Ja hueyu

const passport = require('passport');
const FacebookStrategy = require('passport-facebook').Strategy;
const keys = require('./keys');
const User = require('../models/user-model');
const router = require('express').Router();

passport.serializeUser((user, done) => {
    done(null, user.id);
});

passport.deserializeUser((id, done) => {
    User.findById(id).then((user) => {
        done(null, user);
    });
});

passport.use(
    new FacebookStrategy({
        // options for the facebook strategy
        clientID: keys.facebook.clientID,
        clientSecret: keys.facebook.clientSecret,
        callbackURL: '/auth/facebook/redirect',
    }, (accessToken, refreshToken, profile, done) => {
        // check if the user already exists
        User.findOne({facebookid: profile.id}).then((currentUser) => {
            if (currentUser) {
                // already have the user
                done(null, currentUser);
            } else {
                // if not, create user
                new User({  // add new user to the db
                    username: profile.displayName,
                    facebookid: profile.id
                }).save().then((newUser) => {
                    done(null, newUser);
                });
            }
        });
    })
);

// auth with facebook
router.get('/facebook', passport.authenticate('facebook', {
    scope: ['profile']
}));

// callback route for facebook
router.get('/facebook/redirect', passport.authenticate('facebook'), (req, res) => {
    res.redirect('/profile/');
});

module.exports = router;