04Unfold a letter

<main class="stage">
  <div class="ul-scene is-demo">
    <div class="ul-letter">YOU'RE<br>INVITED</div>
    <div class="ul-flap ul-flap--top"></div>
    <div class="ul-flap ul-flap--bottom"></div>
  </div>
</main>

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

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

@include stage($stage-paper);

.ul-scene {
  position: relative;
  width: 172px;
  height: 112px;
  perspective: 900px;
  border-radius: $r-card;
  box-shadow: $shadow-raised;
}

.ul-letter {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  border-radius: $r-card;
  background: $subject-cream;
  color: $color;
  font: 700 13px/1.35 -apple-system, "Segoe UI", sans-serif;
  letter-spacing: .04em;
}

.ul-flap {
  position: absolute;
  left: 0;
  width: 100%;
  height: 50%;
  background: $color;
  border-radius: $r-card $r-card 0 0;
  transform-style: preserve-3d;
}
.ul-flap--top { top: 0; transform-origin: top center; } // 규칙8: 봉투 플랩 상변 경첩
.ul-flap--bottom { bottom: 0; border-radius: 0 0 $r-card $r-card; transform-origin: bottom center; } // 규칙8: 봉투 플랩 하변 경첩

// 데모 루프: 위 flap 먼저, 아래 flap 이 시차(transition-delay)를 두고 뒤따라 펴진다
@keyframes ul-open-top {
  0%, 25% { transform: rotateX(0); }
  60%, 100% { transform: rotateX(-172deg); }
}
@keyframes ul-open-bottom {
  0%, 40% { transform: rotateX(0); }
  75%, 100% { transform: rotateX(172deg); }
}
.ul-scene.is-demo .ul-flap--top { animation: ul-open-top $duration * 2.6 $easing infinite; }
.ul-scene.is-demo .ul-flap--bottom { animation: ul-open-bottom $duration * 2.6 $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .ul-scene.is-demo .ul-flap--top,
  .ul-scene.is-demo .ul-flap--bottom { animation: 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: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ul-scene {
  position: relative;
  width: 172px;
  height: 112px;
  perspective: 900px;
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.ul-letter {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  border-radius: 16px;
  background: #fff7e6;
  color: #2f6df6;
  font: 700 13px/1.35 -apple-system, "Segoe UI", sans-serif;
  letter-spacing: 0.04em;
}

.ul-flap {
  position: absolute;
  left: 0;
  width: 100%;
  height: 50%;
  background: #2f6df6;
  border-radius: 16px 16px 0 0;
  transform-style: preserve-3d;
}

.ul-flap--top {
  top: 0;
  transform-origin: top center;
}

.ul-flap--bottom {
  bottom: 0;
  border-radius: 0 0 16px 16px;
  transform-origin: bottom center;
}

@keyframes ul-open-top {
  0%, 25% {
    transform: rotateX(0);
  }
  60%, 100% {
    transform: rotateX(-172deg);
  }
}
@keyframes ul-open-bottom {
  0%, 40% {
    transform: rotateX(0);
  }
  75%, 100% {
    transform: rotateX(172deg);
  }
}
.ul-scene.is-demo .ul-flap--top {
  animation: ul-open-top 1560ms cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.ul-scene.is-demo .ul-flap--bottom {
  animation: ul-open-bottom 1560ms cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@media (prefers-reduced-motion: reduce) {
  .ul-scene.is-demo .ul-flap--top,
  .ul-scene.is-demo .ul-flap--bottom {
    animation: none !important;
    transform: none !important;
  }
}

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

export interface UnfoldLetterProps {
  duration?: string;
  easing?: string;
  message?: string;
}

export default function UnfoldLetter({
  duration = "600ms",
  easing = "cubic-bezier(.2, .8, .2, 1)",
  message = "YOU'RE INVITED",
}: UnfoldLetterProps) {
  const [open, setOpen] = useState(false);
  const style = { "--duration": duration, "--easing": easing } as CSSProperties;
  return (
    <div
      className={styles.scene}
      style={style}
      role="button"
      tabIndex={0}
      aria-pressed={open}
      onClick={() => setOpen((v) => !v)}
      onKeyDown={(e: { key: string }) => (e.key === "Enter" || e.key === " ") && setOpen((v) => !v)}
    >
      <div className={styles.letter}>{message}</div>
      <div className={`${styles.flap} ${styles.top} ${open ? styles.openTop : ""}`} />
      <div className={`${styles.flap} ${styles.bottom} ${open ? styles.openBottom : ""}`} />
    </div>
  );
}