/*******************************************************************************
    * 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.constraints.cnf;
  
  import static org.sat4j.core.LiteralsUtils.neg;
  
  import java.io.Serializable;
  
  import org.sat4j.minisat.core.Constr;
  import org.sat4j.minisat.core.ILits;
  import org.sat4j.minisat.core.Propagatable;
  import org.sat4j.minisat.core.UnitPropagationListener;
  import org.sat4j.specs.IVecInt;
  
  /**
   * Data structure for binary clause.
   * 
   * @author leberre
   * @since 2.1
   */
  public abstract class BinaryClause implements Propagatable, Constr,
          Serializable {
  
      private static final long serialVersionUID = 1L;
  
      protected double activity;
  
      private final ILits voc;
  
      protected int head;
  
      protected int tail;
  
      /**
       * Creates a new basic clause
       * 
       * @param voc
       *            the vocabulary of the formula
       * @param ps
       *            A VecInt that WILL BE EMPTY after calling that method.
       */
      public BinaryClause(IVecInt ps, ILits voc) {
          assert ps.size() == 2;
          this.head = ps.get(0);
          this.tail = ps.get(1);
          this.voc = voc;
          this.activity = 0;
      }
  
      /*
       * (non-Javadoc)
       * 
       * @see Constr#calcReason(Solver, Lit, Vec)
       */
      public void calcReason(int p, IVecInt outReason) {
          if (this.voc.isFalsified(this.head)) {
              outReason.push(neg(this.head));
          }
          if (this.voc.isFalsified(this.tail)) {
              outReason.push(neg(this.tail));
          }
      }
  
      /*
       * (non-Javadoc)
       * 
       * @see Constr#remove(Solver)
       */
      public void remove(UnitPropagationListener upl) {
          this.voc.watches(neg(this.head)).remove(this);
          this.voc.watches(neg(this.tail)).remove(this);
      }
 
     /*
      * (non-Javadoc)
      * 
      * @see Constr#simplify(Solver)
      */
     public boolean simplify() {
         if (this.voc.isSatisfied(this.head) || this.voc.isSatisfied(this.tail)) {
             return true;
         }
         return false;
     }
 
     public boolean propagate(UnitPropagationListener s, int p) {
         this.voc.watch(p, this);
         if (this.head == neg(p)) {
             return s.enqueue(this.tail, this);
         }
         assert this.tail == neg(p);
         return s.enqueue(this.head, this);
     }
 
     /*
      * For learnt clauses only @author leberre
      */
     public boolean locked() {
         return this.voc.getReason(this.head) == this
                 || this.voc.getReason(this.tail) == this;
     }
 
     /**
      * @return the activity of the clause
      */
     public double getActivity() {
         return this.activity;
     }
 
     @Override
     public String toString() {
         StringBuffer stb = new StringBuffer();
         stb.append(Lits.toString(this.head));
         stb.append("["); //$NON-NLS-1$
         stb.append(this.voc.valueToString(this.head));
         stb.append("]"); //$NON-NLS-1$
         stb.append(" "); //$NON-NLS-1$
         stb.append(Lits.toString(this.tail));
         stb.append("["); //$NON-NLS-1$
         stb.append(this.voc.valueToString(this.tail));
         stb.append("]"); //$NON-NLS-1$
         return stb.toString();
     }
 
     /**
      * Retourne le ieme literal de la clause. Attention, cet ordre change durant
      * la recherche.
      * 
      * @param i
      *            the index of the literal
      * @return the literal
      */
     public int get(int i) {
         if (i == 0) {
             return this.head;
         }
         assert i == 1;
         return this.tail;
     }
 
     /**
      * @param d
      */
     public void rescaleBy(double d) {
         this.activity *= d;
     }
 
     public int size() {
         return 2;
     }
 
     public void assertConstraint(UnitPropagationListener s) {
         assert this.voc.isUnassigned(this.head);
         boolean ret = s.enqueue(this.head, this);
         assert ret;
     }
 
     public ILits getVocabulary() {
         return this.voc;
     }
 
     public int[] getLits() {
         int[] tmp = new int[2];
         tmp[0] = this.head;
         tmp[1] = this.tail;
         return tmp;
     }
 
     @Override
     public boolean equals(Object obj) {
         if (obj == null) {
             return false;
         }
         try {
             BinaryClause wcl = (BinaryClause) obj;
             if (wcl.head != this.head || wcl.tail != this.tail) {
                 return false;
             }
             return true;
         } catch (ClassCastException e) {
             return false;
         }
     }
 
     @Override
     public int hashCode() {
         long sum = this.head + this.tail;
         return (int) sum / 2;
     }
 
     public void register() {
         this.voc.watch(neg(this.head), this);
         this.voc.watch(neg(this.tail), this);
     }
 
     public boolean canBePropagatedMultipleTimes() {
         return false;
     }
 
     public Constr toConstraint() {
         return this;
     }
 }