04Rubber-band limit — a pull whose extension shrinks sharply once a maximum distance value is passed

<main class="stage">
<div class="prrbo is-demo" id="prrbo">
  <div class="prrbo__panel">
    <div class="prrbo__track" id="prrboTrack">
      <span class="prrbo__cap"></span>
      <span class="prrbo__marker" id="prrboMarker"></span>
    </div>
    <div class="prrbo__phone" id="prrboPhone">
      <div class="prrbo__list" id="prrboList">
        <div class="prrbo__row"></div>
        <div class="prrbo__row"></div>
      </div>
    </div>
  </div>
  <span class="prrbo__hint" id="prrboHint">Pull down</span>
</div>
</main>

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

// 계산 겹(지수 감쇠 displayedOf())은 JS 에 있다 — 여기는 정적 배치만.
@include stage($stage-orange);

.prrbo {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-3;
}

.prrbo__panel {
  display: flex;
  align-items: flex-end;
  gap: $sp-4;
  padding: $sp-4;
  border-radius: $r-card;
  background: $stage-paper;
}

.prrbo__track {
  position: relative;
  width: 20px;
  height: 92px;
  border-radius: $r-xs;
  background: $subject-cream;
}

.prrbo__cap {
  position: absolute;
  left: -4px;
  right: -4px;
  bottom: 77px;
  height: 2px;
  background: $subject-orange-deep;
}

.prrbo__marker {
  position: absolute;
  left: 2px;
  right: 2px;
  bottom: 2px;
  height: 12px;
  border-radius: $r-xs;
  background: $subject-blue-deep;
}

.prrbo__phone {
  position: relative;
  width: 156px;
  height: 108px;
  overflow: hidden;
  border-radius: $r-sm;
  background: $subject-cream;
  touch-action: none;
  cursor: grab;
}

.prrbo__list {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
  padding: $sp-3;
}

.prrbo__row {
  height: 18px;
  border-radius: $r-xs;
  background: $stage-paper;
}

.prrbo__hint {
  color: $subject-ink;
  font-size: 12px;
  text-align: center;
}

@media (max-width: 340px) {
  .prrbo__panel { padding: $sp-3; gap: $sp-2; }
  .prrbo__track { height: 72px; }
  .prrbo__cap { bottom: 60px; }
  .prrbo__phone { width: 128px; height: 88px; }
}

@media (prefers-reduced-motion: reduce) {
  .prrbo__marker, .prrbo__list { 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);
}

.prrbo {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
}

.prrbo__panel {
  display: flex;
  align-items: flex-end;
  gap: 16px;
  padding: 16px;
  border-radius: 16px;
  background: #ffffff;
}

.prrbo__track {
  position: relative;
  width: 20px;
  height: 92px;
  border-radius: 4px;
  background: #fff7e6;
}

.prrbo__cap {
  position: absolute;
  left: -4px;
  right: -4px;
  bottom: 77px;
  height: 2px;
  background: #c93000;
}

.prrbo__marker {
  position: absolute;
  left: 2px;
  right: 2px;
  bottom: 2px;
  height: 12px;
  border-radius: 4px;
  background: #0a4fe8;
}

.prrbo__phone {
  position: relative;
  width: 156px;
  height: 108px;
  overflow: hidden;
  border-radius: 8px;
  background: #fff7e6;
  touch-action: none;
  cursor: grab;
}

.prrbo__list {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: 8px;
  padding: 12px;
}

.prrbo__row {
  height: 18px;
  border-radius: 4px;
  background: #ffffff;
}

.prrbo__hint {
  color: #17141a;
  font-size: 12px;
  text-align: center;
}

@media (max-width: 340px) {
  .prrbo__panel {
    padding: 12px;
    gap: 8px;
  }
  .prrbo__track {
    height: 72px;
  }
  .prrbo__cap {
    bottom: 60px;
  }
  .prrbo__phone {
    width: 128px;
    height: 88px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .prrbo__marker, .prrbo__list {
    transition: none !important;
  }
}

(function () {
  var phone = document.getElementById('prrboPhone');
  var marker = document.getElementById('prrboMarker');
  var list = document.getElementById('prrboList');
  var hint = document.getElementById('prrboHint');
  var root = document.getElementById('prrbo');

  // 계산 겹: LINEAR(70px) 까지는 raw 에 0.9 배로 거의 그대로 따라가다가, 그 뒤로는 MAX_D(120px) 에
  // 점근하는 지수 감쇠(1-e^-x/K)로 늘어나는 폭이 급격히 줄어든다 — 같은 힘이라도 한계 근처에선 거의 안 늘어난다.
  var LINEAR = 70, MAX_D = 120, K = 42, RAW_MAX = 260;
  var TRACK_H = 92, SCALE = TRACK_H / 150;

  function displayedOf(raw) {
    if (raw <= LINEAR) { return raw * 0.9; }
    var base = LINEAR * 0.9;
    var excess = raw - LINEAR;
    return base + (MAX_D - base) * (1 - Math.exp(-excess / K));
  }

  function apply(raw) {
    var displayed = displayedOf(raw);
    marker.style.transform = 'translateY(' + (-(displayed * SCALE)).toFixed(1) + 'px)';
    list.style.transform = 'translateY(' + (displayed * 0.55).toFixed(1) + 'px)';
    var pctOfCap = Math.round((displayed / MAX_D) * 100);
    hint.textContent = raw > 4 ? ('Displaced ' + Math.round(displayed) + 'px · of limit ' + pctOfCap + '%') : 'Pull down';
  }

  var raw = 0, target = 0, raf = null;
  function settle() {
    raw += (target - raw) * 0.3;
    if (Math.abs(target - raw) < 0.3) { raw = target; }
    apply(raw);
    if (raw !== target) { raf = requestAnimationFrame(settle); } else { raf = null; }
  }
  function goTo(v) { target = v; if (raf === null) { raf = requestAnimationFrame(settle); } }

  var dragging = false, startY = 0, startRaw = 0;
  function onDown(y) { dragging = true; startY = y; startRaw = raw; if (raf) { cancelAnimationFrame(raf); raf = null; } }
  function onMove(y) {
    if (!dragging) { return; }
    raw = Math.max(0, Math.min(RAW_MAX, startRaw + (y - startY)));
    apply(raw);
  }
  function onUp() { if (!dragging) { return; } dragging = false; goTo(0); }

  function wireReal() {
    phone.addEventListener('pointerdown', function (e) { root.classList.remove('is-demo'); stopAutoplay(); onDown(e.clientY); });
    window.addEventListener('pointermove', function (e) { onMove(e.clientY); });
    window.addEventListener('pointerup', onUp);
  }
  phone.style.touchAction = 'none';
  wireReal();
  apply(0);

  // 자동 루프: raw 를 RAW_MAX 까지 크게 밀어 넣어 한계선에 점근만 하고 못 넘는 모습을 보인다.
  var autoRaw = 0, autoTimer = null, autoDir = 1;
  function autoTick() {
    autoRaw += autoDir * 55;
    if (autoRaw >= RAW_MAX) { autoRaw = RAW_MAX; autoDir = -1; goTo(0); return; }
    if (autoRaw <= 0 && autoDir < 0) { autoRaw = 0; autoDir = 1; }
    if (autoDir > 0) { raw = autoRaw; apply(raw); }
  }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  function stopAutoplay() { if (autoTimer) { clearInterval(autoTimer); autoTimer = null; } }
  if (!reduce) { autoTimer = setInterval(autoTick, 170); }
})();

import { useEffect, useRef } from "react";
import styles from "./PullRefreshRubberBandOverscroll.module.scss";

export type PullRefreshRubberBandOverscrollProps = {
  color?: string;
};

export default function PullRefreshRubberBandOverscroll({
  color = "#0a4fe8",
}: PullRefreshRubberBandOverscrollProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const phone = root.querySelector<HTMLDivElement>(`.${styles.phone}`);
    const marker = root.querySelector<HTMLSpanElement>(`.${styles.marker}`);
    const list = root.querySelector<HTMLDivElement>(`.${styles.list}`);
    const hint = root.querySelector<HTMLSpanElement>(`.${styles.hint}`);
    if (!phone || !marker || !list || !hint) return;

    // 계산 겹: LINEAR(70px) 까지는 raw 에 0.9 배로 거의 그대로 따라가다가, 그 뒤로는 MAX_D(120px) 에
    // 점근하는 지수 감쇠(1-e^-x/K)로 늘어나는 폭이 급격히 줄어든다 — 같은 힘이라도 한계 근처에선 거의 안 늘어난다.
    const LINEAR = 70, MAX_D = 120, K = 42, RAW_MAX = 260;
    const TRACK_H = 92, SCALE = TRACK_H / 150;

    function displayedOf(raw: number) {
      if (raw <= LINEAR) return raw * 0.9;
      const base = LINEAR * 0.9;
      const excess = raw - LINEAR;
      return base + (MAX_D - base) * (1 - Math.exp(-excess / K));
    }

    function apply(raw: number) {
      const displayed = displayedOf(raw);
      marker!.style.transform = "translateY(" + (-(displayed * SCALE)).toFixed(1) + "px)";
      list!.style.transform = "translateY(" + (displayed * 0.55).toFixed(1) + "px)";
      const pctOfCap = Math.round((displayed / MAX_D) * 100);
      hint!.textContent = raw > 4 ? ("밀림 " + Math.round(displayed) + "px · 한계의 " + pctOfCap + "%") : "아래로 당기세요";
    }

    let raw = 0, target = 0, raf: number | null = null;
    function settle() {
      raw += (target - raw) * 0.3;
      if (Math.abs(target - raw) < 0.3) raw = target;
      apply(raw);
      raf = raw !== target ? requestAnimationFrame(settle) : null;
    }
    function goTo(v: number) { target = v; if (raf === null) { raf = requestAnimationFrame(settle); } }

    let dragging = false, startY = 0, startRaw = 0;
    function onDown(y: number) {
      dragging = true; startY = y; startRaw = raw;
      if (raf !== null) { cancelAnimationFrame(raf); raf = null; }
    }
    function onMove(y: number) {
      if (!dragging) return;
      raw = Math.max(0, Math.min(RAW_MAX, startRaw + (y - startY)));
      apply(raw);
    }
    function onUp() { if (!dragging) return; dragging = false; goTo(0); }

    function onPointerDown(e: PointerEvent) { stopAutoplay(); onDown(e.clientY); }
    function onPointerMove(e: PointerEvent) { onMove(e.clientY); }
    phone.style.touchAction = "none";
    phone.addEventListener("pointerdown", onPointerDown);
    window.addEventListener("pointermove", onPointerMove);
    window.addEventListener("pointerup", onUp);
    apply(0);

    // 자동 루프: raw 를 RAW_MAX 까지 크게 밀어 넣어 한계선에 점근만 하고 못 넘는 모습을 보인다.
    let autoRaw = 0, autoTimer: number | null = null, autoDir = 1;
    function autoTick() {
      autoRaw += autoDir * 55;
      if (autoRaw >= RAW_MAX) { autoRaw = RAW_MAX; autoDir = -1; goTo(0); return; }
      if (autoRaw <= 0 && autoDir < 0) { autoRaw = 0; autoDir = 1; }
      if (autoDir > 0) { raw = autoRaw; apply(raw); }
    }
    function stopAutoplay() { if (autoTimer !== null) { window.clearInterval(autoTimer); autoTimer = null; } }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { autoTimer = window.setInterval(autoTick, 170); }

    return () => {
      stopAutoplay();
      if (raf !== null) cancelAnimationFrame(raf);
      phone.removeEventListener("pointerdown", onPointerDown);
      window.removeEventListener("pointermove", onPointerMove);
      window.removeEventListener("pointerup", onUp);
    };
  }, []);

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.prrbo}>
        <div className={styles.panel}>
          <div className={styles.track}>
            <span className={styles.cap} style={{ "--accent": color } as any} />
            <span className={styles.marker} />
          </div>
          <div className={styles.phone}>
            <div className={styles.list}>
              <div className={styles.row} />
              <div className={styles.row} />
            </div>
          </div>
        </div>
        <span className={styles.hint}>아래로 당기세요</span>
      </div>
    </div>
  );
}