import argparse
import math
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, upper_bound):
    if not upper_bound:
        upper_bound = [math.inf, math.inf]
    else:
        upper_bound = version_to_list(upper_bound)

    return lambda version: version_predicate(version, selected) and version_to_list(version) < upper_bound


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")
parser.add_argument("--upper-bound", dest="upper-bound", help="Only look for versions older than this one (useful for pinning dependencies).")


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

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

    # The structure of cache.json: https://gitlab.gnome.org/Infrastructure/sysadmin-bin/blob/master/ftpadmin#L762
    cache = json.loads(requests.get(f"https://ftp.gnome.org/pub/GNOME/sources/{package_name}/cache.json").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])