def METHOD_NAME(self, package_id=None):
    """Estimate shipping date."""
    self.ensure_one()
    if self.date_done:
        shipping_date = self.date_done.date()
    else:
        shipping_date = self.scheduled_date.date()
    tomorrow = date.today() + timedelta(1)
    if shipping_date < tomorrow:
        # don't send in the past
        shipping_date = tomorrow
    return shipping_date