03Chấm điều hướng theo section

<main class="stage">
  <nav class="dots is-demo" aria-label="Điều hướng section">
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
  </nav>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;                               // 점 하나가 켜졌다 꺼지는 한 순환
$easing: $ease-out;
$color: $subject-cream;                             // 활성 점 색

@include stage($stage-orange);

.dots {
  position: fixed;
  right: $sp-6; top: 50%;
  transform: translateY(-50%);
  display: flex;
  flex-direction: column;
  gap: $sp-3;
}

.dot {
  width: 8px; height: 8px;
  border-radius: 50%;
  background: rgba(23, 20, 26, .28);
  transition: transform 200ms $easing, background 200ms $easing;
}

// ── 실제 사용: 섹션이 뷰포트에 들어오는 순간 그 섹션의 점에 .is-active 를 켠다 (IntersectionObserver) ──
.dot.is-active { transform: scale(1.6); background: $color; }

// ── 데모: 점을 순서대로 하나씩 밝힌다 ────────────────────
.dots.is-demo .dot { animation: pulse $duration linear infinite; }
.dots.is-demo .dot:nth-child(1) { animation-delay: 0s; }
.dots.is-demo .dot:nth-child(2) { animation-delay: .333s; }
.dots.is-demo .dot:nth-child(3) { animation-delay: .667s; }
.dots.is-demo .dot:nth-child(4) { animation-delay: 1s; }
.dots.is-demo .dot:nth-child(5) { animation-delay: 1.333s; }
.dots.is-demo .dot:nth-child(6) { animation-delay: 1.667s; }

@keyframes pulse {
  0%, 83.34%, 100% { transform: scale(1);   background: rgba(23, 20, 26, .28); }
  8.33%, 16.66%     { transform: scale(1.6); background: $color; }
}

@media (prefers-reduced-motion: reduce) {
  .dots.is-demo .dot { animation: none !important; }
  .dots.is-demo .dot:first-child { transform: scale(1.6); background: $color; }
}

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);
}

.dots {
  position: fixed;
  right: 24px;
  top: 50%;
  transform: translateY(-50%);
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: rgba(23, 20, 26, 0.28);
  transition: transform 200ms ease-out, background 200ms ease-out;
}

.dot.is-active {
  transform: scale(1.6);
  background: #fff7e6;
}

.dots.is-demo .dot {
  animation: pulse 2s linear infinite;
}

.dots.is-demo .dot:nth-child(1) {
  animation-delay: 0s;
}

.dots.is-demo .dot:nth-child(2) {
  animation-delay: 0.333s;
}

.dots.is-demo .dot:nth-child(3) {
  animation-delay: 0.667s;
}

.dots.is-demo .dot:nth-child(4) {
  animation-delay: 1s;
}

.dots.is-demo .dot:nth-child(5) {
  animation-delay: 1.333s;
}

.dots.is-demo .dot:nth-child(6) {
  animation-delay: 1.667s;
}

@keyframes pulse {
  0%, 83.34%, 100% {
    transform: scale(1);
    background: rgba(23, 20, 26, 0.28);
  }
  8.33%, 16.66% {
    transform: scale(1.6);
    background: #fff7e6;
  }
}
@media (prefers-reduced-motion: reduce) {
  .dots.is-demo .dot {
    animation: none !important;
  }
  .dots.is-demo .dot:first-child {
    transform: scale(1.6);
    background: #fff7e6;
  }
}

import { useEffect, useState } from "react";
import styles from "./SectionDots.module.scss";

export type SectionDotsProps = {
  /** 관찰할 섹션 id 목록 (순서대로) */
  sectionIds: string[];
  /** 활성 점 색 */
  color?: string;
};

// 실제 쓰임: IntersectionObserver 로 지금 뷰포트에 가장 많이 걸친 섹션을 찾아 그 점만 켠다.
export default function SectionDots({ sectionIds, color = "#fff7e6" }: SectionDotsProps) {
  const [active, setActive] = useState(0);

  useEffect(() => {
    const els = sectionIds.map((id) => document.getElementById(id)).filter(Boolean) as HTMLElement[];
    const io = new IntersectionObserver(
      (entries) => {
        const top = entries.filter((e) => e.isIntersecting).sort((a, b) => b.intersectionRatio - a.intersectionRatio)[0];
        if (top) setActive(els.indexOf(top.target as HTMLElement));
      },
      { threshold: [0.3, 0.6] }
    );
    els.forEach((el) => io.observe(el));
    return () => io.disconnect();
  }, [sectionIds]);

  return (
    <nav className={styles.dots} aria-label="Section navigation">
      {sectionIds.map((id, i) => (
        <a
          key={id}
          href={`#${id}`}
          className={`${styles.dot} ${i === active ? styles.active : ""}`}
          style={i === active ? { background: color } : undefined}
          aria-hidden="true"
          tabIndex={-1}
        />
      ))}
    </nav>
  );
}