#!/usr/bin/env python3
"""Minimal NFQUEUE example: randomly drop packets by percentage."""

import random
import signal
import sys

from netfilterqueue import NetfilterQueue

DEFAULT_LOSS_PERCENT = 10.0

nfq = NetfilterQueue()
loss_percent = DEFAULT_LOSS_PERCENT


def _handle_packet(packet) -> None:
    if random.random() < (loss_percent / 100.0):
        packet.drop()
        return

    packet.accept()


def _stop(_sig, _frame) -> None:
    raise SystemExit(0)


def main() -> int:
    global loss_percent

    if len(sys.argv) not in (2, 3):
        print("Usage: packet_loss.py <qnum> [loss_percent]", file=sys.stderr)
        return 1

    try:
        qnum = int(sys.argv[1])
    except ValueError:
        print("qnum must be an integer", file=sys.stderr)
        return 1

    if len(sys.argv) == 3:
        try:
            loss_percent = float(sys.argv[2])
        except ValueError:
            print("loss_percent must be a number between 0 and 100", file=sys.stderr)
            return 1

    if not 0.0 <= loss_percent <= 100.0:
        print("loss_percent must be between 0 and 100", file=sys.stderr)
        return 1

    signal.signal(signal.SIGINT, _stop)
    signal.signal(signal.SIGTERM, _stop)

    nfq.bind(qnum, _handle_packet)
    try:
        nfq.run()
    except KeyboardInterrupt:
        pass
    finally:
        nfq.unbind()

    return 0


if __name__ == "__main__":
    raise SystemExit(main())