// panel-grid.js — reusable N-panel animated-scatter grid.
//
// Single public export: mountPanels({ host, controls, stems }) mounts one
// three.js panel per stem inside `host`, and wires the shared control strip
// in `controls` to drive all of them (play/scrub, speed, motion, axes, color,
// linked hover). Works identically for 1, 2, or N stems.

import * as THREE from 'three';

// ---- viridis (8-stop, RGB lerp) -----------------------------------------

const VIRIDIS_HEX = [
  '#440154', '#482878', '#3E4989', '#31688E',
  '#26828E', '#1F9E89', '#6DCD59', '#FDE725',
];

const VIRIDIS_RGB = VIRIDIS_HEX.map(h => [
  parseInt(h.slice(1, 3), 16),
  parseInt(h.slice(3, 5), 16),
  parseInt(h.slice(5, 7), 16),
]);

function lerpStops(t) {
  const n = VIRIDIS_RGB.length;
  if (t <= 0) return VIRIDIS_RGB[0];
  if (t >= 1) return VIRIDIS_RGB[n - 1];
  const x = t * (n - 1);
  const i = Math.floor(x);
  const f = x - i;
  const a = VIRIDIS_RGB[i];
  const b = VIRIDIS_RGB[i + 1];
  return [
    Math.round(a[0] + (b[0] - a[0]) * f),
    Math.round(a[1] + (b[1] - a[1]) * f),
    Math.round(a[2] + (b[2] - a[2]) * f),
  ];
}

function rgbToHex([r, g, b]) {
  const h = (v) => v.toString(16).padStart(2, '0');
  return `#${h(r)}${h(g)}${h(b)}`;
}

function viridisColor(i, total) {
  if (total >= 9) return VIRIDIS_HEX[i % VIRIDIS_HEX.length];
  if (total <= 1) return rgbToHex(lerpStops(0.5));
  return rgbToHex(lerpStops(i / (total - 1)));
}

// ---- tiny helpers -------------------------------------------------------

function makeDiskTexture(size = 64) {
  const c = document.createElement('canvas');
  c.width = c.height = size;
  const g = c.getContext('2d');
  const r = size / 2;
  const grd = g.createRadialGradient(r, r, 0, r, r, r);
  grd.addColorStop(0.0, 'rgba(255,255,255,1)');
  grd.addColorStop(0.55, 'rgba(255,255,255,1)');
  grd.addColorStop(0.85, 'rgba(255,255,255,0.35)');
  grd.addColorStop(1.0, 'rgba(255,255,255,0)');
  g.fillStyle = grd;
  g.fillRect(0, 0, size, size);
  const tex = new THREE.CanvasTexture(c);
  tex.needsUpdate = true;
  return tex;
}

function rampContinuous(t, out) {
  const hue = (1 - t) * 215 + t * 28;
  const sat = 0.62;
  const lit = 0.50 + (t - 0.5) * 0.08;
  return (out || new THREE.Color()).setHSL(hue / 360, sat, lit);
}

const CATEGORICAL_HEX = [
  '#1f4e5f', '#c97b3f', '#8b5a9f', '#5a8560',
  '#c74a5e', '#6b7d8f', '#b89f51', '#4a6fa5',
];
const CATEGORICAL = CATEGORICAL_HEX.map(h => new THREE.Color(h));

function buildIdColorsRGB(data) {
  const n = data.point_ids.length;
  const rgb = new Float32Array(n * 3);
  const labels = data.labels || [];
  const kind = data.label_kind || null;
  const hasRealLabels = kind && labels.some(v => v != null && v !== '');

  if (hasRealLabels) {
    const tmp = new THREE.Color();
    if (kind === 'categorical') {
      for (let i = 0; i < n; i++) {
        const v = labels[i];
        if (v == null) continue;
        const c = CATEGORICAL[((v | 0) % CATEGORICAL.length + CATEGORICAL.length) % CATEGORICAL.length];
        rgb[i * 3 + 0] = c.r;
        rgb[i * 3 + 1] = c.g;
        rgb[i * 3 + 2] = c.b;
      }
    } else {
      let lo = Infinity, hi = -Infinity;
      for (const v of labels) { if (v == null) continue; if (v < lo) lo = v; if (v > hi) hi = v; }
      const range = (hi - lo) || 1;
      for (let i = 0; i < n; i++) {
        const v = labels[i];
        if (v == null) continue;
        rampContinuous((v - lo) / range, tmp);
        rgb[i * 3 + 0] = tmp.r;
        rgb[i * 3 + 1] = tmp.g;
        rgb[i * 3 + 2] = tmp.b;
      }
    }
    return rgb;
  }

  const frame0 = data.frames[0];
  if (!frame0) return rgb;
  const originalPositions = [];
  for (let i = 0; i < n; i++) {
    if (frame0.x[i] != null && frame0.y[i] != null
        && !Number.isNaN(frame0.x[i]) && !Number.isNaN(frame0.y[i])) {
      originalPositions.push(i);
    }
  }
  originalPositions.sort((a, b) => data.point_ids[a] - data.point_ids[b]);
  const nOrig = originalPositions.length;
  const tmp = new THREE.Color();
  for (let k = 0; k < nOrig; k++) {
    const t = nOrig > 1 ? k / (nOrig - 1) : 0.5;
    rampContinuous(t, tmp);
    const idx = originalPositions[k];
    rgb[idx * 3 + 0] = tmp.r;
    rgb[idx * 3 + 1] = tmp.g;
    rgb[idx * 3 + 2] = tmp.b;
  }
  return rgb;
}

function readVar(name, fallback) {
  const v = getComputedStyle(document.documentElement).getPropertyValue(name).trim();
  return v || fallback;
}

function readPanelBg(el) {
  const v = getComputedStyle(el).getPropertyValue('--picker-panel').trim();
  return v || readVar('--panel', '#ffffff');
}

function readPanelColor(el, fallback) {
  const v = getComputedStyle(el).getPropertyValue('--panel-color').trim();
  return v || fallback;
}

function highlightColor() {
  return readVar('--alarm', '#8a3a2a');
}

const PARAM_FIELDS = [
  { key: 'num_points',    prefix: 'N' },
  { key: 'num_timesteps', prefix: 'T' },
  { key: 'jitter_scale',  prefix: 'J' },
  { key: 'seed',          prefix: 's' },
];

function renderHeader(panelEl, data) {
  const m = data.meta || {};
  panelEl.querySelector('[data-role="embedder"]').textContent = m.embedder || '—';
  panelEl.querySelector('[data-role="generator"]').textContent = m.generator || '—';
  const host = panelEl.querySelector('[data-role="params"]');
  host.textContent = '';
  PARAM_FIELDS.forEach(({ key, prefix }, i) => {
    if (i > 0) host.appendChild(document.createTextNode(' / '));
    const span = document.createElement('span');
    span.className = 'param';
    span.dataset.key = key;
    span.textContent = `${prefix}${m[key] ?? '?'}`;
    host.appendChild(span);
  });
  const stemLink = panelEl.querySelector('[data-role="stem-link"]');
  if (stemLink && panelEl.dataset.stem) {
    stemLink.href = `/api/runs/${encodeURIComponent(panelEl.dataset.stem)}/frames.json`;
  }
}

function renderError(panelEl, stem, msg) {
  const statusEl = panelEl.querySelector('[data-role="status"]');
  statusEl.style.display = '';
  statusEl.classList.add('is-error');
  statusEl.textContent = `could not load ${stem}: ${msg}`;
  panelEl.querySelector('[data-role="embedder"]').textContent = '—';
  panelEl.querySelector('[data-role="generator"]').textContent = '—';
  panelEl.querySelector('[data-role="params"]').textContent = '(error)';
}

function markParamDiffs(panels) {
  if (panels.length < 2) return;
  const metas = panels.map(p => p.data.meta || {});
  for (const { key } of PARAM_FIELDS) {
    const vals = metas.map(m => m[key]);
    const differs = vals.some(v => v !== vals[0]);
    for (const p of panels) {
      const span = p.panelEl.querySelector(`[data-role="params"] .param[data-key="${key}"]`);
      if (span) span.classList.toggle('diff', differs);
    }
  }
  for (const role of ['embedder', 'generator']) {
    const vals = metas.map(m => m[role]);
    const differs = vals.some(v => v !== vals[0]);
    for (const p of panels) {
      const span = p.panelEl.querySelector(`[data-role="${role}"]`);
      if (span) span.classList.toggle('diff', differs);
    }
  }
}

// ---- Panel factory ------------------------------------------------------

const DISK_TEX = makeDiskTexture();

function createPanel({ panelEl, data }) {
  const canvasEl = panelEl.querySelector('[data-role="canvas"]');
  const statusEl = panelEl.querySelector('[data-role="status"]');

  const scene = new THREE.Scene();
  scene.background = new THREE.Color(readPanelBg(panelEl));

  const camera = new THREE.OrthographicCamera(-1, 1, 1, -1, -10, 10);
  const renderer = new THREE.WebGLRenderer({ antialias: true, alpha: false });
  renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
  canvasEl.appendChild(renderer.domElement);

  const maxN = data.point_ids.length;
  const positions = new Float32Array(maxN * 3);
  const colors = new Float32Array(maxN * 3);
  const idColorRGB = buildIdColorsRGB(data);

  const geo = new THREE.BufferGeometry();
  geo.setAttribute('position', new THREE.BufferAttribute(positions, 3));
  geo.setAttribute('color', new THREE.BufferAttribute(colors, 3));
  geo.setDrawRange(0, 0);

  const matMono = new THREE.PointsMaterial({
    size: 6.0,
    sizeAttenuation: false,
    map: DISK_TEX,
    transparent: true,
    alphaTest: 0.2,
    depthWrite: false,
    color: new THREE.Color(readPanelColor(panelEl, '#26828E')),
  });
  const matRainbow = new THREE.PointsMaterial({
    size: 6.0,
    sizeAttenuation: false,
    map: DISK_TEX,
    transparent: false,
    alphaTest: 0.5,
    vertexColors: true,
  });
  let mat = matMono;
  const points = new THREE.Points(geo, mat);
  scene.add(points);

  const hiPos = new Float32Array(3);
  const hiGeo = new THREE.BufferGeometry();
  hiGeo.setAttribute('position', new THREE.BufferAttribute(hiPos, 3));
  hiGeo.setDrawRange(0, 0);
  const hiMat = new THREE.PointsMaterial({
    size: 14.0,
    sizeAttenuation: false,
    map: DISK_TEX,
    transparent: true,
    alphaTest: 0.05,
    depthWrite: false,
    color: new THREE.Color(highlightColor()),
    opacity: 0.9,
  });
  const hiPoints = new THREE.Points(hiGeo, hiMat);
  hiPoints.renderOrder = 1;
  scene.add(hiPoints);

  let packedN = 0;
  const packedX = new Float32Array(maxN);
  const packedY = new Float32Array(maxN);
  const packedId = new Int32Array(maxN);

  const camRect = { xmin: -1, xmax: 1, ymin: -1, ymax: 1 };

  function applyCamRect(rect) {
    const pad = 0.05;
    const dx = rect.xmax - rect.xmin || 1;
    const dy = rect.ymax - rect.ymin || 1;
    const cx = (rect.xmin + rect.xmax) / 2;
    const cy = (rect.ymin + rect.ymax) / 2;
    const rx = dx * (0.5 + pad);
    const ry = dy * (0.5 + pad);
    const rect2 = canvasEl.getBoundingClientRect();
    const vw = Math.max(1, rect2.width);
    const vh = Math.max(1, rect2.height);
    const aspect = vw / vh;
    const dataAspect = (rx * 2) / (ry * 2);
    let halfW, halfH;
    if (aspect > dataAspect) {
      halfH = ry;
      halfW = ry * aspect;
    } else {
      halfW = rx;
      halfH = rx / aspect;
    }
    camera.left = cx - halfW;
    camera.right = cx + halfW;
    camera.top = cy + halfH;
    camera.bottom = cy - halfH;
    camera.updateProjectionMatrix();
    camRect.xmin = rect.xmin;
    camRect.xmax = rect.xmax;
    camRect.ymin = rect.ymin;
    camRect.ymax = rect.ymax;
  }

  function resize() {
    const rect = canvasEl.getBoundingClientRect();
    const w = Math.max(1, Math.floor(rect.width));
    const h = Math.max(1, Math.floor(rect.height));
    renderer.setSize(w, h, false);
    applyCamRect(camRect);
  }

  function setBounds(b) {
    applyCamRect({ xmin: b.x[0], xmax: b.x[1], ymin: b.y[0], ymax: b.y[1] });
  }

  function applyColorsFromTheme() {
    matMono.color.set(readPanelColor(panelEl, '#26828E'));
    hiMat.color.set(highlightColor());
    scene.background = new THREE.Color(readPanelBg(panelEl));
  }

  function setColorMode(mode) {
    const next = mode === 'mono' ? matMono : matRainbow;
    if (points.material !== next) {
      points.material = next;
      mat = next;
    }
  }

  function writePackedColor(j, i) {
    colors[j * 3 + 0] = idColorRGB[i * 3 + 0];
    colors[j * 3 + 1] = idColorRGB[i * 3 + 1];
    colors[j * 3 + 2] = idColorRGB[i * 3 + 2];
  }

  function setFrame(f) {
    const frame = data.frames[f];
    if (!frame) return;
    const xs = frame.x, ys = frame.y;
    const ptIds = data.point_ids;
    let j = 0;
    for (let i = 0; i < xs.length; i++) {
      const x = xs[i], y = ys[i];
      if (x === null || y === null || x === undefined || y === undefined
          || Number.isNaN(x) || Number.isNaN(y)) continue;
      positions[j * 3 + 0] = x;
      positions[j * 3 + 1] = y;
      positions[j * 3 + 2] = 0;
      writePackedColor(j, i);
      packedX[j] = x;
      packedY[j] = y;
      packedId[j] = ptIds[i];
      j++;
    }
    packedN = j;
    geo.attributes.position.needsUpdate = true;
    geo.attributes.color.needsUpdate = true;
    geo.setDrawRange(0, packedN);
    applyHighlightForCurrentFrame();
  }

  function setFrameInterpolated(uLocal) {
    const T = data.frames.length;
    if (T === 0) return;
    if (uLocal <= 0)        return setFrame(0);
    if (uLocal >= T - 1)    return setFrame(T - 1);
    const f0 = Math.floor(uLocal);
    const f1 = f0 + 1;
    const t  = uLocal - f0;
    const fr0 = data.frames[f0], fr1 = data.frames[f1];
    const x0 = fr0.x, y0 = fr0.y, x1 = fr1.x, y1 = fr1.y;
    const ptIds = data.point_ids;
    let j = 0;
    for (let i = 0; i < x0.length; i++) {
      const a = x0[i], b = x1[i], c = y0[i], d = y1[i];
      if (a === null || a === undefined || Number.isNaN(a)
          || b === null || b === undefined || Number.isNaN(b)
          || c === null || c === undefined || Number.isNaN(c)
          || d === null || d === undefined || Number.isNaN(d)) continue;
      const xi = a + (b - a) * t;
      const yi = c + (d - c) * t;
      positions[j * 3 + 0] = xi;
      positions[j * 3 + 1] = yi;
      positions[j * 3 + 2] = 0;
      writePackedColor(j, i);
      packedX[j] = xi;
      packedY[j] = yi;
      packedId[j] = ptIds[i];
      j++;
    }
    packedN = j;
    geo.attributes.position.needsUpdate = true;
    geo.attributes.color.needsUpdate = true;
    geo.setDrawRange(0, packedN);
    applyHighlightForCurrentFrame();
  }

  let currentHighlightId = -1;

  function applyHighlightForCurrentFrame() {
    if (currentHighlightId < 0) {
      hiGeo.setDrawRange(0, 0);
      return;
    }
    for (let i = 0; i < packedN; i++) {
      if (packedId[i] === currentHighlightId) {
        hiPos[0] = packedX[i];
        hiPos[1] = packedY[i];
        hiPos[2] = 0.01;
        hiGeo.attributes.position.needsUpdate = true;
        hiGeo.setDrawRange(0, 1);
        return;
      }
    }
    hiGeo.setDrawRange(0, 0);
  }

  function setHighlight(pointId) {
    currentHighlightId = (pointId === null || pointId === undefined) ? -1 : pointId;
    applyHighlightForCurrentFrame();
  }

  function clientToWorld(clientX, clientY) {
    const rect = canvasEl.getBoundingClientRect();
    const u = (clientX - rect.left) / Math.max(1, rect.width);
    const v = (clientY - rect.top) / Math.max(1, rect.height);
    const wx = camera.left + u * (camera.right - camera.left);
    const wy = camera.top - v * (camera.top - camera.bottom);
    return { wx, wy };
  }

  function pickAt(clientX, clientY) {
    if (packedN === 0) return -1;
    const { wx, wy } = clientToWorld(clientX, clientY);
    const rect = canvasEl.getBoundingClientRect();
    const worldPerPx = (camera.right - camera.left) / Math.max(1, rect.width);
    const pickPx = 14;
    const maxR = pickPx * worldPerPx;
    const maxR2 = maxR * maxR;
    let bestI = -1;
    let bestD2 = Infinity;
    for (let i = 0; i < packedN; i++) {
      const dx = packedX[i] - wx;
      const dy = packedY[i] - wy;
      const d2 = dx * dx + dy * dy;
      if (d2 < bestD2 && d2 < maxR2) {
        bestD2 = d2;
        bestI = i;
      }
    }
    return bestI < 0 ? -1 : packedId[bestI];
  }

  function render() {
    renderer.render(scene, camera);
  }

  function dispose() {
    geo.dispose();
    hiGeo.dispose();
    matMono.dispose();
    matRainbow.dispose();
    hiMat.dispose();
    renderer.dispose();
    if (renderer.domElement.parentNode) {
      renderer.domElement.parentNode.removeChild(renderer.domElement);
    }
  }

  statusEl.style.display = 'none';

  return {
    canvasEl,
    panelEl,
    data,
    setFrame,
    setFrameInterpolated,
    setColorMode,
    setBounds,
    setHighlight,
    resize,
    render,
    pickAt,
    applyColorsFromTheme,
    dispose,
    applyCamRect,
    get packedN() { return packedN; },
    get camRect() { return camRect; },
  };
}

// ---- frames.json fetch --------------------------------------------------

async function fetchFrames(stem) {
  const res = await fetch(`/api/runs/${encodeURIComponent(stem)}/frames.json`, { cache: 'no-store' });
  if (!res.ok) throw new Error(`${res.status} ${res.statusText}`);
  return res.json();
}

// ---- public API ---------------------------------------------------------

/**
 * Mount one three.js panel per stem into `host`, driven by the control strip
 * at `controls`. Returns `{ destroy }` for teardown (disposes every WebGL
 * context and removes the panel DOM nodes).
 */
export function mountPanels({ host, controls, stems }) {
  const tpl = document.getElementById('compare-panel-tpl');
  if (!tpl) throw new Error('panel-grid: #compare-panel-tpl not found');

  host.innerHTML = '';
  const total = stems.length;

  const slots = stems.map((stem, i) => {
    const frag = tpl.content.cloneNode(true);
    const panelEl = frag.querySelector('.compare-panel');
    const color = viridisColor(i, total);
    panelEl.style.setProperty('--panel-color', color);
    panelEl.dataset.stem = stem;
    host.appendChild(panelEl);
    return { stem, panelEl, color, panel: null };
  });

  // Build the per-panel time segments inside #cc-times.
  const timesHost = controls.querySelector('#cc-times');
  if (timesHost) {
    timesHost.innerHTML = '';
    slots.forEach((s, i) => {
      if (i > 0) {
        const sep = document.createElement('span');
        sep.className = 'cc-time-sep';
        sep.textContent = '/';
        timesHost.appendChild(sep);
      }
      const seg = document.createElement('span');
      seg.className = 'cc-time-seg';
      seg.style.setProperty('--panel-color', s.color);
      seg.textContent = '—';
      timesHost.appendChild(seg);
      s.timeEl = seg;
    });
  }

  const playBtn  = controls.querySelector('#cc-play');
  const scrub    = controls.querySelector('#cc-scrub');
  const speedSel = controls.querySelector('#cc-speed');
  const syncSel  = controls.querySelector('#cc-sync');
  const motionSel= controls.querySelector('#cc-motion');
  const colorSel = controls.querySelector('#cc-color');

  // Reset controls to a clean state (they may be reused across opens).
  if (scrub)   scrub.value = '0';
  if (playBtn) { playBtn.textContent = '▶'; playBtn.setAttribute('aria-label', 'play'); }
  // Axes dropdown is meaningless for a single-panel view (nothing to lock
  // against; aspect is fixed by the modal dialog's own sizing).
  if (syncSel) syncSel.disabled = total < 2;

  // Parallel fetch; each panel's error is independent.
  const ready = Promise.allSettled(stems.map(fetchFrames)).then((results) => {
    results.forEach((res, i) => {
      const slot = slots[i];
      if (res.status === 'fulfilled') {
        renderHeader(slot.panelEl, res.value);
        slot.panel = createPanel({ panelEl: slot.panelEl, data: res.value });
      } else {
        renderError(slot.panelEl, slot.stem, res.reason?.message || String(res.reason));
      }
    });

    const live = slots.filter(s => s.panel);
    markParamDiffs(live.map(s => s.panel));
    if (!live.length) return;

    for (const s of live) {
      s.panel.setBounds(s.panel.data.bounds);
      s.panel.resize();
      s.panel.setFrame(0);
    }

    wireDrivers(live);
  });

  function wireDrivers(live) {
    const SCRUB_MAX = 1000;

    function framesOf(p) { return p ? p.data.frames.length : 0; }
    function maxT() {
      let m = 2;
      for (const s of live) m = Math.max(m, framesOf(s.panel));
      return m;
    }
    function timeLabelFor(p, uLocal) {
      const T = framesOf(p);
      if (T <= 0) return '—';
      const idx = Math.max(0, Math.min(T - 1, Math.round(uLocal)));
      return p.data.times?.[idx] ?? String(idx);
    }

    function applyU(u) {
      u = Math.max(0, Math.min(1, u));
      const smooth = motionSel.value === 'smooth';
      const tMax = maxT();
      const uGlobal = u * (tMax - 1);
      for (const s of live) {
        const p = s.panel;
        const T = framesOf(p);
        if (T <= 0) continue;
        const uLocal = Math.min(uGlobal, T - 1);
        if (smooth) p.setFrameInterpolated(uLocal);
        else {
          const idx = Math.max(0, Math.min(T - 1, Math.round(uLocal)));
          p.setFrame(idx);
        }
        if (s.timeEl) s.timeEl.textContent = timeLabelFor(p, uLocal);
      }
    }

    function parseAxes(value) {
      // Accepted: "scaled-1x1", "scaled-3x2", "locked-1x1", "locked-3x2",
      // plus legacy "independent" / "locked" (assume 1:1).
      const v = value || 'scaled-1x1';
      if (v === 'independent') return { sync: 'scaled', aspect: '1 / 1' };
      if (v === 'locked')      return { sync: 'locked', aspect: '1 / 1' };
      const [sync, ratio] = v.split('-');
      const aspect = ratio === '3x2' ? '3 / 2' : '1 / 1';
      return { sync: sync === 'locked' ? 'locked' : 'scaled', aspect };
    }

    function applyAxes() {
      const { sync, aspect } = parseAxes(syncSel ? syncSel.value : 'scaled-3x2');
      host.style.setProperty('--canvas-aspect', aspect);
      if (sync === 'locked' && live.length > 1) {
        let xmin = +Infinity, xmax = -Infinity, ymin = +Infinity, ymax = -Infinity;
        for (const s of live) {
          const b = s.panel.data.bounds;
          if (b.x[0] < xmin) xmin = b.x[0];
          if (b.x[1] > xmax) xmax = b.x[1];
          if (b.y[0] < ymin) ymin = b.y[0];
          if (b.y[1] > ymax) ymax = b.y[1];
        }
        const union = { x: [xmin, xmax], y: [ymin, ymax] };
        for (const s of live) s.panel.setBounds(union);
      } else {
        for (const s of live) s.panel.setBounds(s.panel.data.bounds);
      }
      // Canvas size changes with aspect — let the panels re-fit next frame.
      requestAnimationFrame(() => { for (const s of live) s.panel.resize(); });
    }
    if (syncSel) onCtl(syncSel, 'change', applyAxes);
    applyAxes();

    let playing = false;
    let lastTs = 0;
    let u = 0;
    function baseMsPerFrame() { return 1600 / parseFloat(speedSel?.value || '1'); }

    function tick(ts) {
      if (stopped) return;
      rafId = requestAnimationFrame(tick);
      for (const s of live) s.panel.render();
      if (!playing) { lastTs = ts; return; }
      if (!lastTs) { lastTs = ts; return; }
      const dt = ts - lastTs;
      lastTs = ts;
      if (dt <= 0) return;
      const perFrame = baseMsPerFrame();
      const T = maxT();
      u += dt / (perFrame * (T - 1));
      if (u >= 1) u -= Math.floor(u);
      if (scrub) scrub.value = String(Math.round(u * SCRUB_MAX));
      applyU(u);
    }
    rafId = requestAnimationFrame(tick);

    function setPlaying(v) {
      playing = v;
      lastTs = 0;
      if (playBtn) {
        playBtn.textContent = playing ? '▮▮' : '▶';
        playBtn.setAttribute('aria-label', playing ? 'pause' : 'play');
      }
    }
    if (playBtn) onCtl(playBtn, 'click', () => setPlaying(!playing));

    if (scrub) onCtl(scrub, 'input', () => {
      u = parseFloat(scrub.value) / SCRUB_MAX;
      applyU(u);
    });

    if (speedSel) onCtl(speedSel, 'change', () => { lastTs = 0; });

    if (motionSel) onCtl(motionSel, 'change', () => {
      applyU(parseFloat(scrub?.value || '0') / SCRUB_MAX);
    });

    function applyColorMode() {
      const mode = colorSel ? colorSel.value : 'original';
      for (const s of live) s.panel.setColorMode(mode);
    }
    if (colorSel) onCtl(colorSel, 'change', applyColorMode);
    applyColorMode();

    // Linked hover + click-to-pin. Hover shows the point under the cursor
    // across all panels. Click toggles a "pinned" id that stays highlighted
    // once the cursor leaves; hover temporarily overrides the display.
    let pinnedId = null;
    let hoveredId = null;
    function paintHighlight() {
      const id = hoveredId !== null ? hoveredId : pinnedId;
      for (const t of live) t.panel.setHighlight(id);
    }
    for (const s of live) {
      const mm = (ev) => {
        const id = s.panel.pickAt(ev.clientX, ev.clientY);
        hoveredId = id >= 0 ? id : null;
        paintHighlight();
      };
      const ml = () => { hoveredId = null; paintHighlight(); };
      const mc = (ev) => {
        const id = s.panel.pickAt(ev.clientX, ev.clientY);
        pinnedId = (id < 0 || id === pinnedId) ? null : id;
        paintHighlight();
      };
      s.panel.canvasEl.addEventListener('mousemove', mm);
      s.panel.canvasEl.addEventListener('mouseleave', ml);
      s.panel.canvasEl.addEventListener('click', mc);
      listeners.push({ el: s.panel.canvasEl, ev: 'mousemove', fn: mm });
      listeners.push({ el: s.panel.canvasEl, ev: 'mouseleave', fn: ml });
      listeners.push({ el: s.panel.canvasEl, ev: 'click', fn: mc });
    }

    // Resize + theme observers.
    ro = new ResizeObserver(() => { for (const s of live) s.panel.resize(); });
    for (const s of live) ro.observe(s.panel.canvasEl);

    themeFn = () => { for (const s of live) s.panel.applyColorsFromTheme(); };
    document.addEventListener('themechange', themeFn);

    applyU(0);
  }

  // ---- teardown bookkeeping ---------------------------------------------
  const listeners = [];
  const ctlListeners = [];
  let rafId = 0;
  let stopped = false;
  let ro = null;
  let themeFn = null;

  function onCtl(el, ev, fn) {
    el.addEventListener(ev, fn);
    ctlListeners.push({ el, ev, fn });
  }

  function destroy() {
    stopped = true;
    if (rafId) cancelAnimationFrame(rafId);
    if (ro) ro.disconnect();
    if (themeFn) document.removeEventListener('themechange', themeFn);
    for (const { el, ev, fn } of listeners) el.removeEventListener(ev, fn);
    for (const { el, ev, fn } of ctlListeners) el.removeEventListener(ev, fn);
    for (const s of slots) {
      if (s.panel) s.panel.dispose();
      if (s.panelEl.parentNode) s.panelEl.parentNode.removeChild(s.panelEl);
    }
    host.innerHTML = '';
    const timesHost2 = controls.querySelector('#cc-times');
    if (timesHost2) timesHost2.innerHTML = '';
  }

  return { destroy, ready };
}