09Header synced to scroll-snap

<main class="stage">
  <header class="head is-demo">
    <span class="head__logo">GODRICH</span>
    <span class="head__dots"><i class="is-current"></i><i></i><i></i></span>
  </header>
  <section class="snap-section" data-i="0"><p>01</p></section>
  <section class="snap-section" data-i="1"><p>02</p></section>
  <section class="snap-section" data-i="2"><p>03</p></section>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-quick;                              // 점이 옮겨가는 시간
$easing: $ease-pop;
$color: $subject-cream;                             // 활성 점 색

// ── 데모 무대 ──────────────────────────────────────────
html, body { margin: 0; overflow: hidden; }
.stage {
  min-height: 100vh;
  margin: 0;
  background: $stage-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  scroll-snap-type: y mandatory;                     // 본문이 섹션 단위로 멈춘다
}

.head {
  position: sticky;
  top: 0;
  z-index: 1;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 clamp(16px, 5vw, 24px);
  background: $stage-ink;

  &__logo { color: $subject-cream; font-weight: 800; font-size: 18px; line-height: 1; font-family: inherit; letter-spacing: .04em; }

  // 인디케이터: 점 3개 중 지금 멈춘 섹션의 것만 커진다
  &__dots {
    display: flex; gap: 8px;
    i {
      width: 8px; height: 8px; border-radius: 50%;
      background: rgba(255, 255, 255, .3);
      transform: scale(1);
      transition: transform $duration $easing, background $duration $easing;
      &.is-current { background: $color; transform: scale(1.4); }
    }
  }
}

// ── 데모(.is-demo): 점이 1→2→3→1 순서로 2초 루프 ──────────
.head.is-demo .head__dots i:nth-child(1) { animation: dot-1 $dur-loop $easing infinite; }
.head.is-demo .head__dots i:nth-child(2) { animation: dot-2 $dur-loop $easing infinite; }
.head.is-demo .head__dots i:nth-child(3) { animation: dot-3 $dur-loop $easing infinite; }
@mixin dot-phase($on-from, $on-to) {
  0%, #{$on-from - 1}#{'%'}    { background: rgba(255, 255, 255, .3); transform: scale(1); }
  #{$on-from}#{'%'}, #{$on-to}#{'%'} { background: $color; transform: scale(1.4); }
  #{$on-to + 1}#{'%'}, 100%     { background: rgba(255, 255, 255, .3); transform: scale(1); }
}
@keyframes dot-1 { @include dot-phase(5, 25); }
@keyframes dot-2 { @include dot-phase(38, 58); }
@keyframes dot-3 { @include dot-phase(71, 91); }

// ── 섹션: 순서를 알아볼 수 있는 카드 3개 ───────────────────
// 실제 페이지에서는 섹션 하나가 화면 높이만큼(scroll-snap-align: start) 이어진다.
// 데모 무대에서는 세 칸을 압축해 보여준다 — 320×200 렌더에서도 넘치면 안 되니 vh 로 줄인다
.snap-section {
  height: clamp(24px, 13vh, 78px);
  display: grid;
  place-items: center;
  scroll-snap-align: start;
  border-top: 1px solid rgba(255, 255, 255, .08);
  p { margin: 0; color: $subject-cream; font-weight: 800; font-size: 28px; line-height: 1; font-family: inherit; opacity: .35; }
}

@media (prefers-reduced-motion: reduce) {
  .head__dots i { transition: none; }
  .head.is-demo .head__dots i { animation: none !important; }
  .head.is-demo .head__dots i:first-child { background: $color; transform: scale(1.4); }
}

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

.stage {
  min-height: 100vh;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  scroll-snap-type: y mandatory;
}

.head {
  position: sticky;
  top: 0;
  z-index: 1;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 clamp(16px, 5vw, 24px);
  background: #17141a;
}
.head__logo {
  color: #fff7e6;
  font-weight: 800;
  font-size: 18px;
  line-height: 1;
  font-family: inherit;
  letter-spacing: 0.04em;
}
.head__dots {
  display: flex;
  gap: 8px;
}
.head__dots i {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.3);
  transform: scale(1);
  transition: transform 220ms cubic-bezier(0.2, 1.4, 0.4, 1), background 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}
.head__dots i.is-current {
  background: #fff7e6;
  transform: scale(1.4);
}

.head.is-demo .head__dots i:nth-child(1) {
  animation: dot-1 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

.head.is-demo .head__dots i:nth-child(2) {
  animation: dot-2 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

.head.is-demo .head__dots i:nth-child(3) {
  animation: dot-3 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

@keyframes dot-1 {
  0%, 4% {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1);
  }
  5%, 25% {
    background: #fff7e6;
    transform: scale(1.4);
  }
  26%, 100% {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1);
  }
}
@keyframes dot-2 {
  0%, 37% {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1);
  }
  38%, 58% {
    background: #fff7e6;
    transform: scale(1.4);
  }
  59%, 100% {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1);
  }
}
@keyframes dot-3 {
  0%, 70% {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1);
  }
  71%, 91% {
    background: #fff7e6;
    transform: scale(1.4);
  }
  92%, 100% {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1);
  }
}
.snap-section {
  height: clamp(24px, 13vh, 78px);
  display: grid;
  place-items: center;
  scroll-snap-align: start;
  border-top: 1px solid rgba(255, 255, 255, 0.08);
}
.snap-section p {
  margin: 0;
  color: #fff7e6;
  font-weight: 800;
  font-size: 28px;
  line-height: 1;
  font-family: inherit;
  opacity: 0.35;
}

@media (prefers-reduced-motion: reduce) {
  .head__dots i {
    transition: none;
  }
  .head.is-demo .head__dots i {
    animation: none !important;
  }
  .head.is-demo .head__dots i:first-child {
    background: #fff7e6;
    transform: scale(1.4);
  }
}

// 실제 페이지: scroll-snap 으로 멈춘 섹션 번호에 맞춰 점을 옮긴다 (IntersectionObserver, 7줄)
var dots = document.querySelectorAll('.head__dots i');
document.querySelectorAll('.snap-section').forEach(function (s) {
  new IntersectionObserver(function (es) {
    if (es[0].isIntersecting) dots.forEach(function (d, i) { d.classList.toggle('is-current', i == s.dataset.i); });
  }, { threshold: .6 }).observe(s);
});

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

export type ScrollSnapHeaderProps = {
  logo: string;
  /** 스냅 섹션 개수만큼의 ref */
  sectionRefs: { current: HTMLElement | null }[];
};

type Vars = CSSProperties;

export default function ScrollSnapHeader({ logo, sectionRefs }: ScrollSnapHeaderProps) {
  const [active, setActive] = useState(0);
  const vars: Vars = {};

  useEffect(() => {
    const observers = sectionRefs.map((ref, i) => {
      const io = new IntersectionObserver(([e]) => { if (e.isIntersecting) setActive(i); }, { threshold: 0.6 });
      if (ref.current) io.observe(ref.current);
      return io;
    });
    return () => observers.forEach((io) => io.disconnect());
  }, [sectionRefs]);

  return (
    <header className={styles.head} style={vars}>
      <span className={styles.logo}>{logo}</span>
      <span className={styles.dots}>
        {sectionRefs.map((_, i) => (
          <i key={i} className={i === active ? styles.current : undefined} />
        ))}
      </span>
    </header>
  );
}