# vim: tabstop=4 shiftwidth=4 softtabstop=4

# Copyright 2012 Red Hat, 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.

r"""
Configuration options which may be set on the command line or in config files.

The schema for each option is defined using the Opt sub-classes, e.g.:

::

    common_opts = [
        cfg.StrOpt('bind_host',
                   default='0.0.0.0',
                   help='IP address to listen on'),
        cfg.IntOpt('bind_port',
                   default=9292,
                   help='Port number to listen on')
    ]

Options can be strings, integers, floats, booleans, lists or 'multi strings'::

    enabled_apis_opt = cfg.ListOpt('enabled_apis',
                                   default=['ec2', 'osapi_compute'],
                                   help='List of APIs to enable by default')

    DEFAULT_EXTENSIONS = [
        'nova.api.openstack.compute.contrib.standard_extensions'
    ]
    osapi_compute_extension_opt = cfg.MultiStrOpt('osapi_compute_extension',
                                                  default=DEFAULT_EXTENSIONS)

Option schemas are registered with the config manager at runtime, but before
the option is referenced::

    class ExtensionManager(object):

        enabled_apis_opt = cfg.ListOpt(...)

        def __init__(self, conf):
            self.conf = conf
            self.conf.register_opt(enabled_apis_opt)
            ...

        def _load_extensions(self):
            for ext_factory in self.conf.osapi_compute_extension:
                ....

A common usage pattern is for each option schema to be defined in the module or
class which uses the option::

    opts = ...

    def add_common_opts(conf):
        conf.register_opts(opts)

    def get_bind_host(conf):
        return conf.bind_host

    def get_bind_port(conf):
        return conf.bind_port

An option may optionally be made available via the command line. Such options
must registered with the config manager before the command line is parsed (for
the purposes of --help and CLI arg validation)::

    cli_opts = [
        cfg.BoolOpt('verbose',
                    short='v',
                    default=False,
                    help='Print more verbose output'),
        cfg.BoolOpt('debug',
                    short='d',
                    default=False,
                    help='Print debugging output'),
    ]

    def add_common_opts(conf):
        conf.register_cli_opts(cli_opts)

The config manager has two CLI options defined by default, --config-file
and --config-dir::

    class ConfigOpts(object):

        def __call__(self, ...):

            opts = [
                MultiStrOpt('config-file',
                        ...),
                StrOpt('config-dir',
                       ...),
            ]

            self.register_cli_opts(opts)

Option values are parsed from any supplied config files using
openstack.common.iniparser. If none are specified, a default set is used
e.g. glance-api.conf and glance-common.conf::

    glance-api.conf:
      [DEFAULT]
      bind_port = 9292

    glance-common.conf:
      [DEFAULT]
      bind_host = 0.0.0.0

Option values in config files override those on the command line. Config files
are parsed in order, with values in later files overriding those in earlier
files.

The parsing of CLI args and config files is initiated by invoking the config
manager e.g.::

    conf = ConfigOpts()
    conf.register_opt(BoolOpt('verbose', ...))
    conf(sys.argv[1:])
    if conf.verbose:
        ...

Options can be registered as belonging to a group::

    rabbit_group = cfg.OptGroup(name='rabbit',
                                title='RabbitMQ options')

    rabbit_host_opt = cfg.StrOpt('host',
                                 default='localhost',
                                 help='IP/hostname to listen on'),
    rabbit_port_opt = cfg.IntOpt('port',
                                 default=5672,
                                 help='Port number to listen on')

    def register_rabbit_opts(conf):
        conf.register_group(rabbit_group)
        # options can be registered under a group in either of these ways:
        conf.register_opt(rabbit_host_opt, group=rabbit_group)
        conf.register_opt(rabbit_port_opt, group='rabbit')

If it no group attributes are required other than the group name, the group
need not be explicitly registered e.g.

    def register_rabbit_opts(conf):
        # The group will automatically be created, equivalent calling::
        #   conf.register_group(OptGroup(name='rabbit'))
        conf.register_opt(rabbit_port_opt, group='rabbit')

If no group is specified, options belong to the 'DEFAULT' section of config
files::

    glance-api.conf:
      [DEFAULT]
      bind_port = 9292
      ...

      [rabbit]
      host = localhost
      port = 5672
      use_ssl = False
      userid = guest
      password = guest
      virtual_host = /

Command-line options in a group are automatically prefixed with the
group name::

    --rabbit-host localhost --rabbit-port 9999

Option values in the default group are referenced as attributes/properties on
the config manager; groups are also attributes on the config manager, with
attributes for each of the options associated with the group::

    server.start(app, conf.bind_port, conf.bind_host, conf)

    self.connection = kombu.connection.BrokerConnection(
        hostname=conf.rabbit.host,
        port=conf.rabbit.port,
        ...)

Option values may reference other values using PEP 292 string substitution::

    opts = [
        cfg.StrOpt('state_path',
                   default=os.path.join(os.path.dirname(__file__), '../'),
                   help='Top-level directory for maintaining nova state'),
        cfg.StrOpt('sqlite_db',
                   default='nova.sqlite',
                   help='file name for sqlite'),
        cfg.StrOpt('sql_connection',
                   default='sqlite:///$state_path/$sqlite_db',
                   help='connection string for sql database'),
    ]

Note that interpolation can be avoided by using '$$'.

For command line utilities that dispatch to other command line utilities, the
disable_interspersed_args() method is available. If this this method is called,
then parsing e.g.::

  script --verbose cmd --debug /tmp/mything

will no longer return::

  ['cmd', '/tmp/mything']

as the leftover arguments, but will instead return::

  ['cmd', '--debug', '/tmp/mything']

i.e. argument parsing is stopped at the first non-option argument.

Options may be declared as required so that an error is raised if the user
does not supply a value for the option.

Options may be declared as secret so that their values are not leaked into
log files:

     opts = [
        cfg.StrOpt('s3_store_access_key', secret=True),
        cfg.StrOpt('s3_store_secret_key', secret=True),
        ...
     ]

This module also contains a global instance of the CommonConfigOpts class
in order to support a common usage pattern in OpenStack:

  from openstack.common import cfg

  opts = [
    cfg.StrOpt('bind_host' default='0.0.0.0'),
    cfg.IntOpt('bind_port', default=9292),
  ]

  CONF = cfg.CONF
  CONF.register_opts(opts)

  def start(server, app):
      server.start(app, CONF.bind_port, CONF.bind_host)

"""

import collections
import copy
import functools
import glob
import optparse
import os
import string
import sys

from keystone.openstack.common import iniparser


class Error(Exception):
    """Base class for cfg exceptions."""

    def __init__(self, msg=None):
        self.msg = msg

    def __str__(self):
        return self.msg


class ArgsAlreadyParsedError(Error):
    """Raised if a CLI opt is registered after parsing."""

    def __str__(self):
        ret = "arguments already parsed"
        if self.msg:
            ret += ": " + self.msg
        return ret


class NoSuchOptError(Error, AttributeError):
    """Raised if an opt which doesn't exist is referenced."""

    def __init__(self, opt_name, group=None):
        self.opt_name = opt_name
        self.group = group

    def __str__(self):
        if self.group is None:
            return "no such option: %s" % self.opt_name
        else:
            return "no such option in group %s: %s" % (self.group.name,
                                                       self.opt_name)


class NoSuchGroupError(Error):
    """Raised if a group which doesn't exist is referenced."""

    def __init__(self, group_name):
        self.group_name = group_name

    def __str__(self):
        return "no such group: %s" % self.group_name


class DuplicateOptError(Error):
    """Raised if multiple opts with the same name are registered."""

    def __init__(self, opt_name):
        self.opt_name = opt_name

    def __str__(self):
        return "duplicate option: %s" % self.opt_name


class RequiredOptError(Error):
    """Raised if an option is required but no value is supplied by the user."""

    def __init__(self, opt_name, group=None):
        self.opt_name = opt_name
        self.group = group

    def __str__(self):
        if self.group is None:
            return "value required for option: %s" % self.opt_name
        else:
            return "value required for option: %s.%s" % (self.group.name,
                                                         self.opt_name)


class TemplateSubstitutionError(Error):
    """Raised if an error occurs substituting a variable in an opt value."""

    def __str__(self):
        return "template substitution error: %s" % self.msg


class ConfigFilesNotFoundError(Error):
    """Raised if one or more config files are not found."""

    def __init__(self, config_files):
        self.config_files = config_files

    def __str__(self):
        return ('Failed to read some config files: %s' %
                string.join(self.config_files, ','))


class ConfigFileParseError(Error):
    """Raised if there is an error parsing a config file."""

    def __init__(self, config_file, msg):
        self.config_file = config_file
        self.msg = msg

    def __str__(self):
        return 'Failed to parse %s: %s' % (self.config_file, self.msg)


class ConfigFileValueError(Error):
    """Raised if a config file value does not match its opt type."""
    pass


def _fixpath(p):
    """Apply tilde expansion and absolutization to a path."""
    return os.path.abspath(os.path.expanduser(p))


def _get_config_dirs(project=None):
    """Return a list of directors where config files may be located.

    :param project: an optional project name

    If a project is specified, following directories are returned::

      ~/.${project}/
      ~/
      /etc/${project}/
      /etc/

    Otherwise, these directories::

      ~/
      /etc/
    """
    cfg_dirs = [
        _fixpath(os.path.join('~', '.' + project)) if project else None,
        _fixpath('~'),
        os.path.join('/etc', project) if project else None,
        '/etc'
    ]

    return filter(bool, cfg_dirs)


def _search_dirs(dirs, basename, extension=""):
    """Search a list of directories for a given filename.

    Iterator over the supplied directories, returning the first file
    found with the supplied name and extension.

    :param dirs: a list of directories
    :param basename: the filename, e.g. 'glance-api'
    :param extension: the file extension, e.g. '.conf'
    :returns: the path to a matching file, or None
    """
    for d in dirs:
        path = os.path.join(d, '%s%s' % (basename, extension))
        if os.path.exists(path):
            return path


def find_config_files(project=None, prog=None, extension='.conf'):
    """Return a list of default configuration files.

    :param project: an optional project name
    :param prog: the program name, defaulting to the basename of sys.argv[0]
    :param extension: the type of the config file

    We default to two config files: [${project}.conf, ${prog}.conf]

    And we look for those config files in the following directories::

      ~/.${project}/
      ~/
      /etc/${project}/
      /etc/

    We return an absolute path for (at most) one of each the default config
    files, for the topmost directory it exists in.

    For example, if project=foo, prog=bar and /etc/foo/foo.conf, /etc/bar.conf
    and ~/.foo/bar.conf all exist, then we return ['/etc/foo/foo.conf',
    '~/.foo/bar.conf']

    If no project name is supplied, we only look for ${prog.conf}.
    """
    if prog is None:
        prog = os.path.basename(sys.argv[0])

    cfg_dirs = _get_config_dirs(project)

    config_files = []
    if project:
        config_files.append(_search_dirs(cfg_dirs, project, extension))
    config_files.append(_search_dirs(cfg_dirs, prog, extension))

    return filter(bool, config_files)


def _is_opt_registered(opts, opt):
    """Check whether an opt with the same name is already registered.

    The same opt may be registered multiple times, with only the first
    registration having any effect. However, it is an error to attempt
    to register a different opt with the same name.

    :param opts: the set of opts already registered
    :param opt: the opt to be registered
    :returns: True if the opt was previously registered, False otherwise
    :raises: DuplicateOptError if a naming conflict is detected
    """
    if opt.dest in opts:
        if opts[opt.dest]['opt'] != opt:
            raise DuplicateOptError(opt.name)
        return True
    else:
        return False


class Opt(object):

    """Base class for all configuration options.

    An Opt object has no public methods, but has a number of public string
    properties:

      name:
        the name of the option, which may include hyphens
      dest:
        the (hyphen-less) ConfigOpts property which contains the option value
      short:
        a single character CLI option name
      default:
        the default value of the option
      metavar:
        the name shown as the argument to a CLI option in --help output
      help:
        an string explaining how the options value is used
    """
    multi = False

    def __init__(self, name, dest=None, short=None, default=None,
                 metavar=None, help=None, secret=False, required=False,
                 deprecated_name=None):
        """Construct an Opt object.

        The only required parameter is the option's name. However, it is
        common to also supply a default and help string for all options.

        :param name: the option's name
        :param dest: the name of the corresponding ConfigOpts property
        :param short: a single character CLI option name
        :param default: the default value of the option
        :param metavar: the option argument to show in --help
        :param help: an explanation of how the option is used
        :param secret: true iff the value should be obfuscated in log output
        :param required: true iff a value must be supplied for this option
        :param deprecated_name: deprecated name option.  Acts like an alias
        """
        self.name = name
        if dest is None:
            self.dest = self.name.replace('-', '_')
        else:
            self.dest = dest
        self.short = short
        self.default = default
        self.metavar = metavar
        self.help = help
        self.secret = secret
        self.required = required
        if deprecated_name is not None:
            self.deprecated_name = deprecated_name.replace('-', '_')
        else:
            self.deprecated_name = None

    def __ne__(self, another):
        return vars(self) != vars(another)

    def _get_from_config_parser(self, cparser, section):
        """Retrieves the option value from a MultiConfigParser object.

        This is the method ConfigOpts uses to look up the option value from
        config files. Most opt types override this method in order to perform
        type appropriate conversion of the returned value.

        :param cparser: a ConfigParser object
        :param section: a section name
        """
        return self._cparser_get_with_deprecated(cparser, section)

    def _cparser_get_with_deprecated(self, cparser, section):
        """If cannot find option as dest try deprecated_name alias."""
        if self.deprecated_name is not None:
            return cparser.get(section, [self.dest, self.deprecated_name])
        return cparser.get(section, [self.dest])

    def _add_to_cli(self, parser, group=None):
        """Makes the option available in the command line interface.

        This is the method ConfigOpts uses to add the opt to the CLI interface
        as appropriate for the opt type. Some opt types may extend this method,
        others may just extend the helper methods it uses.

        :param parser: the CLI option parser
        :param group: an optional OptGroup object
        """
        container = self._get_optparse_container(parser, group)
        kwargs = self._get_optparse_kwargs(group)
        prefix = self._get_optparse_prefix('', group)
        self._add_to_optparse(container, self.name, self.short, kwargs, prefix,
                              self.deprecated_name)

    def _add_to_optparse(self, container, name, short, kwargs, prefix='',
                         deprecated_name=None):
        """Add an option to an optparse parser or group.

        :param container: an optparse.OptionContainer object
        :param name: the opt name
        :param short: the short opt name
        :param kwargs: the keyword arguments for add_option()
        :param prefix: an optional prefix to prepend to the opt name
        :raises: DuplicateOptError if a naming confict is detected
        """
        args = ['--' + prefix + name]
        if short:
            args += ['-' + short]
        if deprecated_name:
            args += ['--' + prefix + deprecated_name]
        for a in args:
            if container.has_option(a):
                raise DuplicateOptError(a)
        container.add_option(*args, **kwargs)

    def _get_optparse_container(self, parser, group):
        """Returns an optparse.OptionContainer.

        :param parser: an optparse.OptionParser
        :param group: an (optional) OptGroup object
        :returns: an optparse.OptionGroup if a group is given, else the parser
        """
        if group is not None:
            return group._get_optparse_group(parser)
        else:
            return parser

    def _get_optparse_kwargs(self, group, **kwargs):
        """Build a dict of keyword arguments for optparse's add_option().

        Most opt types extend this method to customize the behaviour of the
        options added to optparse.

        :param group: an optional group
        :param kwargs: optional keyword arguments to add to
        :returns: a dict of keyword arguments
        """
        dest = self.dest
        if group is not None:
            dest = group.name + '_' + dest
        kwargs.update({'dest': dest,
                       'metavar': self.metavar,
                       'help': self.help, })
        return kwargs

    def _get_optparse_prefix(self, prefix, group):
        """Build a prefix for the CLI option name, if required.

        CLI options in a group are prefixed with the group's name in order
        to avoid conflicts between similarly named options in different
        groups.

        :param prefix: an existing prefix to append to (e.g. 'no' or '')
        :param group: an optional OptGroup object
        :returns: a CLI option prefix including the group name, if appropriate
        """
        if group is not None:
            return group.name + '-' + prefix
        else:
            return prefix


class StrOpt(Opt):
    """
    String opts do not have their values transformed and are returned as
    str objects.
    """
    pass


class BoolOpt(Opt):

    """
    Bool opts are set to True or False on the command line using --optname or
    --noopttname respectively.

    In config files, boolean values are case insensitive and can be set using
    1/0, yes/no, true/false or on/off.
    """

    _boolean_states = {'1': True, 'yes': True, 'true': True, 'on': True,
                       '0': False, 'no': False, 'false': False, 'off': False}

    def _get_from_config_parser(self, cparser, section):
        """Retrieve the opt value as a boolean from ConfigParser."""
        def convert_bool(v):
            value = self._boolean_states.get(v.lower())
            if value is None:
                raise ValueError('Unexpected boolean value %r' % v)

            return value

        return [convert_bool(v) for v in
                self._cparser_get_with_deprecated(cparser, section)]

    def _add_to_cli(self, parser, group=None):
        """Extends the base class method to add the --nooptname option."""
        super(BoolOpt, self)._add_to_cli(parser, group)
        self._add_inverse_to_optparse(parser, group)

    def _add_inverse_to_optparse(self, parser, group):
        """Add the --nooptname option to the option parser."""
        container = self._get_optparse_container(parser, group)
        kwargs = self._get_optparse_kwargs(group, action='store_false')
        prefix = self._get_optparse_prefix('no', group)
        kwargs["help"] = "The inverse of --" + self.name
        self._add_to_optparse(container, self.name, None, kwargs, prefix,
                              self.deprecated_name)

    def _get_optparse_kwargs(self, group, action='store_true', **kwargs):
        """Extends the base optparse keyword dict for boolean options."""
        return super(BoolOpt,
                     self)._get_optparse_kwargs(group, action=action, **kwargs)


class IntOpt(Opt):

    """Int opt values are converted to integers using the int() builtin."""

    def _get_from_config_parser(self, cparser, section):
        """Retrieve the opt value as a integer from ConfigParser."""
        return [int(v) for v in self._cparser_get_with_deprecated(cparser,
                section)]

    def _get_optparse_kwargs(self, group, **kwargs):
        """Extends the base optparse keyword dict for integer options."""
        return super(IntOpt,
                     self)._get_optparse_kwargs(group, type='int', **kwargs)


class FloatOpt(Opt):

    """Float opt values are converted to floats using the float() builtin."""

    def _get_from_config_parser(self, cparser, section):
        """Retrieve the opt value as a float from ConfigParser."""
        return [float(v) for v in
                self._cparser_get_with_deprecated(cparser, section)]

    def _get_optparse_kwargs(self, group, **kwargs):
        """Extends the base optparse keyword dict for float options."""
        return super(FloatOpt,
                     self)._get_optparse_kwargs(group, type='float', **kwargs)


class ListOpt(Opt):

    """
    List opt values are simple string values separated by commas. The opt value
    is a list containing these strings.
    """

    def _get_from_config_parser(self, cparser, section):
        """Retrieve the opt value as a list from ConfigParser."""
        return [v.split(',') for v in
                self._cparser_get_with_deprecated(cparser, section)]

    def _get_optparse_kwargs(self, group, **kwargs):
        """Extends the base optparse keyword dict for list options."""
        return super(ListOpt,
                     self)._get_optparse_kwargs(group,
                                                type='string',
                                                action='callback',
                                                callback=self._parse_list,
                                                **kwargs)

    def _parse_list(self, option, opt, value, parser):
        """An optparse callback for parsing an option value into a list."""
        setattr(parser.values, self.dest, value.split(','))


class MultiStrOpt(Opt):

    """
    Multistr opt values are string opts which may be specified multiple times.
    The opt value is a list containing all the string values specified.
    """
    multi = True

    def _get_optparse_kwargs(self, group, **kwargs):
        """Extends the base optparse keyword dict for multi str options."""
        return super(MultiStrOpt,
                     self)._get_optparse_kwargs(group, action='append')

    def _cparser_get_with_deprecated(self, cparser, section):
        """If cannot find option as dest try deprecated_name alias."""
        if self.deprecated_name is not None:
            return cparser.get(section, [self.dest, self.deprecated_name],
                               multi=True)
        return cparser.get(section, [self.dest], multi=True)


class OptGroup(object):

    """
    Represents a group of opts.

    CLI opts in the group are automatically prefixed with the group name.

    Each group corresponds to a section in config files.

    An OptGroup object has no public methods, but has a number of public string
    properties:

      name:
        the name of the group
      title:
        the group title as displayed in --help
      help:
        the group description as displayed in --help
    """

    def __init__(self, name, title=None, help=None):
        """Constructs an OptGroup object.

        :param name: the group name
        :param title: the group title for --help
        :param help: the group description for --help
        """
        self.name = name
        if title is None:
            self.title = "%s options" % title
        else:
            self.title = title
        self.help = help

        self._opts = {}  # dict of dicts of (opt:, override:, default:)
        self._optparse_group = None

    def _register_opt(self, opt):
        """Add an opt to this group.

        :param opt: an Opt object
        :returns: False if previously registered, True otherwise
        :raises: DuplicateOptError if a naming conflict is detected
        """
        if _is_opt_registered(self._opts, opt):
            return False

        self._opts[opt.dest] = {'opt': opt}

        return True

    def _unregister_opt(self, opt):
        """Remove an opt from this group.

        :param opt: an Opt object
        """
        if opt.dest in self._opts:
            del self._opts[opt.dest]

    def _get_optparse_group(self, parser):
        """Build an optparse.OptionGroup for this group."""
        if self._optparse_group is None:
            self._optparse_group = optparse.OptionGroup(parser, self.title,
                                                        self.help)
        return self._optparse_group

    def _clear(self):
        """Clear this group's option parsing state."""
        self._optparse_group = None


class ParseError(iniparser.ParseError):
    def __init__(self, msg, lineno, line, filename):
        super(ParseError, self).__init__(msg, lineno, line)
        self.filename = filename

    def __str__(self):
        return 'at %s:%d, %s: %r' % (self.filename, self.lineno,
                                     self.msg, self.line)


class ConfigParser(iniparser.BaseParser):
    def __init__(self, filename, sections):
        super(ConfigParser, self).__init__()
        self.filename = filename
        self.sections = sections
        self.section = None

    def parse(self):
        with open(self.filename) as f:
            return super(ConfigParser, self).parse(f)

    def new_section(self, section):
        self.section = section
        self.sections.setdefault(self.section, {})

    def assignment(self, key, value):
        if not self.section:
            raise self.error_no_section()

        self.sections[self.section].setdefault(key, [])
        self.sections[self.section][key].append('\n'.join(value))

    def parse_exc(self, msg, lineno, line=None):
        return ParseError(msg, lineno, line, self.filename)

    def error_no_section(self):
        return self.parse_exc('Section must be started before assignment',
                              self.lineno)


class MultiConfigParser(object):
    def __init__(self):
        self.parsed = []

    def read(self, config_files):
        read_ok = []

        for filename in config_files:
            sections = {}
            parser = ConfigParser(filename, sections)

            try:
                parser.parse()
            except IOError:
                continue
            self.parsed.insert(0, sections)
            read_ok.append(filename)

        return read_ok

    def get(self, section, names, multi=False):
        rvalue = []
        for sections in self.parsed:
            if section not in sections:
                continue
            for name in names:
                if name in sections[section]:
                    if multi:
                        rvalue = sections[section][name] + rvalue
                    else:
                        return sections[section][name]
        if multi and rvalue != []:
            return rvalue
        raise KeyError


class ConfigOpts(collections.Mapping):

    """
    Config options which may be set on the command line or in config files.

    ConfigOpts is a configuration option manager with APIs for registering
    option schemas, grouping options, parsing option values and retrieving
    the values of options.
    """

    def __init__(self):
        """Construct a ConfigOpts object."""
        self._opts = {}  # dict of dicts of (opt:, override:, default:)
        self._groups = {}

        self._args = None
        self._oparser = None
        self._cparser = None
        self._cli_values = {}
        self.__cache = {}
        self._config_opts = []
        self._disable_interspersed_args = False

    def _setup(self, project, prog, version, usage, default_config_files):
        """Initialize a ConfigOpts object for option parsing."""
        if prog is None:
            prog = os.path.basename(sys.argv[0])

        if default_config_files is None:
            default_config_files = find_config_files(project, prog)

        self._oparser = optparse.OptionParser(prog=prog,
                                              version=version,
                                              usage=usage)
        if self._disable_interspersed_args:
            self._oparser.disable_interspersed_args()

        self._config_opts = [
            MultiStrOpt('config-file',
                        default=default_config_files,
                        metavar='PATH',
                        help='Path to a config file to use. Multiple config '
                             'files can be specified, with values in later '
                             'files taking precedence. The default files '
                             ' used are: %s' % (default_config_files, )),
            StrOpt('config-dir',
                   metavar='DIR',
                   help='Path to a config directory to pull *.conf '
                        'files from. This file set is sorted, so as to '
                        'provide a predictable parse order if individual '
                        'options are over-ridden. The set is parsed after '
                        'the file(s), if any, specified via --config-file, '
                        'hence over-ridden options in the directory take '
                        'precedence.'),
        ]
        self.register_cli_opts(self._config_opts)

        self.project = project
        self.prog = prog
        self.version = version
        self.usage = usage
        self.default_config_files = default_config_files

    def __clear_cache(f):
        @functools.wraps(f)
        def __inner(self, *args, **kwargs):
            if kwargs.pop('clear_cache', True):
                self.__cache.clear()
            return f(self, *args, **kwargs)

        return __inner

    def __call__(self,
                 args=None,
                 project=None,
                 prog=None,
                 version=None,
                 usage=None,
                 default_config_files=None):
        """Parse command line arguments and config files.

        Calling a ConfigOpts object causes the supplied command line arguments
        and config files to be parsed, causing opt values to be made available
        as attributes of the object.

        The object may be called multiple times, each time causing the previous
        set of values to be overwritten.

        Automatically registers the --config-file option with either a supplied
        list of default config files, or a list from find_config_files().

        If the --config-dir option is set, any *.conf files from this
        directory are pulled in, after all the file(s) specified by the
        --config-file option.

        :param args: command line arguments (defaults to sys.argv[1:])
        :param project: the toplevel project name, used to locate config files
        :param prog: the name of the program (defaults to sys.argv[0] basename)
        :param version: the program version (for --version)
        :param usage: a usage string (%prog will be expanded)
        :param default_config_files: config files to use by default
        :returns: the list of arguments left over after parsing options
        :raises: SystemExit, ConfigFilesNotFoundError, ConfigFileParseError,
                 RequiredOptError, DuplicateOptError
        """
        self.clear()

        self._setup(project, prog, version, usage, default_config_files)

        self._cli_values, leftovers = self._parse_cli_opts(args)

        self._parse_config_files()

        self._check_required_opts()

        return leftovers

    def __getattr__(self, name):
        """Look up an option value and perform string substitution.

        :param name: the opt name (or 'dest', more precisely)
        :returns: the option value (after string subsititution) or a GroupAttr
        :raises: NoSuchOptError,ConfigFileValueError,TemplateSubstitutionError
        """
        return self._get(name)

    def __getitem__(self, key):
        """Look up an option value and perform string substitution."""
        return self.__getattr__(key)

    def __contains__(self, key):
        """Return True if key is the name of a registered opt or group."""
        return key in self._opts or key in self._groups

    def __iter__(self):
        """Iterate over all registered opt and group names."""
        for key in self._opts.keys() + self._groups.keys():
            yield key

    def __len__(self):
        """Return the number of options and option groups."""
        return len(self._opts) + len(self._groups)

    def reset(self):
        """Clear the object state and unset overrides and defaults."""
        self._unset_defaults_and_overrides()
        self.clear()

    @__clear_cache
    def clear(self):
        """Clear the state of the object to before it was called."""
        self._args = None
        self._cli_values.clear()
        self._oparser = None
        self._cparser = None
        self.unregister_opts(self._config_opts)
        for group in self._groups.values():
            group._clear()

    @__clear_cache
    def register_opt(self, opt, group=None):
        """Register an option schema.

        Registering an option schema makes any option value which is previously
        or subsequently parsed from the command line or config files available
        as an attribute of this object.

        :param opt: an instance of an Opt sub-class
        :param group: an optional OptGroup object or group name
        :return: False if the opt was already register, True otherwise
        :raises: DuplicateOptError
        """
        if group is not None:
            return self._get_group(group, autocreate=True)._register_opt(opt)

        if _is_opt_registered(self._opts, opt):
            return False

        self._opts[opt.dest] = {'opt': opt}

        return True

    @__clear_cache
    def register_opts(self, opts, group=None):
        """Register multiple option schemas at once."""
        for opt in opts:
            self.register_opt(opt, group, clear_cache=False)

    @__clear_cache
    def register_cli_opt(self, opt, group=None):
        """Register a CLI option schema.

        CLI option schemas must be registered before the command line and
        config files are parsed. This is to ensure that all CLI options are
        show in --help and option validation works as expected.

        :param opt: an instance of an Opt sub-class
        :param group: an optional OptGroup object or group name
        :return: False if the opt was already register, True otherwise
        :raises: DuplicateOptError, ArgsAlreadyParsedError
        """
        if self._args is not None:
            raise ArgsAlreadyParsedError("cannot register CLI option")

        return self.register_opt(opt, group, clear_cache=False)

    @__clear_cache
    def register_cli_opts(self, opts, group=None):
        """Register multiple CLI option schemas at once."""
        for opt in opts:
            self.register_cli_opt(opt, group, clear_cache=False)

    def register_group(self, group):
        """Register an option group.

        An option group must be registered before options can be registered
        with the group.

        :param group: an OptGroup object
        """
        if group.name in self._groups:
            return

        self._groups[group.name] = copy.copy(group)

    @__clear_cache
    def unregister_opt(self, opt, group=None):
        """Unregister an option.

        :param opt: an Opt object
        :param group: an optional OptGroup object or group name
        :raises: ArgsAlreadyParsedError, NoSuchGroupError
        """
        if self._args is not None:
            raise ArgsAlreadyParsedError("reset before unregistering options")

        if group is not None:
            self._get_group(group)._unregister_opt(opt)
        elif opt.dest in self._opts:
            del self._opts[opt.dest]

    @__clear_cache
    def unregister_opts(self, opts, group=None):
        """Unregister multiple CLI option schemas at once."""
        for opt in opts:
            self.unregister_opt(opt, group, clear_cache=False)

    def import_opt(self, name, module_str, group=None):
        """Import an option definition from a module.

        Import a module and check that a given option is registered.

        This is intended for use with global configuration objects
        like cfg.CONF where modules commonly register options with
        CONF at module load time. If one module requires an option
        defined by another module it can use this method to explicitly
        declare the dependency.

        :param name: the name/dest of the opt
        :param module_str: the name of a module to import
        :param group: an option OptGroup object or group name
        :raises: NoSuchOptError, NoSuchGroupError
        """
        __import__(module_str)
        self._get_opt_info(name, group)

    @__clear_cache
    def set_override(self, name, override, group=None):
        """Override an opt value.

        Override the command line, config file and default values of a
        given option.

        :param name: the name/dest of the opt
        :param override: the override value
        :param group: an option OptGroup object or group name
        :raises: NoSuchOptError, NoSuchGroupError
        """
        opt_info = self._get_opt_info(name, group)
        opt_info['override'] = override

    @__clear_cache
    def set_default(self, name, default, group=None):
        """Override an opt's default value.

        Override the default value of given option. A command line or
        config file value will still take precedence over this default.

        :param name: the name/dest of the opt
        :param default: the default value
        :param group: an option OptGroup object or group name
        :raises: NoSuchOptError, NoSuchGroupError
        """
        opt_info = self._get_opt_info(name, group)
        opt_info['default'] = default

    @__clear_cache
    def clear_override(self, name, group=None):
        """Clear an override an opt value.

        Clear a previously set override of the command line, config file
        and default values of a given option.

        :param name: the name/dest of the opt
        :param group: an option OptGroup object or group name
        :raises: NoSuchOptError, NoSuchGroupError
        """
        opt_info = self._get_opt_info(name, group)
        opt_info.pop('override', None)

    @__clear_cache
    def clear_default(self, name, group=None):
        """Clear an override an opt's default value.

        Clear a previously set override of the default value of given option.

        :param name: the name/dest of the opt
        :param group: an option OptGroup object or group name
        :raises: NoSuchOptError, NoSuchGroupError
        """
        opt_info = self._get_opt_info(name, group)
        opt_info.pop('default', None)

    def _all_opt_infos(self):
        """A generator function for iteration opt infos."""
        for info in self._opts.values():
            yield info, None
        for group in self._groups.values():
            for info in group._opts.values():
                yield info, group

    def _all_opts(self):
        """A generator function for iteration opts."""
        for info, group in self._all_opt_infos():
            yield info['opt'], group

    def _unset_defaults_and_overrides(self):
        """Unset any default or override on all options."""
        for info, group in self._all_opt_infos():
            info.pop('default', None)
            info.pop('override', None)

    def disable_interspersed_args(self):
        """Set parsing to stop on the first non-option.

        If this this method is called, then parsing e.g.

          script --verbose cmd --debug /tmp/mything

        will no longer return:

          ['cmd', '/tmp/mything']

        as the leftover arguments, but will instead return:

          ['cmd', '--debug', '/tmp/mything']

        i.e. argument parsing is stopped at the first non-option argument.
        """
        self._disable_interspersed_args = True

    def enable_interspersed_args(self):
        """Set parsing to not stop on the first non-option.

        This it the default behaviour."""
        self._disable_interspersed_args = False

    def find_file(self, name):
        """Locate a file located alongside the config files.

        Search for a file with the supplied basename in the directories
        which we have already loaded config files from and other known
        configuration directories.

        The directory, if any, supplied by the config_dir option is
        searched first. Then the config_file option is iterated over
        and each of the base directories of the config_files values
        are searched. Failing both of these, the standard directories
        searched by the module level find_config_files() function is
        used. The first matching file is returned.

        :param basename: the filename, e.g. 'policy.json'
        :returns: the path to a matching file, or None
        """
        dirs = []
        if self.config_dir:
            dirs.append(_fixpath(self.config_dir))

        for cf in reversed(self.config_file):
            dirs.append(os.path.dirname(_fixpath(cf)))

        dirs.extend(_get_config_dirs(self.project))

        return _search_dirs(dirs, name)

    def log_opt_values(self, logger, lvl):
        """Log the value of all registered opts.

        It's often useful for an app to log its configuration to a log file at
        startup for debugging. This method dumps to the entire config state to
        the supplied logger at a given log level.

        :param logger: a logging.Logger object
        :param lvl: the log level (e.g. logging.DEBUG) arg to logger.log()
        """
        logger.log(lvl, "*" * 80)
        logger.log(lvl, "Configuration options gathered from:")
        logger.log(lvl, "command line args: %s", self._args)
        logger.log(lvl, "config files: %s", self.config_file)
        logger.log(lvl, "=" * 80)

        def _sanitize(opt, value):
            """Obfuscate values of options declared secret"""
            return value if not opt.secret else '*' * len(str(value))

        for opt_name in sorted(self._opts):
            opt = self._get_opt_info(opt_name)['opt']
            logger.log(lvl, "%-30s = %s", opt_name,
                       _sanitize(opt, getattr(self, opt_name)))

        for group_name in self._groups:
            group_attr = self.GroupAttr(self, self._get_group(group_name))
            for opt_name in sorted(self._groups[group_name]._opts):
                opt = self._get_opt_info(opt_name, group_name)['opt']
                logger.log(lvl, "%-30s = %s",
                           "%s.%s" % (group_name, opt_name),
                           _sanitize(opt, getattr(group_attr, opt_name)))

        logger.log(lvl, "*" * 80)

    def print_usage(self, file=None):
        """Print the usage message for the current program."""
        self._oparser.print_usage(file)

    def print_help(self, file=None):
        """Print the help message for the current program."""
        self._oparser.print_help(file)

    def _get(self, name, group=None):
        if isinstance(group, OptGroup):
            key = (group.name, name)
        else:
            key = (group, name)
        try:
            return self.__cache[key]
        except KeyError:
            value = self._substitute(self._do_get(name, group))
            self.__cache[key] = value
            return value

    def _do_get(self, name, group=None):
        """Look up an option value.

        :param name: the opt name (or 'dest', more precisely)
        :param group: an OptGroup
        :returns: the option value, or a GroupAttr object
        :raises: NoSuchOptError, NoSuchGroupError, ConfigFileValueError,
                 TemplateSubstitutionError
        """
        if group is None and name in self._groups:
            return self.GroupAttr(self, self._get_group(name))

        info = self._get_opt_info(name, group)
        opt = info['opt']

        if 'override' in info:
            return info['override']

        values = []
        if self._cparser is not None:
            section = group.name if group is not None else 'DEFAULT'
            try:
                value = opt._get_from_config_parser(self._cparser, section)
            except KeyError:
                pass
            except ValueError as ve:
                raise ConfigFileValueError(str(ve))
            else:
                if not opt.multi:
                    # No need to continue since the last value wins
                    return value[-1]
                values.extend(value)

        name = name if group is None else group.name + '_' + name
        value = self._cli_values.get(name)
        if value is not None:
            if not opt.multi:
                return value

            return value + values

        if values:
            return values

        if 'default' in info:
            return info['default']

        return opt.default

    def _substitute(self, value):
        """Perform string template substitution.

        Substitute any template variables (e.g. $foo, ${bar}) in the supplied
        string value(s) with opt values.

        :param value: the string value, or list of string values
        :returns: the substituted string(s)
        """
        if isinstance(value, list):
            return [self._substitute(i) for i in value]
        elif isinstance(value, str):
            tmpl = string.Template(value)
            return tmpl.safe_substitute(self.StrSubWrapper(self))
        else:
            return value

    def _get_group(self, group_or_name, autocreate=False):
        """Looks up a OptGroup object.

        Helper function to return an OptGroup given a parameter which can
        either be the group's name or an OptGroup object.

        The OptGroup object returned is from the internal dict of OptGroup
        objects, which will be a copy of any OptGroup object that users of
        the API have access to.

        :param group_or_name: the group's name or the OptGroup object itself
        :param autocreate: whether to auto-create the group if it's not found
        :raises: NoSuchGroupError
        """
        group = group_or_name if isinstance(group_or_name, OptGroup) else None
        group_name = group.name if group else group_or_name

        if not group_name in self._groups:
            if not group is None or not autocreate:
                raise NoSuchGroupError(group_name)

            self.register_group(OptGroup(name=group_name))

        return self._groups[group_name]

    def _get_opt_info(self, opt_name, group=None):
        """Return the (opt, override, default) dict for an opt.

        :param opt_name: an opt name/dest
        :param group: an optional group name or OptGroup object
        :raises: NoSuchOptError, NoSuchGroupError
        """
        if group is None:
            opts = self._opts
        else:
            group = self._get_group(group)
            opts = group._opts

        if not opt_name in opts:
            raise NoSuchOptError(opt_name, group)

        return opts[opt_name]

    def _parse_config_files(self):
        """Parse the config files from --config-file and --config-dir.

        :raises: ConfigFilesNotFoundError, ConfigFileParseError
        """
        config_files = list(self.config_file)

        if self.config_dir:
            config_dir_glob = os.path.join(self.config_dir, '*.conf')
            config_files += sorted(glob.glob(config_dir_glob))

        config_files = [_fixpath(p) for p in config_files]

        self._cparser = MultiConfigParser()

        try:
            read_ok = self._cparser.read(config_files)
        except iniparser.ParseError as pe:
            raise ConfigFileParseError(pe.filename, str(pe))

        if read_ok != config_files:
            not_read_ok = filter(lambda f: f not in read_ok, config_files)
            raise ConfigFilesNotFoundError(not_read_ok)

    def _check_required_opts(self):
        """Check that all opts marked as required have values specified.

        :raises: RequiredOptError
        """
        for info, group in self._all_opt_infos():
            opt = info['opt']

            if opt.required:
                if ('default' in info or 'override' in info):
                    continue

                if self._get(opt.name, group) is None:
                    raise RequiredOptError(opt.name, group)

    def _parse_cli_opts(self, args):
        """Parse command line options.

        Initializes the command line option parser and parses the supplied
        command line arguments.

        :param args: the command line arguments
        :returns: a dict of parsed option values
        :raises: SystemExit, DuplicateOptError

        """
        self._args = args

        for opt, group in self._all_opts():
            opt._add_to_cli(self._oparser, group)

        values, leftovers = self._oparser.parse_args(args)

        return vars(values), leftovers

    class GroupAttr(collections.Mapping):

        """
        A helper class representing the option values of a group as a mapping
        and attributes.
        """

        def __init__(self, conf, group):
            """Construct a GroupAttr object.

            :param conf: a ConfigOpts object
            :param group: an OptGroup object
            """
            self.conf = conf
            self.group = group

        def __getattr__(self, name):
            """Look up an option value and perform template substitution."""
            return self.conf._get(name, self.group)

        def __getitem__(self, key):
            """Look up an option value and perform string substitution."""
            return self.__getattr__(key)

        def __contains__(self, key):
            """Return True if key is the name of a registered opt or group."""
            return key in self.group._opts

        def __iter__(self):
            """Iterate over all registered opt and group names."""
            for key in self.group._opts.keys():
                yield key

        def __len__(self):
            """Return the number of options and option groups."""
            return len(self.group._opts)

    class StrSubWrapper(object):

        """
        A helper class exposing opt values as a dict for string substitution.
        """

        def __init__(self, conf):
            """Construct a StrSubWrapper object.

            :param conf: a ConfigOpts object
            """
            self.conf = conf

        def __getitem__(self, key):
            """Look up an opt value from the ConfigOpts object.

            :param key: an opt name
            :returns: an opt value
            :raises: TemplateSubstitutionError if attribute is a group
            """
            value = getattr(self.conf, key)
            if isinstance(value, self.conf.GroupAttr):
                raise TemplateSubstitutionError(
                    'substituting group %s not supported' % key)
            return value


class CommonConfigOpts(ConfigOpts):

    DEFAULT_LOG_FORMAT = "%(asctime)s %(levelname)8s [%(name)s] %(message)s"
    DEFAULT_LOG_DATE_FORMAT = "%Y-%m-%d %H:%M:%S"

    common_cli_opts = [
        BoolOpt('debug',
                short='d',
                default=False,
                help='Print debugging output'),
        BoolOpt('verbose',
                short='v',
                default=False,
                help='Print more verbose output'),
    ]

    logging_cli_opts = [
        StrOpt('log-config',
               metavar='PATH',
               help='If this option is specified, the logging configuration '
                    'file specified is used and overrides any other logging '
                    'options specified. Please see the Python logging module '
                    'documentation for details on logging configuration '
                    'files.'),
        StrOpt('log-format',
               default=DEFAULT_LOG_FORMAT,
               metavar='FORMAT',
               help='A logging.Formatter log message format string which may '
                    'use any of the available logging.LogRecord attributes. '
                    'Default: %default'),
        StrOpt('log-date-format',
               default=DEFAULT_LOG_DATE_FORMAT,
               metavar='DATE_FORMAT',
               help='Format string for %(asctime)s in log records. '
                    'Default: %default'),
        StrOpt('log-file',
               metavar='PATH',
               help='(Optional) Name of log file to output to. '
                    'If not set, logging will go to stdout.'),
        StrOpt('log-dir',
               help='(Optional) The directory to keep log files in '
                    '(will be prepended to --logfile)'),
        BoolOpt('use-syslog',
                default=False,
                help='Use syslog for logging.'),
        StrOpt('syslog-log-facility',
               default='LOG_USER',
               help='syslog facility to receive log lines')
    ]

    def __init__(self):
        super(CommonConfigOpts, self).__init__()
        self.register_cli_opts(self.common_cli_opts)
        self.register_cli_opts(self.logging_cli_opts)


CONF = CommonConfigOpts()
