/*******************************************************************************
    * SAT4J: a SATisfiability library for Java Copyright (C) 2004, 2012 Artois University and CNRS
    *
    * All rights reserved. This program and the accompanying materials
    * are made available under the terms of the Eclipse Public License v1.0
    * which accompanies this distribution, and is available at
    *  http://www.eclipse.org/legal/epl-v10.html
    *
    * Alternatively, the contents of this file may be used under the terms of
   * either the GNU Lesser General Public License Version 2.1 or later (the
   * "LGPL"), in which case the provisions of the LGPL are applicable instead
   * of those above. If you wish to allow use of your version of this file only
   * under the terms of the LGPL, and not to allow others to use your version of
   * this file under the terms of the EPL, indicate your decision by deleting
   * the provisions above and replace them with the notice and other provisions
   * required by the LGPL. If you do not delete the provisions above, a recipient
   * may use your version of this file under the terms of the EPL or the LGPL.
   *
   * Based on the original MiniSat specification from:
   *
   * An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
   * Sixth International Conference on Theory and Applications of Satisfiability
   * Testing, LNCS 2919, pp 502-518, 2003.
   *
   * See www.minisat.se for the original solver in C++.
   *
   * Contributors:
   *   CRIL - initial API and implementation
   *******************************************************************************/
  package org.sat4j.pb;
  
  import java.io.Serializable;
  import java.math.BigInteger;
  
  import org.sat4j.core.ReadOnlyVec;
  import org.sat4j.core.ReadOnlyVecInt;
  import org.sat4j.specs.ISolver;
  import org.sat4j.specs.IVec;
  import org.sat4j.specs.IVecInt;
  
  /**
   * Abstraction for an Objective Function for Pseudo Boolean Optimization.
   * 
   * May be generalized in the future to deal with other optimization functions.
   * 
   * @author leberre
   * 
   */
  public class ObjectiveFunction implements Serializable {
  
      /**
       * 
       */
      private static final long serialVersionUID = 1L;
  
      // contains the coeffs of the objective function for each variable
      private final IVec<BigInteger> coeffs;
  
      private final IVecInt vars;
  
      private BigInteger correction = BigInteger.ZERO;
  
      public ObjectiveFunction(IVecInt vars, IVec<BigInteger> coeffs) {
          this.vars = new ReadOnlyVecInt(vars);
          this.coeffs = new ReadOnlyVec<BigInteger>(coeffs);
      }
  
      // calculate the degree of the objective function
      public BigInteger calculateDegree(ISolver solver) {
          BigInteger tempDegree = BigInteger.ZERO;
          for (int i = 0; i < this.vars.size(); i++) {
              BigInteger coeff = this.coeffs.get(i);
              if (varInModel(this.vars.get(i), solver)) {
                  tempDegree = tempDegree.add(coeff);
              } else if (coeff.signum() < 0
                      && !varInModel(-this.vars.get(i), solver)) {
                  // the variable does not appear in the model: it can be assigned
                  // either way
                  tempDegree = tempDegree.add(coeff);
              }
          }
          return tempDegree;
      }
  
      // calculate the degree of the objective function
      public BigInteger calculateDegreeImplicant(ISolver solver) {
          BigInteger tempDegree = BigInteger.ZERO;
          solver.primeImplicant();
          for (int i = 0; i < this.vars.size(); i++) {
              BigInteger coeff = this.coeffs.get(i);
              if (solver.primeImplicant(this.vars.get(i))) {
                  tempDegree = tempDegree.add(coeff);
              } else if (coeff.signum() < 0
                      && !solver.primeImplicant(-this.vars.get(i))) {
                  // the variable does not appear in the model: it can be assigned
                  // either way
                  tempDegree = tempDegree.add(coeff);
              }
          }
         return tempDegree;
     }
 
     private boolean varInModel(int var, ISolver solver) {
         if (var > 0) {
             return solver.model(var);
         }
         return !solver.model(-var);
     }
 
     public IVec<BigInteger> getCoeffs() {
         return this.coeffs;
     }
 
     public IVecInt getVars() {
         return this.vars;
     }
 
     public void setCorrection(BigInteger correction) {
         this.correction = correction;
     }
 
     public BigInteger getCorrection() {
         return this.correction;
     }
 
     @Override
     public String toString() {
         StringBuffer stb = new StringBuffer();
         IVecInt lits = getVars();
         IVec<BigInteger> coefs = getCoeffs();
         BigInteger coef;
         int lit;
         for (int i = 0; i < lits.size(); i++) {
             coef = coefs.get(i);
             lit = lits.get(i);
             if (lit < 0) {
                 lit = -lit;
                 coef = coef.negate();
             }
             stb.append((coef.signum() < 0 ? "" : "+") + coef + " x" + lit + " ");
         }
         return stb.toString();
     }
 
     public BigInteger minValue() {
         BigInteger tempDegree = BigInteger.ZERO;
         for (int i = 0; i < this.vars.size(); i++) {
             BigInteger coeff = this.coeffs.get(i);
             if (coeff.signum() < 0) {
                 tempDegree = tempDegree.add(coeff);
             }
         }
         return tempDegree;
     }
 
     public BigInteger calculateDegree(int[] model) {
         BigInteger tempDegree = BigInteger.ZERO;
 
         for (int i = 0; i < this.vars.size(); i++) {
             BigInteger coeff = this.coeffs.get(i);
             if (varInModel(this.vars.get(i), model)) {
                 tempDegree = tempDegree.add(coeff);
             } else if (coeff.signum() < 0
                     && !varInModel(-this.vars.get(i), model)) {
                 tempDegree = tempDegree.add(coeff);
             }
         }
         return tempDegree;
     }
 
     private boolean varInModel(int var, int[] model) {
         for (int element : model) {
             if (var == element) {
                 return true;
             }
         }
         return false;
     }
 
 }