#!/usr/bin/env node
/**
 * Renders docs/manual-de-uso.html to PDF with page numbers.
 *
 * Chrome's `--print-to-pdf` flag cannot produce a custom footer, and Blink does
 * not implement CSS paged-media margin boxes (`@page { @bottom-center { … } }`),
 * so page numbers are impossible from CSS alone. Driving Chrome through the
 * DevTools protocol instead gives access to `Page.printToPDF`, which accepts a
 * footer template.
 *
 * Usage:  node docs/build-pdf.mjs
 */

import { spawn } from 'node:child_process';
import { readFile, writeFile, mkdtemp } from 'node:fs/promises';
import { tmpdir } from 'node:os';
import { join, resolve, dirname } from 'node:path';
import { fileURLToPath, pathToFileURL } from 'node:url';

const HERE = dirname(fileURLToPath(import.meta.url));
const SOURCE = resolve(HERE, 'manual-de-uso.html');
const TARGET = resolve(HERE, 'manual-de-uso.pdf');
const PORT = 9333;

const CHROME_CANDIDATES = [
  '/Applications/Google Chrome.app/Contents/MacOS/Google Chrome',
  '/Applications/Chromium.app/Contents/MacOS/Chromium',
  '/usr/bin/google-chrome',
  '/usr/bin/chromium',
];

async function findChrome() {
  for (const path of CHROME_CANDIDATES) {
    try {
      await readFile(path);
      return path;
    } catch {
      // Not readable as a file but may still be executable; probe via access.
      try {
        const { accessSync, constants } = await import('node:fs');
        accessSync(path, constants.X_OK);
        return path;
      } catch { /* keep looking */ }
    }
  }
  throw new Error('No Chrome or Chromium found. Install one, or add its path to CHROME_CANDIDATES.');
}

/** Poll the debugging endpoint until Chrome is ready to talk. */
async function waitForDebugger(timeoutMs = 15000) {
  const deadline = Date.now() + timeoutMs;

  while (Date.now() < deadline) {
    try {
      const response = await fetch(`http://127.0.0.1:${PORT}/json/version`);
      if (response.ok) return (await response.json()).webSocketDebuggerUrl;
    } catch { /* not up yet */ }

    await new Promise((r) => setTimeout(r, 150));
  }

  throw new Error('Chrome did not expose its debugging port in time.');
}

/** Minimal CDP client over the WebSocket built into Node 22. */
function connect(url) {
  const socket = new WebSocket(url);
  const pending = new Map();
  const listeners = new Map();
  let nextId = 0;

  socket.addEventListener('message', (event) => {
    const message = JSON.parse(event.data);

    if (message.id !== undefined && pending.has(message.id)) {
      const { resolve: ok, reject } = pending.get(message.id);
      pending.delete(message.id);
      message.error ? reject(new Error(message.error.message)) : ok(message.result);
      return;
    }

    (listeners.get(message.method) ?? []).forEach((fn) => fn(message.params));
  });

  const ready = new Promise((ok, reject) => {
    socket.addEventListener('open', ok, { once: true });
    socket.addEventListener('error', () => reject(new Error('Could not open the CDP socket.')), { once: true });
  });

  return {
    ready,
    send(method, params = {}, sessionId) {
      const id = ++nextId;
      return new Promise((ok, reject) => {
        pending.set(id, { resolve: ok, reject });
        socket.send(JSON.stringify({ id, method, params, ...(sessionId ? { sessionId } : {}) }));
      });
    },
    on(method, fn) {
      listeners.set(method, [...(listeners.get(method) ?? []), fn]);
    },
    close: () => socket.close(),
  };
}

const FOOTER = `
  <div style="width:100%;font-size:8px;font-family:Helvetica,Arial,sans-serif;
              color:#8a8f9c;padding:0 18mm;display:flex;justify-content:space-between;">
    <span>Manual de uso · Panel del colectivo</span>
    <span><span class="pageNumber"></span> / <span class="totalPages"></span></span>
  </div>`;

const chrome = await findChrome();
const profile = await mkdtemp(join(tmpdir(), 'pdf-chrome-'));

const process_ = spawn(chrome, [
  '--headless',
  '--disable-gpu',
  '--no-first-run',
  `--remote-debugging-port=${PORT}`,
  `--user-data-dir=${profile}`,
  'about:blank',
], { stdio: 'ignore' });

try {
  const browserUrl = await waitForDebugger();
  const client = connect(browserUrl);
  await client.ready;

  const { targetId } = await client.send('Target.createTarget', { url: 'about:blank' });
  const { sessionId } = await client.send('Target.attachToTarget', { targetId, flatten: true });

  await client.send('Page.enable', {}, sessionId);

  const loaded = new Promise((ok) => client.on('Page.loadEventFired', ok));
  await client.send('Page.navigate', { url: pathToFileURL(SOURCE).href }, sessionId);
  await loaded;

  // Give web fonts and layout a moment to settle before measuring pages.
  await new Promise((r) => setTimeout(r, 400));

  const { data } = await client.send('Page.printToPDF', {
    printBackground: true,
    preferCSSPageSize: true,
    displayHeaderFooter: true,
    headerTemplate: '<div></div>',
    footerTemplate: FOOTER,
    marginTop: 0.79,
    marginBottom: 0.71,
    marginLeft: 0.71,
    marginRight: 0.71,
  }, sessionId);

  await writeFile(TARGET, Buffer.from(data, 'base64'));
  client.close();

  console.log(`PDF escrito en ${TARGET}`);
} finally {
  process_.kill();
}