/* Copyright 2009-2016 David Hadka
 *
 * This file is part of the MOEA Framework.
 *
 * The MOEA Framework is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * The MOEA Framework is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the MOEA Framework.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.moeaframework.algorithm;

import java.io.NotSerializableException;
import java.io.Serializable;

import org.moeaframework.core.EpsilonBoxDominanceArchive;
import org.moeaframework.core.EpsilonBoxEvolutionaryAlgorithm;
import org.moeaframework.core.Selection;
import org.moeaframework.core.Variation;

/**
 * Extends {@link AdaptiveTimeContinuation} to trigger restarts using
 * ε-progress.  ε-progress measures search progress by counting
 * the number of significant improvements, as measured by the number of
 * unoccupied ε-boxes filled during a fixed time window.  
 * <p>
 * References:
 * <ol>
 *   <li>Hadka, D. and Reed, P.  "Borg: An Auto-Adaptive Many-Objective
 *       Evolutionary Computing Framework."  Evolutionary Computation,
 *       21(2):231-259, 2013.
 * </ol>
 */
public class EpsilonProgressContinuation extends AdaptiveTimeContinuation {

	/**
	 * The number of ε-progress improvements since the last invocation 
	 * of {@code check}.
	 */
	private int improvementsAtLastCheck;

	/**
	 * Decorates the specified algorithm with ε-progress triggered time
	 * continuation.
	 * 
	 * @param algorithm the algorithm being decorated
	 * @param windowSize the number of iterations between invocations of
	 *        {@code check}
	 * @param maxWindowSize the maximum number of iterations allowed since the
	 *        last restart before forcing a restart
	 * @param populationRatio the population-to-archive ratio
	 * @param minimumPopulationSize the minimum size of the population
	 * @param maximumPopulationSize the maximum size of the population
	 * @param selection the selection operator for selecting solutions from the
	 *        archive during a restart
	 * @param variation the variation operator for mutating solutions selected
	 *        from the archive during a restart
	 */
	public EpsilonProgressContinuation(
			EpsilonBoxEvolutionaryAlgorithm algorithm, int windowSize,
			int maxWindowSize, double populationRatio,
			int minimumPopulationSize, int maximumPopulationSize,
			Selection selection, Variation variation) {
		super(algorithm, windowSize, maxWindowSize, populationRatio,
				minimumPopulationSize, maximumPopulationSize, selection,
				variation);
	}

	@Override
	public EpsilonBoxDominanceArchive getArchive() {
		return (EpsilonBoxDominanceArchive)super.getArchive();
	}

	@Override
	protected RestartType check() {
		RestartType superType = super.check();

		if (superType.equals(RestartType.NONE)) {
			if (getArchive().getNumberOfImprovements() <= 
					improvementsAtLastCheck) {
				superType = RestartType.HARD;
			}
		}

		improvementsAtLastCheck = getArchive().getNumberOfImprovements();

		return superType;
	}

	@Override
	protected void restart(RestartType type) {
		super.restart(type);

		improvementsAtLastCheck = getArchive().getNumberOfImprovements();
	}
	
	/**
	 * Proxy for serializing and deserializing the state of an
	 * {@code EpsilonProgressContinuation} instance. This proxy supports saving
	 * the underlying algorithm state and {@code improvementsAtLastCheck}.
	 */
	private static class EpsilonProgressContinuationState implements
	Serializable {

		private static final long serialVersionUID = -4773227519517581809L;

		/**
		 * The state of the underlying algorithm.
		 */
		private final Serializable algorithmState;
		
		/**
		 * The {@code improvementsAtLastCheck} value of the
		 * {@code EpsilonProgressContinuation} instance.
		 */
		private final int improvementsAtLastCheck;

		/**
		 * Constructs a proxy for storing the state of an
		 * {@code EpsilonProgressContinuation} instance.
		 * 
		 * @param algorithmState the state of the underlying algorithm
		 * @param improvementsAtLastCheck the {@code improvementsAtLastCheck}
		 *        value of the {@code EpsilonProgressContinuation} instance
		 */
		public EpsilonProgressContinuationState(Serializable algorithmState,
				int improvementsAtLastCheck) {
			super();
			this.algorithmState = algorithmState;
			this.improvementsAtLastCheck = improvementsAtLastCheck;
		}

		/**
		 * Returns the underlying algorithm state.
		 * 
		 * @return the underlying algorithm state
		 */
		public Serializable getAlgorithmState() {
			return algorithmState;
		}

		/**
		 * Returns the {@code improvementsAtLastCheck} value of the
		 * {@code EpsilonProgressContinuation} instance.
		 * 
		 * @return the {@code improvementsAtLastCheck} value of the
		 *         {@code EpsilonProgressContinuation} instance
		 */
		public int getImprovementsAtLastCheck() {
			return improvementsAtLastCheck;
		}
		
	}

	@Override
	public Serializable getState() throws NotSerializableException {
		return new EpsilonProgressContinuationState(super.getState(),
				improvementsAtLastCheck);
	}

	@Override
	public void setState(Object objState) throws NotSerializableException {
		EpsilonProgressContinuationState state =
				(EpsilonProgressContinuationState)objState;
		
		super.setState(state.getAlgorithmState());
		improvementsAtLastCheck = state.getImprovementsAtLastCheck();
	}

}