03이전 위치와의 거리를 계산해 미끄러지는 정렬 전환

<main class="stage">
<div class="srt is-demo" id="srtRoot">
  <div class="srt__head">
    <button type="button" class="srt__sortBtn" id="srtSortBtn" aria-pressed="false">
      <svg class="srt__sortIcon" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M176 48v160H80V48Z" opacity=".2"/><path d="M117.66 170.34a8 8 0 0 1 0 11.32l-32 32a8 8 0 0 1-11.32 0l-32-32a8 8 0 0 1 11.32-11.32L72 188.69V48a8 8 0 0 1 16 0v140.69l18.34-18.35a8 8 0 0 1 11.32 0m96-96l-32-32a8 8 0 0 0-11.32 0l-32 32a8 8 0 0 0 11.32 11.32L168 67.31V208a8 8 0 0 0 16 0V67.31l18.34 18.35a8 8 0 0 0 11.32-11.32"/></g></svg>
      <span class="srt__sortLabel" id="srtSortLabel">최신순</span>
    </button>
  </div>
  <ul class="srt__list" role="list" id="srtList">
    <li class="srt__item" data-id="c1" data-likes="12">
      <span class="srt__avatar" aria-hidden="true"></span>
      <div class="srt__body">
        <p class="srt__meta"><strong class="srt__name">하늘연필</strong><span class="srt__time">방금</span></p>
        <p class="srt__text">정리 잘 되어있네요.</p>
      </div>
      <span class="srt__likes">♥ 12</span>
    </li>
    <li class="srt__item" data-id="c2" data-likes="41">
      <span class="srt__avatar" aria-hidden="true"></span>
      <div class="srt__body">
        <p class="srt__meta"><strong class="srt__name">노을풍경</strong><span class="srt__time">3분 전</span></p>
        <p class="srt__text">코드 그대로 써도 되나요?</p>
      </div>
      <span class="srt__likes">♥ 41</span>
    </li>
    <li class="srt__item" data-id="c3" data-likes="7">
      <span class="srt__avatar" aria-hidden="true"></span>
      <div class="srt__body">
        <p class="srt__meta"><strong class="srt__name">초록달빛</strong><span class="srt__time">9분 전</span></p>
        <p class="srt__text">감사합니다, 큰 도움 됐어요.</p>
      </div>
      <span class="srt__likes">♥ 7</span>
    </li>
    <li class="srt__item" data-id="c4" data-likes="25">
      <span class="srt__avatar" aria-hidden="true"></span>
      <div class="srt__body">
        <p class="srt__meta"><strong class="srt__name">바람소리</strong><span class="srt__time">22분 전</span></p>
        <p class="srt__text">다음 편도 기대할게요.</p>
      </div>
      <span class="srt__likes">♥ 25</span>
    </li>
    <li class="srt__item" data-id="c5" data-likes="3">
      <span class="srt__avatar" aria-hidden="true"></span>
      <div class="srt__body">
        <p class="srt__meta"><strong class="srt__name">모래시계</strong><span class="srt__time">41분 전</span></p>
        <p class="srt__text">이 부분 설명 최고예요.</p>
      </div>
      <span class="srt__likes">♥ 3</span>
    </li>
  </ul>
  <p class="srt__sr" id="srtStatus" aria-live="polite"></p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-ink);

.srt {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $tick-panel;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  box-sizing: border-box;
  padding: $sp-4;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
}

.srt__head {
  display: flex;
  justify-content: flex-end;
}

.srt__sortBtn {
  display: inline-flex;
  align-items: center;
  gap: $sp-1;
  border: 0;
  background: rgba(255, 255, 255, .07);
  color: $subject-blue-light;
  font-size: 11.5px;
  font-weight: 600;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  cursor: pointer;
}

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

.srt__sortIcon { width: 13px; height: 13px; }

.srt__list {
  position: relative;
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
  flex: 1;
}

.srt__item {
  display: flex;
  align-items: flex-start;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
  background: rgba(255, 255, 255, .05);
  border-radius: $r-sm;
  will-change: transform;
}

.srt__avatar {
  flex: none;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: linear-gradient(160deg, $subject-mint, $subject-sky);
  margin-top: 4px;
}

.srt__body { min-width: 0; flex: 1; }
.srt__meta { margin: 0 0 4px; display: flex; align-items: baseline; gap: $sp-2; }
.srt__name { color: #fff; font-size: 12px; font-weight: 700; }
.srt__time { color: rgba(255, 255, 255, .5); font-size: 10.5px; }
.srt__text { margin: 0; color: rgba(255, 255, 255, .86); font-size: 12px; line-height: 1.5; }

.srt__likes {
  flex: none;
  color: $subject-pink;
  font-size: 11px;
  font-weight: 600;
  white-space: nowrap;
}

.srt__sr {
  position: absolute;
  width: 1px; height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

@media (max-width: 340px) {
  .srt { padding: $sp-3; }
  .srt__text, .srt__name { font-size: 11px; }
}

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

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);
}

.srt {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #231f28;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  box-sizing: border-box;
  padding: 16px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.srt__head {
  display: flex;
  justify-content: flex-end;
}

.srt__sortBtn {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  border: 0;
  background: rgba(255, 255, 255, 0.07);
  color: #5b8cf8;
  font-size: 11.5px;
  font-weight: 600;
  padding: 4px 12px;
  border-radius: 999px;
  cursor: pointer;
}

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

.srt__sortIcon {
  width: 13px;
  height: 13px;
}

.srt__list {
  position: relative;
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 8px;
  flex: 1;
}

.srt__item {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  padding: 8px 12px;
  background: rgba(255, 255, 255, 0.05);
  border-radius: 8px;
  will-change: transform;
}

.srt__avatar {
  flex: none;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: linear-gradient(160deg, #4cd4a6, #6ec8ff);
  margin-top: 2px;
}

.srt__body {
  min-width: 0;
  flex: 1;
}

.srt__meta {
  margin: 0 0 2px;
  display: flex;
  align-items: baseline;
  gap: 8px;
}

.srt__name {
  color: #fff;
  font-size: 12px;
  font-weight: 700;
}

.srt__time {
  color: rgba(255, 255, 255, 0.5);
  font-size: 10.5px;
}

.srt__text {
  margin: 0;
  color: rgba(255, 255, 255, 0.86);
  font-size: 12px;
  line-height: 1.5;
}

.srt__likes {
  flex: none;
  color: #ff9ebb;
  font-size: 11px;
  font-weight: 600;
  white-space: nowrap;
}

.srt__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

@media (max-width: 340px) {
  .srt {
    padding: 12px;
  }
  .srt__text, .srt__name {
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .srt__item {
    transition: none !important;
  }
}

(function () {
  // 기법: FLIP(First-Last-Invert-Play). 정렬 기준을 바꾸기 전 각 항목의 getBoundingClientRect
  // 를 기록(First)하고, DOM 순서를 새 정렬로 바로 바꾼 뒤(Last, 레이아웃은 이 한 번만 재계산)
  // 다시 rect 를 재서 두 값의 차이(Invert)를 transform 으로 되돌려 놓았다가 0 으로 애니메이션
  // (Play)한다. 실제로는 항상 최종 DOM 위치에 있고, 눈에 보이는 "이동"은 transform 뿐이다.
  var SORT_FLIP_DURATION_MS = 320;

  var root = document.getElementById('srtRoot');
  var list = document.getElementById('srtList');
  var sortBtn = document.getElementById('srtSortBtn');
  var sortLabel = document.getElementById('srtSortLabel');
  var status = document.getElementById('srtStatus');

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (reduce) root.classList.remove('is-demo');

  var byNewestOrder = ['c1', 'c2', 'c3', 'c4', 'c5'];
  var popular = false;

  function sortedIds() {
    if (!popular) return byNewestOrder.slice();
    var items = list.querySelectorAll('.srt__item');
    var arr = [];
    for (var i = 0; i < items.length; i += 1) arr.push(items[i]);
    arr.sort(function (a, b) { return parseInt(b.getAttribute('data-likes'), 10) - parseInt(a.getAttribute('data-likes'), 10); });
    return arr.map(function (el) { return el.getAttribute('data-id'); });
  }

  function applySort(animate, delayMs) {
    var items = list.querySelectorAll('.srt__item');
    var before = {};
    for (var i = 0; i < items.length; i += 1) {
      before[items[i].getAttribute('data-id')] = items[i].getBoundingClientRect();
    }

    var order = sortedIds();
    var byId = {};
    for (var j = 0; j < items.length; j += 1) byId[items[j].getAttribute('data-id')] = items[j];
    for (var k = 0; k < order.length; k += 1) list.appendChild(byId[order[k]]);

    if (!animate || reduce) return;

    for (var m = 0; m < order.length; m += 1) {
      var el = byId[order[m]];
      var after = el.getBoundingClientRect();
      var b = before[order[m]];
      var dy = b.top - after.top;
      if (Math.abs(dy) < 0.5) continue;
      var sideX = (m % 2 === 0 ? 1 : -1) * Math.min(14, Math.abs(dy) * 0.12);
      el.style.zIndex = String(10 - m);
      el.animate(
        [
          { transform: 'translate(0px,' + dy + 'px)' },
          { transform: 'translate(' + sideX + 'px,' + (dy * 0.4) + 'px)' },
          { transform: 'translate(0px,0px)' }
        ],
        { duration: SORT_FLIP_DURATION_MS, delay: delayMs || 0, easing: 'cubic-bezier(.2,.7,.2,1)', fill: 'both' }
      );
    }
  }

  function setPopular(next, animate, delayMs) {
    popular = next;
    sortBtn.setAttribute('aria-pressed', String(popular));
    sortLabel.textContent = popular ? '인기순' : '최신순';
    status.textContent = popular ? '좋아요 많은 순으로 정렬했습니다.' : '최신 순으로 정렬했습니다.';
    applySort(animate, delayMs);
  }

  sortBtn.addEventListener('click', function () {
    root.classList.remove('is-demo');
    setPopular(!popular, true, 0);
  });
  sortBtn.addEventListener('keydown', function (e) {
    if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); sortBtn.click(); }
  });

  var seqTimer = null;
  function playSequence() {
    if (seqTimer) { window.clearTimeout(seqTimer); seqTimer = null; }
    setPopular(false, false, 0);
    setPopular(true, true, 240);
    seqTimer = window.setTimeout(function () {
      setPopular(false, true, 0);
    }, 1080);
  }

  if (reduce) {
    setPopular(false, false, 0);
  } else {
    playSequence();
    window.setInterval(function () {
      if (!root.classList.contains('is-demo')) return;
      setPopular(!popular, true, 0);
    }, 2400);
  }
})();

import { useEffect, useRef } from "react";
import styles from "./CommentThreadSortReorderFlip.module.scss";

// 기법: FLIP(First-Last-Invert-Play). 정렬 기준을 바꾸기 전 각 항목의 rect 를 기록(First)하고
// DOM 순서를 새 정렬로 바로 바꾼 뒤(Last) 다시 rect 를 재서 차이(Invert)를 transform 으로
// 되돌렸다가 0 으로 애니메이션(Play)한다.
const SORT_FLIP_DURATION_MS = 320;

const NEWEST_ORDER = ["c1", "c2", "c3", "c4", "c5"];
const LIKES: Record<string, number> = { c1: 12, c2: 41, c3: 7, c4: 25, c5: 3 };

export default function CommentThreadSortReorderFlip() {
  const rootRef = useRef<HTMLDivElement>(null);
  const listRef = useRef<HTMLUListElement>(null);
  const sortBtnRef = useRef<HTMLButtonElement>(null);
  const sortLabelRef = useRef<HTMLSpanElement>(null);
  const statusRef = useRef<HTMLParagraphElement>(null);
  const itemRefs = useRef<Record<string, HTMLLIElement | null>>({});

  useEffect(() => {
    const root = rootRef.current;
    const list = listRef.current;
    const sortBtn = sortBtnRef.current;
    const sortLabel = sortLabelRef.current;
    const status = statusRef.current;
    if (!root || !list || !sortBtn || !sortLabel || !status) return;

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (reduce) root.classList.remove("is-demo");

    let popular = false;

    function sortedIds(): string[] {
      if (!popular) return NEWEST_ORDER.slice();
      return NEWEST_ORDER.slice().sort((a, b) => LIKES[b] - LIKES[a]);
    }

    function applySort(animate: boolean, delayMs: number) {
      const refs = itemRefs.current!;
      const ids = NEWEST_ORDER;
      const before: Record<string, DOMRect> = {};
      for (const id of ids) {
        const el = refs[id];
        if (el) before[id] = el.getBoundingClientRect();
      }

      const order = sortedIds();
      for (const id of order) {
        const el = refs[id];
        if (el) list!.appendChild(el);
      }

      if (!animate || reduce) return;

      order.forEach((id, m) => {
        const el = refs[id];
        if (!el) return;
        const after = el.getBoundingClientRect();
        const b = before[id];
        const dy = b.top - after.top;
        if (Math.abs(dy) < 0.5) return;
        const sideX = (m % 2 === 0 ? 1 : -1) * Math.min(14, Math.abs(dy) * 0.12);
        el.style.zIndex = String(10 - m);
        el.animate(
          [
            { transform: `translate(0px,${dy}px)` },
            { transform: `translate(${sideX}px,${dy * 0.4}px)` },
            { transform: "translate(0px,0px)" },
          ],
          { duration: SORT_FLIP_DURATION_MS, delay: delayMs, easing: "cubic-bezier(.2,.7,.2,1)", fill: "both" }
        );
      });
    }

    function setPopular(next: boolean, animate: boolean, delayMs: number) {
      popular = next;
      sortBtn!.setAttribute("aria-pressed", String(popular));
      sortLabel!.textContent = popular ? "인기순" : "최신순";
      status!.textContent = popular ? "좋아요 많은 순으로 정렬했습니다." : "최신 순으로 정렬했습니다.";
      applySort(animate, delayMs);
    }

    const onActivate = () => { root.classList.remove("is-demo"); setPopular(!popular, true, 0); };
    sortBtn.addEventListener("click", onActivate);
    sortBtn.addEventListener("keydown", (e) => {
      if (e.key === "Enter" || e.key === " ") { e.preventDefault(); onActivate(); }
    });

    let seqTimer: number | undefined;
    function playSequence() {
      if (seqTimer) { window.clearTimeout(seqTimer); seqTimer = undefined; }
      setPopular(false, false, 0);
      setPopular(true, true, 240);
      seqTimer = window.setTimeout(() => { setPopular(false, true, 0); }, 1080);
    }

    let timer: number | undefined;
    if (reduce) {
      setPopular(false, false, 0);
    } else {
      playSequence();
      timer = window.setInterval(() => {
        if (!root.classList.contains("is-demo")) return;
        setPopular(!popular, true, 0);
      }, 2400);
    }

    return () => { if (timer) window.clearInterval(timer); if (seqTimer) window.clearTimeout(seqTimer); };
  }, []);

  const comments = [
    { id: "c1", name: "하늘연필", time: "방금", text: "정리 잘 되어있네요.", likes: 12 },
    { id: "c2", name: "노을풍경", time: "3분 전", text: "코드 그대로 써도 되나요?", likes: 41 },
    { id: "c3", name: "초록달빛", time: "9분 전", text: "감사합니다, 큰 도움 됐어요.", likes: 7 },
    { id: "c4", name: "바람소리", time: "22분 전", text: "다음 편도 기대할게요.", likes: 25 },
    { id: "c5", name: "모래시계", time: "41분 전", text: "이 부분 설명 최고예요.", likes: 3 },
  ];

  return (
    <main className={styles.stage}>
      <div className={`${styles.srt} is-demo`} ref={rootRef}>
        <div className={styles.srt__head}>
          <button type="button" className={styles.srt__sortBtn} ref={sortBtnRef} aria-pressed="false">
            <svg className={styles.srt__sortIcon} viewBox="0 0 256 256" aria-hidden="true">
              <g fill="currentColor">
                <path d="M176 48v160H80V48Z" opacity=".2" />
                <path d="M117.66 170.34a8 8 0 0 1 0 11.32l-32 32a8 8 0 0 1-11.32 0l-32-32a8 8 0 0 1 11.32-11.32L72 188.69V48a8 8 0 0 1 16 0v140.69l18.34-18.35a8 8 0 0 1 11.32 0m96-96l-32-32a8 8 0 0 0-11.32 0l-32 32a8 8 0 0 0 11.32 11.32L168 67.31V208a8 8 0 0 0 16 0V67.31l18.34 18.35a8 8 0 0 0 11.32-11.32" />
              </g>
            </svg>
            <span className={styles.srt__sortLabel} ref={sortLabelRef}>최신순</span>
          </button>
        </div>
        <ul className={styles.srt__list} role="list" ref={listRef}>
          {comments.map((c) => (
            <li
              key={c.id}
              className={styles.srt__item}
              data-id={c.id}
              data-likes={c.likes}
              ref={(el: HTMLLIElement | null) => { itemRefs.current![c.id] = el; }}
            >
              <span className={styles.srt__avatar} aria-hidden="true" />
              <div className={styles.srt__body}>
                <p className={styles.srt__meta}>
                  <strong className={styles.srt__name}>{c.name}</strong>
                  <span className={styles.srt__time}>{c.time}</span>
                </p>
                <p className={styles.srt__text}>{c.text}</p>
              </div>
              <span className={styles.srt__likes}>♥ {c.likes}</span>
            </li>
          ))}
        </ul>
        <p className={styles.srt__sr} ref={statusRef} aria-live="polite" />
      </div>
    </main>
  );
}