05Timeline stagger

<main class="stage">
  <section class="sw is-demo" id="sw" aria-label="Timeline stagger demo">
    <header class="sw__head">
      <p class="sw__title">Timeline stagger</p>
      <p class="sw__attr"><code>data-stagger="90"</code></p>
    </header>
    <div class="sw__view" id="sw-view" tabindex="0" role="region" aria-label="Headline preview — scroll and words appear in order">
      <div class="sw__track">
        <p class="sw__hint">Scroll down</p>
        <article class="sw__card" id="sw-card" data-stagger="90">
          <h2 class="sw__line">One scroll turns a sentence into a timeline</h2>
          <p class="sw__meta">Magazine headline reveal</p>
        </article>
        <p class="sw__filler" aria-hidden="true">Next section</p>
      </div>
    </div>
    <footer class="sw__foot">
      <span class="sw__dot" aria-hidden="true"></span>
      <span class="sw__state">Six words flow in order</span>
    </footer>
  </section>
</main>

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

// 타임라인 시퀀스 — transition-delay: calc(var(--i) * var(--stagger)) 로 단어가 순번 지연을 받는다
// 진입 시점은 관찰자가 is-visible 로 연다. 미리보기(.is-demo)는 낱개 animation 속성으로 같은 시차를 재생한다
$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-paper);

.sw {
  position: relative;
  box-sizing: border-box;
  width: min(312px, 92vw);
  border-radius: $r-card;
  background: $subject-cream;
  color: $subject-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.sw__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
}
.sw__title {
  margin: 0;
  font-size: 13px;
  font-weight: 800;
  line-height: 1.3;
}
.sw__attr {
  margin: 0;
  font-size: 10px;
  font-weight: 400;
  line-height: 1.3;
  color: rgba($subject-ink, .72);
  code { font-family: "Consolas", "Menlo", monospace; }
}

.sw__view {
  height: 168px;
  overflow-y: auto;
  padding: 0 $sp-3;
  outline: none;
}
.sw__track {
  display: grid;
  gap: $sp-3;
  padding-top: $sp-2;
  padding-bottom: 96px;
}

.sw__hint {
  margin: 0;
  box-sizing: border-box;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: rgba($subject-ink, .72);
  border: 1px dashed rgba($subject-ink, .28);
  border-radius: $r-control;
  padding: $sp-3 0;
  text-align: center;
}

// 카드는 접힌 아래에 있다가 관찰자가 부른다 — margin 으로 첫 화면 밖까지 민다
.sw__card {
  box-sizing: border-box;
  margin-top: 120px;
  padding: $sp-4;
  border-radius: $r-card;
  background: $subject-blue-deep;
  color: $subject-cream;
}
.sw__line {
  margin: 0;
  font-size: 22px;
  font-weight: 800;
  line-height: 1.35;
}
// 단어 조각 — 순번 지연의 주인공. delay 는 calc(var(--i) * var(--stagger)) 하나로 순번을 만든다
.sw__word {
  display: inline-block;
  opacity: 0;
  transform: translateY(14px);
  transition-property: opacity, transform;
  transition-duration: $dur-quick, 420ms;
  transition-timing-function: ease-out, $easing;
  transition-delay: calc(var(--i) * var(--stagger, 90ms)), calc(var(--i) * var(--stagger, 90ms));
}
.sw__card.is-visible .sw__word {
  opacity: 1;
  transform: none;
}
.sw__meta {
  margin: $sp-2 0 0;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: $subject-cream;
}

.sw__filler {
  margin: 0;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: rgba($subject-ink, .72);
  border-radius: $r-control;
  background: rgba($subject-ink, .06);
  padding: $sp-6 0;
  text-align: center;
}

.sw__foot {
  display: flex;
  align-items: center;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
  border-top: 1px solid rgba($subject-ink, .12);
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
}
.sw__dot {
  width: 8px;
  height: 8px;
  border-radius: $r-pill;
  background: $color;
}

// 미리보기 — 트랙을 밀어 올리고 단어가 순번대로 들어온다
// animation: 단축을 쓰면 delay 가 0 으로 리셋되므로 낱개 속성으로만 쓴다 (240 함정)
.sw.is-demo {
  .sw__track {
    animation-name: sw-flow;
    animation-duration: $duration;
    animation-timing-function: $easing;
    animation-iteration-count: infinite;
    animation-fill-mode: backwards;
  }
  // 진 순간의 일괄 감춤은 라인 통째로 한 프레임 컷 — 페이드 중간 프레임이 유령으로 찍히지 않는다
  .sw__line {
    animation-name: sw-cut;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
  // 나타남은 컷(sw-show), 떠오름은 이징(sw-rise)
  .sw__word {
    animation-name: sw-show, sw-rise;
    animation-duration: $duration, $duration;
    animation-timing-function: steps(1, end), $easing;
    animation-iteration-count: infinite, infinite;
    animation-fill-mode: backwards, backwards;
    animation-delay: calc(#{$duration * .2} + var(--i) * var(--stagger, 90ms)), calc(#{$duration * .2} + var(--i) * var(--stagger, 90ms));
  }
  .sw__dot {
    animation-name: sw-blink;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
}

@keyframes sw-flow {
  0%, 8% { transform: translateY(0); }
  20%, 84% { transform: translateY(-144px); }
  86%, 100% { transform: translateY(0); }
}
@keyframes sw-cut {
  0%, 84% { opacity: 1; }
  86%, 96% { opacity: 0; }
  100% { opacity: 1; }
}
@keyframes sw-show {
  0% { opacity: 0; }
  2%, 100% { opacity: 1; }
}
@keyframes sw-rise {
  0% { transform: translateY(14px); }
  20%, 100% { transform: none; }
}
@keyframes sw-blink {
  0% { background: rgba($subject-ink, .2); }
  24% { background: $color; }
  88% { background: rgba($subject-ink, .2); }
}

@media (max-width: 340px) {
  .sw { width: 100%; }
  .sw__view { height: 112px; }
  .sw__line { font-size: 18px; }
  .sw__card { margin-top: 96px; }
  .sw__filler { padding: $sp-4 0; }
}

@media (prefers-reduced-motion: reduce) {
  .sw__word { transition: none !important; }
  .sw.is-demo .sw__track,
  .sw.is-demo .sw__line,
  .sw.is-demo .sw__word,
  .sw.is-demo .sw__dot { animation: none !important; }
  // 정지 상태 — 단어가 전부 보인다
  .sw.is-demo .sw__word { opacity: 1 !important; transform: none !important; }
  .sw.is-demo .sw__dot { background: $color !important; }
}

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

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

.sw {
  position: relative;
  box-sizing: border-box;
  width: min(312px, 92vw);
  border-radius: 16px;
  background: #fff7e6;
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.sw__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
  padding: 8px 12px;
}

.sw__title {
  margin: 0;
  font-size: 13px;
  font-weight: 800;
  line-height: 1.3;
}

.sw__attr {
  margin: 0;
  font-size: 10px;
  font-weight: 400;
  line-height: 1.3;
  color: rgba(23, 20, 26, 0.72);
}
.sw__attr code {
  font-family: "Consolas", "Menlo", monospace;
}

.sw__view {
  height: 168px;
  overflow-y: auto;
  padding: 0 12px;
  outline: none;
}

.sw__track {
  display: grid;
  gap: 12px;
  padding-top: 8px;
  padding-bottom: 96px;
}

.sw__hint {
  margin: 0;
  box-sizing: border-box;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: rgba(23, 20, 26, 0.72);
  border: 1px dashed rgba(23, 20, 26, 0.28);
  border-radius: 12px;
  padding: 12px 0;
  text-align: center;
}

.sw__card {
  box-sizing: border-box;
  margin-top: 120px;
  padding: 16px;
  border-radius: 16px;
  background: #0a4fe8;
  color: #fff7e6;
}

.sw__line {
  margin: 0;
  font-size: 22px;
  font-weight: 800;
  line-height: 1.35;
}

.sw__word {
  display: inline-block;
  opacity: 0;
  transform: translateY(14px);
  transition-property: opacity, transform;
  transition-duration: 220ms, 420ms;
  transition-timing-function: ease-out, cubic-bezier(0.2, 0.8, 0.2, 1);
  transition-delay: calc(var(--i) * var(--stagger, 90ms)), calc(var(--i) * var(--stagger, 90ms));
}

.sw__card.is-visible .sw__word {
  opacity: 1;
  transform: none;
}

.sw__meta {
  margin: 8px 0 0;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: #fff7e6;
}

.sw__filler {
  margin: 0;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: rgba(23, 20, 26, 0.72);
  border-radius: 12px;
  background: rgba(23, 20, 26, 0.06);
  padding: 24px 0;
  text-align: center;
}

.sw__foot {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-top: 1px solid rgba(23, 20, 26, 0.12);
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
}

.sw__dot {
  width: 8px;
  height: 8px;
  border-radius: 999px;
  background: #2f6df6;
}

.sw.is-demo .sw__track {
  animation-name: sw-flow;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
}
.sw.is-demo .sw__line {
  animation-name: sw-cut;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.sw.is-demo .sw__word {
  animation-name: sw-show, sw-rise;
  animation-duration: 2s, 2s;
  animation-timing-function: steps(1, end), cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite, infinite;
  animation-fill-mode: backwards, backwards;
  animation-delay: calc(0.4s + var(--i) * var(--stagger, 90ms)), calc(0.4s + var(--i) * var(--stagger, 90ms));
}
.sw.is-demo .sw__dot {
  animation-name: sw-blink;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

@keyframes sw-flow {
  0%, 8% {
    transform: translateY(0);
  }
  20%, 84% {
    transform: translateY(-144px);
  }
  86%, 100% {
    transform: translateY(0);
  }
}
@keyframes sw-cut {
  0%, 84% {
    opacity: 1;
  }
  86%, 96% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
@keyframes sw-show {
  0% {
    opacity: 0;
  }
  2%, 100% {
    opacity: 1;
  }
}
@keyframes sw-rise {
  0% {
    transform: translateY(14px);
  }
  20%, 100% {
    transform: none;
  }
}
@keyframes sw-blink {
  0% {
    background: rgba(23, 20, 26, 0.2);
  }
  24% {
    background: #2f6df6;
  }
  88% {
    background: rgba(23, 20, 26, 0.2);
  }
}
@media (max-width: 340px) {
  .sw {
    width: 100%;
  }
  .sw__view {
    height: 112px;
  }
  .sw__line {
    font-size: 18px;
  }
  .sw__card {
    margin-top: 96px;
  }
  .sw__filler {
    padding: 16px 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sw__word {
    transition: none !important;
  }
  .sw.is-demo .sw__track,
  .sw.is-demo .sw__line,
  .sw.is-demo .sw__word,
  .sw.is-demo .sw__dot {
    animation: none !important;
  }
  .sw.is-demo .sw__word {
    opacity: 1 !important;
    transform: none !important;
  }
  .sw.is-demo .sw__dot {
    background: #2f6df6 !important;
  }
}

// Timeline stagger — 문장을 단어로 쪼개 각 조각에 순번(--i) 을 물려준다
// 딜레이는 CSS 의 transition-delay calc(var(--i) * var(--stagger)) 가 계산하고 시점은 관찰자가 is-visible 로 연다
var root = document.getElementById('sw');
var view = document.getElementById('sw-view');
var card = document.getElementById('sw-card');
var line = card.querySelector('.sw__line');
var stag = parseInt(card.getAttribute('data-stagger'), 10) || 90;
card.style.setProperty('--stagger', stag + 'ms');
var words = line.textContent.trim().split(/\s+/);
line.textContent = '';
words.forEach(function (word, i) {
  var span = document.createElement('span');
  span.className = 'sw__word';
  span.textContent = word;
  span.style.setProperty('--i', i);
  line.appendChild(span);
  if (i < words.length - 1) line.appendChild(document.createTextNode(' '));
});
var started = false;
function start() {
  root.classList.remove('is-demo');
  if (started) return;
  started = true;
  var io = new IntersectionObserver(function (entries) {
    entries.forEach(function (entry) {
      if (entry.isIntersecting) entry.target.classList.add('is-visible');
      else entry.target.classList.remove('is-visible');
    });
  }, { root: view, threshold: 0.35 });
  io.observe(card);
}
view.addEventListener('scroll', start, { passive: true });
view.addEventListener('pointerdown', start);
view.addEventListener('keydown', function (e) {
  if (e.key === 'ArrowDown' || e.key === 'ArrowUp') start();
});

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

export type StaggerWordRevealProps = {
  title?: string;
  attr?: string;
  hint?: string;
  headline?: string;
  meta?: string;
  state?: string;
  groupLabel?: string;
  listLabel?: string;
  filler?: string;
  stagger?: number;
  /** 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; "--stagger"?: string };
// ambient 가 얇아 DOM 요소 타입을 못 쓴다 — 필요한 꼴만 로컬 타입으로 선언
type Box<T> = { current: T };
type KeyEvt = { key: string };

export default function StaggerWordReveal({
  title = "타임라인 시퀀스",
  attr = 'data-stagger="90"',
  hint = "아래로 스크롤",
  headline = "스크롤 한 번에 문장이 시간선이 된다",
  meta = "매거진 헤드라인 등장",
  state = "여섯 단어가 순서대로 흐른다",
  groupLabel = "타임라인 시퀀스 데모",
  listLabel = "헤드라인 미리보기 — 스크롤하면 단어가 순서대로 나타납니다",
  filler = "다음 섹션",
  stagger = 90,
  demo = true,
  duration = 2000,
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#2f6df6",
}: StaggerWordRevealProps) {
  const [live, setLive] = useState(demo);
  const [visible, setVisible] = useState(false);
  const viewRef = useRef<HTMLDivElement>(null) as unknown as Box<HTMLDivElement | null>;
  const cardRef = useRef<HTMLElement | null>(null) as unknown as Box<HTMLElement | null>;

  useEffect(() => {
    if (live) return;
    const root = viewRef.current;
    const card = cardRef.current;
    if (!root || !card) return;
    // 진입마다 재생 — 카드가 화면을 벗어나면 단어를 되돌려 다시 흐르게 한다
    const io = new IntersectionObserver(
      (entries) => {
        entries.forEach((entry) => setVisible(entry.isIntersecting));
      },
      { root, threshold: 0.35 }
    );
    io.observe(card);
    return () => io.disconnect();
  }, [live]);

  // 문장을 단어로 쪼개 각 조각에 순번(--i) 을 물려준다 — 딜레이는 CSS 가 계산한다
  const words = headline.trim().split(/\s+/);

  const vars: Vars = {
    "--duration": `${duration}ms`,
    "--easing": easing,
    "--color": color,
    "--stagger": `${stagger}ms`,
  };

  return (
    <section
      className={`${styles.sw} ${live ? styles.isDemo : ""}`}
      style={vars}
      aria-label={groupLabel}
    >
      <header className={styles.head}>
        <p className={styles.title}>{title}</p>
        <p className={styles.attr}><code>{attr}</code></p>
      </header>
      <div
        className={styles.view}
        ref={viewRef as unknown as Box<HTMLDivElement>}
        onScroll={() => setLive(false)}
        onPointerDown={() => setLive(false)}
        onKeyDown={(e: KeyEvt) => {
          if (e.key === "ArrowDown" || e.key === "ArrowUp") setLive(false);
        }}
        tabIndex={0}
        role="region"
        aria-label={listLabel}
      >
        <div className={styles.track}>
          <p className={styles.hint}>{hint}</p>
          <article
            ref={(el: HTMLElement | null) => {
              cardRef.current = el;
            }}
            className={`${styles.card} ${visible ? styles.isVisible : ""}`}
          >
            <h2 className={styles.line}>
              {words.map((word, i) => (
                <span key={word + String(i)} className={styles.word} style={{ "--i": String(i) } as CSSProperties}>
                  {word}
                  {i < words.length - 1 ? " " : ""}
                </span>
              ))}
            </h2>
            <p className={styles.meta}>{meta}</p>
          </article>
          <p className={styles.filler} aria-hidden="true">{filler}</p>
        </div>
      </div>
      <footer className={styles.foot}>
        <span className={styles.dot} aria-hidden="true" />
        <span className={styles.state}>{state}</span>
      </footer>
    </section>
  );
}