07Bước theo chương

<main class="stage">
  <ol class="steps is-demo" aria-label="Tiến độ chương">
    <li class="step"><span class="step__circle">1</span></li>
    <li class="step"><span class="step__circle">2</span></li>
    <li class="step"><span class="step__circle">3</span></li>
    <li class="step"><span class="step__circle">4</span></li>
  </ol>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$color: $subject-cream;                             // 채워진 원 색
$track: rgba(255, 255, 255, .22);                    // 연결선 색

@include stage($stage-orange);

.steps {
  position: relative;
  display: flex;
  gap: $sp-6;
  margin: 0; padding: 0;
  list-style: none;
}

.step {
  position: relative;
  &:not(:first-child)::before {
    content: "";
    position: absolute;
    right: 100%; top: 50%;
    width: $sp-6; height: 2px;
    background: $track;
  }
}

.step__circle {
  display: grid;
  place-items: center;
  width: 28px; height: 28px;
  border-radius: 50%;
  border: 2px solid $track;
  background: transparent;
  color: $subject-ink;                 // AA: 채워지기 전 원 숫자 — 주황 무대 위 5.50:1
  font-weight: 700;
  font-size: 13px;
  line-height: 1;
  font-family: inherit;
}

// ── 실제 사용: 같은 스텝 키프레임을 시간 대신 스크롤 구간(animation-range)에 건다 ──
// .step:nth-child(2) .step__circle { animation: fill-2 linear both; animation-timeline: scroll(root); }

// ── 데모: 챕터 번호가 순서대로 하나씩 부풀며 채워지고, 루프가 돌면 처음으로 되돌아간다 ──
// (색만 순간 전환하면 프레임 사이 변화가 한두 장뿐이라 눈에 덜 띈다 — scale 팝으로 구간을 넓힌다)
.steps.is-demo .step:nth-child(1) .step__circle { animation: fill-1 $duration ease-out infinite; }
.steps.is-demo .step:nth-child(2) .step__circle { animation: fill-2 $duration ease-out infinite; }
.steps.is-demo .step:nth-child(3) .step__circle { animation: fill-3 $duration ease-out infinite; }
.steps.is-demo .step:nth-child(4) .step__circle { animation: fill-4 $duration ease-out infinite; }

@keyframes fill-1 {
  0%          { background: transparent; color: $subject-ink; border-color: $track; transform: scale(1); }
  8%          { background: $color; color: $subject-ink; border-color: $color; transform: scale(1.25); }
  15%, 100%   { background: $color; color: $subject-ink; border-color: $color; transform: scale(1); }
}
@keyframes fill-2 {
  0%, 25%     { background: transparent; color: $subject-ink; border-color: $track; transform: scale(1); }
  33%         { background: $color; color: $subject-ink; border-color: $color; transform: scale(1.25); }
  40%, 100%   { background: $color; color: $subject-ink; border-color: $color; transform: scale(1); }
}
@keyframes fill-3 {
  0%, 50%     { background: transparent; color: $subject-ink; border-color: $track; transform: scale(1); }
  58%         { background: $color; color: $subject-ink; border-color: $color; transform: scale(1.25); }
  65%, 100%   { background: $color; color: $subject-ink; border-color: $color; transform: scale(1); }
}
@keyframes fill-4 {
  0%, 75%     { background: transparent; color: $subject-ink; border-color: $track; transform: scale(1); }
  83%         { background: $color; color: $subject-ink; border-color: $color; transform: scale(1.25); }
  90%, 100%   { background: $color; color: $subject-ink; border-color: $color; transform: scale(1); }
}

@media (prefers-reduced-motion: reduce) {
  .steps.is-demo .step__circle { animation: none !important; background: $color; border-color: $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);
}

.steps {
  position: relative;
  display: flex;
  gap: 24px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.step {
  position: relative;
}
.step:not(:first-child)::before {
  content: "";
  position: absolute;
  right: 100%;
  top: 50%;
  width: 24px;
  height: 2px;
  background: rgba(255, 255, 255, 0.22);
}

.step__circle {
  display: grid;
  place-items: center;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  border: 2px solid rgba(255, 255, 255, 0.22);
  background: transparent;
  color: #17141a;
  font-weight: 700;
  font-size: 13px;
  line-height: 1;
  font-family: inherit;
}

.steps.is-demo .step:nth-child(1) .step__circle {
  animation: fill-1 2s ease-out infinite;
}

.steps.is-demo .step:nth-child(2) .step__circle {
  animation: fill-2 2s ease-out infinite;
}

.steps.is-demo .step:nth-child(3) .step__circle {
  animation: fill-3 2s ease-out infinite;
}

.steps.is-demo .step:nth-child(4) .step__circle {
  animation: fill-4 2s ease-out infinite;
}

@keyframes fill-1 {
  0% {
    background: transparent;
    color: #17141a;
    border-color: rgba(255, 255, 255, 0.22);
    transform: scale(1);
  }
  8% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1.25);
  }
  15%, 100% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1);
  }
}
@keyframes fill-2 {
  0%, 25% {
    background: transparent;
    color: #17141a;
    border-color: rgba(255, 255, 255, 0.22);
    transform: scale(1);
  }
  33% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1.25);
  }
  40%, 100% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1);
  }
}
@keyframes fill-3 {
  0%, 50% {
    background: transparent;
    color: #17141a;
    border-color: rgba(255, 255, 255, 0.22);
    transform: scale(1);
  }
  58% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1.25);
  }
  65%, 100% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1);
  }
}
@keyframes fill-4 {
  0%, 75% {
    background: transparent;
    color: #17141a;
    border-color: rgba(255, 255, 255, 0.22);
    transform: scale(1);
  }
  83% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1.25);
  }
  90%, 100% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1);
  }
}
@media (prefers-reduced-motion: reduce) {
  .steps.is-demo .step__circle {
    animation: none !important;
    background: #fff7e6;
    border-color: #fff7e6;
  }
}

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

export type ChapterStepsProps = {
  /** 챕터 수 */
  total: number;
  /** 채워진 원 색 */
  color?: string;
};

// 실제 쓰임: 전체 스크롤 진행률을 챕터 수로 나눠 지금 챕터를 계산한다.
export default function ChapterSteps({ total, color = "#fff7e6" }: ChapterStepsProps) {
  const [current, setCurrent] = useState(0);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      const p = max > 0 ? Math.min(1, window.scrollY / max) : 0;
      setCurrent(Math.min(total - 1, Math.floor(p * total)));
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, [total]);

  return (
    <ol className={styles.steps} aria-label="Chapter progress">
      {Array.from({ length: total }, (_, i) => (
        <li key={i} className={styles.step}>
          <span className={styles.circle} style={i <= current ? { background: color, borderColor: color } : undefined}>
            {i + 1}
          </span>
        </li>
      ))}
    </ol>
  );
}