"""
MySQL Connector.

Manages interactions with MySQL
for transcoder RDS databse.
"""

from contextlib import contextmanager

from sqlalchemy import create_engine
from sqlalchemy import pool
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session
from sqlalchemy.orm import sessionmaker

from asset_transcoder import config
from asset_transcoder.api import app


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

    return create_engine(db_url, poolclass=config.POOL_CLASS)


asset_transcoder_db_engine = _create_engine(config.TRANSCODER_DB_URL)
asset_transcoder_session_factory = sessionmaker(bind=asset_transcoder_db_engine)
asset_transcoder_db_session = scoped_session(asset_transcoder_session_factory)
sessions = (asset_transcoder_db_session, )

BaseModel = declarative_base()


@app.teardown_request
def remove_session(exception):
    """For scoped_session, explicitly close session at end of each request.

    Args:
        exception (object): When a teardown function was called because of an
            exception it will be passed an error object.
    """
    for session in sessions:
        session.remove()


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

    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 transcoder_database_session() as session:
            session.execute(query)
    """
    session = asset_transcoder_db_session()
    try:
        yield session
        if not read_only:
            session.commit()
    except Exception:
        session.rollback()
        raise