03使う量に合わせて価格を計算し直す

<main class="stage">
  <div class="us is-demo">
    <div class="us__row">
      <span class="us__lab">月の使用量</span>
      <span class="us__slot">
        <span class="us__live"><span class="us__n" id="us-seatn">3</span><span class="us__u">席</span></span>
        <span class="us__f" data-step="1"><span class="us__n">3</span><span class="us__u">席</span></span>
        <span class="us__f" data-step="2"><span class="us__n">5</span><span class="us__u">席</span></span>
        <span class="us__f" data-step="3"><span class="us__n">10</span><span class="us__u">席</span></span>
        <span class="us__f" data-step="4"><span class="us__n">20</span><span class="us__u">席</span></span>
        <span class="us__f" data-step="5"><span class="us__n">50</span><span class="us__u">席</span></span>
      </span>
    </div>
    <div class="us__track">
      <span class="us__rail" aria-hidden="true"><span class="us__fill"></span></span>
      <input class="us__range" type="range" min="1" max="5" step="1" value="1" id="us-range" aria-label="月の使用量" aria-valuetext="3 席">
      <span class="us__knobrail" aria-hidden="true"><span class="us__knob"></span></span>
    </div>
    <div class="us__ticks" aria-hidden="true">
      <i class="us__tick"></i><i class="us__tick"></i><i class="us__tick"></i><i class="us__tick"></i><i class="us__tick"></i>
    </div>
    <div class="us__row">
      <span class="us__lab">概算料金</span>
      <span class="us__slot us__slot--fee" aria-live="polite">
        <span class="us__live"><span class="us__n" id="us-fee">$24</span><span class="us__u">/ 月</span></span>
        <span class="us__f" data-step="1"><span class="us__n">$24</span><span class="us__u">/ 月</span></span>
        <span class="us__f" data-step="2"><span class="us__n">$40</span><span class="us__u">/ 月</span></span>
        <span class="us__f" data-step="3"><span class="us__n">$80</span><span class="us__u">/ 月</span></span>
        <span class="us__f" data-step="4"><span class="us__n">$160</span><span class="us__u">/ 月</span></span>
        <span class="us__f" data-step="5"><span class="us__n">$400</span><span class="us__u">/ 月</span></span>
      </span>
    </div>
  </div>
</main>

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

// 단계(1~5)를 담는 자리 — 등록해 두면 루프에서 단계 사이가 부드럽게 채워진다.
// 요금 숫자 자체는 이 값으로 만들지 않는다 (그건 JS 가 글자로 갈아 끼운다)
@property --p {
  syntax: "<number>";
  initial-value: 1;
  inherits: true;
}

$duration: $dur-quick;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-yellow);

.us {
  --p: 1;
  box-sizing: border-box;
  width: min(360px, 88vw);
  display: flex;
  flex-direction: column;
  gap: $sp-2;
  padding: $sp-4;
  border: 2px solid $subject-ink;
  border-radius: $r-card;
  background: $stage-paper;
  box-shadow: $shadow-raised;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: $subject-ink;
}

.us__row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: $sp-2;
}
.us__lab {
  font-size: 12px;
  line-height: 18px;
  font-weight: 700;
  opacity: .6;
}

// 값 자리 — 사람이 만진 뒤엔 JS 가 쓰는 .us__live 한 장, 루프에서는 겹쳐 둔 얼굴 다섯 장
.us__slot {
  position: relative;
  display: flex;
  justify-content: flex-end;
  transform-origin: right center; // 규칙8: 오른쪽 정렬 금액 — 정렬 변을 고정해야 팝이 자리를 안 흔든다
}
.us__live,
.us__f {
  display: flex;
  align-items: baseline;
  gap: $sp-1;
  white-space: nowrap;
}
.us__f {
  position: absolute;
  right: 0;
  top: 0;
  opacity: 0;
}
.us__n {
  font-size: 16px;
  line-height: 20px;
  font-weight: 800;
}
.us__u {
  font-size: 11px;
  line-height: 16px;
  font-weight: 700;
  opacity: .6;
}
.us__slot--fee .us__n {
  color: $color;
  font-size: 26px;
  line-height: 32px;
}

.us__track {
  position: relative;
  height: 24px;
}
// 채움은 네이티브 range 위가 아니라 따로 그린 트랙에 그린다 — scaleX 는 폭 계산 없이 0~1 로 끝난다
.us__rail {
  position: absolute;
  left: 12px;
  right: 12px;
  top: 8px;
  height: 8px;
  overflow: hidden;
  border-radius: $r-pill;
  background: rgba($subject-ink, .12);
}
.us__fill {
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 100%;
  transform-origin: left center; // 규칙8: 슬라이더 채움 좌측 기준
  transform: scaleX(calc(var(--p) * .2));   // 단계 1~5 → 0.2~1.0
  background: $color;
}
// 진짜 입력은 트랙 위에 투명하게 겹쳐 둔다 — 끌기·클릭·키보드가 전부 살아 있다
.us__range {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  width: 100%;
  margin: 0;
  opacity: 0;
  cursor: pointer;
  accent-color: $color;
}
.us__knobrail {
  position: absolute;
  left: 12px;
  right: 12px;
  top: 0;
  bottom: 0;
}
.us__knob {
  position: absolute;
  top: 50%;
  left: calc(100% * (var(--p) - .5) * .2);   // 칸 한가운데 — 채움이 덮은 칸의 중심에 선다
  width: 20px;
  height: 20px;
  box-sizing: border-box;
  border: 2px solid $stage-paper;
  border-radius: 50%;
  background: $subject-ink;
  box-shadow: $shadow-press;
  transform: translate(-50%, -50%);
}
.us__range:focus-visible ~ .us__knobrail .us__knob {
  outline: 2px solid $color;
  outline-offset: 2px;
}

// 눈금 다섯 칸은 균등 그리드로 — 칸마다 고정 px 로 밀면 실제 폭과 어긋난다
.us__ticks {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  padding: 0 $sp-3;
}
.us__tick {
  justify-self: center;
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: rgba($subject-ink, .3);
}

// ── 사람이 만진 뒤(정적 경로) — 단계는 --p 하나에만 들어 있다 ──
.us:not(.is-demo) .us__fill,
.us:not(.is-demo) .us__knob {
  transition-property: transform, left;
  transition-duration: $duration;
  transition-timing-function: $easing;
}

// ── 자동 루프(2초) — 손잡이와 채움은 1→5 로 부드럽게, 값 얼굴은 컷. 복귀는 86% 에 끝난다 ──
.us.is-demo {
  animation-name: us-p;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
@keyframes us-p {
  0%, 6%    { --p: 1; }
  22%       { --p: 2; }
  38%       { --p: 3; }
  54%       { --p: 4; }
  70%       { --p: 5; }
  74%       { --p: 5; animation-timing-function: linear; }
  86%, 100% { --p: 1; }
}

.us.is-demo .us__live { opacity: 0; }
.us.is-demo .us__f {
  animation-duration: $dur-loop;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.us.is-demo .us__f[data-step="1"] { animation-name: us-f1; }
.us.is-demo .us__f[data-step="2"] { animation-name: us-f2; }
.us.is-demo .us__f[data-step="3"] { animation-name: us-f3; }
.us.is-demo .us__f[data-step="4"] { animation-name: us-f4; }
.us.is-demo .us__f[data-step="5"] { animation-name: us-f5; }
// 되돌아가는 구간(74~86%)에서도 얼굴이 손잡이를 따라간다 — --p 가 선형으로 5→1 로 내려가며
// 4·3·2 를 지나는 시각(77·80·83%)에 맞춰 컷한다. 이 컷을 안 두면 손잡이는 왼쪽으로 미끄러지는데
// 숫자만 「50 좌석 · $400」에 멈춰 있는 어긋난 장면이 대표 이미지로 뽑힌다 (242-06 계열)
// 컷은 손잡이가 **눈금과 눈금의 한가운데**를 지나는 순간에 둔다 — step 슬라이더가 실제로 값을 바꾸는
// 지점이 그 중간이기 때문이다. 도착 시각(22·38·54·70%)에 맞추면 미끄러지는 네 프레임 내내 숫자만
// 뒤처져 「손잡이는 5번 눈금, 숫자는 20 좌석」인 어긋난 장면이 대표 이미지로 뽑힌다 (242-06 계열)
@keyframes us-f1 {
  0%     { opacity: 1; }
  14%    { opacity: 0; }
  84.5%  { opacity: 1; }
  100%   { opacity: 1; }
}
@keyframes us-f2 {
  0%     { opacity: 0; }
  14%    { opacity: 1; }
  30%    { opacity: 0; }
  81.5%  { opacity: 1; }
  84.5%  { opacity: 0; }
  100%   { opacity: 0; }
}
@keyframes us-f3 {
  0%     { opacity: 0; }
  30%    { opacity: 1; }
  46%    { opacity: 0; }
  78.5%  { opacity: 1; }
  81.5%  { opacity: 0; }
  100%   { opacity: 0; }
}
@keyframes us-f4 {
  0%     { opacity: 0; }
  46%    { opacity: 1; }
  62%    { opacity: 0; }
  75.5%  { opacity: 1; }
  78.5%  { opacity: 0; }
  100%   { opacity: 0; }
}
@keyframes us-f5 {
  0%     { opacity: 0; }
  62%    { opacity: 1; }
  75.5%  { opacity: 0; }
  100%   { opacity: 0; }
}

// 요금이 갈릴 때마다 그 자리가 한 번 튄다 — 컷 옆에 움직인 프레임을 채운다
.us.is-demo .us__slot--fee {
  animation-name: us-pop;
  animation-duration: $dur-loop;
  animation-timing-function: $ease-pop;
  animation-iteration-count: infinite;
}
@keyframes us-pop {
  0%, 10%   { transform: scale(1); }
  16%       { transform: scale(1.07); }
  22%, 26%  { transform: scale(1); }
  32%       { transform: scale(1.07); }
  38%, 42%  { transform: scale(1); }
  48%       { transform: scale(1.07); }
  54%, 58%  { transform: scale(1); }
  64%       { transform: scale(1.07); }
  70%, 82%  { transform: scale(1); }
  86%       { transform: scale(1.05); }
  92%, 100% { transform: scale(1); }
}

@media (max-width: 340px) {
  .us {
    width: min(280px, 90vw);
    gap: $sp-1;
    padding: $sp-3;
  }
  .us__lab { font-size: 11px; line-height: 16px; }
  .us__n { font-size: 14px; line-height: 18px; }
  .us__slot--fee .us__n { font-size: 21px; line-height: 26px; }
  .us__track { height: 20px; }
  .us__rail { top: 6px; }
  .us__knob { width: 16px; height: 16px; }
}

@media (prefers-reduced-motion: reduce) {
  .us.is-demo,
  .us.is-demo .us__f,
  .us.is-demo .us__slot--fee { animation: none !important; }
  .us:not(.is-demo) .us__fill,
  .us:not(.is-demo) .us__knob { transition: none !important; }
  .us.is-demo .us__f[data-step="1"] { opacity: 1; }
}

@property --p {
  syntax: "<number>";
  initial-value: 1;
  inherits: true;
}
html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.us {
  --p: 1;
  box-sizing: border-box;
  width: min(360px, 88vw);
  display: flex;
  flex-direction: column;
  gap: 8px;
  padding: 16px;
  border: 2px solid #17141a;
  border-radius: 16px;
  background: #ffffff;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: #17141a;
}

.us__row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
}

.us__lab {
  font-size: 12px;
  line-height: 18px;
  font-weight: 700;
  opacity: 0.6;
}

.us__slot {
  position: relative;
  display: flex;
  justify-content: flex-end;
  transform-origin: right center;
}

.us__live,
.us__f {
  display: flex;
  align-items: baseline;
  gap: 4px;
  white-space: nowrap;
}

.us__f {
  position: absolute;
  right: 0;
  top: 0;
  opacity: 0;
}

.us__n {
  font-size: 16px;
  line-height: 20px;
  font-weight: 800;
}

.us__u {
  font-size: 11px;
  line-height: 16px;
  font-weight: 700;
  opacity: 0.6;
}

.us__slot--fee .us__n {
  color: #2f6df6;
  font-size: 26px;
  line-height: 32px;
}

.us__track {
  position: relative;
  height: 24px;
}

.us__rail {
  position: absolute;
  left: 12px;
  right: 12px;
  top: 8px;
  height: 8px;
  overflow: hidden;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.12);
}

.us__fill {
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 100%;
  transform-origin: left center;
  transform: scaleX(calc(var(--p) * 0.2));
  background: #2f6df6;
}

.us__range {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  width: 100%;
  margin: 0;
  opacity: 0;
  cursor: pointer;
  accent-color: #2f6df6;
}

.us__knobrail {
  position: absolute;
  left: 12px;
  right: 12px;
  top: 0;
  bottom: 0;
}

.us__knob {
  position: absolute;
  top: 50%;
  left: calc(100% * (var(--p) - 0.5) * 0.2);
  width: 20px;
  height: 20px;
  box-sizing: border-box;
  border: 2px solid #ffffff;
  border-radius: 50%;
  background: #17141a;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  transform: translate(-50%, -50%);
}

.us__range:focus-visible ~ .us__knobrail .us__knob {
  outline: 2px solid #2f6df6;
  outline-offset: 2px;
}

.us__ticks {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  padding: 0 12px;
}

.us__tick {
  justify-self: center;
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: rgba(23, 20, 26, 0.3);
}

.us:not(.is-demo) .us__fill,
.us:not(.is-demo) .us__knob {
  transition-property: transform, left;
  transition-duration: 220ms;
  transition-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
}

.us.is-demo {
  animation-name: us-p;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

@keyframes us-p {
  0%, 6% {
    --p: 1;
  }
  22% {
    --p: 2;
  }
  38% {
    --p: 3;
  }
  54% {
    --p: 4;
  }
  70% {
    --p: 5;
  }
  74% {
    --p: 5;
    animation-timing-function: linear;
  }
  86%, 100% {
    --p: 1;
  }
}
.us.is-demo .us__live {
  opacity: 0;
}

.us.is-demo .us__f {
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

.us.is-demo .us__f[data-step="1"] {
  animation-name: us-f1;
}

.us.is-demo .us__f[data-step="2"] {
  animation-name: us-f2;
}

.us.is-demo .us__f[data-step="3"] {
  animation-name: us-f3;
}

.us.is-demo .us__f[data-step="4"] {
  animation-name: us-f4;
}

.us.is-demo .us__f[data-step="5"] {
  animation-name: us-f5;
}

@keyframes us-f1 {
  0% {
    opacity: 1;
  }
  14% {
    opacity: 0;
  }
  84.5% {
    opacity: 1;
  }
  100% {
    opacity: 1;
  }
}
@keyframes us-f2 {
  0% {
    opacity: 0;
  }
  14% {
    opacity: 1;
  }
  30% {
    opacity: 0;
  }
  81.5% {
    opacity: 1;
  }
  84.5% {
    opacity: 0;
  }
  100% {
    opacity: 0;
  }
}
@keyframes us-f3 {
  0% {
    opacity: 0;
  }
  30% {
    opacity: 1;
  }
  46% {
    opacity: 0;
  }
  78.5% {
    opacity: 1;
  }
  81.5% {
    opacity: 0;
  }
  100% {
    opacity: 0;
  }
}
@keyframes us-f4 {
  0% {
    opacity: 0;
  }
  46% {
    opacity: 1;
  }
  62% {
    opacity: 0;
  }
  75.5% {
    opacity: 1;
  }
  78.5% {
    opacity: 0;
  }
  100% {
    opacity: 0;
  }
}
@keyframes us-f5 {
  0% {
    opacity: 0;
  }
  62% {
    opacity: 1;
  }
  75.5% {
    opacity: 0;
  }
  100% {
    opacity: 0;
  }
}
.us.is-demo .us__slot--fee {
  animation-name: us-pop;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 1.4, 0.4, 1);
  animation-iteration-count: infinite;
}

@keyframes us-pop {
  0%, 10% {
    transform: scale(1);
  }
  16% {
    transform: scale(1.07);
  }
  22%, 26% {
    transform: scale(1);
  }
  32% {
    transform: scale(1.07);
  }
  38%, 42% {
    transform: scale(1);
  }
  48% {
    transform: scale(1.07);
  }
  54%, 58% {
    transform: scale(1);
  }
  64% {
    transform: scale(1.07);
  }
  70%, 82% {
    transform: scale(1);
  }
  86% {
    transform: scale(1.05);
  }
  92%, 100% {
    transform: scale(1);
  }
}
@media (max-width: 340px) {
  .us {
    width: min(280px, 90vw);
    gap: 4px;
    padding: 12px;
  }
  .us__lab {
    font-size: 11px;
    line-height: 16px;
  }
  .us__n {
    font-size: 14px;
    line-height: 18px;
  }
  .us__slot--fee .us__n {
    font-size: 21px;
    line-height: 26px;
  }
  .us__track {
    height: 20px;
  }
  .us__rail {
    top: 6px;
  }
  .us__knob {
    width: 16px;
    height: 16px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .us.is-demo,
  .us.is-demo .us__f,
  .us.is-demo .us__slot--fee {
    animation: none !important;
  }
  .us:not(.is-demo) .us__fill,
  .us:not(.is-demo) .us__knob {
    transition: none !important;
  }
  .us.is-demo .us__f[data-step="1"] {
    opacity: 1;
  }
}

// 실제 동작: 진짜 range 입력이다. input 마다 단계(1~5)를 --p 로 넘겨 채움·손잡이 자리를 정하고,
// 席 수와 요금 글자는 JS 가 갈아 끼운다(01 처럼 CSS 로 보간하지 않는다).
// 화면을 못 보는 사람에게는 눈금 숫자 대신 aria-valuetext 로 읽을 문장을 준다
var root = document.querySelector('.us');
var range = document.getElementById('us-range');
var seatn = document.getElementById('us-seatn');
var fee = document.getElementById('us-fee');
var SEATS = [3, 5, 10, 20, 50];
function apply(v) {
  var seats = SEATS[v - 1];
  root.style.setProperty('--p', String(v));
  seatn.textContent = String(seats);
  fee.textContent = '$' + (seats * 8);
  range.setAttribute('aria-valuetext', seats + ' ' + '席');
}
range.addEventListener('input', function () {
  root.classList.remove('is-demo');
  apply(parseInt(range.value, 10));
});

import { useState } from "react";
import type { CSSProperties } from "react";
import styles from "./UsageSlider.module.scss";

export type UsageSliderProps = {
  usageLabel?: string;
  feeLabel?: string;
  seatUnit?: string;
  unit?: string;
  currency?: string;
  seats?: number[];
  perSeat?: number;
  duration?: number;
  easing?: string;
  color?: string;
};

// React 이벤트 타입은 import 하지 않는다 — 필요한 모양만 여기서 적는다
type RangeEvt = { currentTarget: { value: string } };

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

export default function UsageSlider({
  usageLabel = "Monthly usage",
  feeLabel = "Estimated fee",
  seatUnit = "seats",
  unit = "/ mo",
  currency = "$",
  seats = [3, 5, 10, 20, 50],
  perSeat = 8,
  duration = 220,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
}: UsageSliderProps) {
  const [demo, setDemo] = useState(true);
  const [step, setStep] = useState(1);
  const now = seats[step - 1];
  const vars: Vars = {
    "--p": String(step),
    "--duration": `${duration}ms`,
    "--easing": easing,
    "--color": color,
  };

  // 요금 숫자는 CSS 보간이 아니라 여기서 글자로 만든다
  function fee(n: number) {
    return `${currency}${n * perSeat}`;
  }
  function onInput(e: RangeEvt) {
    setDemo(false);
    setStep(parseInt(e.currentTarget.value, 10));
  }

  return (
    <div className={`${styles.us} ${demo ? styles.isDemo : ""}`} style={vars}>
      <div className={styles.row}>
        <span className={styles.lab}>{usageLabel}</span>
        <span className={styles.slot}>
          <span className={styles.live}>
            <span className={styles.n}>{now}</span>
            <span className={styles.u}>{seatUnit}</span>
          </span>
          {seats.map((s, i) => (
            <span key={s} className={styles.f} data-step={i + 1}>
              <span className={styles.n}>{s}</span>
              <span className={styles.u}>{seatUnit}</span>
            </span>
          ))}
        </span>
      </div>
      <div className={styles.track}>
        <span className={styles.rail} aria-hidden="true">
          <span className={styles.fill} />
        </span>
        <input
          className={styles.range}
          type="range"
          min={1}
          max={seats.length}
          step={1}
          value={step}
          aria-label={usageLabel}
          aria-valuetext={`${now} ${seatUnit}`}
          onChange={onInput}
        />
        <span className={styles.knobrail} aria-hidden="true">
          <span className={styles.knob} />
        </span>
      </div>
      <div className={styles.ticks} aria-hidden="true">
        {seats.map((s) => (
          <i key={s} className={styles.tick} />
        ))}
      </div>
      <div className={styles.row}>
        <span className={styles.lab}>{feeLabel}</span>
        <span className={`${styles.slot} ${styles.slotFee}`} aria-live="polite">
          <span className={styles.live}>
            <span className={styles.n}>{fee(now)}</span>
            <span className={styles.u}>{unit}</span>
          </span>
          {seats.map((s, i) => (
            <span key={s} className={styles.f} data-step={i + 1}>
              <span className={styles.n}>{fee(s)}</span>
              <span className={styles.u}>{unit}</span>
            </span>
          ))}
        </span>
      </div>
    </div>
  );
}