04Waiting List That Springs Into Place by a Calculated Shift Distance

<main class="stage">
<div class="wls is-demo" id="wlsRoot">
  <ul class="wls__list" role="list" id="wlsList">
    <li class="wls__item is-next" data-id="d1">
      <span class="wls__ticket">101</span>
      <span class="wls__note">3 min waiting</span>
    </li>
    <li class="wls__item" data-id="d2">
      <span class="wls__ticket">102</span>
      <span class="wls__note">9 min waiting</span>
    </li>
    <li class="wls__item" data-id="d3">
      <span class="wls__ticket">103</span>
      <span class="wls__note">14 min waiting</span>
    </li>
    <li class="wls__item" data-id="d4">
      <span class="wls__ticket">104</span>
      <span class="wls__note">18 min waiting</span>
    </li>
    <li class="wls__item" data-id="d5">
      <span class="wls__ticket">105</span>
      <span class="wls__note">22 min waiting</span>
    </li>
  </ul>
  <div class="wls__controls">
    <button type="button" class="wls__btn" id="wlsReset">Undo</button>
    <button type="button" class="wls__btn wls__btn--primary" id="wlsCallBtn">Served</button>
  </div>
  <p class="wls__status" id="wlsStatus" aria-live="polite"></p>
</div>
</main>

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

// 핵심: 앞 순번이 빠지면 아래 행들이 이동할 거리(gap)를 실측해 스프링 감쇠로 자리를 메운다.
// 새로 맨 앞이 된 행은 is-next 로 계산되어 살짝 커지고 테두리가 강조된다.

@include stage($stage-paper);

.wls {
  position: relative;
  display: grid;
  gap: $sp-3;
  justify-items: center;
  width: min(92vw, 320px);
}

.wls__list {
  width: 100%;
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
}

.wls__item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
  border-radius: $r-sm;
  background: rgba($stage-ink, .05);
  transform-origin: left center;
}

.wls__item.is-next {
  background: rgba($subject-blue-deep, .12);
  outline: 1.5px solid $subject-blue-deep;
  transform: scale(1.03);
}

.wls__ticket {
  font-size: 15px;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  color: $stage-ink;
}

.wls__note {
  font-size: 11px;
  font-weight: 600;
  color: rgba($stage-ink, .55);
}

.wls__controls {
  display: flex;
  gap: $sp-2;
}

.wls__btn {
  border: 1px solid rgba($stage-ink, .25);
  background: transparent;
  color: $stage-ink;
  border-radius: $r-control;
  padding: $sp-2 $sp-4;
  font-size: 12px;
  font-weight: 600;
  cursor: pointer;
}

.wls__btn--primary {
  background: $subject-blue-deep;
  border-color: $subject-blue-deep;
  color: $stage-paper;
}

.wls__btn:disabled { opacity: .4; cursor: default; }

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

.wls__status {
  margin: 0;
  font-size: 11px;
  font-weight: 600;
  color: rgba($stage-ink, .6);
}

@media (max-width: 340px) {
  .wls__ticket { font-size: 13px; }
  .wls__note { font-size: 10px; }
}

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

// 화면 높이가 낮을 때 줄을 촘촘하게 — 예고 없이 스크롤바가 생기지 않게 한다.
.wls__list { gap: $sp-1; }
.wls__item { padding-top: $sp-1; padding-bottom: $sp-1; }

@media (max-height: 240px) {
  .wls { gap: $sp-2; }
  .wls__item { padding-top: 0; padding-bottom: 0; min-height: 24px; }
  .wls__status { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); }
  .wls__btn { padding-top: $sp-1; padding-bottom: $sp-1; }
}

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);
}

.wls {
  position: relative;
  display: grid;
  gap: 12px;
  justify-items: center;
  width: min(92vw, 320px);
}

.wls__list {
  width: 100%;
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.wls__item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  padding: 8px 12px;
  border-radius: 8px;
  background: rgba(23, 20, 26, 0.05);
  transform-origin: left center;
}

.wls__item.is-next {
  background: rgba(10, 79, 232, 0.12);
  outline: 1.5px solid #0a4fe8;
  transform: scale(1.03);
}

.wls__ticket {
  font-size: 15px;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  color: #17141a;
}

.wls__note {
  font-size: 11px;
  font-weight: 600;
  color: rgba(23, 20, 26, 0.55);
}

.wls__controls {
  display: flex;
  gap: 8px;
}

.wls__btn {
  border: 1px solid rgba(23, 20, 26, 0.25);
  background: transparent;
  color: #17141a;
  border-radius: 12px;
  padding: 8px 16px;
  font-size: 12px;
  font-weight: 600;
  cursor: pointer;
}

.wls__btn--primary {
  background: #0a4fe8;
  border-color: #0a4fe8;
  color: #ffffff;
}

.wls__btn:disabled {
  opacity: 0.4;
  cursor: default;
}

.wls__btn:focus-visible {
  outline: 2px solid #0a4fe8;
  outline-offset: 2px;
}

.wls__status {
  margin: 0;
  font-size: 11px;
  font-weight: 600;
  color: rgba(23, 20, 26, 0.6);
}

@media (max-width: 340px) {
  .wls__ticket {
    font-size: 13px;
  }
  .wls__note {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .wls__item {
    transition: none;
  }
}
.wls__list {
  gap: 4px;
}

.wls__item {
  padding-top: 4px;
  padding-bottom: 4px;
}

@media (max-height: 240px) {
  .wls {
    gap: 8px;
  }
  .wls__item {
    padding-top: 0;
    padding-bottom: 0;
    min-height: 24px;
  }
  .wls__status {
    position: absolute;
    width: 1px;
    height: 1px;
    overflow: hidden;
    clip: rect(0 0 0 0);
  }
  .wls__btn {
    padding-top: 4px;
    padding-bottom: 4px;
  }
}

(function () {
  // 기법: 맨 앞 순번이 빠지면 그 행의 높이를 실측해 0 으로 접고, 아래 행들은 접힌 높이만큼
  // 위로 이동할 거리를 First/Last 로 계산해 스프링 감쇠(LIST_SHIFT_SPRING_STIFFNESS)로 되돌아온다.
  // 이동이 끝난 새 맨 앞 행에는 is-next 를 계산해 붙여 살짝 커지게 한다.
  var LIST_SHIFT_SPRING_STIFFNESS = 260;
  var SPRING_SETTLE_EASING = 'linear(0.0, 0.051, 0.176, 0.341, 0.518, 0.685, 0.831, 0.947, 1.032, 1.087, 1.117, 1.126, 1.121, 1.105, 1.085, 1.062, 1.041, 1.022, 1.008, 0.997, 1)';

  var ORDER = ['d1', 'd2', 'd3', 'd4', 'd5'];

  var root = document.getElementById('wlsRoot');
  var list = document.getElementById('wlsList');
  var status = document.getElementById('wlsStatus');

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

  var frontIndex = 0;

  function shiftDuration(gapPx) {
    return Math.round(60 + 100000 / LIST_SHIFT_SPRING_STIFFNESS + Math.min(240, gapPx * 0.55));
  }

  function visibleRows() {
    var all = list.querySelectorAll('.wls__item');
    var vis = [];
    for (var i = 0; i < all.length; i += 1) {
      if (all[i].getBoundingClientRect().height > 0 && all[i].style.display !== 'none') vis.push(all[i]);
    }
    return vis;
  }

  function callFront() {
    if (frontIndex >= ORDER.length) { status.textContent = 'The waiting list is empty.'; return; }
    var id = ORDER[frontIndex];
    var row = list.querySelector('.wls__item[data-id="' + id + '"]');
    if (!row) return;
    var ticket = row.querySelector('.wls__ticket').textContent;
    row.classList.remove('is-next');

    var below = visibleRows().filter(function (el) { return el !== row; });
    var before = below.map(function (el) { return el.getBoundingClientRect().top; });
    var gap = row.offsetHeight + 8;

    if (reduce) {
      row.style.display = 'none';
    } else {
      var h = row.offsetHeight;
      row.style.height = h + 'px';
      row.style.overflow = 'hidden';
      row.style.boxSizing = 'border-box';
      row.style.marginTop = '0px';
      row.style.marginBottom = '0px';
      row.animate(
        [{ height: h + 'px', opacity: 1 }, { height: '0px', opacity: 0 }],
        { duration: 220, easing: 'ease-in', fill: 'forwards' }
      ).onfinish = function () { row.style.display = 'none'; };

      var dur = shiftDuration(gap);
      below.forEach(function (el, i) {
        el.animate(
          [
            { transform: 'translateY(0px)' },
            { transform: 'translateY(' + gap + 'px)' },
            { transform: 'translateY(0px)' }
          ],
          { duration: dur, delay: 220, easing: SPRING_SETTLE_EASING, fill: 'both' }
        );
      });
    }

    frontIndex += 1;
    var nextId = ORDER[frontIndex];
    var nextTicket = '';
    if (nextId) {
      var nextRow = list.querySelector('.wls__item[data-id="' + nextId + '"]');
      if (nextRow) { nextRow.classList.add('is-next'); nextTicket = nextRow.querySelector('.wls__ticket').textContent; }
    }

    var callBtn = document.getElementById('wlsCallBtn');
    if (callBtn) callBtn.disabled = frontIndex >= ORDER.length;

    status.textContent = nextTicket
      ? ticket + ' served · next is ' + nextTicket
      : ticket + ' served · the waiting list is empty.';
  }

  function restoreAll() {
    var all = list.querySelectorAll('.wls__item');
    for (var i = 0; i < all.length; i += 1) {
      all[i].getAnimations().forEach(function (a) { a.cancel(); });
      all[i].style.display = '';
      all[i].style.height = '';
      all[i].style.overflow = '';
      all[i].style.marginTop = '';
      all[i].style.marginBottom = '';
      all[i].classList.remove('is-next');
    }
    frontIndex = 0;
    var firstRow = list.querySelector('.wls__item[data-id="' + ORDER[0] + '"]');
    if (firstRow) firstRow.classList.add('is-next');
    var callBtn = document.getElementById('wlsCallBtn');
    if (callBtn) callBtn.disabled = false;
    status.textContent = 'The waiting list has been restored.';
  }

  var callBtn = document.getElementById('wlsCallBtn');
  var resetBtn = document.getElementById('wlsReset');

  function onCall() { root.classList.remove('is-demo'); callFront(); }
  function onReset() { root.classList.remove('is-demo'); restoreAll(); }

  callBtn.addEventListener('click', onCall);
  callBtn.addEventListener('keydown', function (e) {
    if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); onCall(); }
  });
  resetBtn.addEventListener('click', onReset);
  resetBtn.addEventListener('keydown', function (e) {
    if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); onReset(); }
  });

  var demoSchedule = [200, 1200];
  var demoIndex = 0;
  var t0 = null;

  function tick(ts) {
    if (t0 === null) t0 = ts;
    var now = ts - t0;
    if (!reduce && root.classList.contains('is-demo') && demoIndex < demoSchedule.length && now >= demoSchedule[demoIndex]) {
      if (frontIndex >= ORDER.length) { restoreAll(); } else { callFront(); }
      demoIndex += 1;
      if (demoIndex >= demoSchedule.length) { demoIndex = 0; demoSchedule = demoSchedule.map(function (v) { return v + now + 2000; }); }
    }
    requestAnimationFrame(tick);
  }

  status.textContent = '101 is next in line.';
  requestAnimationFrame(tick);
})();

// WaitingQueueListShiftPositionSpring — vanilla 판(04-waiting-queue-list-shift-position-spring) 의
// React 포트. 맨 앞 순번이 빠지면 아래 행들이 이동할 거리(gap)를 실측해 FLIP + 스프링 감쇠
// (LIST_SHIFT_SPRING_STIFFNESS)로 자리를 메우고, 새 맨 앞 행은 is-next 계산으로 강조한다.
import { useEffect, useRef, useState } from "react";
import styles from "./WaitingQueueListShiftPositionSpring.module.scss";

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

const LIST_SHIFT_SPRING_STIFFNESS = 260;
const SPRING_SETTLE_EASING = "linear(0.0, 0.051, 0.176, 0.341, 0.518, 0.685, 0.831, 0.947, 1.032, 1.087, 1.117, 1.126, 1.121, 1.105, 1.085, 1.062, 1.041, 1.022, 1.008, 0.997, 1)";

type Row = { id: string; ticket: string; note: string };

const ROWS: Row[] = [
  { id: "d1", ticket: "101번", note: "대기 3분" },
  { id: "d2", ticket: "102번", note: "대기 9분" },
  { id: "d3", ticket: "103번", note: "대기 14분" },
  { id: "d4", ticket: "104번", note: "대기 18분" },
  { id: "d5", ticket: "105번", note: "대기 22분" }
];

function shiftDuration(gapPx: number): number {
  return Math.round(60 + 100000 / LIST_SHIFT_SPRING_STIFFNESS + Math.min(240, gapPx * 0.55));
}

export default function WaitingQueueListShiftPositionSpring() {
  const [frontIndex, setFrontIndex] = useState(0);
  const [hiddenIds, setHiddenIds] = useState<string[]>([]);
  const [status, setStatus] = useState("101번이 다음 차례입니다.");
  const [reduce, setReduce] = useState(false);
  const rowRefs = useRef<Record<string, HTMLLIElement | null>>({}) as Box<Record<string, HTMLLIElement | null>>;
  const demoRef = useRef<boolean>(true) as Box<boolean>;
  const demoIndexRef = useRef<number>(0) as Box<number>;
  const demoScheduleRef = useRef<number[]>([200, 1200]) as Box<number[]>;
  const frameRef = useRef<number>(0) as Box<number>;

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

  function visibleRows(excludeId?: string): HTMLLIElement[] {
    return ROWS.filter((r) => !hiddenIds.includes(r.id) && r.id !== excludeId)
      .map((r) => rowRefs.current[r.id])
      .filter((el): el is HTMLLIElement => !!el);
  }

  function callFront(): void {
    if (frontIndex >= ROWS.length) { setStatus("대기 목록이 비었습니다."); return; }
    const row = ROWS[frontIndex];
    const el = rowRefs.current[row.id];
    const below = visibleRows(row.id);
    const before = below.map((r) => r.getBoundingClientRect().top);
    const gap = (el ? el.offsetHeight : 0) + 8;

    if (!reduce && el) {
      const h = el.offsetHeight;
      el.style.height = h + "px";
      el.style.overflow = "hidden";
      el.style.boxSizing = "border-box";
      el.style.marginTop = "0px";
      el.style.marginBottom = "0px";
      el.animate(
        [{ height: h + "px", opacity: 1 }, { height: "0px", opacity: 0 }],
        { duration: 220, easing: "ease-in", fill: "forwards" }
      );
      const dur = shiftDuration(gap);
      below.forEach((rEl) => {
        rEl.animate(
          [
            { transform: "translateY(0px)" },
            { transform: "translateY(" + gap + "px)" },
            { transform: "translateY(0px)" }
          ],
          { duration: dur, delay: 220, easing: SPRING_SETTLE_EASING, fill: "both" }
        );
      });
    }

    setHiddenIds((prev) => prev.concat(row.id));
    const nextIdx = frontIndex + 1;
    setFrontIndex(nextIdx);
    const next = ROWS[nextIdx];
    setStatus(next ? row.ticket + " 호출 완료 · 다음은 " + next.ticket : row.ticket + " 호출 완료 · 대기 목록이 비었습니다.");
    void before;
  }

  function restoreAll(): void {
    Object.keys(rowRefs.current).forEach((id) => {
      const el = rowRefs.current[id];
      if (!el) return;
      el.getAnimations().forEach((a) => a.cancel());
      el.style.height = "";
      el.style.overflow = "";
      el.style.marginTop = "";
      el.style.marginBottom = "";
    });
    setHiddenIds([]);
    setFrontIndex(0);
    setStatus("대기 목록을 되돌렸습니다.");
  }

  function stopDemo(): void { demoRef.current = false; }

  useEffect(() => {
    let t0 = 0;
    function tick(ts: number): void {
      if (t0 === 0) t0 = ts;
      const now = ts - t0;
      const sched = demoScheduleRef.current;
      if (!reduce && demoRef.current && demoIndexRef.current < sched.length && now >= sched[demoIndexRef.current]) {
        if (frontIndexIsDone()) { restoreAll(); } else { callFront(); }
        demoIndexRef.current += 1;
        if (demoIndexRef.current >= sched.length) {
          demoIndexRef.current = 0;
          demoScheduleRef.current = sched.map((v) => v + now + 2000);
        }
      }
      frameRef.current = requestAnimationFrame(tick);
    }
    function frontIndexIsDone(): boolean { return frontIndex >= ROWS.length; }
    frameRef.current = requestAnimationFrame(tick);
    return () => cancelAnimationFrame(frameRef.current);
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [reduce, frontIndex]);

  function onCall(): void { stopDemo(); callFront(); }
  function onReset(): void { stopDemo(); restoreAll(); }

  function onKeyDown(e: { key: string; preventDefault: () => void }, fn: () => void): void {
    if (e.key === "Enter" || e.key === " ") { e.preventDefault(); fn(); }
  }

  return (
    <main className={styles.stage}>
      <div className={styles.wls}>
        <ul className={styles.list} role="list">
          {ROWS.map((r, i) => (
            <li
              key={r.id}
              className={[styles.item, i === frontIndex ? styles.itemNext : ""].join(" ")}
              style={{ display: hiddenIds.includes(r.id) ? "none" : "" }}
              ref={(el: HTMLLIElement | null) => { rowRefs.current[r.id] = el; }}
            >
              <span className={styles.ticket}>{r.ticket}</span>
              <span className={styles.note}>{r.note}</span>
            </li>
          ))}
        </ul>
        <div className={styles.controls}>
          <button type="button" className={styles.btn} onClick={onReset} onKeyDown={(e: { key: string; preventDefault: () => void }) => onKeyDown(e, onReset)}>되돌리기</button>
          <button type="button" className={[styles.btn, styles.btnPrimary].join(" ")} disabled={frontIndex >= ROWS.length} onClick={onCall} onKeyDown={(e: { key: string; preventDefault: () => void }) => onKeyDown(e, onCall)}>호출 완료</button>
        </div>
        <p className={styles.status} aria-live="polite">{status}</p>
      </div>
    </main>
  );
}