01残りの割合で色が移り、最後の区間で脈打つ減っていくリング

<main class="stage">
  <div class="cd is-demo" id="cd" data-demo="1">
    <div class="cd__view cd__view--ring">
      <div class="cd__halo" data-r="halo"></div>
      <svg class="cd__svg" viewBox="0 0 120 120" role="img" aria-label="減っていくリングのタイマー">
        <circle class="cd__track" cx="60" cy="60" r="48"/>
        <circle class="cd__arc" data-r="arc" cx="60" cy="60" r="48" transform="rotate(-90 60 60)"/>
      </svg>
      <p class="cd__read cd__read--center" role="timer"><b data-r="num">1.5</b><span>秒</span></p>
    </div>
    <div class="cd__bar">
      <button class="cd__btn" type="button" data-r="toggle">一時停止</button>
      <button class="cd__btn" type="button" data-r="reset">リセット</button>
    </div>
    <p class="cd__sr" aria-live="polite" data-r="status"></p>
  </div>
</main>

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

// 핵심: 남은 시간 하나(경과는 rAF 타임스탬프 누적)에서 모양을 계산해 그린다. CSS 는 모양과 색만 맡는다.

$bg: $stage-ink;
$fg: $subject-cream;
$btn: rgba($subject-cream, .14);
@include stage($bg);
.cd {
  --view-h: min(calc(100vh - 2 * clamp(8px, 4vw, 24px) - 48px), 196px);
  position: relative;
  box-sizing: border-box;
  width: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-2;
  color: $fg;
  font-size: 14px;
  line-height: 20px;
  font-weight: 600;
}
.cd__view { position: relative; }
.cd__view--scene { width: 100%; height: var(--view-h); overflow: hidden; border-radius: $r-card; background: mix($stage-ink, $subject-lilac, 88%); }
.cd__cv { display: block; width: 100%; height: 100%; }
.cd__read { margin: 0; display: flex; align-items: baseline; gap: $sp-1; font-variant-numeric: tabular-nums; }
.cd__read b { font-size: 28px; line-height: 32px; font-weight: 800; }
.cd__read--center { position: absolute; left: 50%; top: 50%; transform: translate(-50%, -50%); }
.cd__read--corner { position: absolute; left: $sp-2; top: $sp-2; }
.cd__bar { display: flex; gap: $sp-2; }
.cd__btn {
  box-sizing: border-box;
  height: 36px;
  padding: 0 $sp-4;
  border: 0;
  border-radius: $r-control;
  background: $btn;
  color: $fg;
  font-size: 14px;
  line-height: 20px;
  font-weight: 700;
  cursor: pointer;
}
.cd__btn:focus-visible { outline: 2px solid $subject-lilac; outline-offset: 2px; }
.cd__sr { position: absolute; width: 1px; height: 1px; margin: 0; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
@media (prefers-reduced-motion: reduce) {
  .cd__strip { filter: none !important; }
  .cd__leaf { display: none !important; }
}
.cd {
  --c0: #{$subject-mint};
  --c1: #{mix($stage-yellow, $subject-cream, 60%)};
  --c2: #{$subject-pink};
}
.cd__view--ring { width: 100%; height: var(--view-h); display: grid; place-items: center; }
.cd__halo { position: absolute; inset: 0; }
.cd__svg { position: relative; display: block; width: var(--view-h); height: var(--view-h); }
.cd__track { fill: none; stroke: rgba($subject-cream, .14); stroke-width: 9; }
.cd__arc { fill: none; stroke-linecap: round; stroke-width: 9; }

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);
}

.cd {
  --view-h: min(calc(100vh - 2 * clamp(8px, 4vw, 24px) - 48px), 196px);
  position: relative;
  box-sizing: border-box;
  width: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  color: #fff7e6;
  font-size: 14px;
  line-height: 20px;
  font-weight: 600;
}

.cd__view {
  position: relative;
}

.cd__view--scene {
  width: 100%;
  height: var(--view-h);
  overflow: hidden;
  border-radius: 16px;
  background: rgb(16.6431372549%, 14.431372549%, 20.9725490196%);
}

.cd__cv {
  display: block;
  width: 100%;
  height: 100%;
}

.cd__read {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: 4px;
  font-variant-numeric: tabular-nums;
}

.cd__read b {
  font-size: 28px;
  line-height: 32px;
  font-weight: 800;
}

.cd__read--center {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}

.cd__read--corner {
  position: absolute;
  left: 8px;
  top: 8px;
}

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

.cd__btn {
  box-sizing: border-box;
  height: 36px;
  padding: 0 16px;
  border: 0;
  border-radius: 12px;
  background: rgba(255, 247, 230, 0.14);
  color: #fff7e6;
  font-size: 14px;
  line-height: 20px;
  font-weight: 700;
  cursor: pointer;
}

.cd__btn:focus-visible {
  outline: 2px solid #b9a0ff;
  outline-offset: 2px;
}

.cd__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

@media (prefers-reduced-motion: reduce) {
  .cd__strip {
    filter: none !important;
  }
  .cd__leaf {
    display: none !important;
  }
}
.cd {
  --c0: #4cd4a6;
  --c1: rgb(100%, 88.1568627451%, 50.9019607843%);
  --c2: #ff9ebb;
}

.cd__view--ring {
  width: 100%;
  height: var(--view-h);
  display: grid;
  place-items: center;
}

.cd__halo {
  position: absolute;
  inset: 0;
}

.cd__svg {
  position: relative;
  display: block;
  width: var(--view-h);
  height: var(--view-h);
}

.cd__track {
  fill: none;
  stroke: rgba(255, 247, 230, 0.14);
  stroke-width: 9;
}

.cd__arc {
  fill: none;
  stroke-linecap: round;
  stroke-width: 9;
}

(function () {
    const root = document.getElementById("cd");
    if (!root) return;
    function cx(s) {
        return s;
    }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let running = demo;
    let elapsed = 0;
    let lastTs = -1;
    let lastDraw = -1e9;
    let raf = 0;
    const hooks = { stop: () => { } };
    const offs = [];
    const TOTAL_MS = 1500;
    const HOLD_MS = 300;
    const RING_R = 48;
    const PULSE_AT = 0.4;
    const PULSE_MS = 300;
    const HUE_STOPS = ["--c0", "--c1", "--c2"];
    let totalMs = TOTAL_MS;
    function q(sel) {
        return root.querySelector(sel);
    }
    function on(el, type, fn) {
        el.addEventListener(type, fn);
        offs.push(() => el.removeEventListener(type, fn));
    }
    function clamp(v, lo, hi) {
        return Math.max(lo, Math.min(hi, v));
    }
    // 지수 접근: 프레임률이 달라도 같은 속도가 되도록 dt 를 60fps 프레임 수로 환산해 쓴다
    function approach(x, target, per, dt) {
        return x + (target - x) * (1 - Math.pow(1 - per, dt * 60));
    }
    const toggle = q('[data-r="toggle"]');
    const resetBtn = q('[data-r="reset"]');
    const status = q('[data-r="status"]');
    // 남은 시간. 경과는 rAF 타임스탬프 차이를 누적한 값이라 시계를 따로 읽지 않는다
    function remainMs() {
        return clamp(totalMs - elapsed, 0, totalMs);
    }
    function syncButtons() {
        toggle.textContent = running ? "一時停止" : "開始";
        toggle.setAttribute("aria-pressed", running ? "true" : "false");
    }
    // 스크린리더 안내는 멈출 때와 끝날 때만 갱신한다. 시연 루프 중에는 읽지 않는다
    function say(msg) {
        if (!demo)
            status.textContent = msg;
    }
    function stopDemo() {
        if (!demo)
            return;
        demo = false;
        root.classList.remove("is-demo");
        root.removeAttribute("data-demo");
        hooks.stop();
    }
    function restart() {
        elapsed = 0;
        resetState();
    }
    function update(dt) {
        tick(dt);
        draw();
    }
    function frame(ts) {
        raf = requestAnimationFrame(frame);
        const raw = lastTs < 0 ? 0 : ts - lastTs;
        lastTs = ts;
        if (running) {
            elapsed += raw;
            if (demo) {
                const cycle = totalMs + HOLD_MS;
                if (elapsed >= cycle) {
                    elapsed %= cycle;
                    resetState();
                }
            }
            else if (elapsed >= totalMs) {
                elapsed = totalMs;
                running = false;
                say("時間になりました");
                syncButtons();
            }
        }
        if (reduce && ts - lastDraw < 250)
            return;
        lastDraw = ts;
        update(Math.min(raw, 50) / 1000);
    }
    on(toggle, "click", () => {
        stopDemo();
        if (!running && elapsed >= totalMs)
            restart();
        running = !running;
        say(running ? "" : "一時停止しました");
        syncButtons();
        update(0);
    });
    on(resetBtn, "click", () => {
        stopDemo();
        running = false;
        restart();
        say("");
        syncButtons();
        update(0);
    });
    const arc = q('[data-r="arc"]');
    const num = q('[data-r="num"]');
    const halo = q('[data-r="halo"]');
    const CIRC = 2 * Math.PI * RING_R;
    const BASE_W = 9;
    const PULSE_W = 6;
    let stops = [[127, 220, 180], [255, 233, 159], [255, 158, 187]];
    function parseColor(h) {
        // CSS 변수 값은 #rrggbb 로도, rgb(r, g, b) 로도, rgb(100%, 50%, 0%) 로도 나올 수 있다
        const m6 = /^#([0-9a-f]{6})$/i.exec(h);
        if (m6) {
            const n = parseInt(m6[1], 16);
            return [(n >> 16) & 255, (n >> 8) & 255, n & 255];
        }
        const m = /([0-9.]+)(%?)[ ,]+([0-9.]+)(%?)[ ,]+([0-9.]+)(%?)/.exec(h);
        if (!m)
            return [255, 255, 255];
        const ch = (v, pct) => Math.round(pct ? (Number(v) * 255) / 100 : Number(v));
        return [ch(m[1], m[2]), ch(m[3], m[4]), ch(m[5], m[6])];
    }
    // 색 토큰은 CSS 변수가 갖고, 여기서는 변수 이름만 들고 있다가 읽는다
    function readStops() {
        const cs = getComputedStyle(root);
        stops = HUE_STOPS.map((n) => parseColor(cs.getPropertyValue(n).trim()));
    }
    // 남은 비율 f 를 세 색 사이 보간으로 바꾼다. u = 1 - f 가 0 이면 첫 색, 1 이면 마지막 색
    function blend(u) {
        const s = clamp(u, 0, 1) * (stops.length - 1);
        const i = Math.min(stops.length - 2, Math.floor(s));
        const f = s - i;
        const a = stops[i];
        const b = stops[i + 1];
        return a.map((v, k) => Math.round(v + (b[k] - v) * f));
    }
    // 심박 곡선: 한 주기에 두 번 솟는다(쿵 쿵). 값은 0 에서 1 사이
    function heartbeat(ph) {
        const p = ph - Math.floor(ph);
        const lub = Math.exp(-Math.pow((p - 0.1) / 0.06, 2));
        const dub = 0.6 * Math.exp(-Math.pow((p - 0.3) / 0.07, 2));
        return Math.min(1, lub + dub);
    }
    function resize() {
        readStops();
        arc.style.strokeDasharray = CIRC.toFixed(2);
    }
    function resetState() { }
    function tick(dt) { }
    function draw() {
        const rem = remainMs();
        const f = rem / totalMs;
        arc.style.strokeDashoffset = (CIRC * (1 - f)).toFixed(2);
        const col = blend(1 - f);
        arc.style.stroke = "rgb(" + col.join(",") + ")";
        arc.style.opacity = f > 0 ? "1" : "0";
        let w = BASE_W;
        if (!reduce && f > 0 && f < PULSE_AT) {
            const ramp = 1 - f / PULSE_AT;
            w += PULSE_W * ramp * heartbeat(elapsed / PULSE_MS);
        }
        arc.style.strokeWidth = w.toFixed(2);
        // 같은 색과 같은 박동이 배경 후광에도 번진다: 링 바깥까지 남은 시간이 읽힌다
        const beat = (w - BASE_W) / PULSE_W;
        halo.style.background = "radial-gradient(ellipse at 50% 50%, rgba(" + col.join(",") + "," + (0.34 + 0.2 * beat).toFixed(3) + ") 0%, rgba(" + col.join(",") + ",0) 72%)";
        num.textContent = (rem / 1000).toFixed(1);
    }
    const ro = new ResizeObserver(() => {
        resize();
        draw();
    });
    ro.observe(root);
    offs.push(() => ro.disconnect());
    resize();
    resetState();
    syncButtons();
    update(0);
    raf = requestAnimationFrame(frame);
    return () => {
        cancelAnimationFrame(raf);
        offs.forEach((f) => f());
    };
})();

// RingDrainHueShift - vanilla 판(01-cd-ring-drain-hue-shift) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./RingDrainHueShift.module.scss";

const cx = (s: string): string => s.split(" ").map((n) => styles[n] ?? n).join(" ");

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

  useEffect(() => {
    const rootEl = rootRef.current;
    if (!rootEl) return;
    const root: HTMLElement = rootEl;
    const reduce: boolean = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo: boolean = !reduce;
    let running: boolean = demo;
    let elapsed = 0;
    let lastTs = -1;
    let lastDraw = -1e9;
    let raf = 0;
    const hooks: { stop: () => void } = { stop: () => {} };
    const offs: Array<() => void> = [];
    const TOTAL_MS = 1500;
    const HOLD_MS = 300;
    const RING_R = 48;
    const PULSE_AT = 0.4;
    const PULSE_MS = 300;
    const HUE_STOPS = ["--c0", "--c1", "--c2"];
    let totalMs = TOTAL_MS;
    function q<T extends Element>(sel: string): T {
        return root.querySelector(sel) as T;
    }
    function on(el: EventTarget, type: string, fn: (e: Event) => void): void {
        el.addEventListener(type, fn);
        offs.push(() => el.removeEventListener(type, fn));
    }
    function clamp(v: number, lo: number, hi: number): number {
        return Math.max(lo, Math.min(hi, v));
    }
    // 지수 접근: 프레임률이 달라도 같은 속도가 되도록 dt 를 60fps 프레임 수로 환산해 쓴다
    function approach(x: number, target: number, per: number, dt: number): number {
        return x + (target - x) * (1 - Math.pow(1 - per, dt * 60));
    }
    const toggle = q<HTMLButtonElement>('[data-r="toggle"]');
    const resetBtn = q<HTMLButtonElement>('[data-r="reset"]');
    const status = q<HTMLElement>('[data-r="status"]');
    // 남은 시간. 경과는 rAF 타임스탬프 차이를 누적한 값이라 시계를 따로 읽지 않는다
    function remainMs(): number {
        return clamp(totalMs - elapsed, 0, totalMs);
    }
    function syncButtons(): void {
        toggle.textContent = running ? "멈춤" : "시작";
        toggle.setAttribute("aria-pressed", running ? "true" : "false");
    }
    // 스크린리더 안내는 멈출 때와 끝날 때만 갱신한다. 시연 루프 중에는 읽지 않는다
    function say(msg: string): void {
        if (!demo) status.textContent = msg;
    }
    function stopDemo(): void {
        if (!demo) return;
        demo = false;
        root.classList.remove("is-demo");
        root.removeAttribute("data-demo");
        hooks.stop();
    }
    function restart(): void {
        elapsed = 0;
        resetState();
    }
    function update(dt: number): void {
        tick(dt);
        draw();
    }
    function frame(ts: number): void {
        raf = requestAnimationFrame(frame);
        const raw = lastTs < 0 ? 0 : ts - lastTs;
        lastTs = ts;
        if (running) {
            elapsed += raw;
            if (demo) {
                const cycle = totalMs + HOLD_MS;
                if (elapsed >= cycle) {
                    elapsed %= cycle;
                    resetState();
                }
            } else if (elapsed >= totalMs) {
                elapsed = totalMs;
                running = false;
                say("시간이 다 됐습니다");
                syncButtons();
            }
        }
        if (reduce && ts - lastDraw < 250) return;
        lastDraw = ts;
        update(Math.min(raw, 50) / 1000);
    }
    on(toggle, "click", () => {
        stopDemo();
        if (!running && elapsed >= totalMs) restart();
        running = !running;
        say(running ? "" : "멈췄습니다");
        syncButtons();
        update(0);
    });
    on(resetBtn, "click", () => {
        stopDemo();
        running = false;
        restart();
        say("");
        syncButtons();
        update(0);
    });
    const arc = q<SVGCircleElement>('[data-r="arc"]');
    const num = q<HTMLElement>('[data-r="num"]');
    const halo = q<HTMLElement>('[data-r="halo"]');
    const CIRC = 2 * Math.PI * RING_R;
    const BASE_W = 9;
    const PULSE_W = 6;
    let stops: number[][] = [[127, 220, 180], [255, 233, 159], [255, 158, 187]];
    function parseColor(h: string): number[] {
        // CSS 변수 값은 #rrggbb 로도, rgb(r, g, b) 로도, rgb(100%, 50%, 0%) 로도 나올 수 있다
        const m6 = /^#([0-9a-f]{6})$/i.exec(h);
        if (m6) {
            const n = parseInt(m6[1], 16);
            return [(n >> 16) & 255, (n >> 8) & 255, n & 255];
        }
        const m = /([0-9.]+)(%?)[ ,]+([0-9.]+)(%?)[ ,]+([0-9.]+)(%?)/.exec(h);
        if (!m) return [255, 255, 255];
        const ch = (v: string, pct: string): number => Math.round(pct ? (Number(v) * 255) / 100 : Number(v));
        return [ch(m[1], m[2]), ch(m[3], m[4]), ch(m[5], m[6])];
    }
    // 색 토큰은 CSS 변수가 갖고, 여기서는 변수 이름만 들고 있다가 읽는다
    function readStops(): void {
        const cs = getComputedStyle(root);
        stops = HUE_STOPS.map((n) => parseColor(cs.getPropertyValue(n).trim()));
    }
    // 남은 비율 f 를 세 색 사이 보간으로 바꾼다. u = 1 - f 가 0 이면 첫 색, 1 이면 마지막 색
    function blend(u: number): number[] {
        const s = clamp(u, 0, 1) * (stops.length - 1);
        const i = Math.min(stops.length - 2, Math.floor(s));
        const f = s - i;
        const a = stops[i];
        const b = stops[i + 1];
        return a.map((v, k) => Math.round(v + (b[k] - v) * f));
    }
    // 심박 곡선: 한 주기에 두 번 솟는다(쿵 쿵). 값은 0 에서 1 사이
    function heartbeat(ph: number): number {
        const p = ph - Math.floor(ph);
        const lub = Math.exp(-Math.pow((p - 0.1) / 0.06, 2));
        const dub = 0.6 * Math.exp(-Math.pow((p - 0.3) / 0.07, 2));
        return Math.min(1, lub + dub);
    }
    function resize(): void {
        readStops();
        arc.style.strokeDasharray = CIRC.toFixed(2);
    }
    function resetState(): void {}
    function tick(dt: number): void {}
    function draw(): void {
        const rem = remainMs();
        const f = rem / totalMs;
        arc.style.strokeDashoffset = (CIRC * (1 - f)).toFixed(2);
        const col = blend(1 - f);
        arc.style.stroke = "rgb(" + col.join(",") + ")";
        arc.style.opacity = f > 0 ? "1" : "0";
        let w = BASE_W;
        if (!reduce && f > 0 && f < PULSE_AT) {
            const ramp = 1 - f / PULSE_AT;
            w += PULSE_W * ramp * heartbeat(elapsed / PULSE_MS);
        }
        arc.style.strokeWidth = w.toFixed(2);
        // 같은 색과 같은 박동이 배경 후광에도 번진다: 링 바깥까지 남은 시간이 읽힌다
        const beat = (w - BASE_W) / PULSE_W;
        halo.style.background = "radial-gradient(ellipse at 50% 50%, rgba(" + col.join(",") + "," + (0.34 + 0.2 * beat).toFixed(3) + ") 0%, rgba(" + col.join(",") + ",0) 72%)";
        num.textContent = (rem / 1000).toFixed(1);
    }
    const ro = new ResizeObserver(() => {
        resize();
        draw();
    });
    ro.observe(root);
    offs.push(() => ro.disconnect());
    resize();
    resetState();
    syncButtons();
    update(0);
    raf = requestAnimationFrame(frame);
    return () => {
        cancelAnimationFrame(raf);
        offs.forEach((f) => f());
    };
  }, []);

  return (
    <div className={cx("cd") + " is-demo"} id="cd" data-demo="1" ref={rootRef}>
      <div className={cx("cd__view cd__view--ring")}>
      <div className={cx("cd__halo")} data-r="halo"></div>
      <svg className={cx("cd__svg")} viewBox="0 0 120 120" role="img" aria-label="줄어드는 링 타이머">
      <circle className={cx("cd__track")} cx="60" cy="60" r="48"/>
      <circle className={cx("cd__arc")} data-r="arc" cx="60" cy="60" r="48" transform="rotate(-90 60 60)"/>
      </svg>
      <p className={cx("cd__read cd__read--center")} role="timer"><b data-r="num">1.5</b><span>초</span></p>
      </div>
      <div className={cx("cd__bar")}>
        <button className={cx("cd__btn")} type="button" data-r="toggle">멈춤</button>
        <button className={cx("cd__btn")} type="button" data-r="reset">다시</button>
      </div>
      <p className={cx("cd__sr")} aria-live="polite" data-r="status"></p>
    </div>
  );
}