03Picker That Leaves Its Drag Path as a Sparkline Trail

<main class="stage">
<figure class="spk is-demo" id="spk">
  <div class="spk__head">
    <span class="spk__title">Trail of past values</span>
    <span class="spk__stat" aria-hidden="true">Value <b class="spk__n" id="spk-val">50</b></span>
  </div>

  <div class="spk__zone">
    <svg class="spk__chart" id="chart" viewBox="0 0 480 160" preserveAspectRatio="none" role="img" aria-label="A line graph connecting the last 48 values; each time the value changes, the oldest point shifts left and a new point is added on the right.">
      <line class="spk__base" x1="0" y1="150" x2="480" y2="150"></line>
      <path class="spk__area" id="area"></path>
      <path class="spk__line" id="line"></path>
      <circle class="spk__dot" id="dot" r="5"></circle>
    </svg>
  </div>

  <div class="spk__track" id="track">
    <span class="spk__rail" aria-hidden="true"></span>
    <button class="spk__grab" id="grab" type="button" role="slider" aria-orientation="horizontal"
            aria-label="Choose value" aria-valuemin="0" aria-valuemax="100"
            aria-valuenow="50" aria-valuetext="Value 50">
      <svg class="spk__ic" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M96 64v128a8 8 0 0 1-16 0V64a8 8 0 0 1 16 0m88 0v128a8 8 0 0 1-16 0V64a8 8 0 0 1 16 0" opacity=".2"/><path d="M188 32a8 8 0 0 0-8 8v176a8 8 0 0 0 16 0V40a8 8 0 0 0-8-8M76 32a8 8 0 0 0-8 8v176a8 8 0 0 0 16 0V40a8 8 0 0 0-8-8"/></g></svg>
    </button>
  </div>

  <p class="spk__hint">Drag on the bars or press the arrow keys and the values you pass become part of the trail.</p>

  <div class="sr">
    <span aria-live="polite" id="spk-live"></span>
  </div>
</figure>
</main>

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

// 스파크라인 궤적 피커 — 드래그·키보드로 값(0~100)을 정하면 매 프레임 관성 보간된
// 현재값을 좌표 배열(trail) 끝에 쌓고 맨 앞 값을 버려 고정 길이(48)를 유지한 채
// 그 배열 전체를 꺾은선 경로(d 속성)로 다시 그린다. CSS @keyframes 는 0개
// (궤적이 매 프레임 배열 연산으로 바뀌는 실수라 선언형으로 못 담는다, 398-01/02 와 같은 이유).
// picker-graph-sparkline-trail-length(JS, TRAIL_LENGTH)가 궤적 점 개수를 정한다 — 변형 03 의 조정 대상.

$duration: $dur-loop;
$easing: $ease-lerp-settle;
$color: $subject-blue;

@include stage($stage-orange);

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

.spk {
  box-sizing: border-box;
  width: min(424px, 92vw);
  margin: 0; padding: $sp-3;
  display: flex; flex-direction: column; gap: $sp-2;
  border-radius: $r-card;
  background: $stage-paper;
  box-shadow: $shadow-raised;
  color: $subject-ink;
}

.spk__head { display: flex; align-items: baseline; justify-content: space-between; gap: $sp-2; padding: 0 $sp-1; }
.spk__title { font-size: 13px; line-height: 18px; font-weight: 800; letter-spacing: .02em; }
.spk__stat { font-size: 12px; line-height: 18px; font-weight: 800; font-variant-numeric: tabular-nums; color: rgba($subject-ink, .62); }
.spk__n { color: $subject-blue-deep; }

.spk__zone { padding: 0 $sp-1; }
.spk__chart { display: block; width: 100%; height: 116px; overflow: visible; }
.spk__base { stroke: rgba($subject-ink, .16); stroke-width: 2; }
.spk__area { fill: mix($subject-blue, $stage-paper, 88%); stroke: none; }
.spk__line { fill: none; stroke: $subject-blue-deep; stroke-width: 3; stroke-linejoin: round; stroke-linecap: round; }
.spk__dot { fill: $subject-blue-deep; stroke: $stage-paper; stroke-width: 2; }

.spk__track {
  position: relative;
  height: 24px;
  margin: 0 $sp-1;
  border-radius: $r-pill;
  background: mix($subject-blue, $stage-paper, 14%);
}
.spk__rail {
  position: absolute; left: $sp-3; right: $sp-3; top: 50%;
  height: 3px; transform: translateY(-50%);
  border-radius: $r-pill;
  background: rgba($subject-ink, .18);
}
.spk__grab {
  position: absolute; top: 50%; left: 50%;
  width: 26px; height: 26px;
  margin: 0; padding: 0; border: 0; border-radius: 50%;
  display: grid; place-items: center;
  background: $subject-blue-deep;
  color: $stage-paper;
  transform: translate(-50%, -50%);
  cursor: ew-resize;
  touch-action: none;
}
.spk__grab:focus-visible { outline: 2px solid $subject-blue-deep; outline-offset: 2px; }
.spk__ic { width: 13px; height: 13px; }

.spk__hint { margin: 0; padding: 0 $sp-1; font-size: 11px; line-height: 16px; color: rgba($subject-ink, .62); }

@media (max-width: 340px) {
  .spk { padding: $sp-2; gap: $sp-1; }
  .spk__hint { display: none; }
  .spk__title { font-size: 12px; line-height: 16px; }
  .spk__stat { font-size: 11px; line-height: 16px; }
  .spk__chart { height: 108px; }
  .spk__grab { width: 22px; height: 22px; }
}

// reduce — rAF 루프를 시작하지 않는다. 드래그·키 입력은 current=value 를 즉시 맞추고
// trail 에 한 번 push 한 뒤 paint() 를 그 자리에서 호출해 화면에 반영한다.
@media (prefers-reduced-motion: reduce) {
  .spk.is-still .spk__line { 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: #ff4d1f;
  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;
}

.spk {
  box-sizing: border-box;
  width: min(424px, 92vw);
  margin: 0;
  padding: 12px;
  display: flex;
  flex-direction: column;
  gap: 8px;
  border-radius: 16px;
  background: #ffffff;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  color: #17141a;
}

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

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

.spk__stat {
  font-size: 12px;
  line-height: 18px;
  font-weight: 800;
  font-variant-numeric: tabular-nums;
  color: rgba(23, 20, 26, 0.62);
}

.spk__n {
  color: #0a4fe8;
}

.spk__zone {
  padding: 0 4px;
}

.spk__chart {
  display: block;
  width: 100%;
  height: 116px;
  overflow: visible;
}

.spk__base {
  stroke: rgba(23, 20, 26, 0.16);
  stroke-width: 2;
}

.spk__area {
  fill: rgb(28.2196078431%, 49.6156862745%, 96.8941176471%);
  stroke: none;
}

.spk__line {
  fill: none;
  stroke: #0a4fe8;
  stroke-width: 3;
  stroke-linejoin: round;
  stroke-linecap: round;
}

.spk__dot {
  fill: #0a4fe8;
  stroke: #ffffff;
  stroke-width: 2;
}

.spk__track {
  position: relative;
  height: 24px;
  margin: 0 4px;
  border-radius: 999px;
  background: rgb(88.5803921569%, 91.9843137255%, 99.5058823529%);
}

.spk__rail {
  position: absolute;
  left: 12px;
  right: 12px;
  top: 50%;
  height: 3px;
  transform: translateY(-50%);
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.18);
}

.spk__grab {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 26px;
  height: 26px;
  margin: 0;
  padding: 0;
  border: 0;
  border-radius: 50%;
  display: grid;
  place-items: center;
  background: #0a4fe8;
  color: #ffffff;
  transform: translate(-50%, -50%);
  cursor: ew-resize;
  touch-action: none;
}

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

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

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

@media (max-width: 340px) {
  .spk {
    padding: 8px;
    gap: 4px;
  }
  .spk__hint {
    display: none;
  }
  .spk__title {
    font-size: 12px;
    line-height: 16px;
  }
  .spk__stat {
    font-size: 11px;
    line-height: 16px;
  }
  .spk__chart {
    height: 108px;
  }
  .spk__grab {
    width: 22px;
    height: 22px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .spk.is-still .spk__line {
    transition: none !important;
  }
}

// 실제 동작: pointerdown/move/up 과 keydown(화살표·Home·End) 이 Value(0~100)을 바꾸면,
// 매 프레임 현재(관성 보간) 값을 좌표 배열(trail) 끝에 쌓고 맨 앞 값은 버려
// 고정 길이를 유지한 채 그 배열 전체를 꺾은선 경로(d 속성)로 다시 그린다.
// CSS @keyframes 없음(궤적이 매 프레임 배열 연산으로 바뀌는 실수라 선언형으로 못 담는다, 398-01/02 와 같은 이유).
var root = document.getElementById('spk');
var track = document.getElementById('track');
var grab = document.getElementById('grab');
var lineEl = document.getElementById('line');
var areaEl = document.getElementById('area');
var dotEl = document.getElementById('dot');
var valEl = document.getElementById('spk-val');
var live = document.getElementById('spk-live');

var TRAIL_LENGTH = 48;          // picker-graph-sparkline-trail-length — 변형 03 의 조정 대상
var CHART_W = 480, CHART_H = 150;
var LERP_RATE = 0.24;
var AUTO_PERIOD = 1.3;
var STEP = 5;

var trail = [];
for (var i = 0; i < TRAIL_LENGTH; i++) trail.push(50);

var value = 50;
var current = 50;
var manual = false;
var autoT = 0;
var lastTs = 0;
var trackRect = null;
var rafId = 0;

function reduced() {
  return window.matchMedia && window.matchMedia('(prefers-reduced-motion: reduce)').matches;
}

function yOf(v) { return CHART_H - (v / 100) * CHART_H; }

function buildPoints() {
  var step = CHART_W / (TRAIL_LENGTH - 1);
  var pts = [];
  for (var i = 0; i < TRAIL_LENGTH; i++) pts.push([i * step, yOf(trail[i])]);
  return pts;
}

function paint() {
  var pts = buildPoints();
  var d = 'M ' + pts[0][0] + ' ' + pts[0][1];
  for (var i = 1; i < pts.length; i++) d += ' L ' + pts[i][0] + ' ' + pts[i][1];
  lineEl.setAttribute('d', d);
  areaEl.setAttribute('d', d + ' L ' + pts[pts.length - 1][0] + ' ' + CHART_H + ' L ' + pts[0][0] + ' ' + CHART_H + ' Z');
  var last = pts[pts.length - 1];
  dotEl.setAttribute('cx', String(last[0]));
  dotEl.setAttribute('cy', String(last[1]));
  var rv = Math.round(current);
  valEl.textContent = String(rv);
  grab.style.left = value + '%';
  grab.setAttribute('aria-valuenow', String(Math.round(value)));
  grab.setAttribute('aria-valuetext', 'Value ' + Math.round(value));
}

function announce() {
  live.textContent = 'Value ' + Math.round(current) + ' added to the trail';
}

function setValue(v, isManual) {
  value = Math.max(0, Math.min(100, v));
  if (isManual) { manual = true; root.classList.remove('is-demo'); }
}

function fromPointer(clientX) {
  if (!trackRect) trackRect = track.getBoundingClientRect();
  var ratio = (clientX - trackRect.left) / trackRect.width;
  setValue(ratio * 100, true);
}

function pushTrail() {
  trail.shift();
  trail.push(current);
}

function reflectNow() {
  current = value;
  pushTrail();
  paint();
  announce();
}

function onDown(e) {
  trackRect = track.getBoundingClientRect();
  if (grab.setPointerCapture) { try { grab.setPointerCapture(e.pointerId); } catch (err) {} }
  fromPointer(e.clientX);
  if (reduced()) reflectNow();
}
function onMove(e) { fromPointer(e.clientX); if (reduced()) reflectNow(); }
function onUp() { announce(); }
function onTrackDown(e) { trackRect = track.getBoundingClientRect(); fromPointer(e.clientX); if (reduced()) reflectNow(); }

function onKey(e) {
  var map = { ArrowLeft: -STEP, ArrowDown: -STEP, ArrowRight: STEP, ArrowUp: STEP };
  if (e.key === 'Home') { setValue(0, true); e.preventDefault(); }
  else if (e.key === 'End') { setValue(100, true); e.preventDefault(); }
  else if (map[e.key] !== undefined) { setValue(value + map[e.key], true); e.preventDefault(); }
  else { return; }
  if (reduced()) reflectNow();
}

function onResize() { trackRect = track.getBoundingClientRect(); if (reduced()) paint(); }

function autoStep(dt) {
  autoT += dt;
  var omega = 2 * Math.PI / AUTO_PERIOD;
  value = 50 + 42 * Math.sin(autoT * omega) + 8 * Math.sin(autoT * omega * 2.7);
}

function frame(ts) {
  if (!lastTs) lastTs = ts;
  var dt = Math.min(0.05, (ts - lastTs) / 1000);
  lastTs = ts;
  if (!manual) autoStep(dt);
  current += (value - current) * LERP_RATE;
  pushTrail();
  paint();
  rafId = requestAnimationFrame(frame);
}

grab.addEventListener('pointerdown', onDown);
grab.addEventListener('pointermove', onMove);
grab.addEventListener('pointerup', onUp);
grab.addEventListener('keydown', onKey);
track.addEventListener('pointerdown', onTrackDown);
window.addEventListener('resize', onResize);

if (reduced()) {
  root.classList.add('is-still');
  current = value;
  paint();
} else {
  paint();
  rafId = requestAnimationFrame(frame);
}

// SparklineTrailDrag — vanilla 판(run/398/demo/03-picker-graph-sparkline-trail-drag/index.html) 의 React 포트.
// 드래그·키보드로 값(0~100)을 정하면 매 프레임 관성 보간된 현재값을 좌표 배열(trail) 끝에
// 쌓고 맨 앞 값을 버려 고정 길이를 유지한 채 그 배열 전체를 꺾은선 경로로 다시 그린다.
import { useEffect, useRef } from "react";
import styles from "./SparklineTrailDrag.module.scss";

type Box<T> = { current: T };
type KeyEvt = { key: string; preventDefault(): void };
type PtrEvt = { clientX: number; clientY: number; pointerId: number };

const TRAIL_LENGTH = 48;                 // picker-graph-sparkline-trail-length — 변형 03 의 조정 대상
const CHART_W = 480, CHART_H = 150;
const LERP_RATE = 0.24;
const AUTO_PERIOD = 1.3;
const STEP = 5;

function yOf(v: number): number {
  return CHART_H - (v / 100) * CHART_H;
}

export default function SparklineTrailDrag() {
  const rootRef = useRef<HTMLElement | null>(null);
  const trackRef = useRef<HTMLDivElement | null>(null);
  const grabRef = useRef<HTMLButtonElement | null>(null);
  const lineRef = useRef<SVGPathElement | null>(null);
  const areaRef = useRef<SVGPathElement | null>(null);
  const dotRef = useRef<SVGCircleElement | null>(null);
  const valRef = useRef<HTMLElement | null>(null);
  const liveRef = useRef<HTMLSpanElement | null>(null);

  const trail = useRef(new Array(TRAIL_LENGTH).fill(50)) as Box<number[]>;
  const value = useRef(50) as Box<number>;
  const current = useRef(50) as Box<number>;
  const manual = useRef(false) as Box<boolean>;
  const autoT = useRef(0) as Box<number>;
  const lastTs = useRef(0) as Box<number>;
  const trackRect = useRef<DOMRect | null>(null) as Box<DOMRect | null>;
  const rafId = useRef(0) as Box<number>;

  function reduced(): boolean {
    return window.matchMedia("(prefers-reduced-motion: reduce)").matches;
  }

  function buildPoints(): [number, number][] {
    const step = CHART_W / (TRAIL_LENGTH - 1);
    const pts: [number, number][] = [];
    for (let i = 0; i < TRAIL_LENGTH; i++) pts.push([i * step, yOf(trail.current[i])]);
    return pts;
  }

  function paint(): void {
    const pts = buildPoints();
    let d = "M " + pts[0][0] + " " + pts[0][1];
    for (let i = 1; i < pts.length; i++) d += " L " + pts[i][0] + " " + pts[i][1];
    lineRef.current?.setAttribute("d", d);
    areaRef.current?.setAttribute(
      "d",
      d + " L " + pts[pts.length - 1][0] + " " + CHART_H + " L " + pts[0][0] + " " + CHART_H + " Z"
    );
    const last = pts[pts.length - 1];
    dotRef.current?.setAttribute("cx", String(last[0]));
    dotRef.current?.setAttribute("cy", String(last[1]));
    const rv = Math.round(current.current);
    if (valRef.current) valRef.current.textContent = String(rv);
    const grab = grabRef.current;
    if (grab) {
      grab.style.left = value.current + "%";
      grab.setAttribute("aria-valuenow", String(Math.round(value.current)));
      grab.setAttribute("aria-valuetext", "값 " + Math.round(value.current));
    }
  }

  function announce(): void {
    if (liveRef.current) liveRef.current.textContent = "값 " + Math.round(current.current) + "이(가) 궤적에 더해짐";
  }

  function setValue(v: number, isManual: boolean): void {
    value.current = Math.max(0, Math.min(100, v));
    if (isManual) {
      manual.current = true;
      rootRef.current?.classList.remove("is-demo");
    }
  }

  function fromPointer(clientX: number): void {
    if (!trackRect.current && trackRef.current) trackRect.current = trackRef.current.getBoundingClientRect();
    const rect = trackRect.current;
    if (!rect) return;
    const ratio = (clientX - rect.left) / rect.width;
    setValue(ratio * 100, true);
  }

  function pushTrail(): void {
    trail.current.shift();
    trail.current.push(current.current);
  }

  function reflectNow(): void {
    current.current = value.current;
    pushTrail();
    paint();
    announce();
  }

  function onDown(e: PtrEvt): void {
    if (trackRef.current) trackRect.current = trackRef.current.getBoundingClientRect();
    const grab = grabRef.current;
    if (grab && typeof grab.setPointerCapture === "function") {
      try { grab.setPointerCapture(e.pointerId); } catch { /* 캡처 실패는 치명적이지 않다 */ }
    }
    fromPointer(e.clientX);
    if (reduced()) reflectNow();
  }
  function onMove(e: PtrEvt): void {
    fromPointer(e.clientX);
    if (reduced()) reflectNow();
  }
  function onUp(): void {
    announce();
  }
  function onTrackDown(e: PtrEvt): void {
    if (trackRef.current) trackRect.current = trackRef.current.getBoundingClientRect();
    fromPointer(e.clientX);
    if (reduced()) reflectNow();
  }

  function onKey(e: KeyEvt): void {
    const map: Record<string, number> = { ArrowLeft: -STEP, ArrowDown: -STEP, ArrowRight: STEP, ArrowUp: STEP };
    if (e.key === "Home") { setValue(0, true); e.preventDefault(); }
    else if (e.key === "End") { setValue(100, true); e.preventDefault(); }
    else if (map[e.key] !== undefined) { setValue(value.current + map[e.key], true); e.preventDefault(); }
    else { return; }
    if (reduced()) reflectNow();
  }

  function onResize(): void {
    if (trackRef.current) trackRect.current = trackRef.current.getBoundingClientRect();
    if (reduced()) paint();
  }

  function autoStep(dt: number): void {
    autoT.current += dt;
    const omega = (2 * Math.PI) / AUTO_PERIOD;
    value.current = 50 + 42 * Math.sin(autoT.current * omega) + 8 * Math.sin(autoT.current * omega * 2.7);
  }

  function frame(ts: number): void {
    if (!lastTs.current) lastTs.current = ts;
    const dt = Math.min(0.05, (ts - lastTs.current) / 1000);
    lastTs.current = ts;
    if (!manual.current) autoStep(dt);
    current.current += (value.current - current.current) * LERP_RATE;
    pushTrail();
    paint();
    rafId.current = requestAnimationFrame(frame);
  }

  useEffect(() => {
    window.addEventListener("resize", onResize);
    if (reduced()) {
      rootRef.current?.classList.add("is-still");
      reflectNow();
    } else {
      paint();
      rafId.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafId.current);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <figure className={styles.spk + " is-demo"} ref={rootRef}>
        <div className={styles.head}>
          <span className={styles.title}>지나온 값의 궤적</span>
          <span className={styles.stat} aria-hidden="true">값 <b className={styles.n} ref={valRef}>50</b></span>
        </div>

        <div className={styles.zone}>
          <svg
            className={styles.chart}
            viewBox="0 0 480 160"
            preserveAspectRatio="none"
            role="img"
            aria-label="지나온 48개 값을 이은 꺾은선 그래프, 값이 바뀔 때마다 오래된 점은 왼쪽으로 밀려나고 새 점이 오른쪽에 더해진다"
          >
            <line className={styles.base} x1={0} y1={150} x2={480} y2={150} />
            <path className={styles.area} ref={areaRef} />
            <path className={styles.line} ref={lineRef} />
            <circle className={styles.dot} ref={dotRef} r={5} />
          </svg>
        </div>

        <div className={styles.track} ref={trackRef} onPointerDown={onTrackDown}>
          <span className={styles.rail} aria-hidden="true" />
          <button
            className={styles.grab}
            ref={grabRef}
            type="button"
            role="slider"
            aria-orientation="horizontal"
            aria-label="값 고르기"
            aria-valuemin={0}
            aria-valuemax={100}
            aria-valuenow={50}
            aria-valuetext="값 50"
            onPointerDown={onDown}
            onPointerMove={onMove}
            onPointerUp={onUp}
            onKeyDown={onKey}
          >
            <svg className={styles.ic} viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M96 64v128a8 8 0 0 1-16 0V64a8 8 0 0 1 16 0m88 0v128a8 8 0 0 1-16 0V64a8 8 0 0 1 16 0" opacity=".2" /><path d="M188 32a8 8 0 0 0-8 8v176a8 8 0 0 0 16 0V40a8 8 0 0 0-8-8M76 32a8 8 0 0 0-8 8v176a8 8 0 0 0 16 0V40a8 8 0 0 0-8-8" /></g></svg>
          </button>
        </div>

        <p className={styles.hint}>막대 위를 드래그하거나 화살표키를 누르면 지나온 값이 궤적으로 이어집니다</p>

        <div className={styles.sr}>
          <span aria-live="polite" ref={liveRef} />
        </div>
      </figure>
    </main>
  );
}