"""Database utilities."""
from functools import wraps

from product_review.api import db


class DBTransaction:
    """Database transaction decorator and context manager.

    Instances of this class can be used as a decorator or context manager that wraps
    functionality in a database transaction.
    """

    def __call__(self, func):
        """Call.

        This gets called when the instance is used as a decorator.
        """

        @wraps(func)
        def wrapper(*args, **kwargs):
            with self:
                return func(*args, **kwargs)

        return wrapper

    def __enter__(self):
        """Enter.

        This gets called when the instance is used as a context manager.
        """
        with db.session.begin():
            yield self

    def __exit__(self, exc_type, exc_value, _):
        """Exit.

        This gets called when the instance is used as a context manager.
        """
        if exc_type is None:
            db.session.commit()
        else:
            db.session.rollback()
            raise exc_value


db_transaction = DBTransaction()