element-call/src/lotus/lotusAudioInject.ts

/*
Copyright 2026 Lotus Guild

SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
Please see LICENSE in the repository root for full details.
*/

import { type Room as LivekitRoom, Track } from "livekit-client";
import { logger } from "matrix-js-sdk/lib/logger";
import { type IWidgetApiRequest } from "matrix-widget-api";

import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
import { widget } from "../widget";
import { LotusWidgetActions } from "./lotusActions";
import { lotusFlag } from "./lotusWidget";

/** Hard cap so a malformed/huge clip can't hold a published track open forever. */
const MAX_CLIP_MS = 30_000;

/**
 * Handle the host's `io.lotus.inject_audio` toWidget action (#3): mix a
 * soundboard clip into the call so other participants hear it.
 *
 * Rather than splice into the local mic track (which would fight the denoise
 * pipeline), we publish the clip as a separate `Unknown`-source LiveKit audio
 * track — which `MatrixAudioRenderer` already renders for valid call members —
 * and unpublish it when the clip ends. This is the real call-audio injection
 * that was impossible against the prebuilt EC bundle (LiveKit's
 * LocalParticipant lived in EC's module scope).
 *
 * Action data: `{ url: string, volume?: number }`. `url` must be an https/blob
 * URL (the host resolves mxc → media URL).
 *
 * No effect unless the host sends the action. Returns a teardown function that
 * also aborts any clip still playing.
 */
export function startLotusAudioInject(vm: CallViewModel): () => void {
  const w = widget;
  if (!w) return () => undefined;

  // Track the set of connected LiveKit rooms to publish into.
  let rooms: LivekitRoom[] = [];
  const sub = vm.livekitRoomItems$.subscribe((items) => {
    rooms = items.map((i) => i.livekitRoom);
  });

  // In-flight clips, so we can abort them on teardown (unmount / vm change /
  // call leave) instead of leaving audio blasting to peers.
  const activeClips = new Set<() => void>();

  const handler = (ev: CustomEvent<IWidgetApiRequest>): void => {
    // Always ack so the transport doesn't hang, but only act when the host has
    // explicitly opted in: audio-inject publishes under the local user's
    // identity, so it must not be silently armed for every call.
    void w.api.transport.reply(ev.detail, {});
    if (!lotusFlag("lotusAudioInject")) return;
    const data = ev.detail.data as
      | { url?: unknown; volume?: unknown }
      | undefined;
    const url = typeof data?.url === "string" ? safeMediaUrl(data.url) : null;
    if (!url) {
      logger.warn("[lotus] inject_audio: missing/invalid url");
      return;
    }
    const volume =
      typeof data?.volume === "number" && data.volume >= 0 && data.volume <= 1
        ? data.volume
        : 1;
    void playInjectedClip(url, volume, rooms, activeClips).catch((e) =>
      logger.warn("[lotus] inject_audio failed", e),
    );
  };

  w.lazyActions.on(LotusWidgetActions.InjectAudio, handler);
  return () => {
    sub.unsubscribe();
    w.lazyActions.off(LotusWidgetActions.InjectAudio, handler);
    // Abort anything still playing.
    for (const abort of [...activeClips]) abort();
  };
}

/** Only allow fetchable media URLs; never same-origin credentialed GETs etc. */
function safeMediaUrl(raw: string): string | null {
  try {
    const u = new URL(raw, window.location.href);
    return u.protocol === "https:" || u.protocol === "blob:" ? u.href : null;
  } catch {
    return null;
  }
}

async function playInjectedClip(
  url: string,
  volume: number,
  rooms: LivekitRoom[],
  activeClips: Set<() => void>,
): Promise<void> {
  if (rooms.length === 0) {
    logger.warn("[lotus] inject_audio: no connected rooms");
    return;
  }

  // Max ONE clip at a time (replace mode): stop any in-flight clip before
  // starting a new one, so clips can't overlap or be spammed. Runs
  // synchronously before the first await, and each cleanup() is idempotent and
  // removes itself from activeClips (so no track leak). The host also debounces
  // the button; together they cover the brief fetch window.
  for (const abort of [...activeClips]) abort();

  const resp = await fetch(url, { credentials: "omit", mode: "cors" });
  if (!resp.ok) throw new Error(`fetch ${url} -> ${resp.status}`);
  const arrayBuffer = await resp.arrayBuffer();

  const ctx = new AudioContext();
  // The action arrives via host postMessage, not a gesture in this iframe, so
  // the context may start suspended — resume it or the clip is silent and
  // `onended` never fires.
  try {
    await ctx.resume();
  } catch {
    /* best effort */
  }
  if (ctx.state !== "running")
    logger.warn(`[lotus] inject_audio: AudioContext is ${ctx.state}`);

  let buffer: AudioBuffer;
  try {
    buffer = await ctx.decodeAudioData(arrayBuffer);
  } catch (e) {
    void ctx.close();
    throw e;
  }

  const dest = ctx.createMediaStreamDestination();
  const gain = ctx.createGain();
  gain.gain.value = volume;
  const source = ctx.createBufferSource();
  source.buffer = buffer;
  source.connect(gain).connect(dest);

  const mst = dest.stream.getAudioTracks()[0];
  if (!mst) {
    void ctx.close();
    throw new Error("no audio track from destination");
  }

  // Publish (a clone of) the clip track to every connected room.
  const publications = await Promise.all(
    rooms.map(async (room) => {
      const clone = mst.clone();
      try {
        const pub = await room.localParticipant.publishTrack(clone, {
          source: Track.Source.Unknown,
          name: "lotus-soundboard",
          dtx: false,
          red: false,
        });
        return { room, pub };
      } catch (e) {
        clone.stop(); // don't leak the clone if publish failed
        logger.warn("[lotus] inject_audio: publish failed", e);
        return null;
      }
    }),
  );

  let cleanedUp = false;
  const cleanup = (): void => {
    if (cleanedUp) return;
    cleanedUp = true;
    activeClips.delete(cleanup);
    try {
      source.stop();
    } catch {
      /* already stopped */
    }
    for (const entry of publications) {
      if (entry?.pub.track)
        void entry.room.localParticipant
          .unpublishTrack(entry.pub.track, true)
          .catch(() => undefined);
    }
    void ctx.close().catch(() => undefined);
  };
  activeClips.add(cleanup);

  source.onended = cleanup;
  // Safety net: clip metadata can lie (NaN/huge duration), so force teardown
  // after a sane, capped delay.
  const durationMs = Number.isFinite(buffer.duration)
    ? buffer.duration * 1000 + 500
    : MAX_CLIP_MS;
  const guard = setTimeout(cleanup, Math.min(MAX_CLIP_MS, Math.max(0, durationMs)));
  source.addEventListener("ended", () => clearTimeout(guard));

  source.start();
}