09Reading time left

<main class="stage">
  <p class="time is-demo" role="status">
    <span class="time__label">left</span>
    <span class="time__num" aria-hidden="true"></span>
    <span class="time__label">min</span>
  </p>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$total: 12;                                         // 전체 예상 분 (두 자릿수로 시작해야 자릿수가 바뀌는 순간도 보인다)
$color: $subject-cream;                             // 숫자 색
$duration: $dur-loop;

@include stage($stage-ink);

@property --min {
  syntax: '<integer>';
  initial-value: #{$total};
  inherits: false;
}

.time {
  display: flex;
  align-items: baseline;
  gap: $sp-2;
  margin: 0;
  color: rgba(255, 255, 255, .7);
  font-weight: 600;
  font-size: 16px;
  line-height: 1;
  font-family: inherit;
}

.time__num {
  --min: #{$total};
  counter-reset: min var(--min);
  color: $color;
  font-weight: 800;
  font-size: clamp(34px, 11vw, 46px);
  line-height: 1;
  font-family: inherit;
  font-variant-numeric: tabular-nums;

  &::before { content: counter(min); }

  // 실제 사용: 남은 분수 = 전체 분수 × (1 − 스크롤 진행률)
  @supports (animation-timeline: scroll()) {
    animation: count-down linear both;
    animation-timeline: scroll(root);
  }
}
@keyframes count-down { from { --min: #{$total}; } to { --min: 0; } }

.time.is-demo .time__num { animation: count-down-loop $duration linear infinite; }
@keyframes count-down-loop {
  0%   { --min: #{$total}; }
  92%  { --min: 0; }
  100% { --min: 0; }
}

@media (prefers-reduced-motion: reduce) {
  .time__num, .time.is-demo .time__num { animation: none !important; --min: 0; }
}

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);
}

@property --min {
  syntax: "<integer>";
  initial-value: 12;
  inherits: false;
}
.time {
  display: flex;
  align-items: baseline;
  gap: 8px;
  margin: 0;
  color: rgba(255, 255, 255, 0.7);
  font-weight: 600;
  font-size: 16px;
  line-height: 1;
  font-family: inherit;
}

.time__num {
  --min: 12;
  counter-reset: min var(--min);
  color: #fff7e6;
  font-weight: 800;
  font-size: clamp(34px, 11vw, 46px);
  line-height: 1;
  font-family: inherit;
  font-variant-numeric: tabular-nums;
}
.time__num::before {
  content: counter(min);
}
@supports (animation-timeline: scroll()) {
  .time__num {
    animation: count-down linear both;
    animation-timeline: scroll(root);
  }
}

@keyframes count-down {
  from {
    --min: 12;
  }
  to {
    --min: 0;
  }
}
.time.is-demo .time__num {
  animation: count-down-loop 2s linear infinite;
}

@keyframes count-down-loop {
  0% {
    --min: 12;
  }
  92% {
    --min: 0;
  }
  100% {
    --min: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .time__num, .time.is-demo .time__num {
    animation: none !important;
    --min: 0;
  }
}

import { useEffect, useState } from "react";
import styles from "./ReadingTime.module.scss";

export type ReadingTimeProps = {
  /** 전체 예상 분 */
  totalMinutes: number;
  /** 숫자 색 */
  color?: string;
};

// 실제 쓰임: 남은 분 = 전체 분 × (1 − 스크롤 진행률).
export default function ReadingTime({ totalMinutes, color = "#fff7e6" }: ReadingTimeProps) {
  const [left, setLeft] = useState(totalMinutes);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      const p = max > 0 ? Math.min(1, window.scrollY / max) : 0;
      setLeft(Math.max(0, Math.round(totalMinutes * (1 - p))));
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, [totalMinutes]);

  return (
    <p className={styles.time} role="status">
      <span>left</span>
      <span className={styles.num} style={{ color }}>{left}</span>
      <span>min</span>
    </p>
  );
}