01Crosshair that snaps to the nearest point

<main class="stage">
  <figure class="ch is-demo" id="ch">
    <figcaption class="ch__head">
      <span class="ch__title">Weekly visits</span>
      <span class="ch__val" aria-live="polite" id="ch-val">Day 5 · 398</span>
    </figcaption>
    <div class="ch__plot">
      <svg class="ch__svg" viewBox="0 0 320 132" role="img" aria-label="Visitor trend over 12 days. Day 5 at 398 and day 12 at 401 are the peaks">
        <g class="ch__grid" aria-hidden="true">
          <line x1="0" y1="24" x2="320" y2="24"/><line x1="0" y1="60" x2="320" y2="60"/><line x1="0" y1="96" x2="320" y2="96"/>
        </g>
        <polyline class="ch__line" points="14,66 40,54 66,58 92,47 118,27 144,39 170,53 196,42 222,29 248,45 274,36 300,25"/>
        <g class="ch__dots" aria-hidden="true">
          <circle cx="14" cy="66" r="3"/><circle cx="40" cy="54" r="3"/><circle cx="66" cy="58" r="3"/><circle cx="92" cy="47" r="3"/><circle cx="118" cy="27" r="3"/><circle cx="144" cy="39" r="3"/><circle cx="170" cy="53" r="3"/><circle cx="196" cy="42" r="3"/><circle cx="222" cy="29" r="3"/><circle cx="248" cy="45" r="3"/><circle cx="274" cy="36" r="3"/><circle cx="300" cy="25" r="3"/>
        </g>
        <g class="ch__cursor" aria-hidden="true">
          <line class="ch__x" x1="0" y1="6" x2="0" y2="112"/>
          <g class="ch__mark"><circle class="ch__ring" r="7"/></g>
          <g class="ch__tip"><g class="ch__tipbox"><rect x="-31" y="-32" width="62" height="24" rx="6"/><text x="0" y="-15" text-anchor="middle">398 visits</text></g></g>
        </g>
      </svg>
      <button class="ch__hot" type="button" id="ch-hot" aria-label="Move across the line to read each day"></button>
    </div>
    <p class="ch__hint">Move across the line and it snaps to the nearest day</p>
    <div class="sr"><table>
      <caption>Visitors over 12 days</caption>
      <tbody><tr><th>Day 1</th><td>220</td></tr><tr><th>Day 2</th><td>268</td></tr><tr><th>Day 3</th><td>254</td></tr><tr><th>Day 4</th><td>305</td></tr><tr><th>Day 5</th><td>398</td></tr><tr><th>Day 6</th><td>342</td></tr><tr><th>Day 7</th><td>287</td></tr><tr><th>Day 8</th><td>331</td></tr><tr><th>Day 9</th><td>376</td></tr><tr><th>Day 10</th><td>309</td></tr><tr><th>Day 11</th><td>352</td></tr><tr><th>Day 12</th><td>401</td></tr></tbody>
    </table></div>
  </figure>
</main>

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

// 칸 번호와 그 점의 높이를 등록한다. <integer>·<length> 로 등록해야
// 두 값이 타입을 갖고, 정적 경로의 transition 이 칸 사이를 부드럽게 이어 준다.
// 등록하지 않으면 문자열이라 보간이 아예 일어나지 않는다
@property --i {
  syntax: "<integer>";
  initial-value: 4;
  inherits: true;
}
@property --y {
  syntax: "<length>";
  initial-value: 27px;
  inherits: true;
}

$duration: $dur-quick;
$easing: $ease-out;
$color: $subject-blue;
$step: 26px;             // 칸 간격 = (300 - 14) / 11, viewBox 단위

@include stage($stage-ink);

.sr {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

.ch {
  --i: 4;
  --y: 27px;
  box-sizing: border-box;
  width: min(392px, 88vw);
  display: flex;
  flex-direction: column;
  gap: $sp-2;
  margin: 0;
  padding: $sp-3;
  border-radius: $r-card;
  background: $stage-paper;
  box-shadow: $shadow-raised;
  color: $subject-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}
.ch__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: $sp-2;
  padding: 0 $sp-1;
}
.ch__title { font-size: 13px; line-height: 18px; font-weight: 800; letter-spacing: .02em; }
.ch__val { font-size: 13px; line-height: 18px; font-weight: 800; color: $color; font-variant-numeric: tabular-nums; }

.ch__plot { position: relative; }
.ch__svg { display: block; width: 100%; height: auto; }

.ch__grid line { stroke: rgba(23, 20, 26, .14); stroke-width: 1; }
.ch__line {
  fill: none;
  stroke: $color;
  stroke-width: 3;
  stroke-linecap: round;
  stroke-linejoin: round;
}
.ch__dots circle { fill: $stage-paper; stroke: $color; stroke-width: 2; }

// ── 커서 한 덩어리 ──
// 세로선·고리·툴팁을 **한 그룹** 안에 넣고 그룹만 옮긴다. 셋을 각자 옮기면
// 이징이 조금만 달라도 툴팁이 선을 앞질러 날아간다 (첫 판 실측)
.ch__cursor {
  transform: translateX(calc(var(--i) * #{$step} + 14px));
  opacity: 0;
}
.ch__x {
  stroke: $subject-ink;
  stroke-width: 1.5;
  stroke-dasharray: 3 4;
}
.ch__mark { transform: translateY(var(--y)); }
.ch__ring {
  fill: none;
  stroke: $subject-ink;
  stroke-width: 2.5;
}
// 툴팁은 커서 그룹 안에서 점 높이만 따라간다. 좌우 위치는 그룹이 이미 정했다
.ch__tip { transform: translateY(var(--y)); }
.ch__tipbox {
  transform-box: fill-box;
  transform-origin: center;
}
.ch__tipbox rect { fill: $subject-ink; }
.ch__tipbox text { fill: $stage-paper; font-size: 12px; font-weight: 800; }

.ch__hot {
  position: absolute;
  inset: 0;
  margin: 0;
  padding: 0;
  border: 0;
  border-radius: $r-sm;
  background: transparent;
  cursor: crosshair;
}
.ch__hot:focus-visible { outline: 2px solid $color; outline-offset: -2px; }

.ch__hint { margin: 0; padding: 0 $sp-1; font-size: 11px; line-height: 16px; color: rgba(23, 20, 26, .62); }

// ── 사람이 만진 뒤(정적 경로) — 커서가 보이고 칸 사이를 짧게 미끄러진다 ──
.ch:not(.is-demo) .ch__cursor {
  opacity: 1;
  transition-property: transform;
  transition-duration: $duration;
  transition-timing-function: $easing;
}
.ch:not(.is-demo) .ch__mark,
.ch:not(.is-demo) .ch__tip {
  transition-property: transform;
  transition-duration: $duration;
  transition-timing-function: $easing;
}

// ── 자동 루프(2초): 5일 → 9일 → 12일 → 5일 칸을 짚는다 ──
// 칸 이동은 steps(1, end) 컷이다. 사람 손은 칸을 "건너뛰지" 않으므로
// 중간 프레임에 선이 점 사이에 떠 있으면 그 자체가 거짓말이 된다
.ch.is-demo .ch__cursor {
  animation-name: ch-x;
  animation-duration: $dur-loop;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
  opacity: 1;
}
@keyframes ch-x {
  0%   { transform: translateX(calc(4 * #{$step} + 14px)); }
  28%  { transform: translateX(calc(8 * #{$step} + 14px)); }
  56%  { transform: translateX(calc(11 * #{$step} + 14px)); }
  84%  { transform: translateX(calc(4 * #{$step} + 14px)); }
  100% { transform: translateX(calc(4 * #{$step} + 14px)); }
}
.ch.is-demo .ch__mark,
.ch.is-demo .ch__tip {
  animation-name: ch-y;
  animation-duration: $dur-loop;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
@keyframes ch-y {
  0%   { transform: translateY(27px); }
  28%  { transform: translateY(29px); }
  56%  { transform: translateY(25px); }
  84%  { transform: translateY(27px); }
  100% { transform: translateY(27px); }
}
// 컷 옆에 **반투명이 안 생기는** 움직임을 붙여 프레임을 채운다 — 둘 다 transform 이다
.ch.is-demo .ch__ring {
  animation-name: ch-ring;
  animation-duration: $dur-loop;
  animation-timing-function: $ease-pop;
  animation-iteration-count: infinite;
}
@keyframes ch-ring {
  0%, 28%, 56%, 84% { transform: scale(.45); }
  14%, 42%, 70%, 96% { transform: scale(1.12); }
  22%, 50%, 78%, 100% { transform: scale(1); }
}
.ch.is-demo .ch__tipbox {
  animation-name: ch-tipbox;
  animation-duration: $dur-loop;
  animation-timing-function: $ease-pop;
  animation-iteration-count: infinite;
}
@keyframes ch-tipbox {
  0%, 28%, 56%, 84% { transform: translateY(7px) scale(.8); }
  16%, 44%, 72%, 98% { transform: translateY(0) scale(1.04); }
  24%, 52%, 80%, 100% { transform: translateY(0) scale(1); }
}

@media (max-width: 340px) {
  .ch { padding: $sp-2; gap: $sp-1; }
  .ch__hint { display: none; }
  .ch__title, .ch__val { font-size: 12px; line-height: 16px; }
}

@media (prefers-reduced-motion: reduce) {
  .ch.is-demo .ch__cursor,
  .ch.is-demo .ch__mark,
  .ch.is-demo .ch__tip,
  .ch.is-demo .ch__ring,
  .ch.is-demo .ch__tipbox { animation: none !important; }
  .ch:not(.is-demo) .ch__cursor,
  .ch:not(.is-demo) .ch__mark,
  .ch:not(.is-demo) .ch__tip { transition: none !important; }
  .ch.is-demo .ch__cursor { opacity: 1; transform: translateX(calc(4 * #{$step} + 14px)); }
  .ch.is-demo .ch__mark,
  .ch.is-demo .ch__tip { transform: translateY(27px); }
}

@property --i {
  syntax: "<integer>";
  initial-value: 4;
  inherits: true;
}
@property --y {
  syntax: "<length>";
  initial-value: 27px;
  inherits: true;
}
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);
}

.sr {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

.ch {
  --i: 4;
  --y: 27px;
  box-sizing: border-box;
  width: min(392px, 88vw);
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin: 0;
  padding: 12px;
  border-radius: 16px;
  background: #ffffff;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.ch__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
  padding: 0 4px;
}

.ch__title {
  font-size: 13px;
  line-height: 18px;
  font-weight: 800;
  letter-spacing: 0.02em;
}

.ch__val {
  font-size: 13px;
  line-height: 18px;
  font-weight: 800;
  color: #2f6df6;
  font-variant-numeric: tabular-nums;
}

.ch__plot {
  position: relative;
}

.ch__svg {
  display: block;
  width: 100%;
  height: auto;
}

.ch__grid line {
  stroke: rgba(23, 20, 26, 0.14);
  stroke-width: 1;
}

.ch__line {
  fill: none;
  stroke: #2f6df6;
  stroke-width: 3;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.ch__dots circle {
  fill: #ffffff;
  stroke: #2f6df6;
  stroke-width: 2;
}

.ch__cursor {
  transform: translateX(calc(var(--i) * 26px + 14px));
  opacity: 0;
}

.ch__x {
  stroke: #17141a;
  stroke-width: 1.5;
  stroke-dasharray: 3 4;
}

.ch__mark {
  transform: translateY(var(--y));
}

.ch__ring {
  fill: none;
  stroke: #17141a;
  stroke-width: 2.5;
}

.ch__tip {
  transform: translateY(var(--y));
}

.ch__tipbox {
  transform-box: fill-box;
  transform-origin: center;
}

.ch__tipbox rect {
  fill: #17141a;
}

.ch__tipbox text {
  fill: #ffffff;
  font-size: 12px;
  font-weight: 800;
}

.ch__hot {
  position: absolute;
  inset: 0;
  margin: 0;
  padding: 0;
  border: 0;
  border-radius: 8px;
  background: transparent;
  cursor: crosshair;
}

.ch__hot:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: -2px;
}

.ch__hint {
  margin: 0;
  padding: 0 4px;
  font-size: 11px;
  line-height: 16px;
  color: rgba(23, 20, 26, 0.62);
}

.ch:not(.is-demo) .ch__cursor {
  opacity: 1;
  transition-property: transform;
  transition-duration: 220ms;
  transition-timing-function: ease-out;
}

.ch:not(.is-demo) .ch__mark,
.ch:not(.is-demo) .ch__tip {
  transition-property: transform;
  transition-duration: 220ms;
  transition-timing-function: ease-out;
}

.ch.is-demo .ch__cursor {
  animation-name: ch-x;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
  opacity: 1;
}

@keyframes ch-x {
  0% {
    transform: translateX(calc(4 * 26px + 14px));
  }
  28% {
    transform: translateX(calc(8 * 26px + 14px));
  }
  56% {
    transform: translateX(calc(11 * 26px + 14px));
  }
  84% {
    transform: translateX(calc(4 * 26px + 14px));
  }
  100% {
    transform: translateX(calc(4 * 26px + 14px));
  }
}
.ch.is-demo .ch__mark,
.ch.is-demo .ch__tip {
  animation-name: ch-y;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

@keyframes ch-y {
  0% {
    transform: translateY(27px);
  }
  28% {
    transform: translateY(29px);
  }
  56% {
    transform: translateY(25px);
  }
  84% {
    transform: translateY(27px);
  }
  100% {
    transform: translateY(27px);
  }
}
.ch.is-demo .ch__ring {
  animation-name: ch-ring;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 1.4, 0.4, 1);
  animation-iteration-count: infinite;
}

@keyframes ch-ring {
  0%, 28%, 56%, 84% {
    transform: scale(0.45);
  }
  14%, 42%, 70%, 96% {
    transform: scale(1.12);
  }
  22%, 50%, 78%, 100% {
    transform: scale(1);
  }
}
.ch.is-demo .ch__tipbox {
  animation-name: ch-tipbox;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 1.4, 0.4, 1);
  animation-iteration-count: infinite;
}

@keyframes ch-tipbox {
  0%, 28%, 56%, 84% {
    transform: translateY(7px) scale(0.8);
  }
  16%, 44%, 72%, 98% {
    transform: translateY(0) scale(1.04);
  }
  24%, 52%, 80%, 100% {
    transform: translateY(0) scale(1);
  }
}
@media (max-width: 340px) {
  .ch {
    padding: 8px;
    gap: 4px;
  }
  .ch__hint {
    display: none;
  }
  .ch__title, .ch__val {
    font-size: 12px;
    line-height: 16px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ch.is-demo .ch__cursor,
  .ch.is-demo .ch__mark,
  .ch.is-demo .ch__tip,
  .ch.is-demo .ch__ring,
  .ch.is-demo .ch__tipbox {
    animation: none !important;
  }
  .ch:not(.is-demo) .ch__cursor,
  .ch:not(.is-demo) .ch__mark,
  .ch:not(.is-demo) .ch__tip {
    transition: none !important;
  }
  .ch.is-demo .ch__cursor {
    opacity: 1;
    transform: translateX(calc(4 * 26px + 14px));
  }
  .ch.is-demo .ch__mark,
  .ch.is-demo .ch__tip {
    transform: translateY(27px);
  }
}

// 실제 동작: pointermove 의 x 를 12칸 중 가장 가까운 칸으로 반올림해 **스냅**한다.
// 결과는 커스텀 속성 두 개(--i 칸 번호, --y 그 점의 높이)로만 나가고,
// 세로선·고리·툴팁은 전부 그 두 값을 읽는 같은 그룹 안에 있다 — 그래서 절대 어긋나지 않는다.
var N = 12;
var ch = document.getElementById('ch');
var hot = document.getElementById('ch-hot');
var val = document.getElementById('ch-val');
var tip = ch.querySelector('.ch__tip text');
var ys = [66, 54, 58, 47, 27, 39, 53, 42, 29, 45, 36, 25];
var nums = [220, 268, 254, 305, 398, 342, 287, 331, 376, 309, 352, 401];
var cur = 4;

function snap(i) {
  cur = Math.min(Math.max(i, 0), N - 1);
  ch.classList.remove('is-demo');
  ch.style.setProperty('--i', String(cur));
  ch.style.setProperty('--y', ys[cur] + 'px');
  tip.textContent = nums[cur] + ' visits';
  val.textContent = (cur + 1) + ' days · ' + nums[cur] + ' visits';
}
hot.addEventListener('pointermove', function (e) {
  var r = hot.getBoundingClientRect();
  var t = Math.min(Math.max((e.clientX - r.left) / r.width, 0), 1);
  snap(Math.round(t * (N - 1)));
});
hot.addEventListener('keydown', function (e) {
  var d = e.key === 'ArrowRight' ? 1 : e.key === 'ArrowLeft' ? -1 : 0;
  if (d) { e.preventDefault(); snap(cur + d); hot.focus({ preventScroll: true }); }
  if (e.key === 'Home' || e.key === 'End') { e.preventDefault(); snap(e.key === 'Home' ? 0 : N - 1); }
});

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

export type CrosshairTooltipProps = {
  title?: string;
  hint?: string;
  unit?: string;
  dayLabel?: (i: number) => string;
  chartLabel?: string;
  hotLabel?: string;
  tableCaption?: string;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & {
  "--duration"?: string;
  "--easing"?: string;
  "--color"?: string;
  "--i"?: string;
  "--y"?: string;
};
// ambient 타입에 React 이벤트 제네릭이 없어 필요한 모양만 직접 적는다
type PointerLike = { clientX: number; currentTarget: { getBoundingClientRect(): DOMRect } };
type KeyEvt = { key: string; preventDefault(): void };

const XS = [14, 40, 66, 92, 118, 144, 170, 196, 222, 248, 274, 300];
const YS = [66, 54, 58, 47, 27, 39, 53, 42, 29, 45, 36, 25];
const NUMS = [220, 268, 254, 305, 398, 342, 287, 331, 376, 309, 352, 401];
const N = NUMS.length;

export default function CrosshairTooltip({
  title = "Weekly visits",
  hint = "Move across the line and it snaps to the nearest day",
  unit = "",
  dayLabel = (i: number) => `Day ${i + 1}`,
  chartLabel = "Visitor trend over 12 days. Day 5 at 398 and day 12 at 401 are the peaks",
  hotLabel = "Move across the line to read each day",
  tableCaption = "Visitors over 12 days",
  duration = 220,
  easing = "ease-out",
  color = "#2f6df6",
}: CrosshairTooltipProps) {
  const [demo, setDemo] = useState(true);
  const [i, setI] = useState(4);

  // 칸 번호와 그 점의 높이 두 값만 CSS 로 내보낸다 — 세로선·고리·툴팁이 같은 그룹 안에서 그 값을 읽는다
  const vars: Vars = {
    "--duration": `${duration}ms`,
    "--easing": easing,
    "--color": color,
    "--i": String(i),
    "--y": `${YS[i]}px`,
  };

  function snap(next: number) {
    setDemo(false);
    setI(Math.min(Math.max(next, 0), N - 1));
  }
  function onMove(e: PointerLike) {
    const r = e.currentTarget.getBoundingClientRect();
    const t = Math.min(Math.max((e.clientX - r.left) / r.width, 0), 1);
    snap(Math.round(t * (N - 1)));
  }
  function onKey(e: KeyEvt) {
    if (e.key === "ArrowRight") { e.preventDefault(); snap(i + 1); }
    if (e.key === "ArrowLeft") { e.preventDefault(); snap(i - 1); }
    if (e.key === "Home") { e.preventDefault(); snap(0); }
    if (e.key === "End") { e.preventDefault(); snap(N - 1); }
  }

  const points = XS.map((x, k) => `${x},${YS[k]}`).join(" ");

  return (
    <figure className={`${styles.ch} ${demo ? styles.isDemo : ""}`} style={vars}>
      <figcaption className={styles.head}>
        <span className={styles.title}>{title}</span>
        <span className={styles.val} aria-live="polite">
          {dayLabel(i)} · {NUMS[i]}{unit}
        </span>
      </figcaption>
      <div className={styles.plot}>
        <svg className={styles.svg} viewBox="0 0 320 132" role="img" aria-label={chartLabel}>
          <g className={styles.grid} aria-hidden="true">
            <line x1="0" y1="24" x2="320" y2="24" /><line x1="0" y1="60" x2="320" y2="60" /><line x1="0" y1="96" x2="320" y2="96" />
          </g>
          <polyline className={styles.line} points={points} />
          <g className={styles.dots} aria-hidden="true">
            {XS.map((x, k) => <circle key={x} cx={x} cy={YS[k]} r="3" />)}
          </g>
          <g className={styles.cursor} aria-hidden="true">
            <line className={styles.x} x1="0" y1="6" x2="0" y2="112" />
            <g className={styles.mark}><circle className={styles.ring} r="7" /></g>
            <g className={styles.tip}>
              <g className={styles.tipbox}>
                <rect x="-31" y="-32" width="62" height="24" rx="6" />
                <text x="0" y="-15" textAnchor="middle">{NUMS[i]}{unit}</text>
              </g>
            </g>
          </g>
        </svg>
        <button className={styles.hot} type="button" aria-label={hotLabel} onPointerMove={onMove} onKeyDown={onKey} />
      </div>
      <p className={styles.hint}>{hint}</p>
      <div className={styles.sr}>
        <table>
          <caption>{tableCaption}</caption>
          <tbody>
            {NUMS.map((n, k) => <tr key={n + "-" + k}><th>{dayLabel(k)}</th><td>{n}</td></tr>)}
          </tbody>
        </table>
      </div>
    </figure>
  );
}