04Discount badge — a badge that works out its own percentage from list price and sale price

<main class="stage">
<section class="panel">
  <p class="hint">It derives the percent from the gap between list and sale price, and separately computes the time left until the deadline.</p>
  <div class="priceRow">
    <span class="priceOld" id="priceOld">49</span>
    <span class="priceNew" id="priceNew">32</span>
  </div>
  <p class="badge" id="pctBadge">0% off</p>
  <p class="countdown" id="countdown" aria-live="polite">0:00 left</p>
</section>
</main>

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

$duration: $dur-quick;
$easing: $ease-out;
$color: $subject-blue;

@include stage($stage-paper);

.panel {
  width: 100%;
  max-width: 360px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-2;
}

.hint {
  margin: 0;
  padding: 0 $sp-2;
  text-align: center;
  font-weight: 400;
  font-size: 11px;
  line-height: 1.4;
  color: rgba($subject-ink, .70);
}

.priceRow {
  display: flex;
  align-items: baseline;
  gap: $sp-2;
}

.priceOld {
  font-weight: 500;
  font-size: 16px;
  color: rgba($subject-ink, .55);
  text-decoration: line-through;
}

.priceNew {
  font-weight: 700;
  font-size: 30px;
  color: $subject-ink;
}

.badge {
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: $color;
  color: $subject-cream;
  font-weight: 700;
  font-size: 12px;
  transition: background $duration $easing;
}

.badge.is-urgent {
  background: $error;
}

.countdown {
  margin: 0;
  padding: $sp-1 $sp-2;
  border-radius: $r-xs;
  font-weight: 500;
  font-size: 11px;
  color: rgba($subject-ink, .72);
  transition: color $duration $easing;
}

.countdown.is-urgent {
  color: $error;
  font-weight: 700;
}

@media (max-width: 340px) {
  .panel { max-width: 280px; gap: $sp-1; }
  .hint { font-size: 9px; }
  .priceNew { font-size: 24px; }
}

@media (prefers-reduced-motion: reduce) {
  .badge,
  .countdown {
    transition: none;
  }
}

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);
}

.panel {
  width: 100%;
  max-width: 360px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
}

.hint {
  margin: 0;
  padding: 0 8px;
  text-align: center;
  font-weight: 400;
  font-size: 11px;
  line-height: 1.4;
  color: rgba(23, 20, 26, 0.7);
}

.priceRow {
  display: flex;
  align-items: baseline;
  gap: 8px;
}

.priceOld {
  font-weight: 500;
  font-size: 16px;
  color: rgba(23, 20, 26, 0.55);
  text-decoration: line-through;
}

.priceNew {
  font-weight: 700;
  font-size: 30px;
  color: #17141a;
}

.badge {
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: #2f6df6;
  color: #fff7e6;
  font-weight: 700;
  font-size: 12px;
  transition: background 220ms ease-out;
}

.badge.is-urgent {
  background: #c2361a;
}

.countdown {
  margin: 0;
  padding: 4px 8px;
  border-radius: 4px;
  font-weight: 500;
  font-size: 11px;
  color: rgba(23, 20, 26, 0.72);
  transition: color 220ms ease-out;
}

.countdown.is-urgent {
  color: #c2361a;
  font-weight: 700;
}

@media (max-width: 340px) {
  .panel {
    max-width: 280px;
    gap: 4px;
  }
  .hint {
    font-size: 9px;
  }
  .priceNew {
    font-size: 24px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .badge,
  .countdown {
    transition: none;
  }
}

// 할인 배지(04) — 정가(LIST)와 할인가(SALE)의 차이를 정가로 나눠 퍼센트를 한 번 구해 배지에 채우고,
// 가상 마감까지 남은 시간은 rAF 로 매 프레임 다시 계산해 표시하며, 남은 비율이 낮아지면 배지 색을 바꾼다(계산 한 겹).
(function () {
  var pctBadge = document.getElementById('pctBadge');
  var countdown = document.getElementById('countdown');
  if (!pctBadge || !countdown) return;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var LIST = 49;
  var SALE = 32;
  var pct = Math.round((LIST - SALE) / LIST * 100);
  pctBadge.textContent = pct + '% off';

  var LOOP_MS = 2000;
  var TOTAL_SEC = 12 * 60;
  var URGENT_RATIO = .25;

  function format(sec) {
    var m = Math.floor(sec / 60);
    var s = Math.floor(sec % 60);
    return m + ':' + (s < 10 ? '0' + s : String(s));
  }

  function frame(elapsed) {
    var progress = Math.min(elapsed / LOOP_MS, 1);
    var remainSec = TOTAL_SEC * (1 - progress);
    countdown.textContent = format(remainSec) + ' left';
    var urgent = (remainSec / TOTAL_SEC) < URGENT_RATIO;
    pctBadge.classList.toggle('is-urgent', urgent);
    countdown.classList.toggle('is-urgent', urgent);
    if (progress >= 1) return LOOP_MS;
    return null;
  }

  if (reduce) {
    frame(0);
  } else {
    var start = null;
    function tick(ts) {
      if (start === null) start = ts;
      var elapsed = (ts - start) % LOOP_MS;
      frame(elapsed);
      requestAnimationFrame(tick);
    }
    requestAnimationFrame(tick);
  }
})();

// PricingDiscountBadge — vanilla 판(run/339/demo/04-pricing-discount-badge/index.html) 의 React 포트.
// 정가와 할인가의 차이를 정가로 나눠 퍼센트를 한 번 구해 배지에 채우고, 가상 마감까지 남은 시간은
// rAF 로 매 프레임 다시 계산해 표시하며, 남은 비율이 낮아지면 배지 색을 바꾼다(계산 한 겹).
import { useEffect, useRef } from "react";
import styles from "./PricingDiscountBadge.module.scss";

export type PricingDiscountBadgeProps = {
  duration?: string;
  easing?: string;
  color?: string;
};

const HINT = "정가와 할인가 차이로 퍼센트를 구하고 마감까지 남은 시간을 따로 계산합니다";

const LIST = 49;
const SALE = 32;
const LOOP_MS = 2000;
const TOTAL_SEC = 12 * 60;
const URGENT_RATIO = 0.25;

function format(sec: number): string {
  const m = Math.floor(sec / 60);
  const s = Math.floor(sec % 60);
  return m + ":" + (s < 10 ? "0" + s : String(s));
}

export default function PricingDiscountBadge({
  duration = "220ms",
  easing = "ease-out",
  color = "#2f6df6"
}: PricingDiscountBadgeProps) {
  const pctBadgeRef = useRef<HTMLParagraphElement | null>(null);
  const countdownRef = useRef<HTMLParagraphElement | null>(null);

  useEffect(() => {
    const pctBadge = pctBadgeRef.current;
    const countdown = countdownRef.current;
    if (!pctBadge || !countdown) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    const pct = Math.round(((LIST - SALE) / LIST) * 100);
    pctBadge.textContent = pct + "% 할인";

    function frame(elapsed: number): void {
      const progress = Math.min(elapsed / LOOP_MS, 1);
      const remainSec = TOTAL_SEC * (1 - progress);
      countdown!.textContent = format(remainSec) + " 남아";
      const urgent = remainSec / TOTAL_SEC < URGENT_RATIO;
      pctBadge!.classList.toggle(styles.isUrgent, urgent);
      countdown!.classList.toggle(styles.isUrgent, urgent);
    }

    let raf = 0;
    if (reduce) {
      frame(0);
    } else {
      let start: number | null = null;
      const tick = (ts: number): void => {
        if (start === null) start = ts;
        const elapsed = (ts - start) % LOOP_MS;
        frame(elapsed);
        raf = requestAnimationFrame(tick);
      };
      raf = requestAnimationFrame(tick);
    }

    return () => {
      if (raf) cancelAnimationFrame(raf);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <section className={styles.panel}>
        <p className={styles.hint}>{HINT}</p>
        <div className={styles.priceRow}>
          <span className={styles.priceOld}>49</span>
          <span className={styles.priceNew}>32</span>
        </div>
        <p className={styles.badge} ref={pctBadgeRef}>
          0% 할인
        </p>
        <p className={styles.countdown} aria-live="polite" ref={countdownRef}>
          0:00 남음
        </p>
      </section>
    </main>
  );
}