01Hover preview fill — the filled value previews up to the hovered star's order value, then reverts once the pointer leaves

<main class="stage">
<div class="sr is-demo" id="sr">
  <div class="sr__row" id="srRow" role="radiogroup" aria-label="Star rating">
    <button class="sr__star" type="button" role="radio" aria-checked="false" data-i="1">
      <svg viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg>
    </button>
    <button class="sr__star" type="button" role="radio" aria-checked="false" data-i="2">
      <svg viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg>
    </button>
    <button class="sr__star" type="button" role="radio" aria-checked="false" data-i="3">
      <svg viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg>
    </button>
    <button class="sr__star" type="button" role="radio" aria-checked="false" data-i="4">
      <svg viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg>
    </button>
    <button class="sr__star" type="button" role="radio" aria-checked="false" data-i="5">
      <svg viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg>
    </button>
  </div>
  <div class="sr__readout" id="srReadout">Selected <b id="srNum">3</b>/5 · <span id="srPct">60</span>%</div>
</div>
</main>

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

// 계산 겹: 채움 개수를 전체 별 개수로 나눈 비율(ratioOf())을 정수로 그대로 화면에 보여준다 —
// 채움 클래스와 별개로 숫자 자체가 계산 결과다.
@include stage($stage-ink);

.sr {
  display: grid;
  gap: $sp-5;
  place-items: center;
}

.sr__row {
  display: flex;
  gap: $sp-2;
}

.sr__star {
  width: 44px;
  height: 44px;
  padding: 0;
  border: 0;
  background: none;
  cursor: pointer;
  color: $subject-blue-light;
  transition: transform $dur-quick $ease-out, color $dur-quick $ease-out;

  svg { display: block; width: 100%; height: 100%; fill: currentColor; }

  &--filled {
    color: $subject-pink;
    transform: scale(1.08);
  }
}

.sr__readout {
  font: 600 15px/1.3 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: $stage-paper;
  letter-spacing: .01em;

  b { color: $subject-pink; }

  &--preview { color: $subject-blue-light; b { color: $subject-blue-light; } }
}

@media (max-width: 340px) {
  .sr__star { width: 34px; height: 34px; }
  .sr__row { gap: $sp-1; }
  .sr__readout { font-size: 13px; }
}

@media (prefers-reduced-motion: reduce) {
  .sr__star { transition: 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);
}

.sr {
  display: grid;
  gap: 20px;
  place-items: center;
}

.sr__row {
  display: flex;
  gap: 8px;
}

.sr__star {
  width: 44px;
  height: 44px;
  padding: 0;
  border: 0;
  background: none;
  cursor: pointer;
  color: #5b8cf8;
  transition: transform 220ms ease-out, color 220ms ease-out;
}
.sr__star svg {
  display: block;
  width: 100%;
  height: 100%;
  fill: currentColor;
}
.sr__star--filled {
  color: #ff9ebb;
  transform: scale(1.08);
}

.sr__readout {
  font: 600 15px/1.3 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: #ffffff;
  letter-spacing: 0.01em;
}
.sr__readout b {
  color: #ff9ebb;
}
.sr__readout--preview {
  color: #5b8cf8;
}
.sr__readout--preview b {
  color: #5b8cf8;
}

@media (max-width: 340px) {
  .sr__star {
    width: 34px;
    height: 34px;
  }
  .sr__row {
    gap: 4px;
  }
  .sr__readout {
    font-size: 13px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sr__star {
    transition: none;
  }
}

(function () {
  var root = document.getElementById('sr');
  var row = document.getElementById('srRow');
  var stars = Array.prototype.slice.call(row.querySelectorAll('.sr__star'));
  var numEl = document.getElementById('srNum');
  var pctEl = document.getElementById('srPct');
  var readout = document.getElementById('srReadout');
  var TOTAL = stars.length;
  var value = 3;

  // 계산 겹: 채움 개수 n 을 전체 별 개수로 나눈 비율(산술)을 그대로 화면 숫자로 보여준다 —
  // 채움은 CSS 클래스가 아니라 이 비율 계산에서 나온 정수를 그대로 쓴다.
  function ratioOf(n) { return Math.round((n / TOTAL) * 100); }

  function paint(n, isPreview) {
    stars.forEach(function (s, idx) {
      s.classList.toggle('sr__star--filled', idx < n);
    });
    numEl.textContent = String(n);
    pctEl.textContent = String(ratioOf(n));
    readout.classList.toggle('sr__readout--preview', !!isPreview);
    readout.firstChild.textContent = isPreview ? 'Preview ' : 'Selected ';
  }

  function previewTo(i) { paint(i, true); }
  function revertToValue() { paint(value, false); }
  function commit(i) {
    value = i;
    stars.forEach(function (s, idx) { s.setAttribute('aria-checked', String(idx < value)); });
    paint(value, false);
  }

  stars.forEach(function (s) {
    var i = Number(s.getAttribute('data-i'));
    s.addEventListener('pointerenter', function () { root.classList.remove('is-demo'); stopAutoplay(); previewTo(i); });
    s.addEventListener('click', function () { commit(i); });
  });
  row.addEventListener('pointerleave', function () { revertToValue(); });

  paint(value, false);

  // 자동 루프: 별 순서대로 Preview 값을 올렸다 원래 값으로 되돌리는 것을 반복해 보여준다.
  var step = 0;
  var autoTimer = null;
  function autoTick() {
    if (step < TOTAL) { previewTo(step + 1); }
    else { revertToValue(); }
    step = (step + 1) % (TOTAL + 2);
  }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  function stopAutoplay() { if (autoTimer) { clearInterval(autoTimer); autoTimer = null; } }
  if (!reduce) { autoTimer = setInterval(autoTick, 280); autoTick(); }
})();

import { useEffect, useRef } from "react";
import styles from "./HoverPreviewFill.module.scss";

const STAR_PATH =
  "M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z";

export default function HoverPreviewFill() {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const row = root.querySelector<HTMLDivElement>(`.${styles.row}`);
    const readout = root.querySelector<HTMLDivElement>(`.${styles.readout}`);
    const numEl = root.querySelector<HTMLElement>(`.${styles.num}`);
    const pctEl = root.querySelector<HTMLElement>(`.${styles.pct}`);
    if (!row || !readout || !numEl || !pctEl) return;
    const stars = Array.prototype.slice.call(
      row.querySelectorAll(`.${styles.star}`)
    ) as HTMLElement[];
    const TOTAL = stars.length;
    let value = 3;

    // 계산 겹: 채움 개수 n 을 전체 별 개수로 나눈 비율(산술)을 그대로 화면 숫자로 보여준다 —
    // 채움은 CSS 클래스가 아니라 이 비율 계산에서 나온 정수를 그대로 쓴다.
    function ratioOf(n: number) {
      return Math.round((n / TOTAL) * 100);
    }

    function paint(n: number, isPreview?: boolean) {
      stars.forEach((s, idx) => {
        s.classList.toggle(styles.filled, idx < n);
      });
      numEl!.textContent = String(n);
      pctEl!.textContent = String(ratioOf(n));
      readout!.classList.toggle(styles.preview, !!isPreview);
      readout!.firstChild!.textContent = isPreview ? "미리보기 " : "선택 ";
    }

    function previewTo(i: number) { paint(i, true); }
    function revertToValue() { paint(value, false); }
    function commit(i: number) {
      value = i;
      stars.forEach((s, idx) => s.setAttribute("aria-checked", String(idx < value)));
      paint(value, false);
    }

    function onEnter(i: number) {
      return () => { stopAutoplay(); previewTo(i); };
    }
    function onClick(i: number) {
      return () => commit(i);
    }
    const enterHandlers: Array<() => void> = [];
    const clickHandlers: Array<() => void> = [];
    stars.forEach((s, idx) => {
      const i = idx + 1;
      const eh = onEnter(i);
      const ch = onClick(i);
      enterHandlers.push(eh);
      clickHandlers.push(ch);
      s.addEventListener("pointerenter", eh);
      s.addEventListener("click", ch);
    });
    function onLeave() { revertToValue(); }
    row.addEventListener("pointerleave", onLeave);

    paint(value, false);

    // 자동 루프: 별 순서대로 미리보기 값을 올렸다 원래 값으로 되돌리는 것을 반복해 보여준다.
    let step = 0;
    let autoTimer: number | null = null;
    function autoTick() {
      if (step < TOTAL) { previewTo(step + 1); }
      else { revertToValue(); }
      step = (step + 1) % (TOTAL + 2);
    }
    function stopAutoplay() { if (autoTimer !== null) { window.clearInterval(autoTimer); autoTimer = null; } }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { autoTimer = window.setInterval(autoTick, 280); autoTick(); }

    return () => {
      stopAutoplay();
      stars.forEach((s, idx) => {
        s.removeEventListener("pointerenter", enterHandlers[idx]);
        s.removeEventListener("click", clickHandlers[idx]);
      });
      row.removeEventListener("pointerleave", onLeave);
    };
  }, []);

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.sr}>
        <div className={styles.row} role="radiogroup" aria-label="별점">
          {[1, 2, 3, 4, 5].map((i) => (
            <button key={i} type="button" className={styles.star} role="radio" aria-checked="false">
              <svg viewBox="0 0 24 24"><path d={STAR_PATH} /></svg>
            </button>
          ))}
        </div>
        <div className={styles.readout}>
          선택 <b className={styles.num}>3</b>/5 · <span className={styles.pct}>60</span>%
        </div>
      </div>
    </div>
  );
}