from contextlib import contextmanager

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

from config import config as _config


engine = create_engine(
    'mysql+pymysql://{user}:{password}@{host}:{port}/{database_name}'
    '?binary_prefix=true'.format(
        user=_config.DB_USER,
        password=_config.DB_PASS,
        host=_config.DB_HOST,
        port=_config.DB_PORT,
        database_name=_config.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 Exception:
        _session.rollback()
        raise
    finally:
        _session.close()