/*******************************************************************************
    * 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 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;
  
  /**
   * Lazy data structure for clause using Watched Literals.
   * 
   * @author leberre
   */
  public abstract class WLClause implements Constr, Serializable {
  
  	private static final long serialVersionUID = 1L;
  
  	/**
  	 * @since 2.1
  	 */
  	protected double activity;
  
  	protected final int[] lits;
  
  	protected final ILits voc;
  
  	/**
  	 * 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 WLClause(IVecInt ps, ILits voc) {
  		lits = new int[ps.size()];
  		ps.moveTo(lits);
  		assert ps.size() == 0;
  		this.voc = voc;
  		activity = 0;
  	}
  
  	/*
  	 * (non-Javadoc)
  	 * 
  	 * @see Constr#calcReason(Solver, Lit, Vec)
  	 */
  	public void calcReason(int p, IVecInt outReason) {
  		// assert outReason.size() == 0
  		// && ((p == ILits.UNDEFINED) || (p == lits[0]));
  		final int[] mylits = lits;
  		for (int i = (p == ILits.UNDEFINED) ? 0 : 1; i < mylits.length; i++) {
  			assert voc.isFalsified(mylits[i]);
  			outReason.push(mylits[i] ^ 1);
  		}
  	}
  
  	/**
  	 * @since 2.1
  	 */
  	public void remove(UnitPropagationListener upl) {
  		voc.watches(lits[0] ^ 1).remove(this);
  		voc.watches(lits[1] ^ 1).remove(this);
  		// la clause peut etre effacee
  	}
  
  	/*
  	 * (non-Javadoc)
  	 * 
  	 * @see Constr#simplify(Solver)
  	 */
 	public boolean simplify() {
 		for (int i = 0; i < lits.length; i++) {
 			if (voc.isSatisfied(lits[i])) {
 				return true;
 			}
 		}
 		return false;
 	}
 
 	public boolean propagate(UnitPropagationListener s, int p) {
 		final int[] mylits = lits;
 		// Lits[1] must contain a falsified literal
 		if (mylits[0] == (p ^ 1)) {
 			mylits[0] = mylits[1];
 			mylits[1] = p ^ 1;
 		}
 		// assert mylits[1] == (p ^ 1);
 		int previous = p ^ 1, tmp;
 		// look for new literal to watch: applying move to front strategy
 		for (int i = 2; i < mylits.length; i++) {
 			if (!voc.isFalsified(mylits[i])) {
 				mylits[1] = mylits[i];
 				mylits[i] = previous;
 				voc.watch(mylits[1] ^ 1, this);
 				return true;
 			} else {
 				tmp = previous;
 				previous = mylits[i];
 				mylits[i] = tmp;
 			}
 		}
 		// assert voc.isFalsified(mylits[1]);
 		// the clause is now either unit or null
 		// move back the literals to their initial position
 		for (int i = 2; i < mylits.length; i++) {
 			mylits[i - 1] = mylits[i];
 		}
 		mylits[mylits.length - 1] = previous;
 		voc.watch(p, this);
 		// propagates first watched literal
 		return s.enqueue(mylits[0], this);
 	}
 
 	/*
 	 * For learnt clauses only @author leberre
 	 */
 	public boolean locked() {
 		return voc.getReason(lits[0]) == this;
 	}
 
 	/**
 	 * @return the activity of the clause
 	 */
 	public double getActivity() {
 		return activity;
 	}
 
 	@Override
 	public String toString() {
 		StringBuffer stb = new StringBuffer();
 		for (int i = 0; i < lits.length; i++) {
 			stb.append(Lits.toString(lits[i]));
 			stb.append("["); //$NON-NLS-1$
 			stb.append(voc.valueToString(lits[i]));
 			stb.append("]"); //$NON-NLS-1$
 			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) {
 		return lits[i];
 	}
 
 	/**
 	 * @param d
 	 */
 	public void rescaleBy(double d) {
 		activity *= d;
 	}
 
 	public int size() {
 		return lits.length;
 	}
 
 	public void assertConstraint(UnitPropagationListener s) {
 		boolean ret = s.enqueue(lits[0], this);
 		assert ret;
 	}
 
 	public ILits getVocabulary() {
 		return voc;
 	}
 
 	public int[] getLits() {
 		int[] tmp = new int[size()];
 		System.arraycopy(lits, 0, tmp, 0, size());
 		return tmp;
 	}
 
 	@Override
 	public boolean equals(Object obj) {
 		if (obj == null)
 			return false;
 		try {
 			WLClause wcl = (WLClause) obj;
 			if (lits.length != wcl.lits.length)
 				return false;
 			boolean ok;
 			for (int lit : lits) {
 				ok = false;
 				for (int lit2 : wcl.lits)
 					if (lit == lit2) {
 						ok = true;
 						break;
 					}
 				if (!ok)
 					return false;
 			}
 			return true;
 		} catch (ClassCastException e) {
 			return false;
 		}
 	}
 
 	@Override
 	public int hashCode() {
 		long sum = 0;
 		for (int p : lits) {
 			sum += p;
 		}
 		return (int) sum / lits.length;
 	}
 
 }