/*******************************************************************************
    * 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 java.io.PrintWriter;
  import java.util.LinkedList;
  
  import org.sat4j.minisat.core.ILits;
  import org.sat4j.minisat.core.IOrder;
  import org.sat4j.minisat.core.IPhaseSelectionStrategy;
  
  /**
   * Uses a tabu list to prevent the solver to
   * 
   * @since 2.3.2
   */
  public class TabuListDecorator implements IOrder {
  
      private final VarOrderHeap decorated;
  
      private final int tabuSize;
  
      private ILits voc;
      private int lastVar = -1;
  
      private final LinkedList<Integer> tabuList = new LinkedList<Integer>();
  
      public TabuListDecorator(VarOrderHeap order) {
          this(order, 10);
      }
  
      public TabuListDecorator(VarOrderHeap order, int tabuSize) {
          this.decorated = order;
          this.tabuSize = tabuSize;
      }
  
      public void assignLiteral(int q) {
          this.decorated.assignLiteral(q);
      }
  
      public IPhaseSelectionStrategy getPhaseSelectionStrategy() {
          return this.decorated.getPhaseSelectionStrategy();
      }
  
      public void init() {
          this.decorated.init();
          this.lastVar = -1;
      }
  
      public void printStat(PrintWriter out, String prefix) {
          out.println(prefix + "tabu list size\t: " + this.tabuSize);
          this.decorated.printStat(out, prefix);
      }
  
      public int select() {
          int lit = this.decorated.select();
          if (lit == ILits.UNDEFINED) {
              int var;
              do {
                  if (this.tabuList.isEmpty()) {
                      return ILits.UNDEFINED;
                  }
                  var = this.tabuList.removeFirst();
              } while (!this.voc.isUnassigned(var << 1));
              return getPhaseSelectionStrategy().select(var);
          }
          this.lastVar = lit >> 1;
          return lit;
      }
  
      public void setLits(ILits lits) {
          this.decorated.setLits(lits);
         this.voc = lits;
     }
 
     public void setPhaseSelectionStrategy(IPhaseSelectionStrategy strategy) {
         this.decorated.setPhaseSelectionStrategy(strategy);
     }
 
     public void setVarDecay(double d) {
         this.decorated.setVarDecay(d);
     }
 
     public void undo(int x) {
         if (this.tabuList.size() == this.tabuSize) {
             int var = this.tabuList.removeFirst();
             this.decorated.undo(var);
         }
         if (x == this.lastVar) {
             this.tabuList.add(x);
             this.lastVar = -1;
         } else {
             this.decorated.undo(x);
         }
     }
 
     public void updateVar(int q) {
         this.decorated.updateVar(q);
     }
 
     public double varActivity(int q) {
         return this.decorated.varActivity(q);
     }
 
     public void varDecayActivity() {
         this.decorated.varDecayActivity();
     }
 
     public void updateVarAtDecisionLevel(int q) {
         this.decorated.updateVarAtDecisionLevel(q);
     }
 
     @Override
     public String toString() {
         return this.decorated.toString() + " with tabu list of size "
                 + this.tabuSize;
     }
 
     public double[] getVariableHeuristics() {
         return this.decorated.getVariableHeuristics();
     }
 
 }