// Small CDP client for the installed Chromium. No application dependencies.
import { spawn } from 'node:child_process';
import { mkdtemp, rm, writeFile } from 'node:fs/promises';
import { tmpdir } from 'node:os';
import { join } from 'node:path';

export async function browser() {
  const profile = await mkdtemp(join(tmpdir(), 'dewey-brand-browser-'));
  const child = spawn(process.env.CHROMIUM || '/usr/bin/chromium', [
    '--headless', '--no-first-run', '--no-default-browser-check',
    '--disable-dev-shm-usage', '--remote-debugging-pipe', `--user-data-dir=${profile}`,
  ], { stdio: ['ignore', 'ignore', 'ignore', 'pipe', 'pipe'] });
  let id = 0, buffer = '';
  const pending = new Map();
  child.stdio[4].on('data', chunk => {
    buffer += chunk.toString();
    let end;
    while ((end = buffer.indexOf('\0')) !== -1) {
      const message = JSON.parse(buffer.slice(0, end));
      buffer = buffer.slice(end + 1);
      if (pending.has(message.id)) {
        const { resolve, reject, timeout } = pending.get(message.id);
        clearTimeout(timeout);
        pending.delete(message.id);
        message.error ? reject(new Error(JSON.stringify(message.error))) : resolve(message.result);
      }
    }
  });
  function send(method, params = {}, sessionId) {
    return new Promise((resolve, reject) => {
      const key = ++id;
      const timeout = setTimeout(() => { pending.delete(key); reject(new Error(`CDP timeout: ${method}`)); }, 25000);
      pending.set(key, { resolve, reject, timeout });
      child.stdio[3].write(JSON.stringify({ id: key, method, params, ...(sessionId ? {sessionId} : {}) }) + '\0');
    });
  }
  const { targetId } = await send('Target.createTarget', { url: 'about:blank' });
  const { sessionId } = await send('Target.attachToTarget', { targetId, flatten: true });
  const call = (method, params) => send(method, params, sessionId);
  await call('Page.enable');
  await call('Runtime.enable');
  const evaluate = async expression => {
    const r = await call('Runtime.evaluate', { expression, returnByValue: true, awaitPromise: true });
    if (r.exceptionDetails) throw new Error(r.exceptionDetails.text + ': ' + r.result.description);
    return r.result.value;
  };
  return {
    call, evaluate,
    async viewport(width, height = 1000) {
      await call('Emulation.setDeviceMetricsOverride', { width, height, deviceScaleFactor: 1, mobile: false });
    },
    async navigate(url) {
      const result = await call('Page.navigate', { url });
      if (result.errorText) throw new Error(result.errorText);
      // Bounded page-load check, not an agent wake/watch loop.
      for (let n = 0; n < 50; n++) {
        if (await evaluate('document.readyState === "complete"')) break;
        await new Promise(r => setTimeout(r, 100));
      }
      await evaluate('document.fonts.ready.then(() => true)');
      return result;
    },
    async screenshot(path) {
      const { data } = await call('Page.captureScreenshot', { format: 'png' });
      await writeFile(path, Buffer.from(data, 'base64'));
    },
    async key(key, code = key, modifiers = 0) {
      const virtual = { Tab: 9, Enter: 13, Escape: 27, ArrowDown: 40, ArrowRight: 39, ' ': 32 }[key];
      await call('Input.dispatchKeyEvent', { type: 'keyDown', key, code, modifiers, windowsVirtualKeyCode: virtual, text: key === 'Enter' ? '\r' : key.length === 1 ? key : '' });
      await call('Input.dispatchKeyEvent', { type: 'keyUp', key, code, modifiers, windowsVirtualKeyCode: virtual });
    },
    async close() {
      await send('Browser.close').catch(() => {});
      if (child.exitCode === null) await new Promise(resolve => child.once('exit', resolve));
      await rm(profile, { recursive: true, force: true });
    },
  };
}