// What /proc says about one process. Same-UID process identity: a pid plus
// its start time names one process, so a recycled pid never matches.

import { readFileSync } from "node:fs";

// `/proc/<pid>/stat` field 22, the start time in clock ticks. Null when the
// process is gone or has exited and waits to be reaped (state Z).
export function startTimeOf(pid) {
  try {
    const raw = readFileSync(`/proc/${pid}/stat`, "utf8");
    const fields = raw.slice(raw.lastIndexOf(")") + 2).split(" ");
    return fields[0] === "Z" ? null : fields[19];
  } catch {
    return null;
  }
}

export function cmdlineOf(pid) {
  try {
    return readFileSync(`/proc/${pid}/cmdline`, "utf8").split("\0").filter(Boolean);
  } catch {
    return null;
  }
}

// The pids of pid's direct children, or [] when it has none or is gone.
export function childrenOf(pid) {
  try {
    return readFileSync(`/proc/${pid}/task/${pid}/children`, "utf8").trim().split(/\s+/).filter(Boolean).map(Number);
  } catch {
    return [];
  }
}