"""
MySQL Connector.

Manages interactions with MySQL for art_relations databse.
"""

from contextlib import contextmanager

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

from activity_detector import base_config


def _create_engine(db_url):
    """Create engine based on config settings."""
    if base_config.POOL_CLASS == pool.QueuePool:
        db_engine = create_engine(
            db_url,
            pool_size=base_config.POOL_SIZE,
            max_overflow=base_config.POOL_MAX_OVERFLOW,
            pool_recycle=base_config.POOL_RECYCLE_MS)
        return db_engine

    return create_engine(db_url, poolclass=base_config.POOL_CLASS)


ar_db_engine = _create_engine(base_config.AR_DB_URL)
ar_session_factory = sessionmaker(bind=ar_db_engine)
ar_database_session = scoped_session(ar_session_factory)


@contextmanager
def ar_db_session(read_only=False):
    """
    Provide transactional scope around series of operations for art_relations.

    Taken from http://docs.sqlalchemy.org/en/latest/orm/session_basics.html.
    This handles rollback and closing of session, so there is no need
    to do that throughout the code.

    Usage:
        with ar_database_session() as session:
            session.execute(query)
    """
    session = ar_database_session()
    try:
        yield session
        if not read_only:
            session.commit()
    except:
        session.rollback()
        raise