# Copyright 2014 Huawei Technologies Co. Ltd
#
# 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.

"""Provider interface to manipulate database."""
import logging

from contextlib import contextmanager
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session
from sqlalchemy.orm import sessionmaker
from threading import local

from compass.db import model
from compass.utils import setting_wrapper as setting


ENGINE = create_engine(setting.SQLALCHEMY_DATABASE_URI, convert_unicode=True)
SESSION = sessionmaker(autocommit=False, autoflush=False)
SESSION.configure(bind=ENGINE)
SCOPED_SESSION = scoped_session(SESSION)

model.BASE.query = SCOPED_SESSION.query_property()

SESSION_HOLDER = local()

model.BASE.query = SCOPED_SESSION.query_property()


def init(database_url):
    """Initialize database.

    :param database_url: string, database url.
    """
    global ENGINE
    global SCOPED_SESSION
    ENGINE = create_engine(database_url, convert_unicode=True)
    SESSION.configure(bind=ENGINE)
    SCOPED_SESSION = scoped_session(SESSION)
    model.BASE.query = SCOPED_SESSION.query_property()


def in_session():
    """check if in database session scope."""
    if hasattr(SESSION_HOLDER, 'session'):
        return True
    else:
        return False


@contextmanager
def session():
    """database session scope.

       .. note::
          To operate database, it should be called in database session.
    """
    if hasattr(SESSION_HOLDER, 'session'):
        logging.error('we are already in session')
        raise Exception('session already exist')
    else:
        new_session = SCOPED_SESSION()
        SESSION_HOLDER.session = new_session

    try:
        yield new_session
        new_session.commit()
    except Exception as error:
        new_session.rollback()
        logging.error('failed to commit session')
        logging.exception(error)
        raise error
    finally:
        new_session.close()
        SCOPED_SESSION.remove()
        del SESSION_HOLDER.session


def current_session():
    """Get the current session scope when it is called.

    :return: database session.
    """
    try:
        return SESSION_HOLDER.session
    except Exception as error:
        logging.error('It is not in the session scope')
        logging.exception(error)
        raise error


def create_db():
    """Create database."""
    model.BASE.metadata.create_all(bind=ENGINE)
    with session() as _s:
        # Initialize default user
        user = model.User(email='admin@abc.com', password='admin')
        logging.info('Init user: %s, %s' % (user.email, user.get_password()))
        _s.add(user)


def drop_db():
    """Drop database."""
    model.BASE.metadata.drop_all(bind=ENGINE)


def create_table(table):
    """Create table.

    :param table: Class of the Table defined in the model.
    """
    table.__table__.create(bind=ENGINE, checkfirst=True)


def drop_table(table):
    """Drop table.

    :param table: Class of the Table defined in the model.
    """
    table.__table__.drop(bind=ENGINE, checkfirst=True)