use std::io;
use std::os::unix::process::CommandExt;
use std::process::{Command, Stdio};

/// Spawn a child process fully detached from this process group.
///
/// The child gets its own session via `setsid(2)` and null stdio, so it
/// survives the parent exiting and doesn't take a SIGKILL cascade when
/// pixelpass dies.
///
/// A detached reaper thread `wait()`s the child so it doesn't linger as a
/// `<defunct>` zombie under a long-lived parent — the `--gui` front-end launches
/// players itself and lives for the whole session, and `std::process::Child`
/// (unlike tokio's) has no orphan reaping, so simply dropping the handle would
/// leak a zombie per closed player. If the parent exits while the player is
/// still up, the reaper thread dies with it but the `setsid`'d player survives
/// and is reaped by init. (A double-fork would also avoid the zombie, but
/// `fork(2)` followed by non-trivial work in this multithreaded process is
/// unsound — the reaper thread is the safe equivalent.)
pub fn spawn_detached(prog: &str, args: &[&str]) -> io::Result<()> {
    let child = unsafe {
        Command::new(prog)
            .args(args)
            .stdin(Stdio::null())
            .stdout(Stdio::null())
            .stderr(Stdio::null())
            .pre_exec(|| {
                nix::unistd::setsid().ok();
                Ok(())
            })
            .spawn()?
    };
    std::thread::spawn(move || {
        let mut child = child;
        let _ = child.wait();
    });
    Ok(())
}