04낙관적 좋아요(즉시+되돌림)

<main class="stage">
  <button class="like is-demo" type="button" aria-pressed="false" aria-label="좋아요">
    <span class="like__icon" aria-hidden="true">
      <span class="like__heart like__heart--base"></span>
      <span class="like__heart like__heart--fill"></span>
    </span>
    <span class="like__count" aria-hidden="true">
      <span class="like__count-track">
        <span class="like__count-num">12</span>
        <span class="like__count-num">13</span>
      </span>
    </span>
  </button>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-quick;                              // 하트가 차오르는 시간
$easing: $ease-pop;                                 // 팝업 이징
$color: $subject-blue;                              // 좋아요 강조색

// ── 데모 무대 ──────────────────────────────────────────
@include stage($stage-paper);

@mixin heart-shape {
  content: "";
  position: absolute;
  top: 0;
  width: 50%;
  height: 80%;
  border-radius: 50% 50% 0 0;
  background: currentColor;
}

.like {
  display: inline-flex;
  align-items: center;
  gap: clamp(8px, 2.6vw, 12px);
  border: 0;
  border-radius: $r-pill;
  padding: clamp(12px, 4vw, 16px) clamp(20px, 6vw, 26px);
  font-weight: 700;
  font-size: clamp(15px, 4.2vw, 19px);
  line-height: 1;
  font-family: inherit;
  color: $stage-ink;
  background: $subject-cream;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;

  &__icon { position: relative; width: 22px; height: 20px; flex: none; color: $stage-ink; }

  &__heart {
    position: absolute; inset: 0;
    transform: scale(1);
    &::before { @include heart-shape; left: 50%; transform: rotate(-45deg); transform-origin: 0 100%; } // 규칙8: 하트 로브 꼭짓점 조형
    &::after  { @include heart-shape; left: 0; transform: rotate(45deg); transform-origin: 100% 100%; } // 규칙8: 하트 로브 꼭짓점 조형
  }
  &__heart--base { opacity: .28; }
  &__heart--fill {
    color: $color;
    opacity: 0;
    transform: scale(.5);
    transition: opacity $duration $easing, transform $duration $easing;
  }

  &__count { position: relative; height: 1em; overflow: hidden; }
  &__count-track {
    display: flex;
    flex-direction: column;
    transform: translateY(0);
    transition: transform $duration $easing;
  }
  &__count-num { height: 1em; line-height: 1; }

  &.is-liked &__heart--fill { opacity: 1; transform: scale(1); }
  &.is-liked &__count-track { transform: translateY(-50%); }

  &.is-demo &__heart--fill { animation: fill-loop $dur-loop $easing infinite; }
  &.is-demo &__count-track { animation: count-loop $dur-loop $easing infinite; }
}

@keyframes fill-loop {
  0%, 20%  { opacity: 0; transform: scale(.5); }
  35%, 60% { opacity: 1; transform: scale(1); }
  80%, 100% { opacity: 0; transform: scale(.5); }
}
@keyframes count-loop {
  0%, 20%  { transform: translateY(0); }
  35%, 60% { transform: translateY(-50%); }
  80%, 100% { transform: translateY(0); }
}

// ── 접근성: 움직임 줄이기 설정이면 순간 전환만, 롤백 상태는 유지 ────
@media (prefers-reduced-motion: reduce) {
  .like__heart--fill, .like__count-track { transition: none; }
  .like.is-demo .like__heart--fill,
  .like.is-demo .like__count-track { animation: none !important; }
}

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);
}

.like {
  display: inline-flex;
  align-items: center;
  gap: clamp(8px, 2.6vw, 12px);
  border: 0;
  border-radius: 999px;
  padding: clamp(12px, 4vw, 16px) clamp(20px, 6vw, 26px);
  font-weight: 700;
  font-size: clamp(15px, 4.2vw, 19px);
  line-height: 1;
  font-family: inherit;
  color: #17141a;
  background: #fff7e6;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}
.like__icon {
  position: relative;
  width: 22px;
  height: 20px;
  flex: none;
  color: #17141a;
}
.like__heart {
  position: absolute;
  inset: 0;
  transform: scale(1);
}
.like__heart::before {
  content: "";
  position: absolute;
  top: 0;
  width: 50%;
  height: 80%;
  border-radius: 50% 50% 0 0;
  background: currentColor;
  left: 50%;
  transform: rotate(-45deg);
  transform-origin: 0 100%;
}
.like__heart::after {
  content: "";
  position: absolute;
  top: 0;
  width: 50%;
  height: 80%;
  border-radius: 50% 50% 0 0;
  background: currentColor;
  left: 0;
  transform: rotate(45deg);
  transform-origin: 100% 100%;
}
.like__heart--base {
  opacity: 0.28;
}
.like__heart--fill {
  color: #2f6df6;
  opacity: 0;
  transform: scale(0.5);
  transition: opacity 220ms cubic-bezier(0.2, 1.4, 0.4, 1), transform 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}
.like__count {
  position: relative;
  height: 1em;
  overflow: hidden;
}
.like__count-track {
  display: flex;
  flex-direction: column;
  transform: translateY(0);
  transition: transform 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}
.like__count-num {
  height: 1em;
  line-height: 1;
}
.like.is-liked .like__heart--fill {
  opacity: 1;
  transform: scale(1);
}
.like.is-liked .like__count-track {
  transform: translateY(-50%);
}
.like.is-demo .like__heart--fill {
  animation: fill-loop 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}
.like.is-demo .like__count-track {
  animation: count-loop 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

@keyframes fill-loop {
  0%, 20% {
    opacity: 0;
    transform: scale(0.5);
  }
  35%, 60% {
    opacity: 1;
    transform: scale(1);
  }
  80%, 100% {
    opacity: 0;
    transform: scale(0.5);
  }
}
@keyframes count-loop {
  0%, 20% {
    transform: translateY(0);
  }
  35%, 60% {
    transform: translateY(-50%);
  }
  80%, 100% {
    transform: translateY(0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .like__heart--fill, .like__count-track {
    transition: none;
  }
  .like.is-demo .like__heart--fill,
  .like.is-demo .like__count-track {
    animation: none !important;
  }
}

// 실제 클릭: 서버 응답 없이 즉시 좋아요 표시 → 0.8초 뒤 실패했다고 가정하고 되돌린다.
var b = document.querySelector('.like');
b.addEventListener('click', function () {
  b.classList.remove('is-demo');
  var liked = b.classList.toggle('is-liked');
  b.setAttribute('aria-pressed', liked);
  if (liked) setTimeout(function () { b.classList.remove('is-liked'); b.setAttribute('aria-pressed', 'false'); }, 800);
});

import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./OptimisticLikeButton.module.scss";

export type OptimisticLikeButtonProps = {
  count: number;
  ariaLabel: string;
  /** 낙관적 업데이트가 유지되는 시간 — 이후 실패로 가정하고 롤백 (기본 800ms) */
  rollbackAfter?: number;
  duration?: number;
  easing?: string;
  color?: string;
  /** 실제로는 여기서 서버에 요청을 보내고, 실패하면 되돌린다 */
  onToggle?: (liked: boolean) => Promise<boolean>;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

export default function OptimisticLikeButton({
  count,
  ariaLabel,
  rollbackAfter = 800,
  duration = 220,
  easing = "cubic-bezier(.2,1.4,.4,1)",
  color = "#2f6df6",
  onToggle,
}: OptimisticLikeButtonProps) {
  const [liked, setLiked] = useState(false);
  const timer = useRef<ReturnType<typeof setTimeout> | null>(null);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  useEffect(() => () => { if (timer.current) clearTimeout(timer.current); }, []);

  const handle = async () => {
    setLiked(true); // 서버 응답을 기다리지 않고 즉시 반영
    const ok = onToggle ? await onToggle(true) : false;
    if (!ok) timer.current = setTimeout(() => setLiked(false), rollbackAfter);
  };

  return (
    <button
      type="button"
      className={liked ? `${styles.like} ${styles.liked}` : styles.like}
      style={vars}
      aria-pressed={liked}
      aria-label={ariaLabel}
      onClick={handle}
    >
      <span className={styles.icon} aria-hidden="true">
        <span className={`${styles.heart} ${styles.base}`} />
        <span className={`${styles.heart} ${styles.fill}`} />
      </span>
      <span className={styles.count} aria-hidden="true">
        <span className={styles.track}>
          <span className={styles.num}>{count}</span>
          <span className={styles.num}>{count + 1}</span>
        </span>
      </span>
    </button>
  );
}