09Reduced-motion instant toggle — with reduced motion on, every transition from the prior eight bars switches straight to its target value

<main class="stage">
<div class="rm is-demo" id="rm">
  <div class="rm__panel" data-role="normal">
    <p class="rm__caption">Normal transition</p>
    <div class="rm__track" id="rmTrackA">
      <div class="rm__indicator rm__indicator--a" id="rmIndicatorA"></div>
      <button type="button" class="rm__tab is-active" data-idx="0">
        <svg class="rm__icon" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M216 120v96h-64v-64h-48v64H40v-96a8 8 0 0 1 2.34-5.66l80-80a8 8 0 0 1 11.32 0l80 80A8 8 0 0 1 216 120" opacity=".2"/><path d="m219.31 108.68l-80-80a16 16 0 0 0-22.62 0l-80 80A15.87 15.87 0 0 0 32 120v96a8 8 0 0 0 8 8h64a8 8 0 0 0 8-8v-56h32v56a8 8 0 0 0 8 8h64a8 8 0 0 0 8-8v-96a15.87 15.87 0 0 0-4.69-11.32M208 208h-48v-56a8 8 0 0 0-8-8h-48a8 8 0 0 0-8 8v56H48v-88l80-80l80 80Z"/></g></svg>
        <span class="rm__label">Home</span>
      </button>
      <button type="button" class="rm__tab" data-idx="1">
        <svg class="rm__icon" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M224 80v120a8 8 0 0 1-8 8H40a8 8 0 0 1-8-8V80a8 8 0 0 1 8-8h176a8 8 0 0 1 8 8" opacity=".2"/><path d="M216 64h-40a48 48 0 0 0-96 0H40a16 16 0 0 0-16 16v120a16 16 0 0 0 16 16h176a16 16 0 0 0 16-16V80a16 16 0 0 0-16-16m-88-32a32 32 0 0 1 32 32H96a32 32 0 0 1 32-32m88 168H40V80h176Z"/></g></svg>
        <span class="rm__label">Shopping</span>
      </button>
    </div>
    <p class="rm__readout" id="rmReadoutA">0 / 320ms</p>
  </div>
  <div class="rm__panel" data-role="reduced">
    <p class="rm__caption">Reduced-motion transition</p>
    <div class="rm__track" id="rmTrackB">
      <div class="rm__indicator rm__indicator--b" id="rmIndicatorB"></div>
      <button type="button" class="rm__tab is-active" data-idx="0">
        <svg class="rm__icon" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M216 120v96h-64v-64h-48v64H40v-96a8 8 0 0 1 2.34-5.66l80-80a8 8 0 0 1 11.32 0l80 80A8 8 0 0 1 216 120" opacity=".2"/><path d="m219.31 108.68l-80-80a16 16 0 0 0-22.62 0l-80 80A15.87 15.87 0 0 0 32 120v96a8 8 0 0 0 8 8h64a8 8 0 0 0 8-8v-56h32v56a8 8 0 0 0 8 8h64a8 8 0 0 0 8-8v-96a15.87 15.87 0 0 0-4.69-11.32M208 208h-48v-56a8 8 0 0 0-8-8h-48a8 8 0 0 0-8 8v56H48v-88l80-80l80 80Z"/></g></svg>
        <span class="rm__label">Home</span>
      </button>
      <button type="button" class="rm__tab" data-idx="1">
        <svg class="rm__icon" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M224 80v120a8 8 0 0 1-8 8H40a8 8 0 0 1-8-8V80a8 8 0 0 1 8-8h176a8 8 0 0 1 8 8" opacity=".2"/><path d="M216 64h-40a48 48 0 0 0-96 0H40a16 16 0 0 0-16 16v120a16 16 0 0 0 16 16h176a16 16 0 0 0 16-16V80a16 16 0 0 0-16-16m-88-32a32 32 0 0 1 32 32H96a32 32 0 0 1 32-32m88 168H40V80h176Z"/></g></svg>
        <span class="rm__label">Shopping</span>
      </button>
    </div>
    <p class="rm__readout" id="rmReadoutB">0ms</p>
  </div>
</div>
</main>

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

// 계산 겹: 일반 패널은 easeOutCubic 을 rAF 로 직접 적분해 실제 경과시간(ms)을
// 화면에 그대로 찍고, 축소 패널은 보간 없이 즉시 놓은 뒤 perf.now 차로 실제
// 지연시간을 측정해 찍는다 — 두 패널 다 CSS transition 이 아니라 계산이 위치를 만든다.
@include stage($stage-paper);

// .rm 은 is-demo 클래스와 실제 레이아웃 규칙(너비·flex)을 함께 들고 있는 그리드
// 직계 아이템이다 — is-demo 만 들고 아무 규칙도 없는 빈 래퍼를 한 겹 더 두면
// .stage 의 grid place-items:center 밑에서 자식 width:100% 가 0으로 무너진다
// (367-05 실측). 여기서는 그 빈 래퍼 자체를 두지 않는다.
.rm {
  width: 100%; max-width: 420px; display: flex; gap: $sp-4; justify-content: center;
}

.rm__panel {
  flex: 1 1 0; min-width: 0; display: flex; flex-direction: column; align-items: center; gap: $sp-2;
}
.rm__caption { font-size: 11px; font-weight: 700; color: $subject-ink; margin: 0; }
.rm__track {
  position: relative; width: 100%; display: flex; justify-content: space-around;
  background: $subject-blue-light; border-radius: $r-card; padding: $sp-2 0;
  box-shadow: $shadow-raised;
}
.rm__panel[data-role="reduced"] .rm__track { background: $subject-mint; }
.rm__indicator {
  position: absolute; left: 0; top: 6px; border-radius: $r-pill; background: $subject-cream;
  will-change: transform;
}
.rm__tab {
  position: relative; z-index: 1; flex: 0 0 auto; display: flex; flex-direction: column;
  align-items: center; gap: $sp-1; border: none; background: transparent; cursor: pointer;
  padding: $sp-1 $sp-2; color: rgba($subject-ink, .72); transition: color .15s ease;
}
.rm__tab.is-active { color: $subject-blue-deep; }
.rm__icon { width: 16px; height: 16px; }
.rm__label { font-size: 9px; font-weight: 700; line-height: 1; }
.rm__readout { font-size: 11px; color: $subject-ink; margin: 0; font-weight: 600; }

@media (max-width: 340px) {
  .rm { gap: $sp-2; }
  .rm__tab { padding: $sp-1; }
}

// 장식 요소(탭 글자색 전환)만 줄인다 — 일반 패널의 비교용 이동 자체는 rAF 계산이라
// 이 블록과 무관하게 항상 그대로 재생된다(비교를 보여주는 목적이 실제 설정보다 먼저다).
@media (prefers-reduced-motion: reduce) {
  .rm__tab { transition: none; }
}

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

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

.rm {
  width: 100%;
  max-width: 420px;
  display: flex;
  gap: 16px;
  justify-content: center;
}

.rm__panel {
  flex: 1 1 0;
  min-width: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
}

.rm__caption {
  font-size: 11px;
  font-weight: 700;
  color: #17141a;
  margin: 0;
}

.rm__track {
  position: relative;
  width: 100%;
  display: flex;
  justify-content: space-around;
  background: #5b8cf8;
  border-radius: 16px;
  padding: 8px 0;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.rm__panel[data-role=reduced] .rm__track {
  background: #4cd4a6;
}

.rm__indicator {
  position: absolute;
  left: 0;
  top: 6px;
  border-radius: 999px;
  background: #fff7e6;
  will-change: transform;
}

.rm__tab {
  position: relative;
  z-index: 1;
  flex: 0 0 auto;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  border: none;
  background: transparent;
  cursor: pointer;
  padding: 4px 8px;
  color: rgba(23, 20, 26, 0.72);
  transition: color 0.15s ease;
}

.rm__tab.is-active {
  color: #0a4fe8;
}

.rm__icon {
  width: 16px;
  height: 16px;
}

.rm__label {
  font-size: 9px;
  font-weight: 700;
  line-height: 1;
}

.rm__readout {
  font-size: 11px;
  color: #17141a;
  margin: 0;
  font-weight: 600;
}

@media (max-width: 340px) {
  .rm {
    gap: 8px;
  }
  .rm__tab {
    padding: 4px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .rm__tab {
    transition: none;
  }
}

(function () {
  var DURATION_MS = 320; // 계산 겹: 일반 패널의 전환 실제 시간(ms) — CSS transition 이 아니라 rAF 로 직접 적분
  var CYCLE_MS = 700; // 자동 루프가 좌우 탭을 오가는 간격
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var rm = document.getElementById('rm');
  var trackA = document.getElementById('rmTrackA');
  var indicatorA = document.getElementById('rmIndicatorA');
  var readoutA = document.getElementById('rmReadoutA');
  var trackB = document.getElementById('rmTrackB');
  var indicatorB = document.getElementById('rmIndicatorB');
  var readoutB = document.getElementById('rmReadoutB');
  var tabsA = Array.prototype.slice.call(trackA.querySelectorAll('.rm__tab'));
  var tabsB = Array.prototype.slice.call(trackB.querySelectorAll('.rm__tab'));

  var isDemo = true;

  function human() {
    if (isDemo) { rm.classList.remove('is-demo'); isDemo = false; }
  }

  function measure(track, tabs) {
    var trackRect = track.getBoundingClientRect();
    return tabs.map(function (t) {
      var r = t.getBoundingClientRect();
      return { left: r.left - trackRect.left, width: r.width, height: r.height };
    });
  }

  // ---- 패널 A: Normal transition — easeOutCubic 을 rAF 로 직접 적분해 진짜 경과시간을 잰다.
  // 실제 OS/브라우저의 prefers-reduced-motion 설정과 무관하게 항상 이 계산을 수행한다.
  var geoA = measure(trackA, tabsA);
  indicatorA.style.width = geoA[0].width + 'px';
  indicatorA.style.height = geoA[0].height + 'px';
  var activeA = 0;
  var fromXA = geoA[0].left, toXA = geoA[0].left;
  var transStartA = 0;
  var transitioningA = false;
  indicatorA.style.transform = 'translateX(' + geoA[0].left.toFixed(1) + 'px)';

  function easeOutCubic(t) { return 1 - Math.pow(1 - t, 3); }

  function goToA(idx, ts) {
    activeA = idx;
    tabsA.forEach(function (t, i) { t.classList.toggle('is-active', i === idx); });
    fromXA = currentXA(ts);
    toXA = geoA[idx].left;
    transStartA = ts;
    transitioningA = true;
  }
  function currentXA(ts) {
    if (!transitioningA) return toXA;
    var t = Math.min(1, (ts - transStartA) / DURATION_MS);
    return fromXA + (toXA - fromXA) * easeOutCubic(t);
  }

  // ---- 패널 B: Reduced-motion transition — 보간 없이 즉시 위치를 놓고, 실제 지연시간(perf.now 차)만 잰다.
  // 이 패널은 늘 즉시 전환한다는 사실을 보여주는 쪽이라 실제 설정과 무관하게 동작을 고정한다.
  var geoB = measure(trackB, tabsB);
  indicatorB.style.width = geoB[0].width + 'px';
  indicatorB.style.height = geoB[0].height + 'px';
  var activeB = 0;
  var switchAtB = 0;
  var latencyMeasured = true;
  indicatorB.style.transform = 'translateX(' + geoB[0].left.toFixed(1) + 'px)';

  function goToB(idx, ts) {
    activeB = idx;
    tabsB.forEach(function (t, i) { t.classList.toggle('is-active', i === idx); });
    indicatorB.style.transform = 'translateX(' + geoB[idx].left.toFixed(1) + 'px)';
    switchAtB = ts;
    latencyMeasured = false;
  }

  tabsA.forEach(function (t, i) {
    t.addEventListener('click', function () { human(); if (i !== activeA) goToA(i, performance.now()); });
  });
  tabsB.forEach(function (t, i) {
    t.addEventListener('click', function () { human(); if (i !== activeB) goToB(i, performance.now()); });
  });

  var cycleStart = 0;
  var lastCycleIdx = 0;

  function tick(ts) {
    if (!cycleStart) cycleStart = ts;

    if (isDemo && !reduce) {
      var step = Math.floor((ts - cycleStart) / CYCLE_MS);
      var idx = step % 2;
      if (idx !== lastCycleIdx) {
        lastCycleIdx = idx;
        if (idx !== activeA) goToA(idx, ts);
        if (idx !== activeB) goToB(idx, ts);
      }
    }

    if (transitioningA) {
      var x = currentXA(ts);
      indicatorA.style.transform = 'translateX(' + x.toFixed(1) + 'px)';
      var elapsed = Math.min(DURATION_MS, ts - transStartA);
      readoutA.textContent = Math.round(elapsed) + ' / ' + DURATION_MS + 'ms';
      if (elapsed >= DURATION_MS) { transitioningA = false; }
    }

    if (!latencyMeasured) {
      var lat = ts - switchAtB;
      readoutB.textContent = Math.round(lat) + 'ms (1 frame)';
      latencyMeasured = true;
    }

    requestAnimationFrame(tick);
  }

  requestAnimationFrame(tick);
})();

// ReducedMotionInstant — vanilla 판(run/367/demo/09-bottom-nav-bar-reduced-motion-instant/index.html) 의
// React 포트. 패널 A(일반)는 easeOutCubic 을 rAF 로 직접 적분해 실제 경과시간(ms)을 화면에
// 그대로 찍고, 패널 B(축소)는 보간 없이 즉시 놓은 뒤 perf.now 차로 실제 지연시간을 측정해
// 찍는다 — 두 패널 다 CSS transition 이 아니라 계산이 위치를 만든다.
import { useEffect, useRef } from "react";
import styles from "./ReducedMotionInstant.module.scss";

type Box<T> = { current: T };
type Geo = { left: number; width: number; height: number };

const DURATION_MS = 320; // 계산 겹: 일반 패널의 전환 실제 시간(ms) — CSS transition 이 아니라 rAF 로 직접 적분
const CYCLE_MS = 700; // 자동 루프가 좌우 탭을 오가는 간격

const TABS = [
  { label: "홈", d: "M216 120v96h-64v-64h-48v64H40v-96a8 8 0 0 1 2.34-5.66l80-80a8 8 0 0 1 11.32 0l80 80A8 8 0 0 1 216 120|.2#m219.31 108.68l-80-80a16 16 0 0 0-22.62 0l-80 80A15.87 15.87 0 0 0 32 120v96a8 8 0 0 0 8 8h64a8 8 0 0 0 8-8v-56h32v56a8 8 0 0 0 8 8h64a8 8 0 0 0 8-8v-96a15.87 15.87 0 0 0-4.69-11.32M208 208h-48v-56a8 8 0 0 0-8-8h-48a8 8 0 0 0-8 8v56H48v-88l80-80l80 80Z" },
  { label: "쇼핑", d: "M224 80v120a8 8 0 0 1-8 8H40a8 8 0 0 1-8-8V80a8 8 0 0 1 8-8h176a8 8 0 0 1 8 8|.2#M216 64h-40a48 48 0 0 0-96 0H40a16 16 0 0 0-16 16v120a16 16 0 0 0 16 16h176a16 16 0 0 0 16-16V80a16 16 0 0 0-16-16m-88-32a32 32 0 0 1 32 32H96a32 32 0 0 1 32-32m88 168H40V80h176Z" },
];

function Icon({ spec }: { spec: string }) {
  const [a, b] = spec.split("#");
  const [pathA, opacity] = a.split("|");
  return (
    <svg className={styles.icon} viewBox="0 0 256 256" aria-hidden="true">
      <g fill="currentColor">
        <path d={pathA} opacity={opacity} />
        <path d={b} />
      </g>
    </svg>
  );
}

function easeOutCubic(t: number): number { return 1 - Math.pow(1 - t, 3); }

export default function ReducedMotionInstant() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const trackARef = useRef(null) as unknown as Box<HTMLDivElement>;
  const indicatorARef = useRef(null) as unknown as Box<HTMLDivElement>;
  const readoutARef = useRef(null) as unknown as Box<HTMLParagraphElement>;
  const tabARefs = useRef([null, null]) as unknown as Box<(HTMLButtonElement | null)[]>;
  const trackBRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const indicatorBRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const readoutBRef = useRef(null) as unknown as Box<HTMLParagraphElement>;
  const tabBRefs = useRef([null, null]) as unknown as Box<(HTMLButtonElement | null)[]>;
  const rafRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const trackA = trackARef.current, indicatorA = indicatorARef.current, readoutA = readoutARef.current;
    const trackB = trackBRef.current, indicatorB = indicatorBRef.current, readoutB = readoutBRef.current;
    const tabsA = tabARefs.current, tabsB = tabBRefs.current;
    if (!trackA || !indicatorA || !readoutA || !trackB || !indicatorB || !readoutB) return;

    let isDemo = true;

    function human() {
      if (isDemo) { rootRef.current?.classList.remove(styles.isDemo); isDemo = false; }
    }

    function measure(track: HTMLDivElement, tabs: (HTMLButtonElement | null)[]): Geo[] {
      const trackRect = track.getBoundingClientRect();
      return tabs.map((t) => {
        const r = t!.getBoundingClientRect();
        return { left: r.left - trackRect.left, width: r.width, height: r.height };
      });
    }

    // ---- 패널 A: 일반 전환
    const geoA = measure(trackA, tabsA);
    indicatorA.style.width = geoA[0].width + "px";
    indicatorA.style.height = geoA[0].height + "px";
    let activeA = 0;
    let fromXA = geoA[0].left, toXA = geoA[0].left;
    let transStartA = 0;
    let transitioningA = false;
    indicatorA.style.transform = "translateX(" + geoA[0].left.toFixed(1) + "px)";

    function currentXA(ts: number) {
      if (!transitioningA) return toXA;
      const t = Math.min(1, (ts - transStartA) / DURATION_MS);
      return fromXA + (toXA - fromXA) * easeOutCubic(t);
    }
    function goToA(idx: number, ts: number) {
      activeA = idx;
      tabsA.forEach((t, i) => t?.classList.toggle(styles.isActive, i === idx));
      fromXA = currentXA(ts);
      toXA = geoA[idx].left;
      transStartA = ts;
      transitioningA = true;
    }

    // ---- 패널 B: 축소 모션 전환
    const geoB = measure(trackB, tabsB);
    indicatorB.style.width = geoB[0].width + "px";
    indicatorB.style.height = geoB[0].height + "px";
    let activeB = 0;
    let switchAtB = 0;
    let latencyMeasured = true;
    indicatorB.style.transform = "translateX(" + geoB[0].left.toFixed(1) + "px)";

    function goToB(idx: number, ts: number) {
      activeB = idx;
      tabsB.forEach((t, i) => t?.classList.toggle(styles.isActive, i === idx));
      indicatorB.style.transform = "translateX(" + geoB[idx].left.toFixed(1) + "px)";
      switchAtB = ts;
      latencyMeasured = false;
    }

    const handlersA = tabsA.map((_, i) => () => { human(); if (i !== activeA) goToA(i, performance.now()); });
    tabsA.forEach((t, i) => t?.addEventListener("click", handlersA[i]));
    const handlersB = tabsB.map((_, i) => () => { human(); if (i !== activeB) goToB(i, performance.now()); });
    tabsB.forEach((t, i) => t?.addEventListener("click", handlersB[i]));

    let cycleStart = 0;
    let lastCycleIdx = 0;

    function tick(ts: number) {
      if (!cycleStart) cycleStart = ts;

      if (isDemo && !reduce) {
        const step = Math.floor((ts - cycleStart) / CYCLE_MS);
        const idx = step % 2;
        if (idx !== lastCycleIdx) {
          lastCycleIdx = idx;
          if (idx !== activeA) goToA(idx, ts);
          if (idx !== activeB) goToB(idx, ts);
        }
      }

      if (transitioningA) {
        const x = currentXA(ts);
        indicatorA.style.transform = "translateX(" + x.toFixed(1) + "px)";
        const elapsed = Math.min(DURATION_MS, ts - transStartA);
        readoutA.textContent = Math.round(elapsed) + " / " + DURATION_MS + "ms";
        if (elapsed >= DURATION_MS) { transitioningA = false; }
      }

      if (!latencyMeasured) {
        const lat = ts - switchAtB;
        readoutB.textContent = Math.round(lat) + "ms (1프레임)";
        latencyMeasured = true;
      }

      rafRef.current = requestAnimationFrame(tick);
    }

    rafRef.current = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(rafRef.current);
      tabsA.forEach((t, i) => t?.removeEventListener("click", handlersA[i]));
      tabsB.forEach((t, i) => t?.removeEventListener("click", handlersB[i]));
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.root + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.panel}>
          <p className={styles.caption}>일반 전환</p>
          <div className={styles.track} ref={trackARef}>
            <div className={styles.indicatorA} ref={indicatorARef} />
            {TABS.map((t, i) => (
              <button key={t.label} type="button"
                className={styles.tab + (i === 0 ? " " + styles.isActive : "")}
                aria-current={i === 0 ? "true" : undefined}
                ref={(el: HTMLButtonElement | null) => { tabARefs.current[i] = el; }}>
                <Icon spec={t.d} />
                <span className={styles.label}>{t.label}</span>
              </button>
            ))}
          </div>
          <p className={styles.readout} ref={readoutARef}>0 / 320ms</p>
        </div>
        <div className={styles.panel}>
          <p className={styles.caption}>축소 모션 전환</p>
          <div className={styles.track + " " + styles.trackReduced} ref={trackBRef}>
            <div className={styles.indicatorB} ref={indicatorBRef} />
            {TABS.map((t, i) => (
              <button key={t.label} type="button"
                className={styles.tab + (i === 0 ? " " + styles.isActive : "")}
                aria-current={i === 0 ? "true" : undefined}
                ref={(el: HTMLButtonElement | null) => { tabBRefs.current[i] = el; }}>
                <Icon spec={t.d} />
                <span className={styles.label}>{t.label}</span>
              </button>
            ))}
          </div>
          <p className={styles.readout} ref={readoutBRef}>0ms</p>
        </div>
      </div>
    </main>
  );
}