/*******************************************************************************
   * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
   *
   * 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++.
  * 
  *******************************************************************************/
  package org.sat4j.minisat.orders;
  
  import static org.sat4j.core.LiteralsUtils.var;
  
  import java.io.PrintWriter;
  import java.io.Serializable;
  
  import org.sat4j.minisat.core.Heap;
  import org.sat4j.minisat.core.ILits;
  import org.sat4j.minisat.core.IOrder;
  import org.sat4j.minisat.core.IPhaseSelectionStrategy;
  
  /*
   * Created on 16 oct. 2003
   */
  
  /**
   * @author leberre Heuristique du prouveur. Changement par rapport au MiniSAT
   *         original : la gestion activity est faite ici et non plus dans Solver.
   */
  public class VarOrderHeap implements IOrder, Serializable {
  
      private static final long serialVersionUID = 1L;
  
      private static final double VAR_RESCALE_FACTOR = 1e-100;
  
      private static final double VAR_RESCALE_BOUND = 1 / VAR_RESCALE_FACTOR;
  
      /**
       * mesure heuristique de l'activite d'une variable.
       */
      protected double[] activity = new double[1];
  
      private double varDecay = 1.0;
  
      /**
       * increment pour l'activite des variables.
       */
      private double varInc = 1.0;
  
      protected ILits lits;
  
      private long nullchoice = 0;
  
      protected Heap heap;
  
      protected IPhaseSelectionStrategy phaseStrategy;
      
      public VarOrderHeap() {
          this(new PhaseInLastLearnedClauseSelectionStrategy());
      }
      
      public VarOrderHeap(IPhaseSelectionStrategy strategy) {
          this.phaseStrategy = strategy;
      }
      
      /**
       * Change the selection strategy.
       * 
       * @param strategy
       */
      public void setPhaseSelectionStrategy(IPhaseSelectionStrategy strategy) {
          phaseStrategy = strategy;
      }
      
      public IPhaseSelectionStrategy getPhaseSelectionStrategy() {
          return phaseStrategy;
      }
      
      public void setLits(ILits lits) {
          this.lits = lits;
      }
 
     /**
      * Selectionne une nouvelle variable, non affectee, ayant l'activite
      * la plus elevee.
      * 
      * @return Lit.UNDEFINED si aucune variable n'est trouvee
      */
     public int select() {
         while (!heap.empty()) {
             int var = heap.getmin();
             int next = phaseStrategy.select(var);
             if (lits.isUnassigned(next)) {
                 if (activity[var] < 0.0001) {
                     nullchoice++;
                 }
                 return next;
             }
         }
         return ILits.UNDEFINED;
     }
 
     /**
      * Change la valeur de varDecay.
      * 
      * @param d
      *            la nouvelle valeur de varDecay
      */
     public void setVarDecay(double d) {
         varDecay = d;
     }
 
     /**
      * Methode appelee quand la variable x est desaffectee.
      * 
      * @param x
      */
     public void undo(int x) {
         if (!heap.inHeap(x))
             heap.insert(x);
     }
 
     /**
      * Appelee lorsque l'activite de la variable x a change.
      * 
      * @param p
      *            a literal
      */
     public void updateVar(int p) {
         int var = var(p);
         updateActivity(var);
         phaseStrategy.updateVar(p);
         if (heap.inHeap(var))
             heap.increase(var);
     }
 
     protected void updateActivity(final int var) {
         if ((activity[var] += varInc) > VAR_RESCALE_BOUND) {
             varRescaleActivity();
         }
     }
 
     /**
      * 
      */
     public void varDecayActivity() {
         varInc *= varDecay;
     }
 
     /**
      * 
      */
     private void varRescaleActivity() {
         for (int i = 1; i < activity.length; i++) {
             activity[i] *= VAR_RESCALE_FACTOR;
         }
         varInc *= VAR_RESCALE_FACTOR;
     }
 
     public double varActivity(int p) {
         return activity[var(p)];
     }
 
     /**
      * 
      */
     public int numberOfInterestingVariables() {
         int cpt = 0;
         for (int i = 1; i < activity.length; i++) {
             if (activity[i] > 1.0) {
                 cpt++;
             }
         }
         return cpt;
     }
 
     /**
      * that method has the responsability to initialize all arrays in the
      * heuristics. PLEASE CALL super.init() IF YOU OVERRIDE THAT METHOD.
      */
     public void init() {
         int nlength = lits.nVars() + 1;
         activity = new double[nlength];
         phaseStrategy.init(nlength);
         activity[0] = -1;
         heap = new Heap(activity);
         heap.setBounds(nlength);
         for (int i = 1; i < nlength; i++) {
             assert i > 0;
             assert i <= lits.nVars() : "" + lits.nVars() + "/" + i; //$NON-NLS-1$ //$NON-NLS-2$
             activity[i] = 0.0;
             if (lits.belongsToPool(i)) {
                 heap.insert(i);
             }
         }
     }
 
     @Override
     public String toString() {
         return "VSIDS like heuristics from MiniSAT using a heap "+phaseStrategy; //$NON-NLS-1$
     }
 
     public ILits getVocabulary() {
         return lits;
     }
 
     public void printStat(PrintWriter out, String prefix) {
         out.println(prefix + "non guided choices\t" + nullchoice); //$NON-NLS-1$
     }
 
     public void assignLiteral(int p) {
         // do nothing       
     }
 }