"""Mysql Connector."""

import functools
from contextlib import contextmanager

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

from account import config

# please don't use the following private variables directly;
# use db_session
if config.POOL_CLASS == QueuePool:
    _account_engine = create_engine(
        config.DB_URL,
        pool_size=config.POOL_SIZE,
        max_overflow=config.POOL_MAX_OVERFLOW,
        pool_recycle=config.POOL_RECYCLE_MS,
        connect_args=config.CONNECT_ARGS,
    )
else:
    _account_engine = create_engine(config.DB_URL, connect_args=config.CONNECT_ARGS)

BaseModel = declarative_base()


# A session() instance establishes all conversations with the database
# and represents a "staging zone" for all the objects loaded into the
# database session object. Any change made against the objects in the
# session won't be persisted into the database until you call
# session.commit(). If you're not happy about the changes, you can
# revert all of them back to the last commit by calling
# session.rollback()
#
# Description taken from:
# pythoncentral.io/introductory-tutorial-python-sqlalchemy/
_account_session = sessionmaker(bind=_account_engine)


@contextmanager
def session_scope(read_only=False):
    """Provide transactional scope.

    Taken from http://docs.sqlalchemy.org/en/latest/orm/session_basics.html.
    Handles commit, rollback, and closing of sessions. Usage:

    with session_scope() as session:
        session.execute(query)
    """
    session = _account_session()
    try:
        yield session
        if not read_only:
            session.commit()
    except:
        session.rollback()
        raise
    finally:
        session.close()


def db_read_only_session_wrap(func):
    """Wrap shared read-only session.

    Creates a new read-only session if one isn't passed in. This lets us share/pass-in
    a common session across multiple functions.
    """

    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        session = kwargs.pop('session', None)
        if session:
            return func(*args, session=session, **kwargs)
        else:
            with session_scope(read_only=True) as session:
                return func(*args, session=session, **kwargs)

    return wrapper