Dirigent/plugin/moderator-presence.ts

/**
 * Minimal Discord Gateway connection to keep the moderator bot "online".
 * Uses Node.js built-in WebSocket (Node 22+).
 *
 * IMPORTANT: Only ONE instance should exist per bot token.
 * Uses a singleton guard to prevent multiple connections.
 */

let ws: WebSocket | null = null;
let heartbeatInterval: ReturnType<typeof setInterval> | null = null;
let heartbeatAcked = true;
let lastSequence: number | null = null;
let sessionId: string | null = null;
let resumeUrl: string | null = null;
let reconnectTimer: ReturnType<typeof setTimeout> | null = null;
let destroyed = false;
let started = false; // singleton guard

type Logger = {
  info: (msg: string) => void;
  warn: (msg: string) => void;
};

const GATEWAY_URL = "wss://gateway.discord.gg/?v=10&encoding=json";
const MAX_RECONNECT_DELAY_MS = 60_000;
let reconnectAttempts = 0;

function sendPayload(data: Record<string, unknown>) {
  if (ws?.readyState === WebSocket.OPEN) {
    ws.send(JSON.stringify(data));
  }
}

function startHeartbeat(intervalMs: number) {
  stopHeartbeat();
  heartbeatAcked = true;

  // First heartbeat after jitter
  const jitter = Math.floor(Math.random() * intervalMs);
  const firstTimer = setTimeout(() => {
    if (destroyed) return;
    if (!heartbeatAcked) {
      // Missed ACK — zombie connection, close and reconnect
      ws?.close(4000, "missed heartbeat ack");
      return;
    }
    heartbeatAcked = false;
    sendPayload({ op: 1, d: lastSequence });

    heartbeatInterval = setInterval(() => {
      if (destroyed) return;
      if (!heartbeatAcked) {
        ws?.close(4000, "missed heartbeat ack");
        return;
      }
      heartbeatAcked = false;
      sendPayload({ op: 1, d: lastSequence });
    }, intervalMs);
  }, jitter);

  // Store the first timer so we can clear it
  heartbeatInterval = firstTimer as unknown as ReturnType<typeof setInterval>;
}

function stopHeartbeat() {
  if (heartbeatInterval) {
    clearInterval(heartbeatInterval);
    clearTimeout(heartbeatInterval as unknown as ReturnType<typeof setTimeout>);
    heartbeatInterval = null;
  }
}

function cleanup() {
  stopHeartbeat();
  if (ws) {
    // Remove all handlers to avoid ghost callbacks
    ws.onopen = null;
    ws.onmessage = null;
    ws.onclose = null;
    ws.onerror = null;
    try { ws.close(1000); } catch { /* ignore */ }
    ws = null;
  }
}

function connect(token: string, logger: Logger, isResume = false) {
  if (destroyed) return;

  // Clean up any existing connection first
  cleanup();

  const url = isResume && resumeUrl ? resumeUrl : GATEWAY_URL;

  try {
    ws = new WebSocket(url);
  } catch (err) {
    logger.warn(`dirigent: moderator ws constructor failed: ${String(err)}`);
    scheduleReconnect(token, logger, false);
    return;
  }

  const currentWs = ws; // capture for closure

  ws.onopen = () => {
    if (currentWs !== ws || destroyed) return; // stale

    reconnectAttempts = 0; // reset on successful open

    if (isResume && sessionId) {
      sendPayload({
        op: 6,
        d: { token, session_id: sessionId, seq: lastSequence },
      });
    } else {
      sendPayload({
        op: 2,
        d: {
          token,
          intents: 0,
          properties: {
            os: "linux",
            browser: "dirigent",
            device: "dirigent",
          },
          presence: {
            status: "online",
            activities: [{ name: "Moderating", type: 3 }],
          },
        },
      });
    }
  };

  ws.onmessage = (evt: MessageEvent) => {
    if (currentWs !== ws || destroyed) return;

    try {
      const msg = JSON.parse(typeof evt.data === "string" ? evt.data : String(evt.data));
      const { op, t, s, d } = msg;

      if (s != null) lastSequence = s;

      switch (op) {
        case 10: // Hello
          startHeartbeat(d.heartbeat_interval);
          break;
        case 11: // Heartbeat ACK
          heartbeatAcked = true;
          break;
        case 1: // Heartbeat request
          sendPayload({ op: 1, d: lastSequence });
          break;
        case 0: // Dispatch
          if (t === "READY") {
            sessionId = d.session_id;
            resumeUrl = d.resume_gateway_url;
            logger.info("dirigent: moderator bot connected and online");
          }
          if (t === "RESUMED") {
            logger.info("dirigent: moderator bot resumed");
          }
          break;
        case 7: // Reconnect request
          logger.info("dirigent: moderator bot reconnect requested by Discord");
          cleanup();
          scheduleReconnect(token, logger, true);
          break;
        case 9: // Invalid Session
          logger.warn(`dirigent: moderator bot invalid session, resumable=${d}`);
          cleanup();
          sessionId = d ? sessionId : null;
          // Wait longer before re-identifying
          setTimeout(() => {
            if (!destroyed) connect(token, logger, !!d && !!sessionId);
          }, 3000 + Math.random() * 2000);
          break;
      }
    } catch {
      // ignore parse errors
    }
  };

  ws.onclose = (evt: CloseEvent) => {
    if (currentWs !== ws) return; // stale ws
    stopHeartbeat();
    if (destroyed) return;

    const code = evt.code;

    // Non-recoverable codes — stop reconnecting
    if (code === 4004) {
      logger.warn("dirigent: moderator bot token invalid (4004), stopping");
      started = false;
      return;
    }
    if (code === 4010 || code === 4011 || code === 4013 || code === 4014) {
      logger.warn(`dirigent: moderator bot fatal close (${code}), re-identifying`);
      sessionId = null;
      scheduleReconnect(token, logger, false);
      return;
    }

    logger.info(`dirigent: moderator bot disconnected (code=${code}), will reconnect`);
    const canResume = !!sessionId && code !== 4012;
    scheduleReconnect(token, logger, canResume);
  };

  ws.onerror = () => {
    // onclose will fire after this
  };
}

function scheduleReconnect(token: string, logger: Logger, resume: boolean) {
  if (destroyed) return;
  if (reconnectTimer) clearTimeout(reconnectTimer);

  // Exponential backoff with cap
  reconnectAttempts++;
  const baseDelay = Math.min(1000 * Math.pow(2, reconnectAttempts), MAX_RECONNECT_DELAY_MS);
  const jitter = Math.random() * 1000;
  const delay = baseDelay + jitter;

  logger.info(`dirigent: moderator reconnect in ${Math.round(delay)}ms (attempt ${reconnectAttempts})`);

  reconnectTimer = setTimeout(() => {
    reconnectTimer = null;
    connect(token, logger, resume);
  }, delay);
}

/**
 * Start the moderator bot's Discord Gateway connection.
 * Singleton: calling multiple times with the same token is safe (no-op).
 */
export function startModeratorPresence(token: string, logger: Logger): void {
  if (started) {
    logger.info("dirigent: moderator presence already started, skipping");
    return;
  }
  started = true;
  destroyed = false;
  reconnectAttempts = 0;
  connect(token, logger);
}

/**
 * Disconnect the moderator bot.
 */
export function stopModeratorPresence(): void {
  destroyed = true;
  started = false;
  if (reconnectTimer) {
    clearTimeout(reconnectTimer);
    reconnectTimer = null;
  }
  cleanup();
}