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package com.davidbracewell.apollo.ml;

import com.davidbracewell.apollo.ml.data.Dataset;
import com.davidbracewell.apollo.ml.preprocess.PreprocessorList;
import lombok.NonNull;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.Spliterator;
import java.util.function.BiConsumer;
import java.util.function.Supplier;

/**
 * Encapsulates a set of train/test splits.
 *
 * @param  the example type parameter
 * @author David B. Bracewell
 */
public class TrainTestSet implements Iterable>, Serializable {
   private static final long serialVersionUID = 1L;
   private final Set> splits = new HashSet<>();

   /**
    * Adds a split to the set.
    *
    * @param trainTestSplit the train test split
    */
   public void add(@NonNull TrainTestSplit trainTestSplit) {
      splits.add(trainTestSplit);
   }

   /**
    * Processes each split as a train/test pair
    *
    * @param consumer the consumer to run over the train & test splits
    */
   public void forEach(@NonNull BiConsumer, Dataset> consumer) {
      forEach(tTrainTest -> consumer.accept(tTrainTest.getTrain(), tTrainTest.getTest()));
   }

   /**
    * Evaluates the set using an Evaluation produced by the given supplier. The process begins by resetting the
    * learner and the trains the learner using the training portion of the split. Once the model is built it is
    * evaluated on the testing portion of the split.
    *
    * @param       the model type parameter
    * @param       the evaluation type parameter
    * @param learner  the learner to use for training
    * @param supplier supplies an evaluation metric.
    * @return the result of evaluation
    */
   public > R evaluate(@NonNull Learner learner, @NonNull Supplier supplier) {
      R eval = supplier.get();
      forEach(tt -> eval.merge(tt.evaluate(learner, supplier)));
      return eval;
   }

   @Override
   public Spliterator> spliterator() {
      return splits.spliterator();
   }

   @Override
   public Iterator> iterator() {
      return splits.iterator();
   }

   /**
    * Preprocess each of the training splits using the supplier of {@link PreprocessorList}
    *
    * @param supplier the supplier to produce a {@link PreprocessorList}
    * @return this train test set
    */
   public TrainTestSet preprocess(@NonNull Supplier> supplier) {
      forEach((train, test) -> train.preprocess(supplier.get()));
      return this;
   }


}// END OF TrainTestSet