08Suspense skeleton swap

<main class="stage">
  <div class="sk-card is-demo">
    <div class="sk-skeleton">
      <span class="sk-bar sk-bar--title"></span>
      <span class="sk-bar sk-bar--line"></span>
      <span class="sk-bar sk-bar--line short"></span>
    </div>
    <div class="sk-content">
      <span class="sk-content__title">Widget loaded</span>
      <span class="sk-content__line">Lazy-loaded with React.lazy + Suspense</span>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-enter;
$easing: $ease-out;
$color: $subject-blue;

@include stage($stage-paper);

.sk-card {
  position: relative;
  width: min(260px, 84vw);
  height: 140px;
  box-sizing: border-box;
  padding: $sp-5;
  border-radius: $r-card;
  background: $subject-ink;
  box-shadow: $shadow-raised;
  overflow: hidden;
}

.sk-skeleton, .sk-content {
  position: absolute;
  inset: $sp-5;
  display: flex;
  flex-direction: column;
  gap: $sp-3;
}

.sk-bar {
  height: $sp-3;
  border-radius: $r-xs;
  background: linear-gradient(90deg, rgba(255, 255, 255, .1) 25%, rgba(255, 255, 255, .24) 50%, rgba(255, 255, 255, .1) 75%);
  background-size: 200% 100%;
  animation: sk-shimmer 1.1s linear infinite;
}
.sk-bar--title { width: 60%; height: $sp-4; }
.sk-bar--line.short { width: 40%; }
@keyframes sk-shimmer { 0% { background-position: 200% 0; } 100% { background-position: -200% 0; } }

.sk-content { justify-content: center; color: $subject-cream; font-family: -apple-system, "Segoe UI", sans-serif; }
.sk-content__title { font-weight: 700; font-size: 15px; line-height: 1.3; font-family: inherit; }
.sk-content__line { font-weight: 400; font-size: 12px; line-height: 1.5; font-family: inherit; color: $color; }

// 실사용 원리: React.Suspense 의 fallback 자리를 CSS 셰머로 채워두고, 지연 로드된
// 컴포넌트가 준비되면 fallback 은 빠지고 실제 콘텐츠가 같은 자리에서 페이드로 들어온다.
.sk-content { opacity: 0; }

// 캡처용 루프: 스켈레톤(0~55%) → 콘텐츠(65~100%) 크로스페이드
@keyframes sk-out { 0%, 30% { opacity: 1; } 75%, 100% { opacity: 0; } }
@keyframes sk-in  { 0%, 30% { opacity: 0; } 75%, 100% { opacity: 1; } }
.sk-card.is-demo .sk-skeleton { animation: sk-out $dur-loop $easing infinite; }
.sk-card.is-demo .sk-content  { animation: sk-in $dur-loop $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .sk-bar { animation: none !important; }
  .sk-card.is-demo .sk-skeleton,
  .sk-card.is-demo .sk-content { animation: none !important; }
  .sk-skeleton { opacity: 0; }
  .sk-content { opacity: 1; }
}

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);
}

.sk-card {
  position: relative;
  width: min(260px, 84vw);
  height: 140px;
  box-sizing: border-box;
  padding: 20px;
  border-radius: 16px;
  background: #17141a;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  overflow: hidden;
}

.sk-skeleton, .sk-content {
  position: absolute;
  inset: 20px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.sk-bar {
  height: 12px;
  border-radius: 4px;
  background: linear-gradient(90deg, rgba(255, 255, 255, 0.1) 25%, rgba(255, 255, 255, 0.24) 50%, rgba(255, 255, 255, 0.1) 75%);
  background-size: 200% 100%;
  animation: sk-shimmer 1.1s linear infinite;
}

.sk-bar--title {
  width: 60%;
  height: 16px;
}

.sk-bar--line.short {
  width: 40%;
}

@keyframes sk-shimmer {
  0% {
    background-position: 200% 0;
  }
  100% {
    background-position: -200% 0;
  }
}
.sk-content {
  justify-content: center;
  color: #fff7e6;
  font-family: -apple-system, "Segoe UI", sans-serif;
}

.sk-content__title {
  font-weight: 700;
  font-size: 15px;
  line-height: 1.3;
  font-family: inherit;
}

.sk-content__line {
  font-weight: 400;
  font-size: 12px;
  line-height: 1.5;
  font-family: inherit;
  color: #2f6df6;
}

.sk-content {
  opacity: 0;
}

@keyframes sk-out {
  0%, 30% {
    opacity: 1;
  }
  75%, 100% {
    opacity: 0;
  }
}
@keyframes sk-in {
  0%, 30% {
    opacity: 0;
  }
  75%, 100% {
    opacity: 1;
  }
}
.sk-card.is-demo .sk-skeleton {
  animation: sk-out 2s ease-out infinite;
}

.sk-card.is-demo .sk-content {
  animation: sk-in 2s ease-out infinite;
}

@media (prefers-reduced-motion: reduce) {
  .sk-bar {
    animation: none !important;
  }
  .sk-card.is-demo .sk-skeleton,
  .sk-card.is-demo .sk-content {
    animation: none !important;
  }
  .sk-skeleton {
    opacity: 0;
  }
  .sk-content {
    opacity: 1;
  }
}

import React, { CSSProperties } from "react";
import styles from "./SuspenseSkeletonSwap.module.scss";

function Skeleton() {
  return (
    <div className={styles.skeleton}>
      <span className={`${styles.bar} ${styles.title}`} />
      <span className={styles.bar} />
      <span className={`${styles.bar} ${styles.short}`} />
    </div>
  );
}

// React.lazy simulates a code-split widget — in a real app this import() would be a
// separate chunk fetched over the network, which is exactly what Suspense's fallback
// (the shimmer skeleton above) is there to cover while it loads.
const Widget = React.lazy(
  () =>
    new Promise<{ default: () => any }>((resolve) => {
      setTimeout(() => {
        resolve({
          default: () => (
            <div className={styles.content}>
              <span className={styles.contentTitle}>Widget loaded</span>
              <span className={styles.contentLine}>Lazy-loaded with React.lazy + Suspense</span>
            </div>
          ),
        });
      }, 900);
    })
);

export interface SuspenseSkeletonSwapProps {
  duration?: string;
  easing?: string;
}

export default function SuspenseSkeletonSwap({
  duration = "600ms",
  easing = "ease-out",
}: SuspenseSkeletonSwapProps) {
  const style: CSSProperties & { "--duration"?: string; "--easing"?: string } = {
    "--duration": duration,
    "--easing": easing,
  };

  return (
    <div className={styles.card} style={style}>
      <React.Suspense fallback={<Skeleton />}>
        <Widget />
      </React.Suspense>
    </div>
  );
}