const express = require('express');
// var onHeaders = require('on-headers');

var app = express();



app.use(function(req, res, next){
  console.log('middleware');
  res.writeHead = createWriteHead(res.writeHead);
  function createWriteHead(prevWriteHead){
    var fired = false;
    return function writeHead(statusCode) {
      var args = setWriteHeadHeaders.apply(this, arguments);
      if (!fired) {
        fired = true
        console.log('listener');
        if (typeof args[0] === 'number' && this.statusCode !== args[0]) {
          args[0] = this.statusCode
          args.length = 1
        }
      }

      prevWriteHead.apply(this, args);
    } // function writeHead(statusCode) {




  } // createWriteHead

  function setWriteHeadHeaders(statusCode) {
    var length = arguments.length
    var headerIndex = length > 1 && typeof arguments[1] === 'string'
      ? 2
      : 1
    var headers = length >= headerIndex + 1
      ? arguments[headerIndex]
      : undefined
    this.statusCode = statusCode
    if (Array.isArray(headers)) {
      for (var i = 0, len = headers.length; i < len; ++i) {
        this.setHeader(headers[i][0], headers[i][1])
      }
    } else if (headers) {
      var keys = Object.keys(headers)
      for (var i = 0; i < keys.length; i++) {
        var k = keys[i]
        if (k) this.setHeader(k, headers[k])
      }
    }
    var args = new Array(Math.min(length, headerIndex))
    for (var i = 0; i < args.length; i++) {
      args[i] = arguments[i]
    }
    return args
  } // function setWriteHeadHeaders(statusCode) {



  next();
})// use




// app.use(function(req, res, next){
//   onHeaders(res, function(){
//     // console.log(this);
//     console.log('onHeaders');
//     // res.setHeader('Content-Type', 'text/html')
//   });
//   next();
// })

app.get('/', function(req, res){
  res.set('Content-Type', 'text/html');
  // res.set({
  //   'Content-Type': 'text/plain',
  //   'Content-Length': '123',
  //   'ETag': '12345'
  // })
  // console.log(res.writeHead);
  console.log('begin Hi!');
  res.send('Hi!');
  console.log('after Hi!');
})

app.listen(3000);