03Torch — a flame carrying a wind vector on its back

<main class="stage">
<div class="tc is-demo" id="tcRoot">
  <p class="tc__hint">
    <svg class="tc__ico" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M128 24a16 16 0 0 1 16 16v8a80.06 80.06 0 0 1 63.94 63.94h8a16 16 0 0 1 0 32h-8A80.06 80.06 0 0 1 144 207.94v8a16 16 0 0 1-32 0v-8A80.06 80.06 0 0 1 48.06 144h-8a16 16 0 0 1 0-32h8A80.06 80.06 0 0 1 112 48.06v-8A16 16 0 0 1 128 24m-16 57.35V96a16 16 0 0 0 32 0V81.35A48.09 48.09 0 0 0 81.35 112H96a16 16 0 0 0 0-32h14.65M174.65 144H160a16 16 0 0 0 0 32h14.65A48.09 48.09 0 0 0 144 174.65V160a16 16 0 0 0-32 0v14.65A48.09 48.09 0 0 0 81.35 144" opacity=".2"/><path d="M232 128a104 104 1 1 1-104-104a104 104 0 0 1 104 104m-32 0a8 8 0 0 0-8-8h-9.34A56.1 56.1 0 0 0 136 77.34V68a8 8 0 0 0-16 0v9.34A56.1 56.1 0 0 0 77.34 120H68a8 8 0 0 0 0 16h9.34A56.1 56.1 0 0 0 120 179.66V188a8 8 0 0 0 16 0v-8.34A56.1 56.1 0 0 0 178.66 136H192a8 8 0 0 0 8-8m-40 0a32 32 0 1 1-32-32a32 32 0 0 1 32 32m-16 0a16 16 0 1 0-16 16a16 16 0 0 0 16-16"/></g></svg>
    <span>A steady wind vector with a slow sine wobble sweeps the whole flame to one side — pointer x is wind strength, y is direction</span>
  </p>
  <div class="tc__field" id="tcField" role="application" aria-label="Torch wind vector board" tabindex="0">
    <canvas class="tc__cv" id="tcCv"></canvas>
  </div>
  <div class="tc__bar">
    <span class="tc__meta">wind <b class="tc__val" id="tcW">0.62</b> · sin-based wobble</span>
    <span class="tc__meta tc__meta--dim">requestAnimationFrame · color-temp ladder</span>
  </div>
</div>
</main>

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

// 횃불(03). CSS 애니메이션·@keyframes 를 아예 두지 않는다 —
// 움직임은 전부 캔버스 rAF 루프(일정 바람 벡터 + 느린 sin 요동 + 색온도 냉각)가 만든다.
// 무대는 잉크(#241b1d — 어두운 야외). 파스텔 고정 팔레트를 --fire-* 로 편 공통 규격(01~09 동일).

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

@include stage($stage-ink);

// ── 편 공통 파스텔 팔레트(BD9~11 원칙: 편마다 다시 정하지 않는다) ──
$fire-ink:   #241b1d;   // 배경 — 어두운 실내
$fire-amber: #f0a868;   // 불꽃 코어
$fire-gold:  #f6cf8a;   // 불꽃 팁
$fire-rose:  #eca0a8;   // 로즈 변형
$fire-ember: #d97a52;   // 잔불
$fire-smoke: #c9c2c6;   // 연기

.tc {
  // 렌더러가 읽는 색 — JS 는 getComputedStyle 로 --fire-* 를 받아 쓴다
  --fire-ink:   #{$fire-ink};
  --fire-amber: #{$fire-amber};
  --fire-gold:  #{$fire-gold};
  --fire-rose:  #{$fire-rose};
  --fire-ember: #{$fire-ember};
  --fire-smoke: #{$fire-smoke};

  // 항목 반경 토큰(01~09 공통 — 실사용은 $r-* SCSS 토큰, 표기 참조용)
  --radius-sm: 4px;
  --radius-md: 10px;
  --radius-lg: 20px;

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

.tc__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: $fire-smoke;                       // 잉크 무대 위 — 연기 톤 글자
}
.tc__ico { width: 16px; height: 16px; flex: 0 0 auto; color: $fire-smoke; }

.tc__field {
  position: relative; height: 180px;
  border-radius: $r-card; overflow: hidden;
  background: $fire-ink;
  box-shadow: inset 0 0 0 1px rgba($fire-smoke, .18);
  cursor: crosshair; touch-action: none;
}
.tc__field:focus-visible { outline: 2px solid $fire-amber; outline-offset: 2px; }

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

.tc__bar { display: flex; align-items: baseline; justify-content: space-between; gap: $sp-2; }
.tc__meta { font-size: 10px; font-weight: 500; color: rgba($fire-smoke, .72); }
.tc__val { color: $fire-gold; font-weight: 700; }        // 잉크 위 금빛 라벨
.tc__meta--dim { font-size: 10px; }

@media (max-width: 340px) {
  .tc { gap: $sp-1; }
  .tc__field { height: 100px; }
  .tc__meta--dim { display: none; }
}

// reduce — rAF 를 돌리지 않고 한 장만 남는다. 커서 신호만 거둔다.
@media (prefers-reduced-motion: reduce) {
  .tc.is-still .tc__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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.tc {
  --fire-ink: #241b1d;
  --fire-amber: #f0a868;
  --fire-gold: #f6cf8a;
  --fire-rose: #eca0a8;
  --fire-ember: #d97a52;
  --fire-smoke: #c9c2c6;
  --radius-sm: 4px;
  --radius-md: 10px;
  --radius-lg: 20px;
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 100%;
  max-width: 424px;
}

.tc__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: #c9c2c6;
}

.tc__ico {
  width: 16px;
  height: 16px;
  flex: 0 0 auto;
  color: #c9c2c6;
}

.tc__field {
  position: relative;
  height: 180px;
  border-radius: 16px;
  overflow: hidden;
  background: #241b1d;
  box-shadow: inset 0 0 0 1px rgba(201, 194, 198, 0.18);
  cursor: crosshair;
  touch-action: none;
}

.tc__field:focus-visible {
  outline: 2px solid #f0a868;
  outline-offset: 2px;
}

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

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

.tc__meta {
  font-size: 10px;
  font-weight: 500;
  color: rgba(201, 194, 198, 0.72);
}

.tc__val {
  color: #f6cf8a;
  font-weight: 700;
}

.tc__meta--dim {
  font-size: 10px;
}

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

// 횃불(03). 불꽃 전체를 기울이는 힘은 두 겹이다:
//   1) 일정한 wind 벡터(WIND_VX, WIND_VY) — 매 프레임 변하지 않는 상수 방향
//   2) 느린 요동 — sin(t * 저주파) 로 벡터 자체가 아주 천천히 흔들려 성화가 "숨쉬며" 쏠린다
// 입자는 연료 k(1→0) 로 gold→amber→ember 색온도 사다리를 타고 부력으로 오르며,
// k 가 낮을수록(위로 갈수록) 바람을 더 많이 받는다 — 근원(횃불 머리)은 곧고 끝은 크게 눕는다.
(function () {
  // ── 변형 상수 블록 — 아래 값 하나만 바꿔 변형 3종을 만든다 ──
  var WIND_VX = 46;      // wind 벡터 x(px/s) — 변형 "wind 세기" 축(20 → 70)
  var WIND_VY = -6;      // wind 벡터 y(px/s) — 살짝 위로 미는 성분
  var WOBBLE  = 0.35;    // 느린 요동 진폭(라디안) — 변형 "요동 폭" 축
  var TONE    = 0;       // 코어 색 변형 — 0: amber(#f0a868), 1: rose(#eca0a8)
  // ────────────────────────────────────────────────────

  var root = document.getElementById('tcRoot');
  var field = document.getElementById('tcField');
  var cv = document.getElementById('tcCv');
  var ctx = cv.getContext('2d');
  var wOut = document.getElementById('tcW');

  // 시드 고정 PRNG — mulberry32. 미리보기가 항상 같은 성화로 살아 움직인다
  var SEED = 0x5eed03;
  var prngState = SEED >>> 0;
  function rand() {
    prngState = (prngState + 0x6D2B79F5) >>> 0;
    var t = prngState;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  }

  // 색은 CSS 커스텀 프로퍼티(--fire-*)에서 getComputedStyle 로 읽는다 — 파스텔 토큰이 scss 한 곳에
  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_INK   = tokRGB('--fire-ink');
  var C_AMBER = tokRGB('--fire-amber');
  var C_GOLD  = tokRGB('--fire-gold');
  var C_ROSE  = tokRGB('--fire-rose');
  var C_EMBER = tokRGB('--fire-ember');
  var C_SMOKE = tokRGB('--fire-smoke');
  var C_CORE  = TONE ? C_ROSE : C_AMBER;   // 색 변형 — 코어 톤 교체

  var TAU = Math.PI * 2;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var W = 0, H = 0;
  var raf = 0, t0 = -1;
  var px01 = 0.5, py01 = 0.5;   // 가상 wind 세기/방향 포인터(0..1)
  var manual = false;

  // ── 연료 입자 — 횃불 머리에서 태어나 부력 + wind 벡터로 오르내리며 식는다 ──
  var N_PART = 220;
  var parts = [];
  function spawn(p) {
    p.x = (rand() - 0.5) * 8;
    p.y = 0;
    p.vx = (rand() - 0.5) * 8;
    p.vy = -22 - rand() * 30;
    p.k = 1;
    p.ph = rand() * TAU;
  }
  for (var i = 0; i < N_PART; i++) {
    var p = {}; spawn(p); p.y = -rand() * 46; p.k = rand();
    parts.push(p);
  }

  var K_BURN = 2.1;      // 연료 소모율 (1/s)
  var STILL_T = 1.55;    // reduce 에서 그리는 시각 — 성화가 가장 기운 순간

  function draw(tSec, dt) {
    // 1) 무대 — 어두운 야외
    ctx.globalCompositeOperation = 'source-over';
    ctx.fillStyle = 'rgb(' + C_INK[0] + ',' + C_INK[1] + ',' + C_INK[2] + ')';
    ctx.fillRect(0, 0, W, H);

    var cx = W * 0.5;
    var ground = H * 0.90;
    var poleTop = ground - 96;          // 횃불 자루 윗면 = 머리 밑동
    var strength = 0.5 + px01;          // 포인터 x — wind 세기 배율(0.5~1.5)
    var dirTilt = (py01 - 0.5) * 0.7;   // 포인터 y — wind 방향 미세 회전

    // ── 두 겹 힘 ──
    // 1) 일정한 wind 벡터: (WIND_VX, WIND_VY) * strength, dirTilt 만큼 회전
    // 2) 느린 요동: 벡터 각도에 WOBBLE * sin(t * 0.35) 를 더해 성화가 천천히 숨쉬며 쏠린다
    var baseAng = Math.atan2(WIND_VY, WIND_VX) + dirTilt;
    var wobAng = baseAng + WOBBLE * Math.sin(tSec * 0.35);
    var windMag = Math.hypot(WIND_VX, WIND_VY) * strength;
    var windVX = Math.cos(wobAng) * windMag;
    var windVY = Math.sin(wobAng) * windMag;

    // ── 2) 앙비언트 글로우 — 성화는 밤의 벌판을 밝힌다 ──
    // 반경별 감쇠 빛 겹 LAYERS 장을 lighter 로 쌓는다. 반경은 R0→RMAX(대각선 끝까지),
    // 앞은 촘촘히(밝은 코어)·뒤는 성기게(넓은 은은함). 알파 바닥 0.05 — 가장 바깥 겹도 산다.
    // A0 는 살아있는 연료 총합 flick 과 느린 sin 펄스로 매 프레임 재계산 —
    // 중심(hx,hy)도 요동 각도를 그대로 받아 그 자리에서 움직인다.
    var flick = 0;
    for (var f = 0; f < N_PART; f++) flick += parts[f].k;
    flick = flick / N_PART;
    // 반경 자체가 느리게 부풀었다 줄어든다(breathe) — 겹마다 지름이 진동해 그라디언트 정지점이
    // 프레임마다 재배치되므로, 화면 넓은 영역이(중심에서 멀어도) 실제로 값이 바뀐다.
    var breathe = (0.5 + 0.5 * flick) * (0.72 + 0.28 * Math.sin(tSec * 1.9));
    var hx = cx + windVX * 0.5 + Math.sin(tSec * 1.4) * 6;
    var hy = poleTop - 22 + windVY * 0.5 + Math.cos(tSec * 1.1) * 4;
    var R0 = Math.min(W, H) * 0.16 * breathe;
    var A0 = 0.85 * (0.55 + 0.45 * flick) * (0.62 + 0.38 * Math.sin(tSec * 2.4 + 0.6));
    var RMAX = Math.hypot(W, H) * 0.99;
    var LAYERS = 15;
    var FALLOFF = 0.9;
    ctx.globalCompositeOperation = 'lighter';
    for (var L = 0; L < LAYERS; L++) {
      var Lt = L / (LAYERS - 1);                     // 0..1
      var R = R0 + (RMAX - R0) * Math.pow(Lt, 0.72); // 앞은 촘촘, 뒤는 성기게
      var a = Math.max(0.06, A0 * Math.pow(R0 / R, FALLOFF));
      var m1 = Lt;                                   // 안쪽 gold → 바깥 코어 톤으로 식는다
      var lr = C_GOLD[0] + (C_CORE[0] - C_GOLD[0]) * m1;
      var lg = C_GOLD[1] + (C_CORE[1] - C_GOLD[1]) * m1;
      var lb = C_GOLD[2] + (C_CORE[2] - C_GOLD[2]) * m1;
      var rg = ctx.createRadialGradient(hx, hy, R * 0.04, hx, hy, R);
      rg.addColorStop(0, 'rgba(' + (lr | 0) + ',' + (lg | 0) + ',' + (lb | 0) + ',' + a.toFixed(3) + ')');
      rg.addColorStop(0.72, 'rgba(' + (lr | 0) + ',' + (lg | 0) + ',' + (lb | 0) + ',' + (a * 0.6).toFixed(3) + ')');
      rg.addColorStop(1, 'rgba(0,0,0,0)');
      ctx.fillStyle = rg;
      ctx.fillRect(hx - R, hy - R, R * 2, R * 2);
    }

    // ── 잔열 바닥 띠 — 캔버스 전체 폭이 순수 검정으로 죽지 않게, 벌판 전체가
    // 은은한 잔열로 미세하게 맥동한다(중심이 좌우로 느리게 흘러 폭 전체가 실제로 변한다).
    var hb = ground - 4;
    var hbW = W * 0.78;
    var hbX = cx + Math.sin(tSec * 0.55) * W * 0.3;
    var hbA = 0.12 * (0.6 + 0.4 * flick) * (0.7 + 0.3 * Math.sin(tSec * 1.25 + 2.0));
    var hbg = ctx.createRadialGradient(hbX, hb, 2, hbX, hb, hbW);
    hbg.addColorStop(0, 'rgba(' + C_EMBER[0] + ',' + C_EMBER[1] + ',' + C_EMBER[2] + ',' + hbA.toFixed(3) + ')');
    hbg.addColorStop(1, 'rgba(0,0,0,0)');
    ctx.fillStyle = hbg;
    ctx.fillRect(0, hb - hbW, W, hbW * 2);
    var hb2X = cx - Math.sin(tSec * 0.55) * W * 0.3;
    var hbg2 = ctx.createRadialGradient(hb2X, hb, 2, hb2X, hb, hbW * 0.7);
    hbg2.addColorStop(0, 'rgba(' + C_ROSE[0] + ',' + C_ROSE[1] + ',' + C_ROSE[2] + ',' + (hbA * 0.7).toFixed(3) + ')');
    hbg2.addColorStop(1, 'rgba(0,0,0,0)');
    ctx.fillStyle = hbg2;
    ctx.fillRect(0, hb - hbW * 0.7, W, hbW * 1.4);

    // ── 3) 연료 입자 — 위로 갈수록(k 가 작을수록) 바람을 더 많이 받아 크게 눕는다 ──
    for (var j = 0; j < N_PART; j++) {
      var q = parts[j];
      q.k -= K_BURN * dt;
      if (q.k <= 0) { spawn(q); continue; }
      var lean = (1 - q.k);                     // 0(태생) → 1(다 탐) — wind 노출 정도
      var sway = Math.sin(tSec * 6.6 + q.ph) * 6 * q.k;
      var fx = cx + q.x + q.vx * q.k + sway + windVX * lean * 0.55 * dt * 60;
      var fy = poleTop + q.y * q.k + windVY * lean * 0.4 * dt * 60;
      q.x += (q.vx + windVX * lean * 0.4) * dt;
      q.y += (q.vy + windVY * lean * 0.3) * dt;
      var rC, gC, bC, rad;
      if (q.k > 0.66) {
        rC = C_GOLD[0]; gC = C_GOLD[1]; bC = C_GOLD[2];
        rad = 2.3 + 1.5 * (q.k - 0.66) / 0.34;
      } else if (q.k > 0.33) {
        var m2 = (q.k - 0.33) / 0.33;
        rC = C_GOLD[0] + (C_CORE[0] - C_GOLD[0]) * m2;
        gC = C_GOLD[1] + (C_CORE[1] - C_GOLD[1]) * m2;
        bC = C_GOLD[2] + (C_CORE[2] - C_GOLD[2]) * m2;
        rad = 1.8 + 0.5 * m2;
      } else {
        var m3 = q.k / 0.33;
        rC = C_CORE[0] + (C_EMBER[0] - C_CORE[0]) * (1 - m3);
        gC = C_CORE[1] + (C_EMBER[1] - C_CORE[1]) * (1 - m3);
        bC = C_CORE[2] + (C_EMBER[2] - C_CORE[2]) * (1 - m3);
        rad = 1.0 + 0.7 * m3;
      }
      ctx.fillStyle = 'rgba(' + (rC | 0) + ',' + (gC | 0) + ',' + (bC | 0) + ',' + (0.16 + 0.5 * q.k).toFixed(3) + ')';
      ctx.beginPath();
      ctx.arc(fx, fy, rad, 0, TAU);
      ctx.fill();
    }

    // ── 4) 횃불 자루·묶음 머리 — 면 계산(source-over) 마감 ──
    ctx.globalCompositeOperation = 'source-over';
    var poleAng = wobAng * 0.10;      // 자루는 살짝만 따라 기운다(단단한 나무)
    ctx.save();
    ctx.translate(cx, ground);
    ctx.rotate(poleAng);
    // 자루
    ctx.fillStyle = 'rgb(' + ((C_INK[0] + C_EMBER[0] * 0.3) | 0) + ',' + ((C_INK[1] + C_EMBER[1] * 0.3) | 0) + ',' + ((C_INK[2] + C_EMBER[2] * 0.3) | 0) + ')';
    ctx.fillRect(-6, -(ground - poleTop), 12, ground - poleTop);
    // 묶음 머리(연기 톤 헝겊)
    ctx.fillStyle = 'rgba(' + C_SMOKE[0] + ',' + C_SMOKE[1] + ',' + C_SMOKE[2] + ',0.6)';
    ctx.beginPath();
    ctx.ellipse(0, -(ground - poleTop) - 2, 12, 16, 0, 0, TAU);
    ctx.fill();
    ctx.restore();
  }

  function fit() {
    var r = field.getBoundingClientRect();
    W = r.width; H = r.height;
    cv.width = Math.round(W); cv.height = Math.round(H);
    wOut.textContent = (0.5 + px01).toFixed(2);
  }

  function frame(now) {
    if (t0 < 0) t0 = now;
    var t = (now - t0) / 1000;
    var dt = Math.min(0.05, (now - (frame.prev || now)) / 1000);
    frame.prev = now;
    if (!manual) {
      // 미리보기 가상 wind — 시드 고정 Lissajous. x 가 세기, y 가 방향
      var ph = t * TAU / 3.6;
      px01 = 0.5 + 0.34 * Math.sin(ph + 0.4);
      py01 = 0.5 + 0.24 * Math.sin(2 * ph + 0.7);
    }
    draw(t, dt);
    wOut.textContent = (0.5 + px01).toFixed(2);
    raf = requestAnimationFrame(frame);
  }

  field.addEventListener('pointermove', function (e) {
    var r = field.getBoundingClientRect();
    px01 = Math.min(1, Math.max(0, (e.clientX - r.left) / r.width));
    py01 = Math.min(1, Math.max(0, (e.clientY - r.top) / r.height));
    if (!manual) { manual = true; root.classList.remove('is-demo'); }
    if (reduce) draw(STILL_T, 0.016);
  });
  field.addEventListener('pointerleave', function () {
    if (manual) { px01 = 0.5; py01 = 0.5; }
  });
  field.addEventListener('keydown', function (e) {
    var d = { ArrowLeft: [-0.07, 0], ArrowRight: [0.07, 0], ArrowUp: [0, -0.06], ArrowDown: [0, 0.06] }[e.key];
    if (!d) return;
    e.preventDefault();
    if (!manual) { manual = true; root.classList.remove('is-demo'); }
    px01 = Math.max(0, Math.min(1, px01 + d[0]));
    py01 = Math.max(0, Math.min(1, py01 + d[1]));
    if (reduce) draw(STILL_T, 0.016);
  });
  window.addEventListener('resize', function () { fit(); if (reduce) draw(STILL_T, 0.016); });

  fit();
  if (reduce) {
    // reduce — rAF 를 돌리지 않고 성화가 가장 기운 한 장만 그린다
    draw(STILL_T, 0);
    root.classList.add('is-still');
  } else {
    raf = requestAnimationFrame(frame);
  }
})();

// TorchWindVector — vanilla 판(run/314/demo/03-fire-torch-wind-vector/index.html) 의 React 포트.
// 일정한 바람 벡터 + 느린 sin 요동으로 성화 전체가 한쪽으로 쏠린다. 입자는 연료 k 로
// gold→amber/rose→ember 색온도 사다리를 타고, k 가 낮을수록 바람을 더 받아 크게 눕는다.
import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./TorchWindVector.module.scss";

export type TorchWindVectorProps = {
  duration?: string;
  easing?: string;
  color?: string;
  wind?: number;      // 바람 벡터 x 성분(px/s) — 변형 "바람 세기" 축
  wobble?: number;    // 느린 요동 진폭(라디안) — 변형 "요동 폭" 축
  tone?: 0 | 1;       // 코어 색 변형 — 0: amber, 1: rose
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
// useRef 는 T | null 을 돌려준다 — 처음부터 값이 있고 절대 비지 않는 상자는 이렇게 좁혀 쓴다
type Box<T> = { current: T };
type PointerEvt = { clientX: number; clientY: number };
type KeyEvt = { key: string; preventDefault(): void };
type RGB = [number, number, number];
type Frag = { x: number; y: number; vx: number; vy: number; k: number; ph: number };
type Colors = { ink: RGB; amber: RGB; gold: RGB; rose: RGB; ember: RGB; smoke: RGB };

const TAU = Math.PI * 2;
const FIELD_LABEL = "횃불 바람 벡터 실험판";
const STILL_T = 1.55;   // reduce 에서 그리는 시각 — 성화가 가장 기운 순간
const K_BURN = 2.1;     // 연료 소모율 (1/s)
const N_PART = 220;
const WIND_VY = -6;     // 바람 벡터 y 성분(살짝 위로)

// 시드 고정 PRNG — mulberry32
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 TorchWindVector({
  duration = "2s",
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#f0a868",
  wind = 46,
  wobble = 0.35,
  tone = 0,
}: TorchWindVectorProps) {
  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 sizeRef = useRef({ w: 0, h: 0 }) as Box<{ w: number; h: number }>;
  const colRef = useRef<Colors | null>(null);
  const windRef = useRef(wind) as Box<number>;
  const wobRef = useRef(wobble) as Box<number>;
  const toneRef = useRef(tone) as Box<number>;
  const partsRef = useRef<Frag[]>([]) as Box<Frag[]>;
  const pxRef = useRef(0.5) as Box<number>;
  const pyRef = useRef(0.5) as Box<number>;
  const manualRef = useRef(false) as Box<boolean>;
  const rafRef = useRef(0) as Box<number>;
  const t0Ref = useRef(-1) as Box<number>;
  const prevRef = useRef(0) as Box<number>;
  const [w, setW] = useState((0.5 + pxRef.current).toFixed(2));
  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;
  }

  // 색은 CSS 커스텀 프로퍼티(--fire-*)에서 getComputedStyle 로 읽는다 — 파스텔 토큰이 scss 한 곳에
  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 coreRGB(col: Colors): RGB {
    return toneRef.current ? col.rose : col.amber;
  }

  function buildParts(): void {
    const rand = makePRNG(0x5eed03);
    const arr: Frag[] = [];
    for (let i = 0; i < N_PART; i++) {
      arr.push({
        x: (rand() - 0.5) * 8,
        y: -rand() * 46,
        vx: (rand() - 0.5) * 8,
        vy: -22 - rand() * 30,
        k: rand(),
        ph: rand() * TAU,
      });
    }
    partsRef.current = arr;
  }

  function fit(): void {
    const field = fieldRef.current;
    const cv = cvRef.current;
    if (!field || !cv) return;
    const ctx = cv.getContext("2d");
    if (!ctx) return;
    const r = field.getBoundingClientRect();
    sizeRef.current.w = r.width;
    sizeRef.current.h = r.height;
    cv.width = Math.round(r.width);
    cv.height = Math.round(r.height);
    ctxRef.current = ctx;
    setW((0.5 + pxRef.current).toFixed(2));
  }

  function spawn(f: Frag, rand: () => number): void {
    f.x = (rand() - 0.5) * 8;
    f.y = 0;
    f.vx = (rand() - 0.5) * 8;
    f.vy = -22 - rand() * 30;
    f.k = 1;
    f.ph = rand() * TAU;
  }

  function draw(tSec: number, dt: number): void {
    const ctx = ctxRef.current;
    const col = colRef.current;
    const parts = partsRef.current;
    if (!ctx || !col || parts.length === 0) return;
    const { w: W, h: H } = sizeRef.current;
    const rand = makePRNG(0x5eed03 + ((tSec * 61) | 0));
    const core = coreRGB(col);

    ctx.globalCompositeOperation = "source-over";
    ctx.fillStyle = `rgb(${col.ink[0]},${col.ink[1]},${col.ink[2]})`;
    ctx.fillRect(0, 0, W, H);

    const cx = W * 0.5;
    const ground = H * 0.9;
    const poleTop = ground - 96;
    const strength = 0.5 + pxRef.current;
    const dirTilt = (pyRef.current - 0.5) * 0.7;

    // 두 겹 힘 — 일정 바람 벡터 + 느린 sin 요동
    const baseAng = Math.atan2(WIND_VY, windRef.current) + dirTilt;
    const wobAng = baseAng + wobRef.current * Math.sin(tSec * 0.35);
    const windMag = Math.hypot(windRef.current, WIND_VY) * strength;
    const windVX = Math.cos(wobAng) * windMag;
    const windVY = Math.sin(wobAng) * windMag;

    let flick = 0;
    for (let f = 0; f < parts.length; f++) flick += parts[f].k;
    flick = flick / parts.length;
    // 앙비언트 글로우 — 반경이 breathe 로 진동하고 알파는 flick·sin 펄스로 매 프레임 재계산.
    const breathe = (0.5 + 0.5 * flick) * (0.72 + 0.28 * Math.sin(tSec * 1.9));
    const hx = cx + windVX * 0.5 + Math.sin(tSec * 1.4) * 6;
    const hy = poleTop - 22 + windVY * 0.5 + Math.cos(tSec * 1.1) * 4;
    const R0 = Math.min(W, H) * 0.16 * breathe;
    const A0 = 0.85 * (0.55 + 0.45 * flick) * (0.62 + 0.38 * Math.sin(tSec * 2.4 + 0.6));
    const RMAX = Math.hypot(W, H) * 0.99;
    const LAYERS = 15;
    const FALLOFF = 0.9;

    ctx.globalCompositeOperation = "lighter";
    for (let L = 0; L < LAYERS; L++) {
      const Lt = L / (LAYERS - 1);
      const R = R0 + (RMAX - R0) * Math.pow(Lt, 0.72);
      const a = Math.max(0.06, A0 * Math.pow(R0 / R, FALLOFF));
      const m1 = Lt;
      const lr = col.gold[0] + (core[0] - col.gold[0]) * m1;
      const lg = col.gold[1] + (core[1] - col.gold[1]) * m1;
      const lb = col.gold[2] + (core[2] - col.gold[2]) * m1;
      const rg = ctx.createRadialGradient(hx, hy, R * 0.04, hx, hy, R);
      rg.addColorStop(0, `rgba(${lr | 0},${lg | 0},${lb | 0},${a.toFixed(3)})`);
      rg.addColorStop(0.72, `rgba(${lr | 0},${lg | 0},${lb | 0},${(a * 0.6).toFixed(3)})`);
      rg.addColorStop(1, "rgba(0,0,0,0)");
      ctx.fillStyle = rg;
      ctx.fillRect(hx - R, hy - R, R * 2, R * 2);
    }

    // 잔열 바닥 띠 — 전체 폭이 은은히 맥동(중심 좌우 유동) + 반대 위상 두 번째 점
    const hb = ground - 4;
    const hbW = W * 0.78;
    const hbX = cx + Math.sin(tSec * 0.55) * W * 0.3;
    const hbA = 0.12 * (0.6 + 0.4 * flick) * (0.7 + 0.3 * Math.sin(tSec * 1.25 + 2.0));
    const hbg = ctx.createRadialGradient(hbX, hb, 2, hbX, hb, hbW);
    hbg.addColorStop(0, `rgba(${col.ember[0]},${col.ember[1]},${col.ember[2]},${hbA.toFixed(3)})`);
    hbg.addColorStop(1, "rgba(0,0,0,0)");
    ctx.fillStyle = hbg;
    ctx.fillRect(0, hb - hbW, W, hbW * 2);
    const hb2X = cx - Math.sin(tSec * 0.55) * W * 0.3;
    const hbg2 = ctx.createRadialGradient(hb2X, hb, 2, hb2X, hb, hbW * 0.7);
    hbg2.addColorStop(0, `rgba(${col.rose[0]},${col.rose[1]},${col.rose[2]},${(hbA * 0.7).toFixed(3)})`);
    hbg2.addColorStop(1, "rgba(0,0,0,0)");
    ctx.fillStyle = hbg2;
    ctx.fillRect(0, hb - hbW * 0.7, W, hbW * 1.4);

    for (let j = 0; j < parts.length; j++) {
      const q = parts[j];
      q.k -= K_BURN * dt;
      if (q.k <= 0) { spawn(q, rand); continue; }
      const lean = 1 - q.k;
      const sway = Math.sin(tSec * 6.6 + q.ph) * 6 * q.k;
      const fx = cx + q.x + q.vx * q.k + sway + windVX * lean * 0.55 * dt * 60;
      const fy = poleTop + q.y * q.k + windVY * lean * 0.4 * dt * 60;
      q.x += (q.vx + windVX * lean * 0.4) * dt;
      q.y += (q.vy + windVY * lean * 0.3) * dt;
      let rC: number, gC: number, bC: number, rad: number;
      if (q.k > 0.66) {
        rC = col.gold[0]; gC = col.gold[1]; bC = col.gold[2];
        rad = 2.3 + 1.5 * ((q.k - 0.66) / 0.34);
      } else if (q.k > 0.33) {
        const m2 = (q.k - 0.33) / 0.33;
        rC = col.gold[0] + (core[0] - col.gold[0]) * m2;
        gC = col.gold[1] + (core[1] - col.gold[1]) * m2;
        bC = col.gold[2] + (core[2] - col.gold[2]) * m2;
        rad = 1.8 + 0.5 * m2;
      } else {
        const m3 = q.k / 0.33;
        rC = core[0] + (col.ember[0] - core[0]) * (1 - m3);
        gC = core[1] + (col.ember[1] - core[1]) * (1 - m3);
        bC = core[2] + (col.ember[2] - core[2]) * (1 - m3);
        rad = 1.0 + 0.7 * m3;
      }
      ctx.fillStyle = `rgba(${rC | 0},${gC | 0},${bC | 0},${(0.16 + 0.5 * q.k).toFixed(3)})`;
      ctx.beginPath();
      ctx.arc(fx, fy, rad, 0, TAU);
      ctx.fill();
    }

    // 횃불 자루·묶음 머리 — 면 계산 마감
    ctx.globalCompositeOperation = "source-over";
    const poleAng = wobAng * 0.1;
    ctx.save();
    ctx.translate(cx, ground);
    ctx.rotate(poleAng);
    ctx.fillStyle = `rgb(${(col.ink[0] + col.ember[0] * 0.3) | 0},${(col.ink[1] + col.ember[1] * 0.3) | 0},${(col.ink[2] + col.ember[2] * 0.3) | 0})`;
    ctx.fillRect(-6, -(ground - poleTop), 12, ground - poleTop);
    ctx.fillStyle = `rgba(${col.smoke[0]},${col.smoke[1]},${col.smoke[2]},0.6)`;
    ctx.beginPath();
    ctx.ellipse(0, -(ground - poleTop) - 2, 12, 16, 0, 0, TAU);
    ctx.fill();
    ctx.restore();
  }

  function frame(now: number): void {
    if (t0Ref.current < 0) t0Ref.current = now;
    const t = (now - t0Ref.current) / 1000;
    const dt = Math.min(0.05, (now - (prevRef.current || now)) / 1000);
    prevRef.current = now;
    if (!manualRef.current) {
      const ph = (t * TAU) / 3.6;
      pxRef.current = 0.5 + 0.34 * Math.sin(ph + 0.4);
      pyRef.current = 0.5 + 0.24 * Math.sin(2 * ph + 0.7);
    }
    draw(t, dt);
    setW((0.5 + pxRef.current).toFixed(2));
    rafRef.current = requestAnimationFrame(frame);
  }

  function onPoint(e: PointerEvt): void {
    const field = fieldRef.current;
    if (!field) return;
    const r = field.getBoundingClientRect();
    pxRef.current = Math.min(1, Math.max(0, (e.clientX - r.left) / r.width));
    pyRef.current = Math.min(1, Math.max(0, (e.clientY - r.top) / r.height));
    if (!manualRef.current) manualRef.current = true;
    if (reduced()) draw(STILL_T, 0.016);
  }

  function onLeave(): void {
    if (manualRef.current) { pxRef.current = 0.5; pyRef.current = 0.5; }
  }

  function onKeyDown(e: KeyEvt): void {
    const deltas: Record<string, [number, number]> = {
      ArrowLeft: [-0.07, 0], ArrowRight: [0.07, 0], ArrowUp: [0, -0.06], ArrowDown: [0, 0.06],
    };
    const d = deltas[e.key];
    if (!d) return;
    e.preventDefault();
    if (!manualRef.current) manualRef.current = true;
    pxRef.current = Math.max(0, Math.min(1, pxRef.current + d[0]));
    pyRef.current = Math.max(0, Math.min(1, pyRef.current + d[1]));
    if (reduced()) draw(STILL_T, 0.016);
  }

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    windRef.current = wind;
    wobRef.current = wobble;
    toneRef.current = tone;
    colRef.current = {
      ink: tokRGB(root, "--fire-ink"),
      amber: tokRGB(root, "--fire-amber"),
      gold: tokRGB(root, "--fire-gold"),
      rose: tokRGB(root, "--fire-rose"),
      ember: tokRGB(root, "--fire-ember"),
      smoke: tokRGB(root, "--fire-smoke"),
    };
    buildParts();
    fit();
    function onResize(): void {
      fit();
      if (reduced()) draw(STILL_T, 0.016);
    }
    window.addEventListener("resize", onResize);
    if (reduced()) {
      draw(STILL_T, 0);
      setStill(true);
    } else {
      rafRef.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafRef.current);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [wind, wobble, tone]);

  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}>
          <svg className={styles.ico} viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M128 24a16 16 0 0 1 16 16v8a80.06 80.06 0 0 1 63.94 63.94h8a16 16 0 0 1 0 32h-8A80.06 80.06 0 0 1 144 207.94v8a16 16 0 0 1-32 0v-8A80.06 80.06 0 0 1 48.06 144h-8a16 16 0 0 1 0-32h8A80.06 80.06 0 0 1 112 48.06v-8A16 16 0 0 1 128 24m-16 57.35V96a16 16 0 0 0 32 0V81.35A48.09 48.09 0 0 0 81.35 112H96a16 16 0 0 0 0-32h14.65M174.65 144H160a16 16 0 0 0 0 32h14.65A48.09 48.09 0 0 0 144 174.65V160a16 16 0 0 0-32 0v14.65A48.09 48.09 0 0 0 81.35 144" opacity=".2"/><path d="M232 128a104 104 0 1 1-104-104a104 104 0 0 1 104 104m-32 0a8 8 0 0 0-8-8h-9.34A56.1 56.1 0 0 0 136 77.34V68a8 8 0 0 0-16 0v9.34A56.1 56.1 0 0 0 77.34 120H68a8 8 0 0 0 0 16h9.34A56.1 56.1 0 0 0 120 179.66V188a8 8 0 0 0 16 0v-8.34A56.1 56.1 0 0 0 178.66 136H192a8 8 0 0 0 8-8m-40 0a32 32 0 1 1-32-32a32 32 0 0 1 32 32m-16 0a16 16 0 1 0-16 16a16 16 0 0 0 16-16"/></g></svg>
          <span>일정한 바람 벡터와 느린 sin 요동에 성화 전체가 한쪽으로 쏠립니다 — 포인터 x 는 바람 세기, y 는 방향</span>
        </p>
        <div
          className={styles.field}
          ref={fieldRef}
          role="application"
          aria-label={FIELD_LABEL}
          tabIndex={0}
          onPointerMove={onPoint}
          onPointerLeave={onLeave}
          onKeyDown={onKeyDown}
        >
          <canvas className={styles.cv} ref={cvRef}></canvas>
        </div>
        <div className={styles.bar}>
          <span className={styles.meta}>바람 <b className={styles.val}>{w}</b> · 요동 sin 기반</span>
          <span className={styles.metaDim}>requestAnimationFrame · 색온도 사다리</span>
        </div>
      </div>
    </main>
  );
}