i dont know why my data isnt being saved to the db?

const mongoose= require("mongoose");
const Promise = require('promise');

var UserSchema = new mongoose.Schema({
  email: {
    type: String,
    unique: true,
    required: true,
    trim: true,
  },
  name: {
    type: String,
    required: true,
    trim: true,
  },
  password: {
    type: String,
    required: true
  }
});
UserSchema.statics.authenticate = function(email, password, callback) {
  User.findOne({ email: email })
      .exec(function (error, user) {
        if (error) {
          return callback(error);
        } else if ( !user ) {
          var err = new Error('User not found.');
          err.status = 401;
          return callback(err);
        }
        bcrypt.compare(password, user.password , function(error, result) {
          if (result === true) {
            return callback(null, user);
          } else {
            return callback();
          }
        })
      });
}
// hash password before saving to database
UserSchema.save('save', function(next) {
  var user = this;
  bcrypt.hash(user.password, 10, function(err, hash) {
    if (err) {
      return next(err);
    }
    user.password = hash;
    next();
  })
});
app.js
var User = mongoose.model('User', UserSchema);
module.exports = User;
const express = require("express");
const passport= require("passport");
const mongoose= require("mongoose");
const bodyParser = require('body-parser');
const Promise = require('promise');
const session = require('express-session');
const app = express();
app.use(session({
  secret: 'treehouse love you',
  resave: true,
  saveUninitialized: false
}));
const models = require('./models/user');

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));

app.use(express.static(__dirname + '/public'));


var MongoClient = require('mongodb').MongoClient
  , assert = require('assert');

// Connection URL
var url = 'mongodb://localhost:27017/flash';

// Use connect method to connect to the server
MongoClient.connect(url, function(err, db) {
  assert.equal(null, err);
  console.log("Connected successfully to server");

  db.close();
});

app.set('view engine','pug');
app.set('views', __dirname + '/views');

var routes = require('./routes/index');
app.use('/', routes);

app.get("/",(request,response)=>{
    return response.render("layout",{title:'sighn up'})
});
app.get("/home",(request,response)=>{
    response.render("home");
});
app.get("/register",(request,response)=>{
  response.render("register");
});
app.get("/login",(request,response)=>{
    response.render("login");
});
app.get("/profile",(request,response)=>{
    response.render("profile");
    });

  app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
      message: err.message,
      error: {}
    });
  });
app.listen(3000);

index.js
var express = require('express');
var router = express.Router();
var User = require('../models/user');

router.get('/login', function(req, res, next){
  return res.render('login', {title: "Log in"})
});

router.post('/login', function(req, res, next){
  if(req.body.email && req.body.password){

  }else{
    var err = new Error('Email and password are reqwuired.')
    err.status = 401;
    return next(err);
  }
});

// GET /register
router.get('/register', function(req, res, next) {
  return res.render('register', { title: 'Sign Up' });
});

// POST /register
router.post('/register', function(req, res, next) {
  if (req.body.email &&
    req.body.name &&
    req.body.password &&
    req.body.confirmPassword) {
      return res.send('user created');

      if (req.body.password !== req.body.confirmPassword) {
        var err = new Error('Passwords do not match.');
        err.status = 400;
        return next(err);
      }

      User.create(userData, function (error, user) {
        if (error) {
          return next(error);
        } else {
          return res.redirect('/profile');
        }
      });

    } else {
      var err = new Error('All fields required.');
      err.status = 400;
      return next(err);
    }
})

// GET /
router.get('/', function(req, res, next) {
  return res.render('index', { title: 'Home' });
});

// GET /about
router.get('/about', function(req, res, next) {
  return res.render('about', { title: 'About' });
});

// GET /contact
router.get('/contact', function(req, res, next) {
  return res.render('contact', { title: 'Contact' });
});

module.exports = router;