01Vertical splitter

<main class="stage">
  <div class="vs is-demo" id="vs-root">
    <div class="vs__box" id="vs-box">
      <section class="vs__pane vs__pane--list" aria-label="Mail list">
        <span class="vs__row"></span>
        <span class="vs__row"></span>
        <span class="vs__row"></span>
        <span class="vs__row"></span>
      </section>
      <div class="vs__bar" id="vs-bar" role="separator" tabindex="0"
           aria-orientation="vertical" aria-label="List width" aria-valuemin="20" aria-valuemax="80" aria-valuenow="50">
        <i class="vs__grip" aria-hidden="true"></i>
      </div>
      <section class="vs__pane vs__pane--read" aria-label="Mail body">
        <b class="vs__title"></b>
        <span class="vs__line"></span>
        <span class="vs__line vs__line--short"></span>
        <span class="vs__line"></span>
      </section>
    </div>
    <p class="vs__cap">Drag the handle sideways to set the width</p>
  </div>
</main>

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

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

@include stage($stage-ink);

// 등록해야 키프레임에서 보간된다 — 등록 안 하면 --split 은 문자열이라 27% 에서 툭 끊긴다
@property --split {
  syntax: "<percentage>";
  inherits: true;
  initial-value: 50%;
}

.vs {
  --split: 50%;
  width: min(312px, 88vw);
  display: flex;
  flex-direction: column;
  gap: $sp-2;
}
.vs__box {
  display: grid;
  grid-template-columns: var(--split) 10px 1fr;
  height: 128px;
  border-radius: $r-card;
  overflow: hidden;
  background: rgba(255, 255, 255, .06);
}
.vs__pane {
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
  padding: $sp-3;
  overflow: hidden;
}
.vs__pane--list { background: rgba(47, 109, 246, .18); }
.vs__pane--read { background: rgba(255, 247, 230, .07); }

.vs__row {
  flex: 0 0 auto;
  height: 12px;
  border-radius: $r-xs;
  background: rgba(255, 247, 230, .34);
}
.vs__row:nth-child(2) { background: $color; }
.vs__title {
  flex: 0 0 auto;
  height: 14px;
  width: 60%;
  border-radius: $r-xs;
  background: $subject-cream;
}
.vs__line {
  flex: 0 0 auto;
  height: 8px;
  border-radius: $r-xs;
  background: rgba(255, 247, 230, .26);
}
.vs__line--short { width: 64%; }

.vs__bar {
  display: grid;
  place-items: center;
  background: rgba(255, 247, 230, .14);
  cursor: col-resize;
  touch-action: none;
  transition: background $duration $easing;
}
.vs__grip {
  display: block;
  width: 2px;
  height: 28px;
  border-radius: $r-pill;
  background: $subject-cream;
  transition: transform $duration $easing;
}
.vs__bar:hover,
.vs.is-drag .vs__bar { background: $color; }
.vs__bar:hover .vs__grip,
.vs.is-drag .vs__grip { transform: scaleY(1.5); }
.vs__bar:focus-visible { outline: 2px solid $subject-cream; outline-offset: -2px; }

.vs__cap {
  margin: 0;
  font-size: 11px;
  line-height: 14px;
  font-weight: 600;
  color: rgba(255, 247, 230, .58);
  text-align: center;
}

// ── 자동 루프: 50% → 좁게 → 넓게 → 50%. 복귀는 88% 안에서 끝난다 ──
.vs.is-demo { animation: vs-split $dur-loop $easing infinite; }
@keyframes vs-split {
  0%, 8% { --split: 50%; }
  36% { --split: 26%; }
  64% { --split: 72%; }
  88%, 100% { --split: 50%; }
}
.vs.is-demo .vs__bar { animation: vs-hot $dur-loop $easing infinite; }
@keyframes vs-hot {
  0%, 8% { background: rgba(255, 247, 230, .14); }
  20%, 76% { background: $subject-blue; }
  88%, 100% { background: rgba(255, 247, 230, .14); }
}

@media (prefers-reduced-motion: reduce) {
  .vs.is-demo,
  .vs.is-demo .vs__bar { animation: none !important; }
  .vs__bar, .vs__grip { transition: none; }
}

@media (max-width: 340px) {
  .vs__box { height: 112px; }
  .vs__pane { padding: $sp-2; }
}

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);
}

@property --split {
  syntax: "<percentage>";
  inherits: true;
  initial-value: 50%;
}
.vs {
  --split: 50%;
  width: min(312px, 88vw);
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.vs__box {
  display: grid;
  grid-template-columns: var(--split) 10px 1fr;
  height: 128px;
  border-radius: 16px;
  overflow: hidden;
  background: rgba(255, 255, 255, 0.06);
}

.vs__pane {
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  gap: 8px;
  padding: 12px;
  overflow: hidden;
}

.vs__pane--list {
  background: rgba(47, 109, 246, 0.18);
}

.vs__pane--read {
  background: rgba(255, 247, 230, 0.07);
}

.vs__row {
  flex: 0 0 auto;
  height: 12px;
  border-radius: 4px;
  background: rgba(255, 247, 230, 0.34);
}

.vs__row:nth-child(2) {
  background: #2f6df6;
}

.vs__title {
  flex: 0 0 auto;
  height: 14px;
  width: 60%;
  border-radius: 4px;
  background: #fff7e6;
}

.vs__line {
  flex: 0 0 auto;
  height: 8px;
  border-radius: 4px;
  background: rgba(255, 247, 230, 0.26);
}

.vs__line--short {
  width: 64%;
}

.vs__bar {
  display: grid;
  place-items: center;
  background: rgba(255, 247, 230, 0.14);
  cursor: col-resize;
  touch-action: none;
  transition: background 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.vs__grip {
  display: block;
  width: 2px;
  height: 28px;
  border-radius: 999px;
  background: #fff7e6;
  transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.vs__bar:hover,
.vs.is-drag .vs__bar {
  background: #2f6df6;
}

.vs__bar:hover .vs__grip,
.vs.is-drag .vs__grip {
  transform: scaleY(1.5);
}

.vs__bar:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: -2px;
}

.vs__cap {
  margin: 0;
  font-size: 11px;
  line-height: 14px;
  font-weight: 600;
  color: rgba(255, 247, 230, 0.58);
  text-align: center;
}

.vs.is-demo {
  animation: vs-split 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes vs-split {
  0%, 8% {
    --split: 50%;
  }
  36% {
    --split: 26%;
  }
  64% {
    --split: 72%;
  }
  88%, 100% {
    --split: 50%;
  }
}
.vs.is-demo .vs__bar {
  animation: vs-hot 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes vs-hot {
  0%, 8% {
    background: rgba(255, 247, 230, 0.14);
  }
  20%, 76% {
    background: #2f6df6;
  }
  88%, 100% {
    background: rgba(255, 247, 230, 0.14);
  }
}
@media (prefers-reduced-motion: reduce) {
  .vs.is-demo,
  .vs.is-demo .vs__bar {
    animation: none !important;
  }
  .vs__bar, .vs__grip {
    transition: none;
  }
}
@media (max-width: 340px) {
  .vs__box {
    height: 112px;
  }
  .vs__pane {
    padding: 8px;
  }
}

// 실제 동작: 포인터 델타 → 왼쪽 트랙 폭(--split). 최소 폭 64px 에서 클램프. 화살표 키는 4%씩.
var root = document.getElementById('vs-root');
var box = document.getElementById('vs-box');
var bar = document.getElementById('vs-bar');
var MIN = 64, BAR = 10, dragging = false;

function set(pct) {
  var w = box.clientWidth;
  var lo = MIN / w * 100, hi = (w - MIN - BAR) / w * 100;
  var v = Math.max(lo, Math.min(pct, hi));
  root.style.setProperty('--split', v.toFixed(1) + '%');
  bar.setAttribute('aria-valuenow', String(Math.round(v)));
}
function stop() { root.classList.remove('is-demo'); }

bar.addEventListener('pointerdown', function (e) {
  stop();
  dragging = true;
  bar.setPointerCapture(e.pointerId);
  root.classList.add('is-drag');
  e.preventDefault();
});
bar.addEventListener('pointermove', function (e) {
  if (!dragging) return;
  set((e.clientX - box.getBoundingClientRect().left) / box.clientWidth * 100);
});
function drop() { dragging = false; root.classList.remove('is-drag'); }
bar.addEventListener('pointerup', drop);
bar.addEventListener('pointercancel', drop);
bar.addEventListener('keydown', function (e) {
  var now = Number(bar.getAttribute('aria-valuenow'));
  var d = e.key === 'ArrowLeft' ? -4 : e.key === 'ArrowRight' ? 4 : 0;
  if (!d) return;
  stop();
  set(now + d);
  bar.focus({ preventScroll: true });
  e.preventDefault();
});

import { useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./VerticalSplitter.module.scss";

export type VerticalSplitterProps = {
  /** 시작 비율 (%) */
  start?: number;
  /** 양쪽 최소 폭 (px) */
  minWidth?: number;
  duration?: number;
  easing?: string;
  color?: string;
};

type PEvt = { clientX: number; pointerId: number; preventDefault(): void; currentTarget: { setPointerCapture(id: number): void } };
type KeyEvt = { key: string; preventDefault(): void };
type Vars = CSSProperties & { "--split"?: string; "--duration"?: string; "--easing"?: string; "--color"?: string };

const BAR = 10;

export default function VerticalSplitter({
  start = 50,
  minWidth = 64,
  duration = 220,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
}: VerticalSplitterProps) {
  const [split, setSplit] = useState(start);
  const [drag, setDrag] = useState(false);
  const boxRef = useRef<HTMLDivElement>(null);

  function set(pct: number): void {
    const box = boxRef.current;
    if (!box) return;
    const w = box.clientWidth;
    const lo = (minWidth / w) * 100;
    const hi = ((w - minWidth - BAR) / w) * 100;
    setSplit(Math.max(lo, Math.min(pct, hi)));
  }

  function onDown(e: PEvt): void {
    setDrag(true);
    e.currentTarget.setPointerCapture(e.pointerId);
    e.preventDefault();
  }
  function onMove(e: PEvt): void {
    const box = boxRef.current;
    if (!drag || !box) return;
    set(((e.clientX - box.getBoundingClientRect().left) / box.clientWidth) * 100);
  }
  function onUp(): void { setDrag(false); }
  function onKey(e: KeyEvt): void {
    const d = e.key === "ArrowLeft" ? -4 : e.key === "ArrowRight" ? 4 : 0;
    if (!d) return;
    set(split + d);
    e.preventDefault();
  }

  const vars: Vars = {
    "--split": `${split.toFixed(1)}%`,
    "--duration": `${duration}ms`,
    "--easing": easing,
    "--color": color,
  };

  return (
    <div className={drag ? `${styles.vs} ${styles.isDrag}` : styles.vs} style={vars}>
      <div className={styles.box} ref={boxRef}>
        <section className={`${styles.pane} ${styles.paneList}`} aria-label="Mail list">
          <span className={styles.row} />
          <span className={`${styles.row} ${styles.rowOn}`} />
          <span className={styles.row} />
          <span className={styles.row} />
        </section>
        <div
          className={styles.bar}
          role="separator"
          tabIndex={0}
          aria-orientation="vertical"
          aria-label="List width"
          aria-valuemin={20}
          aria-valuemax={80}
          aria-valuenow={Math.round(split)}
          onPointerDown={onDown}
          onPointerMove={onMove}
          onPointerUp={onUp}
          onPointerCancel={onUp}
          onKeyDown={onKey}
        >
          <i className={styles.grip} aria-hidden="true" />
        </div>
        <section className={`${styles.pane} ${styles.paneRead}`} aria-label="Mail body">
          <b className={styles.title} />
          <span className={styles.line} />
          <span className={`${styles.line} ${styles.lineShort}`} />
          <span className={styles.line} />
        </section>
      </div>
      <p className={styles.cap}>Drag the handle sideways to set the width</p>
    </div>
  );
}