appUserService.js

'use strict';

const appUserRepository = require('../data/repositories/appUserRepository');

const saveAppUser = (profile) => {
  return new Promise((resolve, reject) => {
    Promise.resolve().then(() => {
      return appUserRepository.getAppUserByFacebookId(profile.id);
    }).then((appUser) => {
      if (appUser) {
        return appUserRepository.updateAppUser(profile);
      } else {
        return appUserRepository.insertAppUser(profile);
      }
    }).then((facebookId) => {
      return appUserRepository.getAppUserByFacebookId(facebookId);
    }).then((appUser) => {
      if (!appUser) { throw 'An error occurred attempting to save appUser.'; }
      resolve(appUser);
    }).catch((error) => {
      reject(error);
    });
  });
};

module.exports = {
  saveAppUser: saveAppUser
};

I want to go over this code more with you.