07Spring settle — an indicator whose position value slightly overshoots the target after release before settling

<main class="stage">
<div class="prsp is-demo" id="prsp">
  <div class="prsp__panel">
    <div class="prsp__track" id="prspTrack">
      <span class="prsp__rest"></span>
      <span class="prsp__marker" id="prspMarker"></span>
    </div>
    <div class="prsp__phone" id="prspPhone">
      <div class="prsp__list" id="prspList">
        <div class="prsp__row"></div>
        <div class="prsp__row"></div>
      </div>
    </div>
  </div>
  <span class="prsp__hint" id="prspHint">Pull down</span>
</div>
</main>

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

// 계산 겹(스프링 적분 pos/vel)은 JS 에 있다 — 여기는 정적 배치만.
@include stage($stage-ink);

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

.prsp__panel {
  display: flex;
  align-items: flex-end;
  gap: $sp-4;
  padding: $sp-4;
  border-radius: $r-card;
  background: rgba($subject-cream, .07);
}

.prsp__track {
  position: relative;
  width: 20px;
  height: 110px;
  border-radius: $r-xs;
  background: rgba($subject-cream, .10);
}

.prsp__rest {
  position: absolute;
  left: -4px;
  right: -4px;
  bottom: 50px;
  height: 2px;
  background: $subject-mint;
}

.prsp__marker {
  position: absolute;
  left: 2px;
  right: 2px;
  bottom: 44px;
  height: 12px;
  border-radius: $r-xs;
  background: $subject-blue-light;
}

.prsp__phone {
  position: relative;
  width: 156px;
  height: 108px;
  overflow: hidden;
  border-radius: $r-sm;
  background: rgba($subject-cream, .07);
  touch-action: none;
  cursor: grab;
}

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

.prsp__row {
  height: 18px;
  border-radius: $r-xs;
  background: rgba($subject-cream, .12);
}

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

@media (max-width: 340px) {
  .prsp__panel { padding: $sp-3; gap: $sp-2; }
  .prsp__track { height: 88px; }
  .prsp__rest { bottom: 40px; }
  .prsp__marker { bottom: 34px; }
  .prsp__phone { width: 128px; height: 88px; }
}

@media (prefers-reduced-motion: reduce) {
  .prsp__marker, .prsp__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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

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

.prsp__panel {
  display: flex;
  align-items: flex-end;
  gap: 16px;
  padding: 16px;
  border-radius: 16px;
  background: rgba(255, 247, 230, 0.07);
}

.prsp__track {
  position: relative;
  width: 20px;
  height: 110px;
  border-radius: 4px;
  background: rgba(255, 247, 230, 0.1);
}

.prsp__rest {
  position: absolute;
  left: -4px;
  right: -4px;
  bottom: 50px;
  height: 2px;
  background: #4cd4a6;
}

.prsp__marker {
  position: absolute;
  left: 2px;
  right: 2px;
  bottom: 44px;
  height: 12px;
  border-radius: 4px;
  background: #5b8cf8;
}

.prsp__phone {
  position: relative;
  width: 156px;
  height: 108px;
  overflow: hidden;
  border-radius: 8px;
  background: rgba(255, 247, 230, 0.07);
  touch-action: none;
  cursor: grab;
}

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

.prsp__row {
  height: 18px;
  border-radius: 4px;
  background: rgba(255, 247, 230, 0.12);
}

.prsp__hint {
  color: #fff7e6;
  font-size: 12px;
  text-align: center;
}

@media (max-width: 340px) {
  .prsp__panel {
    padding: 12px;
    gap: 8px;
  }
  .prsp__track {
    height: 88px;
  }
  .prsp__rest {
    bottom: 40px;
  }
  .prsp__marker {
    bottom: 34px;
  }
  .prsp__phone {
    width: 128px;
    height: 88px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .prsp__marker, .prsp__list {
    transition: none !important;
  }
}

(function () {
  var phone = document.getElementById('prspPhone');
  var marker = document.getElementById('prspMarker');
  var list = document.getElementById('prspList');
  var hint = document.getElementById('prspHint');
  var root = document.getElementById('prsp');

  // 계산 겹: 놓는 순간부터는 값을 보간(lerp)하는 게 아니라 위치·속도를 매 프레임 적분한다
  // (스프링 힘 -K*(pos-target) + 감쇠 -C*vel). 임계감쇠보다 C 가 작아 목표를 지나쳐 반동한 뒤 잦아든다.
  var SCALE = 0.35, REF = 110, MAX = 150;
  var K = 170, C = 9;

  var pos = 0, vel = 0, target = 0, integrating = false, dragging = false;
  var startY = 0, startPos = 0;
  var committing = false, pendingCommit = false, commitTimer = null;

  function render() {
    var y = -(pos * SCALE);
    marker.style.transform = 'translateY(' + y.toFixed(1) + 'px)';
    list.style.transform = 'translateY(' + (Math.max(0, pos) * 0.3).toFixed(1) + 'px)';
    if (committing) { hint.textContent = 'Refreshing'; }
    else if (pos > 4) { hint.textContent = 'Displaced ' + Math.round(pos) + 'px'; }
    else if (pos < -2) { hint.textContent = 'Rebound ' + Math.round(-pos) + 'px'; }
    else { hint.textContent = 'Pull down'; }
  }

  function commit() {
    committing = true;
    hint.textContent = 'Refreshing';
    commitTimer = setTimeout(function () {
      committing = false;
      hint.textContent = 'Pull down';
    }, 560);
  }

  var last = null;
  function frame(now) {
    if (last === null) { last = now; }
    var dt = Math.min(0.032, (now - last) / 1000);
    last = now;
    if (integrating) {
      var accel = -K * (pos - target) - C * vel;
      vel += accel * dt;
      pos += vel * dt;
      if (Math.abs(pos - target) < 0.5 && Math.abs(vel) < 5) {
        pos = target; vel = 0; integrating = false;
        if (pendingCommit) { pendingCommit = false; commit(); }
      }
    }
    render();
    requestAnimationFrame(frame);
  }
  requestAnimationFrame(frame);

  function onDown(y) {
    if (committing) { return; }
    dragging = true; integrating = false; vel = 0; startY = y; startPos = pos;
  }
  function onMove(y) {
    if (!dragging) { return; }
    pos = Math.max(0, Math.min(MAX, startPos + (y - startY)));
  }
  function onUp() {
    if (!dragging) { return; }
    dragging = false;
    pendingCommit = pos >= REF;
    target = 0; integrating = true;
  }

  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();

  var autoRaw = 0, autoTimer = null;
  function autoTick() {
    if (committing || integrating || dragging) { return; }
    autoRaw += 14;
    if (autoRaw >= REF) {
      pos = autoRaw; pendingCommit = pos >= REF; target = 0; integrating = true; autoRaw = 0; return;
    }
    pos = autoRaw;
  }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  function stopAutoplay() { if (autoTimer) { clearInterval(autoTimer); autoTimer = null; } if (commitTimer) { clearTimeout(commitTimer); } }
  if (!reduce) { autoTimer = setInterval(autoTick, 160); }
})();

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

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

export default function PullRefreshReleaseSpringSettle({
  color = "#5b8cf8",
}: PullRefreshReleaseSpringSettleProps) {
  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: 놓는 순간부터는 값을 보간(lerp)하는 게 아니라 위치·속도를 매 프레임 적분한다
    // (스프링 힘 -K*(pos-target) + 감쇠 -C*vel). 임계감쇠보다 C 가 작아 목표를 지나쳐 반동한 뒤 잦아든다.
    const SCALE = 0.35, REF = 110, MAX = 150;
    const K = 170, C = 9;

    let pos = 0, vel = 0, target = 0, integrating = false, dragging = false;
    let startY = 0, startPos = 0;
    let committing = false, pendingCommit = false, commitTimer: number | null = null;

    function render() {
      const y = -(pos * SCALE);
      marker!.style.transform = "translateY(" + y.toFixed(1) + "px)";
      list!.style.transform = "translateY(" + (Math.max(0, pos) * 0.3).toFixed(1) + "px)";
      if (committing) { hint!.textContent = "새로고침 중"; }
      else if (pos > 4) { hint!.textContent = "밀림 " + Math.round(pos) + "px"; }
      else if (pos < -2) { hint!.textContent = "되돌림 " + Math.round(-pos) + "px"; }
      else { hint!.textContent = "아래로 당기세요"; }
    }

    function commit() {
      committing = true;
      hint!.textContent = "새로고침 중";
      commitTimer = window.setTimeout(() => {
        committing = false;
        hint!.textContent = "아래로 당기세요";
      }, 560);
    }

    let last: number | null = null;
    let rafId: number | null = null;
    function frame(now: number) {
      if (last === null) last = now;
      const dt = Math.min(0.032, (now - last) / 1000);
      last = now;
      if (integrating) {
        const accel = -K * (pos - target) - C * vel;
        vel += accel * dt;
        pos += vel * dt;
        if (Math.abs(pos - target) < 0.5 && Math.abs(vel) < 5) {
          pos = target; vel = 0; integrating = false;
          if (pendingCommit) { pendingCommit = false; commit(); }
        }
      }
      render();
      rafId = requestAnimationFrame(frame);
    }
    rafId = requestAnimationFrame(frame);

    function onDown(y: number) {
      if (committing) return;
      dragging = true; integrating = false; vel = 0; startY = y; startPos = pos;
    }
    function onMove(y: number) {
      if (!dragging) return;
      pos = Math.max(0, Math.min(MAX, startPos + (y - startY)));
    }
    function onUp() {
      if (!dragging) return;
      dragging = false;
      pendingCommit = pos >= REF;
      target = 0; integrating = true;
    }

    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);

    let autoRaw = 0, autoTimer: number | null = null;
    function autoTick() {
      if (committing || integrating || dragging) return;
      autoRaw += 14;
      if (autoRaw >= REF) {
        pos = autoRaw; pendingCommit = pos >= REF; target = 0; integrating = true; autoRaw = 0; return;
      }
      pos = autoRaw;
    }
    function stopAutoplay() {
      if (autoTimer !== null) { window.clearInterval(autoTimer); autoTimer = null; }
      if (commitTimer !== null) { window.clearTimeout(commitTimer); }
    }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { autoTimer = window.setInterval(autoTick, 160); }

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

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.prsp}>
        <div className={styles.panel}>
          <div className={styles.track}>
            <span className={styles.rest} />
            <span className={styles.marker} style={{ "--accent": color } as any} />
          </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>
  );
}