03Fold in half

<main class="stage">
  <div class="fh-card is-demo">
    <div class="fh-half fh-half--static">MENU</div>
    <div class="fh-half fh-half--fold">
      <div class="fh-half__face fh-half__face--front">MENU</div>
      <div class="fh-half__face fh-half__face--back"></div>
    </div>
  </div>
</main>

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

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

@include stage($stage-orange);

.fh-card {
  position: relative;
  display: flex;
  width: 176px;
  height: 108px;
  perspective: 900px;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.fh-half {
  width: 50%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  background: $subject-blue-deep;
  color: $subject-cream;
  font: 700 12px/1.3 -apple-system, "Segoe UI", sans-serif;
  letter-spacing: .08em;
}

.fh-half--fold {
  position: relative;
  transform-style: preserve-3d;
  transform-origin: left center; // 규칙8: 왼쪽 변 경첩 접힘
  transition: transform $duration $easing;
  background: none;
}

.fh-half__face {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  backface-visibility: hidden;
  font: 700 12px/1.3 -apple-system, "Segoe UI", sans-serif;
  letter-spacing: .08em;
  color: $subject-cream;
}
.fh-half__face--front { background: $subject-blue-deep; }
.fh-half__face--back { background: rgba(23, 20, 26, .78); transform: rotateY(180deg); }

// 데모 루프: 오른쪽 절반이 왼쪽 절반 위로 접힌다
@keyframes fh-fold {
  0%   { transform: rotateY(0); }
  50%  { transform: rotateY(-172deg); }
  100% { transform: rotateY(0); }
}
.fh-card.is-demo .fh-half--fold { animation: fh-fold $duration * 2.4 $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .fh-card.is-demo .fh-half--fold { animation: none !important; transition: none !important; transform: none !important; }
}

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);
}

.fh-card {
  position: relative;
  display: flex;
  width: 176px;
  height: 108px;
  perspective: 900px;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.fh-half {
  width: 50%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #0a4fe8;
  color: #fff7e6;
  font: 700 12px/1.3 -apple-system, "Segoe UI", sans-serif;
  letter-spacing: 0.08em;
}

.fh-half--fold {
  position: relative;
  transform-style: preserve-3d;
  transform-origin: left center;
  transition: transform 600ms cubic-bezier(0.2, 0.8, 0.2, 1);
  background: none;
}

.fh-half__face {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  backface-visibility: hidden;
  font: 700 12px/1.3 -apple-system, "Segoe UI", sans-serif;
  letter-spacing: 0.08em;
  color: #fff7e6;
}

.fh-half__face--front {
  background: #0a4fe8;
}

.fh-half__face--back {
  background: rgba(23, 20, 26, 0.78);
  transform: rotateY(180deg);
}

@keyframes fh-fold {
  0% {
    transform: rotateY(0);
  }
  50% {
    transform: rotateY(-172deg);
  }
  100% {
    transform: rotateY(0);
  }
}
.fh-card.is-demo .fh-half--fold {
  animation: fh-fold 1440ms cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@media (prefers-reduced-motion: reduce) {
  .fh-card.is-demo .fh-half--fold {
    animation: none !important;
    transition: none !important;
    transform: none !important;
  }
}

import { CSSProperties, useState } from "react";
import styles from "./FoldHalf.module.scss";

export interface FoldHalfProps {
  duration?: string;
  easing?: string;
  label?: string;
}

export default function FoldHalf({
  duration = "600ms",
  easing = "cubic-bezier(.2, .8, .2, 1)",
  label = "MENU",
}: FoldHalfProps) {
  const [folded, setFolded] = useState(false);
  const style = { "--duration": duration, "--easing": easing } as CSSProperties;
  return (
    <div
      className={styles.card}
      style={style}
      role="button"
      tabIndex={0}
      aria-pressed={folded}
      onClick={() => setFolded((v) => !v)}
      onKeyDown={(e: { key: string }) => (e.key === "Enter" || e.key === " ") && setFolded((v) => !v)}
    >
      <div className={styles.static}>{label}</div>
      <div className={`${styles.fold} ${folded ? styles.closed : ""}`}>
        <div className={`${styles.face} ${styles.front}`}>{label}</div>
        <div className={`${styles.face} ${styles.back}`} />
      </div>
    </div>
  );
}