04三段階の幅にカチッと止まるサイドバーの縁

<main class="stage">
<div class="rh is-demo" id="rh" data-demo="1">
  <div class="rh__side" data-r="side">
    <p class="rh__item"><i class="rh__ico"></i><span class="rh__lab" data-r="lab">Home</span></p>
    <p class="rh__item"><i class="rh__ico"></i><span class="rh__lab" data-r="lab">Inbox</span></p>
    <p class="rh__item"><i class="rh__ico"></i><span class="rh__lab" data-r="lab">Tasks</span></p>
    <p class="rh__item"><i class="rh__ico"></i><span class="rh__lab" data-r="lab">Setup</span></p>
    <button class="rh__grip" data-r="grip" type="button" aria-label="サイズ変更つまみ"></button>
  </div>
  <i class="rh__tick" data-r="tick"></i><i class="rh__tick" data-r="tick"></i><i class="rh__tick" data-r="tick"></i>
  <div class="rh__main"><i></i><i></i><i></i></div>
  <p class="rh__meta"><span class="rh__tag">DETENT</span> <b data-r="det">1</b> <span class="rh__tag">W</span> <b data-r="w">0</b></p>
  <i class="rh__cursor" data-r="cursor"></i>
</div>
</main>

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

// 핵심: 사이드바 너비는 눈금 3개 중 하나로 끌려가는 스프링이다. 라벨의 투명도는 너비에서 계산한다.

@include stage($stage-ink);

.rh {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  height: min(252px, calc(100vh - 2 * clamp(8px, 4vw, 24px)));
  color: $subject-cream;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}
.rh b { font-weight: 800; font-variant-numeric: tabular-nums; }
.rh__tag { color: $tick-mute; letter-spacing: .5px; }
.rh__cursor {
  position: absolute;
  left: -10px;
  top: -10px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: $subject-cream;
  box-shadow: 0 0 0 3px rgba($subject-ink, .55), $shadow-press;
  opacity: 0;
  pointer-events: none;
  z-index: 6;
}
.rh[data-demo] .rh__cursor { opacity: 1; }
.rh button:focus-visible { outline: 3px solid $subject-pink; outline-offset: 2px; }
@media (prefers-reduced-motion: reduce) {
  .rh__cursor { display: none; }
}

.rh__side {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  height: calc(100% - 32px);
  width: 56px;
  overflow: hidden;
  padding: $sp-3 $sp-3;
  border-radius: $r-card;
  background: linear-gradient(180deg, $subject-sky, $subject-mint);
  color: $subject-ink;
  z-index: 2;
}
.rh__item {
  display: flex;
  align-items: center;
  gap: $sp-3;
  height: 30px;
  margin: 0;
  white-space: nowrap;
  font-weight: 700;
}
.rh__ico {
  flex: none;
  width: 20px;
  height: 20px;
  border-radius: $r-xs;
  background: rgba($subject-ink, .78);
}
.rh__lab { opacity: 0; }
.rh__grip {
  position: absolute;
  right: $sp-1;
  top: 50%;
  width: 12px;
  height: 56px;
  padding: 0;
  border: 0;
  border-radius: $r-pill;
  background: rgba($subject-ink, .7);
  transform: translateY(-50%);
  cursor: col-resize;
  touch-action: none;
}
.rh__main {
  position: absolute;
  inset: 0 0 32px 0;
  display: grid;
  align-content: center;
  justify-items: end;
  gap: $sp-3;
}
.rh__main i {
  width: 40%;
  height: 28px;
  border-radius: $r-sm;
  background: rgba($subject-cream, .16);
}
.rh__tick {
  position: absolute;
  left: 0;
  bottom: 18px;
  width: 4px;
  height: 10px;
  border-radius: $r-xs;
  background: rgba($subject-cream, .35);
  z-index: 3;
}
.rh__tick[data-on="1"] { background: $subject-pink; }
.rh__meta { position: absolute; left: 0; bottom: 0; margin: 0; }

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);
}

.rh {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  height: min(252px, 100vh - 2 * clamp(8px, 4vw, 24px));
  color: #fff7e6;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}

.rh b {
  font-weight: 800;
  font-variant-numeric: tabular-nums;
}

.rh__tag {
  color: #9a93a6;
  letter-spacing: 0.5px;
}

.rh__cursor {
  position: absolute;
  left: -10px;
  top: -10px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: #fff7e6;
  box-shadow: 0 0 0 3px rgba(23, 20, 26, 0.55), 0 6px 12px rgba(23, 20, 26, 0.32);
  opacity: 0;
  pointer-events: none;
  z-index: 6;
}

.rh[data-demo] .rh__cursor {
  opacity: 1;
}

.rh button:focus-visible {
  outline: 3px solid #ff9ebb;
  outline-offset: 2px;
}

@media (prefers-reduced-motion: reduce) {
  .rh__cursor {
    display: none;
  }
}
.rh__side {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  height: calc(100% - 32px);
  width: 56px;
  overflow: hidden;
  padding: 12px 12px;
  border-radius: 16px;
  background: linear-gradient(180deg, #6ec8ff, #4cd4a6);
  color: #17141a;
  z-index: 2;
}

.rh__item {
  display: flex;
  align-items: center;
  gap: 12px;
  height: 30px;
  margin: 0;
  white-space: nowrap;
  font-weight: 700;
}

.rh__ico {
  flex: none;
  width: 20px;
  height: 20px;
  border-radius: 4px;
  background: rgba(23, 20, 26, 0.78);
}

.rh__lab {
  opacity: 0;
}

.rh__grip {
  position: absolute;
  right: 4px;
  top: 50%;
  width: 12px;
  height: 56px;
  padding: 0;
  border: 0;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.7);
  transform: translateY(-50%);
  cursor: col-resize;
  touch-action: none;
}

.rh__main {
  position: absolute;
  inset: 0 0 32px 0;
  display: grid;
  align-content: center;
  justify-items: end;
  gap: 12px;
}

.rh__main i {
  width: 40%;
  height: 28px;
  border-radius: 8px;
  background: rgba(255, 247, 230, 0.16);
}

.rh__tick {
  position: absolute;
  left: 0;
  bottom: 18px;
  width: 4px;
  height: 10px;
  border-radius: 4px;
  background: rgba(255, 247, 230, 0.35);
  z-index: 3;
}

.rh__tick[data-on="1"] {
  background: #ff9ebb;
}

.rh__meta {
  position: absolute;
  left: 0;
  bottom: 0;
  margin: 0;
}

(function () {
    const root = document.getElementById("rh");
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    const offs = [];
    function q(sel) {
        return root.querySelector(sel);
    }
    function clamp(v, lo, hi) {
        return Math.max(lo, Math.min(hi, v));
    }
    function seg(t, a, b) {
        const c = clamp((t - a) / (b - a), 0, 1);
        return c * c * (3 - 2 * c);
    }
    function on(el, type, fn) {
        el.addEventListener(type, fn);
        offs.push(() => el.removeEventListener(type, fn));
    }
    function stopDemo() {
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
    }
    function pos(e) {
        const r = root.getBoundingClientRect();
        return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function spring(x, v, to, k, c, dt) {
        const n = Math.max(1, Math.ceil(dt / 0.008));
        const h = dt / n;
        for (let i = 0; i < n; i += 1) {
            v += (-k * (x - to) - c * v) * h;
            x += v * h;
        }
        return [x, v];
    }
    function sync() {
        if (reduce) {
            snap();
            render();
        }
    }
    // 기법: 끄는 중에는 눈금 가까이에서 PULL_RADIUS 안으로 들어오는 만큼 끌려가고(거리 비례),
    // 놓을 때는 손 속도에 FLING 시간을 곱해 미리 내다본 위치에서 가장 가까운 눈금(NEAREST)으로 간다.
    const DETENTS = [56, 144, 232];
    const PULL_RADIUS = 36;
    const FLING_VEL = 0.2;
    const side = q("[data-r=side]");
    const grip = q("[data-r=grip]");
    const cursor = q("[data-r=cursor]");
    const wEl = q("[data-r=w]");
    const detEl = q("[data-r=det]");
    const labs = Array.prototype.slice.call(root.querySelectorAll("[data-r=lab]"));
    const ticks = Array.prototype.slice.call(root.querySelectorAll("[data-r=tick]"));
    let sw = DETENTS[0];
    let vs = 0;
    let target = DETENTS[0];
    let raw = DETENTS[0];
    let lastRaw = DETENTS[0];
    let vel = 0;
    let px = 0;
    let py = 0;
    let gx = 0;
    let dragging = false;
    function limit() { return Math.min(DETENTS[2], root.clientWidth - 48); }
    function nearest(x) {
        let best = 0;
        for (let i = 1; i < DETENTS.length; i += 1) {
            if (Math.abs(DETENTS[i] - x) < Math.abs(DETENTS[best] - x))
                best = i;
        }
        return best;
    }
    function pulled(x) {
        const d = DETENTS[nearest(x)];
        const dist = Math.abs(x - d);
        if (dist >= PULL_RADIUS)
            return x;
        const t = 1 - dist / PULL_RADIUS;
        return x + (d - x) * t * t * 0.9;
    }
    function release() {
        if (!dragging)
            return;
        dragging = false;
        target = Math.min(DETENTS[nearest(raw + vel * FLING_VEL)], limit());
    }
    function userTakes() {
        stopDemo();
        dragging = false;
    }
    function script(now) {
        const ph = now % 2000;
        const was = dragging;
        dragging = false;
        if (ph >= 200 && ph < 560) {
            raw = 60 + 110 * seg2(ph, 200, 560);
            dragging = true;
        }
        else if (ph >= 1100 && ph < 1500) {
            raw = DETENTS[2] - 132 * seg2(ph, 1100, 1500);
            dragging = true;
        }
        if (!was && dragging) {
            lastRaw = raw;
            vel = 0;
        }
        if (was && !dragging) {
            dragging = true;
            release();
        }
        px = (dragging ? raw : sw) - 4;
        py = root.clientHeight * 0.5;
        gx = 4;
    }
    function seg2(t, a, b) { return clamp((t - a) / (b - a), 0, 1); }
    function snap() {
        sw = target;
        vs = 0;
    }
    function step(dt, now) {
        if (demo)
            script(now);
        if (dragging) {
            if (!demo)
                raw = clamp(px + gx, 40, limit());
            vel += ((raw - lastRaw) / Math.max(dt, 0.001) - vel) * 0.3;
            lastRaw = raw;
            target = clamp(pulled(raw), 40, limit());
        }
        const a = spring(sw, vs, target, 900, 2 * 0.72 * 30, dt);
        sw = a[0];
        vs = a[1];
    }
    function render() {
        side.style.width = sw.toFixed(1) + "px";
        const open = clamp((sw - 100) / 60, 0, 1);
        for (let i = 0; i < labs.length; i += 1)
            labs[i].style.opacity = open.toFixed(2);
        for (let i = 0; i < ticks.length; i += 1) {
            ticks[i].style.transform = "translateX(" + DETENTS[i] + "px)";
            ticks[i].setAttribute("data-on", i === nearest(sw) ? "1" : "0");
        }
        wEl.textContent = String(Math.round(sw));
        detEl.textContent = String(nearest(sw) + 1);
        cursor.style.transform = "translate(" + px.toFixed(1) + "px," + py.toFixed(1) + "px)";
    }
    on(grip, "pointerdown", (e) => {
        userTakes();
        grip.setPointerCapture(e.pointerId);
        const p = pos(e);
        px = p.x;
        py = p.y;
        gx = sw - p.x;
        raw = lastRaw = sw;
        vel = 0;
        dragging = true;
    });
    on(grip, "pointermove", (e) => {
        if (!dragging)
            return;
        px = pos(e).x;
        raw = clamp(px + gx, 40, limit());
        if (reduce) {
            target = clamp(pulled(raw), 40, limit());
            sync();
        }
    });
    on(grip, "pointerup", release);
    on(grip, "pointercancel", release);
    on(grip, "keydown", (e) => {
        if (e.key !== "ArrowLeft" && e.key !== "ArrowRight")
            return;
        e.preventDefault();
        userTakes();
        const i = clamp(nearest(target) + (e.key === "ArrowRight" ? 1 : -1), 0, DETENTS.length - 1);
        target = Math.min(DETENTS[i], limit());
        sync();
    });
    function frame(ts) {
        if (t0 < 0) {
            t0 = ts;
            last = ts;
        }
        const dt = Math.min(0.05, (ts - last) / 1000);
        last = ts;
        step(dt, ts - t0);
        render();
        raf = requestAnimationFrame(frame);
    }
    if (reduce) {
        stopDemo();
        snap();
        render();
    }
    else {
        raf = requestAnimationFrame(frame);
    }
    return () => {
        cancelAnimationFrame(raf);
        offs.forEach((f) => f());
    };
})();

// SidebarDetentSnap - vanilla 판(04-rh-sidebar-detent-snap) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./SidebarDetentSnap.module.scss";

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

  useEffect(() => {
    const rootEl = rootRef.current;
    if (!rootEl) return;
    const root: HTMLElement = rootEl;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    const offs: Array<() => void> = [];

    function q<T extends Element>(sel: string): T {
      return root.querySelector(sel) as T;
    }
    function clamp(v: number, lo: number, hi: number): number {
      return Math.max(lo, Math.min(hi, v));
    }
    function seg(t: number, a: number, b: number): number {
      const c = clamp((t - a) / (b - a), 0, 1);
      return c * c * (3 - 2 * c);
    }
    function on(el: EventTarget, type: string, fn: (e: any) => void): void {
      el.addEventListener(type, fn);
      offs.push(() => el.removeEventListener(type, fn));
    }
    function stopDemo(): void {
      demo = false;
      root.removeAttribute("data-demo");
      root.classList.remove("is-demo");
    }
    function pos(e: PointerEvent): { x: number; y: number } {
      const r = root.getBoundingClientRect();
      return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function spring(x: number, v: number, to: number, k: number, c: number, dt: number): number[] {
      const n = Math.max(1, Math.ceil(dt / 0.008));
      const h = dt / n;
      for (let i = 0; i < n; i += 1) {
        v += (-k * (x - to) - c * v) * h;
        x += v * h;
      }
      return [x, v];
    }
    function sync(): void {
      if (reduce) {
        snap();
        render();
      }
    }

    // 기법: 끄는 중에는 눈금 가까이에서 PULL_RADIUS 안으로 들어오는 만큼 끌려가고(거리 비례),
    // 놓을 때는 손 속도에 FLING 시간을 곱해 미리 내다본 위치에서 가장 가까운 눈금(NEAREST)으로 간다.
    const DETENTS = [56, 144, 232];
    const PULL_RADIUS = 36;
    const FLING_VEL = 0.2;
    const side = q<HTMLElement>("[data-r=side]");
    const grip = q<HTMLElement>("[data-r=grip]");
    const cursor = q<HTMLElement>("[data-r=cursor]");
    const wEl = q<HTMLElement>("[data-r=w]");
    const detEl = q<HTMLElement>("[data-r=det]");
    const labs = Array.prototype.slice.call(root.querySelectorAll("[data-r=lab]")) as HTMLElement[];
    const ticks = Array.prototype.slice.call(root.querySelectorAll("[data-r=tick]")) as HTMLElement[];
    let sw = DETENTS[0];
    let vs = 0;
    let target = DETENTS[0];
    let raw = DETENTS[0];
    let lastRaw = DETENTS[0];
    let vel = 0;
    let px = 0;
    let py = 0;
    let gx = 0;
    let dragging = false;

    function limit(): number { return Math.min(DETENTS[2], root.clientWidth - 48); }

    function nearest(x: number): number {
      let best = 0;
      for (let i = 1; i < DETENTS.length; i += 1) {
        if (Math.abs(DETENTS[i] - x) < Math.abs(DETENTS[best] - x)) best = i;
      }
      return best;
    }

    function pulled(x: number): number {
      const d = DETENTS[nearest(x)];
      const dist = Math.abs(x - d);
      if (dist >= PULL_RADIUS) return x;
      const t = 1 - dist / PULL_RADIUS;
      return x + (d - x) * t * t * 0.9;
    }

    function release(): void {
      if (!dragging) return;
      dragging = false;
      target = Math.min(DETENTS[nearest(raw + vel * FLING_VEL)], limit());
    }

    function userTakes(): void {
      stopDemo();
      dragging = false;
    }

    function script(now: number): void {
      const ph = now % 2000;
      const was = dragging;
      dragging = false;
      if (ph >= 200 && ph < 560) { raw = 60 + 110 * seg2(ph, 200, 560); dragging = true; }
      else if (ph >= 1100 && ph < 1500) { raw = DETENTS[2] - 132 * seg2(ph, 1100, 1500); dragging = true; }
      if (!was && dragging) { lastRaw = raw; vel = 0; }
      if (was && !dragging) { dragging = true; release(); }
      px = (dragging ? raw : sw) - 4;
      py = root.clientHeight * 0.5;
      gx = 4;
    }

    function seg2(t: number, a: number, b: number): number { return clamp((t - a) / (b - a), 0, 1); }

    function snap(): void {
      sw = target;
      vs = 0;
    }

    function step(dt: number, now: number): void {
      if (demo) script(now);
      if (dragging) {
        if (!demo) raw = clamp(px + gx, 40, limit());
        vel += ((raw - lastRaw) / Math.max(dt, 0.001) - vel) * 0.3;
        lastRaw = raw;
        target = clamp(pulled(raw), 40, limit());
      }
      const a = spring(sw, vs, target, 900, 2 * 0.72 * 30, dt);
      sw = a[0];
      vs = a[1];
    }

    function render(): void {
      side.style.width = sw.toFixed(1) + "px";
      const open = clamp((sw - 100) / 60, 0, 1);
      for (let i = 0; i < labs.length; i += 1) labs[i].style.opacity = open.toFixed(2);
      for (let i = 0; i < ticks.length; i += 1) {
        ticks[i].style.transform = "translateX(" + DETENTS[i] + "px)";
        ticks[i].setAttribute("data-on", i === nearest(sw) ? "1" : "0");
      }
      wEl.textContent = String(Math.round(sw));
      detEl.textContent = String(nearest(sw) + 1);
      cursor.style.transform = "translate(" + px.toFixed(1) + "px," + py.toFixed(1) + "px)";
    }

    on(grip, "pointerdown", (e: PointerEvent) => {
      userTakes();
      grip.setPointerCapture(e.pointerId);
      const p = pos(e);
      px = p.x;
      py = p.y;
      gx = sw - p.x;
      raw = lastRaw = sw;
      vel = 0;
      dragging = true;
    });
    on(grip, "pointermove", (e: PointerEvent) => {
      if (!dragging) return;
      px = pos(e).x;
      raw = clamp(px + gx, 40, limit());
      if (reduce) { target = clamp(pulled(raw), 40, limit()); sync(); }
    });
    on(grip, "pointerup", release);
    on(grip, "pointercancel", release);
    on(grip, "keydown", (e: KeyboardEvent) => {
      if (e.key !== "ArrowLeft" && e.key !== "ArrowRight") return;
      e.preventDefault();
      userTakes();
      const i = clamp(nearest(target) + (e.key === "ArrowRight" ? 1 : -1), 0, DETENTS.length - 1);
      target = Math.min(DETENTS[i], limit());
      sync();
    });

    function frame(ts: number): void {
      if (t0 < 0) {
        t0 = ts;
        last = ts;
      }
      const dt = Math.min(0.05, (ts - last) / 1000);
      last = ts;
      step(dt, ts - t0);
      render();
      raf = requestAnimationFrame(frame);
    }
    if (reduce) {
      stopDemo();
      snap();
      render();
    } else {
      raf = requestAnimationFrame(frame);
    }
    return () => {
      cancelAnimationFrame(raf);
      offs.forEach((f) => f());
    };

  }, []);

  return (
    <main className={styles["stage"]}>
      <div ref={rootRef} className={styles["rh"] + " is-demo"} data-demo="1">
        <div className={styles["rh__side"]} data-r="side">
          <p className={styles["rh__item"]}><i className={styles["rh__ico"]}></i><span className={styles["rh__lab"]} data-r="lab">Home</span></p>
          <p className={styles["rh__item"]}><i className={styles["rh__ico"]}></i><span className={styles["rh__lab"]} data-r="lab">Inbox</span></p>
          <p className={styles["rh__item"]}><i className={styles["rh__ico"]}></i><span className={styles["rh__lab"]} data-r="lab">Tasks</span></p>
          <p className={styles["rh__item"]}><i className={styles["rh__ico"]}></i><span className={styles["rh__lab"]} data-r="lab">Setup</span></p>
          <button className={styles["rh__grip"]} data-r="grip" type="button" aria-label="크기 조절 손잡이"></button>
        </div>
        <i className={styles["rh__tick"]} data-r="tick"></i><i className={styles["rh__tick"]} data-r="tick"></i><i className={styles["rh__tick"]} data-r="tick"></i>
        <div className={styles["rh__main"]}><i></i><i></i><i></i></div>
        <p className={styles["rh__meta"]}><span className={styles["rh__tag"]}>DETENT</span> <b data-r="det">1</b> <span className={styles["rh__tag"]}>W</span> <b data-r="w">0</b></p>
        <i className={styles["rh__cursor"]} data-r="cursor"></i>
      </div>
    </main>
  );
}