05段階ごとにアイコンの形が変形する難易度選択

<main class="stage">
<div class="ims is-demo" id="ims">
  <svg class="ims__icon" viewBox="0 0 80 80" width="64" height="64" aria-hidden="true">
    <path id="imsPath" class="ims__shape"></path>
  </svg>
  <div class="ims__row" id="imsRow" role="radiogroup" aria-label="難易度">
    <button type="button" class="ims__dot" role="radio" aria-checked="false" aria-label="簡単" data-i="0" tabindex="0"></button>
    <button type="button" class="ims__dot" role="radio" aria-checked="false" aria-label="普通" data-i="1" tabindex="-1"></button>
    <button type="button" class="ims__dot" role="radio" aria-checked="true" aria-label="難しい" data-i="2" tabindex="-1"></button>
    <button type="button" class="ims__dot" role="radio" aria-checked="false" aria-label="とても難しい" data-i="3" tabindex="-1"></button>
    <button type="button" class="ims__dot" role="radio" aria-checked="false" aria-label="最高" data-i="4" tabindex="-1"></button>
  </div>
  <p class="ims__label" id="imsLabel">難しい</p>
</div>
</main>

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

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

// 계산 겹: polygonRadius(theta, sides) 기하 공식으로 다각형 반지름을 구하고, 단계가 바뀌면 그 반지름 배열을 보간한다(JS)
@include stage($stage-ink);

.ims { color: $subject-cream; text-align: center; }
.ims__icon { display: block; margin: 0 auto; }
.ims__shape { fill: $color; stroke: $subject-cream; stroke-width: 1.5; stroke-linejoin: round; }
.ims__row { display: flex; gap: $sp-2; justify-content: center; margin-top: $sp-3; }
.ims__dot {
  appearance: none; width: 14px; height: 14px; border-radius: 50%;
  border: 2px solid rgba($subject-cream, .5); background: transparent; padding: 0; cursor: pointer;
  transition: background $dur-quick $ease-out, border-color $dur-quick $ease-out, transform $dur-quick $ease-pop;
}
.ims__dot:focus-visible { outline: 2px solid $subject-cream; outline-offset: 2px; }
.ims__dot[aria-checked="true"] { background: $color; border-color: $subject-cream; transform: scale(1.2); }
.ims__label { margin: $sp-2 0 0; font-weight: 700; font-size: 15px; }

@media (max-width: 340px) {
  .ims__icon { width: 52px; height: 52px; }
  .ims__label { font-size: 13px; }
}

@media (prefers-reduced-motion: reduce) {
  // 실사용 경로 적용: morphTo() 안에서 reduce 를 확인해 보간 없이 목표 모양으로 즉시 바뀐다(JS 쪽 처리)
  .ims__dot { 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);
}

.ims {
  color: #fff7e6;
  text-align: center;
}

.ims__icon {
  display: block;
  margin: 0 auto;
}

.ims__shape {
  fill: #ff9ebb;
  stroke: #fff7e6;
  stroke-width: 1.5;
  stroke-linejoin: round;
}

.ims__row {
  display: flex;
  gap: 8px;
  justify-content: center;
  margin-top: 12px;
}

.ims__dot {
  appearance: none;
  width: 14px;
  height: 14px;
  border-radius: 50%;
  border: 2px solid rgba(255, 247, 230, 0.5);
  background: transparent;
  padding: 0;
  cursor: pointer;
  transition: background 220ms ease-out, border-color 220ms ease-out, transform 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

.ims__dot:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 2px;
}

.ims__dot[aria-checked=true] {
  background: #ff9ebb;
  border-color: #fff7e6;
  transform: scale(1.2);
}

.ims__label {
  margin: 8px 0 0;
  font-weight: 700;
  font-size: 15px;
}

@media (max-width: 340px) {
  .ims__icon {
    width: 52px;
    height: 52px;
  }
  .ims__label {
    font-size: 13px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ims__dot {
    transition: none;
  }
}

(function () {
  var LEVELS = ['簡単', '普通', '難しい', 'とても難しい', '最高'];
  var SIDES = [3, 4, 5, 6, 7];
  var POINTS = 7, CX = 40, CY = 40, R = 30, MORPH_MS = 420;
  var root = document.getElementById('ims');
  var path = document.getElementById('imsPath');
  var row = document.getElementById('imsRow');
  var dots = Array.prototype.slice.call(row.querySelectorAll('.ims__dot'));
  var label = document.getElementById('imsLabel');
  var tier = 2;
  var raf = 0, t0 = 0, fromR = [], toR = [];
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  // 계산 겹: 정다각형의 변 수(sides)와 각도(theta)로 그 방향의 반지름을 구하는 기하 공식.
  // theta 가 한 변의 중심에서 멀어질수록(꼭짓점에 가까울수록) 반지름이 길어진다
  function polygonRadius(theta, sides) {
    var seg = (2 * Math.PI) / sides;
    var a = ((theta % seg) + seg) % seg - seg / 2;
    return R * Math.cos(seg / 2) / Math.cos(a);
  }
  function angleAt(i) { return (i / POINTS) * Math.PI * 2 - Math.PI / 2; }
  function radiiFor(sides) {
    var out = [];
    for (var i = 0; i < POINTS; i++) out.push(polygonRadius(angleAt(i), sides));
    return out;
  }
  function buildPath(radii) {
    var d = '';
    for (var i = 0; i < POINTS; i++) {
      var a = angleAt(i);
      var x = CX + radii[i] * Math.cos(a);
      var y = CY + radii[i] * Math.sin(a);
      d += (i === 0 ? 'M' : 'L') + x.toFixed(2) + ',' + y.toFixed(2) + ' ';
    }
    return d + 'Z';
  }
  var currentR = radiiFor(SIDES[tier]);
  function lerp(a, b, t) { return a + (b - a) * t; }

  function morphTo(sides) {
    cancelAnimationFrame(raf);
    var target = radiiFor(sides);
    if (reduce) { currentR = target; path.setAttribute('d', buildPath(currentR)); return; }
    fromR = currentR.slice(); toR = target; t0 = performance.now();
    function step(now) {
      var t = Math.min(1, (now - t0) / MORPH_MS);
      var e = 1 - Math.pow(1 - t, 3);
      currentR = fromR.map(function (r, i) { return lerp(r, toR[i], e); });
      path.setAttribute('d', buildPath(currentR));
      if (t < 1) raf = requestAnimationFrame(step);
    }
    raf = requestAnimationFrame(step);
  }
  function human() { root.classList.remove('is-demo'); clearInterval(timer); }
  function select(i) {
    tier = i;
    dots.forEach(function (d, idx) {
      d.setAttribute('aria-checked', idx === i ? 'true' : 'false');
      d.setAttribute('tabindex', idx === i ? '0' : '-1');
    });
    label.textContent = LEVELS[i];
    morphTo(SIDES[i]);
  }
  dots.forEach(function (d, i) {
    d.addEventListener('click', function () { human(); select(i); });
    d.addEventListener('keydown', function (e) {
      if (e.key === 'ArrowRight' || e.key === 'ArrowUp') { e.preventDefault(); human(); select(Math.min(LEVELS.length - 1, tier + 1)); dots[tier].focus({ preventScroll: true }); }
      else if (e.key === 'ArrowLeft' || e.key === 'ArrowDown') { e.preventDefault(); human(); select(Math.max(0, tier - 1)); dots[tier].focus({ preventScroll: true }); }
    });
  });

  var sequence = [4, 0, 3, 1, 2];
  var si = 0;
  function tick() { select(sequence[si % sequence.length]); si++; }
  var timer = reduce ? null : setInterval(tick, 900);
  path.setAttribute('d', buildPath(currentR));
}());

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

const LEVELS = ['쉬움', '보통', '어려움', '매우 어려움', '최고'];
const SIDES = [3, 4, 5, 6, 7];
const POINTS = 7, CX = 40, CY = 40, R = 30, MORPH_MS = 420;
const SEQUENCE = [4, 0, 3, 1, 2];
const TICK_MS = 900;

export default function DifficultySelectorIconMorphShape() {
  const rootRef = useRef<HTMLDivElement>(null);
  const pathRef = useRef<SVGPathElement>(null);
  const rowRef = useRef<HTMLDivElement>(null);
  const dotRefs = useRef<HTMLButtonElement[]>([]);
  const labelRef = useRef<HTMLParagraphElement>(null);

  useEffect(() => {
    const root = rootRef.current;
    const path = pathRef.current;
    const label = labelRef.current;
    if (!root || !path || !label || !dotRefs.current) return undefined;
    const dots = dotRefs.current;
    if (dots.length !== LEVELS.length) return undefined;

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

    // 계산 겹: 정다각형의 변 수(sides)와 각도(theta)로 그 방향의 반지름을 구하는 기하 공식.
    // theta 가 한 변의 중심에서 멀어질수록(꼭짓점에 가까울수록) 반지름이 길어진다
    function polygonRadius(theta: number, sides: number) {
      const seg = (2 * Math.PI) / sides;
      const a = ((theta % seg) + seg) % seg - seg / 2;
      return R * Math.cos(seg / 2) / Math.cos(a);
    }
    function angleAt(i: number) { return (i / POINTS) * Math.PI * 2 - Math.PI / 2; }
    function radiiFor(sides: number) {
      const out: number[] = [];
      for (let i = 0; i < POINTS; i++) out.push(polygonRadius(angleAt(i), sides));
      return out;
    }
    function buildPath(radii: number[]) {
      let d = '';
      for (let i = 0; i < POINTS; i++) {
        const a = angleAt(i);
        const x = CX + radii[i] * Math.cos(a);
        const y = CY + radii[i] * Math.sin(a);
        d += (i === 0 ? 'M' : 'L') + x.toFixed(2) + ',' + y.toFixed(2) + ' ';
      }
      return d + 'Z';
    }
    let currentR = radiiFor(SIDES[tier]);
    function lerp(a: number, b: number, t: number) { return a + (b - a) * t; }

    function morphTo(sides: number) {
      cancelAnimationFrame(raf);
      const target = radiiFor(sides);
      if (reduce) { currentR = target; path!.setAttribute('d', buildPath(currentR)); return; }
      const fromR = currentR.slice();
      t0 = performance.now();
      function step(now: number) {
        const t = Math.min(1, (now - t0) / MORPH_MS);
        const e = 1 - Math.pow(1 - t, 3);
        currentR = fromR.map((r, i) => lerp(r, target[i], e));
        path!.setAttribute('d', buildPath(currentR));
        if (t < 1) raf = requestAnimationFrame(step);
      }
      raf = requestAnimationFrame(step);
    }
    let timer = 0;
    function human() { root!.classList.remove(styles['is-demo']); window.clearInterval(timer); }
    function select(i: number) {
      tier = i;
      dots.forEach((d, idx) => {
        d.setAttribute('aria-checked', idx === i ? 'true' : 'false');
        d.setAttribute('tabindex', idx === i ? '0' : '-1');
      });
      label!.textContent = LEVELS[i];
      morphTo(SIDES[i]);
    }

    const offs = dots.map((d, i) => {
      function onClick() { human(); select(i); }
      function onKey(e: KeyboardEvent) {
        if (e.key === 'ArrowRight' || e.key === 'ArrowUp') { e.preventDefault(); human(); select(Math.min(LEVELS.length - 1, tier + 1)); dots[tier].focus({ preventScroll: true }); }
        else if (e.key === 'ArrowLeft' || e.key === 'ArrowDown') { e.preventDefault(); human(); select(Math.max(0, tier - 1)); dots[tier].focus({ preventScroll: true }); }
      }
      d.addEventListener('click', onClick);
      d.addEventListener('keydown', onKey);
      return () => { d.removeEventListener('click', onClick); d.removeEventListener('keydown', onKey); };
    });

    let si = 0;
    function tick() { select(SEQUENCE[si % SEQUENCE.length]); si++; }
    if (!reduce) timer = window.setInterval(tick, TICK_MS);
    path.setAttribute('d', buildPath(currentR));

    return () => { offs.forEach((off) => off()); cancelAnimationFrame(raf); window.clearInterval(timer); };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.ims + ' ' + styles['is-demo']} ref={rootRef}>
        <svg className={styles.imsIcon} viewBox="0 0 80 80" width={64} height={64} aria-hidden="true">
          <path ref={pathRef} className={styles.imsShape} />
        </svg>
        <div className={styles.imsRow} ref={rowRef} role="radiogroup" aria-label="난이도">
          {LEVELS.map((label, i) => (
            <button
              key={label}
              type="button"
              className={styles.imsDot}
              ref={(el: HTMLButtonElement | null) => { if (el && dotRefs.current) dotRefs.current[i] = el; }}
              role="radio"
              aria-checked={i === 2 ? 'true' : 'false'}
              aria-label={label}
              data-i={i}
              tabIndex={i === 0 ? 0 : -1}
            />
          ))}
        </div>
        <p className={styles.imsLabel} ref={labelRef}>어려움</p>
      </div>
    </main>
  );
}