06Nút hai màu quét

<main class="stage is-demo">
  <button class="btn" type="button">
    <span class="btn__wash" aria-hidden="true"></span>
    <span class="btn__labels">
      <span class="btn__t-on-dark">Bắt đầu</span>
      <span class="btn__t-on-light">Bắt đầu</span>
    </span>
  </button>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;     // 2s — 와이프 한 주기
$easing: $ease-spring;
$color: #e2cec4;          // 피치 (아래에 깔리는 색)

@include stage($stage-yellow);

.btn {
  box-sizing: border-box;
  position: relative;
  width: 240px;
  height: 64px;
  border: none;
  border-radius: $r-pill;
  background: $subject-cream;   // 위에 보이는 색
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-weight: 700;
  font-size: 18px;
  cursor: pointer;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

// 아래 색 레이어 — scaleX 로 왼쪽에서 펼쳐진다
.btn__wash {
  position: absolute;
  inset: 0;
  background: $color;
  transform: scaleX(0);
  transform-origin: left; // 규칙8: 듀오톤 와이프 좌측 전개
  transition: transform $dur-base $easing;
}

// 글자 두 벌 — 바탕색에 따라 보이는 쪽이 바뀐다
.btn__labels {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
}
.btn__t-on-dark,
.btn__t-on-light {
  grid-area: 1 / 1;
  transition: opacity $dur-quick $easing;
}
.btn__t-on-dark  { color: $subject-cream; opacity: 0; }
.btn__t-on-light { color: $subject-ink; }

// 실사용: 올리면 피치가 좌에서 우로 번지고 글자도 뒤집힌다
.btn:hover .btn__wash { transform: scaleX(1); }
.btn:hover .btn__t-on-dark  { opacity: 1; }
.btn:hover .btn__t-on-light { opacity: 0; }

.btn:focus-visible { outline: 3px solid $subject-ink; outline-offset: 4px; }

// 격자 미리보기: 번짐 → 물러남 루프
.stage.is-demo .btn__wash     { animation: wash $duration $easing infinite; }
.stage.is-demo .btn__t-on-dark  { animation: swap-in  $duration $easing infinite; }
.stage.is-demo .btn__t-on-light { animation: swap-out $duration $easing infinite; }

@keyframes wash {
  0%, 12%  { transform: scaleX(0); }
  48%, 70% { transform: scaleX(1); }
  100%     { transform: scaleX(0); }
}
@keyframes swap-in {
  0%, 18%  { opacity: 0; }
  48%, 70% { opacity: 1; }
  88%,100% { opacity: 0; }
}
@keyframes swap-out {
  0%, 18%  { opacity: 1; }
  48%, 70% { opacity: 0; }
  88%,100% { opacity: 1; }
}

@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .btn__wash     { animation: none; transform: scaleX(1); }
  .stage.is-demo .btn__t-on-dark  { animation: none; opacity: 1; }
  .stage.is-demo .btn__t-on-light { animation: none; opacity: 0; }
}

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);
}

.btn {
  box-sizing: border-box;
  position: relative;
  width: 240px;
  height: 64px;
  border: none;
  border-radius: 999px;
  background: #fff7e6;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-weight: 700;
  font-size: 18px;
  cursor: pointer;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.btn__wash {
  position: absolute;
  inset: 0;
  background: #e2cec4;
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.btn__labels {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
}

.btn__t-on-dark,
.btn__t-on-light {
  grid-area: 1/1;
  transition: opacity 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.btn__t-on-dark {
  color: #fff7e6;
  opacity: 0;
}

.btn__t-on-light {
  color: #17141a;
}

.btn:hover .btn__wash {
  transform: scaleX(1);
}

.btn:hover .btn__t-on-dark {
  opacity: 1;
}

.btn:hover .btn__t-on-light {
  opacity: 0;
}

.btn:focus-visible {
  outline: 3px solid #17141a;
  outline-offset: 4px;
}

.stage.is-demo .btn__wash {
  animation: wash 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.stage.is-demo .btn__t-on-dark {
  animation: swap-in 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.stage.is-demo .btn__t-on-light {
  animation: swap-out 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes wash {
  0%, 12% {
    transform: scaleX(0);
  }
  48%, 70% {
    transform: scaleX(1);
  }
  100% {
    transform: scaleX(0);
  }
}
@keyframes swap-in {
  0%, 18% {
    opacity: 0;
  }
  48%, 70% {
    opacity: 1;
  }
  88%, 100% {
    opacity: 0;
  }
}
@keyframes swap-out {
  0%, 18% {
    opacity: 1;
  }
  48%, 70% {
    opacity: 0;
  }
  88%, 100% {
    opacity: 1;
  }
}
@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .btn__wash {
    animation: none;
    transform: scaleX(1);
  }
  .stage.is-demo .btn__t-on-dark {
    animation: none;
    opacity: 1;
  }
  .stage.is-demo .btn__t-on-light {
    animation: none;
    opacity: 0;
  }
}

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

export type DuotoneWipeButtonProps = {
  duration?: number;
  easing?: string;
  color?: string;
  label?: string;
};

export default function DuotoneWipeButton({
  duration = 300,
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#ff9d6f",
  label = "시작하기",
}: DuotoneWipeButtonProps) {
  const vars: CSSProperties = { "--duration": `${duration}ms`, "--easing": easing, "--color": color } as CSSProperties;
  return (
    <button className={styles.btn} style={vars} type="button">
      <span className={styles.wash} aria-hidden="true" />
      <span className={styles.labels}>
        <span className={styles.tOnDark}>{label}</span>
        <span className={styles.tOnLight}>{label}</span>
      </span>
    </button>
  );
}