04A Bar Difficulty Meter With a Gloss Sweep on Change

<main class="stage">
<div class="bmf is-demo" id="bmf">
  <div class="bmf__meter" id="bmfMeter" role="slider" tabindex="0"
    aria-label="Difficulty" aria-valuemin="0" aria-valuemax="4" aria-valuenow="2" aria-valuetext="Hard">
    <div class="bmf__fill" id="bmfFill"></div>
    <div class="bmf__gloss" id="bmfGloss"></div>
  </div>
  <div class="bmf__row">
    <button type="button" class="bmf__btn" id="bmfMinus" aria-label="Lower difficulty">−</button>
    <span class="bmf__name" id="bmfName">Hard</span>
    <button type="button" class="bmf__btn" id="bmfPlus" aria-label="Raise difficulty">+</button>
  </div>
</div>
</main>

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

// 변수 3개
$duration: $dur-base;
$easing: $ease-out;
$color: $subject-sky;

// 계산 겹: sweep() 이 광택 띠 위치를 easeOutCubic(경과비율) 로 매 프레임 계산한다(JS)
@include stage($stage-paper);

.bmf { width: min(280px, 84vw); color: $subject-ink; text-align: center; }
.bmf__meter {
  position: relative; height: 16px; border-radius: $r-sm; overflow: hidden;
  background: rgba($subject-ink, .1); cursor: pointer;
}
.bmf__meter:focus-visible { outline: 2px solid $subject-ink; outline-offset: 2px; }
.bmf__fill {
  position: absolute; top: 0; bottom: 0; left: 0; width: 60%;
  background: $color; transition: width $duration $easing;
}
.bmf__gloss {
  position: absolute; top: 0; bottom: 0; left: 0; width: 28px;
  background: linear-gradient(90deg, rgba($subject-cream, 0), rgba($subject-cream, .85), rgba($subject-cream, 0));
  opacity: 0; transform: translateX(-50%);
}
.bmf__row { display: flex; align-items: center; justify-content: center; gap: $sp-3; margin-top: $sp-4; }
.bmf__btn {
  appearance: none; border: 0; border-radius: $r-control; width: 32px; height: 32px;
  background: $subject-ink; color: $subject-cream; font-size: 18px; font-weight: 700; cursor: pointer;
  transition: transform $dur-quick $ease-pop;
}
.bmf__btn:active { transform: scale(.9); }
.bmf__btn:focus-visible { outline: 2px solid $subject-ink; outline-offset: 2px; }
.bmf__name { font-weight: 700; font-size: 15px; min-width: 78px; }

@media (max-width: 340px) {
  .bmf { width: min(240px, 80vw); }
  .bmf__name { font-size: 13px; min-width: 64px; }
  .bmf__btn { width: 28px; height: 28px; font-size: 16px; }
}

@media (prefers-reduced-motion: reduce) {
  // 실사용 경로 적용: 채움 너비 전환을 끄고, 광택 띠는 JS 의 reduce 분기가 아예 돌리지 않는다(위 스크립트)
  .bmf__fill { 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);
}

.bmf {
  width: min(280px, 84vw);
  color: #17141a;
  text-align: center;
}

.bmf__meter {
  position: relative;
  height: 16px;
  border-radius: 8px;
  overflow: hidden;
  background: rgba(23, 20, 26, 0.1);
  cursor: pointer;
}

.bmf__meter:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

.bmf__fill {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: 60%;
  background: #6ec8ff;
  transition: width 300ms ease-out;
}

.bmf__gloss {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: 28px;
  background: linear-gradient(90deg, rgba(255, 247, 230, 0), rgba(255, 247, 230, 0.85), rgba(255, 247, 230, 0));
  opacity: 0;
  transform: translateX(-50%);
}

.bmf__row {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  margin-top: 16px;
}

.bmf__btn {
  appearance: none;
  border: 0;
  border-radius: 12px;
  width: 32px;
  height: 32px;
  background: #17141a;
  color: #fff7e6;
  font-size: 18px;
  font-weight: 700;
  cursor: pointer;
  transition: transform 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

.bmf__btn:active {
  transform: scale(0.9);
}

.bmf__btn:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

.bmf__name {
  font-weight: 700;
  font-size: 15px;
  min-width: 78px;
}

@media (max-width: 340px) {
  .bmf {
    width: min(240px, 80vw);
  }
  .bmf__name {
    font-size: 13px;
    min-width: 64px;
  }
  .bmf__btn {
    width: 28px;
    height: 28px;
    font-size: 16px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .bmf__fill {
    transition: none;
  }
}

(function () {
  var LEVELS = ['Easy', 'Normal', 'Hard', 'Very Hard', 'Extreme'];
  var N = LEVELS.length;
  var SWEEP_MS = 480;
  var root = document.getElementById('bmf');
  var meter = document.getElementById('bmfMeter');
  var fill = document.getElementById('bmfFill');
  var gloss = document.getElementById('bmfGloss');
  var name = document.getElementById('bmfName');
  var tier = 2;
  var raf = 0, t0 = 0;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function easeOutCubic(t) { return 1 - Math.pow(1 - t, 3); }
  // 계산 겹: 채움이 바뀔 때마다 밝은 띠의 위치를 easeOutCubic(경과비율) 로 매 프레임 계산해 왼쪽에서 오른쪽으로 훑는다
  function sweep() {
    cancelAnimationFrame(raf);
    if (reduce) { gloss.style.opacity = '0'; return; }
    t0 = performance.now();
    gloss.style.opacity = '1';
    function step(now) {
      var t = Math.min(1, (now - t0) / SWEEP_MS);
      gloss.style.left = (easeOutCubic(t) * 100) + '%';
      if (t < 1) raf = requestAnimationFrame(step);
      else gloss.style.opacity = '0';
    }
    raf = requestAnimationFrame(step);
  }
  function paint() {
    fill.style.width = ((tier + 1) / N * 100) + '%';
    meter.setAttribute('aria-valuenow', String(tier));
    meter.setAttribute('aria-valuetext', LEVELS[tier]);
    name.textContent = LEVELS[tier];
  }
  function human() { root.classList.remove('is-demo'); clearInterval(timer); }
  function set(t) {
    var next = Math.max(0, Math.min(N - 1, t));
    if (next === tier) return;
    tier = next; paint(); sweep();
  }
  document.getElementById('bmfPlus').addEventListener('click', function () { human(); set(tier + 1); });
  document.getElementById('bmfMinus').addEventListener('click', function () { human(); set(tier - 1); });
  meter.addEventListener('pointerdown', function (e) {
    human();
    var r = meter.getBoundingClientRect();
    var ratio = Math.max(0, Math.min(1, (e.clientX - r.left) / r.width));
    set(Math.round(ratio * (N - 1)));
  });
  meter.addEventListener('keydown', function (e) {
    if (e.key === 'ArrowRight' || e.key === 'ArrowUp') { e.preventDefault(); human(); set(tier + 1); }
    else if (e.key === 'ArrowLeft' || e.key === 'ArrowDown') { e.preventDefault(); human(); set(tier - 1); }
  });

  var sequence = [4, 1, 3, 0, 2];
  var si = 0;
  function tick() {
    var t = sequence[si % sequence.length]; si++;
    tier = t; paint(); sweep();
  }
  var timer = reduce ? null : setInterval(tick, 900);
  paint();
}());

import { useEffect, useRef } from 'react';
import styles from './DifficultySelectorBarMeterFill.module.scss';

const LEVELS = ['쉬움', '보통', '어려움', '매우 어려움', '최고'];
const N = LEVELS.length;
const SWEEP_MS = 480;
const SEQUENCE = [4, 1, 3, 0, 2];
const TICK_MS = 900;

export default function DifficultySelectorBarMeterFill() {
  const rootRef = useRef<HTMLDivElement>(null);
  const meterRef = useRef<HTMLDivElement>(null);
  const fillRef = useRef<HTMLDivElement>(null);
  const glossRef = useRef<HTMLDivElement>(null);
  const nameRef = useRef<HTMLSpanElement>(null);
  const plusRef = useRef<HTMLButtonElement>(null);
  const minusRef = useRef<HTMLButtonElement>(null);

  useEffect(() => {
    const root = rootRef.current;
    const meter = meterRef.current;
    const fill = fillRef.current;
    const gloss = glossRef.current;
    const name = nameRef.current;
    const plus = plusRef.current;
    const minus = minusRef.current;
    if (!root || !meter || !fill || !gloss || !name || !plus || !minus) return undefined;

    let tier = 2;
    let raf = 0, t0 = 0;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

    function easeOutCubic(t: number) { return 1 - Math.pow(1 - t, 3); }
    // 계산 겹: 채움이 바뀔 때마다 밝은 띠의 위치를 easeOutCubic(경과비율) 로 매 프레임 계산해 왼쪽에서 오른쪽으로 훑는다
    function sweep() {
      cancelAnimationFrame(raf);
      if (reduce) { gloss!.style.opacity = '0'; return; }
      t0 = performance.now();
      gloss!.style.opacity = '1';
      function step(now: number) {
        const t = Math.min(1, (now - t0) / SWEEP_MS);
        gloss!.style.left = (easeOutCubic(t) * 100) + '%';
        if (t < 1) raf = requestAnimationFrame(step);
        else gloss!.style.opacity = '0';
      }
      raf = requestAnimationFrame(step);
    }
    function paint() {
      fill!.style.width = ((tier + 1) / N * 100) + '%';
      meter!.setAttribute('aria-valuenow', String(tier));
      meter!.setAttribute('aria-valuetext', LEVELS[tier]);
      name!.textContent = LEVELS[tier];
    }
    let timer = 0;
    function human() { root!.classList.remove(styles['is-demo']); window.clearInterval(timer); }
    function set(t: number) {
      const next = Math.max(0, Math.min(N - 1, t));
      if (next === tier) return;
      tier = next; paint(); sweep();
    }

    function onPlus() { human(); set(tier + 1); }
    function onMinus() { human(); set(tier - 1); }
    function onDown(e: PointerEvent) {
      human();
      const r = meter!.getBoundingClientRect();
      const ratio = Math.max(0, Math.min(1, (e.clientX - r.left) / r.width));
      set(Math.round(ratio * (N - 1)));
    }
    function onKey(e: KeyboardEvent) {
      if (e.key === 'ArrowRight' || e.key === 'ArrowUp') { e.preventDefault(); human(); set(tier + 1); }
      else if (e.key === 'ArrowLeft' || e.key === 'ArrowDown') { e.preventDefault(); human(); set(tier - 1); }
    }
    plus.addEventListener('click', onPlus);
    minus.addEventListener('click', onMinus);
    meter.addEventListener('pointerdown', onDown);
    meter.addEventListener('keydown', onKey);

    let si = 0;
    function tick() {
      const t = SEQUENCE[si % SEQUENCE.length]; si++;
      tier = t; paint(); sweep();
    }
    if (!reduce) timer = window.setInterval(tick, TICK_MS);
    paint();

    return () => {
      plus!.removeEventListener('click', onPlus);
      minus!.removeEventListener('click', onMinus);
      meter!.removeEventListener('pointerdown', onDown);
      meter!.removeEventListener('keydown', onKey);
      cancelAnimationFrame(raf);
      window.clearInterval(timer);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.bmf + ' ' + styles['is-demo']} ref={rootRef}>
        <div
          className={styles.bmfMeter}
          ref={meterRef}
          role="slider"
          tabIndex={0}
          aria-label="난이도"
          aria-valuemin={0}
          aria-valuemax={N - 1}
          aria-valuenow={2}
          aria-valuetext="어려움"
        >
          <div className={styles.bmfFill} ref={fillRef} />
          <div className={styles.bmfGloss} ref={glossRef} />
        </div>
        <div className={styles.bmfRow}>
          <button type="button" className={styles.bmfBtn} ref={minusRef} aria-label="난이도 낮추기">−</button>
          <span className={styles.bmfName} ref={nameRef}>어려움</span>
          <button type="button" className={styles.bmfBtn} ref={plusRef} aria-label="난이도 높이기">+</button>
        </div>
      </div>
    </main>
  );
}