text: """Routines related to PyPI, indexes"""
  
  # The following comment should be removed at some point in the future.
  # mypy: strict-optional=False
  
  import functools
  import logging
  import re
  from typing import TYPE_CHECKING
  
  from pip._vendor.packaging import specifiers
  from pip._vendor.packaging.utils import canonicalize_name
  from pip._vendor.packaging.version import parse as parse_version
  
  from pip._internal.exceptions import (
      BestVersionAlreadyInstalled,
      DistributionNotFound,
      InvalidWheelFilename,
      UnsupportedWheel,
  )
  from pip._internal.index.collector import parse_links
  from pip._internal.models.candidate import InstallationCandidate
  from pip._internal.models.format_control import FormatControl
  from pip._internal.models.link import Link
  from pip._internal.models.selection_prefs import SelectionPreferences
  from pip._internal.models.target_python import TargetPython
  from pip._internal.models.wheel import Wheel
  from pip._internal.utils.filetypes import WHEEL_EXTENSION
  from pip._internal.utils.logging import indent_log
  from pip._internal.utils.misc import build_netloc
  from pip._internal.utils.packaging import check_requires_python
  from pip._internal.utils.unpacking import SUPPORTED_EXTENSIONS
  from pip._internal.utils.urls import url_to_path
  
  if TYPE_CHECKING:
      from typing import FrozenSet, Iterable, List, Optional, Set, Tuple, Union
  
      from pip._vendor.packaging.tags import Tag
      from pip._vendor.packaging.version import _BaseVersion
  
      from pip._internal.index.collector import LinkCollector
      from pip._internal.models.search_scope import SearchScope
      from pip._internal.req import InstallRequirement
      from pip._internal.utils.hashes import Hashes
  
      BuildTag = Union[Tuple[()], Tuple[int, str]]
      CandidateSortingKey = (
          Tuple[int, int, int, _BaseVersion, BuildTag, Optional[int]]
      )
  
  
  __all__ = ['FormatControl', 'BestCandidateResult', 'PackageFinder']
  
  
  logger = logging.getLogger(__name__)
  
  
  def _check_link_requires_python(
      link,  # type: Link
      version_info,  # type: Tuple[int, int, int]
      ignore_requires_python=False,  # type: bool
  ):
      # type: (...) -> bool
      """
      Return whether the given Python version is compatible with a link's
      "Requires-Python" value.
  
      :param version_info: A 3-tuple of ints representing the Python
          major-minor-micro version to check.
      :param ignore_requires_python: Whether to ignore the "Requires-Python"
          value if the given Python version isn't compatible.
      """
      try:
          is_compatible = check_requires_python(
              link.requires_python, version_info=version_info,
          )
      except specifiers.InvalidSpecifier:
          logger.debug(
              "Ignoring invalid Requires-Python (%r) for link: %s",
              link.requires_python, link,
          )
      else:
          if not is_compatible:
              version = '.'.join(map(str, version_info))
              if not ignore_requires_python:
                  logger.debug(
                      'Link requires a different Python (%s not in: %r): %s',
                      version, link.requires_python, link,
                  )
                  return False
  
              logger.debug(
                  'Ignoring failed Requires-Python check (%s not in: %r) '
                  'for link: %s',
                  version, link.requires_python, link,
              )
  
      return True
  
  
  class LinkEvaluator:
  
      """
      Responsible for evaluating links for a particular project.
      """
  
      _py_version_re = re.compile(r'-py([123]\.?[0-9]?)$')
  
      # Don't include an allow_yanked default value to make sure each call
      # site considers whether yanked releases are allowed. This also causes
      # that decision to be made explicit in the calling code, which helps
      # people when reading the code.
      def __init__(
          self,
          project_name,    # type: str
          canonical_name,  # type: str
          formats,         # type: FrozenSet[str]
          target_python,   # type: TargetPython
          allow_yanked,    # type: bool
          ignore_requires_python=None,  # type: Optional[bool]
      ):
          # type: (...) -> None
          """
          :param project_name: The user supplied package name.
          :param canonical_name: The canonical package name.
          :param formats: The formats allowed for this package. Should be a set
              with 'binary' or 'source' or both in it.
          :param target_python: The target Python interpreter to use when
              evaluating link compatibility. This is used, for example, to
              check wheel compatibility, as well as when checking the Python
              version, e.g. the Python version embedded in a link filename
              (or egg fragment) and against an HTML link's optional PEP 503
              "data-requires-python" attribute.
          :param allow_yanked: Whether files marked as yanked (in the sense
              of PEP 592) are permitted to be candidates for install.
          :param ignore_requires_python: Whether to ignore incompatible
              PEP 503 "data-requires-python" values in HTML links. Defaults
              to False.
          """
          if ignore_requires_python is None:
              ignore_requires_python = False
  
          self._allow_yanked = allow_yanked
          self._canonical_name = canonical_name
          self._ignore_requires_python = ignore_requires_python
          self._formats = formats
          self._target_python = target_python
  
          self.project_name = project_name
  
      def evaluate_link(self, link):
          # type: (Link) -> Tuple[bool, Optional[str]]
          """
          Determine whether a link is a candidate for installation.
  
          :return: A tuple (is_candidate, result), where `result` is (1) a
              version string if `is_candidate` is True, and (2) if
              `is_candidate` is False, an optional string to log the reason
              the link fails to qualify.
          """
          version = None
          if link.is_yanked and not self._allow_yanked:
              reason = link.yanked_reason or '<none given>'
              return (False, f'yanked for reason: {reason}')
  
          if link.egg_fragment:
              egg_info = link.egg_fragment
              ext = link.ext
          else:
              egg_info, ext = link.splitext()
              if not ext:
                  return (False, 'not a file')
              if ext not in SUPPORTED_EXTENSIONS:
                  return (False, f'unsupported archive format: {ext}')
              if "binary" not in self._formats and ext == WHEEL_EXTENSION:
                  reason = 'No binaries permitted for {}'.format(
                      self.project_name)
                  return (False, reason)
              if "macosx10" in link.path and ext == '.zip':
                  return (False, 'macosx10 one')
              if ext == WHEEL_EXTENSION:
                  try:
                      wheel = Wheel(link.filename)
                  except InvalidWheelFilename:
                      return (False, 'invalid wheel filename')
                  if canonicalize_name(wheel.name) != self._canonical_name:
                      reason = 'wrong project name (not {})'.format(
                          self.project_name)
                      return (False, reason)
  
                  supported_tags = self._target_python.get_tags()
                  if not wheel.supported(supported_tags):
                      # Include the wheel's tags in the reason string to
                      # simplify troubleshooting compatibility issues.
                      file_tags = wheel.get_formatted_file_tags()
                      reason = (
                          "none of the wheel's tags ({}) are compatible "
                          "(run pip debug --verbose to show compatible tags)".format(
                              ', '.join(file_tags)
                          )
                      )
                      return (False, reason)
  
                  version = wheel.version
  
          # This should be up by the self.ok_binary check, but see issue 2700.
          if "source" not in self._formats and ext != WHEEL_EXTENSION:
              reason = f'No sources permitted for {self.project_name}'
              return (False, reason)
  
          if not version:
              version = _extract_version_from_fragment(
                  egg_info, self._canonical_name,
              )
          if not version:
              reason = f'Missing project version for {self.project_name}'
              return (False, reason)
  
          match = self._py_version_re.search(version)
          if match:
              version = version[:match.start()]
              py_version = match.group(1)
              if py_version != self._target_python.py_version:
                  return (False, 'Python version is incorrect')
  
          supports_python = _check_link_requires_python(
              link, version_info=self._target_python.py_version_info,
              ignore_requires_python=self._ignore_requires_python,
          )
          if not supports_python:
              # Return None for the reason text to suppress calling
              # _log_skipped_link().
              return (False, None)
  
          logger.debug('Found link %s, version: %s', link, version)
  
          return (True, version)
  
  
  def filter_unallowed_hashes(
      candidates,    # type: List[InstallationCandidate]
      hashes,        # type: Hashes
      project_name,  # type: str
  ):
      # type: (...) -> List[InstallationCandidate]
      """
      Filter out candidates whose hashes aren't allowed, and return a new
      list of candidates.
  
      If at least one candidate has an allowed hash, then all candidates with
      either an allowed hash or no hash specified are returned.  Otherwise,
      the given candidates are returned.
  
      Including the candidates with no hash specified when there is a match
      allows a warning to be logged if there is a more preferred candidate
      with no hash specified.  Returning all candidates in the case of no
      matches lets pip report the hash of the candidate that would otherwise
      have been installed (e.g. permitting the user to more easily update
      their requirements file with the desired hash).
      """
      if not hashes:
          logger.debug(
              'Given no hashes to check %s links for project %r: '
              'discarding no candidates',
              len(candidates),
              project_name,
          )
          # Make sure we're not returning back the given value.
          return list(candidates)
  
      matches_or_no_digest = []
      # Collect the non-matches for logging purposes.
      non_matches = []
      match_count = 0
      for candidate in candidates:
          link = candidate.link
          if not link.has_hash:
              pass
          elif link.is_hash_allowed(hashes=hashes):
              match_count += 1
          else:
              non_matches.append(candidate)
              continue
  
          matches_or_no_digest.append(candidate)
  
      if match_count:
          filtered = matches_or_no_digest
      else:
          # Make sure we're not returning back the given value.
          filtered = list(candidates)
  
      if len(filtered) == len(candidates):
          discard_message = 'discarding no candidates'
      else:
          discard_message = 'discarding {} non-matches:\n  {}'.format(
              len(non_matches),
              '\n  '.join(str(candidate.link) for candidate in non_matches)
          )
  
      logger.debug(
          'Checked %s links for project %r against %s hashes '
          '(%s matches, %s no digest): %s',
          len(candidates),
          project_name,
          hashes.digest_count,
          match_count,
          len(matches_or_no_digest) - match_count,
          discard_message
      )
  
      return filtered
  
  
  class CandidatePreferences:
  
      """
      Encapsulates some of the preferences for filtering and sorting
      InstallationCandidate objects.
      """
  
      def __init__(
          self,
          prefer_binary=False,  # type: bool
          allow_all_prereleases=False,  # type: bool
      ):
          # type: (...) -> None
          """
          :param allow_all_prereleases: Whether to allow all pre-releases.
          """
          self.allow_all_prereleases = allow_all_prereleases
          self.prefer_binary = prefer_binary
  
  
  class BestCandidateResult:
      """A collection of candidates, returned by `PackageFinder.find_best_candidate`.
  
      This class is only intended to be instantiated by CandidateEvaluator's
      `compute_best_candidate()` method.
      """
  
      def __init__(
          self,
          candidates,             # type: List[InstallationCandidate]
          applicable_candidates,  # type: List[InstallationCandidate]
          best_candidate,         # type: Optional[InstallationCandidate]
      ):
          # type: (...) -> None
          """
          :param candidates: A sequence of all available candidates found.
          :param applicable_candidates: The applicable candidates.
          :param best_candidate: The most preferred candidate found, or None
              if no applicable candidates were found.
          """
          assert set(applicable_candidates) <= set(candidates)
  
          if best_candidate is None:
              assert not applicable_candidates
          else:
              assert best_candidate in applicable_candidates
  
          self._applicable_candidates = applicable_candidates
          self._candidates = candidates
  
          self.best_candidate = best_candidate
  
      def iter_all(self):
          # type: () -> Iterable[InstallationCandidate]
          """Iterate through all candidates.
          """
          return iter(self._candidates)
  
      def iter_applicable(self):
          # type: () -> Iterable[InstallationCandidate]
          """Iterate through the applicable candidates.
          """
          return iter(self._applicable_candidates)
  
  
  class CandidateEvaluator:
  
      """
      Responsible for filtering and sorting candidates for installation based
      on what tags are valid.
      """
  
      @classmethod
      def create(
          cls,
          project_name,         # type: str
          target_python=None,   # type: Optional[TargetPython]
          prefer_binary=False,  # type: bool
          allow_all_prereleases=False,  # type: bool
          specifier=None,       # type: Optional[specifiers.BaseSpecifier]
          hashes=None,          # type: Optional[Hashes]
      ):
          # type: (...) -> CandidateEvaluator
          """Create a CandidateEvaluator object.
  
          :param target_python: The target Python interpreter to use when
              checking compatibility. If None (the default), a TargetPython
              object will be constructed from the running Python.
          :param specifier: An optional object implementing `filter`
              (e.g. `packaging.specifiers.SpecifierSet`) to filter applicable
              versions.
          :param hashes: An optional collection of allowed hashes.
          """
          if target_python is None:
              target_python = TargetPython()
          if specifier is None:
              specifier = specifiers.SpecifierSet()
  
          supported_tags = target_python.get_tags()
  
          return cls(
              project_name=project_name,
              supported_tags=supported_tags,
              specifier=specifier,
              prefer_binary=prefer_binary,
              allow_all_prereleases=allow_all_prereleases,
              hashes=hashes,
          )
  
      def __init__(
          self,
          project_name,         # type: str
          supported_tags,       # type: List[Tag]
          specifier,            # type: specifiers.BaseSpecifier
          prefer_binary=False,  # type: bool
          allow_all_prereleases=False,  # type: bool
          hashes=None,                  # type: Optional[Hashes]
      ):
          # type: (...) -> None
          """
          :param supported_tags: The PEP 425 tags supported by the target
              Python in order of preference (most preferred first).
          """
          self._allow_all_prereleases = allow_all_prereleases
          self._hashes = hashes
          self._prefer_binary = prefer_binary
          self._project_name = project_name
          self._specifier = specifier
          self._supported_tags = supported_tags
  
      def get_applicable_candidates(
          self,
          candidates,  # type: List[InstallationCandidate]
      ):
          # type: (...) -> List[InstallationCandidate]
          """
          Return the applicable candidates from a list of candidates.
          """
          # Using None infers from the specifier instead.
          allow_prereleases = self._allow_all_prereleases or None
          specifier = self._specifier
          versions = {
              str(v) for v in specifier.filter(
                  # We turn the version object into a str here because otherwise
                  # when we're debundled but setuptools isn't, Python will see
                  # packaging.version.Version and
                  # pkg_resources._vendor.packaging.version.Version as different
                  # types. This way we'll use a str as a common data interchange
                  # format. If we stop using the pkg_resources provided specifier
                  # and start using our own, we can drop the cast to str().
                  (str(c.version) for c in candidates),
                  prereleases=allow_prereleases,
              )
          }
  
          # Again, converting version to str to deal with debundling.
          applicable_candidates = [
              c for c in candidates if str(c.version) in versions
          ]
  
          filtered_applicable_candidates = filter_unallowed_hashes(
              candidates=applicable_candidates,
              hashes=self._hashes,
              project_name=self._project_name,
          )
  
          return sorted(filtered_applicable_candidates, key=self._sort_key)
  
      def _sort_key(self, candidate):
          # type: (InstallationCandidate) -> CandidateSortingKey
          """
          Function to pass as the `key` argument to a call to sorted() to sort
          InstallationCandidates by preference.
  
          Returns a tuple such that tuples sorting as greater using Python's
          default comparison operator are more preferred.
  
          The preference is as follows:
  
          First and foremost, candidates with allowed (matching) hashes are
          always preferred over candidates without matching hashes. This is
          because e.g. if the only candidate with an allowed hash is yanked,
          we still want to use that candidate.
  
          Second, excepting hash considerations, candidates that have been
          yanked (in the sense of PEP 592) are always less preferred than
          candidates that haven't been yanked. Then:
  
          If not finding wheels, they are sorted by version only.
          If finding wheels, then the sort order is by version, then:
            1. existing installs
            2. wheels ordered via Wheel.support_index_min(self._supported_tags)
            3. source archives
          If prefer_binary was set, then all wheels are sorted above sources.
  
          Note: it was considered to embed this logic into the Link
                comparison operators, but then different sdist links
                with the same version, would have to be considered equal
          """
          valid_tags = self._supported_tags
          support_num = len(valid_tags)
          build_tag = ()  # type: BuildTag
          binary_preference = 0
          link = candidate.link
          if link.is_wheel:
              # can raise InvalidWheelFilename
              wheel = Wheel(link.filename)
              if not wheel.supported(valid_tags):
                  raise UnsupportedWheel(
                      "{} is not a supported wheel for this platform. It "
                      "can't be sorted.".format(wheel.filename)
                  )
              if self._prefer_binary:
                  binary_preference = 1
              pri = -(wheel.support_index_min(valid_tags))
              if wheel.build_tag is not None:
                  match = re.match(r'^(\d+)(.*)$', wheel.build_tag)
                  build_tag_groups = match.groups()
                  build_tag = (int(build_tag_groups[0]), build_tag_groups[1])
          else:  # sdist
              pri = -(support_num)
          has_allowed_hash = int(link.is_hash_allowed(self._hashes))
          yank_value = -1 * int(link.is_yanked)  # -1 for yanked.
          return (
              has_allowed_hash, yank_value, binary_preference, candidate.version,
              build_tag, pri,
          )
  
      def sort_best_candidate(
          self,
          candidates,    # type: List[InstallationCandidate]
      ):
          # type: (...) -> Optional[InstallationCandidate]
          """
          Return the best candidate per the instance's sort order, or None if
          no candidate is acceptable.
          """
          if not candidates:
              return None
          best_candidate = max(candidates, key=self._sort_key)
          return best_candidate
  
      def compute_best_candidate(
          self,
          candidates,      # type: List[InstallationCandidate]
      ):
          # type: (...) -> BestCandidateResult
          """
          Compute and return a `BestCandidateResult` instance.
          """
          applicable_candidates = self.get_applicable_candidates(candidates)
  
          best_candidate = self.sort_best_candidate(applicable_candidates)
  
          return BestCandidateResult(
              candidates,
              applicable_candidates=applicable_candidates,
              best_candidate=best_candidate,
          )
  
  
  class PackageFinder:
      """This finds packages.
  
      This is meant to match easy_install's technique for looking for
      packages, by reading pages and looking for appropriate links.
      """
  
      def __init__(
          self,
          link_collector,       # type: LinkCollector
          target_python,        # type: TargetPython
          allow_yanked,         # type: bool
          format_control=None,  # type: Optional[FormatControl]
          candidate_prefs=None,         # type: CandidatePreferences
          ignore_requires_python=None,  # type: Optional[bool]
      ):
          # type: (...) -> None
          """
          This constructor is primarily meant to be used by the create() class
          method and from tests.
  
          :param format_control: A FormatControl object, used to control
              the selection of source packages / binary packages when consulting
              the index and links.
          :param candidate_prefs: Options to use when creating a
              CandidateEvaluator object.
          """
          if candidate_prefs is None:
              candidate_prefs = CandidatePreferences()
  
          format_control = format_control or FormatControl(set(), set())
  
          self._allow_yanked = allow_yanked
          self._candidate_prefs = candidate_prefs
          self._ignore_requires_python = ignore_requires_python
          self._link_collector = link_collector
          self._target_python = target_python
  
          self.format_control = format_control
  
          # These are boring links that have already been logged somehow.
          self._logged_links = set()  # type: Set[Link]
  
      # Don't include an allow_yanked default value to make sure each call
      # site considers whether yanked releases are allowed. This also causes
      # that decision to be made explicit in the calling code, which helps
      # people when reading the code.
      @classmethod
      def create(
          cls,
          link_collector,      # type: LinkCollector
          selection_prefs,     # type: SelectionPreferences
          target_python=None,  # type: Optional[TargetPython]
      ):
          # type: (...) -> PackageFinder
          """Create a PackageFinder.
  
          :param selection_prefs: The candidate selection preferences, as a
              SelectionPreferences object.
          :param target_python: The target Python interpreter to use when
              checking compatibility. If None (the default), a TargetPython
              object will be constructed from the running Python.
          """
          if target_python is None:
              target_python = TargetPython()
  
          candidate_prefs = CandidatePreferences(
              prefer_binary=selection_prefs.prefer_binary,
              allow_all_prereleases=selection_prefs.allow_all_prereleases,
          )
  
          return cls(
              candidate_prefs=candidate_prefs,
              link_collector=link_collector,
              target_python=target_python,
              allow_yanked=selection_prefs.allow_yanked,
              format_control=selection_prefs.format_control,
              ignore_requires_python=selection_prefs.ignore_requires_python,
          )
  
      @property
      def target_python(self):
          # type: () -> TargetPython
          return self._target_python
  
      @property
      def search_scope(self):
          # type: () -> SearchScope
          return self._link_collector.search_scope
  
      @search_scope.setter
      def search_scope(self, search_scope):
          # type: (SearchScope) -> None
          self._link_collector.search_scope = search_scope
  
      @property
      def find_links(self):
          # type: () -> List[str]
          return self._link_collector.find_links
  
      @property
      def index_urls(self):
          # type: () -> List[str]
          return self.search_scope.index_urls
  
      @property
      def trusted_hosts(self):
          # type: () -> Iterable[str]
          for host_port in self._link_collector.session.pip_trusted_origins:
              yield build_netloc(*host_port)
  
      @property
      def allow_all_prereleases(self):
          # type: () -> bool
          return self._candidate_prefs.allow_all_prereleases
  
      def set_allow_all_prereleases(self):
          # type: () -> None
          self._candidate_prefs.allow_all_prereleases = True
  
      @property
      def prefer_binary(self):
          # type: () -> bool
          return self._candidate_prefs.prefer_binary
  
      def set_prefer_binary(self):
          # type: () -> None
          self._candidate_prefs.prefer_binary = True
  
      def make_link_evaluator(self, project_name):
          # type: (str) -> LinkEvaluator
          canonical_name = canonicalize_name(project_name)
          formats = self.format_control.get_allowed_formats(canonical_name)
  
          return LinkEvaluator(
              project_name=project_name,
              canonical_name=canonical_name,
              formats=formats,
              target_python=self._target_python,
              allow_yanked=self._allow_yanked,
              ignore_requires_python=self._ignore_requires_python,
          )
  
      def _sort_links(self, links):
          # type: (Iterable[Link]) -> List[Link]
          """
          Returns elements of links in order, non-egg links first, egg links
          second, while eliminating duplicates
          """
          eggs, no_eggs = [], []
          seen = set()  # type: Set[Link]
          for link in links:
              if link not in seen:
                  seen.add(link)
                  if link.egg_fragment:
                      eggs.append(link)
                  else:
                      no_eggs.append(link)
          return no_eggs + eggs
  
      def _log_skipped_link(self, link, reason):
          # type: (Link, str) -> None
          if link not in self._logged_links:
              # Put the link at the end so the reason is more visible and because
              # the link string is usually very long.
              logger.debug('Skipping link: %s: %s', reason, link)
              self._logged_links.add(link)
  
      def get_install_candidate(self, link_evaluator, link):
          # type: (LinkEvaluator, Link) -> Optional[InstallationCandidate]
          """
          If the link is a candidate for install, convert it to an
          InstallationCandidate and return it. Otherwise, return None.
          """
          is_candidate, result = link_evaluator.evaluate_link(link)
          if not is_candidate:
              if result:
                  self._log_skipped_link(link, reason=result)
              return None
  
          return InstallationCandidate(
              name=link_evaluator.project_name,
              link=link,
              version=result,
          )
  
      def evaluate_links(self, link_evaluator, links):
          # type: (LinkEvaluator, Iterable[Link]) -> List[InstallationCandidate]
          """
          Convert links that are candidates to InstallationCandidate objects.
          """
          candidates = []
          for link in self._sort_links(links):
              candidate = self.get_install_candidate(link_evaluator, link)
              if candidate is not None:
                  candidates.append(candidate)
  
          return candidates
  
      def process_project_url(self, project_url, link_evaluator):
          # type: (Link, LinkEvaluator) -> List[InstallationCandidate]
          logger.debug(
              'Fetching project page and analyzing links: %s', project_url,
          )
          html_page = self._link_collector.fetch_page(project_url)
          if html_page is None:
              return []
  
          page_links = list(parse_links(html_page))
  
          with indent_log():
              package_links = self.evaluate_links(
                  link_evaluator,
                  links=page_links,
              )
  
          return package_links
  
      @functools.lru_cache(maxsize=None)
      def find_all_candidates(self, project_name):
          # type: (str) -> List[InstallationCandidate]
          """Find all available InstallationCandidate for project_name
  
          This checks index_urls and find_links.
          All versions found are returned as an InstallationCandidate list.
  
          See LinkEvaluator.evaluate_link() for details on which files
          are accepted.
          """
          collected_links = self._link_collector.collect_links(project_name)
  
          link_evaluator = self.make_link_evaluator(project_name)
  
          find_links_versions = self.evaluate_links(
              link_evaluator,
              links=collected_links.find_links,
          )
  
          page_versions = []
          for project_url in collected_links.project_urls:
              package_links = self.process_project_url(
                  project_url, link_evaluator=link_evaluator,
              )
              page_versions.extend(package_links)
  
          file_versions = self.evaluate_links(
              link_evaluator,
              links=collected_links.files,
          )
          if file_versions:
              file_versions.sort(reverse=True)
              logger.debug(
                  'Local files found: %s',
                  ', '.join([
                      url_to_path(candidate.link.url)
                      for candidate in file_versions
                  ])
              )
  
          # This is an intentional priority ordering
          return file_versions + find_links_versions + page_versions
  
      def make_candidate_evaluator(
          self,
          project_name,    # type: str
          specifier=None,  # type: Optional[specifiers.BaseSpecifier]
          hashes=None,     # type: Optional[Hashes]
      ):
          # type: (...) -> CandidateEvaluator
          """Create a CandidateEvaluator object to use.
          """
          candidate_prefs = self._candidate_prefs
          return CandidateEvaluator.create(
              project_name=project_name,
              target_python=self._target_python,
              prefer_binary=candidate_prefs.prefer_binary,
              allow_all_prereleases=candidate_prefs.allow_all_prereleases,
              specifier=specifier,
              hashes=hashes,
          )
  
      @functools.lru_cache(maxsize=None)
      def find_best_candidate(
          self,
          project_name,       # type: str
          specifier=None,     # type: Optional[specifiers.BaseSpecifier]
          hashes=None,        # type: Optional[Hashes]
      ):
          # type: (...) -> BestCandidateResult
          """Find matches for the given project and specifier.
  
          :param specifier: An optional object implementing `filter`
              (e.g. `packaging.specifiers.SpecifierSet`) to filter applicable
              versions.
  
          :return: A `BestCandidateResult` instance.
          """
          candidates = self.find_all_candidates(project_name)
          candidate_evaluator = self.make_candidate_evaluator(
              project_name=project_name,
              specifier=specifier,
              hashes=hashes,
          )
          return candidate_evaluator.compute_best_candidate(candidates)
  
      def find_requirement(self, req, upgrade):
          # type: (InstallRequirement, bool) -> Optional[InstallationCandidate]
          """Try to find a Link matching req
  
          Expects req, an InstallRequirement and upgrade, a boolean
          Returns a InstallationCandidate if found,
          Raises DistributionNotFound or BestVersionAlreadyInstalled otherwise
          """
          hashes = req.hashes(trust_internet=False)
          best_candidate_result = self.find_best_candidate(
              req.name, specifier=req.specifier, hashes=hashes,
          )
          best_candidate = best_candidate_result.best_candidate
  
          installed_version = None    # type: Optional[_BaseVersion]
          if req.satisfied_by is not None:
              installed_version = parse_version(req.satisfied_by.version)
  
          def _format_versions(cand_iter):
              # type: (Iterable[InstallationCandidate]) -> str
              # This repeated parse_version and str() conversion is needed to
              # handle different vendoring sources from pip and pkg_resources.
              # If we stop using the pkg_resources provided specifier and start
              # using our own, we can drop the cast to str().
              return ", ".join(sorted(
                  {str(c.version) for c in cand_iter},
                  key=parse_version,
              )) or "none"
  
          if installed_version is None and best_candidate is None:
              logger.critical(
                  'Could not find a version that satisfies the requirement %s '
                  '(from versions: %s)',
                  req,
                  _format_versions(best_candidate_result.iter_all()),
              )
  
              raise DistributionNotFound(
                  'No matching distribution found for {}'.format(
                      req)
              )
  
          best_installed = False
          if installed_version and (
                  best_candidate is None or
                  best_candidate.version <= installed_version):
              best_installed = True
  
          if not upgrade and installed_version is not None:
              if best_installed:
                  logger.debug(
                      'Existing installed version (%s) is most up-to-date and '
                      'satisfies requirement',
                      installed_version,
                  )
              else:
                  logger.debug(
                      'Existing installed version (%s) satisfies requirement '
                      '(most up-to-date version is %s)',
                      installed_version,
                      best_candidate.version,
                  )
              return None
  
          if best_installed:
              # We have an existing version, and its the best version
              logger.debug(
                  'Installed version (%s) is most up-to-date (past versions: '
                  '%s)',
                  installed_version,
                  _format_versions(best_candidate_result.iter_applicable()),
              )
              raise BestVersionAlreadyInstalled
  
          logger.debug(
              'Using version %s (newest of versions: %s)',
              best_candidate.version,
              _format_versions(best_candidate_result.iter_applicable()),
          )
          return best_candidate
  
  
  def _find_name_version_sep(fragment, canonical_name):
      # type: (str, str) -> int
      """Find the separator's index based on the package's canonical name.
  
      :param fragment: A <package>+<version> filename "fragment" (stem) or
          egg fragment.
      :param canonical_name: The package's canonical name.
  
      This function is needed since the canonicalized name does not necessarily
      have the same length as the egg info's name part. An example::
  
      >>> fragment = 'foo__bar-1.0'
      >>> canonical_name = 'foo-bar'
      >>> _find_name_version_sep(fragment, canonical_name)
      8
      """
      # Project name and version must be separated by one single dash. Find all
      # occurrences of dashes; if the string in front of it matches the canonical
      # name, this is the one separating the name and version parts.
      for i, c in enumerate(fragment):
          if c != "-":
              continue
          if canonicalize_name(fragment[:i]) == canonical_name:
              return i
      raise ValueError(f"{fragment} does not match {canonical_name}")
  
  
  def _extract_version_from_fragment(fragment, canonical_name):
      # type: (str, str) -> Optional[str]
      """Parse the version string from a <package>+<version> filename
      "fragment" (stem) or egg fragment.
  
      :param fragment: The string to parse. E.g. foo-2.1
      :param canonical_name: The canonicalized name of the package this
          belongs to.
      """
      try:
          version_start = _find_name_version_sep(fragment, canonical_name) + 1
      except ValueError:
          return None
      version = fragment[version_start:]
      if not version:
          return None
      return version
  