// Handshake-free /24 port probe for desktop pairing (Change 5).
//
// Unlike `probeSubnetForPeer` (chirp-sync-transport.ts), this does NOT run
// Noise — during code pairing we have no long-term pubkey, and the pairing
// server on port 49142 speaks the plaintext PEACH_HELLO protocol, not Noise
// XX. This probe answers only "is a WebSocket server reachable here?"; the
// 6-digit code + user-confirmed SAS are the actual trust boundary.

const DEFAULT_PROBE_TIMEOUT_MS = 500;
const DEFAULT_PROBE_BATCH = 16;

export interface PortProbeOptions {
  batch?: number;
  timeoutMs?: number;
  /** Injection seam for tests — defaults to the real WebSocket open check. */
  probeOne?: (ip: string, port: number, timeoutMs: number) => Promise<boolean>;
}

/**
 * Scan `subnet` (e.g. "192.168.1") for the first host accepting a WebSocket
 * connection on `port`. Returns the IP string, or null if none answered.
 */
export async function probeSubnetForPort(
  subnet: string,
  port: number,
  options: PortProbeOptions = {},
): Promise<string | null> {
  const batchSize = options.batch ?? DEFAULT_PROBE_BATCH;
  const timeoutMs = options.timeoutMs ?? DEFAULT_PROBE_TIMEOUT_MS;
  const probe = options.probeOne ?? wsPortOpen;

  for (let start = 1; start <= 254; start += batchSize) {
    const end = Math.min(start + batchSize - 1, 254);
    const ips: string[] = [];
    for (let i = start; i <= end; i++) ips.push(`${subnet}.${i}`);

    const results = await Promise.all(
      ips.map(async (ip) => ((await probe(ip, port, timeoutMs)) ? ip : null)),
    );
    const hit = results.find((r): r is string => r !== null);
    if (hit) return hit;
  }
  return null;
}

/** True if a WebSocket to ws://ip:port/ reaches onopen within timeoutMs. */
export function wsPortOpen(ip: string, port: number, timeoutMs: number): Promise<boolean> {
  return new Promise((resolve) => {
    let ws: WebSocket;
    let settled = false;
    const done = (ok: boolean) => {
      if (settled) return;
      settled = true;
      try { ws.close(); } catch { /* ignore */ }
      resolve(ok);
    };
    try {
      ws = new WebSocket(`ws://${ip}:${port}/`);
    } catch {
      resolve(false);
      return;
    }
    const t = setTimeout(() => done(false), timeoutMs);
    ws.onopen = () => { clearTimeout(t); done(true); };
    ws.onerror = () => { clearTimeout(t); done(false); };
    ws.onclose = () => { clearTimeout(t); done(false); };
  });
}