Moltbot/src/slack/streaming.ts

/**
 * Slack native text streaming helpers.
 *
 * Uses the Slack SDK's `ChatStreamer` (via `client.chatStream()`) to stream
 * text responses word-by-word in a single updating message, matching Slack's
 * "Agents & AI Apps" streaming UX.
 *
 * @see https://docs.slack.dev/ai/developing-ai-apps#streaming
 * @see https://docs.slack.dev/reference/methods/chat.startStream
 * @see https://docs.slack.dev/reference/methods/chat.appendStream
 * @see https://docs.slack.dev/reference/methods/chat.stopStream
 */

import type { ChatStreamer, WebClient } from "@slack/web-api";
import { logVerbose } from "../globals.js";

// ---------------------------------------------------------------------------
// Types
// ---------------------------------------------------------------------------

export type SlackStreamSession = {
  /** The SDK ChatStreamer instance managing this stream. */
  streamer: ChatStreamer;
  /** Channel this stream lives in. */
  channel: string;
  /** Thread timestamp (required for streaming). */
  threadTs: string;
  /** True once stop() has been called. */
  stopped: boolean;
};

export type StartSlackStreamParams = {
  client: WebClient;
  channel: string;
  threadTs: string;
  /** Optional initial markdown text to include in the stream start. */
  text?: string;
};

export type AppendSlackStreamParams = {
  session: SlackStreamSession;
  text: string;
};

export type StopSlackStreamParams = {
  session: SlackStreamSession;
  /** Optional final markdown text to append before stopping. */
  text?: string;
};

// ---------------------------------------------------------------------------
// Stream lifecycle
// ---------------------------------------------------------------------------

/**
 * Start a new Slack text stream.
 *
 * Returns a {@link SlackStreamSession} that should be passed to
 * {@link appendSlackStream} and {@link stopSlackStream}.
 *
 * The first chunk of text can optionally be included via `text`.
 */
export async function startSlackStream(
  params: StartSlackStreamParams,
): Promise<SlackStreamSession> {
  const { client, channel, threadTs, text } = params;

  logVerbose(`slack-stream: starting stream in ${channel} thread=${threadTs}`);

  const streamer = client.chatStream({
    channel,
    thread_ts: threadTs,
  });

  const session: SlackStreamSession = {
    streamer,
    channel,
    threadTs,
    stopped: false,
  };

  // If initial text is provided, send it as the first append which will
  // trigger the ChatStreamer to call chat.startStream under the hood.
  if (text) {
    await streamer.append({ markdown_text: text });
    logVerbose(`slack-stream: appended initial text (${text.length} chars)`);
  }

  return session;
}

/**
 * Append markdown text to an active Slack stream.
 */
export async function appendSlackStream(params: AppendSlackStreamParams): Promise<void> {
  const { session, text } = params;

  if (session.stopped) {
    logVerbose("slack-stream: attempted to append to a stopped stream, ignoring");
    return;
  }

  if (!text) {
    return;
  }

  await session.streamer.append({ markdown_text: text });
  logVerbose(`slack-stream: appended ${text.length} chars`);
}

/**
 * Stop (finalize) a Slack stream.
 *
 * After calling this the stream message becomes a normal Slack message.
 * Optionally include final text to append before stopping.
 */
export async function stopSlackStream(params: StopSlackStreamParams): Promise<void> {
  const { session, text } = params;

  if (session.stopped) {
    logVerbose("slack-stream: stream already stopped, ignoring duplicate stop");
    return;
  }

  session.stopped = true;

  logVerbose(
    `slack-stream: stopping stream in ${session.channel} thread=${session.threadTs}${
      text ? ` (final text: ${text.length} chars)` : ""
    }`,
  );

  await session.streamer.stop(text ? { markdown_text: text } : undefined);

  logVerbose("slack-stream: stream stopped");
}