import argparse
import json
import requests
import sys

def version_to_list(version):
    return list(map(int, version.split('.')))

def odd_unstable(version_str, selected):
    version = version_to_list(version_str)
    if len(version) < 2:
        return True

    even = version[1] % 2 == 0
    prerelease = version[1] >= 90
    stable = even and not prerelease
    if selected == 'stable':
        return stable
    else:
        return True

def no_policy(version, selected):
    return True

version_policies = {
    'odd-unstable': odd_unstable,
    'none': no_policy,
}

def make_version_policy(version_predicate, selected):
    return lambda version: version_predicate(version, selected)

parser = argparse.ArgumentParser(description='Find latest version for a GNOME package by crawling their release server.')
parser.add_argument('package-name', help='Name of the directory in https://ftp.gnome.org/pub/GNOME/sources/ containing the package.')
parser.add_argument('version-policy', help='Policy determining which versions are considered stable. For most GNOME packages, odd minor versions are unstable but there are exceptions.', choices=version_policies.keys(), nargs='?', default='odd-unstable')
parser.add_argument('requested-release', help='Most of the time, we will want to update to stable version but sometimes it is useful to test.', choices=['stable', 'unstable'], nargs='?', default='stable')


if __name__ == '__main__':
    args = parser.parse_args()

    package_name = getattr(args, 'package-name')
    requested_release = getattr(args, 'requested-release')
    version_predicate = version_policies[getattr(args, 'version-policy')]
    version_policy = make_version_policy(version_predicate, requested_release)

    # The structure of cache.json: https://gitlab.gnome.org/Infrastructure/sysadmin-bin/blob/master/ftpadmin#L762
    cache = json.loads(requests.get('https://ftp.gnome.org/pub/GNOME/sources/{}/cache.json'.format(package_name)).text)
    if type(cache) != list or cache[0] != 4:
        print('Unknown format of cache.json file.', file=sys.stderr)
        sys.exit(1)

    versions = cache[2][package_name]
    versions = sorted(filter(version_policy, versions), key=version_to_list)

    if len(versions) == 0:
        print('No versions matched.', file=sys.stderr)
        sys.exit(1)

    print(versions[-1])

import argparse
import json
import requests
import sys

def version_to_list(version):
    return list(map(int, version.split('.')))

def odd_unstable(version_str, selected):
    version = version_to_list(version_str)
    if len(version) < 2:
        return True

    even = version[1] % 2 == 0
    prerelease = (version[1] >= 90 and version[1] < 100) or (version[1] >= 900 and version[1] < 1000)
    stable = even and not prerelease
    if selected == 'stable':
        return stable
    else:
        return True

def no_policy(version, selected):
    return True

version_policies = {
    'odd-unstable': odd_unstable,
    'none': no_policy,
}

def make_version_policy(version_predicate, selected):
    return lambda version: version_predicate(version, selected)

parser = argparse.ArgumentParser(description='Find latest version for a GNOME package by crawling their release server.')
parser.add_argument('package-name', help='Name of the directory in https://ftp.gnome.org/pub/GNOME/sources/ containing the package.')
parser.add_argument('version-policy', help='Policy determining which versions are considered stable. For most GNOME packages, odd minor versions are unstable but there are exceptions.', choices=version_policies.keys(), nargs='?', default='odd-unstable')
parser.add_argument('requested-release', help='Most of the time, we will want to update to stable version but sometimes it is useful to test.', choices=['stable', 'unstable'], nargs='?', default='stable')


if __name__ == '__main__':
    args = parser.parse_args()

    package_name = getattr(args, 'package-name')
    requested_release = getattr(args, 'requested-release')
    version_predicate = version_policies[getattr(args, 'version-policy')]
    version_policy = make_version_policy(version_predicate, requested_release)

    # The structure of cache.json: https://gitlab.gnome.org/Infrastructure/sysadmin-bin/blob/master/ftpadmin#L762
    cache = json.loads(requests.get('https://ftp.gnome.org/pub/GNOME/sources/{}/cache.json'.format(package_name)).text)
    if type(cache) != list or cache[0] != 4:
        print('Unknown format of cache.json file.', file=sys.stderr)
        sys.exit(1)

    versions = cache[2][package_name]
    versions = sorted(filter(version_policy, versions), key=version_to_list)

    if len(versions) == 0:
        print('No versions matched.', file=sys.stderr)
        sys.exit(1)

    print(versions[-1])

improve pre-release detection