text: const passport = require('passport');
  const request = require('request');
  const InstagramStrategy = require('passport-instagram').Strategy;
  const LocalStrategy = require('passport-local').Strategy;
  const FacebookStrategy = require('passport-facebook').Strategy;
  const TwitterStrategy = require('passport-twitter').Strategy;
  const GoogleStrategy = require('passport-google-oauth').OAuth2Strategy;
  
  const User = require('../models/User');
  
  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 Twitter.
  //
  // passport.use(new TwitterStrategy({
  //   consumerKey: process.env.TWITTER_KEY,
  //   consumerSecret: process.env.TWITTER_SECRET,
  //   callbackURL: '/auth/twitter/callback',
  //   passReqToCallback: true
  // }, (req, accessToken, tokenSecret, profile, done) => {
  //   if (req.user) {
  //     User.findOne({ twitter: profile.id }, (err, existingUser) => {
  //       if (err) { return done(err); }
  //       if (existingUser) {
  //         req.flash('errors', { msg: 'There is already a Twitter 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.twitter = profile.id;
  //           user.tokens.push({ kind: 'twitter', accessToken, tokenSecret });
  //           user.profile.name = user.profile.name || profile.displayName;
  //           user.profile.location = user.profile.location || profile._json.location;
  //           user.profile.picture = user.profile.picture || profile._json.profile_image_url_https;
  //           user.save((err) => {
  //             if (err) { return done(err); }
  //             req.flash('info', { msg: 'Twitter account has been linked.' });
  //             done(err, user);
  //           });
  //         });
  //       }
  //     });
  //   } else {
  //     User.findOne({ twitter: profile.id }, (err, existingUser) => {
  //       if (err) { return done(err); }
  //       if (existingUser) {
  //         return done(null, existingUser);
  //       }
  //       const user = new User();
  //       // Twitter will not provide an email address.  Period.
  //       // But a person’s twitter username is guaranteed to be unique
  //       // so we can "fake" a twitter email address as follows:
  //       user.email = `${profile.username}@twitter.com`;
  //       user.twitter = profile.id;
  //       user.tokens.push({ kind: 'twitter', accessToken, tokenSecret });
  //       user.profile.name = profile.displayName;
  //       user.profile.location = profile._json.location;
  //       user.profile.picture = profile._json.profile_image_url_https;
  //       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);
            });
          }
        });
      });
    }
  }));
  //
  // /**
  //  * Sign in with Instagram.
  //  */
  // passport.use(new InstagramStrategy({
  //   clientID: process.env.INSTAGRAM_ID,
  //   clientSecret: process.env.INSTAGRAM_SECRET,
  //   callbackURL: '/auth/instagram/callback',
  //   passReqToCallback: true
  // }, (req, accessToken, refreshToken, profile, done) => {
  //   if (req.user) {
  //     User.findOne({ instagram: profile.id }, (err, existingUser) => {
  //       if (err) { return done(err); }
  //       if (existingUser) {
  //         req.flash('errors', { msg: 'There is already an Instagram 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.instagram = profile.id;
  //           user.tokens.push({ kind: 'instagram', accessToken });
  //           user.profile.name = user.profile.name || profile.displayName;
  //           user.profile.picture = user.profile.picture || profile._json.data.profile_picture;
  //           user.profile.website = user.profile.website || profile._json.data.website;
  //           user.save((err) => {
  //             req.flash('info', { msg: 'Instagram account has been linked.' });
  //             done(err, user);
  //           });
  //         });
  //       }
  //     });
  //   } else {
  //     User.findOne({ instagram: profile.id }, (err, existingUser) => {
  //       if (err) { return done(err); }
  //       if (existingUser) {
  //         return done(null, existingUser);
  //       }
  //       const user = new User();
  //       user.instagram = profile.id;
  //       user.tokens.push({ kind: 'instagram', accessToken });
  //       user.profile.name = profile.displayName;
  //       // Similar to Twitter API, assigns a temporary e-mail address
  //       // to get on with the registration process. It can be changed later
  //       // to a valid e-mail address in Profile Management.
  //       user.email = `${profile.username}@instagram.com`;
  //       user.profile.website = profile._json.data.website;
  //       user.profile.picture = profile._json.data.profile_picture;
  //       user.save((err) => {
  //         done(err, user);
  //       });
  //     });
  //   }
  // }));
  
  /**
   * 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}`);
    }
  };
  