// 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';

// P19 #865: teardown is bounded. A browser that does not answer Browser.close is killed, and a
// call to a browser that has exited fails at once instead of waiting for its CDP timeout. A test
// process that ends with a browser still open kills it, so no chromium outlives its test file.
const live = new Set();
// Chromium runs in its own process group: killing only the main process leaves its renderer and
// GPU children writing into the profile, so every kill takes the whole group. The group is
// killed again the moment the main process exits (its children serve nothing after that), and
// never later: once the group is gone its id can be reused, so nothing signals it afterwards.
const killGroup = child => { try { process.kill(-child.pid, 'SIGKILL'); } catch {} };
process.once('exit', () => { for (const child of live) killGroup(child); });

// Row 95 (#1589): the Board's machine sessions are off by default. Most tests read the board scan,
// so by default every page this browser opens starts with Show machine sessions on, as if the
// person had turned it on before. Pass { machine: false } to see the page as a first visit does.
// `args` adds Chromium flags, for example --host-resolver-rules for a test host name.
// #1873 CB5: the system Chromium starts with --disable-extensions, so no host extension (and no
// native host it would start) runs in a test. A CHROMIUM launcher is the zoom tests' wrapper, which
// loads their one extension with --disable-extensions-except, so it gets no blanket flag.
export async function browser({ machine = true, args = [] } = {}) {
  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', ...(process.env.CHROMIUM ? [] : ['--disable-extensions']),
    '--disable-dev-shm-usage', '--remote-debugging-pipe', `--user-data-dir=${profile}`, ...args,
  ], { detached: true, stdio: ['ignore', 'ignore', 'ignore', 'pipe', 'pipe'] });
  live.add(child);
  let id = 0, buffer = '', exited = false;
  const pending = new Map(), events = new Map();
  const gone = new Promise(resolve => child.once('exit', () => {
    exited = true; killGroup(child); live.delete(child);
    for (const [key, { reject, timeout, method }] of pending) { clearTimeout(timeout); pending.delete(key); reject(new Error(`CDP ${method}: browser exited`)); }
    resolve();
  }));
  // The pipes break when chromium dies; the exit handler above reports that to every caller.
  child.stdio[3].on('error', () => {});
  child.stdio[4].on('error', () => {});
  // A browser whose close() never ran (an earlier after hook failed) must not keep the test file
  // alive: the child and its pipes do not hold the event loop, and the exit hook above kills it.
  // Every wait on the browser has its own timer, so a live call still keeps the loop running.
  child.unref(); child.stdio[3].unref(); child.stdio[4].unref();
  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 (message.method) for (const fn of events.get(message.method) ?? []) fn(message.params, message.sessionId);
      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, ms = 25000) {
    return new Promise((resolve, reject) => {
      if (exited) return reject(new Error(`CDP ${method}: browser exited`));
      const key = ++id;
      const timeout = setTimeout(() => { pending.delete(key); reject(new Error(`CDP timeout: ${method}`)); }, ms);
      pending.set(key, { resolve, reject, timeout, method });
      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');
  if (machine) await call('Page.addScriptToEvaluateOnNewDocument', { source: `try { localStorage.setItem('mosaic-console-board', '{"machine":true}'); } catch {}` });
  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, pid: child.pid,
    on(method, fn) { if (!events.has(method)) events.set(method, new Set()); events.get(method).add(fn); return () => events.get(method).delete(fn); },
    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, ArrowUp: 38, ArrowRight: 39, ' ': 32, k: 75 }[key];
      await call('Input.dispatchKeyEvent', { type: 'keyDown', key, code, modifiers, windowsVirtualKeyCode: virtual, text: modifiers ? '' : key === 'Enter' ? '\r' : key.length === 1 ? key : '' });
      await call('Input.dispatchKeyEvent', { type: 'keyUp', key, code, modifiers, windowsVirtualKeyCode: virtual });
    },
    async close() {
      if (!exited) {
        await send('Browser.close', {}, undefined, 5000).catch(() => {});
        let timer;
        const late = new Promise(resolve => { timer = setTimeout(resolve, 5000, 'timeout'); });
        const outcome = await Promise.race([gone, late]);
        clearTimeout(timer);
        if (outcome === 'timeout') { killGroup(child); await gone; }
      }
      await rm(profile, { recursive: true, force: true, maxRetries: 10, retryDelay: 100 });
    },
  };
}