#!/usr/bin/env python3
"""Resolve this host's public IP so the viewer can hide operator traffic.

Loopback/private addresses are ignored. Use `--loop --interval 1800` to run it as a
30-minute refresher; the viewer imports discover() directly and refreshes itself.
"""
import argparse
import ipaddress
import time
import urllib.request

ENDPOINTS = ('https://api.ipify.org', 'https://ifconfig.me/ip',
             'https://icanhazip.com', 'https://1.1.1.1/cdn-cgi/trace')


def discover(timeout=6):
    for url in ENDPOINTS:
        try:
            with urllib.request.urlopen(url, timeout=timeout) as response:
                text = response.read(256).decode('utf-8', 'replace')
        except (OSError, ValueError):
            continue
        for token in text.replace('ip=', ' ').split():
            try:
                ip = ipaddress.ip_address(token.strip())
            except ValueError:
                continue
            if ip.is_global:
                return str(ip)
    return None


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--loop', action='store_true', help='keep refreshing')
    parser.add_argument('--interval', type=int, default=1800)
    args = parser.parse_args()
    while True:
        print(discover() or '', flush=True)
        if not args.loop:
            break
        time.sleep(args.interval)