/*******************************************************************************
    * 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.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.UnitPropagationListener;
  import org.sat4j.specs.IVecInt;
  
  /**
   * Data structure for binary clause.
   * 
   * @author leberre
   * @since 2.1
   */
  public abstract class BinaryClause implements 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;
  		head = ps.get(0);
  		tail = ps.get(1);
  		this.voc = voc;
  		activity = 0;
  	}
  
  	/*
  	 * (non-Javadoc)
  	 * 
  	 * @see Constr#calcReason(Solver, Lit, Vec)
  	 */
  	public void calcReason(int p, IVecInt outReason) {
  		if (voc.isFalsified(head)) {
  			outReason.push(neg(head));
  		}
  		if (voc.isFalsified(tail)) {
  			outReason.push(neg(tail));
  		}
  	}
  
  	/*
  	 * (non-Javadoc)
  	 * 
  	 * @see Constr#remove(Solver)
  	 */
  	public void remove(UnitPropagationListener upl) {
  		voc.watches(neg(head)).remove(this);
  		voc.watches(neg(tail)).remove(this);
  	}
  
  	/*
  	 * (non-Javadoc)
  	 * 
 	 * @see Constr#simplify(Solver)
 	 */
 	public boolean simplify() {
 		if (voc.isSatisfied(head) || voc.isSatisfied(tail)) {
 			return true;
 		}
 		return false;
 	}
 
 	public boolean propagate(UnitPropagationListener s, int p) {
 		voc.watch(p, this);
 		if (head == neg(p)) {
 			return s.enqueue(tail, this);
 		}
 		assert tail == neg(p);
 		return s.enqueue(head, this);
 	}
 
 	/*
 	 * For learnt clauses only @author leberre
 	 */
 	public boolean locked() {
 		return voc.getReason(head) == this || voc.getReason(tail) == this;
 	}
 
 	/**
 	 * @return the activity of the clause
 	 */
 	public double getActivity() {
 		return activity;
 	}
 
 	@Override
 	public String toString() {
 		StringBuffer stb = new StringBuffer();
 		stb.append(Lits.toString(head));
 		stb.append("["); //$NON-NLS-1$
 		stb.append(voc.valueToString(head));
 		stb.append("]"); //$NON-NLS-1$
 		stb.append(" "); //$NON-NLS-1$
 		stb.append(Lits.toString(tail));
 		stb.append("["); //$NON-NLS-1$
 		stb.append(voc.valueToString(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 head;
 		assert i == 1;
 		return tail;
 	}
 
 	/**
 	 * @param d
 	 */
 	public void rescaleBy(double d) {
 		activity *= d;
 	}
 
 	public int size() {
 		return 2;
 	}
 
 	public void assertConstraint(UnitPropagationListener s) {
 		assert voc.isUnassigned(head);
 		boolean ret = s.enqueue(head, this);
 		assert ret;
 	}
 
 	public ILits getVocabulary() {
 		return voc;
 	}
 
 	public int[] getLits() {
 		int[] tmp = new int[2];
 		tmp[0] = head;
 		tmp[1] = tail;
 		return tmp;
 	}
 
 	@Override
 	public boolean equals(Object obj) {
 		if (obj == null)
 			return false;
 		try {
 			BinaryClause wcl = (BinaryClause) obj;
 			if (wcl.head != head || wcl.tail != tail) {
 				return false;
 			}
 			return true;
 		} catch (ClassCastException e) {
 			return false;
 		}
 	}
 
 	@Override
 	public int hashCode() {
 		long sum = head + tail;
 		return (int) sum / 2;
 	}
 
 	public void register() {
 		voc.watch(neg(head), this);
 		voc.watch(neg(tail), this);
 	}
 
 	public boolean canBePropagatedMultipleTimes() {
 		return false;
 	}
 
 }