gistfile1.txt

function redirectToNextChallenge(req, res, next) {
    let challengeId = req.query.id || req.cookies.currentChallengeId;

    if (badIdMap[challengeId]) {
      challengeId = badIdMap[challengeId];
    }

    if (!isMongoId('' + challengeId)) {
      challengeId = null;
    }

    Observable.combineLatest(
      firstChallenge$,
      lastChallenge$
    )
      .flatMap(([firstChallenge, { id: lastChallengeId } ]) => {
        // no id supplied, load first challenge
        if (!challengeId) {
          return Observable.just(firstChallenge);
        }
        // camper just completed last challenge
        if (challengeId === lastChallengeId) {
          return Observable.just()
            .doOnCompleted(() => {
              req.flash('info', {
                msg: dedent`
                  Once you have completed all of our challenges, you should
                  join our <a href="https://gitter.im/freecodecamp/HalfWayClub"
                  target="_blank">Half Way Club</a> and start getting
                  ready for our nonprofit projects.
                `.split('\n').join(' ')
              });
              return res.redirect('/map');
            });
        }

        return getNextChallenge$(challenge$, blocks$, challengeId);
      })
      .doOnNext(({ dashedName } = {}) => {
        if (!dashedName) {
          log('no challenge found for %s', challengeId);
          res.redirect('/map');
        }
        res.redirect('/challenges/' + dashedName);
      })
      .subscribe(() => {}, next);
  }