var express = require('express');

var cookie  = require('cookie-parser')

var crypto = require('crypto');

var app = express();

app.use(cookie());

var salt = 'secret key' 

function mk_hash(s) {

    return crypto.createHash('sha1').update(s).digest('hex')

}

function mk_cookie(c) {

    return c.toString() + '-' + mk_hash(c.toString() + salt)

}

function gt_cookie(s) {

    var splits = s.split("-", 2);

    var counter = parseInt(splits[0])

    var hash = splits[1]

    if (mk_hash(counter.toString() + salt) == hash) {

	return counter

    } else {

	return 0

    }

}

app.get('/', function(req, res){

    var counter = gt_cookie(req.cookies.counter) || 0;

    res.cookie('counter', mk_cookie(counter + 1));

    if (counter >= 5) {

	res.write('You are a valued customer ' + 

		  'visting the site ' + counter + ' times.');

    } else {

	res.write('This is visit number '+ counter +'!');

    }

    res.end();

});

// starting the server

app.listen(8000);

console.log("Server running at http://127.0.0.1:8000/");