09Case footer — a summary badge that works out the average across every story seen so far

<main class="stage">
<section class="panel">
  <p class="hint" id="hint">Each time a new view comes in, instead of recomputing the average from scratch, only the running sum and count are updated to calculate the average.</p>
  <div class="footerBar">
    <div class="stat">
      <p class="statNum" id="countNum">0</p>
      <p class="statLabel">views</p>
    </div>
    <div class="divider" aria-hidden="true"></div>
    <div class="stat">
      <p class="statNum" id="avgNum">0.0</p>
      <p class="statLabel">Average impact score</p>
    </div>
  </div>
  <p class="feedNote" id="feedNote">Recent: —</p>
</section>
</main>

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

$duration: $dur-base;
$easing: $ease-pop;
$color: $subject-blue-light;

@include stage($stage-ink);

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

.hint {
  margin: 0;
  text-align: center;
  color: rgba($subject-cream, .72);
  font-weight: 400;
  font-size: 10px;
  line-height: 1.35;
}

.footerBar {
  border-radius: $r-control;
  background: rgba($subject-cream, .08);
  padding: $sp-3 $sp-4;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: $sp-4;
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-1;
  min-width: 84px;
}

.statNum {
  margin: 0;
  color: $subject-cream;
  font-weight: 700;
  font-size: 22px;
  font-variant-numeric: tabular-nums;
  transform-origin: center;
}

.statNum--bump {
  animation: bump $duration $easing;
}

@keyframes bump {
  0% { transform: scale(1); }
  40% { transform: scale(1.16); color: $color; }
  100% { transform: scale(1); }
}

.statLabel {
  margin: 0;
  color: rgba($subject-cream, .72);
  font-weight: 500;
  font-size: 9px;
}

.divider {
  width: 1px;
  align-self: stretch;
  background: rgba($subject-cream, .18);
}

.feedNote {
  margin: 0;
  text-align: center;
  color: $color;
  font-weight: 600;
  font-size: 10px;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .panel { max-width: 280px; gap: $sp-1; }
  .footerBar { padding: $sp-2 $sp-3; gap: $sp-3; }
  .stat { min-width: 68px; }
  .statNum { font-size: 18px; }
  .hint { font-size: 9px; }
}

@media (prefers-reduced-motion: reduce) {
  .statNum--bump {
    animation: none;
  }
}

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);
}

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

.hint {
  margin: 0;
  text-align: center;
  color: rgba(255, 247, 230, 0.72);
  font-weight: 400;
  font-size: 10px;
  line-height: 1.35;
}

.footerBar {
  border-radius: 12px;
  background: rgba(255, 247, 230, 0.08);
  padding: 12px 16px;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  min-width: 84px;
}

.statNum {
  margin: 0;
  color: #fff7e6;
  font-weight: 700;
  font-size: 22px;
  font-variant-numeric: tabular-nums;
  transform-origin: center;
}

.statNum--bump {
  animation: bump 300ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

@keyframes bump {
  0% {
    transform: scale(1);
  }
  40% {
    transform: scale(1.16);
    color: #5b8cf8;
  }
  100% {
    transform: scale(1);
  }
}
.statLabel {
  margin: 0;
  color: rgba(255, 247, 230, 0.72);
  font-weight: 500;
  font-size: 9px;
}

.divider {
  width: 1px;
  align-self: stretch;
  background: rgba(255, 247, 230, 0.18);
}

.feedNote {
  margin: 0;
  text-align: center;
  color: #5b8cf8;
  font-weight: 600;
  font-size: 10px;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .panel {
    max-width: 280px;
    gap: 4px;
  }
  .footerBar {
    padding: 8px 12px;
    gap: 12px;
  }
  .stat {
    min-width: 68px;
  }
  .statNum {
    font-size: 18px;
  }
  .hint {
    font-size: 9px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .statNum--bump {
    animation: none;
  }
}

// 사례 푸터(09) — 새 열람 이벤트가 들어올 때마다 평균을 처음부터 다시 나누지 않고,
// 누적합(sum)과 누적건수(count)만 갱신해 running average 를 계산한다(계산 한 겹).
(function () {
  var countNum = document.getElementById('countNum');
  var avgNum = document.getElementById('avgNum');
  var feedNote = document.getElementById('feedNote');
  if (!countNum || !avgNum || !feedNote) return;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  // 가상 열람 이벤트: 임팩트 점수(0~100)가 하나씩 도착한다.
  var EVENTS = [72, 55, 88, 61, 94, 47, 76, 83, 59, 68, 91, 64];

  var sum = 0;
  var count = 0;
  var idx = 0;

  function step() {
    if (idx >= EVENTS.length) idx = 0;
    var value = EVENTS[idx];
    sum += value;
    count += 1;
    idx += 1;

    var average = sum / count;

    countNum.textContent = String(count);
    avgNum.textContent = average.toFixed(1);
    feedNote.textContent = 'Recent: impact  ' + value + ' pts viewed';

    if (!reduce) {
      countNum.classList.remove('statNum--bump');
      avgNum.classList.remove('statNum--bump');
      // 리플로우를 강제해 같은 클래스를 다시 걸어도 애니메이션이 재시작되게 한다.
      void countNum.offsetWidth;
      countNum.classList.add('statNum--bump');
      avgNum.classList.add('statNum--bump');
    }
  }

  step();
  if (!reduce) {
    setInterval(step, 550);
  }
})();

// CaseFooter — vanilla 판(run/340/demo/09-case-footer/index.html) 의 React 포트.
// 새 열람 이벤트가 들어올 때마다 평균을 처음부터 다시 나누지 않고, 누적합(sum)과
// 누적건수(count)만 갱신해 running average 를 계산한다.
import { useEffect, useRef, useState } from "react";
import styles from "./CaseFooter.module.scss";

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

const HINT = "새 열람이 들어올 때마다 평균을 처음부터 다시 나누지 않고, 누적합·누적건수만 갱신해 평균을 계산합니다";

const EVENTS = [72, 55, 88, 61, 94, 47, 76, 83, 59, 68, 91, 64];

export default function CaseFooter({
  duration = "300ms",
  easing = "cubic-bezier(.2,1.4,.4,1)",
  color = "#5b8cf8"
}: CaseFooterProps) {
  const [count, setCount] = useState(0);
  const [average, setAverage] = useState(0);
  const [feedNote, setFeedNote] = useState("최근: —");
  const [bump, setBump] = useState(false);
  const sumRef = useRef(0);
  const countRef = useRef(0);
  const idxRef = useRef(0);
  const reduceRef = useRef(false);

  useEffect(() => {
    reduceRef.current = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    function step(): void {
      if (idxRef.current! >= EVENTS.length) idxRef.current = 0;
      const value = EVENTS[idxRef.current!];
      sumRef.current = sumRef.current! + value;
      countRef.current = countRef.current! + 1;
      idxRef.current = idxRef.current! + 1;

      const nextAverage = sumRef.current! / countRef.current!;

      setCount(countRef.current!);
      setAverage(nextAverage);
      setFeedNote("최근: 임팩트 " + value + "점 열람");

      if (!reduceRef.current) {
        setBump(false);
        requestAnimationFrame(() => setBump(true));
      }
    }

    step();
    if (reduceRef.current) return;
    const timer = window.setInterval(step, 550);
    return () => window.clearInterval(timer);
  }, []);

  const bumpClass = bump ? " " + styles.statNumBump : "";

  return (
    <main className={styles.stage}>
      <section className={styles.panel}>
        <p className={styles.hint}>{HINT}</p>
        <div className={styles.footerBar}>
          <div className={styles.stat}>
            <p className={styles.statNum + bumpClass}>{count}</p>
            <p className={styles.statLabel}>건 열람</p>
          </div>
          <div className={styles.divider} aria-hidden="true" />
          <div className={styles.stat}>
            <p className={styles.statNum + bumpClass}>{average.toFixed(1)}</p>
            <p className={styles.statLabel}>평균 임팩트 점수</p>
          </div>
        </div>
        <p className={styles.feedNote}>{feedNote}</p>
      </section>
    </main>
  );
}