package net.bmahe.genetics4j.core.selection;
   
   import java.util.List;
   import java.util.Objects;
   import java.util.random.RandomGenerator;
   
   import org.apache.commons.lang3.Validate;
   
   import net.bmahe.genetics4j.core.Genotype;
  import net.bmahe.genetics4j.core.Population;
  import net.bmahe.genetics4j.core.spec.AbstractEAConfiguration;
  import net.bmahe.genetics4j.core.spec.AbstractEAExecutionContext;
  import net.bmahe.genetics4j.core.spec.selection.RandomSelection;
  import net.bmahe.genetics4j.core.spec.selection.SelectionPolicy;
  
  public class RandomSelectionPolicyHandler<T extends Comparable<T>> implements SelectionPolicyHandler<T> {
  
  	private final RandomGenerator randomGenerator;
  
  	public RandomSelectionPolicyHandler(final RandomGenerator _randomGenerator) {
  		Objects.requireNonNull(_randomGenerator);
  
  		this.randomGenerator = _randomGenerator;
  	}
  
  	@Override
  	public boolean canHandle(final SelectionPolicy selectionPolicy) {
  		Objects.requireNonNull(selectionPolicy);
  		return selectionPolicy instanceof RandomSelection;
  	}
  
  	@Override
  	public Selector<T> resolve(final AbstractEAExecutionContext<T> eaExecutionContext,
  			final AbstractEAConfiguration<T> eaConfiguration,
  			final SelectionPolicyHandlerResolver<T> selectionPolicyHandlerResolver,
  			final SelectionPolicy selectionPolicy) {
  		Objects.requireNonNull(selectionPolicy);
  		Validate.isInstanceOf(RandomSelection.class, selectionPolicy);
  
  		return new Selector<>() {
  
  			@Override
  			public Population<T> select(final AbstractEAConfiguration<T> eaConfiguration, final long generation,
  					final int numIndividuals, final List<Genotype> population, final List<T> fitnessScore) {
  				Objects.requireNonNull(eaConfiguration);
  				Objects.requireNonNull(population);
  				Objects.requireNonNull(fitnessScore);
  				Validate.isTrue(generation >= 0);
  				Validate.isTrue(numIndividuals > 0);
  				Validate.isTrue(population.isEmpty() == false, "population cannot be empty");
  				Validate.isTrue(fitnessScore.isEmpty() == false, "fitnessScore cannot be empty");
  				Validate.isTrue(fitnessScore.size() == population.size());
  
  				final Population<T> selected = new Population<>();
  
  				for (int i = 0; i < numIndividuals; i++) {
  					final int selectedIndex = randomGenerator.nextInt(population.size());
  					selected.add(population.get(selectedIndex), fitnessScore.get(selectedIndex));
  				}
  				return selected;
  			}
  		};
  	}
  }