from contextlib import contextmanager

from sqlalchemy import create_engine
from sqlalchemy.exc import SQLAlchemyError
from sqlalchemy.orm import scoped_session, sessionmaker

from apollo_main_db.apollo.models import ApolloGoVersion
from retrieve_and_save_mobile_versions.config import Config


_config = Config()
engine = create_engine(
    'mysql+pymysql://{user}:{password}@{host}:{port}/{database_name}'.format(
        user=_config.MYSQL_DB_USER,
        password=_config.MYSQL_DB_PASS,
        host=_config.MYSQL_DB_HOST,
        port=_config.MYSQL_DB_PORT,
        database_name=_config.MYSQL_DB_NAME),
    pool_recycle=_config.DB_POOL_RECYCLE, pool_size=_config.DB_POOL_SIZE
)
_session_factory = scoped_session(sessionmaker(bind=engine))
_session = _session_factory()


@contextmanager
def session_scope():
    """Provide a transactional scope around a series of operations.
    """

    try:
        yield _session
        _session.commit()
    except SQLAlchemyError:
        _session.rollback()
        raise
    finally:
        _session.close()


def get_latest_version_query(os):
    """Return latest saved into DB versions data.
    """

    return (
        _session.query(ApolloGoVersion)
        .filter(ApolloGoVersion.os == os)
        .order_by(ApolloGoVersion.created_at.desc())
        .first()
    )