05Like/Nope Stamp That Fades In With Drag Distance

<main class="stage">
<div class="so is-demo" id="so">
  <p class="so__caption">Like/dislike stamps that darken on a nonlinear curve</p>
  <div class="so__scene" id="soScene">
    <div class="so__card" id="soCard" tabindex="0" role="group" aria-roledescription="Swipe card">
      <span class="so__stamp so__stamp--like" id="soLike" aria-hidden="true">LIKE</span>
      <span class="so__stamp so__stamp--nope" id="soNope" aria-hidden="true">NOPE</span>
      <p class="so__label" id="soLabel">Travel notes</p>
    </div>
    <button class="so__btn so__btn--nope" id="soBtnNope" type="button" aria-label="Dislike">✕</button>
    <button class="so__btn so__btn--like" id="soBtnLike" type="button" aria-label="Like">♥</button>
  </div>
  <p class="so__status" id="soStatus" aria-live="polite">Waiting</p>
</div>
</main>

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

// 값 하나: 드래그 거리를 STAMP_OPACITY_CURVE_POWER 승으로 매핑해 LIKE·NOPE 도장이
// 비선형(중심 근처 느림 → 임계 근처 급함)으로 진해진다.

$duration: $dur-base;
$easing: $ease-out;
$color: $subject-mint;

@include stage($stage-paper);

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

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

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

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

.so__stamp {
  position: absolute;
  top: $sp-3;
  border: 3px solid currentColor;
  border-radius: $r-xs;
  padding: $sp-1 $sp-2;
  font-size: 13px;
  font-weight: 800;
  letter-spacing: .08em;
  opacity: 0;
  pointer-events: none;
}
.so__stamp--like { left: $sp-3; color: $subject-mint; transform: rotate(-14deg); }
.so__stamp--nope { right: $sp-3; color: $error; transform: rotate(14deg); }

.so__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;
}
.so__btn--nope { left: $sp-3; color: $error; }
.so__btn--like { right: $sp-3; color: $subject-mint; }
.so__btn:focus-visible { outline: 2px solid $subject-blue-light; outline-offset: 2px; }

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

@media (max-width: 340px) {
  .so { gap: $sp-2; }
  .so__scene { width: 150px; height: 108px; }
  .so__card { width: 78px; height: 92px; }
  .so__label { font-size: 10px; padding: 0 $sp-1; }
  .so__stamp { font-size: 9px; padding: 0 $sp-1; top: $sp-1; }
  .so__btn { width: 22px; height: 22px; font-size: 11px; bottom: $sp-1; }
  .so__btn--nope { left: $sp-1; }
  .so__btn--like { right: $sp-1; }
}

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

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

.so__caption {
  margin: 0;
  font-size: 12px;
  font-weight: 600;
  color: #17141a;
}

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

.so__card {
  position: relative;
  width: 160px;
  height: 180px;
  border-radius: 16px;
  background: linear-gradient(160deg, #fff7e6, #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;
  overflow: hidden;
}

.so__card:active {
  cursor: grabbing;
}

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

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

.so__stamp {
  position: absolute;
  top: 12px;
  border: 3px solid currentColor;
  border-radius: 4px;
  padding: 4px 8px;
  font-size: 13px;
  font-weight: 800;
  letter-spacing: 0.08em;
  opacity: 0;
  pointer-events: none;
}

.so__stamp--like {
  left: 12px;
  color: #4cd4a6;
  transform: rotate(-14deg);
}

.so__stamp--nope {
  right: 12px;
  color: #c2361a;
  transform: rotate(14deg);
}

.so__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;
}

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

.so__btn--like {
  right: 12px;
  color: #4cd4a6;
}

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

.so__status {
  margin: 0;
  font-size: 11px;
  color: #17141a;
  font-weight: 600;
}

@media (max-width: 340px) {
  .so {
    gap: 8px;
  }
  .so__scene {
    width: 150px;
    height: 108px;
  }
  .so__card {
    width: 78px;
    height: 92px;
  }
  .so__label {
    font-size: 10px;
    padding: 0 4px;
  }
  .so__stamp {
    font-size: 9px;
    padding: 0 4px;
    top: 4px;
  }
  .so__btn {
    width: 22px;
    height: 22px;
    font-size: 11px;
    bottom: 4px;
  }
  .so__btn--nope {
    left: 4px;
  }
  .so__btn--like {
    right: 4px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .so__card {
    transition: none;
  }
}

(function () {
  "use strict";

  // 값 하나: 드래그 거리를 STAMP_OPACITY_CURVE_POWER 승으로 매핑해 도장이 선형이 아니라
  // 중심 근처에선 느리게, 임계 근처에선 급하게 진해진다.
  var STAMP_OPACITY_CURVE_POWER = 2.4;
  var STAMP_RANGE_PX = 150;
  var RELEASE_VELOCITY_MIN = 0.38;
  var EXIT_PX = 320;
  var CYCLE_S = 2;

  var root = document.getElementById("so");
  var card = document.getElementById("soCard");
  var label = document.getElementById("soLabel");
  var like = document.getElementById("soLike");
  var nope = document.getElementById("soNope");
  var status = document.getElementById("soStatus");
  var btnLike = document.getElementById("soBtnLike");
  var btnNope = document.getElementById("soBtnNope");
  var reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

  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 = ["Travel notes", "Morning routine", "Evening walk", "Weekend café", "Home workout log", "Reading list"];
  var rand = seedRand(64);
  var idx = Math.floor(rand() * CARDS.length);

  var dragging = false;
  var startX = 0, lastX = 0, lastT = 0, vx = 0;
  var x = 0, phase = "idle", exitDir = 1;

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

  // 비선형 매핑: ratio^POWER — 중심 근처는 낮게 눌려 있다가 끝에서 급격히 1 로 치솟는다.
  function stampOpacity(px) {
    var ratio = clamp(Math.abs(px) / STAMP_RANGE_PX, 0, 1);
    return Math.pow(ratio, STAMP_OPACITY_CURVE_POWER);
  }

  function render() {
    var rot = clamp(x * 0.07, -18, 18);
    card.style.transform = "translateX(" + x.toFixed(1) + "px) rotate(" + rot.toFixed(2) + "deg)";
    var op = stampOpacity(x);
    like.style.opacity = x > 0 ? op.toFixed(3) : "0";
    nope.style.opacity = x < 0 ? op.toFixed(3) : "0";
  }

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

  function judge(velocity, dir) {
    root.classList.remove("is-demo");
    var flung = Math.abs(velocity) >= RELEASE_VELOCITY_MIN;
    if (reduce) {
      if (flung) { status.textContent = dir > 0 ? "Marked as liked" : "Marked as disliked"; nextCard(); }
      else { x = 0; render(); status.textContent = "Snapped back to center"; phase = "idle"; }
      return;
    }
    if (flung) { phase = "exit"; exitDir = dir; status.textContent = dir > 0 ? "Marked as liked" : "Marked as disliked"; }
    else { phase = "settle"; status.textContent = "Snapped back to center"; }
  }

  function startDrag(clientX) {
    root.classList.remove("is-demo");
    dragging = true; phase = "idle";
    startX = clientX; lastX = clientX; lastT = performance.now(); vx = 0;
  }
  function moveDrag(clientX) {
    if (!dragging) return;
    var now = performance.now();
    var dt = Math.max(now - lastT, 1);
    vx = (clientX - lastX) / dt;
    lastX = clientX; lastT = now;
    x = clientX - startX;
    render();
  }
  function endDrag() {
    if (!dragging) return;
    dragging = false;
    judge(vx, x >= 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) {
    root.classList.remove("is-demo");
    x = dir * 60; render();
    judge(dir * (RELEASE_VELOCITY_MIN + 0.3), dir);
  }
  card.addEventListener("keydown", function (e) {
    if (e.key === "ArrowRight") { e.preventDefault(); keyVerdict(1); }
    else if (e.key === "ArrowLeft") { e.preventDefault(); keyVerdict(-1); }
  });
  btnLike.addEventListener("click", function () { keyVerdict(1); });
  btnNope.addEventListener("click", function () { keyVerdict(-1); });

  function step(dt) {
    if (phase === "exit") {
      x += exitDir * Math.max(Math.abs(vx), RELEASE_VELOCITY_MIN * 1.4) * dt;
      render();
      if (Math.abs(x) > EXIT_PX) nextCard();
    } else if (phase === "settle") {
      x += (0 - x) * 0.22;
      render();
      if (Math.abs(x) < 0.4) { x = 0; phase = "idle"; render(); }
    }
  }

  // .is-demo 자동 시연: 실제 pointer 없이 x·judge() 를 같은 경로로 호출한다.
  var start = null, lastNow = 0, prevT = 0, synthPhase = "wait";
  function synth(t) {
    if (t > 0.4 && t < 0.7 && synthPhase === "wait") synthPhase = "peekLike";
    if (synthPhase === "peekLike") {
      var p = clamp((t - 0.4) / 0.3, 0, 1);
      x = p * 90; render();
      if (t >= 0.7) { synthPhase = "afterPeek"; judge(0.1, 1); }
    }
    if (t > 1.25 && t < 1.55 && synthPhase === "afterPeek") synthPhase = "commit";
    if (synthPhase === "commit") {
      var q = clamp((t - 1.25) / 0.3, 0, 1);
      x = -q * 150; render();
      if (t >= 1.55) { synthPhase = "done"; judge(-(RELEASE_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);
})();

// StampOpacityDragSwipeCard — vanilla 판(run/422/demo/05-swipe-deck-precision-stamp-opacity-drag/index.html) 의 React 포트.
// 값 하나: LIKE/NOPE 스탬프의 불투명도는 이동거리에 선형이 아니라
// (|px|/STAMP_RANGE_PX) 를 STAMP_OPACITY_CURVE_POWER 제곱한 값이다(초반은 거의 안 보이다 막판에 확 짙어짐).
import { useEffect, useRef, useState } from "react";
import type { PointerEvent as ReactPointerEvent } from "react";
import styles from "./StampOpacityDragSwipeCard.module.scss";

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

const STAMP_OPACITY_CURVE_POWER = 2.4;
const STAMP_RANGE_PX = 150;
const RELEASE_VELOCITY_MIN = 0.4;
const EXIT_PX = 320;
const CYCLE_S = 2;
const CARDS = ["아침 루틴", "저녁 산책", "주말 카페", "홈트 기록", "독서 목록", "여행 메모"];

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));
}
function stampOpacity(px: number): number {
  return Math.pow(clamp(Math.abs(px) / STAMP_RANGE_PX, 0, 1), STAMP_OPACITY_CURVE_POWER);
}

export default function StampOpacityDragSwipeCard() {
  const cardRef = useRef<HTMLDivElement | null>(null);
  const likeRef = useRef<HTMLSpanElement | null>(null);
  const nopeRef = useRef<HTMLSpanElement | 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(53)() * 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);

  function render(): void {
    const card = cardRef.current;
    const like = likeRef.current;
    const nope = nopeRef.current;
    if (!card || !like || !nope) return;
    const rot = clamp(posRef.current * 0.05, -16, 16);
    card.style.transform = "translateX(" + posRef.current.toFixed(1) + "px) rotate(" + rot.toFixed(2) + "deg)";
    const o = stampOpacity(posRef.current);
    if (posRef.current > 0) { like.style.opacity = o.toFixed(3); nope.style.opacity = "0"; }
    else { nope.style.opacity = o.toFixed(3); like.style.opacity = "0"; }
  }

  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(velocity: number, dir: number): void {
    setDemo(false);
    const flung = Math.abs(velocity) >= RELEASE_VELOCITY_MIN;
    if (reduce) {
      if (flung) { setStatus(dir > 0 ? "좋아요 처리됨" : "싫어요 처리됨"); nextCard(); }
      else { posRef.current = 0; render(); setStatus("제자리로 돌아옴"); phaseRef.current = "idle"; }
      return;
    }
    if (flung) {
      phaseRef.current = "exit"; exitDirRef.current = dir;
      setStatus(dir > 0 ? "좋아요 처리됨" : "싫어요 처리됨");
    } else {
      phaseRef.current = "settle";
      setStatus("제자리로 돌아옴");
    }
  }

  function startDrag(clientX: number): void {
    setDemo(false);
    draggingRef.current = true; phaseRef.current = "idle";
    startXRef.current = clientX; lastXRef.current = clientX; lastTRef.current = performance.now(); velRef.current = 0;
  }
  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;
    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, 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): void {
    setDemo(false);
    posRef.current = dir * 40; render();
    judge(dir * (RELEASE_VELOCITY_MIN + 0.2), dir);
  }
  function onKeyDown(e: any): void {
    if (e.key === "ArrowRight") { e.preventDefault(); keyVerdict(1); }
    else if (e.key === "ArrowLeft") { e.preventDefault(); keyVerdict(-1); }
  }

  function step(dt: number): void {
    if (phaseRef.current === "exit") {
      const speed = Math.max(Math.abs(velRef.current), RELEASE_VELOCITY_MIN * 1.4);
      posRef.current += exitDirRef.current * speed * dt;
      render();
      if (Math.abs(posRef.current) > EXIT_PX) nextCard();
    } else if (phaseRef.current === "settle") {
      posRef.current += (0 - posRef.current) * 0.22;
      render();
      if (Math.abs(posRef.current) < 0.5) { posRef.current = 0; phaseRef.current = "idle"; render(); }
    }
  }

  function synth(t: number, synthPhaseRef: Box<string>): void {
    if (t > 0.4 && t < 0.75 && synthPhaseRef.current === "wait") synthPhaseRef.current = "toLike";
    if (synthPhaseRef.current === "toLike") {
      const p = clamp((t - 0.4) / 0.35, 0, 1);
      posRef.current = p * 130; render();
      if (t >= 0.75) { synthPhaseRef.current = "afterLike"; judge(RELEASE_VELOCITY_MIN + 0.3, 1); }
    }
    if (t > 1.3 && t < 1.65 && synthPhaseRef.current === "afterLike") synthPhaseRef.current = "toNope";
    if (synthPhaseRef.current === "toNope") {
      const q = clamp((t - 1.3) / 0.35, 0, 1);
      posRef.current = -q * 130; render();
      if (t >= 1.65) { synthPhaseRef.current = "done"; judge(-(RELEASE_VELOCITY_MIN + 0.3), -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.so}>
        <p className={styles.caption}>제곱 곡선으로 짙어지는 판정 스탬프</p>
        <div className={styles.scene}>
          <div
            className={styles.card}
            ref={cardRef}
            tabIndex={0}
            role="group"
            aria-roledescription="스와이프 카드"
            onPointerDown={onPointerDown}
            onPointerMove={onPointerMove}
            onPointerUp={onPointerUp}
            onKeyDown={onKeyDown}
          >
            <span className={styles.stampLike} ref={likeRef} aria-hidden="true">LIKE</span>
            <span className={styles.stampNope} ref={nopeRef} aria-hidden="true">NOPE</span>
            <p className={styles.label}>{label}</p>
          </div>
          <button className={styles.btnNope} type="button" aria-label="싫어요" onClick={() => keyVerdict(-1)}>✕</button>
          <button className={styles.btnLike} type="button" aria-label="좋아요" onClick={() => keyVerdict(1)}>♥</button>
        </div>
        <p className={styles.status} aria-live="polite">{status}</p>
      </div>
    </main>
  );
}