import { spawn, spawnSync } from 'node:child_process';
import { createServer } from 'node:http';
import { existsSync, mkdtempSync, readFileSync, rmSync, statSync } from 'node:fs';
import { tmpdir } from 'node:os';
import { extname, join, resolve, sep } from 'node:path';

const sleep = (ms) => new Promise((done) => setTimeout(done, ms));

export const CHROME_PATH =
  ['google-chrome', 'google-chrome-stable', 'chromium', 'chromium-browser'].find(
    (name) => spawnSync('which', [name], { stdio: 'ignore' }).status === 0,
  ) ?? null;

const TYPES = { '.html': 'text/html; charset=utf-8', '.js': 'text/javascript; charset=utf-8', '.css': 'text/css' };

// Serves a directory over http://127.0.0.1 so a page can import ES modules from it.
export function startStaticServer(root) {
  const base = resolve(root);
  const server = createServer((req, res) => {
    const path = resolve(join(base, decodeURIComponent(new URL(req.url, 'http://localhost').pathname)));
    let isFile = false;
    try {
      isFile = path.startsWith(base + sep) && statSync(path).isFile();
    } catch {
      // not found
    }
    if (!isFile) {
      res.writeHead(404).end('not found');
      return;
    }
    res.writeHead(200, { 'content-type': TYPES[extname(path)] ?? 'application/octet-stream' });
    res.end(readFileSync(path));
  });
  return new Promise((done) => {
    server.listen(0, '127.0.0.1', () => {
      done({ origin: `http://127.0.0.1:${server.address().port}`, close: () => new Promise((closed) => server.close(closed)) });
    });
  });
}

export async function launchBrowser() {
  const profile = mkdtempSync(join(tmpdir(), 'outlier-saver-chrome-'));
  // Chrome puts a unix socket in TMPDIR and dies with "Socket path too long" if that path is long.
  const { TMPDIR: _ignored, ...env } = process.env;
  const proc = spawn(
    CHROME_PATH,
    ['--headless=new', '--remote-debugging-port=0', `--user-data-dir=${profile}`, '--no-first-run', '--no-default-browser-check', 'about:blank'],
    { stdio: 'ignore', env },
  );
  const portFile = join(profile, 'DevToolsActivePort');
  let port = null;
  for (let attempt = 0; attempt < 80 && port === null; attempt += 1) {
    if (existsSync(portFile)) port = Number(readFileSync(portFile, 'utf8').split('\n')[0]);
    else await sleep(250);
  }
  if (port === null) {
    proc.kill();
    throw new Error('Chrome did not start');
  }

  return {
    async openPage(url) {
      const target = await (await fetch(`http://127.0.0.1:${port}/json/new?${url}`, { method: 'PUT' })).json();
      const ws = new WebSocket(target.webSocketDebuggerUrl);
      await new Promise((opened, failed) => {
        ws.onopen = opened;
        ws.onerror = failed;
      });
      let nextId = 0;
      const pending = new Map();
      ws.onmessage = ({ data }) => {
        const message = JSON.parse(data);
        const waiter = pending.get(message.id);
        if (!waiter) return;
        pending.delete(message.id);
        if (message.error) waiter.fail(new Error(message.error.message));
        else waiter.done(message.result);
      };
      const send = (method, params = {}) =>
        new Promise((done, fail) => {
          nextId += 1;
          pending.set(nextId, { done, fail });
          ws.send(JSON.stringify({ id: nextId, method, params }));
        });
      const evaluate = async (expression) => {
        const result = await send('Runtime.evaluate', { expression, awaitPromise: true, returnByValue: true });
        if (result.exceptionDetails) {
          throw new Error(result.exceptionDetails.exception?.description ?? result.exceptionDetails.text);
        }
        return result.result.value;
      };
      // A fresh tab is "complete" on about:blank before it navigates, so wait for the real page.
      for (let attempt = 0; attempt < 80; attempt += 1) {
        const state = await evaluate('JSON.stringify([location.href, document.readyState])');
        const [href, readyState] = JSON.parse(state);
        if (href !== 'about:blank' && readyState === 'complete') break;
        await sleep(100);
      }
      return { evaluate, close: () => ws.close() };
    },
    async close() {
      proc.kill('SIGTERM');
      await sleep(300);
      rmSync(profile, { recursive: true, force: true, maxRetries: 3 });
    },
  };
}