08막대는 즉시 솟고 꼭대기 표시는 잠시 머문 뒤 중력처럼 떨어지는 이퀄라이저

<main class="stage">
<div class="wf is-demo" id="wfRoot">
  <canvas class="wf__canvas" data-role="canvas" width="480" height="300" tabindex="0" aria-label="막대는 즉시 솟고 꼭대기 표시는 잠시 머문 뒤 중력처럼 떨어지는 이퀄라이저"></canvas>
  <p class="wf__status" data-role="status" aria-live="polite">대역</p>
  <button class="wf__btn" data-role="btn" type="button">멈춤</button>
  <p class="wf__caption">막대는 즉시 솟고 꼭대기 표시는 잠시 머문 뒤 중력처럼 떨어지는 이퀄라이저</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-ink);

.wf {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $subject-ink;
}

.wf__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: manipulation;
}

.wf__canvas:focus-visible {
  outline: 2px solid rgba(255, 255, 255, .85);
  outline-offset: -6px;
}

.wf__status {
  position: absolute;
  left: $sp-3;
  top: $sp-3;
  max-width: 62%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.wf__btn {
  position: absolute;
  right: $sp-3;
  bottom: $sp-3;
  margin: 0;
  padding: $sp-1 $sp-3;
  border: 0;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font: inherit;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  cursor: pointer;
}

.wf__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.wf__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 68%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .wf__caption, .wf__btn { font-size: 10px; padding: $sp-1 $sp-2; }
  .wf__status { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .wf { cursor: default; }
}

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);
}

.wf {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #17141a;
}

.wf__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: manipulation;
}

.wf__canvas:focus-visible {
  outline: 2px solid rgba(255, 255, 255, 0.85);
  outline-offset: -6px;
}

.wf__status {
  position: absolute;
  left: 12px;
  top: 12px;
  max-width: 62%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.wf__btn {
  position: absolute;
  right: 12px;
  bottom: 12px;
  margin: 0;
  padding: 4px 12px;
  border: 0;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font: inherit;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  cursor: pointer;
}

.wf__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.wf__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 68%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .wf__caption, .wf__btn {
    font-size: 10px;
    padding: 4px 8px;
  }
  .wf__status {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .wf {
    cursor: default;
  }
}

(function () {
const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const IDLE_STEPS = 220;
const REDUCE_STEP_MS = 900;
const REDUCE_WARM_STEPS = 40;
const BTN_PAUSE = '멈춤';
const BTN_PLAY = '재생';
const BTN_NEXT = '다음 순간';
// 파스텔 팔레트와 어두운 바탕 두 끝 색
const PINK = [255, 170, 196];
const MINT = [150, 226, 196];
const LILAC = [196, 176, 255];
const SKY_BLUE = [150, 214, 255];
const BUTTER = [255, 230, 150];
const CREAM = [255, 247, 230];
const INK = [23, 20, 26];
const BG_TOP = [24, 21, 40];
const BG_BOT = [48, 42, 78];
function clamp(v, lo, hi) { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a, b, k) { return a + (b - a) * k; }
function smooth(x) { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function mix(a, b, k) { return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]; }
function rgba(c, a) { return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + a.toFixed(3) + ')'; }
// 시드 고정 난수 — 같은 시드면 언제나 같은 수열 (선형 합동 방식)
function lcg(seed) {
    let s = seed >>> 0;
    return function () {
        s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
        return s / 4294967296;
    };
}
// 정수 하나와 시드로 0 이상 1 미만의 값을 만드는 해시 (같은 입력은 늘 같은 값)
function hash1(i, seed) {
    let h = (Math.imul(i | 0, 374761393) + Math.imul(seed | 0, 668265263)) | 0;
    h = Math.imul(h ^ (h >>> 13), 1274126177);
    h ^= h >>> 16;
    return (h >>> 0) / 4294967296;
}
// 사인 두 개를 음절마다 갈아 끼우고 엔벨로프를 씌운 합성 신호 (소리는 재생하지 않고 수치만 만든다)
function synth(n, seed) {
    const rnd = lcg(seed);
    const out = new Float32Array(n);
    let i = 0;
    let p1 = 0;
    let p2 = 0;
    let peak = 0.0001;
    while (i < n) {
        const len = 1800 + Math.floor(rnd() * 4200);
        const amp = 0.18 + rnd() * 0.82;
        const rest = rnd() < 0.18;
        const f1 = 0.02 + rnd() * 0.09;
        const f2 = f1 * (1.5 + rnd());
        const stop = Math.min(n, i + len);
        for (let k = i; k < stop; k += 1) {
            const x = (k - i) / len;
            const env = Math.min(1, x / 0.06) * Math.pow(1 - x, 0.8);
            p1 += PI2 * f1;
            p2 += PI2 * f2;
            const tone = Math.sin(p1) * 0.7 + Math.sin(p2) * 0.3;
            const gain = rest ? 0.03 : amp * env;
            const v = gain * tone + (rnd() - 0.5) * 0.08 * (rest ? 0.4 : amp);
            out[k] = v;
            const a = Math.abs(v);
            if (a > peak) {
                peak = a;
            }
        }
        i = stop;
    }
    const norm = 0.92 / peak;
    for (let k = 0; k < n; k += 1) {
        out[k] *= norm;
    }
    return out;
}
// 표본 구간 [a, b) 의 최솟값과 최댓값 — 결과는 rangeLo, rangeHi 에 둔다
let rangeLo = 0;
let rangeHi = 0;
function scanRange(sig, a, b) {
    const from = Math.max(0, Math.floor(a));
    const to = Math.min(sig.length, Math.max(from + 1, Math.ceil(b)));
    let lo = 1e9;
    let hi = -1e9;
    for (let i = from; i < to; i += 1) {
        const v = sig[i];
        if (v < lo) {
            lo = v;
        }
        if (v > hi) {
            hi = v;
        }
    }
    if (lo > hi) {
        lo = 0;
        hi = 0;
    }
    rangeLo = lo;
    rangeHi = hi;
}
function paintBg(ctx, top, bot) {
    const g = ctx.createLinearGradient(0, 0, 0, H);
    g.addColorStop(0, rgba(top, 1));
    g.addColorStop(1, rgba(bot, 1));
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, W, H);
}
// 가짜 포인터 — 시연 동안 손이 움직이는 것처럼 보이게 그린다
function drawCursor(ctx, x, y, down) {
    ctx.save();
    ctx.translate(x, y);
    ctx.beginPath();
    ctx.moveTo(0, 0);
    ctx.lineTo(0, 15);
    ctx.lineTo(4, 11.5);
    ctx.lineTo(7.5, 18);
    ctx.lineTo(10, 16.8);
    ctx.lineTo(6.6, 10.4);
    ctx.lineTo(11.5, 10.2);
    ctx.closePath();
    ctx.fillStyle = rgba(CREAM, 1);
    ctx.strokeStyle = rgba(INK, 1);
    ctx.lineWidth = 1.4;
    ctx.fill();
    ctx.stroke();
    if (down) {
        ctx.beginPath();
        ctx.arc(0, 0, 9, 0, PI2);
        ctx.strokeStyle = rgba(PINK, 0.9);
        ctx.lineWidth = 2;
        ctx.stroke();
    }
    ctx.restore();
}
function boot(root, make) {
    const canvasEl = root.querySelector('[data-role="canvas"]');
    const statusEl = root.querySelector('[data-role="status"]');
    const btnEl = root.querySelector('[data-role="btn"]');
    if (!(canvasEl instanceof HTMLCanvasElement) || !statusEl || !(btnEl instanceof HTMLButtonElement)) {
        return function () { };
    }
    const ctxOrNull = canvasEl.getContext('2d');
    if (!ctxOrNull) {
        return function () { };
    }
    const canvas = canvasEl;
    const ctx = ctxOrNull;
    const status = statusEl;
    const btn = btnEl;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    const cleaners = [];
    let paused = false;
    let idle = IDLE_STEPS + 1;
    let clock = 0;
    let lastSayAt = -1e9;
    let lastText = status.textContent || '';
    let scene = null;
    let rafId = 0;
    let acc = 0;
    let lastTs = -1;
    function isAuto() { return !reduce && !paused && idle > IDLE_STEPS; }
    function sync() {
        const on = isAuto();
        if (root.classList.contains('is-demo') !== on) {
            root.classList.toggle('is-demo', on);
        }
    }
    function fit() {
        const r = canvas.getBoundingClientRect();
        const dpr = window.devicePixelRatio || 1;
        const cw = Math.max(1, Math.round(r.width * dpr));
        const ch = Math.max(1, Math.round(r.height * dpr));
        canvas.width = cw;
        canvas.height = ch;
        ctx.setTransform(cw / W, 0, 0, ch / H, 0, 0);
    }
    const host = {
        ctx,
        canvas,
        root,
        reduce,
        touch() {
            idle = 0;
            sync();
        },
        auto: isAuto,
        refresh() {
            if (scene) {
                scene.draw();
            }
        },
        say(text) {
            if (text === lastText) {
                return;
            }
            if (!reduce && clock - lastSayAt < 250) {
                return;
            }
            lastText = text;
            lastSayAt = clock;
            // 시연이 혼자 돌 때는 읽어 주지 않고, 사람이 만졌을 때만 알린다
            status.setAttribute('aria-live', isAuto() ? 'off' : 'polite');
            status.textContent = text;
        },
        local(e) {
            const r = canvas.getBoundingClientRect();
            return [clamp((e.clientX - r.left) * W / Math.max(1, r.width), 0, W), clamp((e.clientY - r.top) * H / Math.max(1, r.height), 0, H)];
        },
        listen(target, type, fn, opts) {
            target.addEventListener(type, fn, opts);
            cleaners.push(function () { target.removeEventListener(type, fn, opts); });
        }
    };
    function advance(ms) {
        if (!scene) {
            return;
        }
        const n = Math.max(1, Math.round(ms / FIXED_DT));
        for (let i = 0; i < n; i += 1) {
            idle += 1;
            clock += FIXED_DT;
            scene.step();
        }
    }
    function frame(ts) {
        if (lastTs < 0) {
            lastTs = ts;
        }
        const dt = Math.min(ts - lastTs, 160);
        lastTs = ts;
        if (!paused && scene) {
            acc += dt;
            while (acc >= FIXED_DT) {
                idle += 1;
                clock += FIXED_DT;
                scene.step();
                acc -= FIXED_DT;
            }
            sync();
            scene.draw();
        }
        rafId = requestAnimationFrame(frame);
    }
    scene = make(host);
    btn.textContent = reduce ? BTN_NEXT : BTN_PAUSE;
    fit();
    if (reduce) {
        root.classList.remove('is-demo');
        advance(REDUCE_WARM_STEPS * FIXED_DT);
    }
    scene.draw();
    host.listen(btn, 'click', function () {
        if (reduce) {
            advance(REDUCE_STEP_MS);
            host.refresh();
            return;
        }
        paused = !paused;
        btn.textContent = paused ? BTN_PLAY : BTN_PAUSE;
        sync();
    });
    host.listen(window, 'resize', function () {
        fit();
        host.refresh();
    });
    if (!reduce) {
        rafId = requestAnimationFrame(frame);
    }
    return function () {
        cancelAnimationFrame(rafId);
        for (let i = 0; i < cleaners.length; i += 1) {
            cleaners[i]();
        }
    };
}
const BAND_N = 24;
const HOLD_FRAMES = 28;
const CAP_FALL_G = 0.0006;
const BAR_FALL_K = 0.12;
const BAR_W = 14;
const BAR_STRIDE = 18;
const BASE_X = 24;
const FLOOR_Y = 232;
const TOP_BAR_Y = 52;
const SEG_H = 6;
const SEG_GAP = 2;
const PUSH_STEPS = 40;
const TXT_BAND = '대역';
function stepBand(s, target, fallK, holdFrames, gravity) {
    if (target > s.bar) {
        s.bar = target;
    }
    else {
        s.bar += (target - s.bar) * fallK;
    }
    if (s.bar >= s.cap) {
        s.cap = s.bar;
        s.hold = holdFrames;
        s.vel = 0;
    }
    else if (s.hold > 0) {
        s.hold -= 1;
    }
    else {
        s.vel += gravity;
        s.cap -= s.vel;
        if (s.cap < s.bar) {
            s.cap = s.bar;
            s.vel = 0;
        }
    }
}
function makeEqScene(h) {
    const bands = [];
    const base = [];
    const level = [];
    const push = [];
    const pushTo = [];
    for (let i = 0; i < BAND_N; i += 1) {
        bands.push({ bar: 0, cap: 0, hold: 0, vel: 0 });
        base.push(0.95 - 0.5 * Math.pow(i / (BAND_N - 1), 0.8) + 0.1 * hash1(i, 11));
        level.push(0);
        push.push(0);
        pushTo.push(0);
    }
    let k = 0;
    let focus = 4;
    let fakeX = 80;
    let fakeY = 200;
    let fakeDown = false;
    function bandAt(x) {
        return clamp(Math.floor((x - BASE_X) / BAR_STRIDE), 0, BAND_N - 1);
    }
    function poke(i, v) {
        push[i] = PUSH_STEPS;
        pushTo[i] = clamp(v, 0, 1);
        focus = i;
        h.touch();
        if (h.reduce) {
            bands[i].bar = pushTo[i];
            bands[i].cap = pushTo[i];
        }
        h.refresh();
    }
    function heightAt(y) {
        return clamp((FLOOR_Y - y) / (FLOOR_Y - TOP_BAR_Y), 0, 1);
    }
    h.listen(h.canvas, 'pointerdown', function (e) {
        const p = h.local(e);
        poke(bandAt(p[0]), heightAt(p[1]));
    });
    h.listen(h.canvas, 'keydown', function (e) {
        const key = e.key;
        if (key === 'ArrowLeft') {
            e.preventDefault();
            focus = clamp(focus - 1, 0, BAND_N - 1);
            h.touch();
            h.refresh();
        }
        else if (key === 'ArrowRight') {
            e.preventDefault();
            focus = clamp(focus + 1, 0, BAND_N - 1);
            h.touch();
            h.refresh();
        }
        else if (key === 'Enter' || key === ' ') {
            e.preventDefault();
            poke(focus, 0.95);
        }
    });
    // 박자마다 낮은 대역이 크게, 높은 대역은 어긋난 주기로 튄다
    function drive(i) {
        const period = 10 + Math.floor(hash1(i, 3) * 26);
        const slot = Math.floor((k + i * 3) / period);
        const burst = hash1(slot, i + 40);
        const age = ((k + i * 3) % period) / period;
        return base[i] * (0.15 + 0.85 * burst) * Math.pow(1 - age, 1.5);
    }
    function script() {
        const j = k % 300;
        fakeDown = false;
        if (j >= 60 && j < 70) {
            fakeX = 80 + (j - 60) * 4;
            fakeY = 120;
        }
        if (j >= 70 && j < 74) {
            fakeDown = true;
            poke(bandAt(fakeX), 0.92);
        }
        if (j >= 100 && j < 140) {
            fakeX = 150 + (j - 100) * 6;
            fakeY = 160;
        }
        if (j >= 140 && j < 144) {
            fakeDown = true;
            poke(bandAt(fakeX), 0.88);
        }
    }
    return {
        step() {
            k += 1;
            if (h.auto()) {
                script();
            }
            for (let i = 0; i < BAND_N; i += 1) {
                let t = drive(i);
                if (push[i] > 0) {
                    push[i] -= 1;
                    t = Math.max(t, pushTo[i] * (push[i] / PUSH_STEPS > 0.7 ? 1 : 0.4));
                }
                level[i] = t;
                stepBand(bands[i], t, BAR_FALL_K, HOLD_FRAMES, CAP_FALL_G);
            }
        },
        draw() {
            const ctx = h.ctx;
            paintBg(ctx, BG_TOP, BG_BOT);
            const segs = Math.floor((FLOOR_Y - TOP_BAR_Y) / (SEG_H + SEG_GAP));
            for (let i = 0; i < BAND_N; i += 1) {
                const x = BASE_X + i * BAR_STRIDE;
                const lit = Math.round(bands[i].bar * segs);
                for (let s = 0; s < segs; s += 1) {
                    const y = FLOOR_Y - (s + 1) * (SEG_H + SEG_GAP);
                    const ratio = s / (segs - 1);
                    const col = ratio < 0.5 ? mix(MINT, SKY_BLUE, ratio * 2) : mix(SKY_BLUE, PINK, (ratio - 0.5) * 2);
                    ctx.fillStyle = s < lit ? rgba(col, 1) : rgba(CREAM, 0.07);
                    ctx.fillRect(x, y, BAR_W, SEG_H);
                }
                const capY = FLOOR_Y - Math.max(1, Math.round(bands[i].cap * segs)) * (SEG_H + SEG_GAP);
                ctx.fillStyle = rgba(BUTTER, 1);
                ctx.fillRect(x, capY, BAR_W, SEG_H);
            }
            ctx.fillStyle = rgba(CREAM, 0.7);
            ctx.fillRect(BASE_X + focus * BAR_STRIDE, FLOOR_Y + 4, BAR_W, 3);
            if (h.auto() && !h.reduce) {
                drawCursor(ctx, fakeX, fakeY, fakeDown);
            }
            h.say(TXT_BAND + ' ' + (focus + 1) + ': ' + bands[focus].bar.toFixed(2) + ' / ' + bands[focus].cap.toFixed(2));
        }
    };
}

    boot(document.getElementById('wfRoot'), makeEqScene);
})();

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

const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const IDLE_STEPS = 220;
const REDUCE_STEP_MS = 900;
const REDUCE_WARM_STEPS = 40;
const BTN_PAUSE = '멈춤';
const BTN_PLAY = '재생';
const BTN_NEXT = '다음 순간';

type RGB = [number, number, number];

// 파스텔 팔레트와 어두운 바탕 두 끝 색
const PINK: RGB = [255, 170, 196];
const MINT: RGB = [150, 226, 196];
const LILAC: RGB = [196, 176, 255];
const SKY_BLUE: RGB = [150, 214, 255];
const BUTTER: RGB = [255, 230, 150];
const CREAM: RGB = [255, 247, 230];
const INK: RGB = [23, 20, 26];
const BG_TOP: RGB = [24, 21, 40];
const BG_BOT: RGB = [48, 42, 78];

interface Host {
    ctx: CanvasRenderingContext2D;
    canvas: HTMLCanvasElement;
    root: HTMLElement;
    reduce: boolean;
    touch(): void;
    auto(): boolean;
    refresh(): void;
    say(text: string): void;
    local(e: MouseEvent): [number, number];
    listen(target: EventTarget, type: string, fn: (e: Event) => void, opts?: AddEventListenerOptions): void;
}

interface Scene {
    step(): void;
    draw(): void;
}

function clamp(v: number, lo: number, hi: number): number { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a: number, b: number, k: number): number { return a + (b - a) * k; }
function smooth(x: number): number { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function mix(a: RGB, b: RGB, k: number): RGB { return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]; }
function rgba(c: RGB, a: number): string { return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + a.toFixed(3) + ')'; }

// 시드 고정 난수 — 같은 시드면 언제나 같은 수열 (선형 합동 방식)
function lcg(seed: number): () => number {
    let s = seed >>> 0;
    return function (): number {
        s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
        return s / 4294967296;
    };
}

// 정수 하나와 시드로 0 이상 1 미만의 값을 만드는 해시 (같은 입력은 늘 같은 값)
function hash1(i: number, seed: number): number {
    let h = (Math.imul(i | 0, 374761393) + Math.imul(seed | 0, 668265263)) | 0;
    h = Math.imul(h ^ (h >>> 13), 1274126177);
    h ^= h >>> 16;
    return (h >>> 0) / 4294967296;
}

// 사인 두 개를 음절마다 갈아 끼우고 엔벨로프를 씌운 합성 신호 (소리는 재생하지 않고 수치만 만든다)
function synth(n: number, seed: number): Float32Array {
    const rnd = lcg(seed);
    const out = new Float32Array(n);
    let i = 0;
    let p1 = 0;
    let p2 = 0;
    let peak = 0.0001;
    while (i < n) {
        const len = 1800 + Math.floor(rnd() * 4200);
        const amp = 0.18 + rnd() * 0.82;
        const rest = rnd() < 0.18;
        const f1 = 0.02 + rnd() * 0.09;
        const f2 = f1 * (1.5 + rnd());
        const stop = Math.min(n, i + len);
        for (let k = i; k < stop; k += 1) {
            const x = (k - i) / len;
            const env = Math.min(1, x / 0.06) * Math.pow(1 - x, 0.8);
            p1 += PI2 * f1;
            p2 += PI2 * f2;
            const tone = Math.sin(p1) * 0.7 + Math.sin(p2) * 0.3;
            const gain = rest ? 0.03 : amp * env;
            const v = gain * tone + (rnd() - 0.5) * 0.08 * (rest ? 0.4 : amp);
            out[k] = v;
            const a = Math.abs(v);
            if (a > peak) { peak = a; }
        }
        i = stop;
    }
    const norm = 0.92 / peak;
    for (let k = 0; k < n; k += 1) { out[k] *= norm; }
    return out;
}

// 표본 구간 [a, b) 의 최솟값과 최댓값 — 결과는 rangeLo, rangeHi 에 둔다
let rangeLo = 0;
let rangeHi = 0;
function scanRange(sig: Float32Array, a: number, b: number): void {
    const from = Math.max(0, Math.floor(a));
    const to = Math.min(sig.length, Math.max(from + 1, Math.ceil(b)));
    let lo = 1e9;
    let hi = -1e9;
    for (let i = from; i < to; i += 1) {
        const v = sig[i];
        if (v < lo) { lo = v; }
        if (v > hi) { hi = v; }
    }
    if (lo > hi) { lo = 0; hi = 0; }
    rangeLo = lo;
    rangeHi = hi;
}

function paintBg(ctx: CanvasRenderingContext2D, top: RGB, bot: RGB): void {
    const g = ctx.createLinearGradient(0, 0, 0, H);
    g.addColorStop(0, rgba(top, 1));
    g.addColorStop(1, rgba(bot, 1));
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, W, H);
}

// 가짜 포인터 — 시연 동안 손이 움직이는 것처럼 보이게 그린다
function drawCursor(ctx: CanvasRenderingContext2D, x: number, y: number, down: boolean): void {
    ctx.save();
    ctx.translate(x, y);
    ctx.beginPath();
    ctx.moveTo(0, 0);
    ctx.lineTo(0, 15);
    ctx.lineTo(4, 11.5);
    ctx.lineTo(7.5, 18);
    ctx.lineTo(10, 16.8);
    ctx.lineTo(6.6, 10.4);
    ctx.lineTo(11.5, 10.2);
    ctx.closePath();
    ctx.fillStyle = rgba(CREAM, 1);
    ctx.strokeStyle = rgba(INK, 1);
    ctx.lineWidth = 1.4;
    ctx.fill();
    ctx.stroke();
    if (down) {
        ctx.beginPath();
        ctx.arc(0, 0, 9, 0, PI2);
        ctx.strokeStyle = rgba(PINK, 0.9);
        ctx.lineWidth = 2;
        ctx.stroke();
    }
    ctx.restore();
}

function boot(root: HTMLElement, make: (h: Host) => Scene): () => void {
    const canvasEl = root.querySelector('[data-role="canvas"]');
    const statusEl = root.querySelector('[data-role="status"]');
    const btnEl = root.querySelector('[data-role="btn"]');
    if (!(canvasEl instanceof HTMLCanvasElement) || !statusEl || !(btnEl instanceof HTMLButtonElement)) {
        return function (): void { /* 필요한 요소가 없으면 아무것도 하지 않는다 */ };
    }
    const ctxOrNull = canvasEl.getContext('2d');
    if (!ctxOrNull) {
        return function (): void { /* 2d 문맥이 없으면 아무것도 하지 않는다 */ };
    }
    const canvas: HTMLCanvasElement = canvasEl;
    const ctx: CanvasRenderingContext2D = ctxOrNull;
    const status: Element = statusEl;
    const btn: HTMLButtonElement = btnEl;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    const cleaners: Array<() => void> = [];
    let paused = false;
    let idle = IDLE_STEPS + 1;
    let clock = 0;
    let lastSayAt = -1e9;
    let lastText = status.textContent || '';
    let scene: Scene | null = null;
    let rafId = 0;
    let acc = 0;
    let lastTs = -1;

    function isAuto(): boolean { return !reduce && !paused && idle > IDLE_STEPS; }
    function sync(): void {
        const on = isAuto();
        if (root.classList.contains('is-demo') !== on) {
            root.classList.toggle('is-demo', on);
        }
    }
    function fit(): void {
        const r = canvas.getBoundingClientRect();
        const dpr = window.devicePixelRatio || 1;
        const cw = Math.max(1, Math.round(r.width * dpr));
        const ch = Math.max(1, Math.round(r.height * dpr));
        canvas.width = cw;
        canvas.height = ch;
        ctx.setTransform(cw / W, 0, 0, ch / H, 0, 0);
    }
    const host: Host = {
        ctx,
        canvas,
        root,
        reduce,
        touch(): void {
            idle = 0;
            sync();
        },
        auto: isAuto,
        refresh(): void {
            if (scene) { scene.draw(); }
        },
        say(text: string): void {
            if (text === lastText) { return; }
            if (!reduce && clock - lastSayAt < 250) { return; }
            lastText = text;
            lastSayAt = clock;
            // 시연이 혼자 돌 때는 읽어 주지 않고, 사람이 만졌을 때만 알린다
            status.setAttribute('aria-live', isAuto() ? 'off' : 'polite');
            status.textContent = text;
        },
        local(e: MouseEvent): [number, number] {
            const r = canvas.getBoundingClientRect();
            return [clamp((e.clientX - r.left) * W / Math.max(1, r.width), 0, W), clamp((e.clientY - r.top) * H / Math.max(1, r.height), 0, H)];
        },
        listen(target: EventTarget, type: string, fn: (e: Event) => void, opts?: AddEventListenerOptions): void {
            target.addEventListener(type, fn, opts);
            cleaners.push(function (): void { target.removeEventListener(type, fn, opts); });
        }
    };
    function advance(ms: number): void {
        if (!scene) { return; }
        const n = Math.max(1, Math.round(ms / FIXED_DT));
        for (let i = 0; i < n; i += 1) {
            idle += 1;
            clock += FIXED_DT;
            scene.step();
        }
    }
    function frame(ts: number): void {
        if (lastTs < 0) { lastTs = ts; }
        const dt = Math.min(ts - lastTs, 160);
        lastTs = ts;
        if (!paused && scene) {
            acc += dt;
            while (acc >= FIXED_DT) {
                idle += 1;
                clock += FIXED_DT;
                scene.step();
                acc -= FIXED_DT;
            }
            sync();
            scene.draw();
        }
        rafId = requestAnimationFrame(frame);
    }
    scene = make(host);
    btn.textContent = reduce ? BTN_NEXT : BTN_PAUSE;
    fit();
    if (reduce) {
        root.classList.remove('is-demo');
        advance(REDUCE_WARM_STEPS * FIXED_DT);
    }
    scene.draw();
    host.listen(btn, 'click', function (): void {
        if (reduce) {
            advance(REDUCE_STEP_MS);
            host.refresh();
            return;
        }
        paused = !paused;
        btn.textContent = paused ? BTN_PLAY : BTN_PAUSE;
        sync();
    });
    host.listen(window, 'resize', function (): void {
        fit();
        host.refresh();
    });
    if (!reduce) {
        rafId = requestAnimationFrame(frame);
    }
    return function (): void {
        cancelAnimationFrame(rafId);
        for (let i = 0; i < cleaners.length; i += 1) { cleaners[i](); }
    };
}

const BAND_N = 24;
const HOLD_FRAMES = 28;
const CAP_FALL_G = 0.0006;
const BAR_FALL_K = 0.12;
const BAR_W = 14;
const BAR_STRIDE = 18;
const BASE_X = 24;
const FLOOR_Y = 232;
const TOP_BAR_Y = 52;
const SEG_H = 6;
const SEG_GAP = 2;
const PUSH_STEPS = 40;
const TXT_BAND = '대역';

// 막대 높이 b 와 꼭대기 표시 cap 의 한 걸음 갱신 — 막대는 즉시 오르고 천천히 내리며, 표시는 잠시 머문 뒤 중력으로 떨어진다
interface BandState { bar: number; cap: number; hold: number; vel: number; }
function stepBand(s: BandState, target: number, fallK: number, holdFrames: number, gravity: number): void {
    if (target > s.bar) { s.bar = target; } else { s.bar += (target - s.bar) * fallK; }
    if (s.bar >= s.cap) {
        s.cap = s.bar;
        s.hold = holdFrames;
        s.vel = 0;
    }
    else if (s.hold > 0) {
        s.hold -= 1;
    }
    else {
        s.vel += gravity;
        s.cap -= s.vel;
        if (s.cap < s.bar) { s.cap = s.bar; s.vel = 0; }
    }
}

function makeEqScene(h: Host): Scene {
    const bands: BandState[] = [];
    const base: number[] = [];
    const level: number[] = [];
    const push: number[] = [];
    const pushTo: number[] = [];
    for (let i = 0; i < BAND_N; i += 1) {
        bands.push({ bar: 0, cap: 0, hold: 0, vel: 0 });
        base.push(0.95 - 0.5 * Math.pow(i / (BAND_N - 1), 0.8) + 0.1 * hash1(i, 11));
        level.push(0);
        push.push(0);
        pushTo.push(0);
    }
    let k = 0;
    let focus = 4;
    let fakeX = 80;
    let fakeY = 200;
    let fakeDown = false;
    function bandAt(x: number): number {
        return clamp(Math.floor((x - BASE_X) / BAR_STRIDE), 0, BAND_N - 1);
    }
    function poke(i: number, v: number): void {
        push[i] = PUSH_STEPS;
        pushTo[i] = clamp(v, 0, 1);
        focus = i;
        h.touch();
        if (h.reduce) {
            bands[i].bar = pushTo[i];
            bands[i].cap = pushTo[i];
        }
        h.refresh();
    }
    function heightAt(y: number): number {
        return clamp((FLOOR_Y - y) / (FLOOR_Y - TOP_BAR_Y), 0, 1);
    }
    h.listen(h.canvas, 'pointerdown', function (e: Event): void {
        const p = h.local(e as PointerEvent);
        poke(bandAt(p[0]), heightAt(p[1]));
    });
    h.listen(h.canvas, 'keydown', function (e: Event): void {
        const key = (e as KeyboardEvent).key;
        if (key === 'ArrowLeft') { e.preventDefault(); focus = clamp(focus - 1, 0, BAND_N - 1); h.touch(); h.refresh(); }
        else if (key === 'ArrowRight') { e.preventDefault(); focus = clamp(focus + 1, 0, BAND_N - 1); h.touch(); h.refresh(); }
        else if (key === 'Enter' || key === ' ') { e.preventDefault(); poke(focus, 0.95); }
    });
    // 박자마다 낮은 대역이 크게, 높은 대역은 어긋난 주기로 튄다
    function drive(i: number): number {
        const period = 10 + Math.floor(hash1(i, 3) * 26);
        const slot = Math.floor((k + i * 3) / period);
        const burst = hash1(slot, i + 40);
        const age = ((k + i * 3) % period) / period;
        return base[i] * (0.15 + 0.85 * burst) * Math.pow(1 - age, 1.5);
    }
    function script(): void {
        const j = k % 300;
        fakeDown = false;
        if (j >= 60 && j < 70) { fakeX = 80 + (j - 60) * 4; fakeY = 120; }
        if (j >= 70 && j < 74) { fakeDown = true; poke(bandAt(fakeX), 0.92); }
        if (j >= 100 && j < 140) { fakeX = 150 + (j - 100) * 6; fakeY = 160; }
        if (j >= 140 && j < 144) { fakeDown = true; poke(bandAt(fakeX), 0.88); }
    }
    return {
        step(): void {
            k += 1;
            if (h.auto()) { script(); }
            for (let i = 0; i < BAND_N; i += 1) {
                let t = drive(i);
                if (push[i] > 0) {
                    push[i] -= 1;
                    t = Math.max(t, pushTo[i] * (push[i] / PUSH_STEPS > 0.7 ? 1 : 0.4));
                }
                level[i] = t;
                stepBand(bands[i], t, BAR_FALL_K, HOLD_FRAMES, CAP_FALL_G);
            }
        },
        draw(): void {
            const ctx = h.ctx;
            paintBg(ctx, BG_TOP, BG_BOT);
            const segs = Math.floor((FLOOR_Y - TOP_BAR_Y) / (SEG_H + SEG_GAP));
            for (let i = 0; i < BAND_N; i += 1) {
                const x = BASE_X + i * BAR_STRIDE;
                const lit = Math.round(bands[i].bar * segs);
                for (let s = 0; s < segs; s += 1) {
                    const y = FLOOR_Y - (s + 1) * (SEG_H + SEG_GAP);
                    const ratio = s / (segs - 1);
                    const col = ratio < 0.5 ? mix(MINT, SKY_BLUE, ratio * 2) : mix(SKY_BLUE, PINK, (ratio - 0.5) * 2);
                    ctx.fillStyle = s < lit ? rgba(col, 1) : rgba(CREAM, 0.07);
                    ctx.fillRect(x, y, BAR_W, SEG_H);
                }
                const capY = FLOOR_Y - Math.max(1, Math.round(bands[i].cap * segs)) * (SEG_H + SEG_GAP);
                ctx.fillStyle = rgba(BUTTER, 1);
                ctx.fillRect(x, capY, BAR_W, SEG_H);
            }
            ctx.fillStyle = rgba(CREAM, 0.7);
            ctx.fillRect(BASE_X + focus * BAR_STRIDE, FLOOR_Y + 4, BAR_W, 3);
            if (h.auto() && !h.reduce) { drawCursor(ctx, fakeX, fakeY, fakeDown); }
            h.say(TXT_BAND + ' ' + (focus + 1) + ': ' + bands[focus].bar.toFixed(2) + ' / ' + bands[focus].cap.toFixed(2));
        }
    };
}

export default function WfEqualizerPeakHoldGravityFall() {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    return boot(root, makeEqScene);
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.wf} is-demo`} ref={rootRef}>
        <canvas className={styles.canvas} data-role="canvas" width={480} height={300} tabIndex={0} aria-label="막대는 즉시 솟고 꼭대기 표시는 잠시 머문 뒤 중력처럼 떨어지는 이퀄라이저" />
        <p className={styles.status} data-role="status" aria-live="polite">대역</p>
        <button className={styles.btn} data-role="btn" type="button">멈춤</button>
        <p className={styles.caption}>막대는 즉시 솟고 꼭대기 표시는 잠시 머문 뒤 중력처럼 떨어지는 이퀄라이저</p>
      </div>
    </main>
  );
}