code: /*
   * Copyright 2015 recommenders.net.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package net.recommenders.rival.evaluation.strategy;
  
  import java.io.PrintStream;
  import java.util.List;
  import java.util.Set;
  import net.recommenders.rival.evaluation.Pair;
  
  /**
   * An interface for evaluation strategies.
   *
   * @author <a href="http://github.com/abellogin">Alejandro</a>
   *
   * @param <U> generic type for users
   * @param <I> generic type for items
   */
  public interface EvaluationStrategy<U, I> {
  
      /**
       * Enumeration that defines two output formats: a simple one (tab-separated)
       * and another compatible with the one used by the treceval program.
       */
      public enum OUTPUT_FORMAT {
  
          /**
           * Tab-separated format.
           */
          SIMPLE,
          /**
           * Format as followed by the trec_eval program.
           */
          TRECEVAL;
      }
  
      /**
       * Get the items to rank.
       *
       * @param user The user.
       * @return The items to rank.
       */
      Set<I> getCandidateItemsToRank(U user);
  
      /**
       * Print rankings for a user.
       *
       * @param user The user.
       * @param scoredItems The scored items to print.
       * @param out Where to print.
       * @param format The format of the printer (see {@link OUTPUT_FORMAT}).
       */
      void printRanking(U user, List<Pair<I, Double>> scoredItems, PrintStream out, OUTPUT_FORMAT format);
  
      /**
       * Print the ground truth.
       *
       * @param user The user.
       * @param out Where to print.
       * @param format The format of the printer (see {@link OUTPUT_FORMAT}).
       */
      void printGroundtruth(U user, PrintStream out, OUTPUT_FORMAT format);
  }
  