02Color band that sweeps across and swaps the content behind it

<main class="stage">
  <section class="ws is-demo" id="ws" aria-label="Wipe swap transition preview">
    <div class="ws__screen">
      <div class="ws__pages" id="ws-pages" aria-busy="false">
        <article class="ws__page ws__page--a">
          <p class="ws__eyebrow">Work</p>
          <p class="ws__head">Twelve photographs</p>
          <p class="ws__text">The band comes in from the left and covers the screen.</p>
        </article>
        <article class="ws__page ws__page--b">
          <p class="ws__eyebrow">Notes</p>
          <p class="ws__head">How it was made</p>
          <p class="ws__text">The content swaps only while it is covered.</p>
        </article>
      </div>
      <span class="ws__band" id="ws-band" aria-hidden="true"></span>
    </div>
    <button class="ws__go" type="button" id="ws-go">Next screen</button>
  </section>
</main>

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

// 한 장짜리 색 띠가 좌→우 한 방향으로 훑고 지나가며 그 아래 내용을 갈아 끼운다
$duration: $dur-enter;
$easing: $ease-spring;
$color: $subject-ink;

@include stage($stage-yellow);

.ws {
  box-sizing: border-box;
  display: grid;
  gap: $sp-3;
  width: min(320px, 88vw);
  color: $subject-ink;
}
.ws * { box-sizing: border-box; }

.ws__screen {
  position: relative;
  overflow: hidden;
  border: 2px solid $subject-ink;
  border-radius: $r-card;
  background: $subject-cream;
}

// 두 장을 같은 칸에 겹쳐 둔다 — 자리가 고정이라 갈아 끼워도 아래가 밀리지 않는다
.ws__pages {
  display: grid;
  min-height: 120px;
  padding: $sp-3;
}
.ws__page {
  grid-area: 1 / 1;
  display: grid;
  gap: $sp-2;
  align-content: start;
}
.ws__page--b { opacity: 0; }
// 정적(손으로 조작) 경로 — 클래스 하나로 두 장이 컷으로 바뀐다. 반투명으로 겹치는 구간이 없다
.ws__pages.is-b .ws__page--a { opacity: 0; }
.ws__pages.is-b .ws__page--b { opacity: 1; }

.ws__eyebrow {
  justify-self: start;
  margin: 0;
  padding: $sp-1 $sp-2;
  border-radius: $r-pill;
  background: $color;
  color: $subject-cream;
  font-size: 11px;
  font-weight: 800;
  line-height: 1;
}
.ws__head {
  margin: 0;
  font-size: 20px;
  font-weight: 800;
  line-height: 1.2;
}
.ws__text {
  margin: 0;
  font-size: 12px;
  font-weight: 500;
  line-height: 1.5;
}

// ── 색 띠 ──
// 화면 한 장 크기 그대로 두고 translateX 로만 민다.
// clip-path 로 깎지 않는 이유: steps 타이밍 안에서 clip-path 는 보간되지 않아 위프가 컷으로 죽는다
.ws__band {
  position: absolute;
  inset: 0;
  background: $color;
  transform: translateX(-101%);
}

// 실제 클릭 경로 — 한 번만 훑고 지나간다. 한가운데(덮은 순간)에 JS 가 본문을 갈아 끼운다
.ws__band.is-run {
  animation-name: ws-once;
  animation-duration: $duration * 1.2;
  animation-timing-function: $easing;
  animation-iteration-count: 1;
  animation-fill-mode: both;
}
@keyframes ws-once {
  0% { transform: translateX(-101%); }
  45%, 55% { transform: translateX(0); }
  100% { transform: translateX(101%); }
}

.ws__go {
  justify-self: center;
  margin: 0;
  padding: $sp-2 $sp-4;
  border: 0;
  border-radius: $r-pill;
  background: $color;
  color: $subject-cream;
  font-family: inherit;
  font-size: 13px;
  font-weight: 800;
  line-height: 1;
  cursor: pointer;
}
.ws__go:focus-visible { outline: 2px solid $subject-ink; outline-offset: 2px; }

// ── 격자 미리보기 전용 2초 루프 ──
// 한 방향 훑기를 두 번(A→B, B→A) 돌린다. 두 번째 훑기가 처음 상태로 돌려놓으므로
// 되돌아가는 장면이 따로 필요 없고, 교체는 언제나 띠 아래에서 일어난다
// 덮고 있는 구간은 짧게, 내용이 보이는 구간은 길게 잡는다.
// 빠져나가는 구간(8%)이 들어오는 구간(22%)보다 짧아서, 프레임당 변화가 가장 큰 장면은
// 언제나 "띠가 빠지며 새 내용이 드러나는 순간" 이 된다 — 대표 이미지가 거기서 잡힌다
@keyframes ws-sweep {
  0% { transform: translateX(-101%); }
  22%, 25% { transform: translateX(0); }
  33% { transform: translateX(101%); animation-timing-function: steps(1, end); }
  46% { transform: translateX(-101%); }
  68%, 71% { transform: translateX(0); }
  79%, 100% { transform: translateX(101%); }
}
// 교체는 띠가 완전히 덮은 구간(22~25% · 68~71%) 안에서 한 프레임에 컷
@keyframes ws-a {
  0%, 22% { opacity: 1; }
  23%, 68% { opacity: 0; }
  69%, 100% { opacity: 1; }
}
@keyframes ws-b {
  0%, 22% { opacity: 0; }
  23%, 68% { opacity: 1; }
  69%, 100% { opacity: 0; }
}

.ws.is-demo {
  .ws__band {
    animation-name: ws-sweep;
    animation-duration: $dur-loop;
    animation-timing-function: $easing;
    animation-iteration-count: infinite;
  }
  .ws__page--a { animation-name: ws-a; }
  .ws__page--b { animation-name: ws-b; }
  .ws__page {
    animation-duration: $dur-loop;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
}

@media (max-width: 340px) {
  .ws { gap: $sp-2; }
  .ws__pages { min-height: 88px; padding: $sp-2; }
  .ws__page { gap: $sp-1; }
  .ws__eyebrow { font-size: 10px; }
  .ws__head { font-size: 15px; }
  .ws__text { font-size: 11px; }
  .ws__go { padding: $sp-1 $sp-3; font-size: 12px; }
}

@media (prefers-reduced-motion: reduce) {
  .ws.is-demo .ws__band,
  .ws.is-demo .ws__page--a,
  .ws.is-demo .ws__page--b,
  .ws__band.is-run { animation: none !important; }
  // 움직임만 끄고 "갈아 끼워진 뒤" 결과는 남긴다
  .ws.is-demo .ws__band { transform: translateX(-101%) !important; }
  .ws.is-demo .ws__page--a { opacity: 0 !important; }
  .ws.is-demo .ws__page--b { opacity: 1 !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);
}

.ws {
  box-sizing: border-box;
  display: grid;
  gap: 12px;
  width: min(320px, 88vw);
  color: #17141a;
}

.ws * {
  box-sizing: border-box;
}

.ws__screen {
  position: relative;
  overflow: hidden;
  border: 2px solid #17141a;
  border-radius: 16px;
  background: #fff7e6;
}

.ws__pages {
  display: grid;
  min-height: 120px;
  padding: 12px;
}

.ws__page {
  grid-area: 1/1;
  display: grid;
  gap: 8px;
  align-content: start;
}

.ws__page--b {
  opacity: 0;
}

.ws__pages.is-b .ws__page--a {
  opacity: 0;
}

.ws__pages.is-b .ws__page--b {
  opacity: 1;
}

.ws__eyebrow {
  justify-self: start;
  margin: 0;
  padding: 4px 8px;
  border-radius: 999px;
  background: #17141a;
  color: #fff7e6;
  font-size: 11px;
  font-weight: 800;
  line-height: 1;
}

.ws__head {
  margin: 0;
  font-size: 20px;
  font-weight: 800;
  line-height: 1.2;
}

.ws__text {
  margin: 0;
  font-size: 12px;
  font-weight: 500;
  line-height: 1.5;
}

.ws__band {
  position: absolute;
  inset: 0;
  background: #17141a;
  transform: translateX(-101%);
}

.ws__band.is-run {
  animation-name: ws-once;
  animation-duration: 720ms;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: 1;
  animation-fill-mode: both;
}

@keyframes ws-once {
  0% {
    transform: translateX(-101%);
  }
  45%, 55% {
    transform: translateX(0);
  }
  100% {
    transform: translateX(101%);
  }
}
.ws__go {
  justify-self: center;
  margin: 0;
  padding: 8px 16px;
  border: 0;
  border-radius: 999px;
  background: #17141a;
  color: #fff7e6;
  font-family: inherit;
  font-size: 13px;
  font-weight: 800;
  line-height: 1;
  cursor: pointer;
}

.ws__go:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

@keyframes ws-sweep {
  0% {
    transform: translateX(-101%);
  }
  22%, 25% {
    transform: translateX(0);
  }
  33% {
    transform: translateX(101%);
    animation-timing-function: steps(1, end);
  }
  46% {
    transform: translateX(-101%);
  }
  68%, 71% {
    transform: translateX(0);
  }
  79%, 100% {
    transform: translateX(101%);
  }
}
@keyframes ws-a {
  0%, 22% {
    opacity: 1;
  }
  23%, 68% {
    opacity: 0;
  }
  69%, 100% {
    opacity: 1;
  }
}
@keyframes ws-b {
  0%, 22% {
    opacity: 0;
  }
  23%, 68% {
    opacity: 1;
  }
  69%, 100% {
    opacity: 0;
  }
}
.ws.is-demo .ws__band {
  animation-name: ws-sweep;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}
.ws.is-demo .ws__page--a {
  animation-name: ws-a;
}
.ws.is-demo .ws__page--b {
  animation-name: ws-b;
}
.ws.is-demo .ws__page {
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

@media (max-width: 340px) {
  .ws {
    gap: 8px;
  }
  .ws__pages {
    min-height: 88px;
    padding: 8px;
  }
  .ws__page {
    gap: 4px;
  }
  .ws__eyebrow {
    font-size: 10px;
  }
  .ws__head {
    font-size: 15px;
  }
  .ws__text {
    font-size: 11px;
  }
  .ws__go {
    padding: 4px 12px;
    font-size: 12px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ws.is-demo .ws__band,
  .ws.is-demo .ws__page--a,
  .ws.is-demo .ws__page--b,
  .ws__band.is-run {
    animation: none !important;
  }
  .ws.is-demo .ws__band {
    transform: translateX(-101%) !important;
  }
  .ws.is-demo .ws__page--a {
    opacity: 0 !important;
  }
  .ws.is-demo .ws__page--b {
    opacity: 1 !important;
  }
}

// 띠가 화면을 완전히 덮은 순간(애니메이션 한가운데)에만 본문을 갈아 끼운다.
var ws = document.getElementById('ws');
var wsBand = document.getElementById('ws-band');
var wsPages = document.getElementById('ws-pages');
var wsGo = document.getElementById('ws-go');
var wsBusy = false;
function wsSweep() {
  ws.classList.remove('is-demo');
  if (wsBusy) return;
  wsBusy = true;
  wsPages.setAttribute('aria-busy', 'true');
  wsBand.classList.remove('is-run');
  void wsBand.offsetWidth;
  wsBand.classList.add('is-run');
  setTimeout(function () { wsPages.classList.toggle('is-b'); }, 360);
  setTimeout(function () {
    wsBand.classList.remove('is-run');
    wsPages.setAttribute('aria-busy', 'false');
    wsBusy = false;
  }, 740);
}
wsGo.addEventListener('click', wsSweep);

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

export type WipePage = { eyebrow: string; head: string; text: string };

export type WipeSwapTransitionProps = {
  /** 갈아 끼울 두 화면. 띠가 완전히 덮은 순간에만 바뀐다 */
  pages?: [WipePage, WipePage];
  buttonLabel?: string;
  groupLabel?: 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 };
// ambient 가 얇아 useRef 가 T | null 을 돌려준다 — 필요한 꼴만 로컬 타입으로 단언
type Box<T> = { current: T };

const DEFAULT_PAGES: [WipePage, WipePage] = [
  { eyebrow: "Work", head: "Twelve photographs", text: "The band comes in from the left and covers the screen." },
  { eyebrow: "Notes", head: "How it was made", text: "The content swaps only while it is covered." },
];

export default function WipeSwapTransition({
  pages = DEFAULT_PAGES,
  buttonLabel = "Next screen",
  groupLabel = "Wipe swap transition preview",
  demo = true,
  duration = 600,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#17141a",
}: WipeSwapTransitionProps) {
  const [live, setLive] = useState(demo);
  const [second, setSecond] = useState(false);
  const [busy, setBusy] = useState(false);
  const [run, setRun] = useState(false);
  const timers = useRef<number[]>([]) as Box<number[]>;

  useEffect(() => () => {
    for (const t of timers.current) clearTimeout(t);
  }, []);

  function sweep() {
    setLive(false);
    if (busy) return;
    setBusy(true);
    setRun(false);
    // 한 프레임 뒤에 켜야 애니메이션이 처음부터 다시 돈다
    const a = window.setTimeout(() => setRun(true), 20);
    // 띠가 화면을 완전히 덮은 한가운데에서만 본문을 갈아 끼운다
    const b = window.setTimeout(() => setSecond((v) => !v), 380);
    const c = window.setTimeout(() => {
      setRun(false);
      setBusy(false);
    }, 780);
    timers.current = [a, b, c];
  }

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  const cls = [styles.ws, live ? styles.isDemo : ""].filter(Boolean).join(" ");
  const pageCls = [styles.pages, second ? styles.isB : ""].filter(Boolean).join(" ");
  const bandCls = [styles.band, run ? styles.isRun : ""].filter(Boolean).join(" ");

  return (
    <section className={cls} style={vars} aria-label={groupLabel}>
      <div className={styles.screen}>
        <div className={pageCls} aria-busy={busy}>
          {pages.map((p, i) => (
            <article className={[styles.page, i === 0 ? styles.pageA : styles.pageB].join(" ")} key={p.head}>
              <p className={styles.eyebrow}>{p.eyebrow}</p>
              <p className={styles.head}>{p.head}</p>
              <p className={styles.text}>{p.text}</p>
            </article>
          ))}
        </div>
        <span className={bandCls} aria-hidden="true" />
      </div>
      <button className={styles.go} type="button" onClick={sweep}>{buttonLabel}</button>
    </section>
  );
}