text: import logging
  import os
  import tempfile
  import threading
  from contextlib import contextmanager
  from distutils.dir_util import copy_tree
  from typing import Iterable
  
  from funcy import cached_property, retry, wrap_with
  
  from dvc.config import NoRemoteError, NotDvcRepoError
  from dvc.exceptions import (
      FileMissingError,
      NoOutputInExternalRepoError,
      NoRemoteInExternalRepoError,
      OutputNotFoundError,
      PathMissingError,
  )
  from dvc.path_info import PathInfo
  from dvc.repo import Repo
  from dvc.repo.tree import RepoTree
  from dvc.scm.git import Git
  from dvc.scm.tree import is_working_tree
  from dvc.utils.fs import remove
  
  logger = logging.getLogger(__name__)
  
  
  @contextmanager
  def external_repo(url, rev=None, for_write=False):
      logger.debug("Creating external repo %s@%s", url, rev)
      path = _cached_clone(url, rev, for_write=for_write)
      if not rev:
          rev = "HEAD"
      try:
          repo = ExternalRepo(path, url, rev, for_write=for_write)
      except NotDvcRepoError:
          repo = ExternalGitRepo(path, url, rev)
  
      try:
          yield repo
      except NoRemoteError:
          raise NoRemoteInExternalRepoError(url)
      except OutputNotFoundError as exc:
          if exc.repo is repo:
              raise NoOutputInExternalRepoError(exc.output, repo.root_dir, url)
          raise
      except FileMissingError as exc:
          raise PathMissingError(exc.path, url)
      finally:
          repo.close()
          if for_write:
              _remove(path)
  
  
  CLONES = {}
  CACHE_DIRS = {}
  
  
  def clean_repos():
      # Outside code should not see cache while we are removing
      paths = list(CLONES.values()) + list(CACHE_DIRS.values())
      CLONES.clear()
      CACHE_DIRS.clear()
  
      for path in paths:
          _remove(path)
  
  
  class BaseExternalRepo:
  
      _local_cache = None
  
      @property
      def local_cache(self):
          if hasattr(self, "cache"):
              return self.cache.local
          return self._local_cache
  
      @contextmanager
      def use_cache(self, cache):
          """Use the specified cache in place of default tmpdir cache for
          download operations.
          """
          if hasattr(self, "cache"):
              save_cache = self.cache.local
              self.cache.local = cache
          self._local_cache = cache
  
          yield
  
          if hasattr(self, "cache"):
              self.cache.local = save_cache
          self._local_cache = None
  
      @cached_property
      def repo_tree(self):
          return RepoTree(self, fetch=True)
  
      def get_rev(self):
          if is_working_tree(self.tree):
              return self.scm.get_rev()
          if hasattr(self.tree, "tree"):
              return self.tree.tree.rev
          return self.tree.rev
  
      def fetch_external(self, paths: Iterable, **kwargs):
          """Fetch specified external repo paths into cache.
  
          Returns 3-tuple in the form
              (downloaded, failed, list(cache_infos))
          where cache_infos can be used as checkout targets for the
          fetched paths.
          """
          download_results = []
          failed = 0
  
          paths = [PathInfo(self.root_dir) / path for path in paths]
  
          def download_update(result):
              download_results.append(result)
  
          save_infos = []
          for path in paths:
              if not self.repo_tree.exists(path):
                  raise PathMissingError(path, self.url)
              save_info = self.local_cache.save(
                  path,
                  self.repo_tree,
                  None,
                  save_link=False,
                  download_callback=download_update,
              )
              save_infos.append(save_info)
  
          return sum(download_results), failed, save_infos
  
      def get_external(self, path, dest):
          """Convenience wrapper for fetch_external and checkout."""
          if self.local_cache:
              # fetch DVC and git files to tmpdir cache, then checkout
              _, _, save_infos = self.fetch_external([path])
              self.local_cache.checkout(PathInfo(dest), save_infos[0])
          else:
              # git-only erepo with no cache, just copy files directly
              # to dest
              path = PathInfo(self.root_dir) / path
              if not self.repo_tree.exists(path):
                  raise PathMissingError(path, self.url)
              self.repo_tree.copytree(path, dest)
  
  
  class ExternalRepo(Repo, BaseExternalRepo):
      def __init__(self, root_dir, url, rev, for_write=False):
          if for_write:
              super().__init__(root_dir)
          else:
              root_dir = os.path.realpath(root_dir)
              super().__init__(root_dir, scm=Git(root_dir), rev=rev)
          self.url = url
          self._set_cache_dir()
          self._fix_upstream()
  
      @wrap_with(threading.Lock())
      def _set_cache_dir(self):
          try:
              cache_dir = CACHE_DIRS[self.url]
          except KeyError:
              cache_dir = CACHE_DIRS[self.url] = tempfile.mkdtemp("dvc-cache")
  
          self.cache.local.cache_dir = cache_dir
          self._local_cache = self.cache.local
  
      def _fix_upstream(self):
          if not os.path.isdir(self.url):
              return
  
          try:
              src_repo = Repo(self.url)
          except NotDvcRepoError:
              # If ExternalRepo does not throw NotDvcRepoError and Repo does,
              # the self.url might be a bare git repo.
              # NOTE: This will fail to resolve remote with relative path,
              # same as if it was a remote DVC repo.
              return
  
          try:
              remote_name = self.config["core"].get("remote")
              if remote_name:
                  self._fix_local_remote(src_repo, remote_name)
              else:
                  self._add_upstream(src_repo)
          finally:
              src_repo.close()
  
      def _fix_local_remote(self, src_repo, remote_name):
          # If a remote URL is relative to the source repo,
          # it will have changed upon config load and made
          # relative to this new repo. Restore the old one here.
          new_remote = self.config["remote"][remote_name]
          old_remote = src_repo.config["remote"][remote_name]
          if new_remote["url"] != old_remote["url"]:
              new_remote["url"] = old_remote["url"]
  
      def _add_upstream(self, src_repo):
          # Fill the empty upstream entry with a new remote pointing to the
          # original repo's cache location.
          cache_dir = src_repo.cache.local.cache_dir
          self.config["remote"]["auto-generated-upstream"] = {"url": cache_dir}
          self.config["core"]["remote"] = "auto-generated-upstream"
  
  
  class ExternalGitRepo(BaseExternalRepo):
      def __init__(self, root_dir, url, rev):
          self.root_dir = os.path.realpath(root_dir)
          self.url = url
          self.tree = self.scm.get_tree(rev)
  
      @cached_property
      def scm(self):
          return Git(self.root_dir)
  
      def close(self):
          if "scm" in self.__dict__:
              self.scm.close()
  
      def find_out_by_relpath(self, path):
          raise OutputNotFoundError(path, self)
  
      @contextmanager
      def open_by_relpath(self, path, mode="r", encoding=None, **kwargs):
          """Opens a specified resource as a file object."""
          tree = RepoTree(self)
          try:
              with tree.open(
                  path, mode=mode, encoding=encoding, **kwargs
              ) as fobj:
                  yield fobj
          except FileNotFoundError:
              raise PathMissingError(path, self.url)
  
  
  def _cached_clone(url, rev, for_write=False):
      """Clone an external git repo to a temporary directory.
  
      Returns the path to a local temporary directory with the specified
      revision checked out. If for_write is set prevents reusing this dir via
      cache.
      """
      # even if we have already cloned this repo, we may need to
      # fetch/fast-forward to get specified rev
      clone_path = _clone_default_branch(url, rev)
  
      if not for_write and (url) in CLONES:
          return CLONES[url]
  
      # Copy to a new dir to keep the clone clean
      repo_path = tempfile.mkdtemp("dvc-erepo")
      logger.debug("erepo: making a copy of %s clone", url)
      copy_tree(clone_path, repo_path)
  
      # Check out the specified revision
      if for_write:
          _git_checkout(repo_path, rev)
      else:
          CLONES[url] = repo_path
      return repo_path
  
  
  @wrap_with(threading.Lock())
  def _clone_default_branch(url, rev):
      """Get or create a clean clone of the url.
  
      The cloned is reactualized with git pull unless rev is a known sha.
      """
      clone_path = CLONES.get(url)
  
      git = None
      try:
          if clone_path:
              git = Git(clone_path)
              # Do not pull for known shas, branches and tags might move
              if not Git.is_sha(rev) or not git.has_rev(rev):
                  logger.debug("erepo: git pull %s", url)
                  git.pull()
          else:
              logger.debug("erepo: git clone %s to a temporary dir", url)
              clone_path = tempfile.mkdtemp("dvc-clone")
              git = Git.clone(url, clone_path)
              CLONES[url] = clone_path
      finally:
          if git:
              git.close()
  
      return clone_path
  
  
  def _git_checkout(repo_path, rev):
      logger.debug("erepo: git checkout %s@%s", repo_path, rev)
      git = Git(repo_path)
      try:
          git.checkout(rev)
      finally:
          git.close()
  
  
  def _remove(path):
      if os.name == "nt":
          # git.exe may hang for a while not permitting to remove temp dir
          os_retry = retry(5, errors=OSError, timeout=0.1)
          os_retry(remove)(path)
      else:
          remove(path)
  