index.js

#!/usr/bin/env node

const {
  existsSync,
  readFileSync,
} = require('fs');
const {
  resolve,
  basename,
  extname,
} = require('path');
const chalk = require('chalk');
const arg = require('arg');

const args = arg({
  '--help': Boolean,
  '--version': Boolean,
  '--github-api-url': String,
  '--browser': String,
  '--host': String,
  '--port': Number,
  '-h': '--help',
  '-v': '--version',
  '-b': '--browser',
  '-H': '--host',
  '-p': '--port',
});

if (args['--version']) {
  const pkg = require(resolve(__dirname, './package.json'));
  console.log(`gfm-preview v${pkg.version}`);
  process.exit(0);
}

let filename = args._[0];
if (args['--help'] || (!filename)) {
  console.log(chalk`
    {bold.cyan gfm-preview} - Preview your markdown with GitHub API in real time

    {bold USAGE}

      {bold $} {cyan preview} --help
      {bold $} {cyan preview} --version
      {bold $} {cyan preview} {underline file.md}
      {bold $} {cyan preview} {underline file.md} [--brower {underline brower_name_or_executable}]
      {bold $} {cyan preview} {underline file.md} [--host {underline hostname}] [--port {underline port_number}]
      {bold $} {cyan preview} {underline file.md} [--github-api-url {underline github_api_url}]

    {bold OPTIONS}

      --help, -h                               shows this help message
      --version, -v                            displays the current version of gfm-preview
      --browser, -b {underline brower_name_or_executable}  sets the browser to open a preview
      --host, -H {underline hostname}                      sets the hostname
      --port, -p {underline port_number}                   sets the port number
      --github-api-url {underline github_api_url}          sets the GitHub API URL (default: {underline https://api.github.com})
  `);
  process.exit(0);
}

let currentFile = resolve(filename);
let existsCurrentFile = existsSync(currentFile);
const files = [];
const port = args['--port'] ? args['--port'] : 4649;
const encoding = 'utf-8';
const apiUrl = args['--github-api-url'] ? args['--github-api-url'] : 'https://api.github.com';
const axios = require('axios');
const app = require('express')();
const { watch } = require('chokidar');
let watcher;

app.get('/gfm/favicon.ico', async (_req, res) => {
  res.header('Content-Type', 'image/x-icon');
  res.send(readFileSync(resolve(__dirname, 'favicon.ico')));
});

app.get('/gfm/favicon.png', async (_req, res) => {
  res.header('Content-Type', 'image/png');
  res.send(readFileSync(resolve(__dirname, 'favicon.png')));
});

app.get('/gfm/app.css', async (_req, res) => {
  res.header('Content-Type', 'text/css; charset=' + encoding);
  res.send(readFileSync(resolve(__dirname, 'app.css'), encoding));
});

app.get('/gfm/hl.css', async (_req, res) => {
  res.header('Content-Type', 'text/css; charset=' + encoding);
  res.send(readFileSync(resolve(__dirname, 'hl.css'), encoding));
});

app.get('/gfm/hl.js', async (_req, res) => {
  res.header('Content-Type', 'text/javascript; charset=' + encoding);
  res.send(readFileSync(resolve(__dirname, 'hl.js'), encoding));
});

app.get('/gfm/socket.io.js', async (_req, res) => {
  res.header('Content-Type', 'text/javascript; charset=' + encoding);
  res.send(readFileSync(resolve(__dirname, 'node_modules/socket.io-client/dist/socket.io.js'), encoding));
});

app.get('/gfm/socket.io.js.map', async (_req, res) => {
  res.header('Content-Type', 'text/plain; charset=' + encoding);
  res.send(readFileSync(resolve(__dirname, 'node_modules/socket.io-client/dist/socket.io.js.map'), encoding));
});

app.get('*', async (req, res) => {
  if (req.params[0] === '/') {
    res.send('Please select a file to preview');
    return;
  }

  const file = resolve(req.params[0].slice(1));
  currentFile = file;
  existsCurrentFile = existsSync(file);
  if (existsCurrentFile) {
    if (!files.includes(currentFile)) {
      files.push(currentFile);
      if (watcher) {
        watcher.close();
      }
      watcher = watch(files);
    }
    res.header('Content-Type', 'text/html; charset=' + encoding);
    let html = readFileSync(resolve(__dirname, 'index.html'), encoding);
    html = html.replace(/{%TITLE%}/, basename(currentFile)).replace(/{%HOST%}/g, host).replace(/{%PORT%}/g, port);
    res.send(html);
  } else {
    res.header('Content-Type', 'text/html; charset=' + encoding);
    let html = readFileSync(resolve(__dirname, 'index.html'), encoding);
    html = html.replace(/{%TITLE%}/, `Not found: ${basename(currentFile)}`).replace(/{%HOST%}/g, host).replace(/{%PORT%}/g, port);
    res.send(html);
  }
});

const server = require('http').createServer(app);
const io = require('socket.io')(server);

io.on('connection', (socket) => {
  const responseContent = async () => {
    let content;
    const text = existsCurrentFile ? readFileSync(currentFile, encoding) : `Not found: ${currentFile}`;
    const markdownExtension = /\.m(arkdown|kdn?|d(o?wn)?)(\?.*)?(#.*)?$/i;
    if (markdownExtension.test(extname(currentFile))) {
      try {
        const response = await axios.post(apiUrl + '/markdown', { text, mode: 'gfm' });
        content = response.data;
      } catch (e) {
        content = e.response.data.message;
      }
    } else {
      content = `<pre><code>${text}</code></pre>`;
    }
    socket.emit('response content', content);
  }

  watcher.on('change', () => {
    console.log(chalk`> {cyan gfm-preview}: Detect changes and reloaded content (${basename(currentFile)})`);
    responseContent();
  });

  socket.on('request content', () => {
    responseContent();
  });

  socket.on('clicking', () => {
    clicking = true;
    socket.emit('clickable');
  });

  socket.on('clicked', () => {
    clicking = false;
  });

  socket.on('disconnect', () => {
    if (!clicking && io.sockets.server.engine.clientsCount === 0) {
      console.log(chalk`> {cyan gfm-preview}: Have a nice code!`);
      process.exit(0);
    }
  });
});

const host = args['--host'] ? args['--host'] : 'localhost';
const url = `http://${host}:${port}`;
const start = async () => {
  try {
    if (args['--browser']) {
      require('open')(url + '/' + basename(currentFile), { app: args['--browser'] });
    } else {
      require('open')(url + '/' + basename(currentFile));
    }
    await server.listen(port, host, () => {
      console.log(chalk`> {cyan gfm-preview}: Ready on ${url}`);
    });
  } catch (err) {
    console.error(err);
    process.exit(1);
  }
}

start();