#! /usr/bin/env nix-shell
#! nix-shell -p nix-prefetch-git "python3.withPackages (ps: with ps; [ lxml ])"
#! nix-shell -i python

import base64
import json
import re
import shlex
import subprocess
from codecs import iterdecode
from os.path import abspath, dirname, splitext
from lxml import etree
from lxml.etree import HTMLParser
from urllib.request import urlopen

git_path = 'chromiumos/platform/crosvm'
git_root = 'https://chromium.googlesource.com/'
manifest_versions = f'{git_root}chromiumos/manifest-versions'
buildspecs_url = f'{manifest_versions}/+/refs/heads/master/full/buildspecs/'

# CrOS version numbers look like this:
# [<chrome-major-version>.]<tip-build>.<branch-build>.<branch-branch-build>
#
# As far as I can tell, branches are where internal Google
# modifications are added to turn Chromium OS into Chrome OS, and
# branch branches are used for fixes for specific devices.  So for
# Chromium OS they will always be 0.  This is a best guess, and is not
# documented.
with urlopen('https://cros-updates-serving.appspot.com/') as resp:
    document = etree.parse(resp, HTMLParser())
    # bgcolor="lightgreen" is set on the most up-to-date version for
    # each channel, so find a lightgreen cell in the "Stable" column.
    (platform_version, chrome_version) = document.xpath("""
        (//table[@id="cros-updates"]/tr/td[1 + count(
            //table[@id="cros-updates"]/thead/tr[1]/th[text() = "Stable"]
            /preceding-sibling::*)
        ][@bgcolor="lightgreen"])[1]/text()
    """)

chrome_major_version = re.match(r'\d+', chrome_version)[0]
chromeos_tip_build = re.match(r'\d+', platform_version)[0]

# Find the most recent buildspec for the stable Chrome version and
# Chromium OS build number.  Its branch build and branch branch build
# numbers will (almost?) certainly be 0.  It will then end with an rc
# number -- presumably these are release candidates, one of which
# becomes the final release.  Presumably the one with the highest rc
# number.
with urlopen(f'{buildspecs_url}{chrome_major_version}/?format=TEXT') as resp:
    listing = base64.decodebytes(resp.read()).decode('utf-8')
    buildspecs = [(line.split('\t', 1)[1]) for line in listing.splitlines()]
    buildspecs = [s for s in buildspecs if s.startswith(chromeos_tip_build)]
    buildspecs.sort(reverse=True)
    buildspec = splitext(buildspecs[0])[0]

# Read the buildspec, and extract the git revision.
with urlopen(f'{buildspecs_url}{chrome_major_version}/{buildspec}.xml?format=TEXT') as resp:
    xml = base64.decodebytes(resp.read())
    root = etree.fromstring(xml)
    revision = root.find(f'./project[@name="{git_path}"]').get('revision')

# Initialize the data that will be output from this script.  Leave the
# rc number in buildspec so nobody else is subject to the same level
# of confusion I have been.
data = {'version': f'{chrome_major_version}.{buildspec}'}

# Fill in the 'src' key with the output from nix-prefetch-git, which
# can be passed straight to fetchGit when imported by Nix.
argv = ['nix-prefetch-git',
        '--fetch-submodules',
        '--url', git_root + git_path,
        '--rev', revision]
output = subprocess.check_output(argv)
data['src'] = json.loads(output.decode('utf-8'))

# Find the path to crosvm's default.nix, so the src data can be
# written into the same directory.
argv = ['nix-instantiate', '--eval', '--json', '-A', 'crosvm.meta.position']
position = json.loads(subprocess.check_output(argv).decode('utf-8'))
filename = re.match(r'[^:]*', position)[0]

# Write the output.
with open(dirname(filename) + '/upstream-info.json', 'w') as out:
    json.dump(data, out, indent=2)
    out.write('\n')

# Generate a Cargo.lock
run = ['.',
       dirname(abspath(__file__)) + '/generate-cargo.sh',
       dirname(filename) + '/Cargo.lock']
expr = '(import ./. {}).crosvm.overrideAttrs (_: { dontCargoSetupPostUnpack = true; })'
subprocess.run(['nix-shell', '-E', expr, '--run', shlex.join(run)])