#!/usr/bin/env python3
"""Run one command in its own session and process group, with a timeout.

usage: run_group.py TIMEOUT_S LOGFILE CWD -- CMD [ARGS...]

Child stdout and stderr go to LOGFILE. On timeout the whole process group gets
SIGTERM, then SIGKILL after 5 s. After the child exits, anything still left in
its group is killed too, so nothing from one step outlives it.
Exit status: the child's, or 124 on timeout.
"""
import os
import signal
import subprocess
import sys


def group_kill(pgid, sig):
    try:
        os.killpg(pgid, sig)
    except ProcessLookupError:
        pass


def main():
    timeout = float(sys.argv[1])
    log = sys.argv[2]
    cwd = sys.argv[3]
    cmd = sys.argv[sys.argv.index('--') + 1:]
    with open(log, 'w') as out:
        p = subprocess.Popen(
            cmd,
            cwd=cwd,
            stdout=out,
            stderr=subprocess.STDOUT,
            stdin=subprocess.DEVNULL,
            start_new_session=True,
        )
        try:
            rc = p.wait(timeout=timeout)
        except subprocess.TimeoutExpired:
            group_kill(p.pid, signal.SIGTERM)
            try:
                p.wait(timeout=5)
            except subprocess.TimeoutExpired:
                pass
            group_kill(p.pid, signal.SIGKILL)
            p.wait()
            out.write(f"\nTIMEOUT after {timeout:.0f}s: process group {p.pid} killed\n")
            rc = 124
        group_kill(p.pid, signal.SIGKILL)
    sys.exit(rc)


if __name__ == '__main__':
    main()