06Nested Popovers Whose Shadow and Size Step Up with Each Depth

<main class="stage">
<div class="pm is-demo" id="pm" data-demo="1">
  <p class="pm__live" data-r="live" aria-live="off" aria-atomic="true"></p>
  <button class="pm__open pm__open--a" data-r="op" type="button" aria-expanded="false">Settings</button>
  <div class="pm__pop" data-r="lv"><b class="pm__ttl">Settings</b><button class="pm__open" data-r="op" type="button" aria-expanded="false">Alerts</button></div>
  <div class="pm__pop" data-r="lv"><b class="pm__ttl">Alerts</b><button class="pm__open" data-r="op" type="button" aria-expanded="false">Sound</button></div>
  <div class="pm__pop" data-r="lv"><b class="pm__ttl">Sound</b><span class="pm__txt">Volume, vibrate</span></div>
</div>
</main>

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

// 핵심: 중첩 깊이 d 를 세어 그림자 높이는 키우고(위로 뜬 것처럼) 크기와 밝기는 한 단계씩 줄여 위아래 관계를 보인다.

@include stage($stage-yellow);

.pm {
  position: relative;
  box-sizing: border-box;
  overflow: hidden;
  width: min(100%, 440px);
  height: min(252px, calc(100vh - 2 * clamp(8px, 4vw, 24px)));
  border-radius: $r-card;
  background: rgba($subject-ink, .07);
  color: $subject-ink;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}
.pm b { font-weight: 800; font-variant-numeric: tabular-nums; }
.pm__live {
  position: absolute;
  left: $sp-3;
  top: $sp-2;
  margin: 0;
  z-index: 9;
  color: rgba($subject-ink, .72);
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
  pointer-events: none;
}
.pm button { font-family: inherit; }
.pm button:focus-visible { outline: 3px solid $subject-ink; outline-offset: 2px; }


.pm__open {
  box-sizing: border-box;
  height: 28px;
  padding: 0 $sp-3;
  border: 0;
  border-radius: $r-pill;
  background: $subject-lilac;
  color: $subject-ink;
  font-size: 12px;
  line-height: 16px;
  font-weight: 700;
  cursor: pointer;
}
.pm__open--a { position: absolute; left: 12px; top: 34px; width: 64px; padding: 0; background: $subject-pink; z-index: 8; }
.pm__open[aria-expanded="true"] { background: $subject-ink; color: $subject-cream; }
.pm__pop {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: $sp-1;
  width: 128px;
  height: 70px;
  padding: $sp-3;
  border-radius: $r-control;
  background: $subject-cream;
  color: $subject-ink;
  transform-origin: 0 0;
  visibility: hidden;
}
.pm__pop:nth-of-type(1) { z-index: 3; }
.pm__pop:nth-of-type(2) { z-index: 4; }
.pm__pop:nth-of-type(3) { z-index: 5; }
.pm__ttl { display: block; font-size: 13px; line-height: 20px; }
.pm__txt { display: block; color: rgba($subject-ink, .72); }
@media (prefers-reduced-motion: reduce) {
  .pm__open { 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);
}

.pm {
  position: relative;
  box-sizing: border-box;
  overflow: hidden;
  width: min(100%, 440px);
  height: min(252px, 100vh - 2 * clamp(8px, 4vw, 24px));
  border-radius: 16px;
  background: rgba(23, 20, 26, 0.07);
  color: #17141a;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}

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

.pm__live {
  position: absolute;
  left: 12px;
  top: 8px;
  margin: 0;
  z-index: 9;
  color: rgba(23, 20, 26, 0.72);
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
  pointer-events: none;
}

.pm button {
  font-family: inherit;
}

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

.pm__open {
  box-sizing: border-box;
  height: 28px;
  padding: 0 12px;
  border: 0;
  border-radius: 999px;
  background: #b9a0ff;
  color: #17141a;
  font-size: 12px;
  line-height: 16px;
  font-weight: 700;
  cursor: pointer;
}

.pm__open--a {
  position: absolute;
  left: 12px;
  top: 34px;
  width: 64px;
  padding: 0;
  background: #ff9ebb;
  z-index: 8;
}

.pm__open[aria-expanded=true] {
  background: #17141a;
  color: #fff7e6;
}

.pm__pop {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 4px;
  width: 128px;
  height: 70px;
  padding: 12px;
  border-radius: 12px;
  background: #fff7e6;
  color: #17141a;
  transform-origin: 0 0;
  visibility: hidden;
}

.pm__pop:nth-of-type(1) {
  z-index: 3;
}

.pm__pop:nth-of-type(2) {
  z-index: 4;
}

.pm__pop:nth-of-type(3) {
  z-index: 5;
}

.pm__ttl {
  display: block;
  font-size: 13px;
  line-height: 20px;
}

.pm__txt {
  display: block;
  color: rgba(23, 20, 26, 0.72);
}

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

(function () {
    const root = document.getElementById("pm");
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    let acc = 0;
    let clock = 0;
    const offs = [];
    const live = root.querySelector("[data-r=live]");
    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() {
        if (!demo)
            return;
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
        live.setAttribute("aria-live", "polite");
    }
    if (reduce)
        live.setAttribute("aria-live", "polite");
    let shown = "";
    function say(s) {
        if (s === shown)
            return;
        shown = s;
        live.textContent = s;
    }
    function makeRng(seed) {
        let s = seed >>> 0;
        return () => {
            s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
            return s / 4294967296;
        };
    }
    function local(e) {
        const r = root.getBoundingClientRect();
        return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function sync() {
        if (reduce) {
            snap();
            render();
        }
    }
    // 기법: 팝오버 안에서 또 열리는 팝오버의 깊이 d 를 세어, 그림자 높이는 d 에 비례해 키우고 크기·밝기는 d 가 늘 때마다 한 단계씩 줄인다.
    const DEPTH_STEP = 0.1;
    const SHADOW_LIFT = 7;
    const SCALE_STEP = 0.07;
    const STAGGER = 260;
    const POP_W = 128;
    const POP_H = 70;
    const X0 = 84;
    const Y0 = 34;
    const STEP_Y = 28;
    const CYCLE_MS = 3000;
    const ops = Array.from(root.querySelectorAll("[data-r=op]"));
    const lv = Array.from(root.querySelectorAll("[data-r=lv]"));
    const openAmt = [0, 0, 0];
    let depth = reduce ? 3 : 0;
    let lastDepth = -1;
    function script(ms) {
        const t = ms % CYCLE_MS;
        const base = 300;
        depth = t < base ? 0 : t < base + STAGGER ? 1 : t < base + 2 * STAGGER ? 2 : t < 1900 ? 3 : t < 1900 + STAGGER ? 2 : t < 1900 + 2 * STAGGER ? 1 : 0;
    }
    function tick(ms) {
        if (demo)
            script(ms);
        for (let i = 0; i < 3; i += 1)
            openAmt[i] += ((depth > i ? 1 : 0) - openAmt[i]) * 0.22;
    }
    function snap() {
        for (let i = 0; i < 3; i += 1)
            openAmt[i] = depth > i ? 1 : 0;
    }
    function render() {
        const w = root.clientWidth;
        const stepX = clamp((w - X0 - POP_W - 8) / 2, 28, 84);
        for (let i = 0; i < 3; i += 1) {
            const d = i + 1;
            const o = openAmt[i];
            const sc = (1 - (d - 1) * SCALE_STEP) * (0.92 + 0.08 * o);
            const lift = d * SHADOW_LIFT * o;
            const x = X0 + i * stepX - (1 - o) * 14;
            const y = Y0 + i * STEP_Y - (1 - o) * 8;
            lv[i].style.transform = "translate3d(" + x.toFixed(1) + "px," + y.toFixed(1) + "px,0) scale(" + sc.toFixed(3) + ")";
            lv[i].style.opacity = o.toFixed(2);
            lv[i].style.visibility = o > 0.02 ? "visible" : "hidden";
            lv[i].style.filter = "brightness(" + (1 - (d - 1) * DEPTH_STEP).toFixed(2) + ")";
            lv[i].style.boxShadow = "0 " + lift.toFixed(1) + "px " + (lift * 2).toFixed(1) + "px rgba(23, 20, 26, .34)";
        }
        if (depth !== lastDepth) {
            lastDepth = depth;
            for (let i = 0; i < 3; i += 1)
                ops[i].setAttribute("aria-expanded", depth > i ? "true" : "false");
        }
        const dd = Math.max(1, depth);
        say("depth " + depth + "  lift " + (dd * SHADOW_LIFT) + "  scale " + (1 - (dd - 1) * SCALE_STEP).toFixed(2));
    }
    ops.forEach((el, i) => {
        on(el, "click", () => {
            stopDemo();
            depth = depth > i ? i : i + 1;
            sync();
        });
    });
    on(root, "keydown", (e) => {
        if (e.key !== "Escape" || depth === 0)
            return;
        e.preventDefault();
        stopDemo();
        depth -= 1;
        ops[depth].focus({ preventScroll: true });
        sync();
    });
    const FRAME_MS = 1000 / 60;
    function frame(ts) {
        if (t0 < 0) {
            t0 = ts;
            last = ts;
        }
        acc += Math.min(100, ts - last);
        last = ts;
        let n = 0;
        while (acc >= FRAME_MS && n < 6) {
            clock += FRAME_MS;
            tick(clock);
            acc -= FRAME_MS;
            n += 1;
        }
        if (n === 6)
            acc = 0;
        render();
        raf = requestAnimationFrame(frame);
    }
    const ro = new ResizeObserver(() => sync());
    ro.observe(root);
    if (reduce) {
        stopDemo();
        snap();
        render();
    }
    else {
        raf = requestAnimationFrame(frame);
    }
    return () => {
        cancelAnimationFrame(raf);
        offs.forEach((f) => f());
        ro.disconnect();
    };
})();

// NestedCascadeStack - vanilla 판(06-pm-nested-cascade-stack) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./NestedCascadeStack.module.scss";

export default function NestedCascadeStack() {
  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;
    let acc = 0;
    let clock = 0;
    const offs: Array<() => void> = [];
    const live = root.querySelector("[data-r=live]") as HTMLElement;

    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 {
      if (!demo) return;
      demo = false;
      root.removeAttribute("data-demo");
      root.classList.remove("is-demo");
      live.setAttribute("aria-live", "polite");
    }
    if (reduce) live.setAttribute("aria-live", "polite");
    let shown = "";
    function say(s: string): void {
      if (s === shown) return;
      shown = s;
      live.textContent = s;
    }
    function makeRng(seed: number): () => number {
      let s = seed >>> 0;
      return () => {
        s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
        return s / 4294967296;
      };
    }
    function local(e: PointerEvent): { x: number; y: number } {
      const r = root.getBoundingClientRect();
      return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function sync(): void {
      if (reduce) {
        snap();
        render();
      }
    }

    // 기법: 팝오버 안에서 또 열리는 팝오버의 깊이 d 를 세어, 그림자 높이는 d 에 비례해 키우고 크기·밝기는 d 가 늘 때마다 한 단계씩 줄인다.
    const DEPTH_STEP = 0.1;
    const SHADOW_LIFT = 7;
    const SCALE_STEP = 0.07;
    const STAGGER = 260;
    const POP_W = 128;
    const POP_H = 70;
    const X0 = 84;
    const Y0 = 34;
    const STEP_Y = 28;
    const CYCLE_MS = 3000;
    const ops = Array.from(root.querySelectorAll("[data-r=op]")) as HTMLElement[];
    const lv = Array.from(root.querySelectorAll("[data-r=lv]")) as HTMLElement[];
    const openAmt = [0, 0, 0];
    let depth = reduce ? 3 : 0;
    let lastDepth = -1;

    function script(ms: number): void {
      const t = ms % CYCLE_MS;
      const base = 300;
      depth = t < base ? 0 : t < base + STAGGER ? 1 : t < base + 2 * STAGGER ? 2 : t < 1900 ? 3 : t < 1900 + STAGGER ? 2 : t < 1900 + 2 * STAGGER ? 1 : 0;
    }
    function tick(ms: number): void {
      if (demo) script(ms);
      for (let i = 0; i < 3; i += 1) openAmt[i] += ((depth > i ? 1 : 0) - openAmt[i]) * 0.22;
    }
    function snap(): void {
      for (let i = 0; i < 3; i += 1) openAmt[i] = depth > i ? 1 : 0;
    }
    function render(): void {
      const w = root.clientWidth;
      const stepX = clamp((w - X0 - POP_W - 8) / 2, 28, 84);
      for (let i = 0; i < 3; i += 1) {
        const d = i + 1;
        const o = openAmt[i];
        const sc = (1 - (d - 1) * SCALE_STEP) * (0.92 + 0.08 * o);
        const lift = d * SHADOW_LIFT * o;
        const x = X0 + i * stepX - (1 - o) * 14;
        const y = Y0 + i * STEP_Y - (1 - o) * 8;
        lv[i].style.transform = "translate3d(" + x.toFixed(1) + "px," + y.toFixed(1) + "px,0) scale(" + sc.toFixed(3) + ")";
        lv[i].style.opacity = o.toFixed(2);
        lv[i].style.visibility = o > 0.02 ? "visible" : "hidden";
        lv[i].style.filter = "brightness(" + (1 - (d - 1) * DEPTH_STEP).toFixed(2) + ")";
        lv[i].style.boxShadow = "0 " + lift.toFixed(1) + "px " + (lift * 2).toFixed(1) + "px rgba(23, 20, 26, .34)";
      }
      if (depth !== lastDepth) {
        lastDepth = depth;
        for (let i = 0; i < 3; i += 1) ops[i].setAttribute("aria-expanded", depth > i ? "true" : "false");
      }
      const dd = Math.max(1, depth);
      say("depth " + depth + "  lift " + (dd * SHADOW_LIFT) + "  scale " + (1 - (dd - 1) * SCALE_STEP).toFixed(2));
    }
    ops.forEach((el, i) => {
      on(el, "click", () => {
        stopDemo();
        depth = depth > i ? i : i + 1;
        sync();
      });
    });
    on(root, "keydown", (e: KeyboardEvent) => {
      if (e.key !== "Escape" || depth === 0) return;
      e.preventDefault();
      stopDemo();
      depth -= 1;
      ops[depth].focus({ preventScroll: true });
      sync();
    });

    const FRAME_MS = 1000 / 60;
    function frame(ts: number): void {
      if (t0 < 0) {
        t0 = ts;
        last = ts;
      }
      acc += Math.min(100, ts - last);
      last = ts;
      let n = 0;
      while (acc >= FRAME_MS && n < 6) {
        clock += FRAME_MS;
        tick(clock);
        acc -= FRAME_MS;
        n += 1;
      }
      if (n === 6) acc = 0;
      render();
      raf = requestAnimationFrame(frame);
    }
    const ro = new ResizeObserver(() => sync());
    ro.observe(root);
    if (reduce) {
      stopDemo();
      snap();
      render();
    } else {
      raf = requestAnimationFrame(frame);
    }
    return () => {
      cancelAnimationFrame(raf);
      offs.forEach((f) => f());
      ro.disconnect();
    };

  }, []);

  return (
    <main className={styles["stage"]}>
      <div ref={rootRef} className={styles["pm"] + " is-demo"} data-demo="1">
        <p className={styles["pm__live"]} data-r="live" aria-live="off" aria-atomic="true"></p>
        <button className={styles["pm__open"] + " " + styles["pm__open--a"]} data-r="op" type="button" aria-expanded="false">설정</button>
        <div className={styles["pm__pop"]} data-r="lv"><b className={styles["pm__ttl"]}>설정</b><button className={styles["pm__open"]} data-r="op" type="button" aria-expanded="false">알림</button></div>
        <div className={styles["pm__pop"]} data-r="lv"><b className={styles["pm__ttl"]}>알림</b><button className={styles["pm__open"]} data-r="op" type="button" aria-expanded="false">소리</button></div>
        <div className={styles["pm__pop"]} data-r="lv"><b className={styles["pm__ttl"]}>소리</b><span className={styles["pm__txt"]}>볼륨 · 진동</span></div>
      </div>
    </main>
  );
}