04Nested Transition That Moves Parent and Child as One Group

<main class="stage">
<div class="gn is-demo" id="gn">
  <button type="button" class="gn__card" id="gnCard" aria-label="Expand card">
    <span class="gn__thumb" id="gnThumb"></span>
    <span class="gn__title" id="gnTitle">Grouped card</span>
  </button>
</div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-enter;
$easing: $ease-spring;
$color: $subject-blue-deep;

@include stage($stage-paper);

.gn { width: min(100%, 280px); }

.gn__card {
  view-transition-name: gn-card;
  position: relative; width: 100%; box-sizing: border-box; border: none; cursor: pointer;
  display: flex; align-items: center; gap: $sp-3; text-align: left;
  background: $subject-cream; border-radius: $r-card; padding: $sp-3;
  box-shadow: $shadow-raised;
}
.gn__card:focus-visible { outline: 2px solid $color; outline-offset: 2px; }

.gn__thumb {
  view-transition-name: gn-thumb;
  view-transition-group: nearest;
  width: 56px; height: 56px; border-radius: $r-control; background: $color; flex: 0 0 auto;
}
.gn__title {
  view-transition-name: gn-title;
  view-transition-group: nearest;
  font: 700 14px/1.3 -apple-system, "Segoe UI", sans-serif; color: $subject-ink;
}

.gn__card.is-open {
  flex-direction: column; align-items: flex-start; gap: $sp-3; padding: $sp-5;
}
.gn__card.is-open .gn__thumb { width: 100%; height: 96px; border-radius: $r-card; }
.gn__card.is-open .gn__title { font-size: 18px; }

// 실사용 원리: 바깥 카드가 gn-card 값으로, 안쪽 썸네일·제목이 각각 gn-thumb·gn-title 값으로
// 스스로 전환에 참여하면서 view-transition-group:nearest 가 자식 그룹을 부모(gn-card) 그룹
// 아래에 중첩시켜, 부모 크기 변화와 같은 비율로 자식도 함께 보간된다(따로 놀지 않는다).
::view-transition-group(gn-card),
::view-transition-group(gn-thumb),
::view-transition-group(gn-title) {
  animation-duration: $duration;
  animation-timing-function: $easing;
}

@media (max-width: 340px) {
  .gn__card { padding: $sp-2; gap: $sp-2; }
  .gn__thumb { width: 44px; height: 44px; }
  .gn__title { font-size: 12px; }
  .gn__card.is-open { padding: $sp-3; }
  .gn__card.is-open .gn__thumb { height: 70px; }
  .gn__card.is-open .gn__title { font-size: 15px; }
}

@media (prefers-reduced-motion: reduce) {
  ::view-transition-group(*),
  ::view-transition-old(*),
  ::view-transition-new(*) { animation: none !important; }
}

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);
}

.gn {
  width: min(100%, 280px);
}

.gn__card {
  view-transition-name: gn-card;
  position: relative;
  width: 100%;
  box-sizing: border-box;
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 12px;
  text-align: left;
  background: #fff7e6;
  border-radius: 16px;
  padding: 12px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.gn__card:focus-visible {
  outline: 2px solid #0a4fe8;
  outline-offset: 2px;
}

.gn__thumb {
  view-transition-name: gn-thumb;
  view-transition-group: nearest;
  width: 56px;
  height: 56px;
  border-radius: 12px;
  background: #0a4fe8;
  flex: 0 0 auto;
}

.gn__title {
  view-transition-name: gn-title;
  view-transition-group: nearest;
  font: 700 14px/1.3 -apple-system, "Segoe UI", sans-serif;
  color: #17141a;
}

.gn__card.is-open {
  flex-direction: column;
  align-items: flex-start;
  gap: 12px;
  padding: 20px;
}

.gn__card.is-open .gn__thumb {
  width: 100%;
  height: 96px;
  border-radius: 16px;
}

.gn__card.is-open .gn__title {
  font-size: 18px;
}

::view-transition-group(gn-card),
::view-transition-group(gn-thumb),
::view-transition-group(gn-title) {
  animation-duration: 600ms;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
}

@media (max-width: 340px) {
  .gn__card {
    padding: 8px;
    gap: 8px;
  }
  .gn__thumb {
    width: 44px;
    height: 44px;
  }
  .gn__title {
    font-size: 12px;
  }
  .gn__card.is-open {
    padding: 12px;
  }
  .gn__card.is-open .gn__thumb {
    height: 70px;
  }
  .gn__card.is-open .gn__title {
    font-size: 15px;
  }
}
@media (prefers-reduced-motion: reduce) {
  ::view-transition-group(*),
  ::view-transition-old(*),
  ::view-transition-new(*) {
    animation: none !important;
  }
}

(function () {
  var SUPPORTS_VT = 'startViewTransition' in document;

  var root = document.getElementById('gn');
  var card = document.getElementById('gnCard');
  var thumb = document.getElementById('gnThumb');
  var title = document.getElementById('gnTitle');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var open = false;
  var isDemo = true;

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

  function render() {
    card.classList.toggle('is-open', open);
  }

  function change(fn) {
    if (SUPPORTS_VT) { document.startViewTransition(fn); }
    else { fn(); }
  }

  function toggle() {
    open = !open;
    change(render);
  }

  card.addEventListener('click', function () { human(); toggle(); });
  root.addEventListener('keydown', function (e) {
    if (e.key === 'Enter' || e.key === ' ') { human(); e.preventDefault(); toggle(); }
  });

  var HOLD_MS = 1000;
  function loop() {
    if (!isDemo) return;
    toggle();
    window.setTimeout(loop, HOLD_MS);
  }

  if (!reduce) {
    window.setTimeout(loop, HOLD_MS);
  } else {
    root.classList.remove('is-demo');
  }
})();

// GroupNested — vanilla 판(run/401/demo/04-view-transition-group-nested/index.html) 의 React 포트.
// 계산 겹 없음(브리프 지정) — view-transition-group: nearest 로 부모·자식이 중첩 그룹을 이룬다.
import { useEffect, useRef } from "react";
import styles from "./GroupNested.module.scss";

type Box<T> = { current: T };

const HOLD_MS = 1000;

export default function GroupNested() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const cardRef = useRef(null) as unknown as Box<HTMLButtonElement>;
  const timerRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const SUPPORTS_VT = "startViewTransition" in document;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let isDemo = true;
    let open = false;

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

    function render() {
      cardRef.current?.classList.toggle(styles.isOpen, open);
    }

    function change(fn: () => void) {
      if (SUPPORTS_VT) { document.startViewTransition(fn); }
      else { fn(); }
    }

    function toggle() {
      open = !open;
      change(render);
    }

    function onClick() { human(); toggle(); }
    function onKeydown(e: KeyboardEvent) {
      if (e.key === "Enter" || e.key === " ") { human(); e.preventDefault(); toggle(); }
    }

    cardRef.current?.addEventListener("click", onClick);
    rootRef.current?.addEventListener("keydown", onKeydown);

    function loop() {
      if (!isDemo) return;
      toggle();
      timerRef.current = window.setTimeout(loop, HOLD_MS);
    }

    if (!reduce) {
      timerRef.current = window.setTimeout(loop, HOLD_MS);
    } else {
      rootRef.current?.classList.remove(styles.isDemo);
    }

    return () => {
      window.clearTimeout(timerRef.current);
      cardRef.current?.removeEventListener("click", onClick);
      rootRef.current?.removeEventListener("keydown", onKeydown);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.gn + " " + styles.isDemo} ref={rootRef}>
        <button type="button" className={styles.card} ref={cardRef} aria-label="카드 펼치기">
          <span className={styles.thumb} />
          <span className={styles.title}>묶음 카드</span>
        </button>
      </div>
    </main>
  );
}