04Pointer food or repellent — the network grows toward or flees your click

<main class="stage">
<div class="sm is-demo" id="smRoot">
  <p class="sm__hint">
    <span>Click to plant a new food source and branches reach toward it — switch modes to drop salt (a repellent) and the trail bends away instead</span>
  </p>
  <div class="sm__field" id="smField" role="application" aria-label="Pointer Food & Repellent Slime Demo" tabindex="0">
    <canvas class="sm__cv" id="smCv"></canvas>
  </div>
  <div class="sm__bar">
    <button class="sm__toggle" id="smMode" type="button" aria-pressed="false">
      <span id="smModeLabel">Click = food</span>
    </button>
    <span class="sm__meta sm__meta--dim">canvas · pointermove · requestAnimationFrame</span>
  </div>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 포인터 먹이·기피물(04). @keyframes 를 두지 않는다 —
// 움직임은 전부 캔버스 rAF 루프(클릭·자동각본 앵커 + 3센서 감지 → 회전 → 트레일 → 확산·증발)가 만든다.
// 무대는 코랄빛 노을 — 01(밤)·02(종이)·03(밀짚) 다음 네 번째 순환.

$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-cream;

// ── 이 항목만의 파스텔 팔레트(밝은 계열, L 0.83 이상 — BD26 안전) ──
$sm-stage: #ffe3ce;   // 코랄빛 노을 무대

@include stage($sm-stage);

$sm-floor: #ffe3ce;   // 필드 바닥 — 무대와 같은 톤
$sm-trail: #ffcdb0;   // 트레일 — 살짝 진한 코랄
$sm-food:  #ffc2ad;   // 먹이 앵커 글로우 — 파스텔 코랄(끌림)
$sm-salt:  #bfe3ff;   // 소금 앵커 글로우 — 파스텔 스카이(기피, 무대와 색상 대비)
$sm-text:  #4a2e18;   // 노을 무대 위 — 짙은 테라코타 글자(대비)

.sm {
  --sm-floor: #{$sm-floor};
  --sm-trail: #{$sm-trail};
  --sm-food:  #{$sm-food};
  --sm-salt:  #{$sm-salt};

  display: flex; flex-direction: column; gap: $sp-2;
  width: 100%; max-width: 424px;
}

.sm__hint {
  display: flex; align-items: center; gap: $sp-1; margin: 0;
  font-weight: 700; font-size: clamp(10px, 2.8vw, 12px); line-height: 1.35;
  color: $sm-text;
}

.sm__field {
  position: relative; height: 180px;
  border-radius: $r-card; overflow: hidden;
  background: $sm-floor;
  box-shadow: inset 0 0 0 1px rgba($sm-text, .18);
  cursor: crosshair;
}
.sm__field:focus-visible { outline: 2px solid $sm-text; outline-offset: 2px; }

.sm__cv { display: block; width: 100%; height: 100%; }

.sm__bar { display: flex; align-items: center; justify-content: space-between; gap: $sp-2; }

.sm__toggle {
  display: inline-flex; align-items: center; gap: $sp-1;
  padding: $sp-1 $sp-2; border: 0; border-radius: $r-pill;
  background: $sm-trail; color: $sm-text;
  font-size: 10px; font-weight: 700; line-height: 1;
  cursor: pointer; transition: background $dur-quick $ease-out;
}
.sm__toggle:hover { background: $sm-food; }
.sm__toggle:focus-visible { outline: 2px solid $sm-text; outline-offset: 2px; }
.sm__toggle[aria-pressed="true"] { background: $sm-salt; }

.sm__meta--dim { font-size: 10px; font-weight: 500; color: rgba($sm-text, .72); }

@media (max-width: 340px) {
  .sm { gap: $sp-1; }
  .sm__field { height: 100px; }
  .sm__meta--dim { display: none; }
}

// reduce — rAF 를 돌리지 않고 앵커 세 개가 자리 잡은 한 장만 남는다.
@media (prefers-reduced-motion: reduce) {
  .sm.is-still .sm__field { cursor: default !important; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffe3ce;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.sm {
  --sm-floor: #ffe3ce;
  --sm-trail: #ffcdb0;
  --sm-food: #ffc2ad;
  --sm-salt: #bfe3ff;
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 100%;
  max-width: 424px;
}

.sm__hint {
  display: flex;
  align-items: center;
  gap: 4px;
  margin: 0;
  font-weight: 700;
  font-size: clamp(10px, 2.8vw, 12px);
  line-height: 1.35;
  color: #4a2e18;
}

.sm__field {
  position: relative;
  height: 180px;
  border-radius: 16px;
  overflow: hidden;
  background: #ffe3ce;
  box-shadow: inset 0 0 0 1px rgba(74, 46, 24, 0.18);
  cursor: crosshair;
}

.sm__field:focus-visible {
  outline: 2px solid #4a2e18;
  outline-offset: 2px;
}

.sm__cv {
  display: block;
  width: 100%;
  height: 100%;
}

.sm__bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
}

.sm__toggle {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 4px 8px;
  border: 0;
  border-radius: 999px;
  background: #ffcdb0;
  color: #4a2e18;
  font-size: 10px;
  font-weight: 700;
  line-height: 1;
  cursor: pointer;
  transition: background 220ms ease-out;
}

.sm__toggle:hover {
  background: #ffc2ad;
}

.sm__toggle:focus-visible {
  outline: 2px solid #4a2e18;
  outline-offset: 2px;
}

.sm__toggle[aria-pressed=true] {
  background: #bfe3ff;
}

.sm__meta--dim {
  font-size: 10px;
  font-weight: 500;
  color: rgba(74, 46, 24, 0.72);
}

@media (max-width: 340px) {
  .sm {
    gap: 4px;
  }
  .sm__field {
    height: 100px;
  }
  .sm__meta--dim {
    display: none;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sm.is-still .sm__field {
    cursor: default !important;
  }
}

// 포인터 먹이·기피물(04). Physarum 스티그머지 + 실시간 유인/기피 앵커 —
// 클릭한 좌표를 부호 있는 향(sign: +먹이 / -소금)으로 심고 센싱값에 더한다. 에이전트는
// 먹이 앵커 쪽은 끌리고 소금 앵커 쪽은 밀려난다. .is-demo 동안은 실제 클릭 없이도 화면이
// 살아 있도록 스크립트가 좌표를 골라 자동으로 같은 심기 함수를 호출하고, 사람이 실제로
// 클릭·모드 버튼을 누르면 그 즉시 같은 로직이 반응한다(자동·수동 경로가 완전히 같다).
//
// 화면이 사는 장치 — 077 캔버스 기준의 "매 프레임 계산":
//  · 캔버스는 절대 clear 하지 않는다. 필드 전체를 매 프레임 새로 계산해 얹는다.
//  · 앰비언트 글로우 레이어(두 옥타브 값노이즈)가 전면을 확산 구조로 흔들어 누적면적을 채운다.
//  · 먹이·소금 앵커는 심은 뒤 서서히 옅어지며 사라져(수명) 다음 클릭 자리를 비운다.
(function () {
  // ── 변형 상수 블록 ──
  var AGENTS = 1500;        // 동시에 걷는 에이전트 수
  var DECAY = 0.05;         // 증발률
  var ANCHOR_LIFE = 5.2;    // 앵커(먹이·소금) 수명(초)
  // ────────────────────────────────────
  var SENSOR_ANGLE = 0.5;
  var SENSOR_DIST = 5.0;
  var TURN = 0.5;
  var STEP = 1.05;
  var DEPOSIT = 4.2;
  var DIFFUSE = 0.5;
  var CAP = 7;
  var SUBSTEPS = 3;
  var ANCHOR_W = 2.2;
  var MAX_ANCHORS = 7;

  var root = document.getElementById('smRoot');
  var field = document.getElementById('smField');
  var cv = document.getElementById('smCv');
  var ctx = cv.getContext('2d', { alpha: false });
  var modeBtn = document.getElementById('smMode');
  var modeLabel = document.getElementById('smModeLabel');

  function makeRand(seed) {
    var st = seed >>> 0;
    return function () {
      st = (st + 0x6D2B79F5) >>> 0;
      var t = st;
      t = Math.imul(t ^ (t >>> 15), t | 1);
      t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
      return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
    };
  }
  var rand = makeRand(0x320A04);

  var css = getComputedStyle(root);
  function tokRGB(name) {
    var s = css.getPropertyValue(name).trim();
    var hx = s.length === 4
      ? s.charAt(1) + s.charAt(1) + s.charAt(2) + s.charAt(2) + s.charAt(3) + s.charAt(3)
      : s.slice(1);
    return [parseInt(hx.slice(0, 2), 16), parseInt(hx.slice(2, 4), 16), parseInt(hx.slice(4, 6), 16)];
  }
  var C_FLOOR = tokRGB('--sm-floor');
  var C_TRAIL = tokRGB('--sm-trail');
  var C_FOOD  = tokRGB('--sm-food');
  var C_SALT  = tokRGB('--sm-salt');

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var W = 0, H = 0, fw = 0, fh = 0, raf = 0, t0 = -1;
  var trail, trailB, img, data;
  var ax, ay, ah;
  var anchors = [];   // {x,y,sign,born}
  var mode = 1;        // 1=먹이(끌림) · -1=소금(기피)
  var curT = 0;
  var autoIdx = 0;

  // ── 값노이즈(앰비언트 글로우용) ──
  var perm = new Uint8Array(512);
  (function () {
    var p = [];
    for (var i = 0; i < 256; i++) p.push(i);
    for (var i2 = 255; i2 > 0; i2--) {
      var k2 = Math.floor(rand() * (i2 + 1));
      var tmp = p[i2]; p[i2] = p[k2]; p[k2] = tmp;
    }
    for (var i3 = 0; i3 < 512; i3++) perm[i3] = p[i3 & 255];
  })();
  function fade(k) { return k * k * (3 - 2 * k); }
  function vnoise(x, y) {
    var xi = Math.floor(x), yi = Math.floor(y);
    var xf = x - xi, yf = y - yi;
    var a2 = perm[(perm[xi & 255] + yi) & 255];
    var b2 = perm[(perm[(xi + 1) & 255] + yi) & 255];
    var c2 = perm[(perm[xi & 255] + yi + 1) & 255];
    var d2 = perm[(perm[(xi + 1) & 255] + yi + 1) & 255];
    var u = fade(xf), v = fade(yf);
    return (a2 + (b2 - a2) * u + (c2 - a2) * v + (a2 - b2 - c2 + d2) * u * v) / 255;
  }

  function idx(x, y) {
    x = x % fw; if (x < 0) x += fw;
    y = y % fh; if (y < 0) y += fh;
    return (y * fw + x) | 0;
  }
  function clampIdx(x, y) {
    x = Math.max(0, Math.min(fw - 1, Math.round(x)));
    y = Math.max(0, Math.min(fh - 1, Math.round(y)));
    return y * fw + x;
  }

  function placeAnchor(fx, fy, sign) {
    anchors.push({ x: fx, y: fy, sign: sign, born: curT });
    if (anchors.length > MAX_ANCHORS) anchors.shift();
  }

  function anchorField(x, y) {
    var v = 0;
    for (var i = 0; i < anchors.length; i++) {
      var a = anchors[i];
      var age = curT - a.born;
      if (age < 0 || age > ANCHOR_LIFE) continue;
      var life = 1 - age / ANCHOR_LIFE;
      var dx = x - a.x, dy = y - a.y;
      var d2 = dx * dx + dy * dy;
      v += a.sign * life * Math.exp(-d2 / 30);
    }
    return v;
  }

  function sense(x, y) {
    var i = clampIdx(x, y);
    return trail[i] + anchorField(x, y) * ANCHOR_W * CAP;
  }

  function initAgents() {
    ax = new Float32Array(AGENTS); ay = new Float32Array(AGENTS); ah = new Float32Array(AGENTS);
    var cx = fw / 2, cy = fh / 2, r = Math.min(fw, fh) * 0.16;
    for (var i = 0; i < AGENTS; i++) {
      var a = rand() * Math.PI * 2, rr = rand() * r;
      ax[i] = cx + Math.cos(a) * rr;
      ay[i] = cy + Math.sin(a) * rr;
      ah[i] = rand() * Math.PI * 2;
    }
  }

  function stepAgents() {
    for (var i = 0; i < AGENTS; i++) {
      var x = ax[i], y = ay[i], h = ah[i];
      var sf = sense(x + Math.cos(h) * SENSOR_DIST, y + Math.sin(h) * SENSOR_DIST);
      var sl = sense(x + Math.cos(h + SENSOR_ANGLE) * SENSOR_DIST, y + Math.sin(h + SENSOR_ANGLE) * SENSOR_DIST);
      var sr = sense(x + Math.cos(h - SENSOR_ANGLE) * SENSOR_DIST, y + Math.sin(h - SENSOR_ANGLE) * SENSOR_DIST);
      if (sf >= sl && sf >= sr) {
        // 직진
      } else if (sl > sr) {
        h += TURN;
      } else if (sr > sl) {
        h -= TURN;
      } else {
        h += (rand() < 0.5 ? 1 : -1) * TURN;
      }
      h += (rand() - 0.5) * 0.14;
      var nx = x + Math.cos(h) * STEP, ny = y + Math.sin(h) * STEP;
      nx = ((nx % fw) + fw) % fw; ny = ((ny % fh) + fh) % fh;
      ax[i] = nx; ay[i] = ny; ah[i] = h;
      var ii = idx(Math.round(nx), Math.round(ny));
      trail[ii] = Math.min(CAP, trail[ii] + DEPOSIT);
    }
  }

  function diffuseEvap() {
    for (var y = 0; y < fh; y++) {
      var ym = y === 0 ? fh - 1 : y - 1, yp = y === fh - 1 ? 0 : y + 1;
      var rowY = y * fw, rowYm = ym * fw, rowYp = yp * fw;
      for (var x = 0; x < fw; x++) {
        var xm = x === 0 ? fw - 1 : x - 1, xp = x === fw - 1 ? 0 : x + 1;
        var i = rowY + x;
        var avg = (trail[rowY + xm] + trail[rowY + xp] + trail[rowYm + x] + trail[rowYp + x]) * 0.25;
        trailB[i] = (trail[i] * (1 - DIFFUSE) + avg * DIFFUSE) * (1 - DECAY);
      }
    }
    var t = trail; trail = trailB; trailB = t;
  }

  function render(t) {
    for (var y = 0; y < fh; y++) {
      for (var x = 0; x < fw; x++) {
        var i = y * fw + x;
        var j = i * 4;
        var v = trail[i] / CAP; if (v > 1) v = 1;
        var k = v * v * (3 - 2 * v);
        var rr = C_FLOOR[0] + (C_TRAIL[0] - C_FLOOR[0]) * k;
        var gg = C_FLOOR[1] + (C_TRAIL[1] - C_FLOOR[1]) * k;
        var bb = C_FLOOR[2] + (C_TRAIL[2] - C_FLOOR[2]) * k;
        for (var ai = 0; ai < anchors.length; ai++) {
          var a = anchors[ai];
          var age = t - a.born;
          if (age < 0 || age > ANCHOR_LIFE) continue;
          var life = 1 - age / ANCHOR_LIFE;
          var dx = x - a.x, dy = y - a.y;
          var d2 = dx * dx + dy * dy;
          var pulse = 0.6 + 0.4 * Math.sin(t * 3.1 + ai);
          var glow = Math.exp(-d2 / 22) * life * pulse;
          var col = a.sign > 0 ? C_FOOD : C_SALT;
          rr += (col[0] - rr) * glow; gg += (col[1] - gg) * glow; bb += (col[2] - bb) * glow;
        }
        var n1 = vnoise(x * 0.09, y * 0.09 + t * 0.9);
        var n2 = vnoise(x * 0.03 + 40, y * 0.03 + t * 0.6);
        var sh = (n1 - 0.5) * 26 + (n2 - 0.5) * 16;
        rr += sh; gg += sh; bb += sh;
        data[j] = rr; data[j + 1] = gg; data[j + 2] = bb; data[j + 3] = 255;
      }
    }
    ctx.putImageData(img, 0, 0);
  }

  function fit() {
    var r = field.getBoundingClientRect();
    W = Math.round(r.width); H = Math.round(r.height);
    fw = Math.max(96, Math.min(200, Math.round(W / 3)));
    fh = Math.max(52, Math.min(120, Math.round(H / 3)));
    cv.width = fw; cv.height = fh;
    cv.style.width = '100%'; cv.style.height = '100%';
    ctx = cv.getContext('2d', { alpha: false });
    img = ctx.createImageData(fw, fh); data = img.data;
    trail = new Float32Array(fw * fh); trailB = new Float32Array(fw * fh);
    anchors = []; curT = 0; autoIdx = 0;
    initAgents();
  }

  function stillFrame() {
    curT = 0.4; placeAnchor(fw * 0.28, fh * 0.5, 1);
    curT = 1.1; placeAnchor(fw * 0.74, fh * 0.32, 1);
    curT = 1.7; placeAnchor(fw * 0.5, fh * 0.78, -1);
    curT = 2.4;
    for (var k = 0; k < 240; k++) { stepAgents(); diffuseEvap(); curT += 0.02; }
    render(curT);
  }

  // .is-demo 자동 시연 각본 — 사람이 안 눌러도 동일 placeAnchor() 로 화면이 산다.
  var script = [
    { t: 0.3, x: 0.26, y: 0.5, sign: 1 },
    { t: 1.1, x: 0.7, y: 0.28, sign: 1 },
    { t: 1.9, x: 0.5, y: 0.78, sign: -1 },
    { t: 2.7, x: 0.78, y: 0.7, sign: 1 },
    { t: 3.6, x: 0.22, y: 0.24, sign: -1 }
  ];

  function frame(now) {
    if (t0 < 0) t0 = now;
    curT = (now - t0) / 1000;
    if (root.classList.contains('is-demo')) {
      while (autoIdx < script.length && curT >= script[autoIdx].t) {
        var s = script[autoIdx];
        placeAnchor(fw * s.x, fh * s.y, s.sign);
        autoIdx++;
      }
      if (autoIdx >= script.length && curT > script[script.length - 1].t + ANCHOR_LIFE) autoIdx = 0, t0 = now;
    }
    for (var i = 0; i < SUBSTEPS; i++) { stepAgents(); diffuseEvap(); }
    render(curT);
    raf = requestAnimationFrame(frame);
  }

  function setMode(next) {
    mode = next;
    modeBtn.setAttribute('aria-pressed', mode < 0 ? 'true' : 'false');
    if (modeLabel) modeLabel.textContent = mode > 0 ? 'Click = food' : 'Click = salt';
  }

  field.addEventListener('pointerdown', function (e) {
    var rect = field.getBoundingClientRect();
    var fx = (e.clientX - rect.left) / rect.width * fw;
    var fy = (e.clientY - rect.top) / rect.height * fh;
    placeAnchor(fx, fy, mode);
  });
  modeBtn.addEventListener('click', function () { setMode(-mode); });

  window.addEventListener('resize', function () {
    fit();
    if (reduce) stillFrame();
  });

  fit();
  if (reduce) {
    stillFrame();
    root.classList.add('is-still');
  } else {
    raf = requestAnimationFrame(frame);
  }
})();

// PointerAttractRepel — vanilla 판(run/320/demo/04-slime-pointer-attract-repel/index.html) 의 React 포트.
// 포인터 먹이·기피물. Physarum 스티그머지 + 실시간 유인/기피 앵커 — 클릭한 좌표를 부호 있는
// 향(sign: +먹이 / -소금)으로 심고 센싱값에 더한다. 에이전트는 먹이 앵커 쪽은 끌리고 소금
// 앵커 쪽은 밀려난다. 사람이 클릭하지 않아도 자동 각본이 같은 심기 함수를 호출해 화면이 산다
// (자동·수동 경로가 완전히 같다).
import { useEffect, useRef, useState } from "react";
import type { CSSProperties, PointerEvent as ReactPointerEvent } from "react";
import styles from "./PointerAttractRepel.module.scss";

export type PointerAttractRepelProps = {
  duration?: string;
  easing?: string;
  color?: string;
  agents?: number;       // 동시에 걷는 에이전트 수
  decay?: number;          // 증발률
  anchorLife?: number;      // 앵커(먹이·소금) 수명(초)
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };
type RGB = [number, number, number];
type Anchor = { x: number; y: number; sign: number; born: number };
type Script = { t: number; x: number; y: number; sign: number };

const FIELD_LABEL = "포인터 먹이·기피물 점균 실험판";
const SENSOR_ANGLE = 0.5;
const SENSOR_DIST = 5.0;
const TURN = 0.5;
const STEP = 1.05;
const DEPOSIT = 4.2;
const DIFFUSE = 0.5;
const CAP = 7;
const SUBSTEPS = 3;
const ANCHOR_W = 2.2;
const MAX_ANCHORS = 7;
const AUTO_SCRIPT: Script[] = [
  { t: 0.3, x: 0.26, y: 0.5, sign: 1 },
  { t: 1.1, x: 0.7, y: 0.28, sign: 1 },
  { t: 1.9, x: 0.5, y: 0.78, sign: -1 },
  { t: 2.7, x: 0.78, y: 0.7, sign: 1 },
  { t: 3.6, x: 0.22, y: 0.24, sign: -1 },
];

function makePRNG(seed: number): () => number {
  let s = seed >>> 0;
  return function () {
    s = (s + 0x6d2b79f5) >>> 0;
    let t = s;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

export default function PointerAttractRepel({
  duration = "2s",
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#ffcdb0",
  agents = 1500,
  decay = 0.05,
  anchorLife = 5.2,
}: PointerAttractRepelProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const fieldRef = useRef<HTMLDivElement | null>(null);
  const cvRef = useRef<HTMLCanvasElement | null>(null);
  const ctxRef = useRef<CanvasRenderingContext2D | null>(null);
  const colRef = useRef<{ floor: RGB; trail: RGB; food: RGB; salt: RGB } | null>(null);
  const agentsRef = useRef(agents) as Box<number>;
  const decayRef = useRef(decay) as Box<number>;
  const anchorLifeRef = useRef(anchorLife) as Box<number>;
  const randRef = useRef(makePRNG(0x320a04)) as Box<() => number>;
  const fwRef = useRef(0) as Box<number>;
  const fhRef = useRef(0) as Box<number>;
  const trailRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const trailBRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const axRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const ayRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const ahRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const imgRef = useRef<ImageData | null>(null) as Box<ImageData | null>;
  const permRef = useRef<Uint8Array>(new Uint8Array(512)) as Box<Uint8Array>;
  const anchorsRef = useRef<Anchor[]>([]) as Box<Anchor[]>;
  const modeRef = useRef(1) as Box<number>;
  const curTRef = useRef(0) as Box<number>;
  const autoIdxRef = useRef(0) as Box<number>;
  const rafRef = useRef(0) as Box<number>;
  const [modePressed, setModePressed] = useState(false);
  const [still, setStill] = useState(false);
  const vars: Vars = { "--duration": duration, "--easing": easing, "--color": color };

  function reduced(): boolean {
    return window.matchMedia("(prefers-reduced-motion: reduce)").matches;
  }

  function tokRGB(root: HTMLDivElement, name: string): RGB {
    const s = getComputedStyle(root).getPropertyValue(name).trim();
    const hx = s.length === 4
      ? s.charAt(1) + s.charAt(1) + s.charAt(2) + s.charAt(2) + s.charAt(3) + s.charAt(3)
      : s.slice(1);
    return [parseInt(hx.slice(0, 2), 16), parseInt(hx.slice(2, 4), 16), parseInt(hx.slice(4, 6), 16)];
  }

  function buildPerm(): void {
    const rand = randRef.current;
    const p: number[] = [];
    for (let i = 0; i < 256; i++) p.push(i);
    for (let i2 = 255; i2 > 0; i2--) {
      const k2 = Math.floor(rand() * (i2 + 1));
      const tmp = p[i2]; p[i2] = p[k2]; p[k2] = tmp;
    }
    const perm = new Uint8Array(512);
    for (let i3 = 0; i3 < 512; i3++) perm[i3] = p[i3 & 255];
    permRef.current = perm;
  }
  function fade(k: number): number { return k * k * (3 - 2 * k); }
  function vnoise(x: number, y: number): number {
    const perm = permRef.current;
    const xi = Math.floor(x), yi = Math.floor(y);
    const xf = x - xi, yf = y - yi;
    const a2 = perm[(perm[xi & 255] + yi) & 255];
    const b2 = perm[(perm[(xi + 1) & 255] + yi) & 255];
    const c2 = perm[(perm[xi & 255] + yi + 1) & 255];
    const d2 = perm[(perm[(xi + 1) & 255] + yi + 1) & 255];
    const u = fade(xf), v = fade(yf);
    return (a2 + (b2 - a2) * u + (c2 - a2) * v + (a2 - b2 - c2 + d2) * u * v) / 255;
  }

  function idx(x: number, y: number): number {
    const fw = fwRef.current, fh = fhRef.current;
    let xx = x % fw; if (xx < 0) xx += fw;
    let yy = y % fh; if (yy < 0) yy += fh;
    return (yy * fw + xx) | 0;
  }
  function clampIdx(x: number, y: number): number {
    const fw = fwRef.current, fh = fhRef.current;
    const xx = Math.max(0, Math.min(fw - 1, Math.round(x)));
    const yy = Math.max(0, Math.min(fh - 1, Math.round(y)));
    return yy * fw + xx;
  }

  function placeAnchor(fx: number, fy: number, sign: number): void {
    const anchors = anchorsRef.current;
    anchors.push({ x: fx, y: fy, sign, born: curTRef.current });
    if (anchors.length > MAX_ANCHORS) anchors.shift();
  }

  function anchorField(x: number, y: number): number {
    const anchors = anchorsRef.current;
    const life0 = anchorLifeRef.current;
    let v = 0;
    for (let i = 0; i < anchors.length; i++) {
      const a = anchors[i];
      const age = curTRef.current - a.born;
      if (age < 0 || age > life0) continue;
      const life = 1 - age / life0;
      const dx = x - a.x, dy = y - a.y;
      const d2 = dx * dx + dy * dy;
      v += a.sign * life * Math.exp(-d2 / 30);
    }
    return v;
  }

  function sense(x: number, y: number): number {
    const i = clampIdx(x, y);
    return trailRef.current[i] + anchorField(x, y) * ANCHOR_W * CAP;
  }

  function initAgents(): void {
    const rand = randRef.current;
    const fw = fwRef.current, fh = fhRef.current;
    const A = agentsRef.current;
    const ax = new Float32Array(A), ay = new Float32Array(A), ah = new Float32Array(A);
    const cx = fw / 2, cy = fh / 2, r = Math.min(fw, fh) * 0.16;
    for (let i = 0; i < A; i++) {
      const a = rand() * Math.PI * 2, rr = rand() * r;
      ax[i] = cx + Math.cos(a) * rr;
      ay[i] = cy + Math.sin(a) * rr;
      ah[i] = rand() * Math.PI * 2;
    }
    axRef.current = ax; ayRef.current = ay; ahRef.current = ah;
  }

  function stepAgents(): void {
    const rand = randRef.current;
    const A = agentsRef.current;
    const fw = fwRef.current, fh = fhRef.current;
    const ax = axRef.current, ay = ayRef.current, ah = ahRef.current;
    const trail = trailRef.current;
    for (let i = 0; i < A; i++) {
      const x = ax[i], y = ay[i];
      let h = ah[i];
      const sf = sense(x + Math.cos(h) * SENSOR_DIST, y + Math.sin(h) * SENSOR_DIST);
      const sl = sense(x + Math.cos(h + SENSOR_ANGLE) * SENSOR_DIST, y + Math.sin(h + SENSOR_ANGLE) * SENSOR_DIST);
      const sr = sense(x + Math.cos(h - SENSOR_ANGLE) * SENSOR_DIST, y + Math.sin(h - SENSOR_ANGLE) * SENSOR_DIST);
      if (sf >= sl && sf >= sr) {
        // 직진
      } else if (sl > sr) {
        h += TURN;
      } else if (sr > sl) {
        h -= TURN;
      } else {
        h += (rand() < 0.5 ? 1 : -1) * TURN;
      }
      h += (rand() - 0.5) * 0.14;
      let nx = x + Math.cos(h) * STEP, ny = y + Math.sin(h) * STEP;
      nx = ((nx % fw) + fw) % fw; ny = ((ny % fh) + fh) % fh;
      ax[i] = nx; ay[i] = ny; ah[i] = h;
      const ii = idx(Math.round(nx), Math.round(ny));
      trail[ii] = Math.min(CAP, trail[ii] + DEPOSIT);
    }
  }

  function diffuseEvap(): void {
    const fw = fwRef.current, fh = fhRef.current;
    const trail = trailRef.current, trailB = trailBRef.current;
    const dc = decayRef.current;
    for (let y = 0; y < fh; y++) {
      const ym = y === 0 ? fh - 1 : y - 1, yp = y === fh - 1 ? 0 : y + 1;
      const rowY = y * fw, rowYm = ym * fw, rowYp = yp * fw;
      for (let x = 0; x < fw; x++) {
        const xm = x === 0 ? fw - 1 : x - 1, xp = x === fw - 1 ? 0 : x + 1;
        const i = rowY + x;
        const avg = (trail[rowY + xm] + trail[rowY + xp] + trail[rowYm + x] + trail[rowYp + x]) * 0.25;
        trailB[i] = (trail[i] * (1 - DIFFUSE) + avg * DIFFUSE) * (1 - dc);
      }
    }
    trailRef.current = trailB; trailBRef.current = trail;
  }

  function render(t: number): void {
    const ctx = ctxRef.current;
    const col = colRef.current;
    const img = imgRef.current;
    if (!ctx || !col || !img) return;
    const fw = fwRef.current, fh = fhRef.current;
    const trail = trailRef.current;
    const anchors = anchorsRef.current;
    const life0 = anchorLifeRef.current;
    const data = img.data;
    for (let y = 0; y < fh; y++) {
      for (let x = 0; x < fw; x++) {
        const i = y * fw + x;
        const j = i * 4;
        let v = trail[i] / CAP; if (v > 1) v = 1;
        const k = v * v * (3 - 2 * v);
        let rr = col.floor[0] + (col.trail[0] - col.floor[0]) * k;
        let gg = col.floor[1] + (col.trail[1] - col.floor[1]) * k;
        let bb = col.floor[2] + (col.trail[2] - col.floor[2]) * k;
        for (let ai = 0; ai < anchors.length; ai++) {
          const a = anchors[ai];
          const age = t - a.born;
          if (age < 0 || age > life0) continue;
          const life = 1 - age / life0;
          const dx = x - a.x, dy = y - a.y;
          const d2 = dx * dx + dy * dy;
          const pulse = 0.6 + 0.4 * Math.sin(t * 3.1 + ai);
          const glow = Math.exp(-d2 / 22) * life * pulse;
          const acol = a.sign > 0 ? col.food : col.salt;
          rr += (acol[0] - rr) * glow; gg += (acol[1] - gg) * glow; bb += (acol[2] - bb) * glow;
        }
        const n1 = vnoise(x * 0.09, y * 0.09 + t * 0.9);
        const n2 = vnoise(x * 0.03 + 40, y * 0.03 + t * 0.6);
        const sh = (n1 - 0.5) * 26 + (n2 - 0.5) * 16;
        rr += sh; gg += sh; bb += sh;
        data[j] = rr; data[j + 1] = gg; data[j + 2] = bb; data[j + 3] = 255;
      }
    }
    ctx.putImageData(img, 0, 0);
  }

  function fit(): void {
    const field = fieldRef.current;
    const cv = cvRef.current;
    if (!field || !cv) return;
    const r = field.getBoundingClientRect();
    const W = Math.round(r.width), H = Math.round(r.height);
    const fw = Math.max(96, Math.min(200, Math.round(W / 3)));
    const fh = Math.max(52, Math.min(120, Math.round(H / 3)));
    fwRef.current = fw; fhRef.current = fh;
    cv.width = fw; cv.height = fh;
    cv.style.width = "100%"; cv.style.height = "100%";
    const ctx = cv.getContext("2d", { alpha: false });
    if (!ctx) return;
    ctxRef.current = ctx;
    const img = ctx.createImageData(fw, fh);
    imgRef.current = img;
    trailRef.current = new Float32Array(fw * fh);
    trailBRef.current = new Float32Array(fw * fh);
    anchorsRef.current = []; curTRef.current = 0; autoIdxRef.current = 0;
    initAgents();
  }

  function stillFrame(): void {
    curTRef.current = 0.4; placeAnchor(fwRef.current * 0.28, fhRef.current * 0.5, 1);
    curTRef.current = 1.1; placeAnchor(fwRef.current * 0.74, fhRef.current * 0.32, 1);
    curTRef.current = 1.7; placeAnchor(fwRef.current * 0.5, fhRef.current * 0.78, -1);
    curTRef.current = 2.4;
    for (let k = 0; k < 240; k++) { stepAgents(); diffuseEvap(); curTRef.current += 0.02; }
    render(curTRef.current);
  }

  let t0 = -1;
  function frame(now: number): void {
    if (t0 < 0) t0 = now;
    curTRef.current = (now - t0) / 1000;
    const script = AUTO_SCRIPT;
    while (autoIdxRef.current < script.length && curTRef.current >= script[autoIdxRef.current].t) {
      const s = script[autoIdxRef.current];
      placeAnchor(fwRef.current * s.x, fhRef.current * s.y, s.sign);
      autoIdxRef.current++;
    }
    if (autoIdxRef.current >= script.length && curTRef.current > script[script.length - 1].t + anchorLifeRef.current) {
      autoIdxRef.current = 0; t0 = now;
    }
    for (let i = 0; i < SUBSTEPS; i++) { stepAgents(); diffuseEvap(); }
    render(curTRef.current);
    rafRef.current = requestAnimationFrame(frame);
  }

  function setMode(next: number): void {
    modeRef.current = next;
    setModePressed(next < 0);
  }

  function onFieldPointerDown(e: ReactPointerEvent<HTMLDivElement>): void {
    const field = fieldRef.current;
    if (!field) return;
    const rect = field.getBoundingClientRect();
    const fx = (e.clientX - rect.left) / rect.width * fwRef.current;
    const fy = (e.clientY - rect.top) / rect.height * fhRef.current;
    placeAnchor(fx, fy, modeRef.current);
  }

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    agentsRef.current = agents;
    decayRef.current = decay;
    anchorLifeRef.current = anchorLife;
    randRef.current = makePRNG(0x320a04);
    colRef.current = {
      floor: tokRGB(root, "--sm-floor"),
      trail: tokRGB(root, "--sm-trail"),
      food: tokRGB(root, "--sm-food"),
      salt: tokRGB(root, "--sm-salt"),
    };
    buildPerm();
    fit();
    function onResize(): void {
      fit();
      if (reduced()) stillFrame();
    }
    window.addEventListener("resize", onResize);
    if (reduced()) {
      stillFrame();
      setStill(true);
    } else {
      t0 = -1;
      rafRef.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafRef.current);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [agents, decay, anchorLife]);

  const rootCls = still ? `${styles.root} ${styles.isStill}` : styles.root;

  return (
    <main className={styles.stage}>
      <div className={rootCls} ref={rootRef} style={vars}>
        <p className={styles.hint}>
          <span>클릭한 좌표를 새 먹이로 심으면 네트워크가 그쪽으로 가지를 뻗고, 모드를 바꿔 소금(기피물질)로 두면 트레일이 그 자리를 피해 휘어 자랍니다</span>
        </p>
        <div
          className={styles.field}
          ref={fieldRef}
          role="application"
          aria-label={FIELD_LABEL}
          tabIndex={0}
          onPointerDown={onFieldPointerDown}
        >
          <canvas className={styles.cv} ref={cvRef}></canvas>
        </div>
        <div className={styles.bar}>
          <button
            className={styles.toggle}
            type="button"
            aria-pressed={modePressed}
            onClick={() => setMode(-modeRef.current)}
          >
            <span>{modePressed ? "클릭 = 소금" : "클릭 = 먹이"}</span>
          </button>
          <span className={styles.metaDim}>canvas · pointermove · requestAnimationFrame</span>
        </div>
      </div>
    </main>
  );
}