// timeline.js — SCENEGOD master clock, tracks, keyframe evaluation (Lane B).
// Talks to Stage ONLY through the PLAN §4.2 API. NO DOM, NO three.js import,
// so it runs headless under `node` for timeline_test.mjs. All the vector /
// quaternion math it needs is inlined below (a few lines each).

// ---- tiny math (self-contained; euler XYZ radians) --------------------------
const lerp = (a, b, u) => a + (b - a) * u;
const lerpArr = (a, b, u) => a.map((v, i) => lerp(v, b[i], u));

function eulerToQuat([x, y, z]) {                     // XYZ order, matches three
  const c1 = Math.cos(x / 2), s1 = Math.sin(x / 2);
  const c2 = Math.cos(y / 2), s2 = Math.sin(y / 2);
  const c3 = Math.cos(z / 2), s3 = Math.sin(z / 2);
  return [
    s1 * c2 * c3 + c1 * s2 * s3,
    c1 * s2 * c3 - s1 * c2 * s3,
    c1 * c2 * s3 + s1 * s2 * c3,
    c1 * c2 * c3 - s1 * s2 * s3,
  ];
}
function quatToEuler([x, y, z, w]) {                  // XYZ order
  const m11 = 1 - 2 * (y * y + z * z), m12 = 2 * (x * y - z * w), m13 = 2 * (x * z + y * w);
  const m22 = 1 - 2 * (x * x + z * z), m23 = 2 * (y * z - x * w);
  const m33 = 1 - 2 * (x * x + y * y);
  const ey = Math.asin(Math.max(-1, Math.min(1, m13)));
  let ex, ez;
  if (Math.abs(m13) < 0.9999999) { ex = Math.atan2(-m23, m33); ez = Math.atan2(-m12, m11); }
  else { ex = Math.atan2(m22 !== undefined ? 2 * (y * z + x * w) : 0, m22); ez = 0; }
  return [ex, ey, ez];
}
function slerp(a, b, u) {                              // quaternion slerp, sign-safe
  let [ax, ay, az, aw] = a, [bx, by, bz, bw] = b;
  let cos = ax * bx + ay * by + az * bz + aw * bw;
  if (cos < 0) { bx = -bx; by = -by; bz = -bz; bw = -bw; cos = -cos; }
  if (cos > 0.9995) {                                 // nearly parallel → nlerp
    const q = [lerp(ax, bx, u), lerp(ay, by, u), lerp(az, bz, u), lerp(aw, bw, u)];
    const n = Math.hypot(...q) || 1;
    return q.map((v) => v / n);
  }
  const t = Math.acos(cos), s = Math.sin(t);
  const wa = Math.sin((1 - u) * t) / s, wb = Math.sin(u * t) / s;
  return [ax * wa + bx * wb, ay * wa + by * wb, az * wa + bz * wb, aw * wa + bw * wb];
}

function ease(u, kind) {
  switch (kind) {
    case 'step': return 0;                            // hold start value across segment
    case 'in': return u * u * u;
    case 'out': return 1 - Math.pow(1 - u, 3);
    case 'inout': return u < 0.5 ? 4 * u * u * u : 1 - Math.pow(-2 * u + 2, 3) / 2;
    case 'linear': default: return u;
  }
}

// color helpers for param track (sRGB lerp is fine for v1 per B2)
const isColor = (v) => typeof v === 'string' && v[0] === '#';
function hexToRgb(h) { const n = parseInt(h.slice(1), 16); return [(n >> 16) & 255, (n >> 8) & 255, n & 255]; }
function rgbToHex([r, g, b]) { return '#' + [r, g, b].map((c) => Math.round(Math.max(0, Math.min(255, c))).toString(16).padStart(2, '0')).join(''); }

// find bracketing keys in a t-sorted array. ponytail: linear scan — key arrays
// are tiny (handfuls); swap for binary search only if a lane ever profiles hot.
function bracket(keys, t) {
  if (keys.length === 0) return null;
  if (t <= keys[0].t) return [keys[0], keys[0], 0];
  const last = keys[keys.length - 1];
  if (t >= last.t) return [last, last, 0];
  for (let i = 0; i < keys.length - 1; i++) {
    if (t >= keys[i].t && t < keys[i + 1].t) {
      const span = keys[i + 1].t - keys[i].t;
      return [keys[i], keys[i + 1], span > 0 ? (t - keys[i].t) / span : 0];
    }
  }
  return [last, last, 0];
}

// ---- Timeline ---------------------------------------------------------------
export class Timeline {
  constructor(stage) {
    this.stage = stage;
    this.scene = { version: 1, name: 'untitled', fps: 30, duration: 10, entities: [], cameraCuts: [], audio: [] };
    this.time = 0;
    this.playing = false;
    this._tickCbs = [];
    this._loadCbs = [];
    this._raf = null;
    this._last = 0;
    this._qcache = new WeakMap();       // key obj -> cached quat (keeps keys pure for round-trip)
    this._clipActions = new Map();      // block obj -> {action, clip}
    this._activeCam = undefined;        // last camera pushed (avoid re-spamming setActiveCamera)
    this.undoStack = [];

    if (typeof window !== 'undefined') {
      window.addEventListener('scenegod:capturekey', (e) => {
        const id = e.detail && e.detail.id;
        if (id) this.addKey(id, 'transform', { t: this.time, ...this.stage.entityTransform(id), ease: 'inout' });
      });
      // Lane A dock drops a clip on a character → add a block at the playhead.
      window.addEventListener('scenegod:clipdrop', (e) => {
        if (e.detail && e.detail.id) this.addClipDrop(e.detail);
      });
      // M5 DIRECTOR MODE: Lane A presets dispatch ops → normal keys/cuts at
      // the playhead (contract: lanes/A §M5.3 / PLAN §5 M5).
      window.addEventListener('scenegod:direct', (e) => {
        if (e.detail && e.detail.op) this.applyDirect(e.detail);
      });
    }
    // SYNC2 seam: mirror live stage adds/removes into scene.entities so
    // dock-added entities can be keyframed without a scene load.
    if (stage && stage.onChange) stage.onChange((en) => this._mirror(en));
  }

  _mirror(en) {
    if (!en || !en.id) return;
    const list = this.scene.entities;
    const i = list.findIndex((x) => x.id === en.id);
    if (!this.stage.getEntity(en.id)) {         // gone from stage → drop entity + its tracks
      if (i >= 0) list.splice(i, 1);
      return;
    }
    if (i >= 0) return;                          // known — timeline already owns its tracks
    list.push({
      id: en.id, kind: en.kind, label: en.label,
      source: en.source ? structuredClone(en.source) : { type: 'upload' },
      params: en.params ? structuredClone(en.params) : {},
      transform: this.stage.entityTransform(en.id),
      tracks: { transform: [], params: [], clips: [] },
    });
  }

  get fps() { return this.scene.fps; }
  get duration() { return this.scene.duration; }
  get entities() { return this.scene.entities; }
  get cameraCuts() { return this.scene.cameraCuts; }

  // ---- load / save (lossless round-trip) ----
  load(sceneJson) {
    this.scene = structuredClone(sceneJson);
    if (this.scene.fps == null) this.scene.fps = 30;
    if (this.scene.duration == null) this.scene.duration = 10;
    this.scene.entities = this.scene.entities || [];
    this.scene.cameraCuts = this.scene.cameraCuts || [];
    this.scene.audio = this.scene.audio || [];
    for (const e of this.scene.entities) this._sortTracks(e);
    this.scene.cameraCuts.sort((a, b) => a.t - b.t);
    this._clipActions.clear();
    this._activeCam = undefined;
    this.seek(0);
    for (const cb of this._loadCbs) cb(this.scene);   // UI: rebuild rows + refresh scene bar (SYNC1 #3)
    return this;
  }
  onLoad(cb) { this._loadCbs.push(cb); }
  toJSON() { return structuredClone(this.scene); }

  // Programmatic duration change (dur field or code). Keys past the new end are
  // kept (lossless) but unreachable; clamp the playhead and refresh the UI —
  // plain `scene.duration = x` skips both. Reuses the onLoad hook to redraw +
  // resync the scene bar.
  setDuration(x) {
    this.scene.duration = Math.max(0.1, +x || 0.1);
    if (this.time > this.scene.duration) this.time = this.scene.duration;
    for (const cb of this._loadCbs) cb(this.scene);
    this.seek(this.time);
    return this.scene.duration;
  }

  // Lane A clip-drop: fetch the clip (for its duration), drop a block at the
  // playhead, add a default crossfade where it abuts a neighbour, preload.
  async addClipDrop({ id, path, clipIndex = 0 }) {
    const clip = await this.stage.prepareClip(id, path, clipIndex);
    const dur = (clip && clip.duration) || 1;
    this.addClipBlock(id, { path, clipIndex, start: this.time, in: 0, out: dur, loop: 1, fade: 0 });
    this._setAbutFades(id);
    await this.preload();
    this.seek(this.time);                              // re-evaluate + redraw
  }
  _setAbutFades(id) {                                  // 0.25s fade on any block that abuts its successor
    const blocks = (this._tracks(id).clips) || [];
    for (let i = 0; i < blocks.length - 1; i++) {
      const b = blocks[i], n = blocks[i + 1];
      const end = b.start + ((b.out - b.in) || 0) * (b.loop || 1);
      if (Math.abs(end - n.start) < 1e-3 && !b.fade) b.fade = 0.25;
    }
  }

  _sortTracks(e) {
    const tr = e.tracks;
    if (!tr) return;
    if (tr.transform) tr.transform.sort((a, b) => a.t - b.t);
    if (tr.params) tr.params.sort((a, b) => a.t - b.t);
    if (tr.morphs) tr.morphs.sort((a, b) => a.t - b.t);
    if (tr.clips) tr.clips.sort((a, b) => a.start - b.start);
  }
  _quat(key) {
    let q = this._qcache.get(key);
    if (!q) { q = eulerToQuat(key.rot || [0, 0, 0]); this._qcache.set(key, q); }
    return q;
  }

  // ---- clock ----
  onTick(cb) { this._tickCbs.push(cb); }
  play() {
    if (this.playing || typeof requestAnimationFrame === 'undefined') return;
    this.playing = true;
    this._last = performance.now();
    const loop = (now) => {
      if (!this.playing) return;
      const dt = (now - this._last) / 1000;
      this._last = now;
      let t = this.time + dt;
      if (t >= this.duration) { t = this.duration; this.playing = false; }
      this.seek(t);
      if (this.playing) this._raf = requestAnimationFrame(loop);
    };
    this._raf = requestAnimationFrame(loop);
  }
  pause() {
    this.playing = false;
    if (this._raf) cancelAnimationFrame(this._raf);
    this._raf = null;
    if (this.stage.entityVideo) this.evaluate(this.time);   // M6: videos pause with the clock
  }
  seek(t) {
    this.time = Math.max(0, Math.min(this.duration, t));
    this.evaluate(this.time);
    for (const cb of this._tickCbs) cb(this.time);
  }
  step(frame) { this.time = Math.max(0, Math.min(this.duration, frame / this.fps)); this.evaluate(this.time); return this.time; }

  // ---- clip preload (async fetch/retarget once; evaluate stays sync) ----
  async preload() {
    for (const e of this.entities) {
      const clips = e.tracks && e.tracks.clips;
      if (!clips) continue;
      const mixer = this.stage.entityMixer(e.id);
      for (const b of clips) {
        if (this._clipActions.has(b)) continue;
        const clip = await this.stage.prepareClip(e.id, b.path, b.clipIndex || 0);
        const action = mixer.clipAction(clip);
        action.play(); action.paused = true; action.enabled = false; action.weight = 0;
        this._clipActions.set(b, { action, clip });
      }
    }
  }

  // ---- evaluation ----
  evaluate(t) {
    for (const e of this.entities) {
      if (e.kind === 'camera' || e.tracks) this._evalTransform(e, t);
      this._evalParams(e, t);
      if (e.tracks && e.tracks.morphs) this._evalMorphs(e, t);
      if (e.tracks && e.tracks.clips) this._evalClips(e, t);
      if ((e.kind === 'backdrop' || e.kind === 'screen') && this.stage.entityVideo) this._evalVideo(e, t);
    }
    this._evalCameraCuts(t);
  }

  // M6 FLOW VIDEO PLATES: video backdrops/screens follow the master clock.
  // Cheap scrub-follow — seek only when drift >50ms; play/pause with the
  // clock. NEVER awaits (step() stays sync — the deterministic render path
  // awaits stage.syncVideos(t) per frame instead, Lane A/C's seam).
  _evalVideo(e, t) {
    const v = this.stage.entityVideo(e.id);
    if (!v) return;                                   // nullable: image backdrop / not loaded
    const dur = v.duration;
    if (Number.isFinite(dur) && dur > 0) {
      const want = Math.max(0, t - ((e.params && e.params.videoStart) || 0)) % dur;
      if (Math.abs(v.currentTime - want) > 0.05) v.currentTime = want;
    }
    if (this.playing && v.paused) { const p = v.play(); if (p && p.catch) p.catch(() => {}); }
    else if (!this.playing && !v.paused) v.pause();
  }

  _evalMorphs(e, t) {   // viseme/blendshape weights → stage.setMorph (M4-B)
    const keys = e.tracks && e.tracks.morphs;
    if (!keys || !keys.length || !this.stage.setMorph) return;
    const byKey = new Map();
    for (const k of keys) { if (!byKey.has(k.key)) byKey.set(k.key, []); byKey.get(k.key).push(k); }
    for (const [name, ks] of byKey) {
      const [k0, k1, u] = bracket(ks, t);
      const w = k0 === k1 ? k0.value : lerp(k0.value, k1.value, ease(u, k0.ease));
      this.stage.setMorph(e.id, name, w);
    }
  }

  _evalTransform(e, t) {
    const keys = e.tracks && e.tracks.transform;
    if (!keys || keys.length === 0) return;           // 0 keys → leave rest pose alone
    const br = bracket(keys, t);
    const [k0, k1, u] = br;
    if (k0 === k1) { this.stage.setTransform(e.id, { pos: k0.pos, rot: k0.rot, scale: k0.scale }); return; }
    const eu = ease(u, k0.ease);
    const pos = lerpArr(k0.pos, k1.pos, eu);
    const scale = typeof k0.scale === 'number'
      ? lerp(k0.scale, k1.scale, eu)
      : lerpArr(k0.scale, k1.scale, eu);
    const rot = k0.ease === 'step' ? k0.rot.slice() : quatToEuler(slerp(this._quat(k0), this._quat(k1), eu));
    this.stage.setTransform(e.id, { pos, rot, scale });
  }

  _evalParams(e, t) {
    const keys = e.tracks && e.tracks.params;
    if (!keys || keys.length === 0) return;
    const byKey = new Map();
    for (const k of keys) { if (!byKey.has(k.key)) byKey.set(k.key, []); byKey.get(k.key).push(k); }
    for (const [name, ks] of byKey) {
      const br = bracket(ks, t);
      const [k0, k1, u] = br;
      let val;
      if (k0 === k1) val = k0.value;
      else {
        const eu = ease(u, k0.ease);
        val = isColor(k0.value)
          ? rgbToHex(lerpArr(hexToRgb(k0.value), hexToRgb(k1.value), eu))
          : lerp(k0.value, k1.value, eu);
      }
      this.stage.setParam(e.id, name, val);
    }
  }

  _evalClips(e, t) {
    const blocks = e.tracks.clips;
    if (!blocks || !blocks.length) return;
    const mixer = this.stage.entityMixer(e.id);
    if (!mixer) return;   // SYNC1: real Stage returns null for non-characters (stub always had one)
    for (let i = 0; i < blocks.length; i++) {
      const b = blocks[i];
      const rec = this._clipActions.get(b);
      if (!rec) continue;                             // not preloaded yet → silent
      const span = (b.out - b.in) || 0.0001;
      const blockEnd = b.start + span * (b.loop || 1);
      // pre-roll: a predecessor's fade pulls THIS block's playback start earlier
      // by pred.fade so it advances during the crossfade (continuous local time).
      const pred = blocks[i - 1];
      const preroll = (pred && pred.fade > 0) ? pred.fade : 0;
      const inStart = b.start - preroll;
      let w = 0, local = b.in;
      if (t >= inStart && t < blockEnd) {
        local = b.in + ((t - inStart) % span);        // continuous across the boundary
        w = 1;
        if (t < b.start) w = (t - inStart) / preroll;  // fade-IN 0→1 over the pred's fade window
        const succ = blocks[i + 1];                    // fade-OUT 1→0 over own fade window
        if (succ && b.fade > 0 && t >= blockEnd - b.fade) w = Math.min(w, (blockEnd - t) / b.fade);
      }
      rec.action.time = local;
      rec.action.weight = Math.max(0, w);
      rec.action.enabled = w > 0;
    }
    mixer.update(0);                                  // set-time style — exact when scrubbing
  }

  _evalCameraCuts(t) {
    const cuts = this.cameraCuts;
    let cam = null;
    for (const c of cuts) { if (c.t <= t) cam = c.camera; else break; }
    if (cam !== this._activeCam) { this._activeCam = cam; this.stage.setActiveCamera(cam); }
  }

  // ---- keyframe / block mutators (keep sorted, push inverse for undo) ----
  _tracks(id) {
    const e = this.scene.entities.find((x) => x.id === id);
    if (!e) throw new Error(`no entity ${id}`);
    e.tracks = e.tracks || {};
    return e.tracks;
  }
  addKey(id, track, key) {
    const tr = this._tracks(id);
    const arr = (tr[track] = tr[track] || []);
    // a key replaces any existing at the same t; named tracks (params/morphs)
    // are keyed by (t, key name) since many names share the lane.
    const named = track === 'params' || track === 'morphs';
    const same = (k) => k.t === key.t && (!named || k.key === key.key);
    const prevIdx = arr.findIndex(same);
    const prev = prevIdx >= 0 ? arr[prevIdx] : null;
    if (prevIdx >= 0) arr.splice(prevIdx, 1);
    arr.push(key);
    arr.sort((a, b) => a.t - b.t);
    this._qcache.delete(key);
    this.undoStack.push({ undo: () => { const i = arr.indexOf(key); if (i >= 0) arr.splice(i, 1); if (prev) { arr.push(prev); arr.sort((a, b) => a.t - b.t); } } });
    return key;
  }
  moveKey(id, track, key, newT) {
    const oldT = key.t; key.t = newT;
    this._tracks(id)[track].sort((a, b) => a.t - b.t);
    this.undoStack.push({ undo: () => { key.t = oldT; this._tracks(id)[track].sort((a, b) => a.t - b.t); } });
  }
  deleteKey(id, track, key) {
    const arr = this._tracks(id)[track] || [];
    const i = arr.indexOf(key);
    if (i < 0) return;
    arr.splice(i, 1);
    this.undoStack.push({ undo: () => { arr.push(key); arr.sort((a, b) => a.t - b.t); } });
  }
  addClipBlock(id, block) {
    const tr = this._tracks(id);
    const arr = (tr.clips = tr.clips || []);
    arr.push(block); arr.sort((a, b) => a.start - b.start);
    this._clipActions.delete(block);
    this.undoStack.push({ undo: () => { const i = arr.indexOf(block); if (i >= 0) arr.splice(i, 1); } });
    return block;
  }
  moveClipBlock(id, block, newStart) {
    const old = block.start; block.start = newStart;
    this._tracks(id).clips.sort((a, b) => a.start - b.start);
    this.undoStack.push({ undo: () => { block.start = old; this._tracks(id).clips.sort((a, b) => a.start - b.start); } });
  }
  trimClipBlock(id, block, { in: inV, out: outV } = {}) {
    const oldIn = block.in, oldOut = block.out;
    if (inV != null) block.in = inV;
    if (outV != null) block.out = outV;
    this.undoStack.push({ undo: () => { block.in = oldIn; block.out = oldOut; } });
  }
  addCut(t, cameraId) {
    const cut = { t, camera: cameraId };
    this.scene.cameraCuts.push(cut);
    this.scene.cameraCuts.sort((a, b) => a.t - b.t);
    this._activeCam = undefined;                      // force re-eval of active cam
    this.undoStack.push({ undo: () => { const i = this.scene.cameraCuts.indexOf(cut); if (i >= 0) this.scene.cameraCuts.splice(i, 1); } });
    return cut;
  }
  undo() { const op = this.undoStack.pop(); if (op) op.undo(); this.evaluate(this.time); }

  // Run fn (which may push many undo entries) and collapse everything it
  // pushed into ONE undo entry — a multi-key preset op reverts in one Ctrl+Z.
  group(fn) {
    const n = this.undoStack.length;
    const r = fn();
    if (this.undoStack.length > n + 1) {
      const ops = this.undoStack.splice(n);
      this.undoStack.push({ undo: () => { for (let i = ops.length - 1; i >= 0; i--) ops[i].undo(); } });
    }
    return r;
  }

  // ---- M5 DIRECTOR MODE: scenegod:direct ops → keys/cuts at the playhead.
  // Accepts BOTH Lane A's live presets.js payloads (values spread at top level:
  //   shot  {camId, pos, rot, fov, …, entityIds:[camId, subjectId]}
  //   light {sun:{color,intensity}, ambient:{…}, bg, sunId, ambientId}
  //   mark  {id, pos?, rot?, entityIds:[id]} )
  // and the PLAN §5 contract shapes ({transform:{pos,rot}}, {params:{k:v}},
  // walkTo). One op = ONE undo entry (group()).
  applyDirect(d) {
    const t = this.time;
    const key = (id, k) => this.addKey(id, 'params', { t, key: k[0], value: k[1], ease: 'inout' });
    this.group(() => {
      if (d.op === 'shot') {
        const camId = d.camId ?? (d.entityIds && d.entityIds[0]);
        const cur = this.stage.entityTransform(camId);
        const tr = d.transform || d;                  // Lane A spreads pos/rot at top level
        this.addKey(camId, 'transform', {
          t, pos: tr.pos || cur.pos, rot: tr.rot || cur.rot,
          scale: tr.scale ?? cur.scale ?? 1, ease: 'inout',
        });
        if (d.fov != null) key(camId, ['fov', d.fov]);
        this.addCut(t, camId);
      } else if (d.op === 'light') {
        if (d.sunId != null && d.sun) {               // Lane A applyLight shape
          key(d.sunId, ['color', d.sun.color]);
          key(d.sunId, ['intensity', d.sun.intensity]);
          // sun boom pos/aim moved per preset — capture it so presets scrub
          this.addKey(d.sunId, 'transform', { t, ...this.stage.entityTransform(d.sunId), ease: 'inout' });
          if (d.ambientId != null && d.ambient) {
            key(d.ambientId, ['color', d.ambient.color]);
            key(d.ambientId, ['intensity', d.ambient.intensity]);
            if (d.bg != null) key(d.ambientId, ['bg', d.bg]);
          }
        } else {                                      // generic: entityId(s) + params map
          const ids = d.entityIds || (d.entityId != null ? [d.entityId] : []);
          for (const id of ids) for (const kv of Object.entries(d.params || {})) key(id, kv);
        }
      } else if (d.op === 'mark') {
        const ids = d.entityIds || (d.entityId != null ? [d.entityId] : (d.id != null ? [d.id] : []));
        for (const id of ids) {
          const cur = this.stage.entityTransform(id);
          const tr = d.transform || d;                // Lane A spreads pos/rot at top level
          const target = { pos: tr.pos || cur.pos, rot: tr.rot || cur.rot, scale: tr.scale ?? cur.scale ?? 1 };
          if (d.walkTo) {                             // walk: from prevPos (or current) → mark over 2s
            const from = d.prevPos ? { ...cur, pos: d.prevPos } : cur;
            this.addKey(id, 'transform', { t, ...from, ease: 'inout' });
            this.addKey(id, 'transform', { t: t + 2, ...target, ease: 'inout' });
          } else {
            this.addKey(id, 'transform', { t, ...target, ease: 'inout' });
          }
        }
      }
    });
    this.seek(t);                                     // re-evaluate: cut/keys take effect now
  }

  // ---- audio track (M4-B). Clips are {path, start, gain}; duration is a
  // client-side draw concern (decode + cache in tlui). Server muxes from
  // scene.audio at render, so step()/evaluate never touch audio. ----
  addAudio(clip) {
    this.scene.audio = this.scene.audio || [];
    this.scene.audio.push(clip);
    this.undoStack.push({ undo: () => { const i = this.scene.audio.indexOf(clip); if (i >= 0) this.scene.audio.splice(i, 1); } });
    return clip;
  }
  moveAudio(clip, newStart) {
    const old = clip.start; clip.start = Math.max(0, newStart);
    this.undoStack.push({ undo: () => { clip.start = old; } });
  }
  setAudioGain(clip, gain) {
    const old = clip.gain; clip.gain = gain;
    this.undoStack.push({ undo: () => { clip.gain = old; } });
  }
  removeAudio(clip) {
    const i = (this.scene.audio || []).indexOf(clip);
    if (i < 0) return;
    this.scene.audio.splice(i, 1);
    this.undoStack.push({ undo: () => { this.scene.audio.splice(i, 0, clip); } });
  }
  // Trim within the source file, like clip blocks: {in, out} seconds. Absent =
  // untrimmed (schema stays {path,start,gain} for untouched clips). Server-side
  // mux honoring in/out is a Lane C REQUEST (logged); draft Web Audio playback
  // honors it client-side already.
  trimAudio(clip, { in: inV, out: outV } = {}) {
    const oldIn = clip.in, oldOut = clip.out;
    if (inV != null) clip.in = Math.max(0, inV);
    if (outV != null) clip.out = Math.max((clip.in || 0) + 0.05, outV);
    this.undoStack.push({ undo: () => {
      if (oldIn === undefined) delete clip.in; else clip.in = oldIn;
      if (oldOut === undefined) delete clip.out; else clip.out = oldOut;
    } });
  }

  // Rhubarb lip-sync JSON → morph keys. { mouthCues: [{start, end, value}] }.
  // ponytail: per-cue ramp (shape 1 at cue start → 0 at cue end); hold/crossfade
  // tuning deferred until it looks wrong on a real blendshape character.
  importRhubarb(id, rhubarbJson, t0 = 0) {
    const cues = (rhubarbJson && rhubarbJson.mouthCues) || [];
    this.group(() => {                                // one undo reverts the whole import
      for (const c of cues) {
        if (!c.value) continue;
        this.addKey(id, 'morphs', { t: t0 + c.start, key: c.value, value: 1, ease: 'linear' });
        this.addKey(id, 'morphs', { t: t0 + c.end, key: c.value, value: 0, ease: 'linear' });
      }
    });
    return (this._tracks(id).morphs || []).length;
  }
}

export default Timeline;