05그룹 고정 헤더 — 목록을 그룹으로 나누고 스크롤에 헤더가 붙어 내려오는 구조

<main class="stage">
<div class="gh" id="gh">
  <p class="gh__hint">스크롤해도 지금 보는 그룹 이름이 위에 붙어 옵니다</p>
  <div class="gh__list" id="ghList" role="listbox" aria-label="그룹 목록" tabindex="0">
    <div class="gh__group" role="group" aria-label="제품">
      <div class="gh__head" id="ghHead0">제품</div>
      <ul class="gh__rows">
        <li class="gh__item" role="option">바나나</li>
        <li class="gh__item" role="option">파인애플</li>
        <li class="gh__item" role="option">수박</li>
        <li class="gh__item" role="option">자몽</li>
      </ul>
    </div>
    <div class="gh__group" role="group" aria-label="브랜드">
      <div class="gh__head" id="ghHead1">브랜드</div>
      <ul class="gh__rows">
        <li class="gh__item" role="option">체리</li>
        <li class="gh__item" role="option">복숭아</li>
        <li class="gh__item" role="option">딸기</li>
      </ul>
    </div>
    <div class="gh__group" role="group" aria-label="카테고리">
      <div class="gh__head" id="ghHead2">카테고리</div>
      <ul class="gh__rows">
        <li class="gh__item" role="option">아보카도</li>
        <li class="gh__item" role="option">망고</li>
        <li class="gh__item" role="option">파파야</li>
      </ul>
    </div>
  </div>
</div>
</main>

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

$duration: $dur-base;
$easing: $ease-out;
$color: $subject-blue-deep;

@include stage($stage-ink);

.gh {
  width: 100%;
  max-width: 360px;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
}

.gh__hint {
  margin: 0;
  padding: 0 $sp-1;
  font-weight: 400;
  font-size: 11px;
  line-height: 1.4;
  color: rgba($subject-cream, .72);
}

.gh__list {
  height: 176px;
  overflow-y: auto;
  background: $subject-cream;
  border-radius: $r-card;
  box-shadow: $shadow-press;
  position: relative;
}

.gh__group {
  &:first-child .gh__head {
    border-top-left-radius: $r-card;
    border-top-right-radius: $r-card;
  }
}

.gh__head {
  position: sticky;
  top: 0;
  z-index: 1;
  padding: $sp-1 $sp-3;
  background: $subject-cream;
  border-bottom: 1px solid rgba($subject-ink, .08);
  font-weight: 600;
  font-size: 11px;
  color: $color;
  transition: box-shadow $duration $easing, border-color $duration $easing;
}

.gh__rows {
  margin: 0;
  padding: 0 $sp-1 $sp-1;
  list-style: none;
}

.gh__item {
  padding: $sp-1 $sp-2;
  border-radius: $r-sm;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.7;
  color: $subject-ink;
}

@media (max-width: 340px) {
  .gh { max-width: 240px; }
  .gh__list { height: 124px; }
}

@media (prefers-reduced-motion: reduce) {
  .gh__head {
    transition: none;
  }
}

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);
}

.gh {
  width: 100%;
  max-width: 360px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.gh__hint {
  margin: 0;
  padding: 0 4px;
  font-weight: 400;
  font-size: 11px;
  line-height: 1.4;
  color: rgba(255, 247, 230, 0.72);
}

.gh__list {
  height: 176px;
  overflow-y: auto;
  background: #fff7e6;
  border-radius: 16px;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  position: relative;
}

.gh__group:first-child .gh__head {
  border-top-left-radius: 16px;
  border-top-right-radius: 16px;
}

.gh__head {
  position: sticky;
  top: 0;
  z-index: 1;
  padding: 4px 12px;
  background: #fff7e6;
  border-bottom: 1px solid rgba(23, 20, 26, 0.08);
  font-weight: 600;
  font-size: 11px;
  color: #0a4fe8;
  transition: box-shadow 300ms ease-out, border-color 300ms ease-out;
}

.gh__rows {
  margin: 0;
  padding: 0 4px 4px;
  list-style: none;
}

.gh__item {
  padding: 4px 8px;
  border-radius: 8px;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.7;
  color: #17141a;
}

@media (max-width: 340px) {
  .gh {
    max-width: 240px;
  }
  .gh__list {
    height: 124px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .gh__head {
    transition: none;
  }
}

// 그룹 고정 헤더(05) — 각 그룹 헤더는 CSS position: sticky 로 스크롤 컨테이너 상단에
// 붙는다. 계산 층은 그 위에 얹는다: 다음 헤더가 현재 헤더를 밀어내기 직전 구간을
// getBoundingClientRect 로 매 프레임 재서 overlapRatio(0~1) 를 구하고, 그 값을 그림자
// 진하기(box-shadow alpha)로 환산해 "곧 교체된다"를 시각적으로 앞당겨 보여준다.
(function () {
  var list = document.getElementById('ghList');
  if (!list) return;

  var heads = Array.prototype.slice.call(list.querySelectorAll('.gh__head'));

  function applyShadow(i, ratio) {
    var head = heads[i];
    if (!head) return;
    var alpha = 0.10 + 0.28 * ratio;
    head.style.boxShadow = '0 6px 10px rgba(23,20,26,' + alpha.toFixed(3) + ')';
    head.style.borderBottomColor = 'rgba(23,20,26,' + (0.08 + 0.4 * ratio).toFixed(3) + ')';
  }

  function measureStuck() {
    var listTop = list.getBoundingClientRect().top;
    for (var i = 0; i < heads.length; i++) {
      var next = heads[i + 1];
      if (!next) { applyShadow(i, 0); continue; }
      var headH = heads[i].offsetHeight;
      var nextTop = next.getBoundingClientRect().top - listTop;
      var ratio = 1 - Math.min(1, Math.max(0, (nextTop - headH) / headH));
      ratio = Math.min(1, Math.max(0, ratio));
      applyShadow(i, ratio);
    }
  }
  measureStuck();

  var playing = true;
  function stop() { playing = false; }
  list.addEventListener('wheel', stop, { passive: true });
  list.addEventListener('pointerdown', stop);
  list.addEventListener('scroll', measureStuck, { passive: true });

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  if (!reduce) {
    var period = 2000;
    var start = performance.now();
    (function tick(now) {
      if (playing) {
        var t = (now - start) % period;
        var half = period / 2;
        var p = t < half ? (t / half) : ((period - t) / half);
        var max = list.scrollHeight - list.clientHeight;
        list.scrollTop = p * max;
        measureStuck();
      }
      requestAnimationFrame(tick);
    })(start);
  }
})();

// SearchAutocompleteGroupedStickyHeader — vanilla 판(run/335/demo/05-search-autocomplete-grouped-sticky-header/index.html)
// 의 React 포트. 각 그룹 헤더는 CSS position: sticky 로 붙는다. 계산 층은 다음 헤더가
// 현재 헤더를 밀어내기 직전 구간을 getBoundingClientRect 로 매 프레임 재서
// overlapRatio(0~1) 를 구하고, 그 값을 그림자 진하기로 환산해 시각적으로 앞당겨 보여준다.
import { useEffect, useRef } from "react";
import styles from "./SearchAutocompleteGroupedStickyHeader.module.scss";

export type SearchAutocompleteGroupedStickyHeaderProps = {
  duration?: string;
  easing?: string;
  color?: string;
};

const HINT = "스크롤해도 지금 보는 그룹 이름이 위에 붙어 옵니다";
const LIST_LABEL = "그룹 목록";

const GROUPS: { label: string; items: string[] }[] = [
  { label: "제품", items: ["바나나", "파인애플", "수박", "자몽"] },
  { label: "브랜드", items: ["체리", "복숭아", "딸기"] },
  { label: "카테고리", items: ["아보카도", "망고", "파파야"] }
];

export default function SearchAutocompleteGroupedStickyHeader({
  duration = "300ms",
  easing = "ease-out",
  color = "#0a4fe8"
}: SearchAutocompleteGroupedStickyHeaderProps) {
  const listRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const list = listRef.current;
    if (!list) return;

    const heads = Array.prototype.slice.call(list.querySelectorAll<HTMLElement>("." + styles.head)) as HTMLElement[];

    function applyShadow(i: number, ratio: number): void {
      const head = heads[i];
      if (!head) return;
      const alpha = 0.1 + 0.28 * ratio;
      head.style.boxShadow = "0 6px 10px rgba(23,20,26," + alpha.toFixed(3) + ")";
      head.style.borderBottomColor = "rgba(23,20,26," + (0.08 + 0.4 * ratio).toFixed(3) + ")";
    }

    function measureStuck(): void {
      const listTop = list!.getBoundingClientRect().top;
      for (let i = 0; i < heads.length; i++) {
        const next = heads[i + 1];
        if (!next) {
          applyShadow(i, 0);
          continue;
        }
        const headH = heads[i].offsetHeight;
        const nextTop = next.getBoundingClientRect().top - listTop;
        let ratio = 1 - Math.min(1, Math.max(0, (nextTop - headH) / headH));
        ratio = Math.min(1, Math.max(0, ratio));
        applyShadow(i, ratio);
      }
    }
    measureStuck();

    let playing = true;
    function stop(): void {
      playing = false;
    }
    list.addEventListener("wheel", stop, { passive: true });
    list.addEventListener("pointerdown", stop);
    list.addEventListener("scroll", measureStuck, { passive: true });

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let raf = 0;

    if (!reduce) {
      const period = 2000;
      const start = performance.now();
      const tick = (now: number): void => {
        if (playing) {
          const t = (now - start) % period;
          const half = period / 2;
          const p = t < half ? t / half : (period - t) / half;
          const max = list!.scrollHeight - list!.clientHeight;
          list!.scrollTop = p * max;
          measureStuck();
        }
        raf = requestAnimationFrame(tick);
      };
      raf = requestAnimationFrame(tick);
    }

    return () => {
      cancelAnimationFrame(raf);
      list.removeEventListener("wheel", stop);
      list.removeEventListener("pointerdown", stop);
      list.removeEventListener("scroll", measureStuck);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.gh}>
        <p className={styles.hint}>{HINT}</p>
        <div
          className={styles.list}
          ref={listRef}
          role="listbox"
          aria-label={LIST_LABEL}
          tabIndex={0}
          style={{ transitionDuration: duration, transitionTimingFunction: easing, caretColor: color }}
        >
          {GROUPS.map((g, gi) => (
            <div className={styles.group} role="group" aria-label={g.label} key={g.label}>
              <div className={styles.head} id={"gh-head-react-" + gi}>
                {g.label}
              </div>
              <ul className={styles.rows}>
                {g.items.map((it) => (
                  <li className={styles.item} role="option" key={it}>
                    {it}
                  </li>
                ))}
              </ul>
            </div>
          ))}
        </div>
      </div>
    </main>
  );
}