RX make your head explode

  Observable<String> createAccount(final String username, final String password, final String emailAddress) {

    mongoDatabase.getCollection(UserCodec.COLLETION_NAME, User)
      .find(eq(UserCodec.USERNAME_PROPERTY, username))
      .toObservable()
      .isEmpty()
      .map { final Boolean userStreamIsEmpty ->

      if (!userStreamIsEmpty) {

        throw new Exception("A user with the same username '${username}' was found in the DB")
      }

      userStreamIsEmpty
    }.flatMap({ final Boolean userStreamIsEmpty ->

      // MONGO DB REFERENCE IS RX MONGO, PASSWORD GENERATION IS BLOCKING. NOT SURE WHAT HAPPENS IN TERMS OF THREADING HERE...
      mongoDatabase.getCollection(UserCodec.COLLETION_NAME, User)
        .insertOne(new User(username: username, password: PasswordFactory.create().hash(password), emailAddress: emailAddress))
        .asObservable()
    } as Func1).map { final Success success ->

      mongoDatabase.getCollection(UserCodec.COLLETION_NAME, User)
        .find(eq(UserCodec.USERNAME_PROPERTY, username))
    }.flatMap({ final User retrievedUser ->

      Jwts
        .builder()
        .setPayload(Jackson.json(retrievedUser) as String)
        .setIssuedAt(new Date())
        .setExpiration(Date.from(LocalDateTime.now().plusHours(48).toInstant(ZoneOffset.UTC)))
    } as Func1)
    .bindExec()
  }