text: #!/usr/bin/env python3
  """
  Copyright 2018 Google Inc. All rights reserved.
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
      http://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  """
  
  from contextlib import closing
  from distutils.version import LooseVersion
  import json
  import os
  import os.path
  import platform
  import re
  import shutil
  import subprocess
  import sys
  import tempfile
  import time
  
  try:
      from urllib.request import urlopen
  except ImportError:
      # Python 2.x compatibility hack.
      from urllib2 import urlopen
  
  ONE_HOUR = 1 * 60 * 60
  
  LATEST_PATTERN = re.compile(r"latest(-(?P<offset>\d+))?$")
  
  LAST_GREEN_COMMIT_BASE_PATH = (
      "https://storage.googleapis.com/bazel-untrusted-builds/last_green_commit/"
  )
  
  LAST_GREEN_COMMIT_PATH_SUFFIXES = {
      "last_green": "github.com/bazelbuild/bazel.git/bazel-bazel",
      "last_downstream_green": "downstream_pipeline",
  }
  
  BAZEL_GCS_PATH_PATTERN = (
      "https://storage.googleapis.com/bazel-builds/artifacts/{platform}/{commit}/bazel"
  )
  
  SUPPORTED_PLATFORMS = {"linux": "ubuntu1404", "windows": "windows", "darwin": "macos"}
  
  TOOLS_BAZEL_PATH = "./tools/bazel"
  
  BAZEL_REAL = "BAZEL_REAL"
  
  BAZEL_UPSTREAM = "bazelbuild"
  
  
  def decide_which_bazel_version_to_use():
      # Check in this order:
      # - env var "USE_BAZEL_VERSION" is set to a specific version.
      # - env var "USE_NIGHTLY_BAZEL" or "USE_BAZEL_NIGHTLY" is set -> latest
      #   nightly. (TODO)
      # - env var "USE_CANARY_BAZEL" or "USE_BAZEL_CANARY" is set -> latest
      #   rc. (TODO)
      # - the file workspace_root/tools/bazel exists -> that version. (TODO)
      # - workspace_root/.bazelversion exists -> read contents, that version.
      # - workspace_root/WORKSPACE contains a version -> that version. (TODO)
      # - fallback: latest release
      if "USE_BAZEL_VERSION" in os.environ:
          return os.environ["USE_BAZEL_VERSION"]
  
      workspace_root = find_workspace_root()
      if workspace_root:
          bazelversion_path = os.path.join(workspace_root, ".bazelversion")
          if os.path.exists(bazelversion_path):
              with open(bazelversion_path, "r") as f:
                  return f.read().strip()
  
      return "latest"
  
  
  def find_workspace_root(root=None):
      if root is None:
          root = os.getcwd()
      if os.path.exists(os.path.join(root, "WORKSPACE")):
          return root
      new_root = os.path.dirname(root)
      return find_workspace_root(new_root) if new_root != root else None
  
  
  def resolve_version_label_to_number_or_commit(bazelisk_directory, version):
      """Resolves the given label to a released version of Bazel or a commit.
  
      Args:
          bazelisk_directory: string; path to a directory that can store
              temporary data for Bazelisk.
          version: string; the version label that should be resolved.
      Returns:
          A (string, bool) tuple that consists of two parts:
          1. the resolved number of a Bazel release (candidate), or the commit
              of an unreleased Bazel binary,
          2. An indicator for whether the returned version refers to a commit.
      """
      suffix = LAST_GREEN_COMMIT_PATH_SUFFIXES.get(version)
      if suffix:
          return get_last_green_commit(suffix), True
  
      if "latest" in version:
          match = LATEST_PATTERN.match(version)
          if not match:
              raise Exception(
                  'Invalid version "{}". In addition to using a version '
                  'number such as "0.20.0", you can use values such as '
                  '"latest" and "latest-N", with N being a non-negative '
                  "integer.".format(version)
              )
  
          history = get_version_history(bazelisk_directory)
          offset = int(match.group("offset") or "0")
          return resolve_latest_version(history, offset), False
  
      return version, False
  
  
  def get_last_green_commit(path_suffix):
      return read_remote_text_file(LAST_GREEN_COMMIT_BASE_PATH + path_suffix).strip()
  
  
  def get_releases_json(bazelisk_directory):
      """Returns the most recent versions of Bazel, in descending order."""
      releases = os.path.join(bazelisk_directory, "releases.json")
  
      # Use a cached version if it's fresh enough.
      if os.path.exists(releases):
          if abs(time.time() - os.path.getmtime(releases)) < ONE_HOUR:
              with open(releases, "rb") as f:
                  try:
                      return json.loads(f.read().decode("utf-8"))
                  except ValueError:
                      print("WARN: Could not parse cached releases.json.")
                      pass
  
      with open(releases, "wb") as f:
          body = read_remote_text_file("https://api.github.com/repos/bazelbuild/bazel/releases")
          f.write(body.encode("utf-8"))
          return json.loads(body)
  
  
  def read_remote_text_file(url):
      with closing(urlopen(url)) as res:
          body = res.read()
          try:
              return body.decode(res.info().get_content_charset("iso-8859-1"))
          except AttributeError:
              # Python 2.x compatibility hack
              return body.decode(res.info().getparam("charset") or "iso-8859-1")
  
  
  def get_version_history(bazelisk_directory):
      ordered = sorted(
          (
              LooseVersion(release["tag_name"])
              for release in get_releases_json(bazelisk_directory)
              if not release["prerelease"]
          ),
          reverse=True,
      )
      return [str(v) for v in ordered]
  
  
  def resolve_latest_version(version_history, offset):
      if offset >= len(version_history):
          version = "latest-{}".format(offset) if offset else "latest"
          raise Exception(
              'Cannot resolve version "{}": There are only {} Bazel '
              "releases.".format(version, len(version_history))
          )
  
      # This only works since we store the history in descending order.
      return version_history[offset]
  
  
  def get_operating_system():
      operating_system = platform.system().lower()
      if operating_system not in ("linux", "darwin", "windows"):
          raise Exception(
              'Unsupported operating system "{}". '
              "Bazel currently only supports Linux, macOS and Windows.".format(operating_system)
          )
      return operating_system
  
  
  def determine_executable_filename_suffix():
      operating_system = get_operating_system()
      return ".exe" if operating_system == "windows" else ""
  
  
  def determine_bazel_filename(version):
      machine = normalized_machine_arch_name()
      if machine != "x86_64":
          raise Exception(
              'Unsupported machine architecture "{}". Bazel currently only supports x86_64.'.format(
                  machine
              )
          )
  
      operating_system = get_operating_system()
  
      filename_suffix = determine_executable_filename_suffix()
      return "bazel-{}-{}-{}{}".format(version, operating_system, machine, filename_suffix)
  
  
  def normalized_machine_arch_name():
      machine = platform.machine().lower()
      if machine == "amd64":
          machine = "x86_64"
      return machine
  
  
  def determine_url(version, is_commit, bazel_filename):
      if is_commit:
          sys.stderr.write("Using unreleased version at commit {}\n".format(version))
          # No need to validate the platform thanks to determine_bazel_filename().
          return BAZEL_GCS_PATH_PATTERN.format(
              platform=SUPPORTED_PLATFORMS[platform.system().lower()], commit=version
          )
  
      # Split version into base version and optional additional identifier.
      # Example: '0.19.1' -> ('0.19.1', None), '0.20.0rc1' -> ('0.20.0', 'rc1')
      (version, rc) = re.match(r"(\d*\.\d*(?:\.\d*)?)(rc\d+)?", version).groups()
      return "https://releases.bazel.build/{}/{}/{}".format(
          version, rc if rc else "release", bazel_filename
      )
  
  
  def trim_suffix(string, suffix):
      if string.endswith(suffix):
          return string[:len(string) - len(suffix)]
      else:
          return string
  
  
  def download_bazel_into_directory(version, is_commit, directory):
      bazel_filename = determine_bazel_filename(version)
      url = determine_url(version, is_commit, bazel_filename)
  
      filename_suffix = determine_executable_filename_suffix()
      bazel_directory_name = trim_suffix(bazel_filename, filename_suffix)
      destination_dir = os.path.join(directory, bazel_directory_name, "bin")
      maybe_makedirs(destination_dir)
  
      destination_path = os.path.join(destination_dir, "bazel" + filename_suffix)
      if not os.path.exists(destination_path):
          sys.stderr.write("Downloading {}...\n".format(url))
          with tempfile.NamedTemporaryFile(prefix="bazelisk", dir=destination_dir, delete=False) as t:
              with closing(urlopen(url)) as response:
                  shutil.copyfileobj(response, t)
              t.flush()
              os.fsync(t.fileno())
          os.rename(t.name, destination_path)
          os.chmod(destination_path, 0o755)
  
      return destination_path
  
  
  def get_bazelisk_directory():
      bazelisk_home = os.environ.get("BAZELISK_HOME")
      if bazelisk_home is not None:
          return bazelisk_home
  
      operating_system = get_operating_system()
  
      base_dir = None
  
      if operating_system == "windows":
          base_dir = os.environ.get("LocalAppData")
          if base_dir is None:
              raise Exception("%LocalAppData% is not defined")
      elif operating_system == "darwin":
          base_dir = os.environ.get("HOME")
          if base_dir is None:
              raise Exception("$HOME is not defined")
          base_dir = os.path.join(base_dir, "Library/Caches")
      elif operating_system == "linux":
          base_dir = os.environ.get("XDG_CACHE_HOME")
          if base_dir is None:
              base_dir = os.environ.get("HOME")
              if base_dir is None:
                  raise Exception("neither $XDG_CACHE_HOME nor $HOME are defined")
              base_dir = os.path.join(base_dir, ".cache")
      else:
          raise Exception("Unsupported operating system '{}'".format(operating_system))
  
      return os.path.join(base_dir, "bazelisk")
  
  
  def maybe_makedirs(path):
      """
    Creates a directory and its parents if necessary.
    """
      try:
          os.makedirs(path)
      except OSError as e:
          if not os.path.isdir(path):
              raise e
  
  
  def delegate_tools_bazel(bazel_path):
      """Match Bazel's own delegation behavior in the builds distributed by most
      package managers: use tools/bazel if it's present, executable, and not this
      script.
      """
      root = find_workspace_root()
      if root:
          wrapper = os.path.join(root, TOOLS_BAZEL_PATH)
          if os.path.exists(wrapper) and os.access(wrapper, os.X_OK):
              try:
                  if not os.path.samefile(wrapper, __file__):
                      return wrapper
              except AttributeError:
                  # Python 2 on Windows does not support os.path.samefile
                  if os.path.abspath(wrapper) != os.path.abspath(__file__):
                      return wrapper
      return None
  
  
  def prepend_directory_to_path(env, directory):
      """
      Prepend binary directory to PATH
      """
      if "PATH" in env:
          env["PATH"] = directory + os.pathsep + env["PATH"]
      else:
          env["PATH"] = directory
  
  
  def make_bazel_cmd(bazel_path, argv):
      env = os.environ.copy()
  
      wrapper = delegate_tools_bazel(bazel_path)
      if wrapper:
          env[BAZEL_REAL] = bazel_path
          bazel_path = wrapper
  
      directory = os.path.dirname(bazel_path)
      prepend_directory_to_path(env, directory)
      return {
          'exec': bazel_path,
          'args': argv,
          'env': env,
      }
  
  
  def execute_bazel(bazel_path, argv):
      cmd = make_bazel_cmd(bazel_path, argv)
  
      # We cannot use close_fds on Windows, so disable it there.
      p = subprocess.Popen([cmd['exec']] + cmd['args'], close_fds=os.name != "nt", env=cmd['env'])
      while True:
          try:
              return p.wait()
          except KeyboardInterrupt:
              # Bazel will also get the signal and terminate.
              # We should continue waiting until it does so.
              pass
  
  
  def get_bazel_path():
      bazelisk_directory = get_bazelisk_directory()
      maybe_makedirs(bazelisk_directory)
  
      bazel_version = decide_which_bazel_version_to_use()
      bazel_version, is_commit = resolve_version_label_to_number_or_commit(
          bazelisk_directory, bazel_version
      )
  
      # TODO: Support other forks just like Go version
      bazel_directory = os.path.join(bazelisk_directory, "downloads", BAZEL_UPSTREAM)
      return download_bazel_into_directory(bazel_version, is_commit, bazel_directory)
  
  
  def main(argv=None):
      if argv is None:
          argv = sys.argv
  
      bazel_path = get_bazel_path()
  
      argv = argv[1:]
  
      if argv and argv[0] == "--print_env":
          cmd = make_bazel_cmd(bazel_path, argv)
          env = cmd['env']
          for key in env:
              print('{}={}'.format(key, env[key]))
          return 0
  
      return execute_bazel(bazel_path, argv)
  
  
  if __name__ == "__main__":
      sys.exit(main())
  