import net from 'node:net';
import { createInterface } from 'node:readline';
export function supervisorChannel(): { deadline: (ms: number) => void; reap: () => Promise<void> } | undefined {
  const fd = process.env.AGENT_SUPERVISOR_FD;
  if (!fd || !/^\d+$/.test(fd)) return undefined;
  const socket = new net.Socket({ fd: Number(fd), readable: true, writable: true });
  const lines = createInterface({ input: socket });
  let awaiting: { resolve: () => void; reject: (err: Error) => void } | undefined;
  lines.on('line', line => {
    if (line !== '{"type":"reaped"}' || !awaiting) { socket.destroy(); return; }
    awaiting.resolve(); awaiting = undefined;
  });
  socket.on('error', () => { awaiting?.reject(new Error('Supervisor unavailable')); awaiting = undefined; });
  socket.on('close', () => { awaiting?.reject(new Error('Supervisor unavailable')); awaiting = undefined; });
  return {
    deadline: ms => { socket.write(JSON.stringify({ type: 'set_deadline', remaining_ms: ms }) + '\n'); },
    reap: () => new Promise<void>((resolve, reject) => {
      awaiting = { resolve, reject };
      socket.write('{"type":"reap_descendants"}\n');
    }),
  };
}