Rhythm Trainer

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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
<title>Rhythm Trainer — sloprun.dev</title>
<link rel="icon" href="data:,">
<style>
/* ── sloprun design tokens (verbatim from demos/tokens.css) ───────────────── */
:root {
  --bg: #F6F6F3;          /* neutral paper, not cream */
  --surface: #FFFFFF;
  --ink: #1A1D21;
  --muted: #5A6068;
  --line: #E3E2DC;
  --accent: #C05600;      /* phosphor amber, darkened for light bg */
  --accent-soft: #FFF3E6;
  --run: #1A7F37;         /* earned green */
  --run-soft: #E7F4EA;
  --danger: #C93C37;
  --radius: 10px;
  --font-sans: system-ui, -apple-system, "Segoe UI", sans-serif;
  --font-mono: ui-monospace, "SF Mono", "Cascadia Code", Menlo, Consolas, monospace;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #14161A; --surface: #1C1F26; --ink: #E8E6E1; --muted: #9AA0A8;
    --line: #2A2E36; --accent: #FFB454; --accent-soft: #2A2118;
    --run: #3FB950; --run-soft: #16281B; --danger: #F47067;
  }
}
:root[data-theme="dark"] {
  --bg: #14161A; --surface: #1C1F26; --ink: #E8E6E1; --muted: #9AA0A8;
  --line: #2A2E36; --accent: #FFB454; --accent-soft: #2A2118;
  --run: #3FB950; --run-soft: #16281B; --danger: #F47067;
}
body { background: var(--bg); color: var(--ink); font-family: var(--font-sans); }
/* ── end tokens ───────────────────────────────────────────────────────────── */

/* demo-local values the shared tokens don't carry */
:root {
  color-scheme: light;
  --shadow: 0 1px 2px rgba(26,29,33,.05);
  --shadow-lift: 0 6px 18px rgba(26,29,33,.07);
  --well: #F1F0EC;
  --grid: #DDDCD5;
  --glow: rgba(192,86,0,.20);
  --btn-ink: #FFFFFF;
  --danger-soft: #FBEDEC;
  --lane-h: 116px;
  --rib-h: 132px;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    color-scheme: dark;
    --shadow: 0 1px 2px rgba(0,0,0,.35);
    --shadow-lift: 0 8px 22px rgba(0,0,0,.45);
    --well: #16181D; --grid: #30343D;
    --glow: rgba(255,180,84,.26); --btn-ink: #14161A;
    --danger-soft: #2B1A19;
  }
}
:root[data-theme="dark"] {
  color-scheme: dark;
  --shadow: 0 1px 2px rgba(0,0,0,.35);
  --shadow-lift: 0 8px 22px rgba(0,0,0,.45);
  --well: #16181D; --grid: #30343D;
  --glow: rgba(255,180,84,.26); --btn-ink: #14161A;
  --danger-soft: #2B1A19;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
html { -webkit-text-size-adjust: 100%; }
body { min-height: 100%; overflow-x: hidden; }

.wrap {
  max-width: 900px; margin: 0 auto;
  padding: 22px 16px 26px;
  display: flex; flex-direction: column; gap: 13px;
}
@media (max-width: 460px) { .wrap { padding: 15px 9px 20px; gap: 10px; } }

h1 { margin: 0 0 6px; font-size: clamp(21px, 3.6vw, 29px); letter-spacing: -.021em; line-height: 1.15; }
.lede { margin: 0; max-width: 68ch; color: var(--muted); font-size: 14.5px; line-height: 1.55; }
.lede b { color: var(--ink); font-weight: 600; }

.card {
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); box-shadow: var(--shadow);
  padding: 14px;
}
@media (max-width: 460px) { .card { padding: 10px 9px; } }

.cardhead {
  display: flex; align-items: baseline; gap: 9px; flex-wrap: wrap;
  font-family: var(--font-mono); font-size: 11px; letter-spacing: .09em;
  color: var(--muted); margin-bottom: 10px;
}
.cardhead .tag { color: var(--ink); font-weight: 600; }

/* ── transport ────────────────────────────────────────────────────────────── */
.transport {
  display: flex; flex-wrap: wrap; align-items: center; gap: 9px 13px;
}
.btn {
  font: inherit; font-size: 13.5px; font-weight: 600;
  color: var(--ink); background: var(--surface);
  border: 1px solid var(--line); border-radius: 8px;
  padding: 8px 13px; cursor: pointer;
  display: inline-flex; align-items: center; gap: 7px;
  transition: background .12s ease, border-color .12s ease, color .12s ease, transform .06s ease;
  -webkit-tap-highlight-color: transparent;
}
.btn:hover { background: var(--accent-soft); border-color: var(--accent); }
.btn:active { transform: translateY(1px); }
.btn:focus-visible, .chip:focus-visible, .pad:focus-visible, input[type=range]:focus-visible {
  outline: 2px solid var(--ink); outline-offset: 2px;
}
.btn.primary {
  background: var(--accent); border-color: var(--accent); color: var(--btn-ink);
  min-width: 122px; justify-content: center; padding: 9px 15px;
}
.btn.primary:hover { filter: brightness(1.07); background: var(--accent); }
.btn.primary.on { background: var(--surface); color: var(--ink); border-color: var(--ink); }
.btn .gl { font-size: 11px; line-height: 1; }
.btn.small { font-size: 12px; padding: 6px 10px; font-weight: 500; color: var(--muted); }
.btn.small:hover { color: var(--ink); }
.btn.small.off { color: var(--muted); border-style: dashed; }

.status {
  display: inline-flex; align-items: center; gap: 6px;
  font-family: var(--font-mono); font-size: 11.5px; letter-spacing: .08em;
  padding: 5px 9px; border-radius: 99px;
  background: var(--well); color: var(--muted); border: 1px solid var(--line);
  white-space: nowrap;
}
.status .led { width: 7px; height: 7px; border-radius: 50%; background: var(--muted); opacity: .45; flex: none; }
.status.live { background: var(--accent-soft); color: var(--accent); border-color: transparent; }
.status.live .led { background: var(--accent); opacity: 1; animation: blink 1.05s steps(1) infinite; }
.status.good { background: var(--run-soft); color: var(--run); border-color: transparent; }
.status.good .led { background: var(--run); opacity: 1; }
@keyframes blink { 0%,55% { opacity: 1 } 56%,100% { opacity: .25 } }

.readout {
  font-family: var(--font-mono); font-size: 12.5px; color: var(--muted);
  display: inline-flex; gap: 5px; align-items: baseline; white-space: nowrap;
}
.readout b { color: var(--ink); font-weight: 600; font-variant-numeric: tabular-nums; }
.readout .sep { opacity: .45; }
.readout b.good { color: var(--run); }
.spacer { flex: 1 1 auto; }

.controls {
  display: flex; flex-wrap: wrap; align-items: center; gap: 12px 18px;
  margin-top: 12px; padding-top: 12px; border-top: 1px dashed var(--line);
}
.knob { flex: 1 1 210px; min-width: 165px; max-width: 320px; }
.knob .kl {
  display: flex; justify-content: space-between; align-items: baseline; gap: 8px;
  font-family: var(--font-mono); font-size: 11px; letter-spacing: .08em;
  color: var(--muted); margin-bottom: 3px;
}
.knob .kv { color: var(--ink); font-weight: 600; font-variant-numeric: tabular-nums; }

input[type=range] {
  -webkit-appearance: none; appearance: none;
  width: 100%; background: transparent; margin: 0; height: 20px; cursor: pointer;
}
input[type=range]::-webkit-slider-runnable-track { height: 5px; border-radius: 99px; background: var(--line); }
input[type=range]::-webkit-slider-thumb {
  -webkit-appearance: none; width: 17px; height: 17px; margin-top: -6px;
  border-radius: 50%; background: var(--accent);
  border: 2px solid var(--surface); box-shadow: 0 1px 3px rgba(0,0,0,.25);
}
input[type=range]::-moz-range-track { height: 5px; border-radius: 99px; background: var(--line); }
input[type=range]::-moz-range-thumb {
  width: 13px; height: 13px; border-radius: 50%; background: var(--accent);
  border: 2px solid var(--surface); box-shadow: 0 1px 3px rgba(0,0,0,.25);
}

.pat { display: flex; flex-wrap: wrap; align-items: center; gap: 7px; }
.pat .grouplabel {
  font-family: var(--font-mono); font-size: 11px; letter-spacing: .08em;
  color: var(--muted); margin-right: 2px;
}
.chip {
  font: inherit; font-size: 12.5px; color: var(--muted);
  background: var(--surface); border: 1px solid var(--line);
  border-radius: 99px; padding: 6px 12px; cursor: pointer;
  transition: background .12s ease, color .12s ease, border-color .12s ease;
  -webkit-tap-highlight-color: transparent;
}
.chip:hover { color: var(--ink); border-color: var(--accent); background: var(--accent-soft); }
.chip[aria-pressed="true"] { color: var(--ink); border-color: var(--accent); background: var(--accent-soft); font-weight: 600; }
.pending {
  font-family: var(--font-mono); font-size: 11px; letter-spacing: .05em;
  color: var(--accent); background: var(--accent-soft);
  border-radius: 99px; padding: 4px 9px; white-space: nowrap;
}
.pending[hidden] { display: none; }

/* ── lane ─────────────────────────────────────────────────────────────────── */
.lanewrap { position: relative; }
.lane {
  position: relative; height: var(--lane-h);
  background: var(--well); border: 1px solid var(--line);
  border-radius: 8px; overflow: hidden;
}
.gl-line { position: absolute; top: 0; bottom: 0; width: 1px; background: var(--grid); opacity: .8; }
.gl-line.beat { background: var(--line); width: 1px; opacity: 1; box-shadow: 0 0 0 .5px var(--grid); }
.midline { position: absolute; left: 0; right: 0; top: 50%; height: 1px; background: var(--grid); }

.note {
  position: absolute; top: 50%; width: 15px; height: 15px; margin: -7.5px 0 0 -7.5px;
  border-radius: 50%; border: 2px solid var(--accent); background: var(--surface);
  transition: background .14s ease, border-color .14s ease, transform .14s ease, box-shadow .14s ease;
}
.note.dim { border-color: var(--muted); opacity: .45; }
.note.lit { box-shadow: 0 0 0 5px var(--glow); }
.note.g-tight { background: var(--run); border-color: var(--run); }
.note.g-close { background: var(--accent); border-color: var(--accent); }
.note.g-off   { background: var(--danger); border-color: var(--danger); }
.note.g-miss  { border-color: var(--danger); border-style: dashed; background: transparent; opacity: .85; }

.tapmark {
  position: absolute; top: 14%; bottom: 14%; width: 2px; margin-left: -1px;
  background: var(--muted); border-radius: 2px; opacity: .9;
}
.tapmark.g-tight { background: var(--run); }
.tapmark.g-close { background: var(--accent); }
.tapmark.g-off   { background: var(--danger); }
.tapmark.g-extra { background: var(--danger); opacity: .5; top: 30%; bottom: 30%; }

.head {
  position: absolute; top: 0; bottom: 0; width: 2px; margin-left: -1px;
  background: var(--ink); opacity: .8;
}
.head::after {
  content: ""; position: absolute; top: 0; left: -3px; width: 8px; height: 5px;
  background: var(--ink); border-radius: 0 0 3px 3px;
}
.lane.idle .head { opacity: .30; }

.beatnums { position: relative; height: 16px; margin-top: 5px; }
.beatnums span {
  position: absolute; transform: translateX(-50%);
  font-family: var(--font-mono); font-size: 10.5px; letter-spacing: .06em;
  color: var(--muted); transition: color .1s ease;
}
.beatnums span.on { color: var(--ink); font-weight: 700; }

/* ── tap pad ──────────────────────────────────────────────────────────────── */
.pad {
  display: block; width: 100%; margin-top: 11px;
  font: inherit; text-align: center; cursor: pointer;
  background: var(--surface); border: 1px solid var(--line);
  border-left: 3px solid var(--line);
  border-radius: 9px; padding: 12px 12px 13px;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
  transition: background .16s ease, border-color .16s ease;
  overflow: hidden;
}
.pad:hover { border-color: var(--accent); }
.padtop {
  display: block; font-family: var(--font-mono); font-size: 10.5px;
  letter-spacing: .14em; color: var(--muted); margin-bottom: 3px;
}
.padbig {
  display: block; font-family: var(--font-mono); font-size: clamp(23px, 6.4vw, 34px);
  font-weight: 700; line-height: 1.05; color: var(--ink); font-variant-numeric: tabular-nums;
}
.padsub {
  display: block; font-size: 12.5px; color: var(--muted); margin-top: 4px; min-height: 1.2em;
}
.pad.g-tight { background: var(--run-soft); border-color: var(--run); border-left-color: var(--run); }
.pad.g-tight .padbig, .pad.g-tight .padtop { color: var(--run); }
.pad.g-close { background: var(--accent-soft); border-color: var(--accent); border-left-color: var(--accent); }
.pad.g-close .padbig, .pad.g-close .padtop { color: var(--accent); }
.pad.g-off, .pad.g-extra { background: var(--danger-soft); border-color: var(--danger); border-left-color: var(--danger); }
.pad.g-off .padbig, .pad.g-off .padtop, .pad.g-extra .padbig, .pad.g-extra .padtop { color: var(--danger); }
.pad.idle .padbig { font-size: clamp(16px, 4.2vw, 21px); font-weight: 600; letter-spacing: -.01em; }

/* ── ribbon ───────────────────────────────────────────────────────────────── */
.rib {
  position: relative; height: var(--rib-h);
  background: var(--well); border: 1px solid var(--line);
  border-radius: 8px; overflow: hidden;
}
.band { position: absolute; top: 0; bottom: 0; }
.band.ontime { left: 30%; right: 30%; background: var(--accent-soft); }
.band.tight  { left: 42%; right: 42%; background: var(--run-soft); }
.edgelab {
  position: absolute; top: 7px; font-family: var(--font-mono); font-size: 10px;
  letter-spacing: .12em; color: var(--muted); opacity: .8;
}
.edgelab.l { left: 9px; } .edgelab.r { right: 9px; }
.zero { position: absolute; left: 50%; top: 0; bottom: 0; width: 1px; background: var(--ink); opacity: .45; }
.gline { position: absolute; top: 0; bottom: 0; width: 1px; background: var(--grid); }
.mk {
  position: absolute; width: 3px; height: 10px; margin-left: -1.5px;
  border-radius: 2px; background: var(--muted);
  transition: left .18s ease, bottom .18s ease, opacity .18s ease;
}
.mk.tight { background: var(--run); }
.mk.close { background: var(--accent); }
.mk.off   { background: var(--danger); }
.meanline {
  position: absolute; top: 0; bottom: 0; width: 1px; margin-left: -.5px;
  background: var(--ink); opacity: .55;
  border-left: 1px dashed var(--ink);
  transition: left .2s ease;
}
.meanline span {
  position: absolute; top: 3px; left: 50%; transform: translateX(-50%);
  font-family: var(--font-mono); font-size: 10px; letter-spacing: .04em;
  background: var(--surface); border: 1px solid var(--line); border-radius: 99px;
  padding: 2px 6px; color: var(--ink); white-space: nowrap;
}
/* near an edge the label grows inwards, so it never runs off the ribbon */
.meanline.at-l span { left: 0; transform: none; }
.meanline.at-r span { left: auto; right: 0; transform: none; }
.meanline[hidden] { display: none; }
.ribaxis { position: relative; height: 15px; margin-top: 5px; }
.ribaxis span {
  position: absolute; transform: translateX(-50%);
  font-family: var(--font-mono); font-size: 10px; color: var(--muted);
}
.legend {
  display: flex; flex-wrap: wrap; gap: 5px 14px; margin-top: 9px;
  font-family: var(--font-mono); font-size: 10.5px; letter-spacing: .05em; color: var(--muted);
}
.legend i { display: inline-block; width: 8px; height: 8px; border-radius: 2px; margin-right: 5px; vertical-align: baseline; }
.legend i.t { background: var(--run); } .legend i.c { background: var(--accent); } .legend i.o { background: var(--danger); }

/* ── summary ──────────────────────────────────────────────────────────────── */
.sum { display: flex; flex-wrap: wrap; gap: 12px; align-items: stretch; }
/* Six tiles, so the column count is pinned to 6 / 3 / 2 rather than left to
   auto-fit — every layout lands on full rows instead of orphaning one tile. */
.hero {
  flex: 1 1 100%; min-width: 148px;
  background: var(--well); border: 1px solid var(--line); border-radius: 8px;
  padding: 11px 14px 12px; display: flex; flex-direction: column; justify-content: center;
}
@media (min-width: 620px) { .hero { flex: 0 1 auto; max-width: 190px; } }
.hero .hv {
  font-family: var(--font-mono); font-size: clamp(34px, 8.5vw, 46px); font-weight: 700;
  line-height: 1; letter-spacing: -.02em; font-variant-numeric: tabular-nums; color: var(--ink);
}
.hero .hv.good { color: var(--run); }
.hero .hl { font-family: var(--font-mono); font-size: 10.5px; letter-spacing: .12em; color: var(--muted); margin-top: 7px; }
.hero .hn { font-size: 12.5px; color: var(--muted); margin-top: 4px; }

.tiles {
  flex: 1 1 300px; min-width: 0;
  display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 8px;
}
@media (min-width: 540px) { .tiles { grid-template-columns: repeat(3, minmax(0, 1fr)); } }
@media (min-width: 880px) { .tiles { grid-template-columns: repeat(6, minmax(0, 1fr)); } }
.tile { border: 1px solid var(--line); border-radius: 8px; padding: 8px 10px 9px; min-width: 0; }
.tile .tv {
  font-family: var(--font-mono); font-size: 17px; font-weight: 600;
  font-variant-numeric: tabular-nums; color: var(--ink); line-height: 1.15;
  white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
}
.tile .tv.good { color: var(--run); }
.tile .tl { font-family: var(--font-mono); font-size: 9.5px; letter-spacing: .1em; color: var(--muted); margin-top: 4px; }

.spark { margin-top: 12px; }
.sparkbars {
  display: grid; grid-template-columns: repeat(16, 1fr); gap: 3px;
  height: 46px; align-items: end;
  padding: 6px 7px; background: var(--well); border: 1px solid var(--line); border-radius: 8px;
}
.sb { border-radius: 2px 2px 0 0; background: var(--line); min-height: 2px; transition: height .2s ease, background .2s ease; }
.sb.good { background: var(--run); } .sb.mid { background: var(--accent); } .sb.bad { background: var(--danger); }
.sb.none { background: transparent; border: 1px dashed var(--line); height: 100% !important; border-radius: 3px; }
.sparklab {
  display: flex; justify-content: space-between; margin-top: 4px;
  font-family: var(--font-mono); font-size: 9.5px; letter-spacing: .08em; color: var(--muted);
}
.verdict { margin: 11px 0 0; font-size: 13.5px; line-height: 1.55; color: var(--muted); }
.verdict b { color: var(--ink); font-weight: 600; }

.hint { margin: 0; color: var(--muted); font-size: 12.5px; line-height: 1.65; }
.hint kbd {
  font-family: var(--font-mono); font-size: 11px;
  border: 1px solid var(--line); border-bottom-width: 2px; border-radius: 5px;
  padding: 1px 5px; background: var(--surface); color: var(--ink);
}
.note-audio { font-family: var(--font-mono); font-size: 11.5px; color: var(--danger); margin: 9px 0 0; }
footer { font-family: var(--font-mono); font-size: 11.5px; color: var(--muted); letter-spacing: .04em; padding-top: 2px; }
.sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); clip-path: inset(50%); white-space: nowrap; }

@media (max-width: 460px) {
  :root { --lane-h: 96px; --rib-h: 112px; }
  .transport { gap: 8px 10px; }
  .chip { font-size: 12px; padding: 6px 10px; }
  .btn.primary { min-width: 108px; }
  .tile .tv { font-size: 15.5px; }
}

@media (prefers-reduced-motion: reduce) {
  * { animation-duration: .001ms !important; animation-iteration-count: 1 !important; transition-duration: .001ms !important; }
}
</style>
</head>
<body>
<div class="wrap">

  <header>
    <h1>Rhythm Trainer</h1>
    <p class="lede">The click marks the beat. Tap along with the dots &mdash; every tap is measured
      against the grid and reported in <b>milliseconds early or late</b>, then rolled into a
      16&#8209;bar report card.</p>
  </header>

  <section class="card" aria-label="Transport and settings">
    <div class="transport">
      <button id="play" class="btn primary" type="button"><span class="gl" aria-hidden="true">&#9654;</span><span id="playTxt">Play</span></button>
      <span id="stat" class="status"><i class="led" aria-hidden="true"></i><span id="statTxt">READY</span></span>
      <span class="readout">BAR&nbsp;<b id="barNo">&mdash;&mdash;</b><span class="sep">/</span><b>16</b></span>
      <span class="readout">ACC&nbsp;<b id="accNo">&mdash;&mdash;</b></span>
      <span class="readout">STREAK&nbsp;<b id="strNo">0</b></span>
      <span class="spacer"></span>
      <button id="mute" class="btn small" type="button">Sound on</button>
    </div>
    <div class="controls">
      <div class="knob">
        <label class="kl" for="tempo"><span>TEMPO</span><span class="kv"><span id="tempoV">96</span> BPM</span></label>
        <input id="tempo" type="range" min="50" max="180" step="1" value="96" aria-label="Tempo in beats per minute">
      </div>
      <div class="pat" role="group" aria-label="Pattern">
        <span class="grouplabel">PATTERN</span>
        <button class="chip" type="button" data-pat="quarters" aria-pressed="true">Quarters</button>
        <button class="chip" type="button" data-pat="eighths" aria-pressed="false">Eighths</button>
        <button class="chip" type="button" data-pat="offbeats" aria-pressed="false">Offbeats</button>
        <span id="pending" class="pending" hidden></span>
      </div>
    </div>
    <p id="audioNote" class="note-audio" hidden>Sound is unavailable in this browser &mdash; the visual metronome and scoring still work.</p>
  </section>

  <section class="card" aria-label="Bar view">
    <div class="cardhead"><span class="tag">THIS BAR</span><span id="laneNote">clicks on 1 2 3 4 &middot; tap every dot</span></div>
    <div class="lanewrap">
      <div class="lane idle" id="lane">
        <div class="midline"></div>
        <div id="glines"></div>
        <div id="notes"></div>
        <div id="taps"></div>
        <div class="head" id="head" style="left:3.5%"></div>
      </div>
      <div class="beatnums" id="beatnums"></div>
    </div>
    <button class="pad idle" id="pad" type="button" aria-label="Tap in time with the beat">
      <span class="padtop" id="padTop">TAP HERE</span>
      <span class="padbig" id="padBig">Tap here &mdash; or press Play &mdash; to start</span>
      <span class="padsub" id="padSub">space bar, mouse, or touch &mdash; whatever you have</span>
    </button>
  </section>

  <section class="card" aria-label="Timing ribbon">
    <div class="cardhead"><span class="tag">TIMING RIBBON</span><span>last 26 scored taps &middot; newest at the bottom</span></div>
    <div class="rib" id="rib">
      <div class="band ontime"></div>
      <div class="band tight"></div>
      <div class="gline" style="left:30%"></div>
      <div class="gline" style="right:30%"></div>
      <div class="zero"></div>
      <span class="edgelab l">EARLY</span><span class="edgelab r">LATE</span>
      <div id="marks"></div>
      <div class="meanline" id="meanline" hidden><span id="meanTxt">+0 ms</span></div>
    </div>
    <div class="ribaxis" id="ribaxis"></div>
    <div class="legend">
      <span><i class="t"></i>TIGHT &plusmn;20 MS</span>
      <span><i class="c"></i>ON TIME &plusmn;50 MS</span>
      <span><i class="o"></i>OFF THE GRID</span>
      <span>DASHED LINE = YOUR AVERAGE</span>
    </div>
  </section>

  <section class="card" aria-label="Session summary">
    <div class="cardhead"><span class="tag">16-BAR SESSION</span><span id="sumNote">sample run &middot; 96 BPM &middot; quarters</span></div>
    <div class="sum">
      <div class="hero">
        <div class="hv" id="sAcc">&mdash;</div>
        <div class="hl">ACCURACY</div>
        <div class="hn" id="sAccNote">taps inside &plusmn;50 ms</div>
      </div>
      <div class="tiles">
        <div class="tile"><div class="tv" id="sOn">&mdash;</div><div class="tl">ON TIME</div></div>
        <div class="tile"><div class="tv" id="sTight">&mdash;</div><div class="tl">TIGHT &plusmn;20 MS</div></div>
        <div class="tile"><div class="tv" id="sAvg">&mdash;</div><div class="tl">AVG OFFSET</div></div>
        <div class="tile"><div class="tv" id="sSd">&mdash;</div><div class="tl">SPREAD</div></div>
        <div class="tile"><div class="tv" id="sStreak">&mdash;</div><div class="tl">BEST STREAK</div></div>
        <div class="tile"><div class="tv" id="sMiss">&mdash;</div><div class="tl">MISSED / EXTRA</div></div>
      </div>
    </div>
    <div class="spark">
      <div class="sparkbars" id="spark"></div>
      <div class="sparklab"><span>BAR 1</span><span>BAR 8</span><span>BAR 16</span></div>
    </div>
    <p class="verdict" id="verdict"></p>
  </section>

  <p class="hint"><kbd>Space</kbd> tap &middot; <kbd>Enter</kbd> on Play to start &middot; <kbd>Esc</kbd> stop.
    A one-bar count-in runs first, then 16 bars are scored. Nothing leaves this page.</p>
  <footer>demo &middot; sloprun.dev</footer>
  <div class="sr" id="live" role="status" aria-live="polite"></div>
</div>

<script>
(function () {
  "use strict";

  var root = document.documentElement;
  function $(id) { return document.getElementById(id); }

  var reduced = false;
  try { reduced = window.matchMedia("(prefers-reduced-motion: reduce)").matches; } catch (e) {}

  /* ── geometry: bar position 0..1 → percent across the lane ───────────────── */
  var PAD_L = 3.5, SPAN = 93;
  function X(p) { return PAD_L + p * SPAN; }
  function clamp(v, a, b) { return v < a ? a : (v > b ? b : v); }
  function pad2(n) { return n < 10 ? "0" + n : "" + n; }

  /* ── the exercise ─────────────────────────────────────────────────────────
     The metronome always clicks the four quarter notes. The pattern says which
     sixteenth-grid slots you are supposed to tap. Offbeats is the hard one:
     nothing sounds where your hands go.                                       */
  var PATTERNS = {
    quarters: { slots: [0, 4, 8, 12],                 label: "quarters",
                note: "clicks on 1 2 3 4 · tap every click" },
    eighths:  { slots: [0, 2, 4, 6, 8, 10, 12, 14],   label: "eighths",
                note: "clicks on 1 2 3 4 · tap twice per click" },
    offbeats: { slots: [2, 6, 10, 14],                label: "offbeats",
                note: "clicks on 1 2 3 4 · tap only between the clicks" }
  };
  var BARS = 16, TIGHT = 20, ONTIME = 50, MARKS = 26, RANGE = 125;

  /* ── audio ────────────────────────────────────────────────────────────────
     Every sound here is synthesised on the spot — no files, no network.       */
  var ctx = null, master = null, bus = null, audioDead = false, lat = 0, muted = false;

  function ensureAudio() {
    if (ctx || audioDead) return;
    var AC = window.AudioContext || window.webkitAudioContext;
    if (!AC) { audioDead = true; $("audioNote").hidden = false; return; }
    try {
      ctx = new AC();
      master = ctx.createGain();
      master.gain.value = muted ? 0 : 0.9;
      master.connect(ctx.destination);
      bus = ctx.createGain(); bus.connect(master);
    } catch (e) { ctx = null; audioDead = true; $("audioNote").hidden = false; }
  }
  var lastResume = -9;
  function resume() {
    /* throttled: if the browser is still holding audio back, do not retry on
       every single tap (each attempt logs a warning). */
    if (!ctx || ctx.state !== "suspended") return;
    var n = T();
    if (n - lastResume < 1) return;
    lastResume = n;
    try { ctx.resume(); } catch (e) {}
  }

  function click(tp, accent) {
    if (!ctx || !bus) return;
    try {
      /* tp is on the page clock; convert to the audio clock at schedule time.
         The two are read microseconds apart, so the offset is exact enough. */
      var t = ctx.currentTime + (tp - T());
      if (t < ctx.currentTime) t = ctx.currentTime;
      var o = ctx.createOscillator(), g = ctx.createGain();
      var f = accent ? 1568 : 1046;
      o.type = "sine";
      o.frequency.setValueAtTime(f, t);
      o.frequency.exponentialRampToValueAtTime(f * 0.7, t + 0.04);
      g.gain.setValueAtTime(0.0001, t);
      g.gain.exponentialRampToValueAtTime(accent ? 0.5 : 0.28, t + 0.002);
      g.gain.exponentialRampToValueAtTime(0.0001, t + 0.055);
      o.connect(g); g.connect(bus);
      o.start(t); o.stop(t + 0.09);
    } catch (e) {}
  }
  function tapSound() {
    if (!ctx || !master) return;
    try {
      var t = ctx.currentTime;
      var o = ctx.createOscillator(), g = ctx.createGain(), f = ctx.createBiquadFilter();
      o.type = "triangle";
      o.frequency.setValueAtTime(600, t);
      o.frequency.exponentialRampToValueAtTime(280, t + 0.045);
      f.type = "lowpass"; f.frequency.value = 2400;
      g.gain.setValueAtTime(0.0001, t);
      g.gain.exponentialRampToValueAtTime(0.15, t + 0.002);
      g.gain.exponentialRampToValueAtTime(0.0001, t + 0.06);
      o.connect(f); f.connect(g); g.connect(master);
      o.start(t); o.stop(t + 0.1);
    } catch (e) {}
  }

  /* ── clock: audio clock when we have one, wall clock when we don't ───────── */
  var perf0 = (window.performance && performance.now) ? performance.now() : Date.now();
  function pnow() { return ((window.performance && performance.now) ? performance.now() : Date.now()) - perf0; }
  function T() { return pnow() / 1000; }

  /* ── session state ───────────────────────────────────────────────────────── */
  var state = "idle";        /* idle | countin | running | done */
  var playing = false;
  var bars = [], notes = [], extras = 0;
  var barIndex = 0, barStart = 0, schedTimer = null, endTime = 0, doneAt = -99;
  var cfg  = { bpm: 96, pat: "quarters" };
  var want = { bpm: 96, pat: "quarters" };
  var shownBar = -99, curBar = null, streak = 0, lastLit = -2, lastBeat = -1, lastCount = -1;
  var recent = [], gradeMap = {};
  var sample = null;

  function barDurOf(bpm) { return 4 * 60 / bpm; }
  function winFor(pat, bpm) {
    var slotDur = barDurOf(bpm) / 16;
    var s = PATTERNS[pat].slots;
    var gap = (s.length > 1 ? (s[1] - s[0]) : 4) * slotDur;
    return Math.min(0.2, gap * 0.48);
  }
  function gradeOf(ms) { var a = Math.abs(ms); return a <= TIGHT ? "tight" : (a <= ONTIME ? "close" : "off"); }
  function isOn(g) { return g === "tight" || g === "close"; }
  function fmtMs(ms) {
    var r = Math.round(ms);
    return (r > 0 ? "+" : (r < 0 ? "−" : "±")) + Math.abs(r) + " ms";
  }
  function mono(txt) {
    return '<b style="font-family:var(--font-mono);font-variant-numeric:tabular-nums">' + txt + "</b>";
  }

  /* ── scheduling ───────────────────────────────────────────────────────────
     Whole bars are queued a fraction of a second ahead, each event pinned to an
     absolute time on the audio clock, so repaints never nudge the beat.        */
  function scheduleBar(i, t0, dur, c) {
    var slotDur = dur / 16, b, k;
    for (b = 0; b < 4; b++) click(t0 + b * 4 * slotDur, b === 0);
    if (i >= 1) {
      /* Each note carries the window it was written with. Bars are queued up to
         0.45 s early, so by the time you tap the last note of a bar the live
         config may already belong to the next one — a note judged by someone
         else's tempo would be scored against a grid that is not on screen. */
      var slots = PATTERNS[c.pat].slots, w = winFor(c.pat, c.bpm);
      for (k = 0; k < slots.length; k++) {
        notes.push({ bar: i, slot: slots[k], time: t0 + slots[k] * slotDur + lat,
                     win: w, resolved: false, off: 0, grade: null });
      }
    }
  }
  function adoptPending() {
    if (cfg.bpm !== want.bpm || cfg.pat !== want.pat) {
      cfg = { bpm: want.bpm, pat: want.pat };
      updatePending();
    }
  }
  /* The engine owns everything the score depends on: queueing bars, advancing the
     bar view, expiring missed notes and ending the session. It runs on a timer,
     not on animation frames — a backgrounded tab throttles frames to nothing, and
     a session that silently froze there would be worse than one that keeps time. */
  function engine() {
    if (!playing) return;
    var now = T(), i, n;

    while (barIndex <= BARS && barStart < now + 0.45) {
      adoptPending();
      var dur = barDurOf(cfg.bpm);
      scheduleBar(barIndex, barStart, dur, cfg);
      bars.push({ i: barIndex, t0: barStart + lat, dur: dur, pat: cfg.pat, bpm: cfg.bpm });
      barStart += dur; barIndex++;
    }
    if (barIndex > BARS && !endTime) {
      var lb = bars[bars.length - 1];
      endTime = lb.t0 + lb.dur + winFor(lb.pat, lb.bpm) + 0.05;
    }

    var cb = null;
    for (i = bars.length - 1; i >= 0; i--) { if (bars[i].t0 <= now) { cb = bars[i]; break; } }
    if (cb) {
      curBar = cb;
      if (cb.i !== shownBar) {
        shownBar = cb.i; lastLit = -2; lastCount = -1;
        clearTaps(); renderLane(cb.i, cb.pat); setLaneNote(cb.pat);
        if (cb.i >= 1) state = "running";
        setStatus(); updateReadouts();
        if (cb.i >= 1) {
          paintSummary(computeStats(notes, extras), "recording · bar " + cb.i + " of " + BARS, false);
        }
      }
    }

    var changed = false;
    for (i = 0; i < notes.length; i++) {
      n = notes[i];
      if (!n.resolved && now > n.time + n.win) {
        n.resolved = true; n.grade = "miss";
        gradeMap[n.bar + ":" + n.slot] = "miss";
        streak = 0; changed = true; markNoteEl(n);
      }
    }
    if (changed) updateReadouts();
    if (endTime && now > endTime) finish();
  }

  /* ── transport ────────────────────────────────────────────────────────────── */
  function start() {
    ensureAudio(); resume();
    lat = 0;
    if (ctx) {
      lat = (typeof ctx.outputLatency === "number" && ctx.outputLatency > 0)
        ? ctx.outputLatency : (ctx.baseLatency || 0);
      if (lat > 0.35) lat = 0.35;
      try { if (bus) bus.disconnect(); } catch (e) {}
      bus = ctx.createGain(); bus.connect(master);
    }
    notes = []; bars = []; extras = 0; recent = []; gradeMap = {};
    streak = 0; shownBar = -99; curBar = null; lastLit = -2; lastBeat = -1; lastCount = -1;
    endTime = 0; doneAt = -99;
    cfg = { bpm: want.bpm, pat: want.pat };
    barIndex = 0; barStart = T() + 0.4;
    playing = true; state = "countin";

    $("lane").classList.remove("idle");
    clearTaps(); renderLane(0, cfg.pat); setLaneNote(cfg.pat);
    setHead(0); setBeat(0);
    renderRibbon(recent); updateReadouts(); setPlayBtn();
    paintSummary(computeStats(notes, 0), "count-in · nothing scored yet", false);
    updatePending(); setStatus();
    setPad("", "COUNT-IN", "–", "one free bar, then 16 scored bars");
    say("Count-in. Tap along with the click.");
    schedTimer = setInterval(engine, 25);
    engine();
    try { $("pad").focus({ preventScroll: true }); } catch (e) { try { $("pad").focus(); } catch (e2) {} }
  }

  function silence() {
    if (ctx && bus) {
      try {
        var n = ctx.currentTime;
        bus.gain.cancelScheduledValues(n);
        bus.gain.setValueAtTime(0, n);
      } catch (e) {}
    }
  }

  function finish() {
    if (!playing) return;
    playing = false;
    if (schedTimer) { clearInterval(schedTimer); schedTimer = null; }
    silence();
    var now = T(), keep = [], i, n;
    for (i = 0; i < notes.length; i++) {
      n = notes[i];
      if (!n.resolved) {
        if (n.time <= now) { n.resolved = true; n.grade = "miss"; gradeMap[n.bar + ":" + n.slot] = "miss"; }
        else continue;                     /* never happened — do not score it */
      }
      keep.push(n);
    }
    notes = keep;
    state = "done"; doneAt = now;
    var st = computeStats(notes, extras);
    var barsPlayed = shownBar >= 1 ? shownBar : 0;
    var label = (barsPlayed >= BARS ? "complete · "
                 : (barsPlayed ? "stopped at bar " + barsPlayed + " · " : "stopped in the count-in · "))
      + cfg.bpm + " BPM · " + PATTERNS[cfg.pat].label;
    $("lane").classList.add("idle");
    if (st.n) paintSummary(st, label, true); else showSample();
    setPlayBtn(); setStatus();
    if (st.n) updateReadouts();   /* nothing scored → keep the sample readouts */
    if (st.n) {
      setPad(st.acc >= 0.9 ? "g-tight" : "", "SESSION DONE",
             Math.round(st.acc * 100) + "%",
             "of " + st.n + " notes landed inside ±50 ms · tap for another 16 bars");
      say("Session finished. " + Math.round(st.acc * 100) + " percent on time, average offset "
        + Math.round(st.mean) + " milliseconds.");
    } else {
      setPad("", "SESSION DONE", "NO SCORE", "it stopped before a scored bar · tap for another 16 bars");
      say("Session finished.");
    }
  }

  /* ── tapping and scoring ─────────────────────────────────────────────────── */
  function tap() {
    ensureAudio(); resume();
    if (!playing) {
      if (state === "done" && T() - doneAt < 0.9) return;   /* stray tap on the last note */
      start(); return;
    }
    var t = T();
    tapSound();
    var best = null, bd = 1e9, i, n, d;
    for (i = 0; i < notes.length; i++) {
      n = notes[i];
      if (n.resolved) continue;
      d = Math.abs(t - n.time);
      if (d < bd) { bd = d; best = n; }
    }
    if (best && bd <= best.win) {
      var off = (t - best.time) * 1000;
      best.resolved = true; best.off = off; best.grade = gradeOf(off);
      gradeMap[best.bar + ":" + best.slot] = best.grade;
      recent.unshift({ off: off, grade: best.grade });
      if (recent.length > MARKS) recent.pop();
      streak = isOn(best.grade) ? streak + 1 : 0;
      addTapMark(t, best.grade); markNoteEl(best);
      renderRibbon(recent); updateReadouts();
      setPad("g-" + best.grade,
             best.grade === "tight" ? "TIGHT" : (best.grade === "close" ? "ON TIME" : "OFF THE GRID"),
             fmtMs(off),
             Math.round(off) === 0 ? "dead on the grid line"
               : (off < 0 ? "ahead of the beat" : "behind the beat"));
    } else if (state === "countin") {
      setPad("", "COUNT-IN", "–", "warming up — scoring starts at bar 1");
    } else {
      extras++; streak = 0;
      addTapMark(t, "extra"); updateReadouts();
      setPad("g-extra", "NO NOTE THERE", "–", "that tap was not near any dot");
    }
  }

  /* ── frame loop: purely what you can see ─────────────────────────────────── */
  function frame() {
    requestAnimationFrame(frame);
    var p;
    if (playing) {
      if (!curBar) return;
      p = clamp((T() - curBar.t0) / curBar.dur, 0, 1);
      setHead(p); setBeat(p); lightNotes(p, curBar.pat);
      if (state === "countin") countIn(p);
    } else if (state === "idle" && !reduced) {
      var dur = barDurOf(want.bpm);
      p = (pnow() / 1000 % dur) / dur;
      setHead(p); setBeat(p); lightNotes(p, want.pat);
    }
  }

  /* ── lane rendering ──────────────────────────────────────────────────────── */
  function buildGrid() {
    var html = "", s;
    for (s = 0; s < 16; s++) {
      html += '<div class="gl-line' + (s % 4 === 0 ? " beat" : "") + '" style="left:' + X(s / 16) + '%"></div>';
    }
    $("glines").innerHTML = html;
    var b, bn = "";
    for (b = 0; b < 4; b++) bn += '<span data-b="' + b + '" style="left:' + X(b / 4) + '%">' + (b + 1) + "</span>";
    $("beatnums").innerHTML = bn;
  }
  function renderLane(barIdx, pat) {
    var slots = PATTERNS[pat].slots, html = "", k, s, g;
    for (k = 0; k < slots.length; k++) {
      s = slots[k];
      g = barIdx >= 1 ? gradeMap[barIdx + ":" + s] : null;
      html += '<div class="note' + (barIdx === 0 ? " dim" : "") + (g ? " g-" + g : "")
        + '" data-slot="' + s + '" style="left:' + X(s / 16) + '%"></div>';
    }
    $("notes").innerHTML = html;
  }
  function markNoteEl(n) {
    if (n.bar !== shownBar) return;
    var el = $("notes").querySelector('[data-slot="' + n.slot + '"]');
    if (el) el.className = "note g-" + n.grade;
  }
  function clearTaps() { $("taps").innerHTML = ""; }
  function addTapMark(t, grade) {
    if (!curBar) return;
    var p = clamp((t - curBar.t0) / curBar.dur, 0, 1);
    var d = document.createElement("div");
    d.className = "tapmark g-" + grade;
    d.style.left = X(p) + "%";
    $("taps").appendChild(d);
  }
  function setHead(p) { $("head").style.left = X(reduced ? Math.floor(p * 16) / 16 : p) + "%"; }
  function setBeat(p) {
    var b = Math.min(3, Math.floor(p * 4));
    if (b === lastBeat) return;
    lastBeat = b;
    var els = $("beatnums").children, i;
    for (i = 0; i < els.length; i++) els[i].className = (i === b ? "on" : "");
  }
  function lightNotes(p, pat) {
    var slots = PATTERNS[pat].slots, cur = -1, k;
    for (k = 0; k < slots.length; k++) if (p >= slots[k] / 16) cur = slots[k];
    if (cur === lastLit) return;
    lastLit = cur;
    var els = $("notes").children, i;
    for (i = 0; i < els.length; i++) els[i].classList.remove("lit");
    if (cur >= 0) {
      var e = $("notes").querySelector('[data-slot="' + cur + '"]');
      if (e) e.classList.add("lit");
    }
  }
  function setLaneNote(pat) { $("laneNote").textContent = PATTERNS[pat].note; }
  function countIn(p) {
    var c = Math.min(4, 1 + Math.floor(p * 4));
    if (c === lastCount) return;
    lastCount = c;
    setPad("", "COUNT-IN", String(c), "one free bar, then 16 scored bars");
  }

  /* ── the timing ribbon ───────────────────────────────────────────────────── */
  var markEls = [], ribH = 132, ribList = [];
  function measureRib() {
    var h = $("rib").clientHeight;
    if (h > 40) ribH = h;
  }
  /* marks stack upward from the floor; the gap between them is derived from the
     ribbon height so all of them fit, and the top strip stays free for the
     average label. */
  function markStep() {
    var s = (ribH - 44) / (MARKS - 1);
    return clamp(s, 2.4, 4.4);
  }
  function buildRibbon() {
    var frag = document.createDocumentFragment(), i, d;
    for (i = 0; i < MARKS; i++) {
      d = document.createElement("div");
      d.className = "mk"; d.style.opacity = "0"; d.style.left = "50%"; d.style.bottom = "7px";
      frag.appendChild(d); markEls.push(d);
    }
    $("marks").appendChild(frag);
    var vals = [-100, -50, 0, 50, 100], html = "";
    for (i = 0; i < vals.length; i++) {
      html += '<span style="left:' + (50 + vals[i] / (RANGE * 2) * 100) + '%">'
        + (vals[i] > 0 ? "+" : (vals[i] < 0 ? "−" : "")) + Math.abs(vals[i])
        + (vals[i] === 0 ? " ms" : "") + "</span>";
    }
    $("ribaxis").innerHTML = html;
  }
  function renderRibbon(list) {
    ribList = list;
    var i, d, sum = 0, step = markStep();
    for (i = 0; i < MARKS; i++) {
      d = list[i];
      if (!d) { markEls[i].style.opacity = "0"; continue; }
      markEls[i].className = "mk " + d.grade;
      markEls[i].style.left = (50 + clamp(d.off, -RANGE, RANGE) / (RANGE * 2) * 100) + "%";
      markEls[i].style.bottom = (7 + i * step) + "px";
      markEls[i].style.opacity = String(Math.max(0.14, 1 - i * 0.033));
      sum += d.off;
    }
    var ml = $("meanline");
    if (list.length >= 4) {
      var m = sum / list.length;
      var pos = 50 + clamp(m, -RANGE, RANGE) / (RANGE * 2) * 100;
      ml.hidden = false;
      ml.style.left = pos + "%";
      ml.className = "meanline" + (pos < 22 ? " at-l" : (pos > 78 ? " at-r" : ""));
      $("meanTxt").textContent = fmtMs(m) + (m < -3 ? " early" : (m > 3 ? " late" : ""));
    } else ml.hidden = true;
  }

  /* ── statistics ──────────────────────────────────────────────────────────── */
  function computeStats(list, extraCount) {
    var st = { n: 0, on: 0, tight: 0, missed: 0, acc: 0, mean: 0, sd: 0, best: 0,
               extras: extraCount || 0, perBar: [] }, i, b;
    for (b = 0; b < BARS; b++) st.perBar.push({ n: 0, on: 0 });
    var offs = [], run = 0;
    for (i = 0; i < list.length; i++) {
      var n = list[i];
      if (!n.resolved) continue;
      st.n++;
      var pb = st.perBar[n.bar - 1];
      if (pb) pb.n++;
      if (n.grade === "miss") { st.missed++; run = 0; }
      else {
        offs.push(n.off);
        if (n.grade === "tight") st.tight++;
        if (isOn(n.grade)) {
          st.on++; if (pb) pb.on++;
          run++; if (run > st.best) st.best = run;
        } else run = 0;
      }
    }
    st.acc = st.n ? st.on / st.n : 0;
    if (offs.length) {
      var s = 0;
      for (i = 0; i < offs.length; i++) s += offs[i];
      st.mean = s / offs.length;
      var v = 0;
      for (i = 0; i < offs.length; i++) v += (offs[i] - st.mean) * (offs[i] - st.mean);
      st.sd = Math.sqrt(v / offs.length);
    }
    return st;
  }

  function paintSummary(st, note, final) {
    $("sumNote").textContent = note;
    var accEl = $("sAcc");
    accEl.textContent = st.n ? Math.round(st.acc * 100) + "%" : "–";
    accEl.className = "hv" + (st.n && st.acc >= 0.9 ? " good" : "");
    $("sAccNote").textContent = st.n
      ? st.on + " of " + st.n + " notes inside ±50 ms"
      : "taps inside ±50 ms of the grid";
    $("sOn").textContent = st.n ? st.on + "/" + st.n : "–";
    $("sOn").className = "tv" + (st.n && st.acc >= 0.9 ? " good" : "");
    $("sTight").textContent = st.n ? String(st.tight) : "–";
    $("sAvg").textContent = st.n - st.missed > 0 ? fmtMs(st.mean) : "–";
    $("sAvg").parentNode.querySelector(".tl").textContent =
      "AVG OFFSET" + (st.n - st.missed > 0 ? (st.mean < -3 ? " · EARLY" : (st.mean > 3 ? " · LATE" : " · CENTRED")) : "");
    $("sSd").textContent = st.n - st.missed > 0 ? "±" + Math.round(st.sd) + " ms" : "–";
    $("sStreak").textContent = st.n ? String(st.best) : "–";
    $("sMiss").textContent = st.n ? st.missed + " / " + st.extras : "–";

    var html = "", i, pb, ratio, cls;
    for (i = 0; i < BARS; i++) {
      pb = st.perBar[i];
      if (!pb.n) { html += '<div class="sb none" title="bar ' + (i + 1) + ': not played"></div>'; continue; }
      ratio = pb.on / pb.n;
      cls = ratio >= 0.9 ? "good" : (ratio >= 0.5 ? "mid" : "bad");
      html += '<div class="sb ' + cls + '" style="height:' + Math.max(8, ratio * 100) + '%" title="bar '
        + (i + 1) + ": " + pb.on + "/" + pb.n + ' on time"></div>';
    }
    $("spark").innerHTML = html;
    $("verdict").innerHTML = verdict(st, final);
  }

  function verdict(st, final) {
    if (!st.n) {
      return final ? "Nothing was scored — the count-in is free, the 16 bars after it are not."
                   : "The report card fills in bar by bar, starting the moment bar 1 begins.";
    }
    var pct = Math.round(st.acc * 100), m = Math.round(st.mean), sd = Math.round(st.sd);
    if (!final) {
      return "Recording. " + mono(pct + "%") + " on time so far, longest clean run "
        + mono(st.best) + " notes.";
    }
    var s1;
    if (st.acc >= 0.95) s1 = "Locked in — " + mono(pct + "%") + " of your taps landed inside " + mono("50 ms") + " of the grid.";
    else if (st.acc >= 0.9) s1 = "Solid: " + mono(pct + "%") + " on time, with " + mono(st.tight) + " taps inside the tight " + mono("20 ms") + " band.";
    else if (st.acc >= 0.7) s1 = "Getting there — " + mono(pct + "%") + " on time. The " + mono("90%") + " line is what turns this panel green.";
    else s1 = "Rough run — " + mono(pct + "%") + " on time. Drop the tempo and let the click lead you.";
    var s2;
    if (st.n - st.missed === 0) s2 = "No taps landed near a dot, so there is no offset to report yet.";
    else if (m < -12) s2 = "You sit ahead of the click by " + mono(Math.abs(m) + " ms") + " on average — the classic rush. Let the click arrive before you move.";
    else if (m > 12) s2 = "You land behind the click by " + mono(m + " ms") + " on average. Aiming a hair early usually fixes it.";
    else s2 = "Your average sits " + mono(Math.abs(m) + " ms") + " from the grid line, which is genuinely centred.";
    var s3 = (st.n - st.missed) < 4 ? ""
      : (sd <= 18 ? " Spread is " + mono("±" + sd + " ms") + ", so the timing is repeatable, not lucky."
                  : " Spread is " + mono("±" + sd + " ms") + " — tightening that is the next win.");
    var s4 = st.missed ? " " + mono(st.missed) + (st.missed === 1 ? " note" : " notes") + " went by untapped." : "";
    return s1 + " " + s2 + s3 + s4;
  }

  /* ── readouts and chrome ─────────────────────────────────────────────────── */
  function rollingAcc() {
    var r = [], i;
    for (i = notes.length - 1; i >= 0 && r.length < 16; i--) if (notes[i].resolved) r.push(notes[i]);
    if (!r.length) return null;
    var ok = 0;
    for (i = 0; i < r.length; i++) if (isOn(r[i].grade)) ok++;
    return ok / r.length;
  }
  function updateReadouts() {
    $("barNo").textContent = shownBar >= 1 ? pad2(Math.min(shownBar, BARS)) : "——";
    /* while you play these track the last 16 notes, so they react as you go; once
       the session is over they switch to the whole run and agree with the card. */
    var a, s;
    if (state === "done") {
      var st = computeStats(notes, extras);
      a = st.n ? st.acc : null; s = st.n ? st.best : 0;
    } else { a = rollingAcc(); s = streak; }
    var el = $("accNo");
    if (a === null) { el.textContent = "——"; el.className = ""; }
    else { el.textContent = Math.round(a * 100) + "%"; el.className = a >= 0.9 ? "good" : ""; }
    $("strNo").textContent = String(s);
  }
  function setStatus() {
    var el = $("stat"), t = $("statTxt");
    el.className = "status";
    if (state === "countin") { el.className = "status live"; t.textContent = "COUNT-IN"; }
    else if (state === "running") { el.className = "status live"; t.textContent = "BAR " + pad2(Math.min(shownBar, BARS)) + "/16"; }
    else if (state === "done") {
      var st = computeStats(notes, extras);
      if (st.n && st.acc >= 0.9) { el.className = "status good"; t.textContent = "DONE · " + Math.round(st.acc * 100) + "%"; }
      else t.textContent = "DONE";
    } else t.textContent = "READY";
  }
  function setPlayBtn() {
    var b = $("play");
    var gl = b.querySelector(".gl");
    if (playing) {
      b.classList.add("on");
      $("playTxt").textContent = "Stop";
      if (gl) gl.innerHTML = "&#9632;";
    } else {
      b.classList.remove("on");
      $("playTxt").textContent = state === "done" ? "Run it again" : "Play";
      if (gl) gl.innerHTML = "&#9654;";
    }
  }
  function setPad(cls, top, big, sub) {
    var p = $("pad");
    p.className = "pad " + (cls || "");
    $("padTop").textContent = top;
    $("padBig").textContent = big;
    $("padSub").textContent = sub;
  }
  function updatePending() {
    var el = $("pending");
    if (playing && (cfg.bpm !== want.bpm || cfg.pat !== want.pat)) {
      var parts = [];
      if (cfg.bpm !== want.bpm) parts.push(want.bpm + " BPM");
      if (cfg.pat !== want.pat) parts.push(PATTERNS[want.pat].label);
      el.textContent = "→ " + parts.join(" · ") + " at the next bar";
      el.hidden = false;
    } else el.hidden = true;
  }
  var liveEl, sayTimer = null;
  function say(msg) {
    clearTimeout(sayTimer);
    liveEl.textContent = "";
    sayTimer = setTimeout(function () { liveEl.textContent = msg; }, 110);
  }

  /* ── the sample run shown on load ────────────────────────────────────────── */
  function makeSample() {
    var seed = 20260813;
    function rnd() { seed = (seed * 1664525 + 1013904223) % 4294967296; return seed / 4294967296; }
    function gauss() { return (rnd() + rnd() + rnd() + rnd() + rnd() + rnd() - 3) / 1.0; }
    var list = [], missAt = { 19: 1, 34: 1, 51: 1, 62: 1 }, b, k, idx = 0;
    var slots = PATTERNS.quarters.slots;
    for (b = 1; b <= BARS; b++) {
      for (k = 0; k < slots.length; k++) {
        var n = { bar: b, slot: slots[k], time: 0, resolved: true, off: 0, grade: null };
        if (missAt[idx]) { n.grade = "miss"; }
        else {
          var drift = 16 + (b - 8) * 0.9;            /* creeps later as the run goes on */
          n.off = drift + gauss() * 30;
          n.grade = gradeOf(n.off);
        }
        list.push(n); idx++;
      }
    }
    return list;
  }
  function showSample() {
    sample = makeSample();
    var st = computeStats(sample, 2);
    paintSummary(st, "sample run · 96 BPM · quarters", true);
    var r = [], i;
    for (i = sample.length - 1; i >= 0 && r.length < MARKS; i--) {
      if (sample[i].grade !== "miss") r.push({ off: sample[i].off, grade: sample[i].grade });
    }
    renderRibbon(r);
    $("barNo").textContent = "——";
    $("accNo").textContent = Math.round(st.acc * 100) + "%";
    $("accNo").className = st.acc >= 0.9 ? "good" : "";
    $("strNo").textContent = "——";
    $("sumNote").textContent = "sample run · 96 BPM · quarters · press Play for your own";
  }

  /* ── controls ────────────────────────────────────────────────────────────── */
  function wire() {
    $("play").addEventListener("click", function () {
      ensureAudio(); resume();
      if (playing) { finish(); say("Stopped."); } else start();
    });

    $("tempo").addEventListener("input", function () {
      want.bpm = +this.value;
      $("tempoV").textContent = want.bpm;
      if (!playing) { cfg.bpm = want.bpm; }
      updatePending();
    });

    var chips = document.querySelectorAll(".chip[data-pat]");
    Array.prototype.forEach.call(chips, function (c) {
      c.addEventListener("click", function () {
        want.pat = c.getAttribute("data-pat");
        Array.prototype.forEach.call(chips, function (o) {
          o.setAttribute("aria-pressed", o === c ? "true" : "false");
        });
        if (!playing) {
          cfg.pat = want.pat; lastLit = -2;
          renderLane(-1, want.pat); setLaneNote(want.pat);
        }
        updatePending();
        say(PATTERNS[want.pat].label + ": " + PATTERNS[want.pat].note);
      });
    });

    /* The label carries the state ("Sound on" / "Sound off"), so no aria-pressed:
       a toggle announced as "Sound off, pressed" reads as its own opposite. */
    $("mute").addEventListener("click", function () {
      muted = !muted;
      this.className = "btn small" + (muted ? " off" : "");
      this.textContent = muted ? "Sound off" : "Sound on";
      ensureAudio();
      if (master) { try { master.gain.value = muted ? 0 : 0.9; } catch (e) {} }
      say(muted ? "Sound off. The visual metronome and scoring keep running."
                : "Sound on.");
    });

    var pad = $("pad");
    function padDown(e) {
      if (e.cancelable) e.preventDefault();
      try { pad.focus({ preventScroll: true }); } catch (e2) { try { pad.focus(); } catch (e3) {} }
      tap();
    }
    if (window.PointerEvent) pad.addEventListener("pointerdown", padDown);
    else {
      pad.addEventListener("touchstart", padDown, { passive: false });
      pad.addEventListener("mousedown", padDown);
    }
    pad.addEventListener("click", function (e) { if (e.detail === 0) tap(); });   /* Enter key */

    document.addEventListener("keydown", function (e) {
      if (e.key === "Escape") { if (playing) { finish(); say("Stopped."); } return; }
      if (e.code === "Space" || e.key === " " || e.key === "Spacebar") {
        var a = document.activeElement;
        if (a && a.tagName === "BUTTON" && a !== pad) return;      /* let the button take it */
        if (a && (a.tagName === "INPUT" || a.tagName === "SELECT")) return;
        e.preventDefault();
        if (!e.repeat) tap();
      }
    });

    var rzTimer = null;
    window.addEventListener("resize", function () {
      clearTimeout(rzTimer);
      rzTimer = setTimeout(function () { measureRib(); renderRibbon(ribList); }, 120);
    });

    /* A hidden tab cannot be tapped, and every note in it would score as missed.
       Ending the run there is the honest outcome. */
    document.addEventListener("visibilitychange", function () {
      if (document.hidden && playing) {
        finish();
        /* finish() writes a generic sub-line; say why it really stopped, on
           screen and not only in the live region. */
        $("padSub").textContent = "the page went to the background, so the run stopped there";
        say("Stopped — the page went to the background.");
      }
    });

    window.addEventListener("message", function (e) {
      var d = e.data;
      if (d && d.type === "sloprun:theme" && (d.theme === "light" || d.theme === "dark")) {
        root.setAttribute("data-theme", d.theme);
      }
    });
  }

  /* ── boot ────────────────────────────────────────────────────────────────── */
  liveEl = $("live");
  /* Say up front that there will be no sound, rather than after the first tap:
     ensureAudio() only runs on a gesture, so the check has to be cheap and
     context-free (creating one here would just leave a suspended context). */
  if (!(window.AudioContext || window.webkitAudioContext)) {
    audioDead = true; $("audioNote").hidden = false;
  }
  buildGrid(); measureRib(); buildRibbon();
  renderLane(-1, want.pat); setLaneNote(want.pat);
  showSample();
  wire();
  setStatus(); setPlayBtn();
  if (reduced) { setHead(0); setBeat(0); }
  requestAnimationFrame(frame);
})();
</script>
</body>
</html>