/*******************************************************************************
    * 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.tools.xplain;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.Map;
  
  import org.sat4j.core.VecInt;
  import org.sat4j.specs.ContradictionException;
  import org.sat4j.specs.IConstr;
  import org.sat4j.specs.IOptimizationProblem;
  import org.sat4j.specs.ISolver;
  import org.sat4j.specs.IVecInt;
  import org.sat4j.specs.IteratorInt;
  import org.sat4j.specs.TimeoutException;
  import org.sat4j.tools.SolverDecorator;
  
  /**
   * An implementation of the QuickXplain algorithm as explained by Ulrich Junker
   * in the following paper:
   * 
   * @inproceedings{ junker01:quickxplain:inp, author={Ulrich Junker},
   *                 title={QUICKXPLAIN: Conflict Detection for Arbitrary
   *                 Constraint Propagation Algorithms}, booktitle={IJCAI'01
   *                 Workshop on Modelling and Solving problems with constraints
   *                 (CONS-1)}, year={2001}, month={August}, address={Seattle, WA,
   *                 USA}, url={citeseer.ist.psu.edu/junker01quickxplain.html},
   *                 url={http://www.lirmm.fr/~bessiere/ws_ijcai01/junker.ps.gz} }
   * 
   *                 The algorithm has been adapted to work properly in a context
   *                 where we can afford to add a selector variable to each clause
   *                 to enable or disable each constraint.
   * 
   *                 Note that for the moment, QuickXplain does not work properly
   *                 in an optimization setting.
   * 
   * @author daniel
   * 
   * @param <T>
   *            a subinterface to ISolver.
   * @since 2.1
   */
  public class Xplain<T extends ISolver> extends SolverDecorator<T> {
  
  	protected Map<Integer, IConstr> constrs = new HashMap<Integer, IConstr>();
  
  	protected IVecInt assump;
  
  	private int lastCreatedVar;
  	private boolean pooledVarId = false;
  
  	private static final XplainStrategy xplainStrategy = new QuickXplainStrategy();
  
  	public Xplain(T solver) {
  		super(solver);
  	}
  
  	@Override
  	public IConstr addClause(IVecInt literals) throws ContradictionException {
  		int newvar = createNewVar(literals);
  		literals.push(newvar);
  		IConstr constr = super.addClause(literals);
  		if (constr == null) {
  			discardLastestVar();
  		} else {
  			constrs.put(newvar, constr);
  		}
  		return constr;
  	}
  
  	/**
  	 * 
 	 * @param literals
 	 * @return
 	 * @since 2.1
 	 */
 	protected int createNewVar(IVecInt literals) {
 		if (pooledVarId) {
 			pooledVarId = false;
 			return lastCreatedVar;
 		}
 		lastCreatedVar = nextFreeVarId(true);
 		return lastCreatedVar;
 	}
 
 	protected void discardLastestVar() {
 		pooledVarId = true;
 	}
 
 	@Override
 	public IConstr addAtLeast(IVecInt literals, int degree)
 			throws ContradictionException {
 		throw new UnsupportedOperationException();
 	}
 
 	@Override
 	public IConstr addAtMost(IVecInt literals, int degree)
 			throws ContradictionException {
 		throw new UnsupportedOperationException();
 	}
 
 	/**
 	 * 
 	 */
 	private static final long serialVersionUID = 1L;
 
 	/**
 	 * @since 2.1
 	 * @return
 	 * @throws TimeoutException
 	 */
 	public Collection<IConstr> explain() throws TimeoutException {
 		assert !isSatisfiable(assump);
 		ISolver solver = decorated();
 		if (solver instanceof IOptimizationProblem) {
 			solver = ((SolverDecorator<? extends ISolver>) solver).decorated();
 		}
 		IVecInt keys = xplainStrategy.explain(solver, constrs, assump);
 		Collection<IConstr> explanation = new ArrayList<IConstr>(keys.size());
 		for (IteratorInt it = keys.iterator(); it.hasNext();) {
 			explanation.add(constrs.get(it.next()));
 		}
 		return explanation;
 	}
 
 	/**
 	 * @since 2.1
 	 */
 	public void cancelExplanation() {
 		xplainStrategy.cancelExplanationComputation();
 	}
 
 	/**
 	 * 
 	 * @since 2.1
 	 */
 	public Collection<IConstr> getConstraints() {
 		return constrs.values();
 	}
 
 	@Override
 	public int[] findModel() throws TimeoutException {
 		assump = VecInt.EMPTY;
 		IVecInt extraVariables = new VecInt();
 		for (Integer p : constrs.keySet()) {
 			extraVariables.push(-p);
 		}
 		return super.findModel(extraVariables);
 	}
 
 	@Override
 	public int[] findModel(IVecInt assumps) throws TimeoutException {
 		assump = assumps;
 		IVecInt extraVariables = new VecInt();
 		assumps.copyTo(extraVariables);
 		for (Integer p : constrs.keySet()) {
 			extraVariables.push(-p);
 		}
 		return super.findModel(extraVariables);
 	}
 
 	@Override
 	public boolean isSatisfiable() throws TimeoutException {
 		assump = VecInt.EMPTY;
 		IVecInt extraVariables = new VecInt();
 		for (Integer p : constrs.keySet()) {
 			extraVariables.push(-p);
 		}
 		return super.isSatisfiable(extraVariables);
 	}
 
 	@Override
 	public boolean isSatisfiable(boolean global) throws TimeoutException {
 		assump = VecInt.EMPTY;
 		IVecInt extraVariables = new VecInt();
 		for (Integer p : constrs.keySet()) {
 			extraVariables.push(-p);
 		}
 		return super.isSatisfiable(extraVariables, global);
 	}
 
 	@Override
 	public boolean isSatisfiable(IVecInt assumps) throws TimeoutException {
 		assump = assumps;
 		IVecInt extraVariables = new VecInt();
 		assumps.copyTo(extraVariables);
 		for (Integer p : constrs.keySet()) {
 			extraVariables.push(-p);
 		}
 		return super.isSatisfiable(extraVariables);
 	}
 
 	@Override
 	public boolean isSatisfiable(IVecInt assumps, boolean global)
 			throws TimeoutException {
 		assump = assumps;
 		IVecInt extraVariables = new VecInt();
 		assumps.copyTo(extraVariables);
 		for (Integer p : constrs.keySet()) {
 			extraVariables.push(-p);
 		}
 		return super.isSatisfiable(extraVariables, global);
 	}
 
 	@Override
 	public int[] model() {
 		int[] fullmodel = super.model();
 		int[] model = new int[fullmodel.length - constrs.size()];
 		int j = 0;
 		for (int i = 0; i < fullmodel.length; i++) {
 			if (constrs.get(Math.abs(fullmodel[i])) == null) {
 				model[j++] = fullmodel[i];
 			}
 		}
 		return model;
 	}
 
 }