/*******************************************************************************
    * 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.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 boolean computationCanceled;
  
  	public void cancelExplanationComputation() {
  		computationCanceled = true;
  	}
  
  	public IVecInt explain(ISolver solver, Map<Integer, ?> constrs,
  			IVecInt assumps) throws TimeoutException {
  		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 (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";
 	}
 }