// Application: parameter form, run loop, live and movie views, spectrogram,
// playback, WAV download, and the test hooks on window.steelsim.

import { defaultParams, type Grid, makeGrid, nodeWeights, type PhysParams } from "./params.ts";
import { encodeFeatures, initialShape } from "./shape.ts";
import { Simulation, type SimStatus } from "./sim/simulation.ts";
import { Renderer, type ViewMode } from "./render/renderer.ts";
import { Spectrogram } from "./audio/spectrogram.ts";
import { Player } from "./audio/player.ts";
import { encodeWav } from "./audio/wav.ts";
import { levelGain, peakDbfs, type LevelMode } from "./audio/level.ts";
import { ParamForm } from "./ui/form.ts";
import { runSelfTest, selfTestPassed, type SelfTestCase } from "./selftest.ts";

const $ = <T extends HTMLElement>(id: string) => document.getElementById(id) as T;

// ---------- State ----------

const params: PhysParams = { ...defaultParams };
let form: ParamForm;
let device: GPUDevice | null = null;
let sim: Simulation | null = null;
let renderer: Renderer | null = null;
let running = false;
let paused = false;
let live = true;
let scrubFrame = 0;
let movieBuf: GPUBuffer | null = null;
let movieBufFrame = -1;
/** Show the stress-free initial shape of the current parameters instead of the simulation. */
let previewMode = true;
let preview: { grid: Grid; w0: GPUBuffer; zero: GPUBuffer; nw: GPUBuffer; wmax: number; stale: boolean } | null = null;
const spec = new Spectrogram({ windowSize: 2048, hop: 512, fmax: 5000, dbFloor: 80, logFrequency: false });
const player = new Player();
let lastStatsTime = 0, lastStatsSteps = 0, stepsPerSec = 0;
let duration = params.duration;

// ---------- Controls ----------

const btnStart = mkButton("Start", "primary");
const btnPause = mkButton("Pause");
const btnStop = mkButton("Stop");
const btnContinue = mkButton("Continue");
const btnLink = mkButton("Copy link");
const durInput = document.createElement("input");

function mkButton(text: string, cls = ""): HTMLButtonElement {
  const b = document.createElement("button");
  b.textContent = text;
  b.className = cls;
  return b;
}

function buildControls(): void {
  const c = $("controls");
  const durRow = document.createElement("div");
  durRow.className = "field";
  durRow.style.width = "100%";
  const l = document.createElement("label");
  l.textContent = "Recorded duration";
  durInput.type = "number";
  durInput.step = "0.5";
  durInput.min = "0.1";
  durInput.value = String(duration);
  durInput.addEventListener("change", () => {
    const v = parseFloat(durInput.value);
    if (isFinite(v) && v > 0) {
      duration = v;
      params.duration = v;
      sim?.setDuration(v);
      form.updateNotes();
      updateButtons();
    }
  });
  const u = document.createElement("span");
  u.className = "unit";
  u.textContent = "s";
  durRow.append(l, durInput, u);
  c.append(durRow, btnStart, btnPause, btnStop, btnContinue, btnLink);
  btnStart.addEventListener("click", () => void start());
  btnLink.title = "Copy a link that opens the simulator with the current parameters";
  btnLink.addEventListener("click", () => void copyLink());
  btnPause.addEventListener("click", () => {
    paused = !paused;
    btnPause.textContent = paused ? "Resume" : "Pause";
    if (!paused) void runLoop();
  });
  btnStop.addEventListener("click", () => {
    if (!sim) return;
    sim.stop();
    paused = false;
    btnPause.textContent = "Pause";
    if (!running) {
      form.setEnabled(true);
      updateButtons();
    }
  });
  btnContinue.addEventListener("click", () => {
    if (!sim) return;
    sim.setDuration(duration);
    if (sim.phase !== "done") void runLoop();
    updateButtons();
  });
  updateButtons();
}

function updateButtons(): void {
  const s = sim?.status();
  btnPause.disabled = !sim || s?.phase === "done" || (!running && !paused);
  btnStop.disabled = !sim || s?.phase === "done";
  btnContinue.disabled = !sim || running || !sim.canContinue();
}

/** The URL of the current parameters (those that differ from the defaults, in SI). */
function currentLink(): string {
  const q = form.toQuery();
  return `${location.origin}${location.pathname}${q ? "?" + q : ""}`;
}

/** Copies the current link to the clipboard and puts it in the address bar. */
async function copyLink(): Promise<void> {
  const url = currentLink();
  history.replaceState(null, "", url);
  let ok = false;
  try {
    await navigator.clipboard.writeText(url);
    ok = true;
  } catch {
    window.prompt("Copy this link:", url);
  }
  if (ok) {
    btnLink.textContent = "Copied";
    setTimeout(() => (btnLink.textContent = "Copy link"), 1500);
  }
}

// ---------- View toolbars ----------

const viewMode = { value: "2d" as ViewMode };
const scrub = document.createElement("input");
const timeLabel = document.createElement("span");
const btnLive = mkButton("Live");
const btnPlay = mkButton("Play");
const btnWav = mkButton("Download .wav");
const levelSel = document.createElement("select");
const gainSlider = document.createElement("input");
const gainLabel = document.createElement("span");
const peakLabel = document.createElement("span");
let exagInput: HTMLInputElement;
let rangeInput: HTMLInputElement;
let shapeCheck: HTMLInputElement;

function gainDb(): number {
  return parseFloat(gainSlider.value) || 0;
}
function levelMode(): LevelMode {
  return levelSel.value as LevelMode;
}

function updateLevelReadout(): void {
  gainLabel.textContent = `${gainDb() >= 0 ? "+" : ""}${gainDb()} dB`;
  gainSlider.disabled = levelMode() !== "absolute";
  if (!sim || sim.samples === 0) { peakLabel.textContent = ""; return; }
  const audio = sim.recordedAudio();
  const db = peakDbfs(audio, levelGain(audio, sim.fs, levelMode(), gainDb()));
  peakLabel.textContent = isFinite(db) ? `peak ${db.toFixed(1)} dBFS${db > 0 ? " (clipped)" : ""}` : "";
  peakLabel.className = db > 0 ? "warn" : "sub";
  peakLabel.style.margin = "0";
}

function buildViewToolbar(): void {
  const tb = $("viewToolbar");
  const seg = document.createElement("span");
  seg.className = "seg";
  const b2 = mkButton("2D", "on"), b3 = mkButton("3D");
  b2.addEventListener("click", () => { viewMode.value = "2d"; b2.classList.add("on"); b3.classList.remove("on"); });
  b3.addEventListener("click", () => { viewMode.value = "3d"; b3.classList.add("on"); b2.classList.remove("on"); });
  seg.append(b2, b3);
  exagInput = numInput(4, 0.5);
  rangeInput = numInput(0, 0.5);
  shapeCheck = document.createElement("input");
  shapeCheck.type = "checkbox";
  shapeCheck.checked = true;
  shapeCheck.title = "Show the total shape (initial shape plus deviation); unticked, only the deviation from the initial shape";
  const hint = document.createElement("span");
  hint.className = "sub";
  hint.style.margin = "0";
  hint.textContent = "3D: drag to orbit, wheel to zoom";
  tb.append(seg, labeled("Exaggeration ×", exagInput), labeled("Color range (mm, 0 = auto)", rangeInput), labeled("Show initial shape", shapeCheck), hint);
}

function buildMovieToolbar(): void {
  const tb = $("movieToolbar");
  scrub.type = "range";
  scrub.min = "0"; scrub.max = "0"; scrub.value = "0";
  timeLabel.className = "time";
  // Playback drives the movie; afterwards the view returns to where it was (live or scrubbed).
  let liveBeforePlay = true;
  const endPlayback = () => {
    btnPlay.textContent = "Play";
    if (liveBeforePlay) {
      live = true;
      updateLiveButton();
    }
  };
  scrub.addEventListener("input", () => {
    live = false;
    liveBeforePlay = false;
    previewMode = false;
    scrubFrame = parseInt(scrub.value);
    if (player.playing) player.stop();
    updateLiveButton();
  });
  btnLive.addEventListener("click", () => { live = true; liveBeforePlay = true; previewMode = false; updateLiveButton(); });
  btnPlay.addEventListener("click", () => {
    if (player.playing) { player.stop(); endPlayback(); return; }
    if (!sim || sim.samples === 0) return;
    liveBeforePlay = live;
    const offset = live ? 0 : scrubFrame / sim.fps;
    live = false;
    previewMode = false;
    player.play(sim.recordedAudio(), sim.fs, offset, levelMode(), gainDb());
    btnPlay.textContent = "Stop";
    updateLiveButton();
  });
  player.onEnded = endPlayback;
  btnWav.addEventListener("click", () => {
    if (!sim || sim.samples === 0) return;
    const blob = encodeWav(sim.recordedAudio(), sim.fs, levelMode(), gainDb());
    const a = document.createElement("a");
    a.href = URL.createObjectURL(blob);
    a.download = `sheet_${sim.samples}samples_${sim.fs}Hz.wav`;
    a.click();
    setTimeout(() => URL.revokeObjectURL(a.href), 5000);
  });
  for (const [v, t] of [["absolute", "Absolute (0 dBFS = 1 Pa at 0 dB)"], ["loudness", "Loudness (RMS, soft clip)"], ["peak", "Peak"]]) {
    const o = document.createElement("option");
    o.value = v; o.textContent = t;
    levelSel.appendChild(o);
  }
  gainSlider.type = "range";
  gainSlider.min = "-40"; gainSlider.max = "60"; gainSlider.step = "1"; gainSlider.value = "20";
  gainSlider.style.width = "120px";
  gainSlider.style.flex = "none";
  const restart = () => {
    updateLevelReadout();
    const pos = player.position();
    if (pos !== null && sim) player.play(sim.recordedAudio(), sim.fs, pos, levelMode(), gainDb());
  };
  gainSlider.addEventListener("input", restart);
  levelSel.addEventListener("change", restart);
  tb.append(btnPlay, btnLive, scrub, timeLabel, labeled("Level", levelSel), labeled("Gain", gainSlider), gainLabel, peakLabel, btnWav);
  updateLevelReadout();
  updateLiveButton();
}

function updateLiveButton(): void {
  btnLive.classList.toggle("on", live);
  btnLive.disabled = live;
}

function buildSpecToolbar(): void {
  const tb = $("specToolbar");
  const win = document.createElement("select");
  for (const n of [512, 1024, 2048, 4096, 8192]) {
    const o = document.createElement("option");
    o.value = String(n); o.textContent = String(n);
    win.appendChild(o);
  }
  win.value = "2048";
  const hop = numInput(512, 64);
  const fmax = numInput(5000, 500);
  const floor = numInput(80, 5);
  const logf = document.createElement("input");
  logf.type = "checkbox";
  const apply = () => {
    if (!sim) return;
    spec.configure(
      { windowSize: parseInt(win.value), hop: Math.max(16, parseInt(hop.value)), fmax: Math.min(sim.fs / 2, parseFloat(fmax.value)), dbFloor: parseFloat(floor.value), logFrequency: logf.checked },
      sim.recordedAudio(), sim.samples,
    );
  };
  for (const el of [win, hop, fmax, floor, logf]) el.addEventListener("change", apply);
  tb.append(document.createTextNode("Spectrogram"), labeled("Window", win), labeled("Hop", hop), labeled("Max Hz", fmax), labeled("dB range", floor), labeled("Log freq.", logf));
}

function numInput(v: number, step: number): HTMLInputElement {
  const i = document.createElement("input");
  i.type = "number"; i.value = String(v); i.step = String(step);
  return i;
}
function labeled(text: string, el: HTMLElement): HTMLLabelElement {
  const l = document.createElement("label");
  l.append(text, el);
  return l;
}

// ---------- Simulation control ----------

async function start(): Promise<void> {
  if (!device) return;
  player.stop();
  running = false;
  await new Promise((r) => setTimeout(r, 0));
  sim?.destroy();
  spec.reset();
  live = true;
  paused = false;
  btnPause.textContent = "Pause";
  params.duration = duration;
  sim = new Simulation(device, params);
  renderer?.setField(sim.grid, sim.w0, sim.nw, sim.w0Max);
  previewMode = false;
  movieBuf?.destroy();
  movieBuf = device.createBuffer({ size: Math.max(16, sim.grid.n * 4), usage: GPUBufferUsage.STORAGE | GPUBufferUsage.COPY_DST });
  movieBufFrame = -1;
  scrub.max = "0"; scrub.value = "0";
  lastStatsTime = performance.now(); lastStatsSteps = 0; stepsPerSec = 0;
  form.setEnabled(false);
  updateLiveButton();
  void runLoop();
}

async function runLoop(): Promise<void> {
  if (!sim || running) return;
  running = true;
  updateButtons();
  try {
    while (sim.phase !== "done" && !paused) {
      await sim.runBatch();
      spec.update(sim.recordedAudio(), sim.samples);
      scrub.max = String(Math.max(0, sim.frames.length - 1));
      if (live) scrub.value = scrub.max;
      updateLevelReadout();
      const now = performance.now();
      if (now - lastStatsTime > 500) {
        stepsPerSec = ((sim.totalSteps - lastStatsSteps) * 1000) / (now - lastStatsTime);
        lastStatsTime = now; lastStatsSteps = sim.totalSteps;
      }
    }
  } catch (e) {
    console.error(e);
    $("info").innerHTML = `<div class="err">Simulation error: ${String(e)}</div>`;
  }
  running = false;
  if (sim.phase === "done") form.setEnabled(true);
  updateButtons();
}

// ---------- Render loop ----------

let frameErrorShown = false;
let lastRenderKey = "";
let lastInfoHtml = "";

function frame(): void {
  requestAnimationFrame(frame);
  try {
    frameBody();
  } catch (e) {
    if (!frameErrorShown) { frameErrorShown = true; console.error("frame exception:", e); }
  }
}

function frameBody(): void {
  if (!device || !renderer) return;
  renderer.mode = viewMode.value;
  renderer.exaggeration = parseFloat(exagInput.value) || 1;
  renderer.colorRange = (parseFloat(rangeInput.value) || 0) * 1e-3;
  renderer.showShape = shapeCheck.checked;
  const canvas = $<HTMLCanvasElement>("view");
  const cam = renderer.camera;
  const viewKey = [
    renderer.mode, renderer.exaggeration, renderer.colorRange, renderer.showShape,
    cam.yaw.toFixed(4), cam.pitch.toFixed(4), cam.dist.toFixed(4),
    canvas.clientWidth, canvas.clientHeight, window.devicePixelRatio,
  ];
  if (previewMode || !sim) {
    // The resting shape of the sheet that the next Start will use.
    ensurePreview(device);
    const renderKey = ["preview", ...viewKey, params.excitation, params.strikeFracX, params.strikeFracY, params.holeInset].join("|");
    if (renderKey !== lastRenderKey) {
      lastRenderKey = renderKey;
      renderPreview(device);
    }
    if (sim) {
      spec.draw($("spec"), sim.fs, Math.max(duration, sim.samples / sim.fs), null);
      updateInfo(sim.status());
    }
    return;
  }
  const pos = player.position();
  if (pos !== null) {
    scrubFrame = Math.min(sim.frames.length - 1, Math.floor(pos * sim.fps));
    scrub.value = String(scrubFrame);
  }
  const st = sim.status();
  // Render only when something visible changed, so an idle or paused page does no work.
  const renderKey = [...viewKey, live, scrubFrame, sim.frames.length, st.totalSteps, st.phase].join("|");
  if (renderKey !== lastRenderKey) {
    lastRenderKey = renderKey;
    renderView(device, st);
  }
  spec.draw($("spec"), sim.fs, Math.max(duration, sim.samples / sim.fs), pos ?? (live ? null : scrubFrame / sim.fps));
  updateInfo(st);
}

/** Builds the preview buffers from the current parameters when they are missing or stale. */
function ensurePreview(dev: GPUDevice): void {
  if (preview && !preview.stale) return;
  if (preview) for (const b of [preview.w0, preview.zero, preview.nw]) b.destroy();
  const grid = makeGrid(params);
  const shape = initialShape(params, grid);
  let wmax = 0;
  for (let k = 0; k < shape.length; k++) wmax = Math.max(wmax, Math.abs(shape[k]));
  const mk = (data: Float32Array<ArrayBuffer>) => {
    const b = dev.createBuffer({ size: Math.max(16, data.byteLength), usage: GPUBufferUsage.STORAGE | GPUBufferUsage.COPY_DST });
    dev.queue.writeBuffer(b, 0, data);
    return b;
  };
  preview = { grid, w0: mk(shape), zero: mk(new Float32Array(grid.n)), nw: mk(nodeWeights(grid)), wmax, stale: false };
  renderer?.setField(grid, preview.zero, preview.nw);
  lastRenderKey = "";
}

/** Marks the preview stale (parameters changed) and shows it; the next frame rebuilds it. */
function showPreview(): void {
  if (preview) preview.stale = true;
  previewMode = true;
  if (!sim) updateIdleInfo();
}

function renderPreview(dev: GPUDevice): void {
  if (!renderer || !preview) return;
  // The renderer's "initial shape" buffer is zero here, and the shape itself is the displayed field.
  if (renderer.fieldGrid !== preview.grid) renderer.setField(preview.grid, preview.zero, preview.nw);
  const enc = dev.createCommandEncoder();
  renderer.render(enc, preview.w0, preview.wmax);
  timeLabel.textContent = "initial shape";
  dev.pushErrorScope("validation");
  dev.queue.submit([enc.finish()]);
  void dev.popErrorScope().then((e) => { if (e && !frameErrorShown) { frameErrorShown = true; console.error("frame validation error:", e.message); } });
}

function updateIdleInfo(): void {
  const { grid, inside } = form.gridInfo();
  const html = `<div class="row"><span>Grid</span><span>${grid.nx} × ${grid.ny} nodes${grid.mask ? ` (${inside} in the sheet)` : ""}</span></div><p class="sub">The view shows the stress-free initial shape. Press Start to run.</p>`;
  if (html !== lastInfoHtml) {
    lastInfoHtml = html;
    $("info").innerHTML = html;
  }
}

function renderView(dev: GPUDevice, st: SimStatus): void {
  if (!sim || !renderer) return;
  if (renderer.fieldGrid !== sim.grid) renderer.setField(sim.grid, sim.w0, sim.nw, sim.w0Max);
  const enc = dev.createCommandEncoder();
  if (live || sim.frames.length === 0) {
    sim.encodeDisplay(enc);
    renderer.render(enc, sim.displayW, st.wmax);
    timeLabel.textContent = `${st.t >= 0 ? "" : "prep "}${st.t.toFixed(3)} s`;
  } else {
    const f = Math.max(0, Math.min(sim.frames.length - 1, scrubFrame));
    if (movieBufFrame !== f) {
      dev.queue.writeBuffer(movieBuf!, 0, sim.frames[f]);
      movieBufFrame = f;
    }
    let wmax = 0;
    const fr = sim.frames[f];
    for (let k = 0; k < fr.length; k += 7) wmax = Math.max(wmax, Math.abs(fr[k]));
    renderer.render(enc, movieBuf!, wmax);
    timeLabel.textContent = `${(f / sim.fps).toFixed(3)} s`;
  }
  dev.pushErrorScope("validation");
  dev.queue.submit([enc.finish()]);
  void dev.popErrorScope().then((e) => { if (e && !frameErrorShown) { frameErrorShown = true; console.error("frame validation error:", e.message); } });
}

function updateInfo(st: SimStatus): void {
  if (!sim) return;
  const g = sim.grid;
  const { inside } = form.gridInfo();
  const spl = st.peakPressure > 0 ? 20 * Math.log10(st.peakPressure / 2e-5) : -Infinity;
  const phase = { push: "pushing", hold: "settling (held)", recording: "ringing (recording)", done: "done" }[st.phase];
  const rows: [string, string][] = [
    ["Phase", phase],
    ["Time", `${st.t.toFixed(3)} s`],
    ["Grid", `${g.nx} × ${g.ny} nodes${g.mask ? ` (${inside} in the sheet)` : ""}, ${(g.hx * 1e3).toFixed(2)} × ${(g.hy * 1e3).toFixed(2)} mm`],
    ["Time step", `${(sim.dt * 1e6).toFixed(3)} µs (${sim.stepsPerSample} per sample)`],
    ["Speed", `${(stepsPerSec / 1e3).toFixed(0)} k steps/s (${(stepsPerSec * sim.dt).toFixed(3)}× real time)`],
    ["Kinetic energy", `${st.ke.toExponential(2)} J`],
    ["Max |w|", `${(st.wmax * 1e3).toFixed(3)} mm`],
    ["Audio", `${(st.samples / sim.fs).toFixed(2)} s, ${st.frames} frames`],
    ["Peak pressure", st.peakPressure > 0 ? `${st.peakPressure.toFixed(3)} Pa (${spl.toFixed(1)} dB SPL)` : "–"],
  ];
  if (st.stick) {
    if (st.hits && st.hits.total > 1) rows.push(["Hits", `${st.hits.done} of ${st.hits.total}`]);
    rows.push(["Stick", `${(st.stick.x * 1e3).toFixed(2)} mm, ${st.stick.v.toFixed(2)} m/s`]);
    rows.push(["Contact force", `${st.stick.force.toFixed(1)} N (max ${st.stick.maxForce.toFixed(1)} N)`]);
  }
  let html = rows.map(([a, b]) => `<div class="row"><span>${a}</span><span>${b}</span></div>`).join("");
  if (st.delayClamped) html += `<div class="warn">The listener is so close that some propagation delays were clamped.</div>`;
  if (!isFinite(st.wmax) || st.wmax > 1) html += `<div class="err">The solution has diverged. Increase the grid spacing (which lengthens the time step) or reduce the excitation.</div>`;
  if (html !== lastInfoHtml) {
    lastInfoHtml = html;
    $("info").innerHTML = html;
  }
}

// ---------- Self-test ----------

let selfTestResult: { done: boolean; passed?: boolean; cases?: SelfTestCase[]; error?: string } = { done: false };

async function selfTest(): Promise<void> {
  if (!device) { selfTestResult = { done: true, passed: false, error: "no GPU device" }; return; }
  $("info").innerHTML = `<p class="sub">Running the GPU-versus-CPU self-test...</p>`;
  try {
    const cases = await runSelfTest(device);
    const passed = cases.every(selfTestPassed);
    selfTestResult = { done: true, passed, cases };
    const rows = cases.map((c) => `<div class="row"><span>${c.name}</span><span class="${selfTestPassed(c) ? "" : "err"}">acc ${c.accError.u.toExponential(1)} / ${c.accError.v.toExponential(1)} / ${c.accError.w.toExponential(1)}, pos ${c.positionError.toExponential(1)}</span></div>`);
    $("info").innerHTML = `<div class="${passed ? "row" : "err"}">Self-test ${passed ? "passed" : "FAILED"}</div>${rows.join("")}<p class="sub">Maximum relative errors of the u, v, w accelerations and of the compensated w update, GPU step versus float64 reference.</p>`;
  } catch (e) {
    selfTestResult = { done: true, passed: false, error: String(e) };
    $("info").innerHTML = `<div class="err">Self-test error: ${String(e)}</div>`;
  }
}

// ---------- Init ----------

async function init(): Promise<void> {
  form = new ParamForm($("params"), params);
  form.onChange = (key, isLive) => {
    if (!isLive) { showPreview(); return; }
    if (!sim) return;
    if (key === "sigma0" || key === "sigma1" || key === "sigmaIn") sim.setDamping(params.sigma0, params.sigma1, params.sigmaIn);
    if (key.startsWith("listener")) sim.setListener(params.listenerDist, params.listenerAzimuth, params.listenerElevation);
  };
  buildControls();
  buildViewToolbar();
  buildMovieToolbar();
  buildSpecToolbar();
  const q = new URLSearchParams(location.search);
  const set = form.applyUrl(q);
  if (set.includes("duration")) {
    duration = params.duration;
    durInput.value = String(duration);
  }
  exposeHooks();
  if (!("gpu" in navigator)) {
    showNoGpu("WebGPU is not available in this browser. Use a recent Chrome or Edge, or Firefox or Safari with WebGPU enabled.");
    return;
  }
  const adapter = (await navigator.gpu.requestAdapter({ powerPreference: "high-performance" })) ?? (await navigator.gpu.requestAdapter());
  if (!adapter) {
    showNoGpu("No WebGPU adapter was found.");
    return;
  }
  device = await adapter.requestDevice();
  device.lost.then((info) => showNoGpu(`WebGPU device lost: ${info.message}`));
  device.addEventListener("uncapturederror", (ev) => console.error("WebGPU error:", (ev as GPUUncapturedErrorEvent).error.message));
  renderer = new Renderer(device, $("view"), params);
  updateIdleInfo();
  requestAnimationFrame(frame);
  if (q.get("selftest") === "1") await selfTest();
  else if (q.get("autostart") === "1") void start();
}

/** Hooks for automated tests, on window.steelsim. */
function exposeHooks(): void {
  (window as unknown as { steelsim: unknown }).steelsim = {
    status: () => (sim ? { ...sim.status(), dt: sim.dt, stepsPerSample: sim.stepsPerSample, nx: sim.grid.nx, ny: sim.grid.ny, stepsPerSec } : null),
    audio: () => (sim ? Array.from(sim.recordedAudio()) : null),
    frames: () => sim?.frames.length ?? 0,
    features: () => encodeFeatures(params.features),
    link: () => currentLink(),
    selftest: () => selfTestResult,
    noGpu: () => { const e = $("nogpu"); return e.hidden ? null : e.textContent; },
  };
}

function showNoGpu(msg: string): void {
  const el = $("nogpu");
  el.hidden = false;
  el.textContent = msg;
  btnStart.disabled = true;
  selfTestResult = { done: true, passed: false, error: msg };
}

void init();