/*******************************************************************************
    * 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;
 		if (activity == null || activity.length < nlength) {
 			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
 	}
 
 	public void updateVarAtDecisionLevel(int q) {
 		phaseStrategy.updateVarAtDecisionLevel(q);
 
 	}
 }