//  ObjectiveComparator.java
//
//  Author:
//       Antonio J. Nebro <antonio@lcc.uma.es>
//       Juan J. Durillo <durillo@lcc.uma.es>
//
//  Copyright (c) 2011 Antonio J. Nebro, Juan J. Durillo
//
//  This program 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.
//
//  This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

package jmetal.util.comparators;

import jmetal.core.Solution;

import java.util.Comparator;

/**
 * This class implements a <code>Comparator</code> (a method for comparing
 * <code>Solution</code> objects) based on a objective values.
 */
public class ObjectiveComparator implements Comparator {

  /**
   * Stores the index of the objective to compare
   */
  private int nObj;
  private boolean ascendingOrder_;

  /**
   * Constructor.
   *
   * @param nObj The index of the objective to compare
   */
  public ObjectiveComparator(int nObj) {
    this.nObj = nObj;
    ascendingOrder_ = true;
  } // ObjectiveComparator

  public ObjectiveComparator(int nObj, boolean descendingOrder) {
    this.nObj = nObj;
    if (descendingOrder)
      ascendingOrder_ = false;
    else
      ascendingOrder_ = true ;
  } // ObjectiveComparator

  /**
   * Compares two solutions.
   *
   * @param o1 Object representing the first <code>Solution</code>.
   * @param o2 Object representing the second <code>Solution</code>.
   * @return -1, or 0, or 1 if o1 is less than, equal, or greater than o2,
   *         respectively.
   */
  public int compare(Object o1, Object o2) {
    if (o1 == null)
      return 1;
    else if (o2 == null)
      return -1;

    double objetive1 = ((Solution) o1).getObjective(this.nObj);
    double objetive2 = ((Solution) o2).getObjective(this.nObj);
    if (ascendingOrder_) {
      if (objetive1 < objetive2) {
        return -1;
      } else if (objetive1 > objetive2) {
        return 1;
      } else {
        return 0;
      }
    } else {
      if (objetive1 < objetive2) {
        return 1;
      } else if (objetive1 > objetive2) {
        return -1;
      } else {
        return 0;
      }
    }
  } // compare
} // ObjectiveComparator
