# coding: utf-8
"""
Package resource API
--------------------

A resource is a logical file contained within a package, or a logical
subdirectory thereof.  The package resource API expects resource names
to have their path parts separated with ``/``, *not* whatever the local
path separator is.  Do not use os.path operations to manipulate resource
names being passed into the API.

The package resource API is designed to work with normal filesystem packages,
.egg files, and unpacked .egg files.  It can also work in a limited way with
.zip files and with custom PEP 302 loaders that support the ``get_data()``
method.
"""

from __future__ import absolute_import

import sys
import os
import io
import time
import re
import types
import zipfile
import zipimport
import warnings
import stat
import functools
import pkgutil
import operator
import platform
import collections
import plistlib
import email.parser
import errno
import tempfile
import textwrap
import itertools
import inspect
from pkgutil import get_importer

try:
    import _imp
except ImportError:
    # Python 3.2 compatibility
    import imp as _imp

from pkg_resources.extern import six
from pkg_resources.extern.six.moves import urllib, map, filter

# capture these to bypass sandboxing
from os import utime
try:
    from os import mkdir, rename, unlink
    WRITE_SUPPORT = True
except ImportError:
    # no write support, probably under GAE
    WRITE_SUPPORT = False

from os import open as os_open
from os.path import isdir, split

try:
    import importlib.machinery as importlib_machinery
    # access attribute to force import under delayed import mechanisms.
    importlib_machinery.__name__
except ImportError:
    importlib_machinery = None

from . import py31compat
from pkg_resources.extern import appdirs
from pkg_resources.extern import packaging
__import__('pkg_resources.extern.packaging.version')
__import__('pkg_resources.extern.packaging.specifiers')
__import__('pkg_resources.extern.packaging.requirements')
__import__('pkg_resources.extern.packaging.markers')


if (3, 0) < sys.version_info < (3, 3):
    raise RuntimeError("Python 3.3 or later is required")

if six.PY2:
    # Those builtin exceptions are only defined in Python 3
    PermissionError = None
    NotADirectoryError = None

# declare some globals that will be defined later to
# satisfy the linters.
require = None
working_set = None
add_activation_listener = None
resources_stream = None
cleanup_resources = None
resource_dir = None
resource_stream = None
set_extraction_path = None
resource_isdir = None
resource_string = None
iter_entry_points = None
resource_listdir = None
resource_filename = None
resource_exists = None
_distribution_finders = None
_namespace_handlers = None
_namespace_packages = None


class PEP440Warning(RuntimeWarning):
    """
    Used when there is an issue with a version or specifier not complying with
    PEP 440.
    """


def parse_version(v):
    try:
        return packaging.version.Version(v)
    except packaging.version.InvalidVersion:
        return packaging.version.LegacyVersion(v)


_state_vars = {}


def _declare_state(vartype, **kw):
    globals().update(kw)
    _state_vars.update(dict.fromkeys(kw, vartype))


def __getstate__():
    state = {}
    g = globals()
    for k, v in _state_vars.items():
        state[k] = g['_sget_' + v](g[k])
    return state


def __setstate__(state):
    g = globals()
    for k, v in state.items():
        g['_sset_' + _state_vars[k]](k, g[k], v)
    return state


def _sget_dict(val):
    return val.copy()


def _sset_dict(key, ob, state):
    ob.clear()
    ob.update(state)


def _sget_object(val):
    return val.__getstate__()


def _sset_object(key, ob, state):
    ob.__setstate__(state)


_sget_none = _sset_none = lambda *args: None


def get_supported_platform():
    """Return this platform's maximum compatible version.

    distutils.util.get_platform() normally reports the minimum version
    of Mac OS X that would be required to *use* extensions produced by
    distutils.  But what we want when checking compatibility is to know the
    version of Mac OS X that we are *running*.  To allow usage of packages that
    explicitly require a newer version of Mac OS X, we must also know the
    current version of the OS.

    If this condition occurs for any other platform with a version in its
    platform strings, this function should be extended accordingly.
    """
    plat = get_build_platform()
    m = macosVersionString.match(plat)
    if m is not None and sys.platform == "darwin":
        try:
            plat = 'macosx-%s-%s' % ('.'.join(_macosx_vers()[:2]), m.group(3))
        except ValueError:
            # not Mac OS X
            pass
    return plat


__all__ = [
    # Basic resource access and distribution/entry point discovery
    'require', 'run_script', 'get_provider', 'get_distribution',
    'load_entry_point', 'get_entry_map', 'get_entry_info',
    'iter_entry_points',
    'resource_string', 'resource_stream', 'resource_filename',
    'resource_listdir', 'resource_exists', 'resource_isdir',

    # Environmental control
    'declare_namespace', 'working_set', 'add_activation_listener',
    'find_distributions', 'set_extraction_path', 'cleanup_resources',
    'get_default_cache',

    # Primary implementation classes
    'Environment', 'WorkingSet', 'ResourceManager',
    'Distribution', 'Requirement', 'EntryPoint',

    # Exceptions
    'ResolutionError', 'VersionConflict', 'DistributionNotFound',
    'UnknownExtra', 'ExtractionError',

    # Warnings
    'PEP440Warning',

    # Parsing functions and string utilities
    'parse_requirements', 'parse_version', 'safe_name', 'safe_version',
    'get_platform', 'compatible_platforms', 'yield_lines', 'split_sections',
    'safe_extra', 'to_filename', 'invalid_marker', 'evaluate_marker',

    # filesystem utilities
    'ensure_directory', 'normalize_path',

    # Distribution "precedence" constants
    'EGG_DIST', 'BINARY_DIST', 'SOURCE_DIST', 'CHECKOUT_DIST', 'DEVELOP_DIST',

    # "Provider" interfaces, implementations, and registration/lookup APIs
    'IMetadataProvider', 'IResourceProvider', 'FileMetadata',
    'PathMetadata', 'EggMetadata', 'EmptyProvider', 'empty_provider',
    'NullProvider', 'EggProvider', 'DefaultProvider', 'ZipProvider',
    'register_finder', 'register_namespace_handler', 'register_loader_type',
    'fixup_namespace_packages', 'get_importer',

    # Deprecated/backward compatibility only
    'run_main', 'AvailableDistributions',
]


class ResolutionError(Exception):
    """Abstract base for dependency resolution errors"""

    def __repr__(self):
        return self.__class__.__name__ + repr(self.args)


class VersionConflict(ResolutionError):
    """
    An already-installed version conflicts with the requested version.

    Should be initialized with the installed Distribution and the requested
    Requirement.
    """

    _template = "{self.dist} is installed but {self.req} is required"

    @property
    def dist(self):
        return self.args[0]

    @property
    def req(self):
        return self.args[1]

    def report(self):
        return self._template.format(**locals())

    def with_context(self, required_by):
        """
        If required_by is non-empty, return a version of self that is a
        ContextualVersionConflict.
        """
        if not required_by:
            return self
        args = self.args + (required_by,)
        return ContextualVersionConflict(*args)


class ContextualVersionConflict(VersionConflict):
    """
    A VersionConflict that accepts a third parameter, the set of the
    requirements that required the installed Distribution.
    """

    _template = VersionConflict._template + ' by {self.required_by}'

    @property
    def required_by(self):
        return self.args[2]


class DistributionNotFound(ResolutionError):
    """A requested distribution was not found"""

    _template = ("The '{self.req}' distribution was not found "
                 "and is required by {self.requirers_str}")

    @property
    def req(self):
        return self.args[0]

    @property
    def requirers(self):
        return self.args[1]

    @property
    def requirers_str(self):
        if not self.requirers:
            return 'the application'
        return ', '.join(self.requirers)

    def report(self):
        return self._template.format(**locals())

    def __str__(self):
        return self.report()


class UnknownExtra(ResolutionError):
    """Distribution doesn't have an "extra feature" of the given name"""


_provider_factories = {}

PY_MAJOR = sys.version[:3]
EGG_DIST = 3
BINARY_DIST = 2
SOURCE_DIST = 1
CHECKOUT_DIST = 0
DEVELOP_DIST = -1


def register_loader_type(loader_type, provider_factory):
    """Register `provider_factory` to make providers for `loader_type`

    `loader_type` is the type or class of a PEP 302 ``module.__loader__``,
    and `provider_factory` is a function that, passed a *module* object,
    returns an ``IResourceProvider`` for that module.
    """
    _provider_factories[loader_type] = provider_factory


def get_provider(moduleOrReq):
    """Return an IResourceProvider for the named module or requirement"""
    if isinstance(moduleOrReq, Requirement):
        return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
    try:
        module = sys.modules[moduleOrReq]
    except KeyError:
        __import__(moduleOrReq)
        module = sys.modules[moduleOrReq]
    loader = getattr(module, '__loader__', None)
    return _find_adapter(_provider_factories, loader)(module)


def _macosx_vers(_cache=[]):
    if not _cache:
        version = platform.mac_ver()[0]
        # fallback for MacPorts
        if version == '':
            plist = '/System/Library/CoreServices/SystemVersion.plist'
            if os.path.exists(plist):
                if hasattr(plistlib, 'readPlist'):
                    plist_content = plistlib.readPlist(plist)
                    if 'ProductVersion' in plist_content:
                        version = plist_content['ProductVersion']

        _cache.append(version.split('.'))
    return _cache[0]


def _macosx_arch(machine):
    return {'PowerPC': 'ppc', 'Power_Macintosh': 'ppc'}.get(machine, machine)


def get_build_platform():
    """Return this platform's string for platform-specific distributions

    XXX Currently this is the same as ``distutils.util.get_platform()``, but it
    needs some hacks for Linux and Mac OS X.
    """
    try:
        # Python 2.7 or >=3.2
        from sysconfig import get_platform
    except ImportError:
        from distutils.util import get_platform

    plat = get_platform()
    if sys.platform == "darwin" and not plat.startswith('macosx-'):
        try:
            version = _macosx_vers()
            machine = os.uname()[4].replace(" ", "_")
            return "macosx-%d.%d-%s" % (
                int(version[0]), int(version[1]),
                _macosx_arch(machine),
            )
        except ValueError:
            # if someone is running a non-Mac darwin system, this will fall
            # through to the default implementation
            pass
    return plat


macosVersionString = re.compile(r"macosx-(\d+)\.(\d+)-(.*)")
darwinVersionString = re.compile(r"darwin-(\d+)\.(\d+)\.(\d+)-(.*)")
# XXX backward compat
get_platform = get_build_platform


def compatible_platforms(provided, required):
    """Can code for the `provided` platform run on the `required` platform?

    Returns true if either platform is ``None``, or the platforms are equal.

    XXX Needs compatibility checks for Linux and other unixy OSes.
    """
    if provided is None or required is None or provided == required:
        # easy case
        return True

    # Mac OS X special cases
    reqMac = macosVersionString.match(required)
    if reqMac:
        provMac = macosVersionString.match(provided)

        # is this a Mac package?
        if not provMac:
            # this is backwards compatibility for packages built before
            # setuptools 0.6. All packages built after this point will
            # use the new macosx designation.
            provDarwin = darwinVersionString.match(provided)
            if provDarwin:
                dversion = int(provDarwin.group(1))
                macosversion = "%s.%s" % (reqMac.group(1), reqMac.group(2))
                if dversion == 7 and macosversion >= "10.3" or \
                        dversion == 8 and macosversion >= "10.4":
                    return True
            # egg isn't macosx or legacy darwin
            return False

        # are they the same major version and machine type?
        if provMac.group(1) != reqMac.group(1) or \
                provMac.group(3) != reqMac.group(3):
            return False

        # is the required OS major update >= the provided one?
        if int(provMac.group(2)) > int(reqMac.group(2)):
            return False

        return True

    # XXX Linux and other platforms' special cases should go here
    return False


def run_script(dist_spec, script_name):
    """Locate distribution `dist_spec` and run its `script_name` script"""
    ns = sys._getframe(1).f_globals
    name = ns['__name__']
    ns.clear()
    ns['__name__'] = name
    require(dist_spec)[0].run_script(script_name, ns)


# backward compatibility
run_main = run_script


def get_distribution(dist):
    """Return a current distribution object for a Requirement or string"""
    if isinstance(dist, six.string_types):
        dist = Requirement.parse(dist)
    if isinstance(dist, Requirement):
        dist = get_provider(dist)
    if not isinstance(dist, Distribution):
        raise TypeError("Expected string, Requirement, or Distribution", dist)
    return dist


def load_entry_point(dist, group, name):
    """Return `name` entry point of `group` for `dist` or raise ImportError"""
    return get_distribution(dist).load_entry_point(group, name)


def get_entry_map(dist, group=None):
    """Return the entry point map for `group`, or the full entry map"""
    return get_distribution(dist).get_entry_map(group)


def get_entry_info(dist, group, name):
    """Return the EntryPoint object for `group`+`name`, or ``None``"""
    return get_distribution(dist).get_entry_info(group, name)


class IMetadataProvider:
    def has_metadata(name):
        """Does the package's distribution contain the named metadata?"""

    def get_metadata(name):
        """The named metadata resource as a string"""

    def get_metadata_lines(name):
        """Yield named metadata resource as list of non-blank non-comment lines

       Leading and trailing whitespace is stripped from each line, and lines
       with ``#`` as the first non-blank character are omitted."""

    def metadata_isdir(name):
        """Is the named metadata a directory?  (like ``os.path.isdir()``)"""

    def metadata_listdir(name):
        """List of metadata names in the directory (like ``os.listdir()``)"""

    def run_script(script_name, namespace):
        """Execute the named script in the supplied namespace dictionary"""


class IResourceProvider(IMetadataProvider):
    """An object that provides access to package resources"""

    def get_resource_filename(manager, resource_name):
        """Return a true filesystem path for `resource_name`

        `manager` must be an ``IResourceManager``"""

    def get_resource_stream(manager, resource_name):
        """Return a readable file-like object for `resource_name`

        `manager` must be an ``IResourceManager``"""

    def get_resource_string(manager, resource_name):
        """Return a string containing the contents of `resource_name`

        `manager` must be an ``IResourceManager``"""

    def has_resource(resource_name):
        """Does the package contain the named resource?"""

    def resource_isdir(resource_name):
        """Is the named resource a directory?  (like ``os.path.isdir()``)"""

    def resource_listdir(resource_name):
        """List of resource names in the directory (like ``os.listdir()``)"""


class WorkingSet(object):
    """A collection of active distributions on sys.path (or a similar list)"""

    def __init__(self, entries=None):
        """Create working set from list of path entries (default=sys.path)"""
        self.entries = []
        self.entry_keys = {}
        self.by_key = {}
        self.callbacks = []

        if entries is None:
            entries = sys.path

        for entry in entries:
            self.add_entry(entry)

    @classmethod
    def _build_master(cls):
        """
        Prepare the master working set.
        """
        ws = cls()
        try:
            from __main__ import __requires__
        except ImportError:
            # The main program does not list any requirements
            return ws

        # ensure the requirements are met
        try:
            ws.require(__requires__)
        except VersionConflict:
            return cls._build_from_requirements(__requires__)

        return ws

    @classmethod
    def _build_from_requirements(cls, req_spec):
        """
        Build a working set from a requirement spec. Rewrites sys.path.
        """
        # try it without defaults already on sys.path
        # by starting with an empty path
        ws = cls([])
        reqs = parse_requirements(req_spec)
        dists = ws.resolve(reqs, Environment())
        for dist in dists:
            ws.add(dist)

        # add any missing entries from sys.path
        for entry in sys.path:
            if entry not in ws.entries:
                ws.add_entry(entry)

        # then copy back to sys.path
        sys.path[:] = ws.entries
        return ws

    def add_entry(self, entry):
        """Add a path item to ``.entries``, finding any distributions on it

        ``find_distributions(entry, True)`` is used to find distributions
        corresponding to the path entry, and they are added.  `entry` is
        always appended to ``.entries``, even if it is already present.
        (This is because ``sys.path`` can contain the same value more than
        once, and the ``.entries`` of the ``sys.path`` WorkingSet should always
        equal ``sys.path``.)
        """
        self.entry_keys.setdefault(entry, [])
        self.entries.append(entry)
        for dist in find_distributions(entry, True):
            self.add(dist, entry, False)

    def __contains__(self, dist):
        """True if `dist` is the active distribution for its project"""
        return self.by_key.get(dist.key) == dist

    def find(self, req):
        """Find a distribution matching requirement `req`

        If there is an active distribution for the requested project, this
        returns it as long as it meets the version requirement specified by
        `req`.  But, if there is an active distribution for the project and it
        does *not* meet the `req` requirement, ``VersionConflict`` is raised.
        If there is no active distribution for the requested project, ``None``
        is returned.
        """
        dist = self.by_key.get(req.key)
        if dist is not None and dist not in req:
            # XXX add more info
            raise VersionConflict(dist, req)
        return dist

    def iter_entry_points(self, group, name=None):
        """Yield entry point objects from `group` matching `name`

        If `name` is None, yields all entry points in `group` from all
        distributions in the working set, otherwise only ones matching
        both `group` and `name` are yielded (in distribution order).
        """
        for dist in self:
            entries = dist.get_entry_map(group)
            if name is None:
                for ep in entries.values():
                    yield ep
            elif name in entries:
                yield entries[name]

    def run_script(self, requires, script_name):
        """Locate distribution for `requires` and run `script_name` script"""
        ns = sys._getframe(1).f_globals
        name = ns['__name__']
        ns.clear()
        ns['__name__'] = name
        self.require(requires)[0].run_script(script_name, ns)

    def __iter__(self):
        """Yield distributions for non-duplicate projects in the working set

        The yield order is the order in which the items' path entries were
        added to the working set.
        """
        seen = {}
        for item in self.entries:
            if item not in self.entry_keys:
                # workaround a cache issue
                continue

            for key in self.entry_keys[item]:
                if key not in seen:
                    seen[key] = 1
                    yield self.by_key[key]

    def add(self, dist, entry=None, insert=True, replace=False):
        """Add `dist` to working set, associated with `entry`

        If `entry` is unspecified, it defaults to the ``.location`` of `dist`.
        On exit from this routine, `entry` is added to the end of the working
        set's ``.entries`` (if it wasn't already present).

        `dist` is only added to the working set if it's for a project that
        doesn't already have a distribution in the set, unless `replace=True`.
        If it's added, any callbacks registered with the ``subscribe()`` method
        will be called.
        """
        if insert:
            dist.insert_on(self.entries, entry, replace=replace)

        if entry is None:
            entry = dist.location
        keys = self.entry_keys.setdefault(entry, [])
        keys2 = self.entry_keys.setdefault(dist.location, [])
        if not replace and dist.key in self.by_key:
            # ignore hidden distros
            return

        self.by_key[dist.key] = dist
        if dist.key not in keys:
            keys.append(dist.key)
        if dist.key not in keys2:
            keys2.append(dist.key)
        self._added_new(dist)

    def resolve(self, requirements, env=None, installer=None,
                replace_conflicting=False, extras=None):
        """List all distributions needed to (recursively) meet `requirements`

        `requirements` must be a sequence of ``Requirement`` objects.  `env`,
        if supplied, should be an ``Environment`` instance.  If
        not supplied, it defaults to all distributions available within any
        entry or distribution in the working set.  `installer`, if supplied,
        will be invoked with each requirement that cannot be met by an
        already-installed distribution; it should return a ``Distribution`` or
        ``None``.

        Unless `replace_conflicting=True`, raises a VersionConflict exception
        if
        any requirements are found on the path that have the correct name but
        the wrong version.  Otherwise, if an `installer` is supplied it will be
        invoked to obtain the correct version of the requirement and activate
        it.

        `extras` is a list of the extras to be used with these requirements.
        This is important because extra requirements may look like `my_req;
        extra = "my_extra"`, which would otherwise be interpreted as a purely
        optional requirement.  Instead, we want to be able to assert that these
        requirements are truly required.
        """

        # set up the stack
        requirements = list(requirements)[::-1]
        # set of processed requirements
        processed = {}
        # key -> dist
        best = {}
        to_activate = []

        req_extras = _ReqExtras()

        # Mapping of requirement to set of distributions that required it;
        # useful for reporting info about conflicts.
        required_by = collections.defaultdict(set)

        while requirements:
            # process dependencies breadth-first
            req = requirements.pop(0)
            if req in processed:
                # Ignore cyclic or redundant dependencies
                continue

            if not req_extras.markers_pass(req, extras):
                continue

            dist = best.get(req.key)
            if dist is None:
                # Find the best distribution and add it to the map
                dist = self.by_key.get(req.key)
                if dist is None or (dist not in req and replace_conflicting):
                    ws = self
                    if env is None:
                        if dist is None:
                            env = Environment(self.entries)
                        else:
                            # Use an empty environment and workingset to avoid
                            # any further conflicts with the conflicting
                            # distribution
                            env = Environment([])
                            ws = WorkingSet([])
                    dist = best[req.key] = env.best_match(
                        req, ws, installer,
                        replace_conflicting=replace_conflicting
                    )
                    if dist is None:
                        requirers = required_by.get(req, None)
                        raise DistributionNotFound(req, requirers)
                to_activate.append(dist)
            if dist not in req:
                # Oops, the "best" so far conflicts with a dependency
                dependent_req = required_by[req]
                raise VersionConflict(dist, req).with_context(dependent_req)

            # push the new requirements onto the stack
            new_requirements = dist.requires(req.extras)[::-1]
            requirements.extend(new_requirements)

            # Register the new requirements needed by req
            for new_requirement in new_requirements:
                required_by[new_requirement].add(req.project_name)
                req_extras[new_requirement] = req.extras

            processed[req] = True

        # return list of distros to activate
        return to_activate

    def find_plugins(
            self, plugin_env, full_env=None, installer=None, fallback=True):
        """Find all activatable distributions in `plugin_env`

        Example usage::

            distributions, errors = working_set.find_plugins(
                Environment(plugin_dirlist)
            )
            # add plugins+libs to sys.path
            map(working_set.add, distributions)
            # display errors
            print('Could not load', errors)

        The `plugin_env` should be an ``Environment`` instance that contains
        only distributions that are in the project's "plugin directory" or
        directories. The `full_env`, if supplied, should be an ``Environment``
        contains all currently-available distributions.  If `full_env` is not
        supplied, one is created automatically from the ``WorkingSet`` this
        method is called on, which will typically mean that every directory on
        ``sys.path`` will be scanned for distributions.

        `installer` is a standard installer callback as used by the
        ``resolve()`` method. The `fallback` flag indicates whether we should
        attempt to resolve older versions of a plugin if the newest version
        cannot be resolved.

        This method returns a 2-tuple: (`distributions`, `error_info`), where
        `distributions` is a list of the distributions found in `plugin_env`
        that were loadable, along with any other distributions that are needed
        to resolve their dependencies.  `error_info` is a dictionary mapping
        unloadable plugin distributions to an exception instance describing the
        error that occurred. Usually this will be a ``DistributionNotFound`` or
        ``VersionConflict`` instance.
        """

        plugin_projects = list(plugin_env)
        # scan project names in alphabetic order
        plugin_projects.sort()

        error_info = {}
        distributions = {}

        if full_env is None:
            env = Environment(self.entries)
            env += plugin_env
        else:
            env = full_env + plugin_env

        shadow_set = self.__class__([])
        # put all our entries in shadow_set
        list(map(shadow_set.add, self))

        for project_name in plugin_projects:

            for dist in plugin_env[project_name]:

                req = [dist.as_requirement()]

                try:
                    resolvees = shadow_set.resolve(req, env, installer)

                except ResolutionError as v:
                    # save error info
                    error_info[dist] = v
                    if fallback:
                        # try the next older version of project
                        continue
                    else:
                        # give up on this project, keep going
                        break

                else:
                    list(map(shadow_set.add, resolvees))
                    distributions.update(dict.fromkeys(resolvees))

                    # success, no need to try any more versions of this project
                    break

        distributions = list(distributions)
        distributions.sort()

        return distributions, error_info

    def require(self, *requirements):
        """Ensure that distributions matching `requirements` are activated

        `requirements` must be a string or a (possibly-nested) sequence
        thereof, specifying the distributions and versions required.  The
        return value is a sequence of the distributions that needed to be
        activated to fulfill the requirements; all relevant distributions are
        included, even if they were already activated in this working set.
        """
        needed = self.resolve(parse_requirements(requirements))

        for dist in needed:
            self.add(dist)

        return needed

    def subscribe(self, callback, existing=True):
        """Invoke `callback` for all distributions

        If `existing=True` (default),
        call on all existing ones, as well.
        """
        if callback in self.callbacks:
            return
        self.callbacks.append(callback)
        if not existing:
            return
        for dist in self:
            callback(dist)

    def _added_new(self, dist):
        for callback in self.callbacks:
            callback(dist)

    def __getstate__(self):
        return (
            self.entries[:], self.entry_keys.copy(), self.by_key.copy(),
            self.callbacks[:]
        )

    def __setstate__(self, e_k_b_c):
        entries, keys, by_key, callbacks = e_k_b_c
        self.entries = entries[:]
        self.entry_keys = keys.copy()
        self.by_key = by_key.copy()
        self.callbacks = callbacks[:]


class _ReqExtras(dict):
    """
    Map each requirement to the extras that demanded it.
    """

    def markers_pass(self, req, extras=None):
        """
        Evaluate markers for req against each extra that
        demanded it.

        Return False if the req has a marker and fails
        evaluation. Otherwise, return True.
        """
        extra_evals = (
            req.marker.evaluate({'extra': extra})
            for extra in self.get(req, ()) + (extras or (None,))
        )
        return not req.marker or any(extra_evals)


class Environment(object):
    """Searchable snapshot of distributions on a search path"""

    def __init__(
            self, search_path=None, platform=get_supported_platform(),
            python=PY_MAJOR):
        """Snapshot distributions available on a search path

        Any distributions found on `search_path` are added to the environment.
        `search_path` should be a sequence of ``sys.path`` items.  If not
        supplied, ``sys.path`` is used.

        `platform` is an optional string specifying the name of the platform
        that platform-specific distributions must be compatible with.  If
        unspecified, it defaults to the current platform.  `python` is an
        optional string naming the desired version of Python (e.g. ``'3.3'``);
        it defaults to the current version.

        You may explicitly set `platform` (and/or `python`) to ``None`` if you
        wish to map *all* distributions, not just those compatible with the
        running platform or Python version.
        """
        self._distmap = {}
        self.platform = platform
        self.python = python
        self.scan(search_path)

    def can_add(self, dist):
        """Is distribution `dist` acceptable for this environment?

        The distribution must match the platform and python version
        requirements specified when this environment was created, or False
        is returned.
        """
        py_compat = (
            self.python is None
            or dist.py_version is None
            or dist.py_version == self.python
        )
        return py_compat and compatible_platforms(dist.platform, self.platform)

    def remove(self, dist):
        """Remove `dist` from the environment"""
        self._distmap[dist.key].remove(dist)

    def scan(self, search_path=None):
        """Scan `search_path` for distributions usable in this environment

        Any distributions found are added to the environment.
        `search_path` should be a sequence of ``sys.path`` items.  If not
        supplied, ``sys.path`` is used.  Only distributions conforming to
        the platform/python version defined at initialization are added.
        """
        if search_path is None:
            search_path = sys.path

        for item in search_path:
            for dist in find_distributions(item):
                self.add(dist)

    def __getitem__(self, project_name):
        """Return a newest-to-oldest list of distributions for `project_name`

        Uses case-insensitive `project_name` comparison, assuming all the
        project's distributions use their project's name converted to all
        lowercase as their key.

        """
        distribution_key = project_name.lower()
        return self._distmap.get(distribution_key, [])

    def add(self, dist):
        """Add `dist` if we ``can_add()`` it and it has not already been added
        """
        if self.can_add(dist) and dist.has_version():
            dists = self._distmap.setdefault(dist.key, [])
            if dist not in dists:
                dists.append(dist)
                dists.sort(key=operator.attrgetter('hashcmp'), reverse=True)

    def best_match(
            self, req, working_set, installer=None, replace_conflicting=False):
        """Find distribution best matching `req` and usable on `working_set`

        This calls the ``find(req)`` method of the `working_set` to see if a
        suitable distribution is already active.  (This may raise
        ``VersionConflict`` if an unsuitable version of the project is already
        active in the specified `working_set`.)  If a suitable distribution
        isn't active, this method returns the newest distribution in the
        environment that meets the ``Requirement`` in `req`.  If no suitable
        distribution is found, and `installer` is supplied, then the result of
        calling the environment's ``obtain(req, installer)`` method will be
        returned.
        """
        try:
            dist = working_set.find(req)
        except VersionConflict:
            if not replace_conflicting:
                raise
            dist = None
        if dist is not None:
            return dist
        for dist in self[req.key]:
            if dist in req:
                return dist
        # try to download/install
        return self.obtain(req, installer)

    def obtain(self, requirement, installer=None):
        """Obtain a distribution matching `requirement` (e.g. via download)

        Obtain a distro that matches requirement (e.g. via download).  In the
        base ``Environment`` class, this routine just returns
        ``installer(requirement)``, unless `installer` is None, in which case
        None is returned instead.  This method is a hook that allows subclasses
        to attempt other ways of obtaining a distribution before falling back
        to the `installer` argument."""
        if installer is not None:
            return installer(requirement)

    def __iter__(self):
        """Yield the unique project names of the available distributions"""
        for key in self._distmap.keys():
            if self[key]:
                yield key

    def __iadd__(self, other):
        """In-place addition of a distribution or environment"""
        if isinstance(other, Distribution):
            self.add(other)
        elif isinstance(other, Environment):
            for project in other:
                for dist in other[project]:
                    self.add(dist)
        else:
            raise TypeError("Can't add %r to environment" % (other,))
        return self

    def __add__(self, other):
        """Add an environment or distribution to an environment"""
        new = self.__class__([], platform=None, python=None)
        for env in self, other:
            new += env
        return new


# XXX backward compatibility
AvailableDistributions = Environment


class ExtractionError(RuntimeError):
    """An error occurred extracting a resource

    The following attributes are available from instances of this exception:

    manager
        The resource manager that raised this exception

    cache_path
        The base directory for resource extraction

    original_error
        The exception instance that caused extraction to fail
    """


class ResourceManager:
    """Manage resource extraction and packages"""
    extraction_path = None

    def __init__(self):
        self.cached_files = {}

    def resource_exists(self, package_or_requirement, resource_name):
        """Does the named resource exist?"""
        return get_provider(package_or_requirement).has_resource(resource_name)

    def resource_isdir(self, package_or_requirement, resource_name):
        """Is the named resource an existing directory?"""
        return get_provider(package_or_requirement).resource_isdir(
            resource_name
        )

    def resource_filename(self, package_or_requirement, resource_name):
        """Return a true filesystem path for specified resource"""
        return get_provider(package_or_requirement).get_resource_filename(
            self, resource_name
        )

    def resource_stream(self, package_or_requirement, resource_name):
        """Return a readable file-like object for specified resource"""
        return get_provider(package_or_requirement).get_resource_stream(
            self, resource_name
        )

    def resource_string(self, package_or_requirement, resource_name):
        """Return specified resource as a string"""
        return get_provider(package_or_requirement).get_resource_string(
            self, resource_name
        )

    def resource_listdir(self, package_or_requirement, resource_name):
        """List the contents of the named resource directory"""
        return get_provider(package_or_requirement).resource_listdir(
            resource_name
        )

    def extraction_error(self):
        """Give an error message for problems extracting file(s)"""

        old_exc = sys.exc_info()[1]
        cache_path = self.extraction_path or get_default_cache()

        tmpl = textwrap.dedent("""
            Can't extract file(s) to egg cache

            The following error occurred while trying to extract file(s)
            to the Python egg cache:

              {old_exc}

            The Python egg cache directory is currently set to:

              {cache_path}

            Perhaps your account does not have write access to this directory?
            You can change the cache directory by setting the PYTHON_EGG_CACHE
            environment variable to point to an accessible directory.
            """).lstrip()
        err = ExtractionError(tmpl.format(**locals()))
        err.manager = self
        err.cache_path = cache_path
        err.original_error = old_exc
        raise err

    def get_cache_path(self, archive_name, names=()):
        """Return absolute location in cache for `archive_name` and `names`

        The parent directory of the resulting path will be created if it does
        not already exist.  `archive_name` should be the base filename of the
        enclosing egg (which may not be the name of the enclosing zipfile!),
        including its ".egg" extension.  `names`, if provided, should be a
        sequence of path name parts "under" the egg's extraction location.

        This method should only be called by resource providers that need to
        obtain an extraction location, and only for names they intend to
        extract, as it tracks the generated names for possible cleanup later.
        """
        extract_path = self.extraction_path or get_default_cache()
        target_path = os.path.join(extract_path, archive_name + '-tmp', *names)
        try:
            _bypass_ensure_directory(target_path)
        except Exception:
            self.extraction_error()

        self._warn_unsafe_extraction_path(extract_path)

        self.cached_files[target_path] = 1
        return target_path

    @staticmethod
    def _warn_unsafe_extraction_path(path):
        """
        If the default extraction path is overridden and set to an insecure
        location, such as /tmp, it opens up an opportunity for an attacker to
        replace an extracted file with an unauthorized payload. Warn the user
        if a known insecure location is used.

        See Distribute #375 for more details.
        """
        if os.name == 'nt' and not path.startswith(os.environ['windir']):
            # On Windows, permissions are generally restrictive by default
            #  and temp directories are not writable by other users, so
            #  bypass the warning.
            return
        mode = os.stat(path).st_mode
        if mode & stat.S_IWOTH or mode & stat.S_IWGRP:
            msg = (
                "%s is writable by group/others and vulnerable to attack "
                "when "
                "used with get_resource_filename. Consider a more secure "
                "location (set with .set_extraction_path or the "
                "PYTHON_EGG_CACHE environment variable)." % path
            )
            warnings.warn(msg, UserWarning)

    def postprocess(self, tempname, filename):
        """Perform any platform-specific postprocessing of `tempname`

        This is where Mac header rewrites should be done; other platforms don't
        have anything special they should do.

        Resource providers should call this method ONLY after successfully
        extracting a compressed resource.  They must NOT call it on resources
        that are already in the filesystem.

        `tempname` is the current (temporary) name of the file, and `filename`
        is the name it will be renamed to by the caller after this routine
        returns.
        """

        if os.name == 'posix':
            # Make the resource executable
            mode = ((os.stat(tempname).st_mode) | 0o555) & 0o7777
            os.chmod(tempname, mode)

    def set_extraction_path(self, path):
        """Set the base path where resources will be extracted to, if needed.

        If you do not call this routine before any extractions take place, the
        path defaults to the return value of ``get_default_cache()``.  (Which
        is based on the ``PYTHON_EGG_CACHE`` environment variable, with various
        platform-specific fallbacks.  See that routine's documentation for more
        details.)

        Resources are extracted to subdirectories of this path based upon
        information given by the ``IResourceProvider``.  You may set this to a
        temporary directory, but then you must call ``cleanup_resources()`` to
        delete the extracted files when done.  There is no guarantee that
        ``cleanup_resources()`` will be able to remove all extracted files.

        (Note: you may not change the extraction path for a given resource
        manager once resources have been extracted, unless you first call
        ``cleanup_resources()``.)
        """
        if self.cached_files:
            raise ValueError(
                "Can't change extraction path, files already extracted"
            )

        self.extraction_path = path

    def cleanup_resources(self, force=False):
        """
        Delete all extracted resource files and directories, returning a list
        of the file and directory names that could not be successfully removed.
        This function does not have any concurrency protection, so it should
        generally only be called when the extraction path is a temporary
        directory exclusive to a single process.  This method is not
        automatically called; you must call it explicitly or register it as an
        ``atexit`` function if you wish to ensure cleanup of a temporary
        directory used for extractions.
        """
        # XXX


def get_default_cache():
    """
    Return the ``PYTHON_EGG_CACHE`` environment variable
    or a platform-relevant user cache dir for an app
    named "Python-Eggs".
    """
    return (
        os.environ.get('PYTHON_EGG_CACHE')
        or appdirs.user_cache_dir(appname='Python-Eggs')
    )


def safe_name(name):
    """Convert an arbitrary string to a standard distribution name

    Any runs of non-alphanumeric/. characters are replaced with a single '-'.
    """
    return re.sub('[^A-Za-z0-9.]+', '-', name)


def safe_version(version):
    """
    Convert an arbitrary string to a standard version string
    """
    try:
        # normalize the version
        return str(packaging.version.Version(version))
    except packaging.version.InvalidVersion:
        version = version.replace(' ', '.')
        return re.sub('[^A-Za-z0-9.]+', '-', version)


def safe_extra(extra):
    """Convert an arbitrary string to a standard 'extra' name

    Any runs of non-alphanumeric characters are replaced with a single '_',
    and the result is always lowercased.
    """
    return re.sub('[^A-Za-z0-9.-]+', '_', extra).lower()


def to_filename(name):
    """Convert a project or version name to its filename-escaped form

    Any '-' characters are currently replaced with '_'.
    """
    return name.replace('-', '_')


def invalid_marker(text):
    """
    Validate text as a PEP 508 environment marker; return an exception
    if invalid or False otherwise.
    """
    try:
        evaluate_marker(text)
    except SyntaxError as e:
        e.filename = None
        e.lineno = None
        return e
    return False


def evaluate_marker(text, extra=None):
    """
    Evaluate a PEP 508 environment marker.
    Return a boolean indicating the marker result in this environment.
    Raise SyntaxError if marker is invalid.

    This implementation uses the 'pyparsing' module.
    """
    try:
        marker = packaging.markers.Marker(text)
        return marker.evaluate()
    except packaging.markers.InvalidMarker as e:
        raise SyntaxError(e)


class NullProvider:
    """Try to implement resources and metadata for arbitrary PEP 302 loaders"""

    egg_name = None
    egg_info = None
    loader = None

    def __init__(self, module):
        self.loader = getattr(module, '__loader__', None)
        self.module_path = os.path.dirname(getattr(module, '__file__', ''))

    def get_resource_filename(self, manager, resource_name):
        return self._fn(self.module_path, resource_name)

    def get_resource_stream(self, manager, resource_name):
        return io.BytesIO(self.get_resource_string(manager, resource_name))

    def get_resource_string(self, manager, resource_name):
        return self._get(self._fn(self.module_path, resource_name))

    def has_resource(self, resource_name):
        return self._has(self._fn(self.module_path, resource_name))

    def has_metadata(self, name):
        return self.egg_info and self._has(self._fn(self.egg_info, name))

    def get_metadata(self, name):
        if not self.egg_info:
            return ""
        value = self._get(self._fn(self.egg_info, name))
        return value.decode('utf-8') if six.PY3 else value

    def get_metadata_lines(self, name):
        return yield_lines(self.get_metadata(name))

    def resource_isdir(self, resource_name):
        return self._isdir(self._fn(self.module_path, resource_name))

    def metadata_isdir(self, name):
        return self.egg_info and self._isdir(self._fn(self.egg_info, name))

    def resource_listdir(self, resource_name):
        return self._listdir(self._fn(self.module_path, resource_name))

    def metadata_listdir(self, name):
        if self.egg_info:
            return self._listdir(self._fn(self.egg_info, name))
        return []

    def run_script(self, script_name, namespace):
        script = 'scripts/' + script_name
        if not self.has_metadata(script):
            raise ResolutionError(
                "Script {script!r} not found in metadata at {self.egg_info!r}"
                .format(**locals()),
            )
        script_text = self.get_metadata(script).replace('\r\n', '\n')
        script_text = script_text.replace('\r', '\n')
        script_filename = self._fn(self.egg_info, script)
        namespace['__file__'] = script_filename
        if os.path.exists(script_filename):
            source = open(script_filename).read()
            code = compile(source, script_filename, 'exec')
            exec(code, namespace, namespace)
        else:
            from linecache import cache
            cache[script_filename] = (
                len(script_text), 0, script_text.split('\n'), script_filename
            )
            script_code = compile(script_text, script_filename, 'exec')
            exec(script_code, namespace, namespace)

    def _has(self, path):
        raise NotImplementedError(
            "Can't perform this operation for unregistered loader type"
        )

    def _isdir(self, path):
        raise NotImplementedError(
            "Can't perform this operation for unregistered loader type"
        )

    def _listdir(self, path):
        raise NotImplementedError(
            "Can't perform this operation for unregistered loader type"
        )

    def _fn(self, base, resource_name):
        if resource_name:
            return os.path.join(base, *resource_name.split('/'))
        return base

    def _get(self, path):
        if hasattr(self.loader, 'get_data'):
            return self.loader.get_data(path)
        raise NotImplementedError(
            "Can't perform this operation for loaders without 'get_data()'"
        )


register_loader_type(object, NullProvider)


class EggProvider(NullProvider):
    """Provider based on a virtual filesystem"""

    def __init__(self, module):
        NullProvider.__init__(self, module)
        self._setup_prefix()

    def _setup_prefix(self):
        # we assume here that our metadata may be nested inside a "basket"
        # of multiple eggs; that's why we use module_path instead of .archive
        path = self.module_path
        old = None
        while path != old:
            if _is_egg_path(path):
                self.egg_name = os.path.basename(path)
                self.egg_info = os.path.join(path, 'EGG-INFO')
                self.egg_root = path
                break
            old = path
            path, base = os.path.split(path)


class DefaultProvider(EggProvider):
    """Provides access to package resources in the filesystem"""

    def _has(self, path):
        return os.path.exists(path)

    def _isdir(self, path):
        return os.path.isdir(path)

    def _listdir(self, path):
        return os.listdir(path)

    def get_resource_stream(self, manager, resource_name):
        return open(self._fn(self.module_path, resource_name), 'rb')

    def _get(self, path):
        with open(path, 'rb') as stream:
            return stream.read()

    @classmethod
    def _register(cls):
        loader_cls = getattr(
            importlib_machinery,
            'SourceFileLoader',
            type(None),
        )
        register_loader_type(loader_cls, cls)


DefaultProvider._register()


class EmptyProvider(NullProvider):
    """Provider that returns nothing for all requests"""

    module_path = None

    _isdir = _has = lambda self, path: False

    def _get(self, path):
        return ''

    def _listdir(self, path):
        return []

    def __init__(self):
        pass


empty_provider = EmptyProvider()


class ZipManifests(dict):
    """
    zip manifest builder
    """

    @classmethod
    def build(cls, path):
        """
        Build a dictionary similar to the zipimport directory
        caches, except instead of tuples, store ZipInfo objects.

        Use a platform-specific path separator (os.sep) for the path keys
        for compatibility with pypy on Windows.
        """
        with zipfile.ZipFile(path) as zfile:
            items = (
                (
                    name.replace('/', os.sep),
                    zfile.getinfo(name),
                )
                for name in zfile.namelist()
            )
            return dict(items)

    load = build


class MemoizedZipManifests(ZipManifests):
    """
    Memoized zipfile manifests.
    """
    manifest_mod = collections.namedtuple('manifest_mod', 'manifest mtime')

    def load(self, path):
        """
        Load a manifest at path or return a suitable manifest already loaded.
        """
        path = os.path.normpath(path)
        mtime = os.stat(path).st_mtime

        if path not in self or self[path].mtime != mtime:
            manifest = self.build(path)
            self[path] = self.manifest_mod(manifest, mtime)

        return self[path].manifest


class ZipProvider(EggProvider):
    """Resource support for zips and eggs"""

    eagers = None
    _zip_manifests = MemoizedZipManifests()

    def __init__(self, module):
        EggProvider.__init__(self, module)
        self.zip_pre = self.loader.archive + os.sep

    def _zipinfo_name(self, fspath):
        # Convert a virtual filename (full path to file) into a zipfile subpath
        # usable with the zipimport directory cache for our target archive
        fspath = fspath.rstrip(os.sep)
        if fspath == self.loader.archive:
            return ''
        if fspath.startswith(self.zip_pre):
            return fspath[len(self.zip_pre):]
        raise AssertionError(
            "%s is not a subpath of %s" % (fspath, self.zip_pre)
        )

    def _parts(self, zip_path):
        # Convert a zipfile subpath into an egg-relative path part list.
        # pseudo-fs path
        fspath = self.zip_pre + zip_path
        if fspath.startswith(self.egg_root + os.sep):
            return fspath[len(self.egg_root) + 1:].split(os.sep)
        raise AssertionError(
            "%s is not a subpath of %s" % (fspath, self.egg_root)
        )

    @property
    def zipinfo(self):
        return self._zip_manifests.load(self.loader.archive)

    def get_resource_filename(self, manager, resource_name):
        if not self.egg_name:
            raise NotImplementedError(
                "resource_filename() only supported for .egg, not .zip"
            )
        # no need to lock for extraction, since we use temp names
        zip_path = self._resource_to_zip(resource_name)
        eagers = self._get_eager_resources()
        if '/'.join(self._parts(zip_path)) in eagers:
            for name in eagers:
                self._extract_resource(manager, self._eager_to_zip(name))
        return self._extract_resource(manager, zip_path)

    @staticmethod
    def _get_date_and_size(zip_stat):
        size = zip_stat.file_size
        # ymdhms+wday, yday, dst
        date_time = zip_stat.date_time + (0, 0, -1)
        # 1980 offset already done
        timestamp = time.mktime(date_time)
        return timestamp, size

    def _extract_resource(self, manager, zip_path):

        if zip_path in self._index():
            for name in self._index()[zip_path]:
                last = self._extract_resource(
                    manager, os.path.join(zip_path, name)
                )
            # return the extracted directory name
            return os.path.dirname(last)

        timestamp, size = self._get_date_and_size(self.zipinfo[zip_path])

        if not WRITE_SUPPORT:
            raise IOError('"os.rename" and "os.unlink" are not supported '
                          'on this platform')
        try:

            real_path = manager.get_cache_path(
                self.egg_name, self._parts(zip_path)
            )

            if self._is_current(real_path, zip_path):
                return real_path

            outf, tmpnam = _mkstemp(
                ".$extract",
                dir=os.path.dirname(real_path),
            )
            os.write(outf, self.loader.get_data(zip_path))
            os.close(outf)
            utime(tmpnam, (timestamp, timestamp))
            manager.postprocess(tmpnam, real_path)

            try:
                rename(tmpnam, real_path)

            except os.error:
                if os.path.isfile(real_path):
                    if self._is_current(real_path, zip_path):
                        # the file became current since it was checked above,
                        #  so proceed.
                        return real_path
                    # Windows, del old file and retry
                    elif os.name == 'nt':
                        unlink(real_path)
                        rename(tmpnam, real_path)
                        return real_path
                raise

        except os.error:
            # report a user-friendly error
            manager.extraction_error()

        return real_path

    def _is_current(self, file_path, zip_path):
        """
        Return True if the file_path is current for this zip_path
        """
        timestamp, size = self._get_date_and_size(self.zipinfo[zip_path])
        if not os.path.isfile(file_path):
            return False
        stat = os.stat(file_path)
        if stat.st_size != size or stat.st_mtime != timestamp:
            return False
        # check that the contents match
        zip_contents = self.loader.get_data(zip_path)
        with open(file_path, 'rb') as f:
            file_contents = f.read()
        return zip_contents == file_contents

    def _get_eager_resources(self):
        if self.eagers is None:
            eagers = []
            for name in ('native_libs.txt', 'eager_resources.txt'):
                if self.has_metadata(name):
                    eagers.extend(self.get_metadata_lines(name))
            self.eagers = eagers
        return self.eagers

    def _index(self):
        try:
            return self._dirindex
        except AttributeError:
            ind = {}
            for path in self.zipinfo:
                parts = path.split(os.sep)
                while parts:
                    parent = os.sep.join(parts[:-1])
                    if parent in ind:
                        ind[parent].append(parts[-1])
                        break
                    else:
                        ind[parent] = [parts.pop()]
            self._dirindex = ind
            return ind

    def _has(self, fspath):
        zip_path = self._zipinfo_name(fspath)
        return zip_path in self.zipinfo or zip_path in self._index()

    def _isdir(self, fspath):
        return self._zipinfo_name(fspath) in self._index()

    def _listdir(self, fspath):
        return list(self._index().get(self._zipinfo_name(fspath), ()))

    def _eager_to_zip(self, resource_name):
        return self._zipinfo_name(self._fn(self.egg_root, resource_name))

    def _resource_to_zip(self, resource_name):
        return self._zipinfo_name(self._fn(self.module_path, resource_name))


register_loader_type(zipimport.zipimporter, ZipProvider)


class FileMetadata(EmptyProvider):
    """Metadata handler for standalone PKG-INFO files

    Usage::

        metadata = FileMetadata("/path/to/PKG-INFO")

    This provider rejects all data and metadata requests except for PKG-INFO,
    which is treated as existing, and will be the contents of the file at
    the provided location.
    """

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

    def has_metadata(self, name):
        return name == 'PKG-INFO' and os.path.isfile(self.path)

    def get_metadata(self, name):
        if name != 'PKG-INFO':
            raise KeyError("No metadata except PKG-INFO is available")

        with io.open(self.path, encoding='utf-8', errors="replace") as f:
            metadata = f.read()
        self._warn_on_replacement(metadata)
        return metadata

    def _warn_on_replacement(self, metadata):
        # Python 2.7 compat for: replacement_char = '�'
        replacement_char = b'\xef\xbf\xbd'.decode('utf-8')
        if replacement_char in metadata:
            tmpl = "{self.path} could not be properly decoded in UTF-8"
            msg = tmpl.format(**locals())
            warnings.warn(msg)

    def get_metadata_lines(self, name):
        return yield_lines(self.get_metadata(name))


class PathMetadata(DefaultProvider):
    """Metadata provider for egg directories

    Usage::

        # Development eggs:

        egg_info = "/path/to/PackageName.egg-info"
        base_dir = os.path.dirname(egg_info)
        metadata = PathMetadata(base_dir, egg_info)
        dist_name = os.path.splitext(os.path.basename(egg_info))[0]
        dist = Distribution(basedir, project_name=dist_name, metadata=metadata)

        # Unpacked egg directories:

        egg_path = "/path/to/PackageName-ver-pyver-etc.egg"
        metadata = PathMetadata(egg_path, os.path.join(egg_path,'EGG-INFO'))
        dist = Distribution.from_filename(egg_path, metadata=metadata)
    """

    def __init__(self, path, egg_info):
        self.module_path = path
        self.egg_info = egg_info


class EggMetadata(ZipProvider):
    """Metadata provider for .egg files"""

    def __init__(self, importer):
        """Create a metadata provider from a zipimporter"""

        self.zip_pre = importer.archive + os.sep
        self.loader = importer
        if importer.prefix:
            self.module_path = os.path.join(importer.archive, importer.prefix)
        else:
            self.module_path = importer.archive
        self._setup_prefix()


_declare_state('dict', _distribution_finders={})


def register_finder(importer_type, distribution_finder):
    """Register `distribution_finder` to find distributions in sys.path items

    `importer_type` is the type or class of a PEP 302 "Importer" (sys.path item
    handler), and `distribution_finder` is a callable that, passed a path
    item and the importer instance, yields ``Distribution`` instances found on
    that path item.  See ``pkg_resources.find_on_path`` for an example."""
    _distribution_finders[importer_type] = distribution_finder


def find_distributions(path_item, only=False):
    """Yield distributions accessible via `path_item`"""
    importer = get_importer(path_item)
    finder = _find_adapter(_distribution_finders, importer)
    return finder(importer, path_item, only)


def find_eggs_in_zip(importer, path_item, only=False):
    """
    Find eggs in zip files; possibly multiple nested eggs.
    """
    if importer.archive.endswith('.whl'):
        # wheels are not supported with this finder
        # they don't have PKG-INFO metadata, and won't ever contain eggs
        return
    metadata = EggMetadata(importer)
    if metadata.has_metadata('PKG-INFO'):
        yield Distribution.from_filename(path_item, metadata=metadata)
    if only:
        # don't yield nested distros
        return
    for subitem in metadata.resource_listdir('/'):
        if _is_egg_path(subitem):
            subpath = os.path.join(path_item, subitem)
            dists = find_eggs_in_zip(zipimport.zipimporter(subpath), subpath)
            for dist in dists:
                yield dist
        elif subitem.lower().endswith('.dist-info'):
            subpath = os.path.join(path_item, subitem)
            submeta = EggMetadata(zipimport.zipimporter(subpath))
            submeta.egg_info = subpath
            yield Distribution.from_location(path_item, subitem, submeta)


register_finder(zipimport.zipimporter, find_eggs_in_zip)


def find_nothing(importer, path_item, only=False):
    return ()


register_finder(object, find_nothing)


def _by_version_descending(names):
    """
    Given a list of filenames, return them in descending order
    by version number.

    >>> names = 'bar', 'foo', 'Python-2.7.10.egg', 'Python-2.7.2.egg'
    >>> _by_version_descending(names)
    ['Python-2.7.10.egg', 'Python-2.7.2.egg', 'foo', 'bar']
    >>> names = 'Setuptools-1.2.3b1.egg', 'Setuptools-1.2.3.egg'
    >>> _by_version_descending(names)
    ['Setuptools-1.2.3.egg', 'Setuptools-1.2.3b1.egg']
    >>> names = 'Setuptools-1.2.3b1.egg', 'Setuptools-1.2.3.post1.egg'
    >>> _by_version_descending(names)
    ['Setuptools-1.2.3.post1.egg', 'Setuptools-1.2.3b1.egg']
    """
    def _by_version(name):
        """
        Parse each component of the filename
        """
        name, ext = os.path.splitext(name)
        parts = itertools.chain(name.split('-'), [ext])
        return [packaging.version.parse(part) for part in parts]

    return sorted(names, key=_by_version, reverse=True)


def find_on_path(importer, path_item, only=False):
    """Yield distributions accessible on a sys.path directory"""
    path_item = _normalize_cached(path_item)

    if _is_unpacked_egg(path_item):
        yield Distribution.from_filename(
            path_item, metadata=PathMetadata(
                path_item, os.path.join(path_item, 'EGG-INFO')
            )
        )
        return

    entries = safe_listdir(path_item)

    # for performance, before sorting by version,
    # screen entries for only those that will yield
    # distributions
    filtered = (
        entry
        for entry in entries
        if dist_factory(path_item, entry, only)
    )

    # scan for .egg and .egg-info in directory
    path_item_entries = _by_version_descending(filtered)
    for entry in path_item_entries:
        fullpath = os.path.join(path_item, entry)
        factory = dist_factory(path_item, entry, only)
        for dist in factory(fullpath):
            yield dist


def dist_factory(path_item, entry, only):
    """
    Return a dist_factory for a path_item and entry
    """
    lower = entry.lower()
    is_meta = any(map(lower.endswith, ('.egg-info', '.dist-info')))
    return (
        distributions_from_metadata
        if is_meta else
        find_distributions
        if not only and _is_egg_path(entry) else
        resolve_egg_link
        if not only and lower.endswith('.egg-link') else
        NoDists()
    )


class NoDists:
    """
    >>> bool(NoDists())
    False

    >>> list(NoDists()('anything'))
    []
    """
    def __bool__(self):
        return False
    if six.PY2:
        __nonzero__ = __bool__

    def __call__(self, fullpath):
        return iter(())


def safe_listdir(path):
    """
    Attempt to list contents of path, but suppress some exceptions.
    """
    try:
        return os.listdir(path)
    except (PermissionError, NotADirectoryError):
        pass
    except OSError as e:
        # Ignore the directory if does not exist, not a directory or
        # permission denied
        ignorable = (
            e.errno in (errno.ENOTDIR, errno.EACCES, errno.ENOENT)
            # Python 2 on Windows needs to be handled this way :(
            or getattr(e, "winerror", None) == 267
        )
        if not ignorable:
            raise
    return ()


def distributions_from_metadata(path):
    root = os.path.dirname(path)
    if os.path.isdir(path):
        if len(os.listdir(path)) == 0:
            # empty metadata dir; skip
            return
        metadata = PathMetadata(root, path)
    else:
        metadata = FileMetadata(path)
    entry = os.path.basename(path)
    yield Distribution.from_location(
        root, entry, metadata, precedence=DEVELOP_DIST,
    )


def non_empty_lines(path):
    """
    Yield non-empty lines from file at path
    """
    with open(path) as f:
        for line in f:
            line = line.strip()
            if line:
                yield line


def resolve_egg_link(path):
    """
    Given a path to an .egg-link, resolve distributions
    present in the referenced path.
    """
    referenced_paths = non_empty_lines(path)
    resolved_paths = (
        os.path.join(os.path.dirname(path), ref)
        for ref in referenced_paths
    )
    dist_groups = map(find_distributions, resolved_paths)
    return next(dist_groups, ())


register_finder(pkgutil.ImpImporter, find_on_path)

if hasattr(importlib_machinery, 'FileFinder'):
    register_finder(importlib_machinery.FileFinder, find_on_path)

_declare_state('dict', _namespace_handlers={})
_declare_state('dict', _namespace_packages={})


def register_namespace_handler(importer_type, namespace_handler):
    """Register `namespace_handler` to declare namespace packages

    `importer_type` is the type or class of a PEP 302 "Importer" (sys.path item
    handler), and `namespace_handler` is a callable like this::

        def namespace_handler(importer, path_entry, moduleName, module):
            # return a path_entry to use for child packages

    Namespace handlers are only called if the importer object has already
    agreed that it can handle the relevant path item, and they should only
    return a subpath if the module __path__ does not already contain an
    equivalent subpath.  For an example namespace handler, see
    ``pkg_resources.file_ns_handler``.
    """
    _namespace_handlers[importer_type] = namespace_handler


def _handle_ns(packageName, path_item):
    """Ensure that named package includes a subpath of path_item (if needed)"""

    importer = get_importer(path_item)
    if importer is None:
        return None
    loader = importer.find_module(packageName)
    if loader is None:
        return None
    module = sys.modules.get(packageName)
    if module is None:
        module = sys.modules[packageName] = types.ModuleType(packageName)
        module.__path__ = []
        _set_parent_ns(packageName)
    elif not hasattr(module, '__path__'):
        raise TypeError("Not a package:", packageName)
    handler = _find_adapter(_namespace_handlers, importer)
    subpath = handler(importer, path_item, packageName, module)
    if subpath is not None:
        path = module.__path__
        path.append(subpath)
        loader.load_module(packageName)
        _rebuild_mod_path(path, packageName, module)
    return subpath


def _rebuild_mod_path(orig_path, package_name, module):
    """
    Rebuild module.__path__ ensuring that all entries are ordered
    corresponding to their sys.path order
    """
    sys_path = [_normalize_cached(p) for p in sys.path]

    def safe_sys_path_index(entry):
        """
        Workaround for #520 and #513.
        """
        try:
            return sys_path.index(entry)
        except ValueError:
            return float('inf')

    def position_in_sys_path(path):
        """
        Return the ordinal of the path based on its position in sys.path
        """
        path_parts = path.split(os.sep)
        module_parts = package_name.count('.') + 1
        parts = path_parts[:-module_parts]
        return safe_sys_path_index(_normalize_cached(os.sep.join(parts)))

    if not isinstance(orig_path, list):
        # Is this behavior useful when module.__path__ is not a list?
        return

    orig_path.sort(key=position_in_sys_path)
    module.__path__[:] = [_normalize_cached(p) for p in orig_path]


def declare_namespace(packageName):
    """Declare that package 'packageName' is a namespace package"""

    _imp.acquire_lock()
    try:
        if packageName in _namespace_packages:
            return

        path, parent = sys.path, None
        if '.' in packageName:
            parent = '.'.join(packageName.split('.')[:-1])
            declare_namespace(parent)
            if parent not in _namespace_packages:
                __import__(parent)
            try:
                path = sys.modules[parent].__path__
            except AttributeError:
                raise TypeError("Not a package:", parent)

        # Track what packages are namespaces, so when new path items are added,
        # they can be updated
        _namespace_packages.setdefault(parent, []).append(packageName)
        _namespace_packages.setdefault(packageName, [])

        for path_item in path:
            # Ensure all the parent's path items are reflected in the child,
            # if they apply
            _handle_ns(packageName, path_item)

    finally:
        _imp.release_lock()


def fixup_namespace_packages(path_item, parent=None):
    """Ensure that previously-declared namespace packages include path_item"""
    _imp.acquire_lock()
    try:
        for package in _namespace_packages.get(parent, ()):
            subpath = _handle_ns(package, path_item)
            if subpath:
                fixup_namespace_packages(subpath, package)
    finally:
        _imp.release_lock()


def file_ns_handler(importer, path_item, packageName, module):
    """Compute an ns-package subpath for a filesystem or zipfile importer"""

    subpath = os.path.join(path_item, packageName.split('.')[-1])
    normalized = _normalize_cached(subpath)
    for item in module.__path__:
        if _normalize_cached(item) == normalized:
            break
    else:
        # Only return the path if it's not already there
        return subpath


register_namespace_handler(pkgutil.ImpImporter, file_ns_handler)
register_namespace_handler(zipimport.zipimporter, file_ns_handler)

if hasattr(importlib_machinery, 'FileFinder'):
    register_namespace_handler(importlib_machinery.FileFinder, file_ns_handler)


def null_ns_handler(importer, path_item, packageName, module):
    return None


register_namespace_handler(object, null_ns_handler)


def normalize_path(filename):
    """Normalize a file/dir name for comparison purposes"""
    return os.path.normcase(os.path.realpath(filename))


def _normalize_cached(filename, _cache={}):
    try:
        return _cache[filename]
    except KeyError:
        _cache[filename] = result = normalize_path(filename)
        return result


def _is_egg_path(path):
    """
    Determine if given path appears to be an egg.
    """
    return path.lower().endswith('.egg')


def _is_unpacked_egg(path):
    """
    Determine if given path appears to be an unpacked egg.
    """
    return (
        _is_egg_path(path) and
        os.path.isfile(os.path.join(path, 'EGG-INFO', 'PKG-INFO'))
    )


def _set_parent_ns(packageName):
    parts = packageName.split('.')
    name = parts.pop()
    if parts:
        parent = '.'.join(parts)
        setattr(sys.modules[parent], name, sys.modules[packageName])


def yield_lines(strs):
    """Yield non-empty/non-comment lines of a string or sequence"""
    if isinstance(strs, six.string_types):
        for s in strs.splitlines():
            s = s.strip()
            # skip blank lines/comments
            if s and not s.startswith('#'):
                yield s
    else:
        for ss in strs:
            for s in yield_lines(ss):
                yield s


MODULE = re.compile(r"\w+(\.\w+)*$").match
EGG_NAME = re.compile(
    r"""
    (?P<name>[^-]+) (
        -(?P<ver>[^-]+) (
            -py(?P<pyver>[^-]+) (
                -(?P<plat>.+)
            )?
        )?
    )?
    """,
    re.VERBOSE | re.IGNORECASE,
).match


class EntryPoint(object):
    """Object representing an advertised importable object"""

    def __init__(self, name, module_name, attrs=(), extras=(), dist=None):
        if not MODULE(module_name):
            raise ValueError("Invalid module name", module_name)
        self.name = name
        self.module_name = module_name
        self.attrs = tuple(attrs)
        self.extras = tuple(extras)
        self.dist = dist

    def __str__(self):
        s = "%s = %s" % (self.name, self.module_name)
        if self.attrs:
            s += ':' + '.'.join(self.attrs)
        if self.extras:
            s += ' [%s]' % ','.join(self.extras)
        return s

    def __repr__(self):
        return "EntryPoint.parse(%r)" % str(self)

    def load(self, require=True, *args, **kwargs):
        """
        Require packages for this EntryPoint, then resolve it.
        """
        if not require or args or kwargs:
            warnings.warn(
                "Parameters to load are deprecated.  Call .resolve and "
                ".require separately.",
                DeprecationWarning,
                stacklevel=2,
            )
        if require:
            self.require(*args, **kwargs)
        return self.resolve()

    def resolve(self):
        """
        Resolve the entry point from its module and attrs.
        """
        module = __import__(self.module_name, fromlist=['__name__'], level=0)
        try:
            return functools.reduce(getattr, self.attrs, module)
        except AttributeError as exc:
            raise ImportError(str(exc))

    def require(self, env=None, installer=None):
        if self.extras and not self.dist:
            raise UnknownExtra("Can't require() without a distribution", self)

        # Get the requirements for this entry point with all its extras and
        # then resolve them. We have to pass `extras` along when resolving so
        # that the working set knows what extras we want. Otherwise, for
        # dist-info distributions, the working set will assume that the
        # requirements for that extra are purely optional and skip over them.
        reqs = self.dist.requires(self.extras)
        items = working_set.resolve(reqs, env, installer, extras=self.extras)
        list(map(working_set.add, items))

    pattern = re.compile(
        r'\s*'
        r'(?P<name>.+?)\s*'
        r'=\s*'
        r'(?P<module>[\w.]+)\s*'
        r'(:\s*(?P<attr>[\w.]+))?\s*'
        r'(?P<extras>\[.*\])?\s*$'
    )

    @classmethod
    def parse(cls, src, dist=None):
        """Parse a single entry point from string `src`

        Entry point syntax follows the form::

            name = some.module:some.attr [extra1, extra2]

        The entry name and module name are required, but the ``:attrs`` and
        ``[extras]`` parts are optional
        """
        m = cls.pattern.match(src)
        if not m:
            msg = "EntryPoint must be in 'name=module:attrs [extras]' format"
            raise ValueError(msg, src)
        res = m.groupdict()
        extras = cls._parse_extras(res['extras'])
        attrs = res['attr'].split('.') if res['attr'] else ()
        return cls(res['name'], res['module'], attrs, extras, dist)

    @classmethod
    def _parse_extras(cls, extras_spec):
        if not extras_spec:
            return ()
        req = Requirement.parse('x' + extras_spec)
        if req.specs:
            raise ValueError()
        return req.extras

    @classmethod
    def parse_group(cls, group, lines, dist=None):
        """Parse an entry point group"""
        if not MODULE(group):
            raise ValueError("Invalid group name", group)
        this = {}
        for line in yield_lines(lines):
            ep = cls.parse(line, dist)
            if ep.name in this:
                raise ValueError("Duplicate entry point", group, ep.name)
            this[ep.name] = ep
        return this

    @classmethod
    def parse_map(cls, data, dist=None):
        """Parse a map of entry point groups"""
        if isinstance(data, dict):
            data = data.items()
        else:
            data = split_sections(data)
        maps = {}
        for group, lines in data:
            if group is None:
                if not lines:
                    continue
                raise ValueError("Entry points must be listed in groups")
            group = group.strip()
            if group in maps:
                raise ValueError("Duplicate group name", group)
            maps[group] = cls.parse_group(group, lines, dist)
        return maps


def _remove_md5_fragment(location):
    if not location:
        return ''
    parsed = urllib.parse.urlparse(location)
    if parsed[-1].startswith('md5='):
        return urllib.parse.urlunparse(parsed[:-1] + ('',))
    return location


def _version_from_file(lines):
    """
    Given an iterable of lines from a Metadata file, return
    the value of the Version field, if present, or None otherwise.
    """
    def is_version_line(line):
        return line.lower().startswith('version:')
    version_lines = filter(is_version_line, lines)
    line = next(iter(version_lines), '')
    _, _, value = line.partition(':')
    return safe_version(value.strip()) or None


class Distribution(object):
    """Wrap an actual or potential sys.path entry w/metadata"""
    PKG_INFO = 'PKG-INFO'

    def __init__(
            self, location=None, metadata=None, project_name=None,
            version=None, py_version=PY_MAJOR, platform=None,
            precedence=EGG_DIST):
        self.project_name = safe_name(project_name or 'Unknown')
        if version is not None:
            self._version = safe_version(version)
        self.py_version = py_version
        self.platform = platform
        self.location = location
        self.precedence = precedence
        self._provider = metadata or empty_provider

    @classmethod
    def from_location(cls, location, basename, metadata=None, **kw):
        project_name, version, py_version, platform = [None] * 4
        basename, ext = os.path.splitext(basename)
        if ext.lower() in _distributionImpl:
            cls = _distributionImpl[ext.lower()]

            match = EGG_NAME(basename)
            if match:
                project_name, version, py_version, platform = match.group(
                    'name', 'ver', 'pyver', 'plat'
                )
        return cls(
            location, metadata, project_name=project_name, version=version,
            py_version=py_version, platform=platform, **kw
        )._reload_version()

    def _reload_version(self):
        return self

    @property
    def hashcmp(self):
        return (
            self.parsed_version,
            self.precedence,
            self.key,
            _remove_md5_fragment(self.location),
            self.py_version or '',
            self.platform or '',
        )

    def __hash__(self):
        return hash(self.hashcmp)

    def __lt__(self, other):
        return self.hashcmp < other.hashcmp

    def __le__(self, other):
        return self.hashcmp <= other.hashcmp

    def __gt__(self, other):
        return self.hashcmp > other.hashcmp

    def __ge__(self, other):
        return self.hashcmp >= other.hashcmp

    def __eq__(self, other):
        if not isinstance(other, self.__class__):
            # It's not a Distribution, so they are not equal
            return False
        return self.hashcmp == other.hashcmp

    def __ne__(self, other):
        return not self == other

    # These properties have to be lazy so that we don't have to load any
    # metadata until/unless it's actually needed.  (i.e., some distributions
    # may not know their name or version without loading PKG-INFO)

    @property
    def key(self):
        try:
            return self._key
        except AttributeError:
            self._key = key = self.project_name.lower()
            return key

    @property
    def parsed_version(self):
        if not hasattr(self, "_parsed_version"):
            self._parsed_version = parse_version(self.version)

        return self._parsed_version

    def _warn_legacy_version(self):
        LV = packaging.version.LegacyVersion
        is_legacy = isinstance(self._parsed_version, LV)
        if not is_legacy:
            return

        # While an empty version is technically a legacy version and
        # is not a valid PEP 440 version, it's also unlikely to
        # actually come from someone and instead it is more likely that
        # it comes from setuptools attempting to parse a filename and
        # including it in the list. So for that we'll gate this warning
        # on if the version is anything at all or not.
        if not self.version:
            return

        tmpl = textwrap.dedent("""
            '{project_name} ({version})' is being parsed as a legacy,
            non PEP 440,
            version. You may find odd behavior and sort order.
            In particular it will be sorted as less than 0.0. It
            is recommended to migrate to PEP 440 compatible
            versions.
            """).strip().replace('\n', ' ')

        warnings.warn(tmpl.format(**vars(self)), PEP440Warning)

    @property
    def version(self):
        try:
            return self._version
        except AttributeError:
            version = _version_from_file(self._get_metadata(self.PKG_INFO))
            if version is None:
                tmpl = "Missing 'Version:' header and/or %s file"
                raise ValueError(tmpl % self.PKG_INFO, self)
            return version

    @property
    def _dep_map(self):
        """
        A map of extra to its list of (direct) requirements
        for this distribution, including the null extra.
        """
        try:
            return self.__dep_map
        except AttributeError:
            self.__dep_map = self._filter_extras(self._build_dep_map())
        return self.__dep_map

    @staticmethod
    def _filter_extras(dm):
        """
        Given a mapping of extras to dependencies, strip off
        environment markers and filter out any dependencies
        not matching the markers.
        """
        for extra in list(filter(None, dm)):
            new_extra = extra
            reqs = dm.pop(extra)
            new_extra, _, marker = extra.partition(':')
            fails_marker = marker and (
                invalid_marker(marker)
                or not evaluate_marker(marker)
            )
            if fails_marker:
                reqs = []
            new_extra = safe_extra(new_extra) or None

            dm.setdefault(new_extra, []).extend(reqs)
        return dm

    def _build_dep_map(self):
        dm = {}
        for name in 'requires.txt', 'depends.txt':
            for extra, reqs in split_sections(self._get_metadata(name)):
                dm.setdefault(extra, []).extend(parse_requirements(reqs))
        return dm

    def requires(self, extras=()):
        """List of Requirements needed for this distro if `extras` are used"""
        dm = self._dep_map
        deps = []
        deps.extend(dm.get(None, ()))
        for ext in extras:
            try:
                deps.extend(dm[safe_extra(ext)])
            except KeyError:
                raise UnknownExtra(
                    "%s has no such extra feature %r" % (self, ext)
                )
        return deps

    def _get_metadata(self, name):
        if self.has_metadata(name):
            for line in self.get_metadata_lines(name):
                yield line

    def activate(self, path=None, replace=False):
        """Ensure distribution is importable on `path` (default=sys.path)"""
        if path is None:
            path = sys.path
        self.insert_on(path, replace=replace)
        if path is sys.path:
            fixup_namespace_packages(self.location)
            for pkg in self._get_metadata('namespace_packages.txt'):
                if pkg in sys.modules:
                    declare_namespace(pkg)

    def egg_name(self):
        """Return what this distribution's standard .egg filename should be"""
        filename = "%s-%s-py%s" % (
            to_filename(self.project_name), to_filename(self.version),
            self.py_version or PY_MAJOR
        )

        if self.platform:
            filename += '-' + self.platform
        return filename

    def __repr__(self):
        if self.location:
            return "%s (%s)" % (self, self.location)
        else:
            return str(self)

    def __str__(self):
        try:
            version = getattr(self, 'version', None)
        except ValueError:
            version = None
        version = version or "[unknown version]"
        return "%s %s" % (self.project_name, version)

    def __getattr__(self, attr):
        """Delegate all unrecognized public attributes to .metadata provider"""
        if attr.startswith('_'):
            raise AttributeError(attr)
        return getattr(self._provider, attr)

    @classmethod
    def from_filename(cls, filename, metadata=None, **kw):
        return cls.from_location(
            _normalize_cached(filename), os.path.basename(filename), metadata,
            **kw
        )

    def as_requirement(self):
        """Return a ``Requirement`` that matches this distribution exactly"""
        if isinstance(self.parsed_version, packaging.version.Version):
            spec = "%s==%s" % (self.project_name, self.parsed_version)
        else:
            spec = "%s===%s" % (self.project_name, self.parsed_version)

        return Requirement.parse(spec)

    def load_entry_point(self, group, name):
        """Return the `name` entry point of `group` or raise ImportError"""
        ep = self.get_entry_info(group, name)
        if ep is None:
            raise ImportError("Entry point %r not found" % ((group, name),))
        return ep.load()

    def get_entry_map(self, group=None):
        """Return the entry point map for `group`, or the full entry map"""
        try:
            ep_map = self._ep_map
        except AttributeError:
            ep_map = self._ep_map = EntryPoint.parse_map(
                self._get_metadata('entry_points.txt'), self
            )
        if group is not None:
            return ep_map.get(group, {})
        return ep_map

    def get_entry_info(self, group, name):
        """Return the EntryPoint object for `group`+`name`, or ``None``"""
        return self.get_entry_map(group).get(name)

    def insert_on(self, path, loc=None, replace=False):
        """Ensure self.location is on path

        If replace=False (default):
            - If location is already in path anywhere, do nothing.
            - Else:
              - If it's an egg and its parent directory is on path,
                insert just ahead of the parent.
              - Else: add to the end of path.
        If replace=True:
            - If location is already on path anywhere (not eggs)
              or higher priority than its parent (eggs)
              do nothing.
            - Else:
              - If it's an egg and its parent directory is on path,
                insert just ahead of the parent,
                removing any lower-priority entries.
              - Else: add it to the front of path.
        """

        loc = loc or self.location
        if not loc:
            return

        nloc = _normalize_cached(loc)
        bdir = os.path.dirname(nloc)
        npath = [(p and _normalize_cached(p) or p) for p in path]

        for p, item in enumerate(npath):
            if item == nloc:
                if replace:
                    break
                else:
                    # don't modify path (even removing duplicates) if
                    # found and not replace
                    return
            elif item == bdir and self.precedence == EGG_DIST:
                # if it's an .egg, give it precedence over its directory
                # UNLESS it's already been added to sys.path and replace=False
                if (not replace) and nloc in npath[p:]:
                    return
                if path is sys.path:
                    self.check_version_conflict()
                path.insert(p, loc)
                npath.insert(p, nloc)
                break
        else:
            if path is sys.path:
                self.check_version_conflict()
            if replace:
                path.insert(0, loc)
            else:
                path.append(loc)
            return

        # p is the spot where we found or inserted loc; now remove duplicates
        while True:
            try:
                np = npath.index(nloc, p + 1)
            except ValueError:
                break
            else:
                del npath[np], path[np]
                # ha!
                p = np

        return

    def check_version_conflict(self):
        if self.key == 'setuptools':
            # ignore the inevitable setuptools self-conflicts  :(
            return

        nsp = dict.fromkeys(self._get_metadata('namespace_packages.txt'))
        loc = normalize_path(self.location)
        for modname in self._get_metadata('top_level.txt'):
            if (modname not in sys.modules or modname in nsp
                    or modname in _namespace_packages):
                continue
            if modname in ('pkg_resources', 'setuptools', 'site'):
                continue
            fn = getattr(sys.modules[modname], '__file__', None)
            if fn and (normalize_path(fn).startswith(loc) or
                       fn.startswith(self.location)):
                continue
            issue_warning(
                "Module %s was already imported from %s, but %s is being added"
                " to sys.path" % (modname, fn, self.location),
            )

    def has_version(self):
        try:
            self.version
        except ValueError:
            issue_warning("Unbuilt egg for " + repr(self))
            return False
        return True

    def clone(self, **kw):
        """Copy this distribution, substituting in any changed keyword args"""
        names = 'project_name version py_version platform location precedence'
        for attr in names.split():
            kw.setdefault(attr, getattr(self, attr, None))
        kw.setdefault('metadata', self._provider)
        return self.__class__(**kw)

    @property
    def extras(self):
        return [dep for dep in self._dep_map if dep]


class EggInfoDistribution(Distribution):
    def _reload_version(self):
        """
        Packages installed by distutils (e.g. numpy or scipy),
        which uses an old safe_version, and so
        their version numbers can get mangled when
        converted to filenames (e.g., 1.11.0.dev0+2329eae to
        1.11.0.dev0_2329eae). These distributions will not be
        parsed properly
        downstream by Distribution and safe_version, so
        take an extra step and try to get the version number from
        the metadata file itself instead of the filename.
        """
        md_version = _version_from_file(self._get_metadata(self.PKG_INFO))
        if md_version:
            self._version = md_version
        return self


class DistInfoDistribution(Distribution):
    """
    Wrap an actual or potential sys.path entry
    w/metadata, .dist-info style.
    """
    PKG_INFO = 'METADATA'
    EQEQ = re.compile(r"([\(,])\s*(\d.*?)\s*([,\)])")

    @property
    def _parsed_pkg_info(self):
        """Parse and cache metadata"""
        try:
            return self._pkg_info
        except AttributeError:
            metadata = self.get_metadata(self.PKG_INFO)
            self._pkg_info = email.parser.Parser().parsestr(metadata)
            return self._pkg_info

    @property
    def _dep_map(self):
        try:
            return self.__dep_map
        except AttributeError:
            self.__dep_map = self._compute_dependencies()
            return self.__dep_map

    def _compute_dependencies(self):
        """Recompute this distribution's dependencies."""
        dm = self.__dep_map = {None: []}

        reqs = []
        # Including any condition expressions
        for req in self._parsed_pkg_info.get_all('Requires-Dist') or []:
            reqs.extend(parse_requirements(req))

        def reqs_for_extra(extra):
            for req in reqs:
                if not req.marker or req.marker.evaluate({'extra': extra}):
                    yield req

        common = frozenset(reqs_for_extra(None))
        dm[None].extend(common)

        for extra in self._parsed_pkg_info.get_all('Provides-Extra') or []:
            s_extra = safe_extra(extra.strip())
            dm[s_extra] = list(frozenset(reqs_for_extra(extra)) - common)

        return dm


_distributionImpl = {
    '.egg': Distribution,
    '.egg-info': EggInfoDistribution,
    '.dist-info': DistInfoDistribution,
}


def issue_warning(*args, **kw):
    level = 1
    g = globals()
    try:
        # find the first stack frame that is *not* code in
        # the pkg_resources module, to use for the warning
        while sys._getframe(level).f_globals is g:
            level += 1
    except ValueError:
        pass
    warnings.warn(stacklevel=level + 1, *args, **kw)


class RequirementParseError(ValueError):
    def __str__(self):
        return ' '.join(self.args)


def parse_requirements(strs):
    """Yield ``Requirement`` objects for each specification in `strs`

    `strs` must be a string, or a (possibly-nested) iterable thereof.
    """
    # create a steppable iterator, so we can handle \-continuations
    lines = iter(yield_lines(strs))

    for line in lines:
        # Drop comments -- a hash without a space may be in a URL.
        if ' #' in line:
            line = line[:line.find(' #')]
        # If there is a line continuation, drop it, and append the next line.
        if line.endswith('\\'):
            line = line[:-2].strip()
            try:
                line += next(lines)
            except StopIteration:
                return
        yield Requirement(line)


class Requirement(packaging.requirements.Requirement):
    def __init__(self, requirement_string):
        """DO NOT CALL THIS UNDOCUMENTED METHOD; use Requirement.parse()!"""
        try:
            super(Requirement, self).__init__(requirement_string)
        except packaging.requirements.InvalidRequirement as e:
            raise RequirementParseError(str(e))
        self.unsafe_name = self.name
        project_name = safe_name(self.name)
        self.project_name, self.key = project_name, project_name.lower()
        self.specs = [
            (spec.operator, spec.version) for spec in self.specifier]
        self.extras = tuple(map(safe_extra, self.extras))
        self.hashCmp = (
            self.key,
            self.specifier,
            frozenset(self.extras),
            str(self.marker) if self.marker else None,
        )
        self.__hash = hash(self.hashCmp)

    def __eq__(self, other):
        return (
            isinstance(other, Requirement) and
            self.hashCmp == other.hashCmp
        )

    def __ne__(self, other):
        return not self == other

    def __contains__(self, item):
        if isinstance(item, Distribution):
            if item.key != self.key:
                return False

            item = item.version

        # Allow prereleases always in order to match the previous behavior of
        # this method. In the future this should be smarter and follow PEP 440
        # more accurately.
        return self.specifier.contains(item, prereleases=True)

    def __hash__(self):
        return self.__hash

    def __repr__(self):
        return "Requirement.parse(%r)" % str(self)

    @staticmethod
    def parse(s):
        req, = parse_requirements(s)
        return req


def _always_object(classes):
    """
    Ensure object appears in the mro even
    for old-style classes.
    """
    if object not in classes:
        return classes + (object,)
    return classes


def _find_adapter(registry, ob):
    """Return an adapter factory for `ob` from `registry`"""
    types = _always_object(inspect.getmro(getattr(ob, '__class__', type(ob))))
    for t in types:
        if t in registry:
            return registry[t]


def ensure_directory(path):
    """Ensure that the parent directory of `path` exists"""
    dirname = os.path.dirname(path)
    py31compat.makedirs(dirname, exist_ok=True)


def _bypass_ensure_directory(path):
    """Sandbox-bypassing version of ensure_directory()"""
    if not WRITE_SUPPORT:
        raise IOError('"os.mkdir" not supported on this platform.')
    dirname, filename = split(path)
    if dirname and filename and not isdir(dirname):
        _bypass_ensure_directory(dirname)
        mkdir(dirname, 0o755)


def split_sections(s):
    """Split a string or iterable thereof into (section, content) pairs

    Each ``section`` is a stripped version of the section header ("[section]")
    and each ``content`` is a list of stripped lines excluding blank lines and
    comment-only lines.  If there are any such lines before the first section
    header, they're returned in a first ``section`` of ``None``.
    """
    section = None
    content = []
    for line in yield_lines(s):
        if line.startswith("["):
            if line.endswith("]"):
                if section or content:
                    yield section, content
                section = line[1:-1].strip()
                content = []
            else:
                raise ValueError("Invalid section heading", line)
        else:
            content.append(line)

    # wrap up last segment
    yield section, content


def _mkstemp(*args, **kw):
    old_open = os.open
    try:
        # temporarily bypass sandboxing
        os.open = os_open
        return tempfile.mkstemp(*args, **kw)
    finally:
        # and then put it back
        os.open = old_open


# Silence the PEP440Warning by default, so that end users don't get hit by it
# randomly just because they use pkg_resources. We want to append the rule
# because we want earlier uses of filterwarnings to take precedence over this
# one.
warnings.filterwarnings("ignore", category=PEP440Warning, append=True)


# from jaraco.functools 1.3
def _call_aside(f, *args, **kwargs):
    f(*args, **kwargs)
    return f


@_call_aside
def _initialize(g=globals()):
    "Set up global resource manager (deliberately not state-saved)"
    manager = ResourceManager()
    g['_manager'] = manager
    g.update(
        (name, getattr(manager, name))
        for name in dir(manager)
        if not name.startswith('_')
    )


@_call_aside
def _initialize_master_working_set():
    """
    Prepare the master working set and make the ``require()``
    API available.

    This function has explicit effects on the global state
    of pkg_resources. It is intended to be invoked once at
    the initialization of this module.

    Invocation by other packages is unsupported and done
    at their own risk.
    """
    working_set = WorkingSet._build_master()
    _declare_state('object', working_set=working_set)

    require = working_set.require
    iter_entry_points = working_set.iter_entry_points
    add_activation_listener = working_set.subscribe
    run_script = working_set.run_script
    # backward compatibility
    run_main = run_script
    # Activate all distributions already on sys.path with replace=False and
    # ensure that all distributions added to the working set in the future
    # (e.g. by calling ``require()``) will get activated as well,
    # with higher priority (replace=True).
    tuple(
        dist.activate(replace=False)
        for dist in working_set
    )
    add_activation_listener(
        lambda dist: dist.activate(replace=True),
        existing=False,
    )
    working_set.entries = []
    # match order
    list(map(working_set.add_entry, sys.path))
    globals().update(locals())
