text: #
  #    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.
  import yaml
  
  from heat.common.i18n import _
  from heat.common import template_format
  
  
  SECTIONS = (
      PARAMETERS, RESOURCE_REGISTRY, PARAMETER_DEFAULTS,
      ENCRYPTED_PARAM_NAMES, EVENT_SINKS
  ) = (
      'parameters', 'resource_registry', 'parameter_defaults',
      'encrypted_param_names', 'event_sinks'
  )
  
  
  def parse(env_str):
      """Takes a string and returns a dict containing the parsed structure."""
      if env_str is None:
          return {}
  
      try:
          env = template_format.yaml.load(env_str,
                                          Loader=template_format.yaml_loader)
      except yaml.YAMLError:
          # NOTE(prazumovsky): we need to return more informative error for
          # user, so use SafeLoader, which return error message with template
          # snippet where error has been occurred.
          try:
              env = yaml.load(env_str, Loader=yaml.SafeLoader)
          except yaml.YAMLError as yea:
              raise ValueError(yea)
      else:
          if env is None:
              env = {}
  
      if not isinstance(env, dict):
          raise ValueError(_('The environment is not a valid '
                             'YAML mapping data type.'))
      for param in env:
          if param not in SECTIONS:
              raise ValueError(_('environment has wrong section "%s"') % param)
  
      return env
  
  
  def default_for_missing(env):
      """Checks a parsed environment for missing sections."""
      for param in SECTIONS:
          if param not in env:
              if param in (ENCRYPTED_PARAM_NAMES, EVENT_SINKS):
                  env[param] = []
              else:
                  env[param] = {}
  