# Copyright 2011 VMware, Inc.
# 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.

from oslo.config import cfg
from oslo.db.sqlalchemy import session
import sqlalchemy as sql

from neutron.db import model_base
from neutron.openstack.common import log as logging

LOG = logging.getLogger(__name__)

BASE = model_base.BASEV2

_FACADE = None


def _create_facade_lazily():
    global _FACADE

    if _FACADE is None:
        _FACADE = session.EngineFacade.from_config(cfg.CONF, sqlite_fk=True)

    return _FACADE


def configure_db():
    """Configure database.

    Establish the database, create an engine if needed, and register
    the models.
    """
    register_models()


def clear_db(base=BASE):
    unregister_models(base)


def get_engine():
    """Helper method to grab engine."""
    facade = _create_facade_lazily()
    return facade.get_engine()


def get_session(autocommit=True, expire_on_commit=False):
    """Helper method to grab session."""
    facade = _create_facade_lazily()
    return facade.get_session(autocommit=autocommit,
                              expire_on_commit=expire_on_commit)


def register_models(base=BASE):
    """Register Models and create properties."""
    try:
        facade = _create_facade_lazily()
        engine = facade.get_engine()
        base.metadata.create_all(engine)
    except sql.exc.OperationalError as e:
        LOG.info(_("Database registration exception: %s"), e)
        return False
    return True


def unregister_models(base=BASE):
    """Unregister Models, useful clearing out data before testing."""
    try:
        facade = _create_facade_lazily()
        engine = facade.get_engine()
        base.metadata.drop_all(engine)
    except Exception:
        LOG.exception(_("Database exception"))