#!/usr/bin/env python3
import argparse
import os


def main():
    ap = argparse.ArgumentParser()
    ap.add_argument("-a", default="qmail-authuser", dest="pam")
    ap.add_argument("fd", type=int)
    ap.add_argument("prog")
    ap.add_argument("args", nargs="*")

    vals = ap.parse_args()

    if vals.fd < 3:
        raise ValueError(f"fd({vals.fd}) must be 3 or greater")

    if vals.fd != 3:
        os.dup2(vals.fd, 3)
        os.close(vals.fd)

    os.execvp(vals.pam, [vals.pam, vals.prog] + vals.args)

    raise ValueError("should not be reachable")


if __name__ == "__main__":
    main()