import { renderControls, type Section } from './controls';
import { LinePlot, css, fmtNum, type Marker } from './plot';
import { Spectrogram } from './spectrogram';
import { spectrum } from './fft';
import { encodeWav } from './wav';
import { BeadScene, type SceneSpec } from './scene3d';
import { Timeline } from './timeline';
import { runInWorker } from '../sim/run';
import { CPU_RATE, parseSettings, runCost, settingsQuery, simOptions, type Settings } from './settings';
import { checkPasscode, getPasscode, loadResult, probeResult, resultKey, setPasscode, storeResult, type Backend } from '../sim/cache';
import type { BeadSystem, Excitation, SimResult } from '../sim/types';

// The page every instrument shares: presets and control panel, 3D model,
// setup summary, run summary, audio, waveform, spectrogram, spectrum, energy.
// An instrument adds its own setup rows, extra result cards and views.

export interface SimParams {
  duration: number;
  fs: number;
  cfl: number;
  frameRate: number;
}

export interface Built {
  sys: BeadSystem;
  exc: Excitation;
  pickup: Float64Array;
  pickupDelay?: Float64Array; // per bead, in samples (a microphone)
  scene: SceneSpec;
}

export interface Preset<P> {
  name: string;
  description: string;
  params: P;
}

export interface Extras<P> {
  show(p: P, built: Built, r: SimResult): void;
}

export interface InstrumentConfig<P extends SimParams> {
  title: string;
  wavName: string;
  audioQuantity?: { label: string; unit: string }; // default: acceleration, m/s²
  presets: Preset<P>[];
  sections: Section<P>[];
  // WebGPU on by default (default true); off where the systems are too small to gain from it
  webgpuDefault?: boolean;
  // instrument-specific summary of the setup; built = null when the parameters are invalid
  setup(p: P): { rows: [string, string][]; warnings: string[]; built: Built | null };
  summaryRows?(p: P, built: Built, r: SimResult): [string, string][];
  spectrumMarkers?(p: P): { markers: Marker[]; legend: string };
  extraCards?: string; // cards with data-r="out" hidden, shown after a run
  mountExtras?(q: <T extends HTMLElement>(r: string) => T, timeline: Timeline): Extras<P>;
}

const statRows = (rows: [string, string][]) => rows.map(([k, v]) => `<div><span>${k}</span><b>${v}</b></div>`).join('');

export function mountInstrumentPage<P extends SimParams>(root: HTMLElement, cfg: InstrumentConfig<P>) {
  root.innerHTML = `
  <div class="instrument">
    <aside class="panel">
      <a href="#/" class="back">← All instruments</a>
      <h1>${cfg.title}</h1>
      <label class="ctl preset"><span class="ctl-name">Preset</span><select data-r="preset"></select></label>
      <p class="sub" data-r="preset-desc"></p>
      <div class="share-row"><button class="btn-small" data-r="share" title="Copy a link that opens this page with the current settings">Copy link to these settings</button><span class="note" data-r="share-msg"></span></div>
      <input class="share-url" data-r="share-url" readonly hidden aria-label="link to these settings">
      <div class="run-row top">
        <button class="btn" data-r="run">Run simulation</button>
        <button class="btn-small" data-r="cancel" hidden>Cancel</button>
        <button class="btn-small" data-r="load-cached" hidden>Load cached</button>
        <label class="inline gpu-toggle" data-r="gpu-label"><input type="checkbox" data-r="gpu"> WebGPU</label>
      </div>
      <p class="note" data-r="cached-avail" hidden></p>
      <progress data-r="progress" max="1" value="0" hidden></progress>
      <p class="error" data-r="error" hidden></p>
      <details class="cache-ctl">
        <summary data-r="cache-state"></summary>
        <p class="note">Results are shared: when someone has already computed a run with these settings, you can load it instead of running it again. With the passcode, this browser also stores its runs there.</p>
        <div class="cache-form"><input type="password" data-r="cache-pass" placeholder="Passcode" autocomplete="off"><button class="btn-small" data-r="cache-save">Save</button><button class="btn-small" data-r="cache-forget">Forget</button></div>
        <p class="note" data-r="cache-msg"></p>
      </details>
      <div data-r="controls"></div>
    </aside>
    <main class="results">
      <section class="card"><h2>Model</h2><div data-r="scene"></div></section>
      <section class="card"><h2>Setup</h2><div data-r="derived" class="stats"></div><ul data-r="warnings" class="warnings"></ul></section>
      <section class="card" data-r="out" hidden>
        <h2>Run</h2><div data-r="summary" class="stats"></div>
        <p class="note" data-r="cache-note"></p>
        <div class="audio-row"><audio controls data-r="audio"></audio><a class="btn-small" data-r="download" download="${cfg.wavName}">Download .wav</a></div>
        <p class="note" data-r="audio-note"></p>
      </section>
      <section class="card" data-r="out" hidden>
        <div class="card-head"><h2>${cap((cfg.audioQuantity ?? { label: 'pickup acceleration' }).label)}</h2>
          <div class="seg" data-r="wave-range"><button data-v="0" class="on">Full</button><button data-v="0.05">First 50 ms</button><button data-v="0.005">First 5 ms</button></div></div>
        <div class="canvas-wrap"><canvas data-r="wave"></canvas></div>
      </section>
      <section class="card" data-r="out" hidden>
        <div class="card-head"><h2>Spectrogram</h2>
          <label class="inline">up to <select data-r="fmax"><option>1000</option><option>2500</option><option selected>5000</option><option>10000</option><option>24000</option></select> Hz</label></div>
        <div class="canvas-wrap tall"><canvas data-r="spec"></canvas></div>
      </section>
      <section class="card" data-r="out" hidden>
        <div class="card-head"><h2>Spectrum</h2><div class="legend" data-r="spec-legend"></div></div>
        <div class="canvas-wrap"><canvas data-r="spectrum"></canvas></div>
      </section>
      ${cfg.extraCards ?? ''}
      <section class="card" data-r="out-contact" hidden>
        <h2>Contact force</h2>
        <div class="canvas-wrap short"><canvas data-r="contact"></canvas></div>
        <p class="note" data-r="contact-note"></p>
      </section>
      <section class="card" data-r="out" hidden>
        <h2>Energy</h2>
        <div class="canvas-wrap short"><canvas data-r="energy"></canvas></div>
        <p class="note">Kinetic plus spring energy of the instrument, minus the energy stored by pre-tension at equilibrium. Without damping or forcing it stays flat; the run summary gives the error of the energy balance (energy + dissipated − work in − initial, mallet included).</p>
      </section>
    </main>
  </div>`;
  const q = <T extends HTMLElement>(r: string) => root.querySelector(`[data-r="${r}"]`) as T;
  const presetSel = q<HTMLSelectElement>('preset');
  cfg.presets.forEach((p, i) => presetSel.add(new Option(p.name, String(i))));
  const presetDesc = q<HTMLParagraphElement>('preset-desc');
  const runBtn = q<HTMLButtonElement>('run');
  const cancelBtn = q<HTMLButtonElement>('cancel');
  const progress = q<HTMLProgressElement>('progress');
  const errorBox = q<HTMLParagraphElement>('error');
  const gpuBox = q<HTMLInputElement>('gpu');
  const loadBtn = q<HTMLButtonElement>('load-cached');
  const availNote = q<HTMLParagraphElement>('cached-avail');
  const cacheNote = q<HTMLParagraphElement>('cache-note');
  const instrumentId = cfg.wavName.replace(/\.wav$/, ''); // e.g. bead-cymbal
  const hasGpu = 'gpu' in navigator;
  const gpuKey = `toy-instruments.webgpu.${cfg.wavName}`;
  let gpuPref: string | null = null;
  try {
    gpuPref = localStorage.getItem(gpuKey);
  } catch {
    /* storage unavailable */
  }
  gpuBox.checked = hasGpu && (gpuPref ? gpuPref === 'on' : cfg.webgpuDefault !== false);
  gpuBox.disabled = !hasGpu;
  q('gpu-label').title = hasGpu
    ? 'Run the solver on the GPU (single precision). Faster for meshes of a few hundred beads or more; slower for small systems. Falls back to the CPU if the GPU cannot run it.'
    : 'This browser does not offer WebGPU; the solver runs on the CPU.';
  gpuBox.addEventListener('change', () => {
    try {
      localStorage.setItem(gpuKey, gpuBox.checked ? 'on' : 'off');
    } catch {
      /* storage unavailable */
    }
    checkCache();
  });

  const wave = new LinePlot(q('wave'));
  const spec = new Spectrogram(q('spec'));
  const specPlot = new LinePlot(q('spectrum'));
  const energyPlot = new LinePlot(q('energy'));
  const contactPlot = new LinePlot(q('contact'));
  const quantity = cfg.audioQuantity ?? { label: 'acceleration', unit: 'm/s²' };
  const timeline = new Timeline();
  const scene = new BeadScene(q('scene'), timeline);
  const extras = cfg.mountExtras?.(q, timeline);
  let waveRange = 0;
  let last: { p: P; r: SimResult } | null = null;
  let cancelRun: (() => void) | null = null; // set while a run (or a cache download) is in progress
  // the cached result for the current settings, if there is one
  let cached: { p: P; built: Built; key: string; stored?: Date } | null = null;
  let probeSeq = 0;
  let probeTimer = 0;
  let audioUrl: string | null = null;
  let pendingAudio: Blob | null = null; // a newer partial result's audio, held back while the player plays

  // settings from a shared link, applied once and then removed from the address
  const shared = readSharedLink(cfg);
  if (shared) {
    presetSel.value = String(shared.preset);
    if (shared.gpu !== undefined && hasGpu) gpuBox.checked = shared.gpu;
  }
  const controls = renderControls(q('controls'), cfg.sections, shared?.params ?? cfg.presets[0].params, () => updateSetup());
  presetDesc.textContent = cfg.presets[Number(presetSel.value)].description;
  presetSel.addEventListener('change', () => {
    const pr = cfg.presets[Number(presetSel.value)];
    presetDesc.textContent = pr.description;
    shareMsg.textContent = '';
    controls.set(pr.params);
  });

  const shareMsg = q<HTMLSpanElement>('share-msg');
  const shareUrl = q<HTMLInputElement>('share-url');
  if (shared) shareMsg.textContent = 'Settings loaded from a shared link.';
  q('share').addEventListener('click', async () => {
    const url = sharedLink(controls.get(), Number(presetSel.value), gpuBox.checked);
    shareUrl.hidden = true;
    try {
      await navigator.clipboard.writeText(url);
      shareMsg.textContent = 'Link copied.';
    } catch {
      // no clipboard access: show the link to copy by hand
      shareMsg.textContent = 'Copy this link:';
      shareUrl.value = url;
      shareUrl.hidden = false;
      shareUrl.select();
    }
  });

  function updateSetup() {
    const p = controls.get();
    const { rows, warnings, built } = cfg.setup(p);
    if (built) {
      scene.showSetup(built.scene);
      const { omegaMax: wmax, stepsPerSample: spp, work } = runCost(p, built);
      rows.push(['Highest frequency', `${fmtNum(wmax / (2 * Math.PI))} Hz`]);
      rows.push(['Time step', `${fmtNum(1 / (p.fs * spp))} s (${spp} per sample)`]);
      rows.push(['Element updates', fmtNum(work)]);
      const frameMB = (Math.round(p.duration * p.frameRate) * 3 * built.sys.n * 4) / 1e6;
      if (frameMB > 400) warnings.push(`Replay frames would take ${fmtNum(frameMB)} MB; lower the replay frame rate or the duration.`);
      if (work > 3e9) warnings.push(`This run is large (${fmtNum(work)} element updates): expect roughly ${fmtNum(work / CPU_RATE / 60)} min on a desktop CPU (WebGPU is usually much faster).`);
    }
    q('derived').innerHTML = statRows(rows);
    q('warnings').innerHTML = warnings.map((w) => `<li>${w}</li>`).join('');
    runBtn.disabled = !built || !!cancelRun;
    checkCache();
  }

  // what the solver gets for parameters p; null when they are invalid
  function inputs(p: P) {
    const { built } = cfg.setup(p);
    if (!built) return null;
    return { built, opt: simOptions(p, built), backend: (gpuBox.checked ? 'gpu' : 'cpu') as Backend };
  }

  // Look up (debounced) whether the shared cache has a result for the current settings,
  // and offer to load it next to Run.
  function checkCache() {
    const seq = ++probeSeq;
    cached = null;
    loadBtn.hidden = availNote.hidden = true;
    clearTimeout(probeTimer);
    probeTimer = window.setTimeout(async () => {
      const p = controls.get();
      const inp = inputs(p);
      if (!inp) return;
      try {
        const key = await resultKey(instrumentId, inp.built.sys, inp.built.exc, inp.opt, inp.backend);
        const hit = await probeResult(key);
        if (seq !== probeSeq || !hit) return;
        cached = { p, built: inp.built, key, stored: hit.stored };
        const when = hit.stored ? `computed ${hit.stored.toISOString().slice(0, 10)}, ` : '';
        availNote.textContent = `A cached result exists for these settings (${when}${fmtNum(hit.bytes / 1e6)} MB). Load it, or run the simulation again.`;
        loadBtn.hidden = availNote.hidden = false;
        loadBtn.disabled = !!cancelRun;
      } catch {
        /* cache unreachable: just don't offer it */
      }
    }, 250);
  }
  updateSetup();

  q('wave-range').addEventListener('click', (e) => {
    const b = (e.target as HTMLElement).closest('button');
    if (!b) return;
    waveRange = Number(b.dataset.v);
    q('wave-range').querySelectorAll('button').forEach((x) => x.classList.toggle('on', x === b));
    drawWave();
  });
  q<HTMLSelectElement>('fmax').addEventListener('change', (e) => {
    spec.fmax = Number((e.target as HTMLSelectElement).value);
    spec.draw();
    drawSpectrum();
  });

  function drawWave() {
    if (!last) return;
    const { p, r } = last;
    const t = new Float64Array(r.audio.length);
    for (let i = 0; i < t.length; i++) t[i] = i / r.fs;
    wave.set([{ x: t, y: r.audio, color: css('--series-1'), label: 'a' }], {
      xLabel: 'time (s)',
      yLabel: `${quantity.label} (${quantity.unit})`,
      // a partial result is drawn on the axis of the whole run
      xRange: [0, waveRange ? Math.min(waveRange, p.duration) : Math.max(p.duration, t[t.length - 1])],
    });
  }

  function drawSpectrum() {
    if (!last) return;
    const { p, r } = last;
    const s = spectrum(r.audio, r.fs);
    let top = -Infinity;
    for (const v of s.db) top = Math.max(top, v);
    const db = s.db.map((v) => Math.max(v - top, -100));
    const m = cfg.spectrumMarkers?.(p);
    q('spec-legend').innerHTML =
      `<span><i class="sw" style="background:var(--series-1)"></i>pickup signal</span>` + (m?.legend ?? '');
    specPlot.set([{ x: s.freq, y: db, color: css('--series-1'), label: 'level (dB)' }], {
      xLabel: 'frequency (Hz)',
      yLabel: 'level (dB re max)',
      xRange: [0, Math.min(spec.fmax, r.fs / 2)],
      yRange: [-100, 5],
      markers: m?.markers,
    });
  }

  // partial: r covers only the start of a run still in progress. update: r
  // extends the result already shown (same run), so the replay position, the
  // exaggeration and the audio player's position are kept.
  function show(p: P, built: Built, r: SimResult, partial = false, update = false) {
    last = { p, r };
    const simulated = r.audio.length / r.fs;
    cacheNote.textContent = partial
      ? `Partial result: ${fmtNum(simulated)} s of ${fmtNum(p.duration)} s simulated so far. It updates every few seconds while the run continues; the audio player picks up the newer sound when it is paused.`
      : '';
    root.querySelectorAll<HTMLElement>('[data-r="out"]').forEach((e) => (e.hidden = false));
    let peak = 0;
    for (const v of r.audio) peak = Math.max(peak, Math.abs(v));
    const emax = Math.max(...r.energy);
    let bal = 0;
    for (const b of r.balance) bal = Math.max(bal, Math.abs(b));
    const rt = simulated / r.wallSeconds;
    q('summary').innerHTML = statRows([
      ...(partial ? ([['Simulated so far', `${fmtNum(simulated)} s of ${fmtNum(p.duration)} s`]] as [string, string][]) : []),
      ['Solver', (r.backend ?? 'CPU') + (r.fallback ? ` (WebGPU failed: ${r.fallback})` : '')],
      ['Time step', `${fmtNum(r.dt)} s, ${r.stepsPerSample} per sample`],
      [partial ? 'Wall time so far' : 'Wall time', `${fmtNum(r.wallSeconds)} s (${rt >= 1 ? fmtNum(rt) + '× faster than' : fmtNum(1 / rt) + '× slower than'} real time)`],
      ['Energy balance error', emax > 0 ? `${fmtNum((bal / emax) * 100)}% of peak energy` : '–'],
      ...(cfg.summaryRows?.(p, built, r) ?? []),
      ...contactRows(r),
      [`Peak ${quantity.label}`, `${fmtNum(peak)} ${quantity.unit}`],
    ]);
    setAudio(encodeWav(r.audio, r.fs), update);
    q('audio-note').textContent = `16-bit mono, ${r.fs} Hz, normalized so the peak is −1 dBFS${partial ? ' (of the sound so far)' : ''}.`;
    drawWave();
    spec.setSignal(r.audio, r.fs);
    drawSpectrum();
    if (update) timeline.extend(r.frameTimes);
    else timeline.setTimes(r.frameTimes);
    scene.showReplay({ ...built.scene, frames: r.frames, malletPos: r.malletPos }, update);
    extras?.show(p, built, r);
    showContact(r);
    energyPlot.set([{ x: r.frameTimes, y: r.energy, color: css('--series-1'), label: 'energy (J)' }], {
      xLabel: 'time (s)',
      xRange: [0, Math.max(p.duration, r.frameTimes[r.frameTimes.length - 1])],
      yLabel: 'energy (J)',
      yRange: [0, emax * 1.05 || 1],
    });
  }

  // Give the player new audio. While it plays, a partial result's audio waits
  // until it pauses or ends (swapping the source would stop it); when it is
  // paused partway, the new audio resumes from the same point.
  const player = q<HTMLAudioElement>('audio');
  function setAudio(wav: Blob, update: boolean) {
    pendingAudio = null;
    if (update && audioUrl && !player.paused && !player.ended) {
      pendingAudio = wav;
      return;
    }
    const at = update && !player.ended ? player.currentTime : 0;
    if (audioUrl) URL.revokeObjectURL(audioUrl);
    audioUrl = URL.createObjectURL(wav);
    player.src = audioUrl;
    q<HTMLAnchorElement>('download').href = audioUrl;
    if (at > 0) player.addEventListener('loadedmetadata', () => (player.currentTime = Math.min(at, player.duration)), { once: true });
  }
  const flushAudio = () => {
    if (pendingAudio) setAudio(pendingAudio, true);
  };
  player.addEventListener('pause', flushAudio);
  player.addEventListener('ended', flushAudio);

  function showContact(r: SimResult) {
    const card = q('out-contact');
    card.hidden = !r.contactForce;
    if (!r.contactForce) return;
    const cf = r.contactForce;
    const c = contacts(cf, r.fs);
    const end = c.length ? c[c.length - 1].start + c[c.length - 1].ms / 1000 : 0.01;
    const nShow = Math.min(cf.length, Math.ceil((end * 1.3 + 0.002) * r.fs));
    const t = new Float64Array(nShow);
    for (let i = 0; i < nShow; i++) t[i] = (i / r.fs) * 1000;
    contactPlot.set([{ x: t, y: cf.subarray(0, nShow), color: css('--series-2'), label: 'force (N)' }], {
      xLabel: 'time (ms)',
      yLabel: 'contact force (N)',
      yRange: [0, Math.max(...cf.subarray(0, nShow)) * 1.08 || 1],
    });
    q('contact-note').textContent = c.length
      ? `${c.length} contact${c.length > 1 ? 's' : ''}: ` +
        c.map((k) => `${fmtNum(k.ms)} ms from ${fmtNum(k.start * 1000)} ms, peak ${fmtNum(k.peak)} N`).join('; ') +
        '. During contact the instrument takes energy from the mallet and gives part of it back as the mallet rebounds, so the energy plot can spike first; the mallet then leaves at constant speed (no gravity).'
      : 'The mallet never touched the instrument.';
  }

  function setBusy(cancel: (() => void) | null) {
    cancelRun = cancel;
    runBtn.disabled = loadBtn.disabled = !!cancel;
    cancelBtn.hidden = !cancel;
    progress.hidden = !cancel;
    progress.value = 0;
    if (cancel) errorBox.hidden = true;
  }

  // Run the simulation and, if this browser has the passcode, store the result.
  async function run() {
    const p = controls.get();
    const inp = inputs(p);
    if (!inp) return;
    const { built, opt, backend } = inp;
    // Partial results are shown as they come; when they arrive faster than the
    // page draws them, only the newest is drawn.
    let shown = false; // a partial result of this run is on the page
    let latest: SimResult | null = null;
    let finished = false;
    const onPartial = (r: SimResult) => {
      if (!latest)
        setTimeout(() => {
          if (!latest || finished) return;
          show(p, built, latest, true, shown);
          shown = true;
          latest = null;
        });
      latest = r;
    };
    const running = runInWorker(pageWorker, built.sys, built.exc, opt, backend === 'gpu', (f) => (progress.value = f), onPartial);
    setBusy(running.cancel);
    try {
      const r = await running.promise;
      finished = true;
      show(p, built, r, false, shown);
      if (getPasscode()) {
        // a WebGPU run that fell back to the CPU is stored as a CPU result
        const actual: Backend = r.backend?.startsWith('WebGPU') ? 'gpu' : 'cpu';
        const key = await resultKey(instrumentId, built.sys, built.exc, opt, actual);
        cacheNote.textContent = 'Storing in the shared cache…';
        storeResult(key, r, { instrument: instrumentId, backend: r.backend, wallSeconds: r.wallSeconds })
          .then(() => {
            if (last?.r === r) cacheNote.textContent = 'Stored in the shared cache.';
            checkCache();
          })
          .catch((e) => {
            if (last?.r === r) cacheNote.textContent = `Not stored in the shared cache: ${(e as Error).message}`;
          });
      }
    } catch (e) {
      finished = true;
      if (shown) cacheNote.textContent = `The run ${(e as Error).message === 'cancelled' ? 'was cancelled' : 'stopped'}; this is the partial result up to ${fmtNum(last!.r.audio.length / last!.r.fs)} s.`;
      if ((e as Error).message !== 'cancelled') {
        errorBox.textContent = `The simulation failed: ${(e as Error).message}`;
        errorBox.hidden = false;
      }
    } finally {
      setBusy(null);
    }
  }

  // Download and show the cached result for the current settings.
  async function loadCached() {
    if (!cached) return;
    const { p, built, key } = cached;
    const abort = new AbortController();
    setBusy(() => abort.abort());
    try {
      const hit = await loadResult(key, (f) => (progress.value = f), abort.signal);
      if (!hit) throw new Error('the entry is no longer in the cache');
      show(p, built, hit.result);
      const when = hit.stored ? ` on ${hit.stored.toISOString().slice(0, 10)}` : '';
      cacheNote.textContent = `Loaded from the shared cache (computed${when}; the wall time is that of the original run).`;
    } catch (e) {
      if (!abort.signal.aborted) {
        errorBox.textContent = `Could not load the cached result: ${(e as Error).message}`;
        errorBox.hidden = false;
        checkCache();
      }
    } finally {
      setBusy(null);
    }
  }
  runBtn.addEventListener('click', run);
  loadBtn.addEventListener('click', loadCached);
  cancelBtn.addEventListener('click', () => cancelRun?.());

  // passcode for writing to the shared cache
  const passInput = q<HTMLInputElement>('cache-pass');
  const cacheMsg = q<HTMLParagraphElement>('cache-msg');
  const showCacheState = () =>
    (q('cache-state').textContent = getPasscode() ? 'Shared cache: runs are stored' : 'Shared cache: read only');
  showCacheState();
  q('cache-save').addEventListener('click', async () => {
    const pass = passInput.value.trim();
    if (!pass) return;
    cacheMsg.textContent = 'Checking…';
    try {
      const { valid, reason } = await checkPasscode(pass);
      if (!valid) {
        cacheMsg.textContent = `Not saved: ${reason ?? 'invalid passcode'}.`;
        return;
      }
      setPasscode(pass);
      passInput.value = '';
      cacheMsg.textContent = 'Saved in this browser. Runs from now on are stored in the cache.';
    } catch (e) {
      cacheMsg.textContent = `Could not check the passcode: ${(e as Error).message}`;
    }
    showCacheState();
  });
  q('cache-forget').addEventListener('click', () => {
    setPasscode(null);
    cacheMsg.textContent = 'Passcode removed from this browser.';
    showCacheState();
  });
}

// A link to this page with settings p (see settings.ts).
function sharedLink<P extends SimParams>(p: P, preset: number, gpu: boolean): string {
  const route = location.hash.split('?')[0];
  return `${location.origin}${location.pathname}${route}?${settingsQuery(p, preset, gpu)}`;
}

// Settings from a shared link in the address (#/<instrument>?...), which is then removed.
function readSharedLink<P extends SimParams>(cfg: InstrumentConfig<P>): Settings<P> | null {
  const [route, query] = location.hash.split('?');
  if (query === undefined) return null;
  history.replaceState(history.state, '', `${location.pathname}${location.search}${route}`);
  return parseSettings(cfg, query);
}

const pageWorker = () => new Worker(new URL('../sim/worker.ts', import.meta.url), { type: 'module' });

// separate contact intervals in the contact-force record
function contacts(cf: Float32Array, fs: number): { start: number; ms: number; peak: number }[] {
  const out: { start: number; ms: number; peak: number }[] = [];
  let i = 0;
  while (i < cf.length) {
    if (cf[i] > 0) {
      const a = i;
      let peak = 0;
      while (i < cf.length && cf[i] > 0) peak = Math.max(peak, cf[i++]);
      out.push({ start: a / fs, ms: ((i - a) / fs) * 1000, peak });
    } else i++;
  }
  return out;
}

function contactRows(r: SimResult): [string, string][] {
  if (!r.contactForce) return [];
  const c = contacts(r.contactForce, r.fs);
  return [
    [
      'Contact',
      c.length
        ? `${fmtNum(c[0].ms)} ms, peak ${fmtNum(c[0].peak)} N${c.length > 1 ? ` (+${c.length - 1} more contact${c.length > 2 ? 's' : ''})` : ''}`
        : 'none',
    ],
  ];
}

const cap = (s: string) => s[0].toUpperCase() + s.slice(1);