# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# Copyright 2011 Justin Santa Barbara
# All Rights Reserved.
#
#    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.

"""Utilities and helper functions."""


import abc
import contextlib
import datetime
import functools
import inspect
import logging as py_logging
import math
import os
import pyclbr
import random
import re
import shutil
import socket
import stat
import sys
import tempfile
import time
import types
from xml.dom import minidom
from xml.parsers import expat
from xml import sax
from xml.sax import expatreader

from os_brick.initiator import connector
from oslo_concurrency import lockutils
from oslo_concurrency import processutils
from oslo_config import cfg
from oslo_log import log as logging
from oslo_utils import encodeutils
from oslo_utils import excutils
from oslo_utils import importutils
from oslo_utils import strutils
from oslo_utils import timeutils
import retrying
import six
import webob.exc

from cinder import exception
from cinder.i18n import _, _LE, _LW


CONF = cfg.CONF
LOG = logging.getLogger(__name__)
ISO_TIME_FORMAT = "%Y-%m-%dT%H:%M:%S"
PERFECT_TIME_FORMAT = "%Y-%m-%dT%H:%M:%S.%f"
VALID_TRACE_FLAGS = {'method', 'api'}
TRACE_METHOD = False
TRACE_API = False

synchronized = lockutils.synchronized_with_prefix('cinder-')


def find_config(config_path):
    """Find a configuration file using the given hint.

    :param config_path: Full or relative path to the config.
    :returns: Full path of the config, if it exists.
    :raises: `cinder.exception.ConfigNotFound`

    """
    possible_locations = [
        config_path,
        os.path.join(CONF.state_path, "etc", "cinder", config_path),
        os.path.join(CONF.state_path, "etc", config_path),
        os.path.join(CONF.state_path, config_path),
        "/etc/cinder/%s" % config_path,
    ]

    for path in possible_locations:
        if os.path.exists(path):
            return os.path.abspath(path)

    raise exception.ConfigNotFound(path=os.path.abspath(config_path))


def as_int(obj, quiet=True):
    # Try "2" -> 2
    try:
        return int(obj)
    except (ValueError, TypeError):
        pass
    # Try "2.5" -> 2
    try:
        return int(float(obj))
    except (ValueError, TypeError):
        pass
    # Eck, not sure what this is then.
    if not quiet:
        raise TypeError(_("Can not translate %s to integer.") % (obj))
    return obj


def check_exclusive_options(**kwargs):
    """Checks that only one of the provided options is actually not-none.

    Iterates over all the kwargs passed in and checks that only one of said
    arguments is not-none, if more than one is not-none then an exception will
    be raised with the names of those arguments who were not-none.
    """

    if not kwargs:
        return

    pretty_keys = kwargs.pop("pretty_keys", True)
    exclusive_options = {}
    for (k, v) in kwargs.items():
        if v is not None:
            exclusive_options[k] = True

    if len(exclusive_options) > 1:
        # Change the format of the names from pythonic to
        # something that is more readable.
        #
        # Ex: 'the_key' -> 'the key'
        if pretty_keys:
            names = [k.replace('_', ' ') for k in kwargs.keys()]
        else:
            names = kwargs.keys()
        names = ", ".join(sorted(names))
        msg = (_("May specify only one of %s") % (names))
        raise exception.InvalidInput(reason=msg)


def execute(*cmd, **kwargs):
    """Convenience wrapper around oslo's execute() method."""
    if 'run_as_root' in kwargs and 'root_helper' not in kwargs:
        kwargs['root_helper'] = get_root_helper()
    return processutils.execute(*cmd, **kwargs)


def check_ssh_injection(cmd_list):
    ssh_injection_pattern = ['`', '$', '|', '||', ';', '&', '&&', '>', '>>',
                             '<']

    # Check whether injection attacks exist
    for arg in cmd_list:
        arg = arg.strip()

        # Check for matching quotes on the ends
        is_quoted = re.match('^(?P<quote>[\'"])(?P<quoted>.*)(?P=quote)$', arg)
        if is_quoted:
            # Check for unescaped quotes within the quoted argument
            quoted = is_quoted.group('quoted')
            if quoted:
                if (re.match('[\'"]', quoted) or
                        re.search('[^\\\\][\'"]', quoted)):
                    raise exception.SSHInjectionThreat(command=cmd_list)
        else:
            # We only allow spaces within quoted arguments, and that
            # is the only special character allowed within quotes
            if len(arg.split()) > 1:
                raise exception.SSHInjectionThreat(command=cmd_list)

        # Second, check whether danger character in command. So the shell
        # special operator must be a single argument.
        for c in ssh_injection_pattern:
            if c not in arg:
                continue

            result = arg.find(c)
            if not result == -1:
                if result == 0 or not arg[result - 1] == '\\':
                    raise exception.SSHInjectionThreat(command=cmd_list)


def cinderdir():
    import cinder
    return os.path.abspath(cinder.__file__).split('cinder/__init__.py')[0]


def last_completed_audit_period(unit=None):
    """This method gives you the most recently *completed* audit period.

    arguments:
            units: string, one of 'hour', 'day', 'month', 'year'
                    Periods normally begin at the beginning (UTC) of the
                    period unit (So a 'day' period begins at midnight UTC,
                    a 'month' unit on the 1st, a 'year' on Jan, 1)
                    unit string may be appended with an optional offset
                    like so:  'day@18'  This will begin the period at 18:00
                    UTC.  'month@15' starts a monthly period on the 15th,
                    and year@3 begins a yearly one on March 1st.


    returns:  2 tuple of datetimes (begin, end)
              The begin timestamp of this audit period is the same as the
              end of the previous.
    """
    if not unit:
        unit = CONF.volume_usage_audit_period

    offset = 0
    if '@' in unit:
        unit, offset = unit.split("@", 1)
        offset = int(offset)

    rightnow = timeutils.utcnow()
    if unit not in ('month', 'day', 'year', 'hour'):
        raise ValueError('Time period must be hour, day, month or year')
    if unit == 'month':
        if offset == 0:
            offset = 1
        end = datetime.datetime(day=offset,
                                month=rightnow.month,
                                year=rightnow.year)
        if end >= rightnow:
            year = rightnow.year
            if 1 >= rightnow.month:
                year -= 1
                month = 12 + (rightnow.month - 1)
            else:
                month = rightnow.month - 1
            end = datetime.datetime(day=offset,
                                    month=month,
                                    year=year)
        year = end.year
        if 1 >= end.month:
            year -= 1
            month = 12 + (end.month - 1)
        else:
            month = end.month - 1
        begin = datetime.datetime(day=offset, month=month, year=year)

    elif unit == 'year':
        if offset == 0:
            offset = 1
        end = datetime.datetime(day=1, month=offset, year=rightnow.year)
        if end >= rightnow:
            end = datetime.datetime(day=1,
                                    month=offset,
                                    year=rightnow.year - 1)
            begin = datetime.datetime(day=1,
                                      month=offset,
                                      year=rightnow.year - 2)
        else:
            begin = datetime.datetime(day=1,
                                      month=offset,
                                      year=rightnow.year - 1)

    elif unit == 'day':
        end = datetime.datetime(hour=offset,
                                day=rightnow.day,
                                month=rightnow.month,
                                year=rightnow.year)
        if end >= rightnow:
            end = end - datetime.timedelta(days=1)
        begin = end - datetime.timedelta(days=1)

    elif unit == 'hour':
        end = rightnow.replace(minute=offset, second=0, microsecond=0)
        if end >= rightnow:
            end = end - datetime.timedelta(hours=1)
        begin = end - datetime.timedelta(hours=1)

    return (begin, end)


class ProtectedExpatParser(expatreader.ExpatParser):
    """An expat parser which disables DTD's and entities by default."""

    def __init__(self, forbid_dtd=True, forbid_entities=True,
                 *args, **kwargs):
        # Python 2.x old style class
        expatreader.ExpatParser.__init__(self, *args, **kwargs)
        self.forbid_dtd = forbid_dtd
        self.forbid_entities = forbid_entities

    def start_doctype_decl(self, name, sysid, pubid, has_internal_subset):
        raise ValueError("Inline DTD forbidden")

    def entity_decl(self, entityName, is_parameter_entity, value, base,
                    systemId, publicId, notationName):
        raise ValueError("<!ENTITY> forbidden")

    def unparsed_entity_decl(self, name, base, sysid, pubid, notation_name):
        # expat 1.2
        raise ValueError("<!ENTITY> forbidden")

    def reset(self):
        expatreader.ExpatParser.reset(self)
        if self.forbid_dtd:
            self._parser.StartDoctypeDeclHandler = self.start_doctype_decl
        if self.forbid_entities:
            self._parser.EntityDeclHandler = self.entity_decl
            self._parser.UnparsedEntityDeclHandler = self.unparsed_entity_decl


def safe_minidom_parse_string(xml_string):
    """Parse an XML string using minidom safely.

    """
    try:
        if six.PY3 and isinstance(xml_string, bytes):
            # On Python 3, minidom.parseString() requires Unicode when
            # the parser parameter is used.
            #
            # Bet that XML used in Cinder is always encoded to UTF-8.
            xml_string = xml_string.decode('utf-8')
        return minidom.parseString(xml_string, parser=ProtectedExpatParser())
    except sax.SAXParseException:
        raise expat.ExpatError()


def is_valid_boolstr(val):
    """Check if the provided string is a valid bool string or not."""
    val = str(val).lower()
    return val in ('true', 'false', 'yes', 'no', 'y', 'n', '1', '0')


def is_none_string(val):
    """Check if a string represents a None value."""
    if not isinstance(val, six.string_types):
        return False

    return val.lower() == 'none'


def monkey_patch():
    """Patches decorators for all functions in a specified module.

    If the CONF.monkey_patch set as True,
    this function patches a decorator
    for all functions in specified modules.

    You can set decorators for each modules
    using CONF.monkey_patch_modules.
    The format is "Module path:Decorator function".
    Example: 'cinder.api.ec2.cloud:' \
     cinder.openstack.common.notifier.api.notify_decorator'

    Parameters of the decorator is as follows.
    (See cinder.openstack.common.notifier.api.notify_decorator)

    :param name: name of the function
    :param function: object of the function
    """
    # If CONF.monkey_patch is not True, this function do nothing.
    if not CONF.monkey_patch:
        return
    # Get list of modules and decorators
    for module_and_decorator in CONF.monkey_patch_modules:
        module, decorator_name = module_and_decorator.split(':')
        # import decorator function
        decorator = importutils.import_class(decorator_name)
        __import__(module)
        # Retrieve module information using pyclbr
        module_data = pyclbr.readmodule_ex(module)
        for key in module_data.keys():
            # set the decorator for the class methods
            if isinstance(module_data[key], pyclbr.Class):
                clz = importutils.import_class("%s.%s" % (module, key))
                # On Python 3, unbound methods are regular functions
                predicate = inspect.isfunction if six.PY3 else inspect.ismethod
                for method, func in inspect.getmembers(clz, predicate):
                    setattr(
                        clz, method,
                        decorator("%s.%s.%s" % (module, key, method), func))
            # set the decorator for the function
            elif isinstance(module_data[key], pyclbr.Function):
                func = importutils.import_class("%s.%s" % (module, key))
                setattr(sys.modules[module], key,
                        decorator("%s.%s" % (module, key), func))


def make_dev_path(dev, partition=None, base='/dev'):
    """Return a path to a particular device.

    >>> make_dev_path('xvdc')
    /dev/xvdc

    >>> make_dev_path('xvdc', 1)
    /dev/xvdc1
    """
    path = os.path.join(base, dev)
    if partition:
        path += str(partition)
    return path


def sanitize_hostname(hostname):
    """Return a hostname which conforms to RFC-952 and RFC-1123 specs."""
    if six.PY3:
        hostname = hostname.encode('latin-1', 'ignore')
        hostname = hostname.decode('latin-1')
    else:
        if isinstance(hostname, six.text_type):
            hostname = hostname.encode('latin-1', 'ignore')

    hostname = re.sub('[ _]', '-', hostname)
    hostname = re.sub('[^\w.-]+', '', hostname)
    hostname = hostname.lower()
    hostname = hostname.strip('.-')

    return hostname


def service_is_up(service):
    """Check whether a service is up based on last heartbeat."""
    last_heartbeat = service['updated_at'] or service['created_at']
    # Timestamps in DB are UTC.
    elapsed = (timeutils.utcnow(with_timezone=True) -
               last_heartbeat).total_seconds()
    return abs(elapsed) <= CONF.service_down_time


def read_file_as_root(file_path):
    """Secure helper to read file as root."""
    try:
        out, _err = execute('cat', file_path, run_as_root=True)
        return out
    except processutils.ProcessExecutionError:
        raise exception.FileNotFound(file_path=file_path)


def robust_file_write(directory, filename, data):
    """Robust file write.

    Use "write to temp file and rename" model for writing the
    persistence file.

    :param directory: Target directory to create a file.
    :param filename: File name to store specified data.
    :param data: String data.
    """
    tempname = None
    dirfd = None
    try:
        dirfd = os.open(directory, os.O_DIRECTORY)

        # write data to temporary file
        with tempfile.NamedTemporaryFile(prefix=filename,
                                         dir=directory,
                                         delete=False) as tf:
            tempname = tf.name
            tf.write(data.encode('utf-8'))
            tf.flush()
            os.fdatasync(tf.fileno())
            tf.close()

            # Fsync the directory to ensure the fact of the existence of
            # the temp file hits the disk.
            os.fsync(dirfd)
            # If destination file exists, it will be replaced silently.
            os.rename(tempname, os.path.join(directory, filename))
            # Fsync the directory to ensure the rename hits the disk.
            os.fsync(dirfd)
    except OSError:
        with excutils.save_and_reraise_exception():
            LOG.error(_LE("Failed to write persistence file: %(path)s."),
                      {'path': os.path.join(directory, filename)})
            if os.path.isfile(tempname):
                os.unlink(tempname)
    finally:
        if dirfd:
            os.close(dirfd)


@contextlib.contextmanager
def temporary_chown(path, owner_uid=None):
    """Temporarily chown a path.

    :params owner_uid: UID of temporary owner (defaults to current user)
    """
    if owner_uid is None:
        owner_uid = os.getuid()

    orig_uid = os.stat(path).st_uid

    if orig_uid != owner_uid:
        execute('chown', owner_uid, path, run_as_root=True)
    try:
        yield
    finally:
        if orig_uid != owner_uid:
            execute('chown', orig_uid, path, run_as_root=True)


@contextlib.contextmanager
def tempdir(**kwargs):
    tmpdir = tempfile.mkdtemp(**kwargs)
    try:
        yield tmpdir
    finally:
        try:
            shutil.rmtree(tmpdir)
        except OSError as e:
            LOG.debug('Could not remove tmpdir: %s',
                      six.text_type(e))


def walk_class_hierarchy(clazz, encountered=None):
    """Walk class hierarchy, yielding most derived classes first."""
    if not encountered:
        encountered = []
    for subclass in clazz.__subclasses__():
        if subclass not in encountered:
            encountered.append(subclass)
            # drill down to leaves first
            for subsubclass in walk_class_hierarchy(subclass, encountered):
                yield subsubclass
            yield subclass


def get_root_helper():
    return 'sudo cinder-rootwrap %s' % CONF.rootwrap_config


def brick_get_connector_properties(multipath=False, enforce_multipath=False):
    """Wrapper to automatically set root_helper in brick calls.

    :param multipath: A boolean indicating whether the connector can
                      support multipath.
    :param enforce_multipath: If True, it raises exception when multipath=True
                              is specified but multipathd is not running.
                              If False, it falls back to multipath=False
                              when multipathd is not running.
    """

    root_helper = get_root_helper()
    return connector.get_connector_properties(root_helper,
                                              CONF.my_ip,
                                              multipath,
                                              enforce_multipath)


def brick_get_connector(protocol, driver=None,
                        execute=processutils.execute,
                        use_multipath=False,
                        device_scan_attempts=3,
                        *args, **kwargs):
    """Wrapper to get a brick connector object.

    This automatically populates the required protocol as well
    as the root_helper needed to execute commands.
    """

    root_helper = get_root_helper()
    return connector.InitiatorConnector.factory(protocol, root_helper,
                                                driver=driver,
                                                execute=execute,
                                                use_multipath=use_multipath,
                                                device_scan_attempts=
                                                device_scan_attempts,
                                                *args, **kwargs)


def require_driver_initialized(driver):
    """Verifies if `driver` is initialized

    If the driver is not initialized, an exception will be raised.

    :params driver: The driver instance.
    :raises: `exception.DriverNotInitialized`
    """
    # we can't do anything if the driver didn't init
    if not driver.initialized:
        driver_name = driver.__class__.__name__
        LOG.error(_LE("Volume driver %s not initialized"), driver_name)
        raise exception.DriverNotInitialized()


def get_file_mode(path):
    """This primarily exists to make unit testing easier."""
    return stat.S_IMODE(os.stat(path).st_mode)


def get_file_gid(path):
    """This primarily exists to make unit testing easier."""
    return os.stat(path).st_gid


def get_file_size(path):
    """Returns the file size."""
    return os.stat(path).st_size


def _get_disk_of_partition(devpath, st=None):
    """Gets a disk device path and status from partition path.

    Returns a disk device path from a partition device path, and stat for
    the device. If devpath is not a partition, devpath is returned as it is.
    For example, '/dev/sda' is returned for '/dev/sda1', and '/dev/disk1' is
    for '/dev/disk1p1' ('p' is prepended to the partition number if the disk
    name ends with numbers).
    """
    diskpath = re.sub('(?:(?<=\d)p)?\d+$', '', devpath)
    if diskpath != devpath:
        try:
            st_disk = os.stat(diskpath)
            if stat.S_ISBLK(st_disk.st_mode):
                return (diskpath, st_disk)
        except OSError:
            pass
    # devpath is not a partition
    if st is None:
        st = os.stat(devpath)
    return (devpath, st)


def get_bool_param(param_string, params):
    param = params.get(param_string, False)
    if not is_valid_boolstr(param):
        msg = _('Value %(param)s for %(param_string)s is not a '
                'boolean.') % {'param': param, 'param_string': param_string}
        raise exception.InvalidParameterValue(err=msg)

    return strutils.bool_from_string(param, strict=True)


def get_blkdev_major_minor(path, lookup_for_file=True):
    """Get 'major:minor' number of block device.

    Get the device's 'major:minor' number of a block device to control
    I/O ratelimit of the specified path.
    If lookup_for_file is True and the path is a regular file, lookup a disk
    device which the file lies on and returns the result for the device.
    """
    st = os.stat(path)
    if stat.S_ISBLK(st.st_mode):
        path, st = _get_disk_of_partition(path, st)
        return '%d:%d' % (os.major(st.st_rdev), os.minor(st.st_rdev))
    elif stat.S_ISCHR(st.st_mode):
        # No I/O ratelimit control is provided for character devices
        return None
    elif lookup_for_file:
        # lookup the mounted disk which the file lies on
        out, _err = execute('df', path)
        devpath = out.split("\n")[1].split()[0]
        if devpath[0] is not '/':
            # the file is on a network file system
            return None
        return get_blkdev_major_minor(devpath, False)
    else:
        msg = _("Unable to get a block device for file \'%s\'") % path
        raise exception.Error(msg)


def check_string_length(value, name, min_length=0, max_length=None):
    """Check the length of specified string.

    :param value: the value of the string
    :param name: the name of the string
    :param min_length: the min_length of the string
    :param max_length: the max_length of the string
    """
    if not isinstance(value, six.string_types):
        msg = _("%s is not a string or unicode") % name
        raise exception.InvalidInput(message=msg)

    if len(value) < min_length:
        msg = _("%(name)s has a minimum character requirement of "
                "%(min_length)s.") % {'name': name, 'min_length': min_length}
        raise exception.InvalidInput(message=msg)

    if max_length and len(value) > max_length:
        msg = _("%(name)s has more than %(max_length)s "
                "characters.") % {'name': name, 'max_length': max_length}
        raise exception.InvalidInput(message=msg)

_visible_admin_metadata_keys = ['readonly', 'attached_mode']


def add_visible_admin_metadata(volume):
    """Add user-visible admin metadata to regular metadata.

    Extracts the admin metadata keys that are to be made visible to
    non-administrators, and adds them to the regular metadata structure for the
    passed-in volume.
    """
    visible_admin_meta = {}

    if volume.get('volume_admin_metadata'):
        if isinstance(volume['volume_admin_metadata'], dict):
            volume_admin_metadata = volume['volume_admin_metadata']
            for key in volume_admin_metadata:
                if key in _visible_admin_metadata_keys:
                    visible_admin_meta[key] = volume_admin_metadata[key]
        else:
            for item in volume['volume_admin_metadata']:
                if item['key'] in _visible_admin_metadata_keys:
                    visible_admin_meta[item['key']] = item['value']
    # avoid circular ref when volume is a Volume instance
    elif (volume.get('admin_metadata') and
            isinstance(volume.get('admin_metadata'), dict)):
        for key in _visible_admin_metadata_keys:
            if key in volume['admin_metadata'].keys():
                visible_admin_meta[key] = volume['admin_metadata'][key]

    if not visible_admin_meta:
        return

    # NOTE(zhiyan): update visible administration metadata to
    # volume metadata, administration metadata will rewrite existing key.
    if volume.get('volume_metadata'):
        orig_meta = list(volume.get('volume_metadata'))
        for item in orig_meta:
            if item['key'] in visible_admin_meta.keys():
                item['value'] = visible_admin_meta.pop(item['key'])
        for key, value in visible_admin_meta.items():
            orig_meta.append({'key': key, 'value': value})
        volume['volume_metadata'] = orig_meta
    # avoid circular ref when vol is a Volume instance
    elif (volume.get('metadata') and
            isinstance(volume.get('metadata'), dict)):
        volume['metadata'].update(visible_admin_meta)
    else:
        volume['metadata'] = visible_admin_meta


def remove_invalid_filter_options(context, filters,
                                  allowed_search_options):
    """Remove search options that are not valid for non-admin API/context."""

    if context.is_admin:
        # Allow all options
        return
    # Otherwise, strip out all unknown options
    unknown_options = [opt for opt in filters
                       if opt not in allowed_search_options]
    bad_options = ", ".join(unknown_options)
    LOG.debug("Removing options '%s' from query.", bad_options)
    for opt in unknown_options:
        del filters[opt]


def is_blk_device(dev):
    try:
        if stat.S_ISBLK(os.stat(dev).st_mode):
            return True
        return False
    except Exception:
        LOG.debug('Path %s not found in is_blk_device check', dev)
        return False


class ComparableMixin(object):
    def _compare(self, other, method):
        try:
            return method(self._cmpkey(), other._cmpkey())
        except (AttributeError, TypeError):
            # _cmpkey not implemented, or return different type,
            # so I can't compare with "other".
            return NotImplemented

    def __lt__(self, other):
        return self._compare(other, lambda s, o: s < o)

    def __le__(self, other):
        return self._compare(other, lambda s, o: s <= o)

    def __eq__(self, other):
        return self._compare(other, lambda s, o: s == o)

    def __ge__(self, other):
        return self._compare(other, lambda s, o: s >= o)

    def __gt__(self, other):
        return self._compare(other, lambda s, o: s > o)

    def __ne__(self, other):
        return self._compare(other, lambda s, o: s != o)


def retry(exceptions, interval=1, retries=3, backoff_rate=2,
          wait_random=False):

    def _retry_on_exception(e):
        return isinstance(e, exceptions)

    def _backoff_sleep(previous_attempt_number, delay_since_first_attempt_ms):
        exp = backoff_rate ** previous_attempt_number
        wait_for = interval * exp

        if wait_random:
            random.seed()
            wait_val = random.randrange(interval * 1000.0, wait_for * 1000.0)
        else:
            wait_val = wait_for * 1000.0

        LOG.debug("Sleeping for %s seconds", (wait_val / 1000.0))

        return wait_val

    def _print_stop(previous_attempt_number, delay_since_first_attempt_ms):
        delay_since_first_attempt = delay_since_first_attempt_ms / 1000.0
        LOG.debug("Failed attempt %s", previous_attempt_number)
        LOG.debug("Have been at this for %s seconds",
                  delay_since_first_attempt)
        return previous_attempt_number == retries

    if retries < 1:
        raise ValueError('Retries must be greater than or '
                         'equal to 1 (received: %s). ' % retries)

    def _decorator(f):

        @six.wraps(f)
        def _wrapper(*args, **kwargs):
            r = retrying.Retrying(retry_on_exception=_retry_on_exception,
                                  wait_func=_backoff_sleep,
                                  stop_func=_print_stop)
            return r.call(f, *args, **kwargs)

        return _wrapper

    return _decorator


def convert_str(text):
    """Convert to native string.

    Convert bytes and Unicode strings to native strings:

    * convert to bytes on Python 2:
      encode Unicode using encodeutils.safe_encode()
    * convert to Unicode on Python 3: decode bytes from UTF-8
    """
    if six.PY2:
        return encodeutils.safe_encode(text)
    else:
        if isinstance(text, bytes):
            return text.decode('utf-8')
        else:
            return text


def trace_method(f):
    """Decorates a function if TRACE_METHOD is true."""
    @functools.wraps(f)
    def trace_method_logging_wrapper(*args, **kwargs):
        if TRACE_METHOD:
            return trace(f)(*args, **kwargs)
        return f(*args, **kwargs)
    return trace_method_logging_wrapper


def trace_api(f):
    """Decorates a function if TRACE_API is true."""
    @functools.wraps(f)
    def trace_api_logging_wrapper(*args, **kwargs):
        if TRACE_API:
            return trace(f)(*args, **kwargs)
        return f(*args, **kwargs)
    return trace_api_logging_wrapper


def trace(f):
    """Trace calls to the decorated function.

    This decorator should always be defined as the outermost decorator so it
    is defined last. This is important so it does not interfere
    with other decorators.

    Using this decorator on a function will cause its execution to be logged at
    `DEBUG` level with arguments, return values, and exceptions.

    :returns: a function decorator
    """

    func_name = f.__name__

    @functools.wraps(f)
    def trace_logging_wrapper(*args, **kwargs):
        if len(args) > 0:
            maybe_self = args[0]
        else:
            maybe_self = kwargs.get('self', None)

        if maybe_self and hasattr(maybe_self, '__module__'):
            logger = logging.getLogger(maybe_self.__module__)
        else:
            logger = LOG

        # NOTE(ameade): Don't bother going any further if DEBUG log level
        # is not enabled for the logger.
        if not logger.isEnabledFor(py_logging.DEBUG):
            return f(*args, **kwargs)

        all_args = inspect.getcallargs(f, *args, **kwargs)
        logger.debug('==> %(func)s: call %(all_args)r',
                     {'func': func_name, 'all_args': all_args})

        start_time = time.time() * 1000
        try:
            result = f(*args, **kwargs)
        except Exception as exc:
            total_time = int(round(time.time() * 1000)) - start_time
            logger.debug('<== %(func)s: exception (%(time)dms) %(exc)r',
                         {'func': func_name,
                          'time': total_time,
                          'exc': exc})
            raise
        total_time = int(round(time.time() * 1000)) - start_time

        logger.debug('<== %(func)s: return (%(time)dms) %(result)r',
                     {'func': func_name,
                      'time': total_time,
                      'result': result})
        return result
    return trace_logging_wrapper


class TraceWrapperMetaclass(type):
    """Metaclass that wraps all methods of a class with trace_method.

    This metaclass will cause every function inside of the class to be
    decorated with the trace_method decorator.

    To use the metaclass you define a class like so:
    @six.add_metaclass(utils.TraceWrapperMetaclass)
    class MyClass(object):
    """
    def __new__(meta, classname, bases, classDict):
        newClassDict = {}
        for attributeName, attribute in classDict.items():
            if isinstance(attribute, types.FunctionType):
                # replace it with a wrapped version
                attribute = functools.update_wrapper(trace_method(attribute),
                                                     attribute)
            newClassDict[attributeName] = attribute

        return type.__new__(meta, classname, bases, newClassDict)


class TraceWrapperWithABCMetaclass(abc.ABCMeta, TraceWrapperMetaclass):
    """Metaclass that wraps all methods of a class with trace."""
    pass


def setup_tracing(trace_flags):
    """Set global variables for each trace flag.

    Sets variables TRACE_METHOD and TRACE_API, which represent
    whether to log method and api traces.

    :param trace_flags: a list of strings
    """
    global TRACE_METHOD
    global TRACE_API
    try:
        trace_flags = [flag.strip() for flag in trace_flags]
    except TypeError:  # Handle when trace_flags is None or a test mock
        trace_flags = []
    for invalid_flag in (set(trace_flags) - VALID_TRACE_FLAGS):
        LOG.warning(_LW('Invalid trace flag: %s'), invalid_flag)
    TRACE_METHOD = 'method' in trace_flags
    TRACE_API = 'api' in trace_flags


def resolve_hostname(hostname):
    """Resolves host name to IP address.

    Resolves a host name (my.data.point.com) to an IP address (10.12.143.11).
    This routine also works if the data passed in hostname is already an IP.
    In this case, the same IP address will be returned.

    :param hostname:  Host name to resolve.
    :returns:         IP Address for Host name.
    """
    result = socket.getaddrinfo(hostname, None)[0]
    (family, socktype, proto, canonname, sockaddr) = result
    LOG.debug('Asked to resolve hostname %(host)s and got IP %(ip)s.',
              {'host': hostname, 'ip': sockaddr[0]})
    return sockaddr[0]


def build_or_str(elements, str_format=None):
    """Builds a string of elements joined by 'or'.

    Will join strings with the 'or' word and if a str_format is provided it
    will be used to format the resulted joined string.
    If there are no elements an empty string will be returned.

    :param elements: Elements we want to join.
    :type elements: String or iterable of strings.
    :param str_format: String to use to format the response.
    :type str_format: String.
    """
    if not elements:
        return ''

    if not isinstance(elements, six.string_types):
        elements = _(' or ').join(elements)

    if str_format:
        return str_format % elements
    return elements


def calculate_virtual_free_capacity(total_capacity,
                                    free_capacity,
                                    provisioned_capacity,
                                    thin_provisioning_support,
                                    max_over_subscription_ratio,
                                    reserved_percentage):
    """Calculate the virtual free capacity based on thin provisioning support.

    :param total_capacity:  total_capacity_gb of a host_state or pool.
    :param free_capacity:   free_capacity_gb of a host_state or pool.
    :param provisioned_capacity:    provisioned_capacity_gb of a host_state
                                    or pool.
    :param thin_provisioning_support:   thin_provisioning_support of
                                        a host_state or a pool.
    :param max_over_subscription_ratio: max_over_subscription_ratio of
                                        a host_state or a pool
    :param reserved_percentage: reserved_percentage of a host_state or
                                a pool.
    :returns: the calculated virtual free capacity.
    """

    total = float(total_capacity)
    reserved = float(reserved_percentage) / 100

    if thin_provisioning_support:
        free = (total * max_over_subscription_ratio
                - provisioned_capacity
                - math.floor(total * reserved))
    else:
        # Calculate how much free space is left after taking into
        # account the reserved space.
        free = free_capacity - math.floor(total * reserved)
    return free


def validate_integer(value, name, min_value=None, max_value=None):
    """Make sure that value is a valid integer, potentially within range.

    :param value: the value of the integer
    :param name: the name of the integer
    :param min_length: the min_length of the integer
    :param max_length: the max_length of the integer
    :returns: integer
    """
    try:
        value = int(value)
    except (TypeError, ValueError, UnicodeEncodeError):
        raise webob.exc.HTTPBadRequest(explanation=(
            _('%s must be an integer.') % name))

    if min_value is not None and value < min_value:
        raise webob.exc.HTTPBadRequest(
            explanation=(_('%(value_name)s must be >= %(min_value)d') %
                         {'value_name': name, 'min_value': min_value}))
    if max_value is not None and value > max_value:
        raise webob.exc.HTTPBadRequest(
            explanation=(_('%(value_name)s must be <= %(max_value)d') %
                         {'value_name': name, 'max_value': max_value}))

    return value
