/*******************************************************************************
    * 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.tools.xplain;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.List;
  
  import org.sat4j.core.VecInt;
  import org.sat4j.specs.ContradictionException;
  import org.sat4j.specs.IConstr;
  import org.sat4j.specs.ISolver;
  import org.sat4j.specs.IVecInt;
  import org.sat4j.specs.IteratorInt;
  import org.sat4j.specs.TimeoutException;
  import org.sat4j.tools.FullClauseSelectorSolver;
  import org.sat4j.tools.SolverDecorator;
  
  /**
   * Explanation framework for SAT4J.
   * 
   * The explanation uses selector variables and assumptions.
   * 
   * It is based on a two steps method: 1) extraction of a set of assumptions
   * implying the inconsistency 2) minimization of that set.
   * 
   * @author daniel
   * 
   * @param <T>
   *            a subinterface to ISolver.
   * @since 2.1
   */
  public class Xplain<T extends ISolver> extends FullClauseSelectorSolver<T>
          implements Explainer {
  
      private IVecInt assump;
  
      private MinimizationStrategy xplainStrategy = new DeletionStrategy();
  
      public Xplain(T solver, boolean skipDuplicatedEntries) {
          super(solver, skipDuplicatedEntries);
      }
  
      public Xplain(T solver) {
          this(solver, true);
      }
  
      @Override
      public IConstr addExactly(IVecInt literals, int n)
              throws ContradictionException {
          throw new UnsupportedOperationException(
                  "Explanation requires Pseudo Boolean support. See XplainPB class instead.");
      }
  
      @Override
      public IConstr addAtLeast(IVecInt literals, int degree)
              throws ContradictionException {
          throw new UnsupportedOperationException(
                  "Explanation requires Pseudo Boolean support. See XplainPB class instead.");
      }
  
      @Override
      public IConstr addAtMost(IVecInt literals, int degree)
              throws ContradictionException {
          throw new UnsupportedOperationException(
                  "Explanation requires Pseudo Boolean support. See XplainPB class instead.");
      }
  
      /**
  	 * 
  	 */
     private static final long serialVersionUID = 1L;
 
     /**
      * @since 2.2.4
      * @return
      * @throws TimeoutException
      */
     private IVecInt explanationKeys() throws TimeoutException {
         assert !isSatisfiable(this.assump);
         ISolver solver = decorated();
         if (solver instanceof SolverDecorator<?>) {
             solver = ((SolverDecorator<? extends ISolver>) solver).decorated();
         }
         return this.xplainStrategy.explain(solver, getConstrs(), this.assump);
     }
 
     /**
      * Provide an explanation of the inconsistency in terms of a subset minimal
      * set of constraints, each constraint being referred to as its index
      * (order) in the solver: first constraint is numbered 1, the second 2, etc.
      * 
      * @return an array of indexes such that the set of indexed constraints is
      *         inconsistent.
      * @throws TimeoutException
      * @see {@link #explain()}
      */
     public int[] minimalExplanation() throws TimeoutException {
         IVecInt keys = explanationKeys();
         keys.sort();
         List<Integer> allKeys = new ArrayList<Integer>(getConstrs().keySet());
         Collections.sort(allKeys);
         int[] model = new int[keys.size()];
         int i = 0;
         for (IteratorInt it = keys.iterator(); it.hasNext();) {
             model[i++] = allKeys.indexOf(it.next()) + 1;
         }
         return model;
     }
 
     /**
      * Provide an explanation of the inconsistency in term of a subset minimal
      * set of constraints. Compared to {@link #minimalExplanation()}, the method
      * returns a reference to the constraint object, instead of an index.
      * 
      * @since 2.1
      * @return
      * @throws TimeoutException
      * @see {@link #minimalExplanation()}
      */
     public Collection<IConstr> explain() throws TimeoutException {
         IVecInt keys = explanationKeys();
         Collection<IConstr> explanation = new ArrayList<IConstr>(keys.size());
         for (IteratorInt it = keys.iterator(); it.hasNext();) {
             explanation.add(getConstrs().get(it.next()));
         }
         return explanation;
     }
 
     /**
      * @since 2.1
      */
     public void cancelExplanation() {
         this.xplainStrategy.cancelExplanationComputation();
     }
 
     @Override
     public int[] findModel() throws TimeoutException {
         this.assump = VecInt.EMPTY;
         return super.findModel();
     }
 
     @Override
     public int[] findModel(IVecInt assumps) throws TimeoutException {
         this.assump = assumps;
         return super.findModel(assumps);
     }
 
     @Override
     public boolean isSatisfiable() throws TimeoutException {
         this.assump = VecInt.EMPTY;
         return super.isSatisfiable();
     }
 
     @Override
     public boolean isSatisfiable(boolean global) throws TimeoutException {
         this.assump = VecInt.EMPTY;
         return super.isSatisfiable(global);
     }
 
     @Override
     public boolean isSatisfiable(IVecInt assumps) throws TimeoutException {
         this.assump = assumps;
         return super.isSatisfiable(assumps);
     }
 
     @Override
     public boolean isSatisfiable(IVecInt assumps, boolean global)
             throws TimeoutException {
         this.assump = assumps;
         return super.isSatisfiable(assumps, global);
     }
 
     @Override
     public String toString(String prefix) {
         System.out.println(prefix + "Explanation (MUS) enabled solver");
         System.out.println(prefix + this.xplainStrategy);
         return super.toString(prefix);
     }
 
     public void setMinimizationStrategy(MinimizationStrategy strategy) {
         this.xplainStrategy = strategy;
     }
 
     @Override
     public boolean removeConstr(IConstr c) {
         if (getLastConstr() == c) {
             getLastClause().clear();
             setLastConstr(null);
         }
         return super.removeConstr(c);
     }
 
     @Override
     public boolean removeSubsumedConstr(IConstr c) {
         if (getLastConstr() == c) {
             getLastClause().clear();
             setLastConstr(null);
         }
         return super.removeSubsumedConstr(c);
     }
 
 }