03Card That Snaps Back With a Spring Overshoot

<main class="stage">
<div class="es is-demo" id="es">
  <p class="es__caption">Card that snaps back with a spring overshoot</p>
  <div class="es__scene" id="esScene">
    <div class="es__peek" id="esPeek" aria-hidden="true"></div>
    <div class="es__card" id="esCard" tabindex="0" role="group" aria-roledescription="Swipe card">
      <p class="es__label" id="esLabel">Weekend café</p>
    </div>
    <button class="es__btn es__btn--nope" id="esNope" type="button" aria-label="Dislike">✕</button>
    <button class="es__btn es__btn--like" id="esLike" type="button" aria-label="Like">♥</button>
  </div>
  <p class="es__status" id="esStatus" aria-live="polite">Waiting</p>
</div>
</main>

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

// 값 하나: 해제 속도가 SPRING_FLING_VELOCITY_MIN 에 못 미치면 스프링(강성·감쇠)을 적분해
// 오버슛하며 원래 자리로 되돌아온다. 뒤 카드는 SWIPE_STACK_DEPTH_SCALE 만큼 줄어 비친다.

$duration: $dur-loop;
$easing: $ease-elastic;
$color: $subject-ink;

@include stage($stage-ink);

.es { display: grid; gap: $sp-2; justify-items: center; width: 100%; }
.es__caption { margin: 0; font-size: 12px; font-weight: 600; color: $subject-cream; }

.es__scene {
  position: relative;
  width: 220px;
  height: 190px;
  display: grid;
  place-items: center;
}

.es__peek {
  position: absolute;
  width: 160px;
  height: 180px;
  border-radius: $r-card;
  background: linear-gradient(160deg, $subject-lilac, $subject-blue);
  opacity: .7;
}

.es__card {
  position: relative;
  width: 160px;
  height: 180px;
  border-radius: $r-card;
  background: linear-gradient(160deg, $subject-mint, $subject-sky);
  box-shadow: $shadow-raised;
  display: grid;
  place-items: center;
  touch-action: none;
  cursor: grab;
  will-change: transform;
}
.es__card:active { cursor: grabbing; }
.es__card:focus-visible { outline: 2px solid $subject-blue-light; outline-offset: 3px; }

.es__label { margin: 0; font-size: 14px; font-weight: 700; color: $subject-ink; padding: 0 $sp-3; text-align: center; }

.es__btn {
  position: absolute;
  bottom: $sp-3;
  width: 34px;
  height: 34px;
  border-radius: $r-pill;
  border: 0;
  background: $stage-paper;
  box-shadow: $shadow-press;
  font-size: 15px;
  line-height: 1;
  cursor: pointer;
  display: grid;
  place-items: center;
  z-index: 2;
}
.es__btn--nope { left: $sp-3; color: $error; }
.es__btn--like { right: $sp-3; color: $subject-blue-deep; }
.es__btn:focus-visible { outline: 2px solid $subject-blue-light; outline-offset: 2px; }

.es__status { margin: 0; font-size: 11px; color: $subject-cream; font-weight: 600; }

@media (max-width: 340px) {
  .es { gap: $sp-2; }
  .es__scene { width: 150px; height: 108px; }
  .es__peek { width: 78px; height: 92px; }
  .es__card { width: 78px; height: 92px; }
  .es__label { font-size: 10px; padding: 0 $sp-1; }
  .es__btn { width: 22px; height: 22px; font-size: 11px; bottom: $sp-1; }
  .es__btn--nope { left: $sp-1; }
  .es__btn--like { right: $sp-1; }
}

@media (prefers-reduced-motion: reduce) {
  .es__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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.es {
  display: grid;
  gap: 8px;
  justify-items: center;
  width: 100%;
}

.es__caption {
  margin: 0;
  font-size: 12px;
  font-weight: 600;
  color: #fff7e6;
}

.es__scene {
  position: relative;
  width: 220px;
  height: 190px;
  display: grid;
  place-items: center;
}

.es__peek {
  position: absolute;
  width: 160px;
  height: 180px;
  border-radius: 16px;
  background: linear-gradient(160deg, #b9a0ff, #2f6df6);
  opacity: 0.7;
}

.es__card {
  position: relative;
  width: 160px;
  height: 180px;
  border-radius: 16px;
  background: linear-gradient(160deg, #4cd4a6, #6ec8ff);
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  display: grid;
  place-items: center;
  touch-action: none;
  cursor: grab;
  will-change: transform;
}

.es__card:active {
  cursor: grabbing;
}

.es__card:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 3px;
}

.es__label {
  margin: 0;
  font-size: 14px;
  font-weight: 700;
  color: #17141a;
  padding: 0 12px;
  text-align: center;
}

.es__btn {
  position: absolute;
  bottom: 12px;
  width: 34px;
  height: 34px;
  border-radius: 999px;
  border: 0;
  background: #ffffff;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  font-size: 15px;
  line-height: 1;
  cursor: pointer;
  display: grid;
  place-items: center;
  z-index: 2;
}

.es__btn--nope {
  left: 12px;
  color: #c2361a;
}

.es__btn--like {
  right: 12px;
  color: #0a4fe8;
}

.es__btn:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 2px;
}

.es__status {
  margin: 0;
  font-size: 11px;
  color: #fff7e6;
  font-weight: 600;
}

@media (max-width: 340px) {
  .es {
    gap: 8px;
  }
  .es__scene {
    width: 150px;
    height: 108px;
  }
  .es__peek {
    width: 78px;
    height: 92px;
  }
  .es__card {
    width: 78px;
    height: 92px;
  }
  .es__label {
    font-size: 10px;
    padding: 0 4px;
  }
  .es__btn {
    width: 22px;
    height: 22px;
    font-size: 11px;
    bottom: 4px;
  }
  .es__btn--nope {
    left: 4px;
  }
  .es__btn--like {
    right: 4px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .es__card {
    transition: none;
  }
}

(function () {
  "use strict";

  // 변형 3: 03 폴더에 SWIPE_STACK_DEPTH_SCALE 를 실재시킨다 — 뒤 카드 한 장을 이 비율만큼 줄여 살짝 비친다.
  var SWIPE_STACK_DEPTH_SCALE = 0.04;
  // 값 하나: 해제 속도가 이 값에 못 미치면 스프링(강성·감쇠)을 적분해 오버슛하며 되돌아온다.
  var SPRING_FLING_VELOCITY_MIN = 0.5;
  var SPRING_STIFFNESS = 120;
  var SPRING_DAMPING = 14;
  var EXIT_PX = 320;
  var CYCLE_S = 2;

  var root = document.getElementById("es");
  var card = document.getElementById("esCard");
  var peek = document.getElementById("esPeek");
  var label = document.getElementById("esLabel");
  var status = document.getElementById("esStatus");
  var btnLike = document.getElementById("esLike");
  var btnNope = document.getElementById("esNope");
  var reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

  peek.style.transform = "translateY(" + (SWIPE_STACK_DEPTH_SCALE * 100).toFixed(1) + "%) scale(" + (1 - SWIPE_STACK_DEPTH_SCALE).toFixed(3) + ")";

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  function clamp(v, lo, hi) { return Math.max(lo, Math.min(hi, v)); }

  var CARDS = ["Weekend café", "Home workout log", "Reading list", "Travel notes", "Morning routine", "Evening walk"];
  var rand = seedRand(37);
  var idx = Math.floor(rand() * CARDS.length);

  var dragging = false;
  var startX = 0, lastX = 0, lastT = 0, vxRaw = 0;
  var pos = 0, vel = 0, phase = "idle", exitDir = 1;

  function setCard() { label.textContent = CARDS[idx % CARDS.length]; }
  setCard();

  function render() {
    var rot = clamp(pos * 0.06, -18, 18);
    card.style.transform = "translateX(" + pos.toFixed(1) + "px) rotate(" + rot.toFixed(2) + "deg)";
  }

  function nextCard() {
    idx += 1; setCard();
    pos = 0; vel = 0; phase = "idle";
    render();
    status.textContent = "Waiting";
  }

  function judge(velocityPxMs, dir) {
    root.classList.remove("is-demo");
    var flung = Math.abs(velocityPxMs) >= SPRING_FLING_VELOCITY_MIN;
    if (reduce) {
      if (flung) { status.textContent = dir > 0 ? "Marked as liked" : "Marked as disliked"; nextCard(); }
      else { pos = 0; vel = 0; render(); status.textContent = "Sprung back with overshoot"; phase = "idle"; }
      return;
    }
    if (flung) {
      phase = "exit"; exitDir = dir;
      status.textContent = dir > 0 ? "Marked as liked" : "Marked as disliked";
    } else {
      phase = "spring";
      vel = velocityPxMs * 1000; // px/ms → px/s, 관성을 스프링에 넘긴다
      status.textContent = "Sprung back with overshoot";
    }
  }

  function startDrag(clientX) {
    root.classList.remove("is-demo");
    dragging = true; phase = "idle";
    startX = clientX; lastX = clientX; lastT = performance.now(); vxRaw = 0;
  }
  function moveDrag(clientX) {
    if (!dragging) return;
    var now = performance.now();
    var dt = Math.max(now - lastT, 1);
    vxRaw = (clientX - lastX) / dt;
    lastX = clientX; lastT = now;
    pos = clientX - startX;
    render();
  }
  function endDrag() {
    if (!dragging) return;
    dragging = false;
    judge(vxRaw, pos >= 0 ? 1 : -1);
  }

  card.addEventListener("pointerdown", function (e) { card.setPointerCapture(e.pointerId); startDrag(e.clientX); });
  card.addEventListener("pointermove", function (e) { moveDrag(e.clientX); });
  card.addEventListener("pointerup", endDrag);
  card.addEventListener("pointercancel", endDrag);

  function keyVerdict(dir, weak) {
    root.classList.remove("is-demo");
    pos = dir * (weak ? 34 : 70); render();
    judge(dir * (weak ? 0.1 : SPRING_FLING_VELOCITY_MIN + 0.4), dir);
  }
  card.addEventListener("keydown", function (e) {
    if (e.key === "ArrowRight") { e.preventDefault(); keyVerdict(1, false); }
    else if (e.key === "ArrowLeft") { e.preventDefault(); keyVerdict(-1, false); }
  });
  btnLike.addEventListener("click", function () { keyVerdict(1, false); });
  btnNope.addEventListener("click", function () { keyVerdict(-1, false); });

  // 스프링 방정식(강성 SPRING_STIFFNESS·감쇠 SPRING_DAMPING)을 매 프레임 적분한다 — 목표(0)를 넘겼다가 되돌아온다.
  function integrate(dt) {
    var accel = SPRING_STIFFNESS * (0 - pos) - SPRING_DAMPING * vel;
    vel += accel * dt;
    pos += vel * dt;
    if (Math.abs(pos) < 0.4 && Math.abs(vel) < 4) { pos = 0; vel = 0; phase = "idle"; }
  }

  function step(dt) {
    var dtS = Math.min(dt / 1000, 0.032);
    if (phase === "exit") {
      pos += exitDir * Math.max(Math.abs(vel) / 1000, SPRING_FLING_VELOCITY_MIN * 1.3) * dt;
      render();
      if (Math.abs(pos) > EXIT_PX) nextCard();
    } else if (phase === "spring") {
      integrate(dtS);
      render();
    }
  }

  // .is-demo 자동 시연: 실제 pointer 없이 pos·judge() 를 같은 경로로 호출한다.
  var start = null, lastNow = 0, prevT = 0, synthPhase = "wait";
  function synth(t) {
    if (t > 0.4 && t < 0.65 && synthPhase === "wait") synthPhase = "pull";
    if (synthPhase === "pull") {
      var p = clamp((t - 0.4) / 0.25, 0, 1);
      pos = p * 60; render();
      if (t >= 0.65) { synthPhase = "afterPull"; judge(0.08, 1); }
    }
    if (t > 1.3 && t < 1.55 && synthPhase === "afterPull") synthPhase = "throw";
    if (synthPhase === "throw") {
      var q = clamp((t - 1.3) / 0.25, 0, 1);
      pos = -q * 140; render();
      if (t >= 1.55) { synthPhase = "done"; judge(-(SPRING_FLING_VELOCITY_MIN + 0.4), -1); }
    }
  }

  function loop(now) {
    if (start === null) { start = now; lastNow = now; lastT = now; }
    var dt = Math.min(now - lastNow, 48);
    lastNow = now;
    var t = ((now - start) / 1000) % CYCLE_S;
    if (t < prevT) synthPhase = "wait";
    prevT = t;
    if (!reduce && root.classList.contains("is-demo")) synth(t);
    if (!reduce) step(dt);
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

// ElasticSnapbackSwipeCard — vanilla 판(run/422/demo/03-swipe-deck-precision-elastic-snapback/index.html) 의 React 포트.
// 변형 3: SWIPE_STACK_DEPTH_SCALE 를 뒤 카드 한 장에 실재시킨다. 값 하나: 해제 속도가
// SPRING_FLING_VELOCITY_MIN 에 못 미치면 스프링(강성·감쇠)을 적분해 오버슛하며 되돌아온다.
import { useEffect, useRef, useState } from "react";
import type { PointerEvent as ReactPointerEvent } from "react";
import styles from "./ElasticSnapbackSwipeCard.module.scss";

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

const SWIPE_STACK_DEPTH_SCALE = 0.04;
const SPRING_FLING_VELOCITY_MIN = 0.5;
const SPRING_STIFFNESS = 120;
const SPRING_DAMPING = 14;
const EXIT_PX = 320;
const CYCLE_S = 2;
const CARDS = ["주말 카페", "홈트 기록", "독서 목록", "여행 메모", "아침 루틴", "저녁 산책"];

function seedRand(seed: number) {
  let s = seed >>> 0;
  return function (): number {
    s = (s * 1664525 + 1013904223) >>> 0;
    return s / 4294967296;
  };
}
function clamp(v: number, lo: number, hi: number): number {
  return Math.max(lo, Math.min(hi, v));
}

export default function ElasticSnapbackSwipeCard() {
  const cardRef = useRef<HTMLDivElement | null>(null);
  const peekRef = useRef<HTMLDivElement | null>(null);
  const posRef = useRef<number>(0) as Box<number>;
  const velRef = useRef<number>(0) as Box<number>;
  const phaseRef = useRef<string>("idle") as Box<string>;
  const exitDirRef = useRef<number>(1) as Box<number>;
  const draggingRef = useRef<boolean>(false) as Box<boolean>;
  const startXRef = useRef<number>(0) as Box<number>;
  const lastXRef = useRef<number>(0) as Box<number>;
  const lastTRef = useRef<number>(0) as Box<number>;
  const idxRef = useRef<number>(Math.floor(seedRand(37)() * CARDS.length)) as Box<number>;
  const frameRef = useRef<number>(0) as Box<number>;
  const [label, setLabel] = useState(CARDS[idxRef.current % CARDS.length]);
  const [status, setStatus] = useState("대기 중");
  const [demo, setDemo] = useState(true);
  const [reduce, setReduce] = useState(false);

  useEffect(() => {
    const peek = peekRef.current;
    if (!peek) return;
    peek.style.transform = "translateY(" + (SWIPE_STACK_DEPTH_SCALE * 100).toFixed(1) + "%) scale(" + (1 - SWIPE_STACK_DEPTH_SCALE).toFixed(3) + ")";
  }, []);

  function render(): void {
    const card = cardRef.current;
    if (!card) return;
    const rot = clamp(posRef.current * 0.06, -18, 18);
    card.style.transform = "translateX(" + posRef.current.toFixed(1) + "px) rotate(" + rot.toFixed(2) + "deg)";
  }

  function nextCard(): void {
    idxRef.current += 1;
    setLabel(CARDS[idxRef.current % CARDS.length]);
    posRef.current = 0; velRef.current = 0; phaseRef.current = "idle";
    render();
    setStatus("대기 중");
  }

  function judge(velocityPxMs: number, dir: number): void {
    setDemo(false);
    const flung = Math.abs(velocityPxMs) >= SPRING_FLING_VELOCITY_MIN;
    if (reduce) {
      if (flung) { setStatus(dir > 0 ? "좋아요 처리됨" : "싫어요 처리됨"); nextCard(); }
      else { posRef.current = 0; velRef.current = 0; render(); setStatus("스프링으로 되돌아옴"); phaseRef.current = "idle"; }
      return;
    }
    if (flung) {
      phaseRef.current = "exit"; exitDirRef.current = dir;
      setStatus(dir > 0 ? "좋아요 처리됨" : "싫어요 처리됨");
    } else {
      phaseRef.current = "spring";
      velRef.current = velocityPxMs * 1000;
      setStatus("스프링으로 되돌아옴");
    }
  }

  function startDrag(clientX: number): void {
    setDemo(false);
    draggingRef.current = true; phaseRef.current = "idle";
    startXRef.current = clientX; lastXRef.current = clientX; lastTRef.current = performance.now();
  }
  function moveDrag(clientX: number): void {
    if (!draggingRef.current) return;
    const now = performance.now();
    const dt = Math.max(now - lastTRef.current, 1);
    velRef.current = ((clientX - lastXRef.current) / dt) * 1000;
    lastXRef.current = clientX; lastTRef.current = now;
    posRef.current = clientX - startXRef.current;
    render();
  }
  function endDrag(): void {
    if (!draggingRef.current) return;
    draggingRef.current = false;
    judge(velRef.current / 1000, posRef.current >= 0 ? 1 : -1);
  }

  function onPointerDown(e: ReactPointerEvent<HTMLDivElement>): void {
    e.currentTarget.setPointerCapture(e.pointerId);
    startDrag(e.clientX);
  }
  function onPointerMove(e: ReactPointerEvent<HTMLDivElement>): void { moveDrag(e.clientX); }
  function onPointerUp(): void { endDrag(); }

  function keyVerdict(dir: number, weak: boolean): void {
    setDemo(false);
    posRef.current = dir * (weak ? 34 : 70); render();
    judge(dir * (weak ? 0.1 : SPRING_FLING_VELOCITY_MIN + 0.4), dir);
  }
  function onKeyDown(e: any): void {
    if (e.key === "ArrowRight") { e.preventDefault(); keyVerdict(1, false); }
    else if (e.key === "ArrowLeft") { e.preventDefault(); keyVerdict(-1, false); }
  }

  function integrate(dt: number): void {
    const accel = SPRING_STIFFNESS * (0 - posRef.current) - SPRING_DAMPING * velRef.current;
    velRef.current += accel * dt;
    posRef.current += velRef.current * dt;
    if (Math.abs(posRef.current) < 0.4 && Math.abs(velRef.current) < 4) { posRef.current = 0; velRef.current = 0; phaseRef.current = "idle"; }
  }

  function step(dt: number): void {
    const dtS = Math.min(dt / 1000, 0.032);
    if (phaseRef.current === "exit") {
      posRef.current += exitDirRef.current * Math.max(Math.abs(velRef.current) / 1000, SPRING_FLING_VELOCITY_MIN * 1.3) * dt;
      render();
      if (Math.abs(posRef.current) > EXIT_PX) nextCard();
    } else if (phaseRef.current === "spring") {
      integrate(dtS);
      render();
    }
  }

  function synth(t: number, synthPhaseRef: Box<string>): void {
    if (t > 0.4 && t < 0.65 && synthPhaseRef.current === "wait") synthPhaseRef.current = "pull";
    if (synthPhaseRef.current === "pull") {
      const p = clamp((t - 0.4) / 0.25, 0, 1);
      posRef.current = p * 60; render();
      if (t >= 0.65) { synthPhaseRef.current = "afterPull"; judge(0.08, 1); }
    }
    if (t > 1.3 && t < 1.55 && synthPhaseRef.current === "afterPull") synthPhaseRef.current = "throw";
    if (synthPhaseRef.current === "throw") {
      const q = clamp((t - 1.3) / 0.25, 0, 1);
      posRef.current = -q * 140; render();
      if (t >= 1.55) { synthPhaseRef.current = "done"; judge(-(SPRING_FLING_VELOCITY_MIN + 0.4), -1); }
    }
  }

  useEffect(() => {
    setReduce(window.matchMedia("(prefers-reduced-motion: reduce)").matches);
  }, []);

  useEffect(() => {
    let start = 0, lastNow = 0, prevT = 0;
    const synthPhaseRef: Box<string> = { current: "wait" };
    function loop(now: number): void {
      if (start === 0) { start = now; lastNow = now; }
      const dt = Math.min(now - lastNow, 48);
      lastNow = now;
      const t = ((now - start) / 1000) % CYCLE_S;
      if (t < prevT) synthPhaseRef.current = "wait";
      prevT = t;
      if (!reduce && demo) synth(t, synthPhaseRef);
      if (!reduce) step(dt);
      frameRef.current = requestAnimationFrame(loop);
    }
    frameRef.current = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(frameRef.current);
  }, [reduce, demo]);

  return (
    <main className={styles.stage}>
      <div className={styles.es}>
        <p className={styles.caption}>스프링 오버슛으로 되돌아오는 카드</p>
        <div className={styles.scene}>
          <div className={styles.peek} ref={peekRef} aria-hidden="true" />
          <div
            className={styles.card}
            ref={cardRef}
            tabIndex={0}
            role="group"
            aria-roledescription="스와이프 카드"
            onPointerDown={onPointerDown}
            onPointerMove={onPointerMove}
            onPointerUp={onPointerUp}
            onKeyDown={onKeyDown}
          >
            <p className={styles.label}>{label}</p>
          </div>
          <button className={styles.btnNope} type="button" aria-label="싫어요" onClick={() => keyVerdict(-1, false)}>✕</button>
          <button className={styles.btnLike} type="button" aria-label="좋아요" onClick={() => keyVerdict(1, false)}>♥</button>
        </div>
        <p className={styles.status} aria-live="polite">{status}</p>
      </div>
    </main>
  );
}