04Header that folds smaller as you scroll

<main class="stage">
  <div class="ns is-demo">
    <header class="ns__head">
      <div class="ns__inner">
        <p class="ns__brand">Newsroom</p>
        <nav class="ns__nav">
          <a class="ns__link" href="#">Home</a>
          <a class="ns__link" href="#">Business</a>
          <a class="ns__link" href="#">Culture</a>
          <a class="ns__link" href="#">Sports</a>
        </nav>
      </div>
    </header>
    <div class="ns__main">
      <div class="ns__feed" tabindex="0">
        <div class="ns__sentinel" aria-hidden="true"></div>
        <div class="ns__track">
          <article class="ns__card">
            <h3 class="ns__t">Morning brief</h3>
            <i class="ns__bar"></i><i class="ns__bar ns__bar--s"></i>
          </article>
          <article class="ns__card">
            <h3 class="ns__t">Weekend weather</h3>
            <i class="ns__bar"></i><i class="ns__bar ns__bar--s"></i>
          </article>
          <article class="ns__card">
            <h3 class="ns__t">New books shelf</h3>
            <i class="ns__bar"></i><i class="ns__bar ns__bar--s"></i>
          </article>
          <article class="ns__card">
            <h3 class="ns__t">Local football</h3>
            <i class="ns__bar"></i><i class="ns__bar ns__bar--s"></i>
          </article>
          <article class="ns__card">
            <h3 class="ns__t">Metro delays</h3>
            <i class="ns__bar"></i><i class="ns__bar ns__bar--s"></i>
          </article>
          <article class="ns__card">
            <h3 class="ns__t">Night opening</h3>
            <i class="ns__bar"></i><i class="ns__bar ns__bar--s"></i>
          </article>
        </div>
      </div>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;   // 격자 미리보기 루프 한 바퀴 2초
$easing: $ease-out;     // 스크롤 관성 — 빠르게 시작해 천천히 멈춘다
$color: $subject-ink;   // 노랑 무대 위 브랜드·기사 제목 글자

@include stage($stage-yellow);

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

.ns { width: min(432px, 94vw); }

// ── 헤더 ── 배경은 비어 있는 ::before 막대가 담당한다(absolute, 좌우 0 위 0).
//    축소는 막대 scaleY · 내용 scale · 본문 translateY 셋 다 transform 이라 reflow 가 0 — 이게 이 데모의 원리.
.ns__head { position: relative; height: 48px; }

.ns__head::before {
  content: "";
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  background: $subject-cream;
  border-radius: 0 0 $r-sm $r-sm;
  transform: scaleY(1);
  transform-origin: top; // 규칙8: 헤더배경 top에서 줄어듦
  transition: transform 220ms $ease-out;
}

.ns__inner {
  position: relative;
  z-index: 1;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  padding: 0 $sp-4;
  transform: scale(1);
  transform-origin: left center; // 규칙8: 왼쪽 브랜드 고정 축소
  transition: transform 220ms $ease-out;
}

.ns__brand { margin: 0; color: $color; font-size: 19px; line-height: 24px; font-weight: 800; }

.ns__nav { display: flex; gap: $sp-3; }

.ns__link { color: rgba(23, 20, 26, .72); font-size: 12px; line-height: 16px; font-weight: 600; text-decoration: none; }

// ── 실제 동작: 센티넬이 화면에서 벗어나면 헤더에 .is-compact 가 붙는다(JS) ──
.ns__head.is-compact::before { transform: scaleY(.62); }
.ns__head.is-compact .ns__inner { transform: scale(.78); }
.ns__head.is-compact + .ns__main { transform: translateY(-14px); }

.ns__main { transition: transform 220ms $ease-out; }

.ns__feed {
  height: min(200px, calc(100vh - 104px));
  overflow-y: auto;
  scrollbar-width: none;
  &::-webkit-scrollbar { display: none; }
}

.ns__sentinel { height: 1px; }

.ns__track { display: grid; gap: $sp-2; padding: $sp-2; }

.ns__card { padding: $sp-2 $sp-3; background: $subject-cream; border-radius: $r-sm; }

.ns__t { margin: 0 0 $sp-1; color: $color; font-size: 13px; line-height: 18px; font-weight: 700; }

.ns__bar { display: block; height: 6px; margin-top: $sp-1; border-radius: $r-xs; background: rgba(23, 20, 26, .14); }
.ns__bar--s { width: 72%; }

// ── 격자 미리보기 루프 ──
//    움직이는 건 안쪽 트랙뿐 — 스크롤 상자(viewport)에 transform 을 걸면
//    100% 기준이 상자 폭이 되어 내용이 통째로 날아간다(051 실측).
//    헤더 축소는 steps(1, end) 컷 — 반투명하게 겹치는 중간 프레임이 없다.
//    0~36% 평화 → 40% 컷(축소가 최대 변화 프레임) → 74% 유지 → 78~88% 원상복귀.
.ns.is-demo .ns__track {
  animation-name: ns-scroll;
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.ns.is-demo .ns__head::before,
.ns.is-demo .ns__inner,
.ns.is-demo .ns__main {
  animation-duration: $duration;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.ns.is-demo .ns__head::before { animation-name: ns-cut-bar; }
.ns.is-demo .ns__inner { animation-name: ns-cut-inner; }
.ns.is-demo .ns__main { animation-name: ns-cut-main; }

@keyframes ns-scroll {
  0%, 36% { transform: translateY(0); }
  74%, 78% { transform: translateY(-132px); }
  88%, 100% { transform: translateY(0); }
}
@keyframes ns-cut-bar {
  0% { transform: scaleY(1); }
  40% { transform: scaleY(.62); }
  78%, 100% { transform: scaleY(1); }
}
@keyframes ns-cut-inner {
  0% { transform: scale(1); }
  40% { transform: scale(.78); }
  78%, 100% { transform: scale(1); }
}
@keyframes ns-cut-main {
  0% { transform: translateY(0); }
  40% { transform: translateY(-14px); }
  78%, 100% { transform: translateY(0); }
}

@media (max-width: 340px) {
  .ns__inner { padding: 0 $sp-3; }
  .ns__brand { font-size: 17px; line-height: 22px; }
  .ns__nav { gap: $sp-2; }
  .ns__link { font-size: 11px; }
  .ns__card { padding: $sp-2; }
  .ns__t { font-size: 12px; }
}

@media (prefers-reduced-motion: reduce) {
  .ns.is-demo .ns__track,
  .ns.is-demo .ns__head::before,
  .ns.is-demo .ns__inner,
  .ns.is-demo .ns__main { animation: none !important; }
  .ns.is-demo .ns__track { transform: none !important; }
  .ns__head::before, .ns__inner, .ns__main { transition: none !important; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

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

.ns {
  width: min(432px, 94vw);
}

.ns__head {
  position: relative;
  height: 48px;
}

.ns__head::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: #fff7e6;
  border-radius: 0 0 8px 8px;
  transform: scaleY(1);
  transform-origin: top;
  transition: transform 220ms ease-out;
}

.ns__inner {
  position: relative;
  z-index: 1;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  padding: 0 16px;
  transform: scale(1);
  transform-origin: left center;
  transition: transform 220ms ease-out;
}

.ns__brand {
  margin: 0;
  color: #17141a;
  font-size: 19px;
  line-height: 24px;
  font-weight: 800;
}

.ns__nav {
  display: flex;
  gap: 12px;
}

.ns__link {
  color: rgba(23, 20, 26, 0.72);
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  text-decoration: none;
}

.ns__head.is-compact::before {
  transform: scaleY(0.62);
}

.ns__head.is-compact .ns__inner {
  transform: scale(0.78);
}

.ns__head.is-compact + .ns__main {
  transform: translateY(-14px);
}

.ns__main {
  transition: transform 220ms ease-out;
}

.ns__feed {
  height: min(200px, 100vh - 104px);
  overflow-y: auto;
  scrollbar-width: none;
}
.ns__feed::-webkit-scrollbar {
  display: none;
}

.ns__sentinel {
  height: 1px;
}

.ns__track {
  display: grid;
  gap: 8px;
  padding: 8px;
}

.ns__card {
  padding: 8px 12px;
  background: #fff7e6;
  border-radius: 8px;
}

.ns__t {
  margin: 0 0 4px;
  color: #17141a;
  font-size: 13px;
  line-height: 18px;
  font-weight: 700;
}

.ns__bar {
  display: block;
  height: 6px;
  margin-top: 4px;
  border-radius: 4px;
  background: rgba(23, 20, 26, 0.14);
}

.ns__bar--s {
  width: 72%;
}

.ns.is-demo .ns__track {
  animation-name: ns-scroll;
  animation-duration: 2s;
  animation-timing-function: ease-out;
  animation-iteration-count: infinite;
}

.ns.is-demo .ns__head::before,
.ns.is-demo .ns__inner,
.ns.is-demo .ns__main {
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

.ns.is-demo .ns__head::before {
  animation-name: ns-cut-bar;
}

.ns.is-demo .ns__inner {
  animation-name: ns-cut-inner;
}

.ns.is-demo .ns__main {
  animation-name: ns-cut-main;
}

@keyframes ns-scroll {
  0%, 36% {
    transform: translateY(0);
  }
  74%, 78% {
    transform: translateY(-132px);
  }
  88%, 100% {
    transform: translateY(0);
  }
}
@keyframes ns-cut-bar {
  0% {
    transform: scaleY(1);
  }
  40% {
    transform: scaleY(0.62);
  }
  78%, 100% {
    transform: scaleY(1);
  }
}
@keyframes ns-cut-inner {
  0% {
    transform: scale(1);
  }
  40% {
    transform: scale(0.78);
  }
  78%, 100% {
    transform: scale(1);
  }
}
@keyframes ns-cut-main {
  0% {
    transform: translateY(0);
  }
  40% {
    transform: translateY(-14px);
  }
  78%, 100% {
    transform: translateY(0);
  }
}
@media (max-width: 340px) {
  .ns__inner {
    padding: 0 12px;
  }
  .ns__brand {
    font-size: 17px;
    line-height: 22px;
  }
  .ns__nav {
    gap: 8px;
  }
  .ns__link {
    font-size: 11px;
  }
  .ns__card {
    padding: 8px;
  }
  .ns__t {
    font-size: 12px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ns.is-demo .ns__track,
  .ns.is-demo .ns__head::before,
  .ns.is-demo .ns__inner,
  .ns.is-demo .ns__main {
    animation: none !important;
  }
  .ns.is-demo .ns__track {
    transform: none !important;
  }
  .ns__head::before, .ns__inner, .ns__main {
    transition: none !important;
  }
}

// 실제 동작: 스크롤 상자 맨 위의 센티넬이 화면에서 벗어나는 순간이 축소 신호다.
// 축소는 전부 transform 이라 리플로우가 0이다.
var ns = document.querySelector('.ns');
var feed = ns.querySelector('.ns__feed');
var head = ns.querySelector('.ns__head');
function stopDemo() { ns.classList.remove('is-demo'); }  // 사람이 만졌으니 자동 루프를 끈다
ns.addEventListener('pointerdown', stopDemo);
feed.addEventListener('scroll', stopDemo, { passive: true });
new IntersectionObserver(function (entries) {
  head.classList.toggle('is-compact', !entries[0].isIntersecting);
}, { root: feed }).observe(ns.querySelector('.ns__sentinel'));

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

export type ShrinkScrollHeaderProps = {
  labels?: { brand?: string; nav?: string[]; articles?: 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 NAV = ["Home", "Business", "Culture", "Sports"];
const ARTICLES = ["Morning briefing", "Weekend weather", "New book shelf", "Neighborhood soccer", "Subway delays", "Night opening"];

export default function ShrinkScrollHeader({
  labels,
  demo = true,
  duration = 2000,
  easing = "ease-out",
  color = "#17141a",
}: ShrinkScrollHeaderProps) {
  const brand = labels?.brand ?? "Newsroom";
  const nav = labels?.nav ?? NAV;
  const articles = labels?.articles ?? ARTICLES;

  const [live, setLive] = useState(demo);
  const [compact, setCompact] = useState(false);
  const feedRef: Box<HTMLDivElement> = useRef(null);
  const sentRef: Box<HTMLDivElement> = useRef(null);

  // 센티넬이 스크롤 상자 밖으로 나가는 순간이 축소 신호다 — 축소는 전부 transform
  useEffect(() => {
    const feed = feedRef.current;
    const sent = sentRef.current;
    if (feed === null || sent === null) return;
    const io = new IntersectionObserver(
      (entries) => entries.forEach((e) => setCompact(!e.isIntersecting)),
      { root: feed }
    );
    io.observe(sent);
    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.ns, live ? styles.isDemo : "", compact ? styles.isCompact : ""].filter(Boolean).join(" ");

  return (
    <section className={cls} style={vars} onPointerDown={touch}>
      <header className={styles.head}>
        <div className={styles.inner}>
          <p className={styles.brand}>{brand}</p>
          <nav className={styles.nav}>
            {nav.map((item) => (
              <a className={styles.link} key={item} href="#">{item}</a>
            ))}
          </nav>
        </div>
      </header>
      <div className={styles.main}>
        <div className={styles.feed} ref={feedRef} tabIndex={0} onScroll={touch}>
          <div className={styles.sentinel} aria-hidden="true" ref={sentRef} />
          <div className={styles.track}>
            {articles.map((t) => (
              <article className={styles.card} key={t}>
                <h3 className={styles.t}>{t}</h3>
                <i className={styles.bar} />
                <i className={styles.barS} />
              </article>
            ))}
          </div>
        </div>
      </div>
    </section>
  );
}