text: const passport = require('passport');
  const request = require('request');
  const LocalStrategy = require('passport-local').Strategy;
  const FacebookStrategy = require('passport-facebook').Strategy;
  const GoogleStrategy = require('passport-google-oauth').OAuth2Strategy;
  const OpenIDStrategy = require('passport-openid').Strategy;
  const OAuthStrategy = require('passport-oauth').OAuthStrategy;
  const OAuth2Strategy = require('passport-oauth').OAuth2Strategy;
  
  const User = require('../models/UserDTO');
  
  passport.serializeUser((user, done) => {
    done(null, user.id);
  });
  
  passport.deserializeUser((id, done) => {
    User.findById(id, (err, user) => {
      done(err, user);
    });
  });
  
  /**
   * Sign in using Email and Password.
   */
  passport.use(new LocalStrategy({ usernameField: 'email' }, (email, password, done) => {
    User.findOne({ email: email.toLowerCase() }, (err, user) => {
      if (err) { return done(err); }
      if (!user) {
        return done(null, false, { msg: `Email ${email} not found.` });
      }
      user.comparePassword(password, (err, isMatch) => {
        if (err) { return done(err); }
        if (isMatch) {
          return done(null, user);
        }
        return done(null, false, { msg: 'Invalid email or password.' });
      });
    });
  }));
  
  /**
   * OAuth Strategy Overview
   *
   * - User is already logged in.
   *   - Check if there is an existing account with a provider id.
   *     - If there is, return an error message. (Account merging not supported)
   *     - Else link new OAuth account with currently logged-in user.
   * - User is not logged in.
   *   - Check if it's a returning user.
   *     - If returning user, sign in and we are done.
   *     - Else check if there is an existing account with user's email.
   *       - If there is, return an error message.
   *       - Else create a new account.
   */
  
  /**
   * Sign in with Facebook.
   */
  passport.use(new FacebookStrategy({
    clientID: process.env.FACEBOOK_ID,
    clientSecret: process.env.FACEBOOK_SECRET,
    callbackURL: '/auth/facebook/callback',
    profileFields: ['name', 'email', 'link', 'locale', 'timezone'],
    passReqToCallback: true
  }, (req, accessToken, refreshToken, profile, done) => {
    if (req.user) {
      User.findOne({ facebook: profile.id }, (err, existingUser) => {
        if (err) { return done(err); }
        if (existingUser) {
          req.flash('errors', { msg: 'There is already a Facebook account that belongs to you. Sign in with that account or delete it, then link it with your current account.' });
          done(err);
        } else {
          User.findById(req.user.id, (err, user) => {
            if (err) { return done(err); }
            user.facebook = profile.id;
            user.tokens.push({ kind: 'facebook', accessToken });
            user.profile.name = user.profile.name || `${profile.name.givenName} ${profile.name.familyName}`;
            user.profile.gender = user.profile.gender || profile._json.gender;
            user.profile.picture = user.profile.picture || `https://graph.facebook.com/${profile.id}/picture?type=large`;
            user.save((err) => {
              req.flash('info', { msg: 'Facebook account has been linked.' });
              done(err, user);
            });
          });
        }
      });
    } else {
      User.findOne({ facebook: profile.id }, (err, existingUser) => {
        if (err) { return done(err); }
        if (existingUser) {
          return done(null, existingUser);
        }
        User.findOne({ email: profile._json.email }, (err, existingEmailUser) => {
          if (err) { return done(err); }
          if (existingEmailUser) {
            req.flash('errors', { msg: 'There is already an account using this email address. Sign in to that account and link it with Facebook manually from Account Settings.' });
            done(err);
          } else {
            const user = new User();
            user.email = profile._json.email;
            user.facebook = profile.id;
            user.tokens.push({ kind: 'facebook', accessToken });
            user.profile.name = `${profile.name.givenName} ${profile.name.familyName}`;
            user.profile.gender = profile._json.gender;
            user.profile.picture = `https://graph.facebook.com/${profile.id}/picture?type=large`;
            user.profile.location = (profile._json.location) ? profile._json.location.name : '';
            user.save((err) => {
              done(err, user);
            });
          }
        });
      });
    }
  }));
  
  
  /**
   * Sign in with Google.
   */
  passport.use(new GoogleStrategy({
    clientID: process.env.GOOGLE_ID,
    clientSecret: process.env.GOOGLE_SECRET,
    callbackURL: '/auth/google/callback',
    passReqToCallback: true
  }, (req, accessToken, refreshToken, profile, done) => {
    if (req.user) {
      User.findOne({ google: profile.id }, (err, existingUser) => {
        if (err) { return done(err); }
        if (existingUser) {
          req.flash('errors', { msg: 'There is already a Google account that belongs to you. Sign in with that account or delete it, then link it with your current account.' });
          done(err);
        } else {
          User.findById(req.user.id, (err, user) => {
            if (err) { return done(err); }
            user.google = profile.id;
            user.tokens.push({ kind: 'google', accessToken });
            user.profile.name = user.profile.name || profile.displayName;
            user.profile.gender = user.profile.gender || profile._json.gender;
            user.profile.picture = user.profile.picture || profile._json.image.url;
            user.save((err) => {
              req.flash('info', { msg: 'Google account has been linked.' });
              done(err, user);
            });
          });
        }
      });
    } else {
      User.findOne({ google: profile.id }, (err, existingUser) => {
        if (err) { return done(err); }
        if (existingUser) {
          return done(null, existingUser);
        }
        User.findOne({ email: profile.emails[0].value }, (err, existingEmailUser) => {
          if (err) { return done(err); }
          if (existingEmailUser) {
            req.flash('errors', { msg: 'There is already an account using this email address. Sign in to that account and link it with Google manually from Account Settings.' });
            done(err);
          } else {
            const user = new User();
            user.email = profile.emails[0].value;
            user.google = profile.id;
            user.tokens.push({ kind: 'google', accessToken });
            user.profile.name = profile.displayName;
            user.profile.gender = profile._json.gender;
            user.profile.picture = profile._json.image.url;
            user.save((err) => {
              done(err, user);
            });
          }
        });
      });
    }
  }));
  
  
  
  /**
   * Steam API OpenID.
   */
  passport.use(new OpenIDStrategy({
    apiKey: process.env.STEAM_KEY,
    providerURL: 'http://steamcommunity.com/openid',
    returnURL: 'http://localhost:3000/auth/steam/callback',
    realm: 'http://localhost:3000/',
    stateless: true
  }, (identifier, done) => {
    const steamId = identifier.match(/\d+$/)[0];
    const profileURL = `http://api.steampowered.com/ISteamUser/GetPlayerSummaries/v0002/?key=${process.env.STEAM_KEY}&steamids=${steamId}`;
  
    User.findOne({ steam: steamId }, (err, existingUser) => {
      if (err) { return done(err); }
      if (existingUser) return done(err, existingUser);
      request(profileURL, (error, response, body) => {
        if (!error && response.statusCode === 200) {
          const data = JSON.parse(body);
          const profile = data.response.players[0];
  
          const user = new User();
          user.steam = steamId;
          user.email = `${steamId}@steam.com`; // steam does not disclose emails, prevent duplicate keys
          user.tokens.push({ kind: 'steam', accessToken: steamId });
          user.profile.name = profile.personaname;
          user.profile.picture = profile.avatarmedium;
          user.save((err) => {
            done(err, user);
          });
        } else {
          done(error, null);
        }
      });
    });
  }));
  
  
  /**
   * Login Required middleware.
   */
  exports.isAuthenticated = (req, res, next) => {
    if (req.isAuthenticated()) {
      return next();
    }
    res.redirect('/login');
  };
  
  /**
   * Authorization Required middleware.
   */
  exports.isAuthorized = (req, res, next) => {
    const provider = req.path.split('/').slice(-1)[0];
    const token = req.user.tokens.find(token => token.kind === provider);
    if (token) {
      next();
    } else {
      res.redirect(`/auth/${provider}`);
    }
  };
  