import io
import os
import re
import abc
import csv
import sys
import email
import pathlib
import zipfile
import operator
import functools
import itertools
import collections

from configparser import ConfigParser
from contextlib import suppress
from importlib import import_module
from importlib.abc import MetaPathFinder
from itertools import starmap


__all__ = [
 'Distribution',
 'DistributionFinder',
 'PackageNotFoundError',
 'distribution',
 'distributions',
 'entry_points',
 'files',
 'metadata',
 'requires',
 'version',
 ]


class PackageNotFoundError(ModuleNotFoundError):
 """The package was not found."""


class EntryPoint(
 collections.namedtuple('EntryPointBase', 'name value group')):
 """An entry point as defined by Python packaging conventions.

 See `the packaging docs on entry points
 <https://packaging.python.org/specifications/entry-points/>`_
 for more information.
 """

 pattern = re.compile(
 r'(?P<module>[\w.]+)\s*'
 r'(:\s*(?P<attr>[\w.]+))?\s*'
 r'(?P<extras>\[.*\])?\s*$'
 )
 """
 A regular expression describing the syntax for an entry point,
 which might look like:

 - module
 - package.module
 - package.module:attribute
 - package.module:object.attribute
 - package.module:attr [extra1, extra2]

 Other combinations are possible as well.

 The expression is lenient about whitespace around the ':',
 following the attr, and following any extras.
 """

 def load(self):
 """Load the entry point from its definition. If only a module
 is indicated by the value, return that module. Otherwise,
 return the named object.
 """
 match = self.pattern.match(self.value)
 module = import_module(match.group('module'))
 attrs = filter(None, (match.group('attr') or '').split('.'))
 return functools.reduce(getattr, attrs, module)

 @property
 def extras(self):
 match = self.pattern.match(self.value)
 return list(re.finditer(r'\w+', match.group('extras') or ''))

 @classmethod
 def _from_config(cls, config):
 return [
 cls(name, value, group)
 for group in config.sections()
 for name, value in config.items(group)
 ]

 @classmethod
 def _from_text(cls, text):
 config = ConfigParser(delimiters='=')
 # case sensitive: https://stackoverflow.com/q/1611799/812183
 config.optionxform = str
 try:
 config.read_string(text)
 except AttributeError: # pragma: nocover
 # Python 2 has no read_string
 config.readfp(io.StringIO(text))
 return EntryPoint._from_config(config)

 def __iter__(self):
 """
 Supply iter so one may construct dicts of EntryPoints easily.
 """
 return iter((self.name, self))

 def __reduce__(self):
 return (
 self.__class__,
 (self.name, self.value, self.group),
 )


class PackagePath(pathlib.PurePosixPath):
 """A reference to a path in a package"""

 def read_text(self, encoding='utf-8'):
 with self.locate().open(encoding=encoding) as stream:
 return stream.read()

 def read_binary(self):
 with self.locate().open('rb') as stream:
 return stream.read()

 def locate(self):
 """Return a path-like object for this path"""
 return self.dist.locate_file(self)


class FileHash:
 def __init__(self, spec):
 self.mode, _, self.value = spec.partition('=')

 def __repr__(self):
 return '<FileHash mode: {} value: {}>'.format(self.mode, self.value)


class Distribution:
 """A Python distribution package."""

 @abc.abstractmethod
 def read_text(self, filename):
 """Attempt to load metadata file given by the name.

 :param filename: The name of the file in the distribution info.
 :return: The text if found, otherwise None.
 """

 @abc.abstractmethod
 def locate_file(self, path):
 """
 Given a path to a file in this distribution, return a path
 to it.
 """

 @classmethod
 def from_name(cls, name):
 """Return the Distribution for the given package name.

 :param name: The name of the distribution package to search for.
 :return: The Distribution instance (or subclass thereof) for the named
 package, if found.
 :raises PackageNotFoundError: When the named package's distribution
 metadata cannot be found.
 """
 for resolver in cls._discover_resolvers():
 dists = resolver(DistributionFinder.Context(name=name))
 dist = next(dists, None)
 if dist is not None:
 return dist
 else:
 raise PackageNotFoundError(name)

 @classmethod
 def discover(cls, **kwargs):
 """Return an iterable of Distribution objects for all packages.

 Pass a ``context`` or pass keyword arguments for constructing
 a context.

 :context: A ``DistributionFinder.Context`` object.
 :return: Iterable of Distribution objects for all packages.
 """
 context = kwargs.pop('context', None)
 if context and kwargs:
 raise ValueError("cannot accept context and kwargs")
 context = context or DistributionFinder.Context(**kwargs)
 return itertools.chain.from_iterable(
 resolver(context)
 for resolver in cls._discover_resolvers()
 )

 @staticmethod
 def at(path):
 """Return a Distribution for the indicated metadata path

 :param path: a string or path-like object
 :return: a concrete Distribution instance for the path
 """
 return PathDistribution(pathlib.Path(path))

 @staticmethod
 def _discover_resolvers():
 """Search the meta_path for resolvers."""
 declared = (
 getattr(finder, 'find_distributions', None)
 for finder in sys.meta_path
 )
 return filter(None, declared)

 @property
 def metadata(self):
 """Return the parsed metadata for this Distribution.

 The returned object will have keys that name the various bits of
 metadata. See PEP 566 for details.
 """
 text = (
 self.read_text('METADATA')
 or self.read_text('PKG-INFO')
 # This last clause is here to support old egg-info files. Its
 # effect is to just end up using the PathDistribution's self._path
 # (which points to the egg-info file) attribute unchanged.
 or self.read_text('')
 )
 return email.message_from_string(text)

 @property
 def version(self):
 """Return the 'Version' metadata for the distribution package."""
 return self.metadata['Version']

 @property
 def entry_points(self):
 return EntryPoint._from_text(self.read_text('entry_points.txt'))

 @property
 def files(self):
 """Files in this distribution.

 :return: List of PackagePath for this distribution or None

 Result is `None` if the metadata file that enumerates files
 (i.e. RECORD for dist-info or SOURCES.txt for egg-info) is
 missing.
 Result may be empty if the metadata exists but is empty.
 """
 file_lines = self._read_files_distinfo() or self._read_files_egginfo()

 def make_file(name, hash=None, size_str=None):
 result = PackagePath(name)
 result.hash = FileHash(hash) if hash else None
 result.size = int(size_str) if size_str else None
 result.dist = self
 return result

 return file_lines and list(starmap(make_file, csv.reader(file_lines)))

 def _read_files_distinfo(self):
 """
 Read the lines of RECORD
 """
 text = self.read_text('RECORD')
 return text and text.splitlines()

 def _read_files_egginfo(self):
 """
 SOURCES.txt might contain literal commas, so wrap each line
 in quotes.
 """
 text = self.read_text('SOURCES.txt')
 return text and map('"{}"'.format, text.splitlines())

 @property
 def requires(self):
 """Generated requirements specified for this Distribution"""
 reqs = self._read_dist_info_reqs() or self._read_egg_info_reqs()
 return reqs and list(reqs)

 def _read_dist_info_reqs(self):
 return self.metadata.get_all('Requires-Dist')

 def _read_egg_info_reqs(self):
 source = self.read_text('requires.txt')
 return source and self._deps_from_requires_text(source)

 @classmethod
 def _deps_from_requires_text(cls, source):
 section_pairs = cls._read_sections(source.splitlines())
 sections = {
 section: list(map(operator.itemgetter('line'), results))
 for section, results in
 itertools.groupby(section_pairs, operator.itemgetter('section'))
 }
 return cls._convert_egg_info_reqs_to_simple_reqs(sections)

 @staticmethod
 def _read_sections(lines):
 section = None
 for line in filter(None, lines):
 section_match = re.match(r'\[(.*)\]$', line)
 if section_match:
 section = section_match.group(1)
 continue
 yield locals()

 @staticmethod
 def _convert_egg_info_reqs_to_simple_reqs(sections):
 """
 Historically, setuptools would solicit and store 'extra'
 requirements, including those with environment markers,
 in separate sections. More modern tools expect each
 dependency to be defined separately, with any relevant
 extras and environment markers attached directly to that
 requirement. This method converts the former to the
 latter. See _test_deps_from_requires_text for an example.
 """
 def make_condition(name):
 return name and 'extra == "{name}"'.format(name=name)

 def parse_condition(section):
 section = section or ''
 extra, sep, markers = section.partition(':')
 if extra and markers:
 markers = '({markers})'.format(markers=markers)
 conditions = list(filter(None, [markers, make_condition(extra)]))
 return '; ' + ' and '.join(conditions) if conditions else ''

 for section, deps in sections.items():
 for dep in deps:
 yield dep + parse_condition(section)


class DistributionFinder(MetaPathFinder):
 """
 A MetaPathFinder capable of discovering installed distributions.
 """

 class Context:
 """
 Keyword arguments presented by the caller to
 ``distributions()`` or ``Distribution.discover()``
 to narrow the scope of a search for distributions
 in all DistributionFinders.

 Each DistributionFinder may expect any parameters
 and should attempt to honor the canonical
 parameters defined below when appropriate.
 """

 name = None
 """
 Specific name for which a distribution finder should match.
 A name of ``None`` matches all distributions.
 """

 def __init__(self, **kwargs):
 vars(self).update(kwargs)

 @property
 def path(self):
 """
 The path that a distribution finder should search.

 Typically refers to Python package paths and defaults
 to ``sys.path``.
 """
 return vars(self).get('path', sys.path)

 @property
 def pattern(self):
 return '.*' if self.name is None else re.escape(self.name)

 @abc.abstractmethod
 def find_distributions(self, context=Context()):
 """
 Find distributions.

 Return an iterable of all Distribution instances capable of
 loading the metadata for packages matching the ``context``,
 a DistributionFinder.Context instance.
 """


class MetadataPathFinder(DistributionFinder):
 @classmethod
 def find_distributions(cls, context=DistributionFinder.Context()):
 """
 Find distributions.

 Return an iterable of all Distribution instances capable of
 loading the metadata for packages matching ``context.name``
 (or all names if ``None`` indicated) along the paths in the list
 of directories ``context.path``.
 """
 found = cls._search_paths(context.pattern, context.path)
 return map(PathDistribution, found)

 @classmethod
 def _search_paths(cls, pattern, paths):
 """Find metadata directories in paths heuristically."""
 return itertools.chain.from_iterable(
 cls._search_path(path, pattern)
 for path in map(cls._switch_path, paths)
 )

 @staticmethod
 def _switch_path(path):
 PYPY_OPEN_BUG = False
 if not PYPY_OPEN_BUG or os.path.isfile(path): # pragma: no branch
 with suppress(Exception):
 return zipfile.Path(path)
 return pathlib.Path(path)

 @classmethod
 def _matches_info(cls, normalized, item):
 template = r'{pattern}(-.*)?\.(dist|egg)-info'
 manifest = template.format(pattern=normalized)
 return re.match(manifest, item.name, flags=re.IGNORECASE)

 @classmethod
 def _matches_legacy(cls, normalized, item):
 template = r'{pattern}-.*\.egg[\\/]EGG-INFO'
 manifest = template.format(pattern=normalized)
 return re.search(manifest, str(item), flags=re.IGNORECASE)

 @classmethod
 def _search_path(cls, root, pattern):
 if not root.is_dir():
 return ()
 normalized = pattern.replace('-', '_')
 return (item for item in root.iterdir()
 if cls._matches_info(normalized, item)
 or cls._matches_legacy(normalized, item))


class PathDistribution(Distribution):
 def __init__(self, path):
 """Construct a distribution from a path to the metadata directory.

 :param path: A pathlib.Path or similar object supporting
 .joinpath(), __div__, .parent, and .read_text().
 """
 self._path = path

 def read_text(self, filename):
 with suppress(FileNotFoundError, IsADirectoryError, KeyError,
 NotADirectoryError, PermissionError):
 return self._path.joinpath(filename).read_text(encoding='utf-8')
 read_text.__doc__ = Distribution.read_text.__doc__

 def locate_file(self, path):
 return self._path.parent / path


def distribution(distribution_name):
 """Get the ``Distribution`` instance for the named package.

 :param distribution_name: The name of the distribution package as a string.
 :return: A ``Distribution`` instance (or subclass thereof).
 """
 return Distribution.from_name(distribution_name)


def distributions(**kwargs):
 """Get all ``Distribution`` instances in the current environment.

 :return: An iterable of ``Distribution`` instances.
 """
 return Distribution.discover(**kwargs)


def metadata(distribution_name):
 """Get the metadata for the named package.

 :param distribution_name: The name of the distribution package to query.
 :return: An email.Message containing the parsed metadata.
 """
 return Distribution.from_name(distribution_name).metadata


def version(distribution_name):
 """Get the version string for the named package.

 :param distribution_name: The name of the distribution package to query.
 :return: The version string for the package as defined in the package's
 "Version" metadata key.
 """
 return distribution(distribution_name).version


def entry_points():
 """Return EntryPoint objects for all installed packages.

 :return: EntryPoint objects for all installed packages.
 """
 eps = itertools.chain.from_iterable(
 dist.entry_points for dist in distributions())
 by_group = operator.attrgetter('group')
 ordered = sorted(eps, key=by_group)
 grouped = itertools.groupby(ordered, by_group)
 return {
 group: tuple(eps)
 for group, eps in grouped
 }


def files(distribution_name):
 """Return a list of files for the named package.

 :param distribution_name: The name of the distribution package to query.
 :return: List of files composing the distribution.
 """
 return distribution(distribution_name).files


def requires(distribution_name):
 """
 Return a list of requirements for the named package.

 :return: An iterator of requirements, suitable for
 packaging.requirement.Requirement.
 """
 return distribution(distribution_name).requires