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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>2048 — sloprun.dev</title>
<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 additions (scrims/shadows need alpha; tokens are opaque hex) */
:root {
  --scrim: rgba(246,246,243,.72);
  --shadow: 0 1px 2px rgba(26,29,33,.06);
  --lift: 0 6px 20px rgba(26,29,33,.10);
  --etch: inset 0 0 0 1px rgba(26,29,33,.06);
  --gap: clamp(7px, 1.7vw, 12px);
  --slide: 118ms;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --scrim: rgba(20,22,26,.72);
    --shadow: 0 1px 2px rgba(0,0,0,.35);
    --lift: 0 6px 20px rgba(0,0,0,.45);
    --etch: inset 0 0 0 1px rgba(255,255,255,.05);
  }
}
:root[data-theme="dark"] {
  --scrim: rgba(20,22,26,.72);
  --shadow: 0 1px 2px rgba(0,0,0,.35);
  --lift: 0 6px 20px rgba(0,0,0,.45);
  --etch: inset 0 0 0 1px rgba(255,255,255,.05);
}

* { 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: 820px; margin: 0 auto;
  padding: 22px 16px 26px;
  display: flex; flex-direction: column; gap: 16px;
}

/* ── header ───────────────────────────────────────────────────────────────── */
h1 {
  margin: 0 0 6px; font-family: var(--font-mono);
  font-size: clamp(26px, 6vw, 38px); letter-spacing: -.03em; line-height: 1;
  font-weight: 700;
}
.lede { margin: 0; max-width: 62ch; color: var(--muted); font-size: 14.5px; line-height: 1.55; }
.lede b { color: var(--ink); font-weight: 600; }
kbd {
  font-family: var(--font-mono); font-size: .84em; color: var(--accent);
  background: var(--accent-soft); border: 1px solid var(--line);
  border-radius: 5px; padding: 1px 5px; white-space: nowrap;
}

/* ── layout ───────────────────────────────────────────────────────────────── */
.stage {
  display: grid; gap: 14px; align-items: start;
  grid-template-columns: minmax(0, 1fr) 244px;
  grid-template-areas: "board panel";
}
.panel { grid-area: panel; display: flex; flex-direction: column; gap: 12px; }
.boardwrap { grid-area: board; display: flex; flex-direction: column; gap: 9px; min-width: 0; }
@media (max-width: 780px) {
  .stage { grid-template-columns: minmax(0, 1fr); grid-template-areas: "score" "board" "extras"; }
  .panel { display: contents; }
  .scorebar { grid-area: score; }
  .extras { grid-area: extras; }
}

/* ── score bar ────────────────────────────────────────────────────────────── */
.scorebar { display: flex; flex-direction: column; gap: 10px; }
@media (max-width: 780px) {
  .scorebar { flex-direction: row; align-items: stretch; }
  .scorebar, .extras { width: 100%; max-width: 452px; margin-left: auto; margin-right: auto; }
}
@media (max-width: 520px) { .scorebar { flex-direction: column; } }

.scores { display: flex; gap: 10px; flex: 1 1 auto; }
.card {
  position: relative; flex: 1 1 0; min-width: 0;
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 9px 11px 10px;
  box-shadow: var(--shadow);
}
.card .k {
  display: block; font-family: var(--font-mono); font-size: 9.5px;
  letter-spacing: .12em; text-transform: uppercase; color: var(--muted);
}
.card .v {
  display: block; font-family: var(--font-mono); font-variant-numeric: tabular-nums;
  font-size: clamp(19px, 4.6vw, 25px); font-weight: 700; line-height: 1.15;
  letter-spacing: -.02em; margin-top: 2px;
}
.card.best .v { color: var(--muted); }
.float {
  position: absolute; right: 11px; top: 6px; pointer-events: none;
  font-family: var(--font-mono); font-size: 13px; font-weight: 700; color: var(--accent);
  animation: floatUp 780ms ease-out forwards;
}
@keyframes floatUp {
  0%   { opacity: 0; transform: translateY(6px) scale(.9); }
  22%  { opacity: 1; transform: translateY(0) scale(1); }
  100% { opacity: 0; transform: translateY(-20px) scale(1); }
}

/* ── buttons ──────────────────────────────────────────────────────────────── */
.acts { display: flex; gap: 8px; align-items: center; }
.btn {
  flex: 1 1 auto; font: inherit; font-size: 13px; font-weight: 550;
  padding: 9px 12px; cursor: pointer;
  color: var(--ink); background: var(--surface);
  border: 1px solid var(--line); border-radius: 8px;
  box-shadow: var(--shadow);
  transition: background 120ms ease, border-color 120ms ease, transform 90ms ease;
  white-space: nowrap;
}
.btn:hover:not(:disabled) { background: var(--accent-soft); border-color: var(--accent); }
.btn:active:not(:disabled) { transform: translateY(1px); }
.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.btn:disabled { opacity: .42; cursor: not-allowed; box-shadow: none; }
.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--surface); }
:root[data-theme="dark"] .btn.primary { color: #14161A; }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .btn.primary { color: #14161A; } }
.btn.primary:hover:not(:disabled) { filter: brightness(1.08); background: var(--accent); }
.btn .mk { font-family: var(--font-mono); color: inherit; opacity: .6; font-size: 11px; margin-left: 5px; }
/* comfortable thumb targets once the layout stacks for phones */
@media (max-width: 780px) { .btn { min-height: 44px; } }

/* ── board ────────────────────────────────────────────────────────────────── */
.board {
  position: relative; width: 100%; max-width: 452px; margin: 0 auto;
  aspect-ratio: 1 / 1; padding: var(--gap);
  background: var(--surface); border: 1px solid var(--line);
  border-radius: calc(var(--radius) + 4px);
  box-shadow: var(--lift);
  touch-action: none; -webkit-user-select: none; user-select: none;
  container-type: inline-size;
}
.board:focus { outline: none; }
.board:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; }

.cells {
  position: absolute; inset: var(--gap);
  display: grid; gap: var(--gap);
  grid-template-columns: repeat(4, 1fr); grid-template-rows: repeat(4, 1fr);
}
.cell { border-radius: calc(var(--radius) - 2px); background: var(--cell, #EEEDE8); }

.layer { position: absolute; inset: var(--gap); }
.layer.nudge { animation: nudge 180ms ease; }
@keyframes nudge {
  0%,100% { transform: translate(0,0); }
  35% { transform: translate(var(--nx, 0), var(--ny, 0)); }
}

.tile {
  position: absolute; top: 0; left: 0;
  width: calc((100% - 3 * var(--gap)) / 4);
  height: calc((100% - 3 * var(--gap)) / 4);
  display: flex; align-items: center; justify-content: center;
  border-radius: calc(var(--radius) - 2px);
  font-family: var(--font-mono); font-weight: 700; letter-spacing: -.03em;
  font-variant-numeric: tabular-nums;
  box-shadow: var(--etch);
  will-change: transform;
  transform: translate(calc((100% + var(--gap)) * var(--c, 0)), calc((100% + var(--gap)) * var(--r, 0)));
  transition: transform var(--slide) cubic-bezier(.22, .72, .3, 1);
}
.tile.veil { opacity: 0; }
.tile.dying { z-index: 3; }
.tile.appear { animation: popIn 190ms cubic-bezier(.2, 1.3, .5, 1) both; }
.tile.merged { animation: popMerge 220ms cubic-bezier(.2, 1.3, .5, 1) both; z-index: 4; }
.tile.restored { animation: fadeIn 170ms ease both; }
@keyframes popIn { from { transform: translate(calc((100% + var(--gap)) * var(--c,0)), calc((100% + var(--gap)) * var(--r,0))) scale(.32); opacity: 0; }
                   to   { transform: translate(calc((100% + var(--gap)) * var(--c,0)), calc((100% + var(--gap)) * var(--r,0))) scale(1); opacity: 1; } }
@keyframes popMerge {
  0%   { transform: translate(calc((100% + var(--gap)) * var(--c,0)), calc((100% + var(--gap)) * var(--r,0))) scale(.6); opacity: .4; }
  55%  { transform: translate(calc((100% + var(--gap)) * var(--c,0)), calc((100% + var(--gap)) * var(--r,0))) scale(1.14); opacity: 1; }
  100% { transform: translate(calc((100% + var(--gap)) * var(--c,0)), calc((100% + var(--gap)) * var(--r,0))) scale(1); opacity: 1; }
}
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }

.tv { font-size: 30px; }
.tv { font-size: 9.6cqw; }
.tile[data-len="3"] .tv { font-size: 24px; font-size: 7.8cqw; }
.tile[data-len="4"] .tv { font-size: 19px; font-size: 6.1cqw; }
.tile[data-len="5"] .tv { font-size: 15px; font-size: 4.9cqw; }

.tile[data-k="1"]  { background: var(--t1);  color: var(--f1); }
.tile[data-k="2"]  { background: var(--t2);  color: var(--f2); }
.tile[data-k="3"]  { background: var(--t3);  color: var(--f3); }
.tile[data-k="4"]  { background: var(--t4);  color: var(--f4); }
.tile[data-k="5"]  { background: var(--t5);  color: var(--f5); }
.tile[data-k="6"]  { background: var(--t6);  color: var(--f6); }
.tile[data-k="7"]  { background: var(--t7);  color: var(--f7); }
.tile[data-k="8"]  { background: var(--t8);  color: var(--f8); }
.tile[data-k="9"]  { background: var(--t9);  color: var(--f9); }
.tile[data-k="10"] { background: var(--t10); color: var(--f10); }
.tile[data-k="11"] { background: var(--t11); color: var(--f11); box-shadow: var(--etch), 0 0 0 2px var(--run-soft); }
.tile[data-k="12"] { background: var(--t12); color: var(--f12); box-shadow: var(--etch), 0 0 0 2px var(--run-soft); }
.tile[data-k="13"] { background: var(--t13); color: var(--f13); box-shadow: var(--etch), 0 0 0 2px var(--run-soft); }

/* ── overlay ──────────────────────────────────────────────────────────────── */
.overlay {
  position: absolute; inset: 0; z-index: 9;
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  padding: 16px; text-align: center;
  background: var(--scrim); backdrop-filter: blur(4px);
  border-radius: calc(var(--radius) + 4px);
  animation: fadeIn 220ms ease both;
}
.overlay[hidden] { display: none; }
.overlay .sheet {
  display: flex; flex-direction: column; align-items: center; gap: 11px;
  width: 100%; max-width: 330px; padding: 18px 18px 17px;
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); box-shadow: var(--lift);
}
.overlay .big {
  font-family: var(--font-mono); font-size: clamp(22px, 6.4vw, 32px);
  font-weight: 700; letter-spacing: -.02em; line-height: 1.1;
}
.overlay .big.good { color: var(--run); }
.overlay .big.stop { color: var(--danger); }
.overlay .sub { font-size: 13.5px; color: var(--muted); max-width: 34ch; line-height: 1.5; }
.overlay .sub b { color: var(--ink); font-family: var(--font-mono); font-weight: 700; }
.overlay .ovacts { display: flex; gap: 8px; flex-wrap: wrap; justify-content: center; }
.overlay .btn { flex: 0 0 auto; }

/* ── extras ───────────────────────────────────────────────────────────────── */
.extras { display: flex; flex-direction: column; gap: 12px; }
.box {
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 11px; box-shadow: var(--shadow);
}
.box > .h {
  font-family: var(--font-mono); font-size: 9.5px; letter-spacing: .12em;
  text-transform: uppercase; color: var(--muted); margin-bottom: 8px;
}
.stats { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 8px 10px; }
@media (max-width: 780px) { .stats { grid-template-columns: repeat(4, minmax(0, 1fr)); } }
.stat .sk {
  display: block; font-family: var(--font-mono); font-size: 9.5px;
  letter-spacing: .1em; text-transform: uppercase; color: var(--muted);
}
.stat .sv {
  display: block; font-family: var(--font-mono); font-size: 15px; font-weight: 700;
  font-variant-numeric: tabular-nums; margin-top: 1px;
}
.stat .sv.good { color: var(--run); }
.stat .sv.stop { color: var(--danger); }
.stat.wide { grid-column: 1 / -1; }
.stat .sv.state { font-size: 12.5px; font-weight: 600; letter-spacing: 0; }

.ladder { display: flex; flex-wrap: wrap; gap: 4px; }
.chip {
  font-family: var(--font-mono); font-size: 10px; font-weight: 700;
  padding: 3px 6px; border-radius: 5px; min-width: 30px; text-align: center;
  box-shadow: var(--etch); opacity: .3; transition: opacity 200ms ease;
  font-variant-numeric: tabular-nums;
}
.chip.on { opacity: 1; }
.chip[data-k="1"]  { background: var(--t1);  color: var(--f1); }
.chip[data-k="2"]  { background: var(--t2);  color: var(--f2); }
.chip[data-k="3"]  { background: var(--t3);  color: var(--f3); }
.chip[data-k="4"]  { background: var(--t4);  color: var(--f4); }
.chip[data-k="5"]  { background: var(--t5);  color: var(--f5); }
.chip[data-k="6"]  { background: var(--t6);  color: var(--f6); }
.chip[data-k="7"]  { background: var(--t7);  color: var(--f7); }
.chip[data-k="8"]  { background: var(--t8);  color: var(--f8); }
.chip[data-k="9"]  { background: var(--t9);  color: var(--f9); }
.chip[data-k="10"] { background: var(--t10); color: var(--f10); }
.chip[data-k="11"] { background: var(--t11); color: var(--f11); }

.hint {
  margin: 0; font-family: var(--font-mono); font-size: 10.5px; color: var(--muted);
  letter-spacing: .04em; text-align: center; line-height: 1.7;
}
.hint .sep { opacity: .45; margin: 0 5px; }
.note { margin: 0; font-size: 12px; color: var(--muted); line-height: 1.5; }
.note b { color: var(--ink); font-weight: 600; font-family: var(--font-mono); font-variant-numeric: tabular-nums; }

footer {
  font-family: var(--font-mono); font-size: 11px; color: var(--muted);
  letter-spacing: .05em; padding-top: 2px;
}

.sr-only {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; border: 0;
}

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

  <header>
    <h1>2048</h1>
    <p class="lede">Slide every tile one direction; two equal numbers that touch merge into their double. Reach <b>2048</b> before the board fills up. A small solver plays the opening for you, so you land in a real mid-game position — take it from there with <kbd>&larr;</kbd><kbd>&uarr;</kbd><kbd>&rarr;</kbd><kbd>&darr;</kbd>, <kbd>WASD</kbd>, or a swipe.</p>
  </header>

  <div class="stage">

    <div class="boardwrap">
      <div class="board" id="board" tabindex="0" role="application"
           aria-label="2048 board, 4 by 4. Press arrow keys or W A S D to slide the tiles."
           aria-describedby="boardhelp boardText">
        <div class="cells" aria-hidden="true"></div>
        <div class="layer" id="layer"></div>
        <div class="overlay" id="overlay" role="dialog" aria-modal="true"
             aria-labelledby="ovTitle" aria-describedby="ovSub" hidden>
          <div class="sheet">
            <div class="big" id="ovTitle"></div>
            <p class="sub" id="ovSub"></p>
            <div class="ovacts">
              <button class="btn primary" id="ovMain" type="button"></button>
              <button class="btn" id="ovAlt" type="button" hidden></button>
            </div>
          </div>
        </div>
      </div>
      <p class="hint" id="boardhelp">
        <span>&larr; &uarr; &rarr; &darr; or WASD</span><span class="sep">·</span><span>swipe</span><span class="sep">·</span><span>U undo</span><span class="sep">·</span><span>N new game</span>
      </p>
    </div>

    <div class="panel">
      <div class="scorebar">
        <div class="scores">
          <div class="card" id="scoreCard">
            <span class="k">Score</span>
            <span class="v" id="score">0</span>
          </div>
          <div class="card best">
            <span class="k">Best</span>
            <span class="v" id="best">0</span>
          </div>
        </div>
        <div class="acts">
          <button class="btn primary" id="newBtn" type="button">New game<span class="mk">N</span></button>
          <button class="btn" id="undoBtn" type="button" disabled>Undo<span class="mk">U</span></button>
        </div>
      </div>

      <div class="extras">
        <div class="box">
          <div class="h">Run stats</div>
          <div class="stats">
            <div class="stat"><span class="sk">Moves</span><span class="sv" id="stMoves">0</span></div>
            <div class="stat"><span class="sk">Merges</span><span class="sv" id="stMerges">0</span></div>
            <div class="stat"><span class="sk">Largest</span><span class="sv" id="stTop">0</span></div>
            <div class="stat"><span class="sk">Free</span><span class="sv" id="stFree">0</span></div>
            <div class="stat wide"><span class="sk">State</span><span class="sv state" id="stState">in play</span></div>
          </div>
          <p class="note" id="origin" style="margin-top:9px"></p>
        </div>

        <div class="box">
          <div class="h">Tile ladder</div>
          <div class="ladder" id="ladder" aria-hidden="true"></div>
          <p class="note" style="margin-top:9px">Colours are mixed live from this page's theme tokens — pale amber heats to red and keeps deepening as the numbers climb, and <b>2048</b> lands on the green this page reserves for a finished job.</p>
        </div>
      </div>
    </div>

  </div>

  <footer>demo · sloprun.dev</footer>
</div>

<div class="sr-only" role="status" aria-live="polite" id="live"></div>
<div class="sr-only" id="boardText" aria-live="off"></div>

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

  var N = 4;
  var root = document.documentElement;
  var mqDark = window.matchMedia ? matchMedia("(prefers-color-scheme: dark)") : null;
  var mqRM   = window.matchMedia ? matchMedia("(prefers-reduced-motion: reduce)") : null;
  var reduced = !!(mqRM && mqRM.matches);

  var board   = document.getElementById("board");
  var layer   = document.getElementById("layer");
  var cellsEl = document.querySelector(".cells");
  var overlay = document.getElementById("overlay");
  var ovTitle = document.getElementById("ovTitle");
  var ovSub   = document.getElementById("ovSub");
  var ovMain  = document.getElementById("ovMain");
  var ovAlt   = document.getElementById("ovAlt");
  var scoreEl = document.getElementById("score");
  var bestEl  = document.getElementById("best");
  var scoreCard = document.getElementById("scoreCard");
  var newBtn  = document.getElementById("newBtn");
  var undoBtn = document.getElementById("undoBtn");
  var ladderEl = document.getElementById("ladder");
  var originEl = document.getElementById("origin");
  var live    = document.getElementById("live");
  var boardText = document.getElementById("boardText");
  var st = {
    moves:  document.getElementById("stMoves"),
    merges: document.getElementById("stMerges"),
    top:    document.getElementById("stTop"),
    free:   document.getElementById("stFree"),
    state:  document.getElementById("stState")
  };

  /* ── colour helpers ─────────────────────────────────────────────────────── */
  function hexToRgb(h) {
    h = String(h).trim();
    if (h.charAt(0) === "#") h = h.slice(1);
    if (h.length === 3) h = h.charAt(0)+h.charAt(0)+h.charAt(1)+h.charAt(1)+h.charAt(2)+h.charAt(2);
    if (h.length !== 6) return null;
    var n = parseInt(h, 16);
    if (isNaN(n)) return null;
    return [(n >> 16) & 255, (n >> 8) & 255, n & 255];
  }
  function tok(name, fb) {
    var v = getComputedStyle(root).getPropertyValue(name);
    return hexToRgb(v) || fb;
  }
  function mix(a, b, t) {
    return [Math.round(a[0] + (b[0]-a[0]) * t),
            Math.round(a[1] + (b[1]-a[1]) * t),
            Math.round(a[2] + (b[2]-a[2]) * t)];
  }
  function css(c) { return "rgb(" + c[0] + "," + c[1] + "," + c[2] + ")"; }
  function lum(c) {
    var f = function (v) { v /= 255; return v <= 0.03928 ? v/12.92 : Math.pow((v+0.055)/1.055, 2.4); };
    return 0.2126*f(c[0]) + 0.7152*f(c[1]) + 0.0722*f(c[2]);
  }
  var DARK_TEXT = [20, 22, 26];    /* dark-theme --bg  */
  var LIGHT_TEXT = [246, 246, 243]; /* light-theme --bg */
  function contrast(a, b) {
    var x = lum(a), y = lum(b);
    if (x < y) { var t = x; x = y; y = t; }
    return (x + 0.05) / (y + 0.05);
  }
  /* Pick the label colour for a tile. The two theme neutrals are preferred so
     the board stays in the palette; if neither clears a comfortable 5:1 (the
     10px ladder chips reuse these pairs, so small text has to hold up too) we
     fall back to flat white or black, whichever reads further from the tile. */
  var CANDIDATES = [DARK_TEXT, LIGHT_TEXT, [255, 255, 255], [0, 0, 0]];
  function textOn(bg) {
    var i, r, bestC = CANDIDATES[0], bestR = 0;
    for (i = 0; i < 2; i++) {
      r = contrast(bg, CANDIDATES[i]);
      if (r > bestR) { bestR = r; bestC = CANDIDATES[i]; }
    }
    if (bestR >= 5) return bestC;
    for (i = 2; i < CANDIDATES.length; i++) {
      r = contrast(bg, CANDIDATES[i]);
      if (r > bestR) { bestR = r; bestC = CANDIDATES[i]; }
    }
    return bestC;
  }

  /* Tile palette, derived entirely from the theme tokens:
     grey steps -> amber ramp -> red heat -> earned green at 2048. */
  function paintPalette() {
    var surface = tok("--surface", [255,255,255]);
    var line    = tok("--line",    [227,226,220]);
    var muted   = tok("--muted",   [90,96,104]);
    var soft    = tok("--accent-soft", [255,243,230]);
    var accent  = tok("--accent",  [192,86,0]);
    var danger  = tok("--danger",  [201,60,55]);
    var run     = tok("--run",     [26,127,55]);
    var ink     = tok("--ink",     [26,29,33]);
    var pageBg  = tok("--bg",      [246,246,243]);

    /* Above 64 the accent → danger travel is almost pure hue: in the light theme
       64, 128, 256, 512 and 1024 all land within three L* of each other, so the
       hot end of the ladder reads as one orange block. The fix is to give that
       half a lightness slope as well, pulling each step toward whichever token is
       darkest in the current theme — --ink on a light page, --bg on a dark one —
       so the ramp keeps moving in a straight line whichever way the page flips. */
    var lightPage = lum(pageBg) > 0.5;
    var deep = lightPage ? ink : pageBg;
    var heat = lightPage ? [0.14, 0.30, 0.44, 0.58] : [0.12, 0.26, 0.40, 0.52];

    var bgs = [
      null,
      mix(line, muted, 0.10),                       /* 2    */
      mix(line, muted, 0.36),                       /* 4    */
      mix(soft, accent, 0.50),                      /* 8    */
      mix(soft, accent, 0.70),                      /* 16   */
      mix(soft, accent, 0.88),                      /* 32   */
      accent,                                       /* 64   */
      mix(mix(accent, danger, 0.40), deep, heat[0]),/* 128  */
      mix(mix(accent, danger, 0.72), deep, heat[1]),/* 256  */
      mix(danger, deep, heat[2]),                   /* 512  */
      mix(danger, deep, heat[3]),                   /* 1024 */
      run,                                          /* 2048 — earned */
      mix(run, ink, 0.34),                          /* 4096 */
      mix(run, ink, 0.60)                           /* 8192+ */
    ];
    for (var k = 1; k <= 13; k++) {
      var c = bgs[k];
      root.style.setProperty("--t" + k, css(c));
      root.style.setProperty("--f" + k, css(textOn(c)));
    }
    root.style.setProperty("--cell", css(mix(surface, line, 0.78)));
  }

  /* ── static board scaffolding ───────────────────────────────────────────── */
  (function buildCells() {
    var frag = document.createDocumentFragment();
    for (var i = 0; i < N * N; i++) {
      var d = document.createElement("div");
      d.className = "cell";
      frag.appendChild(d);
    }
    cellsEl.appendChild(frag);
  })();

  (function buildLadder() {
    var frag = document.createDocumentFragment();
    for (var k = 1; k <= 11; k++) {
      var s = document.createElement("span");
      s.className = "chip";
      s.setAttribute("data-k", String(k));
      s.textContent = Math.pow(2, k);
      frag.appendChild(s);
    }
    ladderEl.appendChild(frag);
  })();

  /* ── game state ─────────────────────────────────────────────────────────── */
  var grid, tiles, idSeq, score, best, moves, merges, won, keepGoing, over, snap, pending;

  function emptyGrid() {
    var g = [];
    for (var r = 0; r < N; r++) { g.push([]); for (var c = 0; c < N; c++) g[r].push(null); }
    return g;
  }

  function tierOf(v) { return Math.min(13, Math.round(Math.log(v) / Math.LN2)); }

  function styleTile(t) {
    var n = t.node;
    n.style.setProperty("--r", String(t.r));
    n.style.setProperty("--c", String(t.c));
    n.setAttribute("data-k", String(tierOf(t.v)));
    n.setAttribute("data-len", String(t.v).length);
    n.firstChild.textContent = t.v;
  }

  function makeTile(v, r, c, cls) {
    var t = { id: ++idSeq, v: v, r: r, c: c, node: null };
    var n = document.createElement("div");
    n.className = "tile" + (cls ? " " + cls : "");
    n.setAttribute("aria-hidden", "true");
    var sp = document.createElement("span");
    sp.className = "tv";
    n.appendChild(sp);
    t.node = n;
    styleTile(t);
    layer.appendChild(n);
    tiles[t.id] = t;
    return t;
  }

  layer.addEventListener("animationend", function (e) {
    if (e.target && e.target.classList) e.target.classList.remove("appear", "merged", "restored");
  });

  function dropTile(t) {
    if (t.node && t.node.parentNode) t.node.parentNode.removeChild(t.node);
    delete tiles[t.id];
  }

  function clearBoard() {
    for (var id in tiles) if (Object.prototype.hasOwnProperty.call(tiles, id)) dropTile(tiles[id]);
    tiles = {};
    grid = emptyGrid();
  }

  /* Finish any in-flight slide immediately (keeps rapid input honest). */
  function flush() {
    if (!pending) return;
    clearTimeout(pending.timer);
    var i;
    for (i = 0; i < pending.kill.length; i++) dropTile(pending.kill[i]);
    for (i = 0; i < pending.show.length; i++) {
      var e = pending.show[i];
      e.t.node.classList.remove("veil");
      if (!reduced) e.t.node.classList.add(e.cls);
    }
    pending = null;
  }

  function schedule(kill, show) {
    pending = { kill: kill, show: show, timer: 0 };
    if (reduced) { flush(); return; }
    pending.timer = setTimeout(flush, 118);
  }

  /* ── board queries ──────────────────────────────────────────────────────── */
  function emptyCells() {
    var out = [];
    for (var r = 0; r < N; r++) for (var c = 0; c < N; c++) if (!grid[r][c]) out.push([r, c]);
    return out;
  }
  function movesLeft() {
    for (var r = 0; r < N; r++) for (var c = 0; c < N; c++) {
      var t = grid[r][c];
      if (!t) return true;
      if (c < N-1 && grid[r][c+1] && grid[r][c+1].v === t.v) return true;
      if (r < N-1 && grid[r+1][c] && grid[r+1][c].v === t.v) return true;
    }
    return false;
  }
  function largest() {
    var m = 0;
    for (var r = 0; r < N; r++) for (var c = 0; c < N; c++) if (grid[r][c] && grid[r][c].v > m) m = grid[r][c].v;
    return m;
  }

  function addRandom(cls, bucket) {
    var free = emptyCells();
    if (!free.length) return null;
    var p = free[(Math.random() * free.length) | 0];
    var v = Math.random() < 0.9 ? 2 : 4;
    var t = makeTile(v, p[0], p[1], "veil");
    grid[p[0]][p[1]] = t;
    bucket.push({ t: t, cls: cls });
    return t;
  }

  /* ── snapshots (one level of undo) ──────────────────────────────────────── */
  function takeSnap() {
    var g = [];
    for (var r = 0; r < N; r++) { g.push([]); for (var c = 0; c < N; c++) g[r].push(grid[r][c] ? grid[r][c].v : 0); }
    return { g: g, score: score, moves: moves, merges: merges, won: won, keepGoing: keepGoing };
  }
  function restore(s) {
    clearBoard();
    for (var r = 0; r < N; r++) for (var c = 0; c < N; c++) {
      if (s.g[r][c]) grid[r][c] = makeTile(s.g[r][c], r, c, reduced ? "" : "restored");
    }
    score = s.score; moves = s.moves; merges = s.merges;
    won = s.won; keepGoing = s.keepGoing; over = false;
  }

  /* ── the move ───────────────────────────────────────────────────────────── */
  var DIRS = { up: 0, right: 1, down: 2, left: 3 };
  var DIRNAME = ["Up", "Right", "Down", "Left"];
  var NUDGE = [[0,"-5px"], ["5px",0], [0,"5px"], ["-5px",0]];

  function lineCells(dir) {
    var lines = [], i, j, r, c, line;
    for (i = 0; i < N; i++) {
      line = [];
      for (j = 0; j < N; j++) {
        if (dir === 3)      { r = i;       c = j; }
        else if (dir === 1) { r = i;       c = N-1-j; }
        else if (dir === 0) { r = j;       c = i; }
        else                { r = N-1-j;   c = i; }
        line.push([r, c]);
      }
      lines.push(line);
    }
    return lines;
  }

  function move(dir) {
    if (over || !overlay.hidden) return false;
    flush();

    var before = takeSnap();
    var moved = false, gained = 0, madeMerges = 0, hitWin = false;
    var kill = [], show = [];
    var lines = lineCells(dir);

    for (var L = 0; L < lines.length; L++) {
      var cells = lines[L], seq = [], i, p;

      for (i = 0; i < cells.length; i++) {
        p = cells[i];
        if (grid[p[0]][p[1]]) seq.push(grid[p[0]][p[1]]);
      }
      for (i = 0; i < cells.length; i++) { p = cells[i]; grid[p[0]][p[1]] = null; }

      var out = [];
      i = 0;
      while (i < seq.length) {
        if (i + 1 < seq.length && seq[i].v === seq[i+1].v) {
          out.push({ a: seq[i], b: seq[i+1], v: seq[i].v * 2 });
          i += 2;
        } else {
          out.push({ t: seq[i] });
          i += 1;
        }
      }

      for (i = 0; i < out.length; i++) {
        var e = out[i], r = cells[i][0], c = cells[i][1];
        if (e.t) {
          if (e.t.r !== r || e.t.c !== c) { moved = true; e.t.r = r; e.t.c = c; styleTile(e.t); }
          grid[r][c] = e.t;
        } else {
          moved = true;
          e.a.r = r; e.a.c = c; e.a.node.classList.add("dying"); styleTile(e.a);
          e.b.r = r; e.b.c = c; e.b.node.classList.add("dying"); styleTile(e.b);
          kill.push(e.a, e.b);
          var nt = makeTile(e.v, r, c, "veil");
          grid[r][c] = nt;
          show.push({ t: nt, cls: "merged" });
          gained += e.v;
          madeMerges++;
          if (e.v >= 2048 && !won) { won = true; hitWin = true; }
        }
      }
    }

    if (!moved) {
      /* nothing shifted: every tile was written straight back to its own cell */
      bump(dir);
      say(DIRNAME[dir] + ". Nothing moves that way.");
      return false;
    }

    snap = before;
    score += gained;
    if (score > best) best = score;
    moves++;
    merges += madeMerges;

    addRandom("appear", show);
    schedule(kill, show);

    if (gained > 0 && !reduced) floatScore(gained);
    sync();

    if (hitWin && !keepGoing) {
      showOverlay("win");
      say("2048 reached. Score " + score + ".");
    } else if (endIfDead()) {
      /* handled */
    } else {
      say(DIRNAME[dir] + ". " + (gained ? "Merged " + gained + " points. " : "") + "Score " + score + ".");
    }
    return true;
  }

  /* The winning merge can also be the one that fills the board. Checking this
     from both the move and the "Keep going" button means a win on a dead board
     still ends in a game-over card instead of a silently unplayable grid. */
  function endIfDead() {
    if (over || movesLeft()) return false;
    over = true;
    sync();
    showOverlay("over");
    say("No moves left. Final score " + score + ".");
    return true;
  }

  var bumpTimer = 0;
  function bump(dir) {
    if (reduced) return;
    layer.style.setProperty("--nx", NUDGE[dir][0]);
    layer.style.setProperty("--ny", NUDGE[dir][1]);
    layer.classList.remove("nudge");
    void layer.offsetWidth;
    layer.classList.add("nudge");
    clearTimeout(bumpTimer);
    bumpTimer = setTimeout(function () { layer.classList.remove("nudge"); }, 220);
  }

  function floatScore(n) {
    var f = document.createElement("span");
    f.className = "float";
    f.textContent = "+" + n;
    scoreCard.appendChild(f);
    setTimeout(function () { if (f.parentNode) f.parentNode.removeChild(f); }, 820);
  }

  /* ── undo ───────────────────────────────────────────────────────────────── */
  function undo() {
    if (!snap) return;
    flush();
    hideOverlay();
    restore(snap);
    snap = null;
    sync();
    say("Move undone. Score " + score + ".");
  }

  /* ── new game / preloaded game ──────────────────────────────────────────── */
  function newGame() {
    flush();
    hideOverlay();
    clearBoard();
    score = 0; moves = 0; merges = 0; won = false; keepGoing = false; over = false; snap = null;
    var show = [];
    addRandom("appear", show);
    addRandom("appear", show);
    schedule([], show);
    setOrigin(0);
    sync();
    say("New game. Two tiles on the board.");
    board.focus();
  }

  /* ── the opening is played, not faked ────────────────────────────────────
     A depth-2 expectimax solver actually plays a game here at load time on a
     plain array of numbers — no DOM, a few milliseconds — and hands over the
     moment it has built a 512 with the board starting to crowd. Every number
     in the panel above is what that game really earned. ------------------- */

  var SIM_LINES = (function () {
    var out = [];
    for (var d = 0; d < 4; d++) {
      var ls = [];
      for (var i = 0; i < N; i++) {
        var line = [];
        for (var j = 0; j < N; j++) {
          var r, c;
          if (d === 3)      { r = i;       c = j; }
          else if (d === 1) { r = i;       c = N-1-j; }
          else if (d === 0) { r = j;       c = i; }
          else              { r = N-1-j;   c = i; }
          line.push(r * N + c);
        }
        ls.push(line);
      }
      out.push(ls);
    }
    return out;
  })();

  function simMove(g, d) {
    var ls = SIM_LINES[d], moved = false, gained = 0, merged = 0;
    var out = g.slice();
    for (var L = 0; L < N; L++) {
      var idx = ls[L], seq = [], i, v;
      for (i = 0; i < N; i++) { v = g[idx[i]]; if (v) seq.push(v); }
      var res = [];
      i = 0;
      while (i < seq.length) {
        if (i + 1 < seq.length && seq[i] === seq[i+1]) { res.push(seq[i] * 2); gained += seq[i] * 2; merged++; i += 2; }
        else { res.push(seq[i]); i += 1; }
      }
      for (i = 0; i < N; i++) {
        var nv = i < res.length ? res[i] : 0;
        if (g[idx[i]] !== nv) moved = true;
        out[idx[i]] = nv;
      }
    }
    return { g: out, moved: moved, gained: gained, merged: merged };
  }

  function simLogs(g) {
    var L = new Array(16);
    for (var i = 0; i < 16; i++) L[i] = g[i] ? Math.log(g[i]) / Math.LN2 : 0;
    return L;
  }
  /* neighbouring tiles that are close in value are easy to merge later */
  function simSmooth(L) {
    var s = 0, r, c, cc, rr, a;
    for (r = 0; r < N; r++) for (c = 0; c < N; c++) {
      a = L[r*N+c]; if (!a) continue;
      for (cc = c+1; cc < N; cc++) if (L[r*N+cc]) { s -= Math.abs(a - L[r*N+cc]); break; }
      for (rr = r+1; rr < N; rr++) if (L[rr*N+c]) { s -= Math.abs(a - L[rr*N+c]); break; }
    }
    return s;
  }
  /* rows and columns that only ever climb (or only ever fall) stay tidy */
  function simMono(L) {
    var t = [0, 0, 0, 0], r, c, cur, next, a, b;
    for (c = 0; c < N; c++) {
      cur = 0; while (cur < N && !L[cur*N+c]) cur++;
      if (cur >= N) cur = N - 1;
      next = cur + 1;
      while (next < N) {
        while (next < N && !L[next*N+c]) next++;
        if (next >= N) next = N - 1;
        a = L[cur*N+c] || 0; b = L[next*N+c] || 0;
        if (a > b) t[0] += b - a; else if (b > a) t[1] += a - b;
        cur = next; next++;
      }
    }
    for (r = 0; r < N; r++) {
      cur = 0; while (cur < N && !L[r*N+cur]) cur++;
      if (cur >= N) cur = N - 1;
      next = cur + 1;
      while (next < N) {
        while (next < N && !L[r*N+next]) next++;
        if (next >= N) next = N - 1;
        a = L[r*N+cur] || 0; b = L[r*N+next] || 0;
        if (a > b) t[2] += b - a; else if (b > a) t[3] += a - b;
        cur = next; next++;
      }
    }
    return Math.max(t[0], t[1]) + Math.max(t[2], t[3]);
  }
  function simEval(g) {
    var L = simLogs(g), free = 0, mx = 0, i;
    for (i = 0; i < 16; i++) { if (!g[i]) free++; if (L[i] > mx) mx = L[i]; }
    return simSmooth(L) * 0.1 + simMono(L) * 1.0 + Math.log(free + 1) * 2.7 + mx;
  }
  function simMax(g, depth) {
    var b = -Infinity, d, m, s;
    for (d = 0; d < 4; d++) {
      m = simMove(g, d);
      if (!m.moved) continue;
      s = depth <= 0 ? simEval(m.g) : simChance(m.g, depth);
      if (s > b) b = s;
    }
    return b === -Infinity ? simEval(g) - 100 : b;
  }
  function simChance(g, depth) {
    var free = [], i;
    for (i = 0; i < 16; i++) if (!g[i]) free.push(i);
    if (!free.length) return simEval(g);
    var pick = free;
    if (pick.length > 4) { pick = []; for (i = 0; i < 4; i++) pick.push(free[(Math.random() * free.length) | 0]); }
    var tot = 0;
    for (i = 0; i < pick.length; i++) {
      var g2 = g.slice(); g2[pick[i]] = 2;
      tot += simMax(g2, depth - 1);
    }
    return tot / pick.length;
  }
  function simBestDir(g) {
    var bs = -Infinity, bd = -1, d, m, s;
    for (d = 0; d < 4; d++) {
      m = simMove(g, d);
      if (!m.moved) continue;
      s = simChance(m.g, 1);
      if (s > bs) { bs = s; bd = d; }
    }
    return bd;
  }
  function simSpawn(g) {
    var free = [], i;
    for (i = 0; i < 16; i++) if (!g[i]) free.push(i);
    if (!free.length) return false;
    g[free[(Math.random() * free.length) | 0]] = Math.random() < 0.9 ? 2 : 4;
    return true;
  }

  /* One solver game, stopped at a handover point that is still fun to play. */
  function simPlay(deadline) {
    var g = [], i;
    for (i = 0; i < 16; i++) g.push(0);
    simSpawn(g); simSpawn(g);
    var sc = 0, mv = 0, mg = 0;
    for (i = 0; i < 2500; i++) {
      var d = simBestDir(g);
      if (d < 0) break;
      var m = simMove(g, d);
      g = m.g; sc += m.gained; mg += m.merged; mv++;
      simSpawn(g);
      var mx = 0, free = 0, k;
      for (k = 0; k < 16; k++) { if (g[k] > mx) mx = g[k]; if (!g[k]) free++; }
      if (mx >= 512 && free >= 3 && free <= 6) return { g: g, score: sc, moves: mv, merges: mg, ok: true };
      if ((i & 31) === 31 && now() > deadline) break;
    }
    return { g: g, score: sc, moves: mv, merges: mg, ok: false };
  }

  function now() {
    return (window.performance && performance.now) ? performance.now() : Date.now();
  }

  /* A hand-written stand-in, used only if the solver somehow comes up empty.
     Its score is exactly what building these tiles out of 2s pays out. */
  var FALLBACK = [512, 256, 64, 4, 32, 16, 8, 4, 4, 2, 2, 0, 2, 0, 0, 0];
  function fallbackRun() {
    var sc = 0, mg = 0, i, v;
    for (i = 0; i < 16; i++) {
      v = FALLBACK[i];
      if (!v) continue;
      sc += v * (Math.round(Math.log(v) / Math.LN2) - 1);
      mg += v / 2 - 1;
    }
    /* -1 marks a move count nobody can honestly claim to know */
    return { g: FALLBACK.slice(), score: sc, moves: -1, merges: mg, ok: false };
  }

  function loadOpening() {
    var deadline = now() + 220;
    var run = null;
    for (var a = 0; a < 4; a++) {
      var r = simPlay(deadline);
      if (r.ok) { run = r; break; }
      if (!run || r.score > run.score) run = r;
      if (now() > deadline) break;
    }
    var mx = 0, free = 0, k;
    for (k = 0; k < 16; k++) { if (run.g[k] > mx) mx = run.g[k]; if (!run.g[k]) free++; }
    if (mx < 128 || free < 2) run = fallbackRun();

    clearBoard();
    for (var r2 = 0; r2 < N; r2++) for (var c2 = 0; c2 < N; c2++) {
      var v = run.g[r2 * N + c2];
      if (v) grid[r2][c2] = makeTile(v, r2, c2, "");
    }
    score = run.score; best = run.score;
    moves = run.moves < 0 ? 0 : run.moves; merges = run.merges;
    won = false; keepGoing = false; over = false; snap = null;
    setOrigin(run.moves);
    sync();
  }

  function setOrigin(solverMoves) {
    if (solverMoves < 0) {
      originEl.innerHTML = "Loaded position (the solver ran out of its time budget). Score and merges are exactly what building this board out of 2s costs; the move count starts at <b>0</b> because nobody can honestly claim to know it.";
    } else if (solverMoves > 0) {
      originEl.innerHTML = "Opening played by the built-in solver: <b>" + solverMoves +
        "</b> moves before you arrived. The counts above are its real totals, and they keep climbing as you play.";
    } else {
      originEl.textContent = "Fresh board, two tiles, nothing played yet. Every count here is yours.";
    }
  }

  /* ── overlays ───────────────────────────────────────────────────────────── */
  var ovMode = "";
  function plural(n, word) { return n === 1 ? word : word + "s"; }
  function showOverlay(mode) {
    ovMode = mode;
    if (mode === "win") {
      /* The winning merge can also be the one that strands the board, so the
         card reports what is actually left rather than promising room. */
      var free = emptyCells().length;
      var tail = !movesLeft() ? "That was also the last legal move."
               : free ? "The board still has <b>" + free + "</b> free " + plural(free, "cell") + "."
               : "The board is full, but there are merges left in it.";
      ovTitle.textContent = "2048";
      ovTitle.className = "big good";
      ovSub.innerHTML = "You built it in <b>" + moves + "</b> " + plural(moves, "move") +
        " for <b>" + score + "</b> points. " + tail;
      ovMain.textContent = "Keep going";
      ovAlt.textContent = "New game";
      ovAlt.hidden = false;
    } else {
      ovTitle.textContent = "no moves left";
      ovTitle.className = "big stop";
      ovSub.innerHTML = "Final score <b>" + score + "</b> across <b>" + moves + "</b> " + plural(moves, "move") + ". Largest tile <b>" + largest() + "</b>.";
      ovMain.textContent = "New game";
      ovAlt.textContent = snap ? "Undo last move" : "";
      ovAlt.hidden = !snap;
    }
    overlay.hidden = false;
    ovMain.focus();
  }
  function hideOverlay() {
    /* keep the keyboard alive: if focus was parked on an overlay button, hand
       it back to the board rather than dropping it on <body> */
    var wasInside = overlay.contains(document.activeElement);
    overlay.hidden = true; ovMode = "";
    if (wasInside) board.focus();
  }

  /* aria-modal="true" hides the rest of the page from assistive tech, so the
     keyboard should not wander out of the sheet either — cycle the buttons. */
  overlay.addEventListener("keydown", function (e) {
    if (e.key !== "Tab" || overlay.hidden) return;
    var stops = ovAlt.hidden ? [ovMain] : [ovMain, ovAlt];
    var i = stops.indexOf(document.activeElement);
    e.preventDefault();
    stops[(i + (e.shiftKey ? stops.length - 1 : 1) + stops.length) % stops.length].focus();
  });

  ovMain.addEventListener("click", function () {
    if (ovMode === "win") {
      keepGoing = true; hideOverlay();
      if (endIfDead()) return;
      sync(); board.focus();
    } else newGame();
  });
  ovAlt.addEventListener("click", function () {
    if (ovMode === "win") newGame();
    else undo();
  });

  /* ── UI sync ────────────────────────────────────────────────────────────── */
  function sync() {
    scoreEl.textContent = score;
    bestEl.textContent = best;
    st.moves.textContent = moves;
    st.merges.textContent = merges;
    var top = largest();
    st.top.textContent = top;
    st.free.textContent = emptyCells().length;

    st.state.className = "sv state";
    if (over) { st.state.textContent = "no moves left"; st.state.className = "sv state stop"; }
    else if (won) { st.state.textContent = "2048 reached"; st.state.className = "sv state good"; }
    else { st.state.textContent = "in play"; }

    undoBtn.disabled = !snap;

    var chips = ladderEl.children;
    for (var k = 0; k < chips.length; k++) {
      chips[k].classList.toggle("on", Math.pow(2, k + 1) <= top);
    }

    var lines = [];
    for (var r = 0; r < N; r++) {
      var row = [];
      for (var c = 0; c < N; c++) row.push(grid[r][c] ? grid[r][c].v : "empty");
      lines.push("Row " + (r+1) + ": " + row.join(", ") + ".");
    }
    boardText.textContent = "Board. " + lines.join(" ");
  }

  var sayTimer = 0;
  function say(msg) {
    clearTimeout(sayTimer);
    sayTimer = setTimeout(function () { live.textContent = msg; }, 130);
  }

  /* ── input ──────────────────────────────────────────────────────────────── */
  var KEYS = {
    ArrowUp: 0, ArrowRight: 1, ArrowDown: 2, ArrowLeft: 3,
    Up: 0, Right: 1, Down: 2, Left: 3,
    w: 0, d: 1, s: 2, a: 3,
    W: 0, D: 1, S: 2, A: 3
  };

  document.addEventListener("keydown", function (e) {
    if (e.metaKey || e.ctrlKey || e.altKey) return;
    var tag = e.target && e.target.tagName;
    if (tag === "INPUT" || tag === "TEXTAREA") return;

    /* Escape dismisses the win card the same way "Keep going" does. The
       game-over card has nothing playable behind it, so Escape leaves it up. */
    if (e.key === "Escape" || e.key === "Esc") {
      if (!overlay.hidden && ovMode === "win") { e.preventDefault(); ovMain.click(); }
      return;
    }

    if (Object.prototype.hasOwnProperty.call(KEYS, e.key)) {
      if (!overlay.hidden) return;
      e.preventDefault();
      move(KEYS[e.key]);
      return;
    }
    if (e.key === "u" || e.key === "U") {
      if (!undoBtn.disabled) { e.preventDefault(); undo(); }
      return;
    }
    if (e.key === "n" || e.key === "N") { e.preventDefault(); newGame(); }
  });

  newBtn.addEventListener("click", newGame);
  undoBtn.addEventListener("click", function () { undo(); board.focus(); });

  /* swipe / drag — pointer events cover touch, pen and mouse */
  var sx = 0, sy = 0, pid = null;
  board.addEventListener("pointerdown", function (e) {
    if (pid !== null) return;
    /* The overlay sits inside the board, so its buttons would otherwise lose
       their click: capturing the pointer here retargets the release to the
       board and the click lands on the common ancestor instead of the button. */
    if (!overlay.hidden || (e.target && e.target.closest && e.target.closest(".overlay"))) return;
    pid = e.pointerId; sx = e.clientX; sy = e.clientY;
    if (board.setPointerCapture) { try { board.setPointerCapture(pid); } catch (err) { void err; } }
  });
  function endPointer(e) {
    if (pid === null || e.pointerId !== pid) return;
    var dx = e.clientX - sx, dy = e.clientY - sy;
    pid = null;
    var ax = Math.abs(dx), ay = Math.abs(dy);
    if (Math.max(ax, ay) < 22) return;
    if (ax > ay) move(dx > 0 ? DIRS.right : DIRS.left);
    else move(dy > 0 ? DIRS.down : DIRS.up);
  }
  board.addEventListener("pointerup", endPointer);
  board.addEventListener("pointercancel", function (e) { if (e.pointerId === pid) pid = null; });
  /* If the capture is ever torn away without an up or a cancel reaching us, the
     gesture id would stay parked and every later swipe would be ignored. */
  board.addEventListener("lostpointercapture", function (e) { if (e.pointerId === pid) pid = null; });

  /* ── theme plumbing ─────────────────────────────────────────────────────── */
  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);
      paintPalette();
    }
  });
  if (mqDark) {
    var onScheme = function () { paintPalette(); };
    if (mqDark.addEventListener) mqDark.addEventListener("change", onScheme);
    else if (mqDark.addListener) mqDark.addListener(onScheme);
  }
  if (mqRM) {
    var onRM = function () { reduced = mqRM.matches; };
    if (mqRM.addEventListener) mqRM.addEventListener("change", onRM);
    else if (mqRM.addListener) mqRM.addListener(onRM);
  }

  /* ── boot ───────────────────────────────────────────────────────────────── */
  idSeq = 0; tiles = {}; grid = emptyGrid(); pending = null;
  score = 0; best = 0; moves = 0; merges = 0;
  won = false; keepGoing = false; over = false; snap = null;

  paintPalette();
  loadOpening();
})();
</script>
</body>
</html>