05Sticky sub-nav that announces the current section

<main class="stage">
  <div class="ss is-demo">
    <div class="ss__win">
      <div class="ss__doc">
        <div class="ss__docHead">
          <h2 class="ss__title">Manual</h2>
        </div>
        <nav class="ss__bar">
          <a class="ss__chip" href="#sec-1">Start</a>
          <a class="ss__chip" href="#sec-2">Settings</a>
          <a class="ss__chip" href="#sec-3">Alerts</a>
          <a class="ss__chip" href="#sec-4">Share</a>
          <a class="ss__chip" href="#sec-5">Extend</a>
        </nav>
        <div class="ss__track">
          <section class="ss__sec" id="sec-1">
            <h3 class="ss__h">Start</h3>
            <i class="ss__line"></i><i class="ss__line ss__line--a"></i><i class="ss__line ss__line--b"></i><i class="ss__line ss__line--c"></i>
          </section>
          <section class="ss__sec" id="sec-2">
            <h3 class="ss__h">Settings</h3>
            <i class="ss__line"></i><i class="ss__line ss__line--a"></i><i class="ss__line ss__line--b"></i><i class="ss__line ss__line--c"></i>
          </section>
          <section class="ss__sec" id="sec-3">
            <h3 class="ss__h">Alerts</h3>
            <i class="ss__line"></i><i class="ss__line ss__line--a"></i><i class="ss__line ss__line--b"></i><i class="ss__line ss__line--c"></i>
          </section>
          <section class="ss__sec" id="sec-4">
            <h3 class="ss__h">Share</h3>
            <i class="ss__line"></i><i class="ss__line ss__line--a"></i><i class="ss__line ss__line--b"></i><i class="ss__line ss__line--c"></i>
          </section>
          <section class="ss__sec" id="sec-5">
            <h3 class="ss__h">Extend</h3>
            <i class="ss__line"></i><i class="ss__line ss__line--a"></i><i class="ss__line ss__line--b"></i><i class="ss__line ss__line--c"></i>
          </section>
        </div>
      </div>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;   // 격자 미리보기 루프 한 바퀴 2초
$easing: linear;        // 칩 컷과 섹션이 같은 속도로 지나가야 하이라이트 타이밍이 맞는다
$color: $subject-ink;   // 크림 카드 위 글자 · 현재 칩 배경

@include stage($stage-orange);

.ss, .ss * { box-sizing: border-box; }

.ss { width: min(420px, 94vw); }

// 스크롤 상자 = 크림 카드 자체. 안에서만 스크롤이 일어난다.
.ss__win {
  height: clamp(160px, 84vh, 272px);
  overflow-y: auto;
  scrollbar-width: none;
  &::-webkit-scrollbar { display: none; }
  border-radius: $r-card;
  background: $subject-cream;
  color: $color;
  scroll-behavior: smooth;
}

// sticky 바는 부모(.ss__doc) 높이만큼만 붙어 있을 수 있다 — 부모가 콘텐츠 전체를 감싼다(260 실측).
.ss__doc { position: relative; }

// 제목 영역 높이 46px(16 + 22 + 8) — 아래 루프 ss-bar 의 시작 오프셋과 같은 값
.ss__docHead { padding: $sp-4 $sp-4 $sp-2; }
.ss__title { margin: 0; font-size: 16px; line-height: 22px; font-weight: 800; }

.ss__bar {
  position: sticky;
  top: 0;
  z-index: 1;
  display: flex;
  gap: $sp-1;
  padding: $sp-2 $sp-4;
  background: $subject-cream;
  border-bottom: 1px solid rgba(23, 20, 26, .08);
}

.ss__chip {
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  color: rgba(23, 20, 26, .7);
  font-size: 12px;
  line-height: 16px;
  font-weight: 700;
  text-decoration: none;
  transition: background-color 140ms $ease-out, color 140ms $ease-out;
}
.ss__chip[aria-current="true"] { background: $color; color: $subject-cream; }

.ss__track { display: grid; gap: $sp-3; padding: $sp-3 $sp-4 $sp-12; }

.ss__sec { min-height: 96px; padding: $sp-3; border: 1px solid rgba(23, 20, 26, .08); border-radius: $r-sm; background: rgba(255, 255, 255, .5); }

.ss__h { margin: 0 0 $sp-2; font-size: 13px; line-height: 18px; font-weight: 700; }

.ss__line { display: block; height: 6px; margin-top: $sp-1; border-radius: $r-xs; background: rgba(23, 20, 26, .12); }
.ss__line--a { width: 92%; }
.ss__line--b { width: 78%; }
.ss__line--c { width: 60%; }

// ── 격자 미리보기 루프 ──
//    .is-demo 동안은 스크롤이 0 이라 sticky 가 안 걸린다 — 바를 absolute 로 무대 위에 고정하고
//    트랙(제목+섹션 묶음)을 translateY 로 흘려 스크롤을 흉내낸다(051: 상자가 아니라 트랙).
//    제목도 트랙과 함께 흘러가고 바만 남는다.
.ss.is-demo .ss__bar {
  position: absolute;
  top: 0; left: 0; right: 0;
  animation-name: ss-bar;
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.ss.is-demo .ss__docHead,
.ss.is-demo .ss__track {
  animation-name: ss-flow;
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
// 칩 하이라이트는 steps(1, end) 컷으로 옮겨간다(이동 아님) — 섹션이 중앙을 지나는 타이밍과 맞춤
.ss.is-demo .ss__chip {
  animation-duration: $duration;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.ss.is-demo .ss__chip:nth-child(1) { animation-name: ss-cur-1; }
.ss.is-demo .ss__chip:nth-child(2) { animation-name: ss-cur-2; }
.ss.is-demo .ss__chip:nth-child(3) { animation-name: ss-cur-3; }
.ss.is-demo .ss__chip:nth-child(4) { animation-name: ss-cur-4; }
.ss.is-demo .ss__chip:nth-child(5) { animation-name: ss-cur-5; }

@keyframes ss-flow {
  0%, 6% { transform: translateY(0); }
  74%, 78% { transform: translateY(-420px); }
  88%, 100% { transform: translateY(0); }
}
@keyframes ss-bar {
  0%, 6% { transform: translateY(46px); }   // 제목 아래 본래 위치
  16% { transform: translateY(0); }         // 제목이 흘러가면 무대 위에 붙는다
  78% { transform: translateY(0); }
  88%, 100% { transform: translateY(46px); }
}
// 시작→설정→알림→공유→확장 순서대로 하이라이트가 컷 이동, 88% 안에 복귀
@keyframes ss-cur-1 { 0% { background: $color; color: $subject-cream; } 18%, 100% { background: transparent; color: rgba(23, 20, 26, .7); } }
@keyframes ss-cur-2 { 0% { background: transparent; color: rgba(23, 20, 26, .7); } 18% { background: $color; color: $subject-cream; } 34%, 100% { background: transparent; color: rgba(23, 20, 26, .7); } }
@keyframes ss-cur-3 { 0% { background: transparent; color: rgba(23, 20, 26, .7); } 34% { background: $color; color: $subject-cream; } 50%, 100% { background: transparent; color: rgba(23, 20, 26, .7); } }
@keyframes ss-cur-4 { 0% { background: transparent; color: rgba(23, 20, 26, .7); } 50% { background: $color; color: $subject-cream; } 66%, 100% { background: transparent; color: rgba(23, 20, 26, .7); } }
@keyframes ss-cur-5 { 0% { background: transparent; color: rgba(23, 20, 26, .7); } 66% { background: $color; color: $subject-cream; } 80%, 100% { background: transparent; color: rgba(23, 20, 26, .7); } }

@media (max-width: 340px) {
  .ss__bar { gap: 0; padding: $sp-2 $sp-3; }
  .ss__chip { padding: $sp-1 $sp-2; font-size: 11px; }
  .ss__sec { min-height: 84px; padding: $sp-2; }
  .ss__track { gap: $sp-2; padding: $sp-2 $sp-3 $sp-10; }
}

@media (prefers-reduced-motion: reduce) {
  .ss.is-demo .ss__bar,
  .ss.is-demo .ss__docHead,
  .ss.is-demo .ss__track,
  .ss.is-demo .ss__chip { animation: none !important; }
  // 정적 상태에서도 바가 제목 아래 붙어 있는 모습이 그대로 보인다(진짜 sticky 로 복귀)
  .ss.is-demo .ss__bar { position: sticky; top: 0; transform: none !important; }
  .ss.is-demo .ss__docHead, .ss.is-demo .ss__track { transform: none !important; }
  .ss__win { scroll-behavior: auto; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ss, .ss * {
  box-sizing: border-box;
}

.ss {
  width: min(420px, 94vw);
}

.ss__win {
  height: clamp(160px, 84vh, 272px);
  overflow-y: auto;
  scrollbar-width: none;
}
.ss__win::-webkit-scrollbar {
  display: none;
}
.ss__win {
  border-radius: 16px;
  background: #fff7e6;
  color: #17141a;
  scroll-behavior: smooth;
}

.ss__doc {
  position: relative;
}

.ss__docHead {
  padding: 16px 16px 8px;
}

.ss__title {
  margin: 0;
  font-size: 16px;
  line-height: 22px;
  font-weight: 800;
}

.ss__bar {
  position: sticky;
  top: 0;
  z-index: 1;
  display: flex;
  gap: 4px;
  padding: 8px 16px;
  background: #fff7e6;
  border-bottom: 1px solid rgba(23, 20, 26, 0.08);
}

.ss__chip {
  padding: 4px 12px;
  border-radius: 999px;
  color: rgba(23, 20, 26, 0.7);
  font-size: 12px;
  line-height: 16px;
  font-weight: 700;
  text-decoration: none;
  transition: background-color 140ms ease-out, color 140ms ease-out;
}

.ss__chip[aria-current=true] {
  background: #17141a;
  color: #fff7e6;
}

.ss__track {
  display: grid;
  gap: 12px;
  padding: 12px 16px 48px;
}

.ss__sec {
  min-height: 96px;
  padding: 12px;
  border: 1px solid rgba(23, 20, 26, 0.08);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.5);
}

.ss__h {
  margin: 0 0 8px;
  font-size: 13px;
  line-height: 18px;
  font-weight: 700;
}

.ss__line {
  display: block;
  height: 6px;
  margin-top: 4px;
  border-radius: 4px;
  background: rgba(23, 20, 26, 0.12);
}

.ss__line--a {
  width: 92%;
}

.ss__line--b {
  width: 78%;
}

.ss__line--c {
  width: 60%;
}

.ss.is-demo .ss__bar {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  animation-name: ss-bar;
  animation-duration: 2s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
}

.ss.is-demo .ss__docHead,
.ss.is-demo .ss__track {
  animation-name: ss-flow;
  animation-duration: 2s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
}

.ss.is-demo .ss__chip {
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

.ss.is-demo .ss__chip:nth-child(1) {
  animation-name: ss-cur-1;
}

.ss.is-demo .ss__chip:nth-child(2) {
  animation-name: ss-cur-2;
}

.ss.is-demo .ss__chip:nth-child(3) {
  animation-name: ss-cur-3;
}

.ss.is-demo .ss__chip:nth-child(4) {
  animation-name: ss-cur-4;
}

.ss.is-demo .ss__chip:nth-child(5) {
  animation-name: ss-cur-5;
}

@keyframes ss-flow {
  0%, 6% {
    transform: translateY(0);
  }
  74%, 78% {
    transform: translateY(-420px);
  }
  88%, 100% {
    transform: translateY(0);
  }
}
@keyframes ss-bar {
  0%, 6% {
    transform: translateY(46px);
  }
  16% {
    transform: translateY(0);
  }
  78% {
    transform: translateY(0);
  }
  88%, 100% {
    transform: translateY(46px);
  }
}
@keyframes ss-cur-1 {
  0% {
    background: #17141a;
    color: #fff7e6;
  }
  18%, 100% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
}
@keyframes ss-cur-2 {
  0% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
  18% {
    background: #17141a;
    color: #fff7e6;
  }
  34%, 100% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
}
@keyframes ss-cur-3 {
  0% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
  34% {
    background: #17141a;
    color: #fff7e6;
  }
  50%, 100% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
}
@keyframes ss-cur-4 {
  0% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
  50% {
    background: #17141a;
    color: #fff7e6;
  }
  66%, 100% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
}
@keyframes ss-cur-5 {
  0% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
  66% {
    background: #17141a;
    color: #fff7e6;
  }
  80%, 100% {
    background: transparent;
    color: rgba(23, 20, 26, 0.7);
  }
}
@media (max-width: 340px) {
  .ss__bar {
    gap: 0;
    padding: 8px 12px;
  }
  .ss__chip {
    padding: 4px 8px;
    font-size: 11px;
  }
  .ss__sec {
    min-height: 84px;
    padding: 8px;
  }
  .ss__track {
    gap: 8px;
    padding: 8px 12px 40px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ss.is-demo .ss__bar,
  .ss.is-demo .ss__docHead,
  .ss.is-demo .ss__track,
  .ss.is-demo .ss__chip {
    animation: none !important;
  }
  .ss.is-demo .ss__bar {
    position: sticky;
    top: 0;
    transform: none !important;
  }
  .ss.is-demo .ss__docHead, .ss.is-demo .ss__track {
    transform: none !important;
  }
  .ss__win {
    scroll-behavior: auto;
  }
}

// 실제 동작: 화면(스크롤 상자) 중앙에 가장 가까운 섹션이 현재 칩이 된다.
var ss = document.querySelector('.ss');
var win = ss.querySelector('.ss__win');
var chips = Array.prototype.slice.call(ss.querySelectorAll('.ss__chip'));
var secs = Array.prototype.slice.call(ss.querySelectorAll('.ss__sec'));
function stopDemo() { ss.classList.remove('is-demo'); }  // 사람이 만졌으니 자동 루프를 끈다
ss.addEventListener('pointerdown', stopDemo);
win.addEventListener('scroll', stopDemo, { passive: true });
function mark(el) {
  chips.forEach(function (c) {
    c.setAttribute('aria-current', c.getAttribute('href') === '#' + el.id ? 'true' : 'false');
  });
}
var io = new IntersectionObserver(function (entries) {
  var w = win.getBoundingClientRect();
  var mid = w.top + w.height / 2;
  var best = null, gap = Infinity;
  entries.forEach(function (e) {
    if (!e.isIntersecting) return;
    var r = e.boundingClientRect;
    var d = Math.abs((r.top + r.bottom) / 2 - mid);
    if (d < gap) { gap = d; best = e.target; }
  });
  if (best) mark(best);
}, { root: win, threshold: 0.5 });
secs.forEach(function (s) { io.observe(s); });
mark(secs[0]);

import { useState, useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./StickySubnav.module.scss";

export type StickySubnavProps = {
  labels?: { title?: string; chips?: string[] };
  /** 격자 미리보기용 2초 자동 루프. 사람이 손대면 꺼진다 */
  demo?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T | null };

const CHIPS = ["Start", "Settings", "Alerts", "Sharing", "Extend"];

export default function StickySubnav({
  labels,
  demo = true,
  duration = 2000,
  easing = "linear",
  color = "#17141a",
}: StickySubnavProps) {
  const title = labels?.title ?? "Manual";
  const chips = labels?.chips ?? CHIPS;

  const [live, setLive] = useState(demo);
  const [cur, setCur] = useState(0);
  const winRef: Box<HTMLDivElement> = useRef(null);
  const trackRef: Box<HTMLDivElement> = useRef(null);

  // 화면(스크롤 상자) 중앙에 가장 가까운 섹션이 현재 칩이 된다
  useEffect(() => {
    const win = winRef.current;
    const track = trackRef.current;
    if (win === null || track === null) return;
    const secs = Array.from(track.children) as HTMLElement[];
    const io = new IntersectionObserver(
      (entries) => {
        const r = win.getBoundingClientRect();
        const mid = r.top + r.height / 2;
        let best: HTMLElement | null = null;
        let gap = Infinity;
        entries.forEach((e) => {
          if (!e.isIntersecting) return;
          const b = e.boundingClientRect;
          const d = Math.abs((b.top + b.bottom) / 2 - mid);
          if (d < gap) {
            gap = d;
            best = e.target as HTMLElement;
          }
        });
        if (best !== null) setCur(secs.indexOf(best));
      },
      { root: win, threshold: 0.5 }
    );
    secs.forEach((s) => io.observe(s));
    return () => io.disconnect();
  }, []);

  function touch() {
    setLive(false); // 사람이 만졌으니 자동 루프를 끈다
  }

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  const cls = [styles.ss, live ? styles.isDemo : ""].filter(Boolean).join(" ");

  return (
    <section className={cls} style={vars} onPointerDown={touch}>
      <div className={styles.win} ref={winRef} onScroll={touch}>
        <div className={styles.doc}>
          <div className={styles.docHead}>
            <h2 className={styles.title}>{title}</h2>
          </div>
          <nav className={styles.bar}>
            {chips.map((c, i) => (
              <a
                className={styles.chip}
                key={c}
                href={`#sec-${i + 1}`}
                aria-current={i === cur ? "true" : "false"}
              >
                {c}
              </a>
            ))}
          </nav>
          <div className={styles.track} ref={trackRef}>
            {chips.map((c, i) => (
              <section className={styles.sec} key={c} id={`sec-${i + 1}`}>
                <h3 className={styles.h}>{c}</h3>
                <i className={styles.line} />
                <i className={`${styles.line} ${styles.lineA}`} />
                <i className={`${styles.line} ${styles.lineB}`} />
                <i className={`${styles.line} ${styles.lineC}`} />
              </section>
            ))}
          </div>
        </div>
      </div>
    </section>
  );
}