08Arc mood slider — a handle traveling a half-circle to set intensity

<main class="stage">
<div class="ms is-demo" id="ms">
  <div class="ms__arc" id="msArc">
    <button class="ms__handle" id="msHandle" type="button" aria-label="Drag along the arc to pick a mood"></button>
  </div>
  <p class="ms__label" id="msLabel">Okay</p>
</div>
</main>

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

// 반원 무드 슬라이더 — 계산 겹은 index.html 의 atan2 각도→진행률(angleToT) 과 진행률→색상(hue) 매핑에 있다.
// 여기는 반원 트랙과 손잡이만 그리고 --x/--y/--hue 세 변수로 위치·색을 구동한다.

$duration: $dur-quick;
$easing: $ease-out;
$color: $subject-pink;

@include stage($stage-orange);

.ms { display: flex; flex-direction: column; align-items: center; gap: $sp-6; }

.ms__arc {
  position: relative;
  width: 220px;
  height: 120px;
  overflow: hidden;
  touch-action: none;
}
.ms__arc::before {
  content: "";
  position: absolute;
  inset: 0 0 auto 0;
  height: 220px;
  border-radius: 50%;
  border: 10px solid rgba($subject-ink, .12);
  clip-path: inset(0 0 50% 0);
}

.ms__handle {
  position: absolute;
  left: calc(50% + var(--x, 0) * 100px - 15px);
  bottom: calc(var(--y, -1) * -100px - 15px);
  width: 30px;
  height: 30px;
  border-radius: 50%;
  border: none;
  cursor: grab;
  background: hsl(calc(var(--hue, 60) * 1deg) 62% 68%);
  box-shadow: $shadow-raised;
  transition: background $duration $easing;
}
.ms__handle:active { cursor: grabbing; }
.ms__handle:focus-visible { outline: 2px solid $subject-ink; outline-offset: 3px; }

.ms__label {
  margin: 0;
  color: $subject-ink;
  font-weight: 800;
  font-size: 16px;
}

@media (max-width: 340px) {
  .ms__arc { width: 168px; height: 92px; overflow: hidden; }
  .ms__arc::before { height: 168px; }
  .ms__handle {
    left: calc(50% + var(--x, 0) * 76px - 12px);
    bottom: calc(var(--y, -1) * -76px - 12px);
    width: 24px;
    height: 24px;
  }
}

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

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ms {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 24px;
}

.ms__arc {
  position: relative;
  width: 220px;
  height: 120px;
  overflow: hidden;
  touch-action: none;
}

.ms__arc::before {
  content: "";
  position: absolute;
  inset: 0 0 auto 0;
  height: 220px;
  border-radius: 50%;
  border: 10px solid rgba(23, 20, 26, 0.12);
  clip-path: inset(0 0 50% 0);
}

.ms__handle {
  position: absolute;
  left: calc(50% + var(--x, 0) * 100px - 15px);
  bottom: calc(var(--y, -1) * -100px - 15px);
  width: 30px;
  height: 30px;
  border-radius: 50%;
  border: none;
  cursor: grab;
  background: hsl(calc(var(--hue, 60) * 1deg), 62%, 68%);
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transition: background 220ms ease-out;
}

.ms__handle:active {
  cursor: grabbing;
}

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

.ms__label {
  margin: 0;
  color: #17141a;
  font-weight: 800;
  font-size: 16px;
}

@media (max-width: 340px) {
  .ms__arc {
    width: 168px;
    height: 92px;
    overflow: hidden;
  }
  .ms__arc::before {
    height: 168px;
  }
  .ms__handle {
    left: calc(50% + var(--x, 0) * 76px - 12px);
    bottom: calc(var(--y, -1) * -76px - 12px);
    width: 24px;
    height: 24px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ms__handle {
    transition: none;
  }
}

(function () {
  var MOODS = ['Down', 'Tired', 'Okay', 'Good', 'Great'];
  var N = MOODS.length;
  var LOOP_MS = 2000;

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var root = document.getElementById('ms');
  var arc = document.getElementById('msArc');
  var handle = document.getElementById('msHandle');
  var labelEl = document.getElementById('msLabel');
  var isDemo = true;
  var dragging = false;
  var t = 0.5;   // 0~1, 반원을 따라 진행한 위치

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

  // 계산 겹: 포인터 좌표를 atan2 로 반원(180~360deg, 왼쪽 끝~오른쪽 끝) 각도로 바꾸고 0~1 로 정규화한다.
  function angleToT(clientX, clientY) {
    var r = arc.getBoundingClientRect();
    var cx = r.left + r.width / 2, cy = r.bottom;
    var deg = Math.atan2(clientY - cy, clientX - cx) * 180 / Math.PI; // -180 ~ 0 (위쪽 반원)
    var clamped = Math.min(0, Math.max(-180, deg));
    return 1 - (clamped + 180) / 180;
  }

  function apply() {
    var deg = -180 + t * 180;
    var x = Math.cos(deg * Math.PI / 180);
    var y = Math.sin(deg * Math.PI / 180);
    handle.style.setProperty('--x', x.toFixed(4));
    handle.style.setProperty('--y', y.toFixed(4));
    handle.style.setProperty('--hue', Math.round(t * 130));
    var idx = Math.min(N - 1, Math.floor(t * N));
    labelEl.textContent = MOODS[idx];
  }

  handle.addEventListener('pointerdown', function (e) {
    human();
    dragging = true;
    handle.setPointerCapture(e.pointerId);
    t = angleToT(e.clientX, e.clientY);
    apply();
  });
  handle.addEventListener('pointermove', function (e) {
    if (!dragging) return;
    t = angleToT(e.clientX, e.clientY);
    apply();
  });
  handle.addEventListener('pointerup', function () { dragging = false; });
  handle.addEventListener('keydown', function (e) {
    if (e.key === 'ArrowRight' || e.key === 'ArrowUp') { human(); t = Math.min(1, t + 1 / (N - 1)); apply(); }
    if (e.key === 'ArrowLeft' || e.key === 'ArrowDown') { human(); t = Math.max(0, t - 1 / (N - 1)); apply(); }
  });

  // 자동 루프: 반원 끝에서 끝까지 왕복하며 같은 angleToT 대응 함수(t) 로 apply() 를 구동한다.
  function loop(ts) {
    if (isDemo) {
      if (!reduce) {
        var phase = (ts % LOOP_MS) / LOOP_MS;
        t = phase < 0.5 ? phase * 2 : 2 - phase * 2;
      } else {
        t = 0.5;
      }
      apply();
    }
    requestAnimationFrame(loop);
  }
  apply();
  requestAnimationFrame(loop);
})();

// MoodArcSlider — vanilla 판(run/374/demo/08-arc-mood-slider/index.html) 의 React 포트.
// 계산 겹: 포인터 좌표를 atan2 로 반원 각도로 바꾼 뒤(angleToT) 0~1 진행률로 정규화하고,
// 그 진행률을 hue 로 그대로 매핑해 색이 기분과 함께 바뀐다.
import { useEffect, useRef, useState } from "react";
import styles from "./MoodArcSlider.module.scss";

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

const MOODS = ["우울", "지침", "보통", "좋음", "최고"];
const N = MOODS.length;
const LOOP_MS = 2000;

export default function MoodArcSlider() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const arcRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const handleRef = useRef(null) as unknown as Box<HTMLButtonElement>;
  const rafRef = useRef(0) as unknown as Box<number>;
  const [label, setLabel] = useState(MOODS[2]);

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const root = rootRef.current;
    const arc = arcRef.current;
    const handle = handleRef.current;
    if (!root || !arc || !handle) return;

    let isDemo = true;
    let dragging = false;
    let t = 0.5;

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

    function angleToT(clientX: number, clientY: number) {
      const r = arc!.getBoundingClientRect();
      const cx = r.left + r.width / 2;
      const cy = r.bottom;
      const deg = (Math.atan2(clientY - cy, clientX - cx) * 180) / Math.PI;
      const clamped = Math.min(0, Math.max(-180, deg));
      return 1 - (clamped + 180) / 180;
    }

    function apply() {
      const deg = -180 + t * 180;
      const x = Math.cos((deg * Math.PI) / 180);
      const y = Math.sin((deg * Math.PI) / 180);
      handle!.style.setProperty("--x", x.toFixed(4));
      handle!.style.setProperty("--y", y.toFixed(4));
      handle!.style.setProperty("--hue", String(Math.round(t * 130)));
      const idx = Math.min(N - 1, Math.floor(t * N));
      setLabel(MOODS[idx]);
    }

    function onDown(e: PointerEvent) {
      human();
      dragging = true;
      handle!.setPointerCapture(e.pointerId);
      t = angleToT(e.clientX, e.clientY);
      apply();
    }
    function onMove(e: PointerEvent) { if (!dragging) return; t = angleToT(e.clientX, e.clientY); apply(); }
    function onUp() { dragging = false; }
    function onKeydown(e: KeyboardEvent) {
      if (e.key === "ArrowRight" || e.key === "ArrowUp") { human(); t = Math.min(1, t + 1 / (N - 1)); apply(); }
      if (e.key === "ArrowLeft" || e.key === "ArrowDown") { human(); t = Math.max(0, t - 1 / (N - 1)); apply(); }
    }
    handle.addEventListener("pointerdown", onDown);
    handle.addEventListener("pointermove", onMove);
    handle.addEventListener("pointerup", onUp);
    handle.addEventListener("keydown", onKeydown);

    function loop(ts: number) {
      if (isDemo) {
        if (!reduce) {
          const phase = (ts % LOOP_MS) / LOOP_MS;
          t = phase < 0.5 ? phase * 2 : 2 - phase * 2;
        } else {
          t = 0.5;
        }
        apply();
      }
      rafRef.current = requestAnimationFrame(loop);
    }
    apply();
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      handle.removeEventListener("pointerdown", onDown);
      handle.removeEventListener("pointermove", onMove);
      handle.removeEventListener("pointerup", onUp);
      handle.removeEventListener("keydown", onKeydown);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.ms + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.arc} ref={arcRef}>
          <button className={styles.handle} ref={handleRef} type="button" aria-label="반원을 따라 드래그해서 기분 고르기" />
        </div>
        <p className={styles.label}>{label}</p>
      </div>
    </main>
  );
}