from datetime import datetime

import sqlalchemy as sa


class Timestamp(object):
    """Adds `created` and `updated` columns to a derived declarative model.

    The `created` column is handled through a default and the `updated`
    column is handled through a `before_update` event that propagates
    for all derived declarative models.

    ::


        import sqlalchemy as sa
        from sqlalchemy_utils import Timestamp


        class SomeModel(Base, Timestamp):
            __tablename__ = 'somemodel'
            id = sa.Column(sa.Integer, primary_key=True)
    """

    created = sa.Column(sa.DateTime, default=datetime.utcnow, nullable=False)
    updated = sa.Column(sa.DateTime, default=datetime.utcnow, nullable=False)


@sa.event.listens_for(Timestamp, 'before_update', propagate=True)
def timestamp_before_update(mapper, connection, target):
    # When a model with a timestamp is updated; force update the updated
    # timestamp.
    target.updated = datetime.utcnow()