#    Copyright 2013 Cloudscaling Group, Inc
#
#    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.

"""Database setup and migration commands."""

from oslo_config import cfg

from gceapi import exception
from gceapi.i18n import _

CONF = cfg.CONF


class LazyPluggable(object):
    """A pluggable backend loaded lazily based on some value."""

    def __init__(self, pivot, config_group=None, **backends):
        self.__backends = backends
        self.__pivot = pivot
        self.__backend = None
        self.__config_group = config_group

    def __get_backend(self):
        if not self.__backend:
            if self.__config_group is None:
                backend_name = CONF[self.__pivot]
            else:
                backend_name = CONF[self.__config_group][self.__pivot]
            if backend_name not in self.__backends:
                msg = _('Invalid backend: %s') % backend_name
                raise exception.GceapiException(msg)

            backend = self.__backends[backend_name]
            if isinstance(backend, tuple):
                name = backend[0]
                fromlist = backend[1]
            else:
                name = backend
                fromlist = backend

            self.__backend = __import__(name, None, None, fromlist)
        return self.__backend

    def __getattr__(self, key):
        backend = self.__get_backend()
        return getattr(backend, key)

IMPL = LazyPluggable('backend',
                     config_group='database',
                     sqlalchemy='gceapi.db.sqlalchemy.migration')


def db_sync(version=None):
    """Migrate the database to `version` or the most recent version."""
    return IMPL.db_sync(version=version)


def db_version():
    """Display the current database version."""
    return IMPL.db_version()


def db_initial_version():
    """The starting version for the database."""
    return IMPL.db_initial_version()