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/");