_plugins = [import_string(p)() for p in plugins]
        return self._auth_plugins

    def get_user(self, user_id):
        """Returns the current user from the session data.

        If authenticated, this return the user object based on the user ID
        and session data.

        .. note::

          This required monkey-patching the ``contrib.auth`` middleware
          to make the ``request`` object available to the auth backend class.

        """
        if (hasattr(self, 'request') and
                user_id == self.request.session["user_id"]):
            token = self.request.session['token']
            endpoint = self.request.session['region_endpoint']
            services_region = self.request.session['services_region']
            user = auth_user.create_user_from_token(self.request, token,
                                                    endpoint, services_region)
            return user

        return None

    def _check_auth_expiry(self, auth_ref, margin=None):
        if not utils.is_token_valid(auth_ref, margin):
            msg = _("The authentication token issued by the Identity service "
                    "has expired.")
            LOG.warning("The authentication token issued by the Identity "
                        "service appears to have expired before it was "
                        "issued. This may indicate a problem with either your "
                        "server or client configuration.")
            raise exceptions.KeystoneTokenExpiredException(msg)
        return True

    def _get_auth_backend(self, auth_url, **kwargs):
        for plugin in self.auth_plugins:
            unscoped_auth = plugin.get_plugin(auth_url=auth_url, **kwargs)
            if unscoped_auth:
                return plugin, unscoped_auth
        else:
            msg = _('No authentication backend could be determined to '
                    'handle the provided credentials.')
            LOG.warning('No authentication backend could be determined to '
                        'handle the provided credentials. This is likely a '
                        'configuration error that should be addressed.')
            raise exceptions.KeystoneNoBackendException(msg)

    def authenticate(self, request, auth_url=None, **kwargs):
        """Authenticates a user via the Keystone Identity API."""
        LOG.debug('Beginning user authentication')

        if not auth_url:
            auth_url = settings.OPENSTACK_KEYSTONE_URL

        auth_url, url_fixed = utils.fix_auth_url_version_prefix(auth_url)
        if url_fixed:
            LOG.warning("The OPENSTACK_KEYSTONE_URL setting points to a v2.0 "
                        "Keystone endpoint, but v3 is specified as the API "
                        "version to use by Horizon. Using v3 endpoint for "
                        "authentication.")

        plugin, unscoped_auth = self._get_auth_backend(auth_url, **kwargs)

        # the recent project id a user might have set in a cookie
        recent_project = None
        if request:
            # Grab recent_project found in the cookie, try to scope
            # to the last project used.
            recent_project = request.COOKIES.get('recent_project')
        unscoped_auth_ref = plugin.get_access_info(unscoped_auth)

        # Check expiry for our unscoped auth ref.
        self._check_auth_expiry(unscoped_auth_ref)

        domain_name = kwargs.get('user_domain_name', None)
        domain_auth, domain_auth_ref = plugin.get_domain_scoped_auth(
            unscoped_auth, unscoped_auth_ref, domain_name)
        scoped_auth, scoped_auth_ref = plugin.get_project_scoped_auth(
            unscoped_auth, unscoped_auth_ref, recent_project=recent_project)

        # Abort if there are no projects for this user and a valid domain
        # token has not been obtained
        #
        # The valid use cases for a user login are:
        #    Keystone v2: user must have a role on a project and be able
        #                 to obtain a project scoped token
        #    Keystone v3: 1) user can obtain a domain scoped token (user
        #                    has a role on the domain they authenticated to),
        #                    only, no roles on a project
        #                 2) user can obtain a domain scoped token and has
        #                    a role on a project in the domain they
        #                    authenticated to (and can obtain a project scoped
        #                    token)
        #                 3) user cannot obtain a domain scoped token, but can
        #                    obtain a project scoped token
        if not scoped_auth_ref and domain_auth_ref:
            # if the user can't obtain a project scoped token, set the scoped
            # token to be the domain token, if valid
            scoped_auth = domain_auth
            scoped_auth_ref = domain_auth_ref
        elif not scoped_auth_ref and not domain_auth_ref:
            msg = _('You are not authorized for any projects or domains.')
            raise exceptions.KeystoneNoProjectsException(msg)

        # Check expiry for our new scoped token.
        self._check_auth_expiry(scoped_auth_ref)

        # We want to try to use the same region we just logged into
        # which may or may not be the default depending upon the order
        # keystone uses
        region_name = None
        id_endpoints = scoped_auth_ref.service_catalog.\
            get_endpoints(service_type='identity')
        for id_endpoint in id_endpoints['identity']:
            if auth_url in id_endpoint.values():
                region_name = id_endpoint['region']
                break

        interface = settings.OPENSTACK_ENDPOINT_TYPE

        endpoint = scoped_auth_ref.service_catalog.url_for(
            service_type='identity',
            interface=interface,
            region_name=region_name)

        # If we made it here we succeeded. Create our User!
        unscoped_token = unscoped_auth_ref.auth_token

        user = auth_user.create_user_from_token(
            request,
            auth_user.Token(scoped_auth_ref, unscoped_token=unscoped_token),
            endpoint,
            services_region=region_name)

        if request is not None:
            # if no k2k providers exist then the function returns quickly
            utils.store_initial_k2k_session(auth_url, request, scoped_auth_ref,
                                            unscoped_auth_ref)
            request.session['unscoped_token'] = unscoped_token
            if domain_auth_ref:
                # check django session engine, if using cookies, this will not
                # work, as it will overflow the cookie so don't add domain
                # scoped token to the session and put error in the log
                if utils.using_cookie_backed_sessions():
                    LOG.error('Using signed cookies as SESSION_ENGINE with '
                              'OPENSTACK_KEYSTONE_MULTIDOMAIN_SUPPORT is '
                              'enabled. This disables the ability to '
                              'perform identity operations due to cookie size '
                              'constraints.')
                else:
                    request.session['domain_token'] = domain_auth_ref

            request.user = user
            timeout = settings.SESSION_TIMEOUT
            token_life = user.token.expires - datetime.datetime.now(pytz.utc)
            session_time = min(timeout, int(token_life.total_seconds()))
            request.session.set_expiry(session_time)

            keystone_client_class = utils.get_keystone_client().Client
            session = utils.get_session()
            scoped_client = keystone_client_class(session=session,
                                                  auth=scoped_auth)

            # Support client caching to save on auth calls.
            setattr(request, KEYSTONE_CLIENT_ATTR, scoped_client)

        LOG.debug('Authentication completed.')
        return user

    def get_group_permissions(self, user, obj=None):
        """Returns an empty set since Keystone doesn't support "groups"."""
        # Keystone V3 added "groups". The Auth token response includes the
        # roles from the user's Group assignment. It should be fine just
        # returning an empty set here.
        return set()

    def get_all_permissions(self, user, obj=None):
        """Returns a set of permission strings that the user has.

        This permission available to the user is derived from the user's
        Keystone "roles".

        The permissions are returned as ``"openstack.{{ role.name }}"``.
        """
        if user.is_anonymous or obj is not None:
            return set()
        # TODO(gabrielhurley): Integrate policy-driven RBAC
        #                      when supported by Keystone.
        role_perms = {utils.get_role_permission(role['name'])
                      for role in user.roles}

        services = []
        for service in user.service_catalog:
            try:
                service_type = service['type']
            except KeyError:
                continue
            service_regions = [utils.get_endpoint_region(endpoint) for endpoint
                               in service.get('endpoints', [])]
            if user.services_region in service_regions:
                services.append(service_type.lower())
        service_perms = {"openstack.services.%s" % service
                         for service in services}
        return role_perms | service_perms

    def has_perm(self, user, perm, obj=None):
        """Returns True if the given user has the specified permission."""
        if not user.is_active:
            return False
        return perm in self.get_all_permissions(user, obj)

    def has_module_perms(self, user, app_label):
        """Returns True if user has any permissions in the given app_label.

        Currently this matches for the app_label ``"openstack"``.
        """
        if not user.is_active:
            return False
        for perm in self.get_all_permissions(user):
            if perm[:perm.index('.')] == app_label:
                return True
        return False