/*******************************************************************************
    * 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.io.PrintWriter;
  import java.util.Map;
  import java.util.Set;
  
  import org.sat4j.core.VecInt;
  import org.sat4j.specs.ISolver;
  import org.sat4j.specs.IVecInt;
  import org.sat4j.specs.IteratorInt;
  import org.sat4j.specs.TimeoutException;
  
  /**
   * An implementation of the deletion based minimization.
   * 
   * 
   * @since 2.1
   */
  public class DeletionStrategy implements MinimizationStrategy {
  
      /**
  	 * 
  	 */
      private static final long serialVersionUID = 1L;
  
      private boolean computationCanceled;
  
      public void cancelExplanationComputation() {
          this.computationCanceled = true;
      }
  
      public IVecInt explain(ISolver solver, Map<Integer, ?> constrs,
              IVecInt assumps) throws TimeoutException {
          this.computationCanceled = false;
          IVecInt encodingAssumptions = new VecInt(constrs.size()
                  + assumps.size());
          assumps.copyTo(encodingAssumptions);
          IVecInt firstExplanation = solver.unsatExplanation();
          IVecInt results = new VecInt(firstExplanation.size());
          if (firstExplanation.size() == 1) {
              results.push(-firstExplanation.get(0));
              return results;
          }
          if (solver.isVerbose()) {
              System.out.print(solver.getLogPrefix() + "initial unsat core ");
              firstExplanation.sort();
              for (IteratorInt it = firstExplanation.iterator(); it.hasNext();) {
                  System.out.print(constrs.get(-it.next()));
                  System.out.print(" ");
              }
              System.out.println();
              solver.printStat(new PrintWriter(System.out, true), "c ");
          }
          for (int i = 0; i < firstExplanation.size();) {
              if (assumps.contains(firstExplanation.get(i))) {
                  firstExplanation.delete(i);
              } else {
                  i++;
              }
          }
          Set<Integer> constraintsVariables = constrs.keySet();
          IVecInt remainingVariables = new VecInt(constraintsVariables.size());
          for (Integer v : constraintsVariables) {
              remainingVariables.push(v);
          }
          int p;
          for (IteratorInt it = firstExplanation.iterator(); it.hasNext();) {
              p = it.next();
              if (p < 0) {
                  p = -p;
             }
             remainingVariables.remove(p);
         }
 
         remainingVariables.copyTo(encodingAssumptions);
         int unsatcorebegin = encodingAssumptions.size();
         firstExplanation.copyTo(encodingAssumptions);
         assert !solver.isSatisfiable(encodingAssumptions);
         int unsatcorelimit = encodingAssumptions.size() - 1;
         for (int i = unsatcorebegin; i < unsatcorelimit; i++) {
             if (this.computationCanceled) {
                 throw new TimeoutException();
             }
             encodingAssumptions.set(i, -encodingAssumptions.get(i));
             if (solver.isVerbose()) {
                 System.out.println(solver.getLogPrefix() + "checking "
                         + constrs.get(encodingAssumptions.get(i)) + " ...");
             }
             if (solver.isSatisfiable(encodingAssumptions)) {
                 encodingAssumptions.set(i, -encodingAssumptions.get(i));
                 results.push(-encodingAssumptions.get(i));
                 if (solver.isVerbose()) {
                     System.out.println(solver.getLogPrefix() + "mandatory.");
                 }
             } else {
                 if (solver.isVerbose()) {
                     System.out.println(solver.getLogPrefix() + "not needed.");
                 }
             }
         }
         if (results.size() == 0) {
             // the last group must be the cause of the inconsistency
             results.push(-encodingAssumptions.get(unsatcorelimit));
             if (solver.isVerbose()) {
                 System.out.println(solver.getLogPrefix()
                         + "skipping last test,the remaining element "
                         + constrs.get(encodingAssumptions.get(unsatcorelimit))
                         + " is causing the inconsistency!");
             }
         } else {
             encodingAssumptions.set(unsatcorelimit,
                     -encodingAssumptions.get(unsatcorelimit));
             if (solver.isVerbose()) {
                 System.out.println(solver.getLogPrefix() + "checking "
                         + constrs.get(encodingAssumptions.get(unsatcorelimit))
                         + " ...");
             }
             if (solver.isSatisfiable(encodingAssumptions)) {
                 encodingAssumptions.set(unsatcorelimit,
                         -encodingAssumptions.get(unsatcorelimit));
                 results.push(-encodingAssumptions.get(unsatcorelimit));
                 if (solver.isVerbose()) {
                     System.out.println(solver.getLogPrefix() + "mandatory.");
                 }
             } else {
                 if (solver.isVerbose()) {
                     System.out.println(solver.getLogPrefix() + "not needed.");
                 }
             }
         }
         return results;
     }
 
     @Override
     public String toString() {
         return "Deletion based minimization strategy";
     }
 }