#!/usr/bin/env python3
import re,sys

def parse(value):
    if not re.fullmatch(r'(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)',value):
        raise ValueError('Expected stable MAJOR.MINOR.PATCH version')
    numbers=tuple(map(int,value.split('.')))
    if any(n>2**64-1 for n in numbers):raise ValueError('Version number is too large')
    return numbers

if __name__=='__main__':
    try:
        if sys.argv[1]=='greater':
            sys.exit(0 if parse(sys.argv[2])>parse(sys.argv[3]) else 1)
        if sys.argv[1]=='latest':
            versions=[]
            for line in sys.stdin:
                fields=line.split()
                if len(fields)!=2 or not fields[1].startswith('refs/tags/v'):continue
                value=fields[1].removeprefix('refs/tags/v').removesuffix('^{}')
                try:versions.append((parse(value),value))
                except ValueError:pass
            if not versions:raise ValueError('No stable release tags found')
            print(max(versions)[1])
        else:raise ValueError('Unknown version command')
    except (ValueError,IndexError) as error:
        print(str(error),file=sys.stderr);sys.exit(2)