var util = require('util'),
    colors = require('colors'),
    http = require('http'),
    httpProxy = require('http-proxy');
 
//
// This is an example of a url-routing middleware.
// This is not intended for production use, but rather as
// an example of how to write a middleware.
//

function matcher (url, dest) {
  // First, turn the URL into a regex.  
  // NOTE: Turning user input directly into a Regular Expression is NOT SAFE.
  var r = new RegExp(url.replace(/\//, '\\/'));
  // This next block of code may look a little confusing. 
  // It returns a closure (anonymous function) for each URL to be matched,
  // storing them in an array - on each request, if the URL matches one that has
  // a function stored for it, the function will be called.
  return function (url) {
    var m = r(url)
    if (!m) {
      return;
    }
    var path = url.slice(m[0].length);
    console.log('proxy:', url, '->', dest);
    return {url: path, dest: dest};
  }
}

exports.urls = function (urls) {
  // This is the entry point for our middleware.
  // 'matchers' is the array of URL matchers, as mentioned above.
  var matchers = [];
  for (var url in urls) {
    // Call the 'matcher' function above, and store the resulting closure.
    matchers.push(matcher(url, urls[url]));
  }

  // This closure is returned as the request handler.
  return function (req, res, next) {
    //
    // in node-http-proxy middlewares, `proxy` is the prototype of `next`
    // (this means node-http-proxy middlewares support both the connect API (req, res, next)
    // and the node-http-proxy API (req, res, proxy)
    //
    var proxy = next;
    for (var k in matchers) {
      // for each URL matcher, try the request's URL.
      var m = matchers[k](req.url);
      // If it's a match:
      if (m) {
        // Replace the local URL with the destination URL.
        req.url = m.url;
        // If routing to a server on another domain, the hostname in the request must be changed.
        req.headers.host = m.host;
        // Once any changes are taken care of, this line makes the magic happen.
        proxy.proxyRequest(req, res, m.dest);
      }
    }
  }
}

// Now we set up our proxy.
httpProxy.createServer(
  // This is where our middlewares go, with any options desired - in this case,
  // the list of routes/URLs and their destinations.
  exports.urls({
    '/hello': { port: 9000, host: 'localhost' },
    '/charlie': { port: 80, host: 'charlieistheman.com' },
    '/google': { port: 80, host: 'google.com' } 
  })
).listen(8000);

//
// Target Http Server (to listen for requests on 'localhost')
//
http.createServer(
  function (req, res) {
    res.writeHead(200, { 'Content-Type': 'text/plain' });
    res.write('request successfully proxied to: ' + req.url + '\n' + JSON.stringify(req.headers, true, 2));
    res.end();
  }).listen(9000);

// And finally, some colored startup output.
util.puts('http proxy server'.blue + ' started '.green.bold + 'on port '.blue + '8000'.yellow);
util.puts('http server '.blue + 'started '.green.bold + 'on port '.blue + '9000 '.yellow);