# vim: tabstop=4 shiftwidth=4 softtabstop=4

# Copyright 2011 OpenStack LLC.
# 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.

"""
This auth module is intended to allow Openstack client-tools to select from a
variety of authentication strategies, including NoAuth (the default), and
Keystone (an identity management system).

    > auth_plugin = AuthPlugin(creds)

    > auth_plugin.authenticate()

    > auth_plugin.auth_token
    abcdefg

    > auth_plugin.management_url
    http://service_endpoint/
"""
import json
import logging
import urlparse

import httplib2

from glance.common import exception


logger = logging.getLogger('glance.common.auth')


class BaseStrategy(object):
    def __init__(self):
        self.auth_token = None
        # TODO(sirp): Should expose selecting public/internal/admin URL.
        self.management_url = None

    def authenticate(self):
        raise NotImplementedError

    @property
    def is_authenticated(self):
        raise NotImplementedError

    @property
    def strategy(self):
        raise NotImplementedError


class NoAuthStrategy(BaseStrategy):
    def authenticate(self):
        pass

    @property
    def is_authenticated(self):
        return True

    @property
    def strategy(self):
        return 'noauth'


class KeystoneStrategy(BaseStrategy):
    MAX_REDIRECTS = 10

    def __init__(self, creds):
        self.creds = creds
        super(KeystoneStrategy, self).__init__()

    def check_auth_params(self):
        # Ensure that supplied credential parameters are as required
        for required in ('username', 'password', 'auth_url',
                         'strategy'):
            if required not in self.creds:
                raise exception.MissingCredentialError(required=required)
        if self.creds['strategy'] != 'keystone':
            raise exception.BadAuthStrategy(expected='keystone',
                                            received=self.creds['strategy'])
        # For v2.0 also check tenant is present
        if self.creds['auth_url'].rstrip('/').endswith('v2.0'):
            if 'tenant' not in self.creds:
                raise exception.MissingCredentialError(required='tenant')

    def authenticate(self):
        """Authenticate with the Keystone service.

        There are a few scenarios to consider here:

        1. Which version of Keystone are we using? v1 which uses headers to
           pass the credentials, or v2 which uses a JSON encoded request body?

        2. Keystone may respond back with a redirection using a 305 status
           code.

        3. We may attempt a v1 auth when v2 is what's called for. In this
           case, we rewrite the url to contain /v2.0/ and retry using the v2
           protocol.
        """
        def _authenticate(auth_url):
            # If OS_AUTH_URL is missing a trailing slash add one
            if not auth_url.endswith('/'):
                auth_url += '/'
            token_url = urlparse.urljoin(auth_url, "tokens")
            # 1. Check Keystone version
            is_v2 = auth_url.rstrip('/').endswith('v2.0')
            if is_v2:
                self._v2_auth(token_url)
            else:
                self._v1_auth(token_url)

        self.check_auth_params()
        auth_url = self.creds['auth_url']
        for _ in range(self.MAX_REDIRECTS):
            try:
                _authenticate(auth_url)
            except exception.AuthorizationRedirect as e:
                # 2. Keystone may redirect us
                auth_url = e.url
            except exception.AuthorizationFailure:
                # 3. In some configurations nova makes redirection to
                # v2.0 keystone endpoint. Also, new location does not
                # contain real endpoint, only hostname and port.
                if 'v2.0' not in auth_url:
                    auth_url = urlparse.urljoin(auth_url, 'v2.0/')
            else:
                # If we sucessfully auth'd, then memorize the correct auth_url
                # for future use.
                self.creds['auth_url'] = auth_url
                break
        else:
            # Guard against a redirection loop
            raise exception.MaxRedirectsExceeded(redirects=self.MAX_REDIRECTS)

    def _v1_auth(self, token_url):
        creds = self.creds

        headers = {}
        headers['X-Auth-User'] = creds['username']
        headers['X-Auth-Key'] = creds['password']

        tenant = creds.get('tenant')
        if tenant:
            headers['X-Auth-Tenant'] = tenant

        resp, resp_body = self._do_request(token_url, 'GET', headers=headers)

        def _management_url(self, resp):
            for url_header in ('x-image-management-url',
                               'x-server-management-url',
                               'x-glance'):
                try:
                    return resp[url_header]
                except KeyError as e:
                    not_found = e
            raise not_found

        if resp.status in (200, 204):
            try:
                self.management_url = _management_url(self, resp)
                self.auth_token = resp['x-auth-token']
            except KeyError:
                raise exception.AuthorizationFailure()
        elif resp.status == 305:
            raise exception.AuthorizationRedirect(resp['location'])
        elif resp.status == 400:
            raise exception.AuthBadRequest(url=token_url)
        elif resp.status == 401:
            raise exception.NotAuthenticated()
        elif resp.status == 404:
            raise exception.AuthUrlNotFound(url=token_url)
        else:
            raise Exception(_('Unexpected response: %s' % resp.status))

    def _v2_auth(self, token_url):
        def get_endpoint(service_catalog):
            """
            Select an endpoint from the service catalog

            We search the full service catalog for services
            matching both type and region. If the client
            supplied no region then any 'image' endpoint
            is considered a match. There must be one -- and
            only one -- successful match in the catalog,
            otherwise we will raise an exception.
            """
            # FIXME(sirp): for now just use the public url.
            endpoint = None
            region = self.creds.get('region')
            for service in service_catalog:
                try:
                    service_type = service['type']
                except KeyError:
                    msg = _('Encountered service with no "type": %s' % service)
                    logger.warn(msg)
                    continue

                if service_type == 'image':
                    for ep in service['endpoints']:
                        if region is None or region == ep['region']:
                            if endpoint is not None:
                                # This is a second match, abort
                                raise exception.RegionAmbiguity(region=region)
                            endpoint = ep
            if endpoint is None:
                raise exception.NoServiceEndpoint()
            return endpoint['publicURL']

        creds = self.creds

        creds = {
            "auth": {
                "tenantName": creds['tenant'],
                "passwordCredentials": {
                    "username": creds['username'],
                    "password": creds['password']
                    }
                }
            }

        headers = {}
        headers['Content-Type'] = 'application/json'
        req_body = json.dumps(creds)

        resp, resp_body = self._do_request(
                token_url, 'POST', headers=headers, body=req_body)

        if resp.status == 200:
            resp_auth = json.loads(resp_body)['access']
            self.management_url = get_endpoint(resp_auth['serviceCatalog'])
            self.auth_token = resp_auth['token']['id']
        elif resp.status == 305:
            raise exception.RedirectException(resp['location'])
        elif resp.status == 400:
            raise exception.AuthBadRequest(url=token_url)
        elif resp.status == 401:
            raise exception.NotAuthenticated()
        elif resp.status == 404:
            raise exception.AuthUrlNotFound(url=token_url)
        else:
            raise Exception(_('Unexpected response: %s') % resp.status)

    @property
    def is_authenticated(self):
        return self.auth_token is not None

    @property
    def strategy(self):
        return 'keystone'

    @staticmethod
    def _do_request(url, method, headers=None, body=None):
        headers = headers or {}
        conn = httplib2.Http()
        conn.force_exception_to_status_code = True
        headers['User-Agent'] = 'glance-client'
        resp, resp_body = conn.request(url, method, headers=headers, body=body)
        return resp, resp_body


def get_plugin_from_strategy(strategy, creds=None):
    if strategy == 'noauth':
        return NoAuthStrategy()
    elif strategy == 'keystone':
        return KeystoneStrategy(creds)
    else:
        raise Exception(_("Unknown auth strategy '%s'") % strategy)
