09Reduced-motion variant

<main class="stage">
  <div class="rm-card is-demo">
    <div class="rm-card__inner">
      <div class="rm-card__face rm-card__face--front">FRONT</div>
      <div class="rm-card__face rm-card__face--back">BACK</div>
    </div>
    <span class="rm-tag">reduced-motion</span>
  </div>
</main>

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

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

@include stage($stage-ink);

.rm-card {
  position: relative;
  perspective: 700px;
  width: 170px;
  height: 108px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-2;
}

.rm-card__inner {
  position: relative;
  width: 170px;
  height: 92px;
  transform-style: preserve-3d;
}

// 실제 사용 경로: 평소엔 3D 회전, reduced-motion 이 켜지면 회전을 끄고 교차 페이드만 남긴다 (BD5)
.rm-card:hover .rm-card__inner { transform: rotateY(180deg); transition: transform $dur-enter $ease-spring; }

.rm-card__face {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: $r-card;
  backface-visibility: hidden;
  font: 700 14px/1 -apple-system, "Segoe UI", sans-serif;
  color: $subject-cream;
}
.rm-card__face--front { background: $subject-blue-deep; }
.rm-card__face--back { background: rgba(255, 255, 255, .14); transform: rotateY(180deg); }

.rm-tag {
  font: 600 10px/1 -apple-system, sans-serif;
  letter-spacing: .05em;
  color: $subject-cream;
  opacity: .6;
}

// 데모 루프: 이 항목은 reduced-motion 결과 자체를 보여준다 — 회전 대신 opacity 교차 페이드만 무한 재생
@keyframes rm-crossfade-front { 0% { opacity: 1; } 50% { opacity: 0; } 100% { opacity: 1; } }
@keyframes rm-crossfade-back  { 0% { opacity: 0; } 50% { opacity: 1; } 100% { opacity: 0; } }
.rm-card.is-demo .rm-card__inner { transform: none; }
.rm-card.is-demo .rm-card__face--front { animation: rm-crossfade-front ($duration * 2.6) $easing infinite; backface-visibility: visible; transform: none; }
.rm-card.is-demo .rm-card__face--back  { animation: rm-crossfade-back  ($duration * 2.6) $easing infinite; backface-visibility: visible; transform: none; }

@media (prefers-reduced-motion: reduce) {
  .rm-card:hover .rm-card__inner { transform: none; transition: none; }
  .rm-card:hover .rm-card__face--front { opacity: 0; transition: opacity $dur-base $ease-out; }
  .rm-card:hover .rm-card__face--back  { opacity: 1; transform: none; transition: opacity $dur-base $ease-out; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.rm-card {
  position: relative;
  perspective: 700px;
  width: 170px;
  height: 108px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
}

.rm-card__inner {
  position: relative;
  width: 170px;
  height: 92px;
  transform-style: preserve-3d;
}

.rm-card:hover .rm-card__inner {
  transform: rotateY(180deg);
  transition: transform 600ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.rm-card__face {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 16px;
  backface-visibility: hidden;
  font: 700 14px/1 -apple-system, "Segoe UI", sans-serif;
  color: #fff7e6;
}

.rm-card__face--front {
  background: #0a4fe8;
}

.rm-card__face--back {
  background: rgba(255, 255, 255, 0.14);
  transform: rotateY(180deg);
}

.rm-tag {
  font: 600 10px/1 -apple-system, sans-serif;
  letter-spacing: 0.05em;
  color: #fff7e6;
  opacity: 0.6;
}

@keyframes rm-crossfade-front {
  0% {
    opacity: 1;
  }
  50% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
@keyframes rm-crossfade-back {
  0% {
    opacity: 0;
  }
  50% {
    opacity: 1;
  }
  100% {
    opacity: 0;
  }
}
.rm-card.is-demo .rm-card__inner {
  transform: none;
}

.rm-card.is-demo .rm-card__face--front {
  animation: rm-crossfade-front 1560ms ease-out infinite;
  backface-visibility: visible;
  transform: none;
}

.rm-card.is-demo .rm-card__face--back {
  animation: rm-crossfade-back 1560ms ease-out infinite;
  backface-visibility: visible;
  transform: none;
}

@media (prefers-reduced-motion: reduce) {
  .rm-card:hover .rm-card__inner {
    transform: none;
    transition: none;
  }
  .rm-card:hover .rm-card__face--front {
    opacity: 0;
    transition: opacity 300ms ease-out;
  }
  .rm-card:hover .rm-card__face--back {
    opacity: 1;
    transform: none;
    transition: opacity 300ms ease-out;
  }
}

import { CSSProperties } from "react";
import styles from "./ReducedMotionFlip.module.scss";

export interface ReducedMotionFlipProps {
  duration?: string;
  easing?: string;
  front?: string;
  back?: string;
}

// prefers-reduced-motion 이 켜진 사용자는 3D 회전 대신 opacity 교차 페이드만 받는다 (CSS @media 블록, JS 분기 없음)
export default function ReducedMotionFlip({
  duration = "600ms",
  easing = "ease-out",
  front = "FRONT",
  back = "BACK",
}: ReducedMotionFlipProps) {
  const style = { "--duration": duration, "--easing": easing } as CSSProperties;
  return (
    <div className={styles.card} style={style}>
      <div className={styles.inner}>
        <div className={`${styles.face} ${styles.front}`}>{front}</div>
        <div className={`${styles.face} ${styles.back}`}>{back}</div>
      </div>
      <span className={styles.tag}>reduced-motion</span>
    </div>
  );
}