/* @getRecommendations:
   * This method implements the Hybrid recommender system, first it finds most similar users by
   * checking their tastes (favorite books, musics, movies and athletes) them the next recommender
   * algorithm filter users based on Demographic correlation (Location, gender and age), it also features
   * their ratings on each product, the output will be a list with the items most appealing to the user */
  @RequestMapping(value = "/recommendations", method = RequestMethod.GET)
  public ResponseEntity<ArrayList<Prediction>> getRecommendations(@RequestParam("id") String id) {

    /* Retrieve all users to cluster */
    User baseUser = userRepository.findOne(id);
    if (baseUser != null) {
      List<User> users = userRepository.findAll();

      /* Knowledge Correlation */
      ArrayList<Neighbor> knowledgeSimilarity =
          ClusterUtils.getKnowledgeNeighborhood(baseUser, users);

      List<User> filteredUsers = new ArrayList<User>();
      for (int i = 0; i <= (knowledgeSimilarity.size() - 1); i++) {
        filteredUsers.add(knowledgeSimilarity.get(i).getUser());
      }

      ArrayList<Neighbor> neighborhood =
          ClusterUtils.getMergedCorrelations(baseUser, filteredUsers);

      /* Order arrayList by similar users from highest to lowest correlation */
      Collections.sort(neighborhood);

      ArrayList<Prediction> predictions = PredictionUtils.getPredictions(baseUser, neighborhood);
      Collections.sort(predictions);

      return new ResponseEntity<>(predictions, HttpStatus.OK);
    } else {
      ArrayList<Prediction> predictions = new ArrayList<>();
      return new ResponseEntity<>(predictions, HttpStatus.OK);
    }
  }
  @RequestMapping(value = "/trending", method = RequestMethod.GET)
  public ResponseEntity<ArrayList<Trending>> getTrending() {

    List<User> userList = userRepository.findAll();
    List<Occupation> occupationList = occupationRepository.findAll();

    ArrayList<Trending> trending = ClusterUtils.getTrendingOccupations(userList, occupationList);
    Collections.sort(trending);

    return new ResponseEntity<>(trending, HttpStatus.OK);
  }
 @RequestMapping(value = "/users", method = RequestMethod.GET)
 public ResponseEntity<List<User>> users() {
   return new ResponseEntity<>(userRepository.findAll(), HttpStatus.OK);
 }