// damped spring step response 0 -> 1. w = speed (8 slow, 14 normal, 22 snappy), z = damping (1 = no overshoot)
function spring(t, w = 14, z = 0.82) {
  if (t <= 0) return 0;
  if (z >= 1) return 1 - Math.exp(-w * t) * (1 + w * t);
  const wd = w * Math.sqrt(1 - z * z);
  return 1 - Math.exp(-z * w * t) * (Math.cos(wd * t) + (z * w / wd) * Math.sin(wd * t));
}
// a value that changes target many times, springing to each: track(start, [[time, value, w?, z?], ...]) -> f(t)
const track = (v0, keys) => t => { let v = v0, p = v0; for (const [tk, val, w, z] of keys) { v += (val - p) * spring(t - tk, w, z); p = val; } return v; };
// precise eased keyframes (best for camera moves): kf([[t0, v0], [t1, v1, easeFn?], ...]) -> f(t)
const kf = keys => t => { if (t <= keys[0][0]) return keys[0][1]; for (let i = 1; i < keys.length; i++) { const [a, va] = keys[i - 1], [b, vb, e = ease] = keys[i]; if (t <= b) return lerp(va, vb, e((t - a) / (b - a))); } return keys[keys.length - 1][1]; };
const clamp = (x, a = 0, b = 1) => Math.min(b, Math.max(a, x));
const ease = x => (x = clamp(x), x < .5 ? 4 * x * x * x : 1 - Math.pow(-2 * x + 2, 3) / 2);   // easeInOutCubic
const lerp = (a, b, k) => a + (b - a) * k;
const seg = (t, a, b) => clamp((t - a) / (b - a));      // 0..1 progress of t through [a, b]
const rng = s => () => (s = (s + 0x6D2B79F5) | 0, s = Math.imul(s ^ (s >>> 15), 1 | s), s ^= s + Math.imul(s ^ (s >>> 7), 61 | s), ((s ^ (s >>> 14)) | 0) / 0x100000000);

let buf, ac, src, startAt = 0, offset = 0, playing = false;
async function play() {
  ac ??= new AudioContext();
  if (!buf) { const off = new OfflineAudioContext(2, Math.ceil(48000 * VIDEO.duration), 48000); await buildAudio(off); buf = await off.startRendering(); }
  src = ac.createBufferSource(); src.buffer = buf; src.connect(ac.destination);
  src.start(0, offset % VIDEO.duration); startAt = ac.currentTime; playing = true;
}
function pause() { if (!playing) return; offset += ac.currentTime - startAt; src.stop(); playing = false; }
function now() { return playing ? (offset + ac.currentTime - startAt) % VIDEO.duration : offset; }
(function loop() { seek(now()); requestAnimationFrame(loop); })();   // the scrubber sets offset (pause, set, play)

// render.mjs: turn a seek(t) page into an MP4 with motion blur and its own audio.
//   node render.mjs page.html out.mp4 [fps=60] [subframes=4] [workers=4]
//   node render.mjs page.html sheet.png --stills 0.5,1.2,3   (full-size contact sheet for checking)
// Optional: window.buildAudio(ctx) schedules the soundtrack on any (Offline)AudioContext.
import { chromium } from 'playwright';
import { spawn } from 'node:child_process';
import { writeFileSync, mkdirSync, rmSync } from 'node:fs';
import path from 'node:path';
import { pathToFileURL } from 'node:url';

const [, , html, out, a3 = '60', a4 = '4', a5 = '4'] = process.argv;
if (!html || !out) { console.log('usage: node render.mjs page.html out.mp4 [fps] [subframes] [workers]'); process.exit(1); }
const run = (args) => new Promise((res, rej) => { const p = spawn('ffmpeg', args, { stdio: 'inherit' }); p.on('close', c => c ? rej(new Error('ffmpeg ' + c)) : res()); });
const url = pathToFileURL(path.resolve(html)).href + '?render';
const proxy = process.env.HTTPS_PROXY || process.env.https_proxy;
const browser = await chromium.launch({ args: ['--allow-file-access-from-files'], ...(proxy ? { proxy: { server: proxy } } : {}) });

// Read the size first, then open every page at exactly that size (pages that measure themselves on load stay correct).
const probe = await browser.newPage();
await probe.goto(url);
await probe.waitForFunction(() => window.VIDEO && typeof window.seek === 'function');
const V = await probe.evaluate(() => window.VIDEO);
await probe.close();

async function openPage() {
  const page = await browser.newPage({ viewport: { width: V.w, height: V.h }, deviceScaleFactor: 1 });
  await page.goto(url);
  await page.waitForFunction(() => window.VIDEO && typeof window.seek === 'function');
  // load every declared font, even ones only used by scenes hidden at t=0
  const bad = await page.evaluate(async () => {
    await Promise.all([...document.fonts].map(f => f.load().catch(() => {})));
    await document.fonts.ready;
    return [...document.fonts].filter(f => f.status !== 'loaded').map(f => f.family);
  });
  if (bad.length) console.warn('WARNING: fonts did not load (fallback in use):', [...new Set(bad)].join(', '), '- embed them as base64.');
  return page;
}
const shot = async (page, t) => { await page.evaluate(t => window.seek(t), t); return page.screenshot({ type: 'jpeg', quality: 95 }); };

if (a3 === '--stills') {
  const page = await openPage();
  const times = a4.split(',').map(Number), dir = out + '.frames';
  mkdirSync(dir, { recursive: true });
  for (let i = 0; i < times.length; i++) writeFileSync(`${dir}/${String(i).padStart(3, '0')}.jpg`, await shot(page, times[i]));
  await browser.close();
  const cols = Math.min(3, times.length), rows = Math.ceil(times.length / cols);
  await run(['-v', 'error', '-y', '-framerate', '1', '-i', `${dir}/%03d.jpg`, '-vf', `scale=${Math.min(960, V.w)}:-1,tile=${cols}x${rows}:padding=6:color=gray`, '-frames:v', '1', out]);
  rmSync(dir, { recursive: true });
  console.log('stills ->', out); process.exit(0);
}

const fps = +a3, sub = Math.max(1, +a4), workers = Math.max(1, +a5), N = Math.round(V.duration * fps);
const base = out.replace(/\.mp4$/, 'silent'), silent = base + '_silent.mp4';
const vf = sub > 1 ? ['-vf', `tmix=frames=${sub},select='eq(mod(n\\,${sub})\\,${sub - 1})',setpts=N/(${fps}*TB)`] : [];
const t0 = Date.now(); let doneFrames = 0;
const per = Math.ceil(N / workers), segs = [];
await Promise.all(Array.from({ length: workers }, async (_, w) => {
  const a = w * per, b = Math.min(N, a + per); if (a >= b) return;
  const seg = `${base}_seg${w}.mp4`; segs[w] = seg;
  const page = await openPage();
  const ff = spawn('ffmpeg', ['-v', 'error', '-y', '-f', 'image2pipe', '-framerate', String(fps * sub), '-i', '-', ...vf,
    '-r', String(fps), '-c:v', 'libx264', '-pix_fmt', 'yuv420p', '-crf', '16', '-preset', 'medium', seg], { stdio: ['pipe', 'inherit', 'inherit'] });
  const closed = new Promise(r => ff.on('close', r));
  for (let f = a; f < b; f++) {
    for (let s = 0; s < sub; s++) {             // 180-degree shutter: sub-frames spread over half a frame
      const buf = await shot(page, (f + (sub > 1 ? (s / sub) * 0.5 : 0)) / fps);
      if (!ff.stdin.write(buf)) await new Promise(r => ff.stdin.once('drain', r));
    }
    if (++doneFrames % 30 === 0) process.stdout.write(`\r${doneFrames}/${N} frames  ${((Date.now() - t0) / 1000).toFixed(0)}s`);
  }
  ff.stdin.end(); await closed; await page.close();
}));
const list = base + '_segs.txt';
writeFileSync(list, segs.filter(Boolean).map(s => `file '${path.resolve(s)}'`).join('\n'));
await run(['-v', 'error', '-y', '-f', 'concat', '-safe', '0', '-i', list, '-c', 'copy', silent]);
segs.filter(Boolean).forEach(s => rmSync(s)); rmSync(list);
console.log(`\nvideo -> ${silent}  (${((Date.now() - t0) / 1000).toFixed(0)}s)`);

const page = await openPage();
const hasAudio = await page.evaluate(() => typeof window.buildAudio === 'function');
if (hasAudio) {
  const b64 = await page.evaluate(async (dur) => {
    const sr = 48000, ctx = new OfflineAudioContext(2, Math.ceil(sr * dur), sr);
    await window.buildAudio(ctx);
    const b = await ctx.startRendering(), L = b.getChannelData(0), R = b.getChannelData(b.numberOfChannels > 1 ? 1 : 0);
    const i16 = new Int16Array(L.length * 2);
    for (let i = 0; i < L.length; i++) { i16[2 * i] = Math.max(-1, Math.min(1, L[i])) * 32767; i16[2 * i + 1] = Math.max(-1, Math.min(1, R[i])) * 32767; }
    const u8 = new Uint8Array(i16.buffer); let s = '';
    for (let i = 0; i < u8.length; i += 0x8000) s += String.fromCharCode.apply(null, u8.subarray(i, i + 0x8000));
    return btoa(s);
  }, V.duration);
  const pcm = base + '.pcm'; writeFileSync(pcm, Buffer.from(b64, 'base64'));
  await run(['-v', 'error', '-y', '-i', silent, '-f', 's16le', '-ar', '48000', '-ac', '2', '-i', pcm,
    '-af', 'loudnorm=I=-16:TP=-1.5:LRA=11', '-c:v', 'copy', '-c:a', 'aac', '-b:a', '192k', '-shortest', out]);
  rmSync(pcm); console.log('with audio ->', out);
}
await browser.close();