02Genre wheel — spinning a disc of categories to pick one

<main class="stage">
<div class="gw is-demo" id="gw">
  <div class="gw__wheel" id="gwWheel" tabindex="0" role="listbox" aria-label="Genre picker wheel">
    <ul class="gw__ring" id="gwRing"></ul>
  </div>
  <div class="gw__pointer" aria-hidden="true"></div>
  <p class="gw__picked" id="gwPicked">Selected: Pop</p>
</div>
</main>

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

// 장르 선택 휠 — 계산 겹은 index.html 의 두 곳: ① 회전각을 STEP_DEG(360/7)로 나눈 나머지로
// "지금 중앙을 지나는 인덱스"를 구하는 나머지 연산 ② 인덱스를 색상환 각도로 그대로 쓰는 색상 각도 매핑(--hue).
// 슬롯 하나의 배치 각도(51.4286deg = 360/7)는 항목 수가 고정이라 SCSS 에 그대로 적는다.

$duration: $dur-quick;
$easing: $ease-spring;
$color: $subject-ink;

@include stage($stage-yellow);

.gw { position: relative; display: flex; flex-direction: column; align-items: center; gap: $sp-3; }

.gw__wheel {
  position: relative;
  width: 220px;
  height: 220px;
  border-radius: 50%;
  background: rgba($subject-ink, .06);
  touch-action: none;
  cursor: grab;
}
.gw__wheel:active { cursor: grabbing; }
.gw__wheel:focus-visible { outline: 2px solid $subject-ink; outline-offset: 3px; }

.gw__ring {
  position: absolute;
  inset: 0;
  margin: 0;
  padding: 0;
  list-style: none;
  transform: rotate(calc(var(--rotation, 0) * 1deg));
}

.gw__slot {
  position: absolute;
  left: 50%;
  top: 50%;
  width: 60px;
  height: 26px;
  margin-left: -30px;
  margin-top: -13px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: $r-pill;
  font-weight: 700;
  font-size: 10.5px;
  color: $subject-ink;
  background: hsl(calc(var(--hue, 0) * 1deg) 46% 80%);
  transform: rotate(calc(var(--i, 0) * 51.4286deg)) translateY(-86px) rotate(calc(var(--i, 0) * -51.4286deg));
  transition: transform $duration $easing, background-color $duration $easing, box-shadow $duration $easing;
}

.gw__slot--active {
  background: hsl(calc(var(--hue, 0) * 1deg) 46% 64%);
  box-shadow: $shadow-press;
  transform: rotate(calc(var(--i, 0) * 51.4286deg)) translateY(-86px) rotate(calc(var(--i, 0) * -51.4286deg)) scale(1.2);
}

.gw__pointer {
  position: absolute;
  top: -2px;
  left: 50%;
  width: 0;
  height: 0;
  transform: translateX(-50%);
  border-left: 7px solid transparent;
  border-right: 7px solid transparent;
  border-top: 10px solid $subject-ink;
}

.gw__picked {
  margin: 0;
  color: $subject-ink;
  font-weight: 800;
  font-size: 12px;
}

@media (max-width: 340px) {
  .gw { gap: $sp-1; }
  .gw__wheel { width: 148px; height: 148px; }
  .gw__slot { width: 44px; height: 20px; margin-left: -22px; margin-top: -10px; font-size: 8.5px;
              transform: rotate(calc(var(--i, 0) * 51.4286deg)) translateY(-58px) rotate(calc(var(--i, 0) * -51.4286deg)); }
  .gw__slot--active { transform: rotate(calc(var(--i, 0) * 51.4286deg)) translateY(-58px) rotate(calc(var(--i, 0) * -51.4286deg)) scale(1.2); }
}

@media (prefers-reduced-motion: reduce) {
  .gw__ring, .gw__slot { transition: none; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.gw {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
}

.gw__wheel {
  position: relative;
  width: 220px;
  height: 220px;
  border-radius: 50%;
  background: rgba(23, 20, 26, 0.06);
  touch-action: none;
  cursor: grab;
}

.gw__wheel:active {
  cursor: grabbing;
}

.gw__wheel:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 3px;
}

.gw__ring {
  position: absolute;
  inset: 0;
  margin: 0;
  padding: 0;
  list-style: none;
  transform: rotate(calc(var(--rotation, 0) * 1deg));
}

.gw__slot {
  position: absolute;
  left: 50%;
  top: 50%;
  width: 60px;
  height: 26px;
  margin-left: -30px;
  margin-top: -13px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 999px;
  font-weight: 700;
  font-size: 10.5px;
  color: #17141a;
  background: hsl(calc(var(--hue, 0) * 1deg), 46%, 80%);
  transform: rotate(calc(var(--i, 0) * 51.4286deg)) translateY(-86px) rotate(calc(var(--i, 0) * -51.4286deg));
  transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1), background-color 220ms cubic-bezier(0.2, 0.8, 0.2, 1), box-shadow 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.gw__slot--active {
  background: hsl(calc(var(--hue, 0) * 1deg), 46%, 64%);
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  transform: rotate(calc(var(--i, 0) * 51.4286deg)) translateY(-86px) rotate(calc(var(--i, 0) * -51.4286deg)) scale(1.2);
}

.gw__pointer {
  position: absolute;
  top: -2px;
  left: 50%;
  width: 0;
  height: 0;
  transform: translateX(-50%);
  border-left: 7px solid transparent;
  border-right: 7px solid transparent;
  border-top: 10px solid #17141a;
}

.gw__picked {
  margin: 0;
  color: #17141a;
  font-weight: 800;
  font-size: 12px;
}

@media (max-width: 340px) {
  .gw {
    gap: 4px;
  }
  .gw__wheel {
    width: 148px;
    height: 148px;
  }
  .gw__slot {
    width: 44px;
    height: 20px;
    margin-left: -22px;
    margin-top: -10px;
    font-size: 8.5px;
    transform: rotate(calc(var(--i, 0) * 51.4286deg)) translateY(-58px) rotate(calc(var(--i, 0) * -51.4286deg));
  }
  .gw__slot--active {
    transform: rotate(calc(var(--i, 0) * 51.4286deg)) translateY(-58px) rotate(calc(var(--i, 0) * -51.4286deg)) scale(1.2);
  }
}
@media (prefers-reduced-motion: reduce) {
  .gw__ring, .gw__slot {
    transition: none;
  }
}

(function () {
  var GENRES = ['Pop', 'Jazz', 'Lo-fi', 'Rock', 'Classical', 'Hip-hop', 'Electronic'];
  var N = GENRES.length;
  var STEP_DEG = 360 / N;          // 장르 하나가 차지하는 각도
  var HUE_STEP_DEG = 360 / N;      // 색상 각도 매핑 — 장르 인덱스를 색상환 각도로 그대로 쓴다
  var LOOP_MS = 2000;

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var root = document.getElementById('gw');
  var wheel = document.getElementById('gwWheel');
  var ring = document.getElementById('gwRing');
  var picked = document.getElementById('gwPicked');
  var isDemo = true;
  var rotation = 0;      // 원판이 돌아간 각도
  var dragging = false;
  var startX = 0, startRotation = 0;

  var lis = GENRES.map(function (g, i) {
    var li = document.createElement('li');
    li.className = 'gw__slot';
    li.textContent = g;
    li.style.setProperty('--i', i);
    // 계산 겹: 색상 각도 매핑. 채도·명도는 토큰 범위 안에서 고정하고 색상각만 인덱스로 돈다.
    li.style.setProperty('--hue', i * HUE_STEP_DEG);
    ring.appendChild(li);
    return li;
  });

  function human() { if (isDemo) { root.classList.remove('is-demo'); isDemo = false; } }

  // 계산 겹: 회전각을 STEP_DEG 로 나눈 나머지로 "지금 중앙을 지나는 인덱스"를 구한다.
  function activeIndex() {
    var norm = ((-rotation % 360) + 360) % 360;
    return Math.round(norm / STEP_DEG) % N;
  }

  function apply() {
    ring.style.setProperty('--rotation', rotation);
    var idx = activeIndex();
    lis.forEach(function (li, i) { li.classList.toggle('gw__slot--active', i === idx); });
    picked.textContent = 'Selected: ' + GENRES[idx];
  }

  wheel.addEventListener('pointerdown', function (e) {
    human();
    dragging = true;
    startX = e.clientX;
    startRotation = rotation;
    wheel.setPointerCapture(e.pointerId);
  });
  wheel.addEventListener('pointermove', function (e) {
    if (!dragging) return;
    rotation = startRotation + (e.clientX - startX) * 0.6;
    apply();
  });
  wheel.addEventListener('pointerup', function () {
    dragging = false;
    // 계산 겹: 놓은 각도를 가장 가까운 STEP_DEG 배수로 붙여 항상 한 장르가 정중앙에 오게 한다.
    rotation = Math.round(rotation / STEP_DEG) * STEP_DEG;
    apply();
  });
  wheel.addEventListener('keydown', function (e) {
    if (e.key === 'ArrowRight' || e.key === 'ArrowDown') { human(); rotation -= STEP_DEG; apply(); e.preventDefault(); }
    else if (e.key === 'ArrowLeft' || e.key === 'ArrowUp') { human(); rotation += STEP_DEG; apply(); e.preventDefault(); }
  });

  function loop(ts) {
    if (isDemo) {
      if (!reduce) {
        var phase = (ts % LOOP_MS) / LOOP_MS;
        rotation = -phase * 360 * 2;   // 두 바퀴를 도는 연속 회전
      } else {
        rotation = 0;
      }
      apply();
    }
    requestAnimationFrame(loop);
  }
  apply();
  requestAnimationFrame(loop);
})();

// GenreWheel — vanilla 판(run/374/demo/02-arc-genre-wheel/index.html) 의 React 포트.
// 계산 겹 ① 회전각을 STEP_DEG(360/7) 로 나눈 나머지로 "지금 중앙을 지나는 인덱스"를 구한다
// ② 인덱스를 색상환 각도로 그대로 쓰는 색상 각도 매핑(hsl, hex 리터럴 없음).
import { useEffect, useRef, useState } from "react";
import styles from "./GenreWheel.module.scss";

type Box<T> = { current: T };

const GENRES = ["팝", "재즈", "로파이", "록", "클래식", "힙합", "전자"];
const N = GENRES.length;
const STEP_DEG = 360 / N;
const HUE_STEP_DEG = 360 / N;
const LOOP_MS = 2000;

export default function GenreWheel() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const wheelRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const ringRef = useRef(null) as unknown as Box<HTMLUListElement>;
  const rafRef = useRef(0) as unknown as Box<number>;
  const [picked, setPicked] = useState(GENRES[0]);

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const root = rootRef.current;
    const wheel = wheelRef.current;
    const ring = ringRef.current;
    if (!root || !wheel || !ring) return;

    const lis: HTMLLIElement[] = Array.prototype.slice.call(ring.querySelectorAll("li"));
    lis.forEach(function (li, i) { li.style.setProperty("--hue", String(i * HUE_STEP_DEG)); });

    let isDemo = true;
    let rotation = 0;
    let dragging = false;
    let startX = 0;
    let startRotation = 0;

    function human() { if (isDemo) { root!.classList.remove(styles.isDemo); isDemo = false; } }

    function activeIndex() {
      const norm = (((-rotation) % 360) + 360) % 360;
      return Math.round(norm / STEP_DEG) % N;
    }

    function apply() {
      ring!.style.setProperty("--rotation", String(rotation));
      const idx = activeIndex();
      lis.forEach(function (li, i) { li.classList.toggle(styles.slotActive, i === idx); });
      setPicked(GENRES[idx]);
    }

    function onPointerDown(e: PointerEvent) {
      human();
      dragging = true;
      startX = e.clientX;
      startRotation = rotation;
      wheel!.setPointerCapture(e.pointerId);
    }
    function onPointerMove(e: PointerEvent) {
      if (!dragging) return;
      rotation = startRotation + (e.clientX - startX) * 0.6;
      apply();
    }
    function onPointerUp() {
      dragging = false;
      rotation = Math.round(rotation / STEP_DEG) * STEP_DEG;
      apply();
    }
    function onKeydown(e: KeyboardEvent) {
      if (e.key === "ArrowRight" || e.key === "ArrowDown") { human(); rotation -= STEP_DEG; apply(); e.preventDefault(); }
      else if (e.key === "ArrowLeft" || e.key === "ArrowUp") { human(); rotation += STEP_DEG; apply(); e.preventDefault(); }
    }
    wheel.addEventListener("pointerdown", onPointerDown);
    wheel.addEventListener("pointermove", onPointerMove);
    wheel.addEventListener("pointerup", onPointerUp);
    wheel.addEventListener("keydown", onKeydown);

    function loop(ts: number) {
      if (isDemo) {
        if (!reduce) {
          const phase = (ts % LOOP_MS) / LOOP_MS;
          rotation = -phase * 360 * 2;
        } else {
          rotation = 0;
        }
        apply();
      }
      rafRef.current = requestAnimationFrame(loop);
    }
    apply();
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      wheel.removeEventListener("pointerdown", onPointerDown);
      wheel.removeEventListener("pointermove", onPointerMove);
      wheel.removeEventListener("pointerup", onPointerUp);
      wheel.removeEventListener("keydown", onKeydown);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.gw + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.wheel} ref={wheelRef} tabIndex={0} role="listbox" aria-label="장르 선택 휠">
          <ul className={styles.ring} ref={ringRef}>
            {GENRES.map(function (g, i) {
              return <li key={g} className={styles.slot} style={{ ["--i" as string]: i }}>{g}</li>;
            })}
          </ul>
        </div>
        <div className={styles.pointer} aria-hidden="true" />
        <p className={styles.picked}>선택: {picked}</p>
      </div>
    </main>
  );
}