text: # Copyright (c) 2013-2014 Rackspace, Inc.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #    http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
  # implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  """
  Interface to the Alembic migration process and environment.
  
  Concepts in this file are based on Quantum's Alembic approach.
  
  Available Alembic commands are detailed here:
  https://alembic.readthedocs.org/en/latest/api.html#module-alembic.command
  """
  
  import os
  
  from alembic import command as alembic_command
  from alembic import config as alembic_config
  
  from barbican.common import config
  from barbican.common import utils
  
  LOG = utils.getLogger(__name__)
  
  
  CONF = config.CONF
  
  
  def init_config(sql_url=None):
      """Initialize and return the Alembic configuration."""
      sqlalchemy_url = sql_url or CONF.sql_connection
      if not sqlalchemy_url:
          raise RuntimeError("Please specify a SQLAlchemy-friendly URL to "
                             "connect to the proper database, either through "
                             "the CLI or the configuration file.")
  
      if sqlalchemy_url and 'sqlite' in sqlalchemy_url:
          LOG.warning('!!! Limited support for migration commands using'
                      ' sqlite databases; This operation may not succeed.')
  
      config = alembic_config.Config(
          os.path.join(os.path.dirname(__file__), 'alembic.ini')
      )
      config.barbican_sqlalchemy_url = sqlalchemy_url
      config.set_main_option('script_location',
                             'barbican.model.migration:alembic_migrations')
      return config
  
  
  def upgrade(to_version='head', sql_url=None):
      """Upgrade to the specified version."""
      alembic_cfg = init_config(sql_url)
      alembic_command.upgrade(alembic_cfg, to_version)
  
  
  def history(verbose, sql_url=None):
      alembic_cfg = init_config(sql_url)
      alembic_command.history(alembic_cfg, verbose=verbose)
  
  
  def current(verbose, sql_url=None):
      alembic_cfg = init_config(sql_url)
      alembic_command.current(alembic_cfg, verbose=verbose)
  
  
  def stamp(to_version='head', sql_url=None):
      """Stamp the specified version, with no migration performed."""
      alembic_cfg = init_config(sql_url)
      alembic_command.stamp(alembic_cfg, to_version)
  
  
  def generate(autogenerate=True, message='generate changes', sql_url=None):
      """Generate a version file."""
      alembic_cfg = init_config(sql_url)
      alembic_command.revision(alembic_cfg, message=message,
                               autogenerate=autogenerate)
  