/*******************************************************************************
    * 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.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) {
          this.phaseStrategy = strategy;
      }
  
      public IPhaseSelectionStrategy getPhaseSelectionStrategy() {
          return this.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 (!this.heap.empty()) {
             int var = this.heap.getmin();
             int next = this.phaseStrategy.select(var);
             if (this.lits.isUnassigned(next)) {
                 if (this.activity[var] < 0.0001) {
                     this.nullchoice++;
                 }
                 return next;
             }
         }
         return ILits.UNDEFINED;
     }
 
     /**
      * Change la valeur de varDecay.
      * 
      * @param d
      *            la nouvelle valeur de varDecay
      */
     public void setVarDecay(double d) {
         this.varDecay = d;
     }
 
     /**
      * Methode appelee quand la variable x est desaffectee.
      * 
      * @param x
      */
     public void undo(int x) {
         if (!this.heap.inHeap(x)) {
             this.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);
         this.phaseStrategy.updateVar(p);
         if (this.heap.inHeap(var)) {
             this.heap.increase(var);
         }
     }
 
     protected void updateActivity(final int var) {
         if ((this.activity[var] += this.varInc) > VAR_RESCALE_BOUND) {
             varRescaleActivity();
         }
     }
 
     /**
      * 
      */
     public void varDecayActivity() {
         this.varInc *= this.varDecay;
     }
 
     /**
      * 
      */
     private void varRescaleActivity() {
         for (int i = 1; i < this.activity.length; i++) {
             this.activity[i] *= VAR_RESCALE_FACTOR;
         }
         this.varInc *= VAR_RESCALE_FACTOR;
     }
 
     public double varActivity(int p) {
         return this.activity[var(p)];
     }
 
     /**
      * 
      */
     public int numberOfInterestingVariables() {
         int cpt = 0;
         for (int i = 1; i < this.activity.length; i++) {
             if (this.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 = this.lits.nVars() + 1;
         if (this.activity == null || this.activity.length < nlength) {
             this.activity = new double[nlength];
         }
         this.phaseStrategy.init(nlength);
         this.activity[0] = -1;
         this.heap = new Heap(this.activity);
         this.heap.setBounds(nlength);
         for (int i = 1; i < nlength; i++) {
             assert i > 0;
             assert i <= this.lits.nVars() : "" + this.lits.nVars() + "/" + i; //$NON-NLS-1$ //$NON-NLS-2$
             this.activity[i] = 0.0;
             if (this.lits.belongsToPool(i)) {
                 this.heap.insert(i);
             }
         }
     }
 
     @Override
     public String toString() {
         return "VSIDS like heuristics from MiniSAT using a heap " + this.phaseStrategy; //$NON-NLS-1$
     }
 
     public ILits getVocabulary() {
         return this.lits;
     }
 
     public void printStat(PrintWriter out, String prefix) {
         out.println(prefix + "non guided choices\t" + this.nullchoice); //$NON-NLS-1$
     }
 
     public void assignLiteral(int p) {
         this.phaseStrategy.assignLiteral(p);
     }
 
     public void updateVarAtDecisionLevel(int q) {
         this.phaseStrategy.updateVarAtDecisionLevel(q);
 
     }
 
     public double[] getVariableHeuristics() {
         return this.activity;
     }
 }