02Sticker With a Peeling Corner

<main class="stage">
<div class="wrap is-demo" id="wrap">
  <div class="cardZone" id="zone">
    <div class="backing" aria-hidden="true"></div>
    <button class="card" id="card" type="button" aria-label="Sticker card; move the cursor toward a corner to peel it">
      <span class="cardMark" aria-hidden="true"></span>
      <span class="peelShade" id="shade" aria-hidden="true"></span>
    </button>
  </div>
</div>
</main>

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

// 계산 겹은 index.html 의 applyFromPoint(px, py) 에 있다 — 카드 우상단 꼭짓점에서 포인터까지의
// 거리로 벗겨지는 크기(--peel-size)를, atan2 각도로 그라디언트 방향(--peel-deg)을 매 프레임 다시 잰다.
// 여기는 그 두 변수를 clip-path 코너 컷과 그라디언트에 그대로 꽂아 쓴다(레이아웃을 건드리지 않는 paint 계산).
@include stage($stage-yellow);

.wrap { display: grid; place-items: center; }

.cardZone {
  position: relative;
  width: 170px;
  height: 170px;
}

.backing {
  position: absolute;
  inset: 0;
  border-radius: $r-card;
  background: $subject-cream;
}

.card {
  position: absolute;
  inset: 0;
  border: 0;
  padding: 0;
  appearance: none;
  cursor: pointer;
  background: $subject-blue;
  --peel-size: 0px;
  clip-path: polygon(0 0, calc(100% - var(--peel-size)) 0, 100% var(--peel-size), 100% 100%, 0 100%);

  &:focus-visible { outline: 2px solid $subject-blue-light; outline-offset: 4px; }
}

.cardMark {
  position: absolute;
  inset: 0;
  margin: auto;
  width: 56px;
  height: 56px;
  border-radius: 50%;
  border: 8px solid rgba($subject-cream, .8);
}

.peelShade {
  position: absolute;
  top: 0;
  right: 0;
  width: var(--peel-size, 0px);
  height: var(--peel-size, 0px);
  --peel-deg: 45deg;
  clip-path: polygon(100% 0, 100% 100%, 0 0);
  background: linear-gradient(var(--peel-deg), rgba(255, 247, 230, .95), rgba(255, 247, 230, 0) 72%);
  pointer-events: none;
}

@media (max-width: 340px) {
  .cardZone { width: 130px; height: 130px; }
  .cardMark { width: 42px; height: 42px; border-width: 6px; }
}

@media (prefers-reduced-motion: reduce) {
  .card { 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);
}

.wrap {
  display: grid;
  place-items: center;
}

.cardZone {
  position: relative;
  width: 170px;
  height: 170px;
}

.backing {
  position: absolute;
  inset: 0;
  border-radius: 16px;
  background: #fff7e6;
}

.card {
  position: absolute;
  inset: 0;
  border: 0;
  padding: 0;
  appearance: none;
  cursor: pointer;
  background: #2f6df6;
  --peel-size: 0px;
  clip-path: polygon(0 0, calc(100% - var(--peel-size)) 0, 100% var(--peel-size), 100% 100%, 0 100%);
}
.card:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 4px;
}

.cardMark {
  position: absolute;
  inset: 0;
  margin: auto;
  width: 56px;
  height: 56px;
  border-radius: 50%;
  border: 8px solid rgba(255, 247, 230, 0.8);
}

.peelShade {
  position: absolute;
  top: 0;
  right: 0;
  width: var(--peel-size, 0px);
  height: var(--peel-size, 0px);
  --peel-deg: 45deg;
  clip-path: polygon(100% 0, 100% 100%, 0 0);
  background: linear-gradient(var(--peel-deg), rgba(255, 247, 230, 0.95), rgba(255, 247, 230, 0) 72%);
  pointer-events: none;
}

@media (max-width: 340px) {
  .cardZone {
    width: 130px;
    height: 130px;
  }
  .cardMark {
    width: 42px;
    height: 42px;
    border-width: 6px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .card {
    transition: none;
  }
}

(function () {
  var PEEL_CORNER_SIZE = 24; // 커서가 모서리에 딱 붙었을 때 벗겨지는 기본 크기(px) — 변형은 44px
  var PEEL_REACH = 190;      // 이 거리(px) 밖이면 벗겨짐이 0 이 된다
  var LERP_RATE = .18;
  var ORBIT_MS = 2600;       // 자동 루프가 코너 주변을 도는 한 바퀴 시간

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var wrap = document.getElementById('wrap');
  var zone = document.getElementById('zone');
  var card = document.getElementById('card');
  var shade = document.getElementById('shade');
  var isDemo = true;

  var targetSize = 0, targetDeg = 45;
  var shownSize = 0, shownDeg = 45;

  // 카드 우상단 꼭짓점(pivot)에서 포인터까지의 벡터로 벗겨짐 크기와 그라디언트 각도를 계산한다.
  // 거리(distance)가 가까울수록 크게 벗겨지고, 각도(atan2)는 그라디언트가 흐르는 방향을 정한다 —
  // 포인터 각도 → clip-path/그라디언트 계산.
  function applyFromPoint(px, py) {
    var r = card.getBoundingClientRect();
    var pivotX = r.right, pivotY = r.top;
    var dx = pivotX - px, dy = py - pivotY;
    var distance = Math.hypot(dx, dy);
    var amt = Math.max(0, Math.min(1, 1 - distance / PEEL_REACH));
    targetSize = amt * PEEL_CORNER_SIZE;
    targetDeg = (Math.atan2(dy, dx) * 180 / Math.PI + 360) % 360;
  }

  function human() { if (isDemo) { wrap.classList.remove('is-demo'); isDemo = false; } }
  function onMove(e) { human(); applyFromPoint(e.clientX, e.clientY); }
  function onLeave() { human(); targetSize = 0; }
  zone.addEventListener('pointermove', onMove);
  zone.addEventListener('pointerleave', onLeave);
  card.addEventListener('focus', function () { human(); applyFromPoint(card.getBoundingClientRect().left, card.getBoundingClientRect().top); });
  card.addEventListener('blur', function () { human(); targetSize = 0; });

  var last = 0;
  function autoAdvance(ts) {
    if (!last) last = ts;
    var r = card.getBoundingClientRect();
    var t = ((ts - last) % ORBIT_MS) / ORBIT_MS;
    var angle = t * Math.PI * 2;
    var px = r.right - 26 + Math.cos(angle) * 30;
    var py = r.top + 26 + Math.sin(angle) * 30;
    applyFromPoint(px, py);
  }

  function loop(ts) {
    if (isDemo && !reduce) autoAdvance(ts);
    if (reduce) { shownSize = targetSize; shownDeg = targetDeg; }
    else {
      shownSize += (targetSize - shownSize) * LERP_RATE;
      shownDeg += (targetDeg - shownDeg) * LERP_RATE;
    }
    card.style.setProperty('--peel-size', shownSize.toFixed(2) + 'px');
    shade.style.setProperty('--peel-deg', shownDeg.toFixed(1) + 'deg');
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

// PeelCorner — vanilla 판(run/378/demo/02-sticker-peel-corner/index.html) 의 React 포트.
// 카드 우상단 꼭짓점에서 포인터까지의 벡터로 벗겨짐 크기와 그라디언트 각도(atan2)를 계산한다.
import { useEffect, useRef } from "react";
import styles from "./PeelCorner.module.scss";

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

const PEEL_CORNER_SIZE = 24; // 변형: 44px
const PEEL_REACH = 190;
const LERP_RATE = 0.18;
const ORBIT_MS = 2600;

export default function PeelCorner() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const zoneRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const cardRef = useRef(null) as unknown as Box<HTMLButtonElement>;
  const shadeRef = useRef(null) as unknown as Box<HTMLSpanElement>;
  const rafRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const wrap = rootRef.current;
    const zone = zoneRef.current;
    const card = cardRef.current;
    const shade = shadeRef.current;
    if (!wrap || !zone || !card || !shade) return;

    let isDemo = true;
    let targetSize = 0, targetDeg = 45;
    let shownSize = 0, shownDeg = 45;

    function applyFromPoint(px: number, py: number) {
      const r = card!.getBoundingClientRect();
      const pivotX = r.right, pivotY = r.top;
      const dx = pivotX - px, dy = py - pivotY;
      const distance = Math.hypot(dx, dy);
      const amt = Math.max(0, Math.min(1, 1 - distance / PEEL_REACH));
      targetSize = amt * PEEL_CORNER_SIZE;
      targetDeg = (Math.atan2(dy, dx) * 180 / Math.PI + 360) % 360;
    }

    function human() { if (isDemo) { wrap!.classList.remove(styles.isDemo); isDemo = false; } }
    function onMove(e: PointerEvent) { human(); applyFromPoint(e.clientX, e.clientY); }
    function onLeave() { human(); targetSize = 0; }
    function onFocus() { human(); const r = card!.getBoundingClientRect(); applyFromPoint(r.left, r.top); }
    function onBlur() { human(); targetSize = 0; }
    zone.addEventListener("pointermove", onMove);
    zone.addEventListener("pointerleave", onLeave);
    card.addEventListener("focus", onFocus);
    card.addEventListener("blur", onBlur);

    let last = 0;
    function autoAdvance(ts: number) {
      if (!last) last = ts;
      const r = card!.getBoundingClientRect();
      const t = ((ts - last) % ORBIT_MS) / ORBIT_MS;
      const angle = t * Math.PI * 2;
      const px = r.right - 26 + Math.cos(angle) * 30;
      const py = r.top + 26 + Math.sin(angle) * 30;
      applyFromPoint(px, py);
    }

    function loop(ts: number) {
      if (isDemo && !reduce) autoAdvance(ts);
      if (reduce) { shownSize = targetSize; shownDeg = targetDeg; }
      else {
        shownSize += (targetSize - shownSize) * LERP_RATE;
        shownDeg += (targetDeg - shownDeg) * LERP_RATE;
      }
      card!.style.setProperty("--peel-size", shownSize.toFixed(2) + "px");
      shade!.style.setProperty("--peel-deg", shownDeg.toFixed(1) + "deg");
      rafRef.current = requestAnimationFrame(loop);
    }
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      zone!.removeEventListener("pointermove", onMove);
      zone!.removeEventListener("pointerleave", onLeave);
      card!.removeEventListener("focus", onFocus);
      card!.removeEventListener("blur", onBlur);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.wrap + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.cardZone} ref={zoneRef}>
          <div className={styles.backing} aria-hidden="true"></div>
          <button className={styles.card} ref={cardRef} type="button" aria-label="스티커 카드, 커서를 모서리 쪽으로 움직이면 벗겨진다">
            <span className={styles.cardMark} aria-hidden="true"></span>
            <span className={styles.peelShade} ref={shadeRef} aria-hidden="true"></span>
          </button>
        </div>
      </div>
    </main>
  );
}