#!/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.
"""

import base64
from contextlib import closing
import hashlib
import json
import netrc
import os
import os.path
import platform
import re
import shutil
import subprocess
import sys
import tempfile
import time

try:
    from urllib.parse import urlparse
    from urllib.request import urlopen, Request
    from urllib.error import HTTPError
except ImportError:
    # Python 2.x compatibility hack.
    # http://python-future.org/compatible_idioms.html?highlight=urllib#urllib-module
    from urlparse import urlparse
    from urllib2 import urlopen, Request, HTTPError

    FileNotFoundError = IOError

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):
    return sorted(
        (
            release["tag_name"]
            for release in get_releases_json(bazelisk_directory)
            if not release["prerelease"]
        ),
        # This only handles versions with numeric components, but that is fine
        # since prerelease verisons have been excluded.
        key=lambda version: tuple(int(component)
                                  for component in version.split('.')),
        reverse=True,
    )


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):
    operating_system = get_operating_system()
    supported_machines = get_supported_machine_archs(version, operating_system)
    machine = normalized_machine_arch_name()
    if machine not in supported_machines:
        raise Exception(
            'Unsupported machine architecture "{}". Bazel {} only supports {} on {}.'.format(
                machine, version, ", ".join(supported_machines), operating_system.capitalize()
            )
        )

    filename_suffix = determine_executable_filename_suffix()
    bazel_flavor = "bazel"
    if os.environ.get("BAZELISK_NOJDK", "0") != "0":
        bazel_flavor = "bazel_nojdk"
    return "{}-{}-{}-{}{}".format(bazel_flavor, version, operating_system, machine, filename_suffix)


def get_supported_machine_archs(version, operating_system):
    supported_machines = ["x86_64"]
    versions = version.split(".")[:2]
    if len(versions) == 2:
        # released version
        major, minor = int(versions[0]), int(versions[1])
        if (
            operating_system == "darwin"
            and (major > 4 or major == 4 and minor >= 1)
            or operating_system == "linux"
            and (major > 3 or major == 3 and minor >= 4)
        ):
            # Linux arm64 was supported since 3.4.0.
            # Darwin arm64 was supported since 4.1.0.
            supported_machines.append("arm64")
    elif operating_system in ("darwin", "linux"):
        # This is needed to run bazelisk_test.sh on Linux and Darwin arm64 machines, which are
        # becoming more and more popular.
        # It works because all recent commits of Bazel support arm64 on Darwin and Linux.
        # However, this would add arm64 by mistake if the commit is too old, which should be
        # a rare scenario.
        supported_machines.append("arm64")
    return supported_machines


def normalized_machine_arch_name():
    machine = platform.machine().lower()
    if machine == "amd64":
        machine = "x86_64"
    elif machine == "aarch64":
        machine = "arm64"
    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()

    if "BAZELISK_BASE_URL" in os.environ:
        return "{}/{}/{}".format(os.environ["BAZELISK_BASE_URL"], version, bazel_filename)
    else:
        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)
    bazel_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):
        download(bazel_url, destination_path)
        os.chmod(destination_path, 0o755)

    sha256_path = destination_path + ".sha256"
    expected_hash = ""
    if not os.path.exists(sha256_path):
        try:
            download(bazel_url + ".sha256", sha256_path)
        except HTTPError as e:
            if e.code == 404:
                sys.stderr.write(
                    "The Bazel mirror does not have a checksum file; skipping checksum verification."
                )
                return destination_path
            raise e
    with open(sha256_path, "r") as sha_file:
        expected_hash = sha_file.read().split()[0]
    sha256_hash = hashlib.sha256()
    with open(destination_path, "rb") as bazel_file:
        for byte_block in iter(lambda: bazel_file.read(4096), b""):
            sha256_hash.update(byte_block)
    actual_hash = sha256_hash.hexdigest()
    if actual_hash != expected_hash:
        os.remove(destination_path)
        os.remove(sha256_path)
        print(
            "The downloaded Bazel binary is corrupted. Expected SHA-256 {}, got {}. Please try again.".format(
                expected_hash, actual_hash
            )
        )
        # Exiting with a special exit code not used by Bazel, so the calling process may retry based on that.
        # https://docs.bazel.build/versions/0.21.0/guide.html#what-exit-code-will-i-get
        sys.exit(22)
    return destination_path


def download(url, destination_path):
    sys.stderr.write("Downloading {}...\n".format(url))
    request = Request(url)
    if "BAZELISK_BASE_URL" in os.environ:
        parts = urlparse(url)
        creds = None
        try:
            creds = netrc.netrc().hosts.get(parts.netloc)
        except Exception:
            pass
        if creds is not None:
            auth = base64.b64encode(("%s:%s" % (creds[0], creds[2])).encode("ascii"))
            request.add_header("Authorization", "Basic %s" % auth.decode("utf-8"))
    with closing(urlopen(request)) as response, open(destination_path, "wb") as file:
        shutil.copyfileobj(response, file)


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())
