001package org.cpsolver.ifs.assignment.context;
002
003import org.cpsolver.ifs.assignment.Assignment;
004import org.cpsolver.ifs.heuristics.NeighbourSelection;
005import org.cpsolver.ifs.model.Value;
006import org.cpsolver.ifs.model.Variable;
007import org.cpsolver.ifs.solver.Solver;
008
009/**
010 * A neighborhood selection with an assignment context. In order to be able to hold multiple assignments in memory
011 * it is desired for all the assignment dependent data a selection may need (to keep its current state),
012 * to store these data in a separate class (implementing the 
013 * {@link AssignmentContext} interface). This context is created by calling
014 * {@link ConstraintWithContext#createAssignmentContext(Assignment)} and accessed by
015 * {@link ConstraintWithContext#getContext(Assignment)}.
016 * 
017 * 
018 * @see AssignmentContext
019 * 
020 * @version IFS 1.3 (Iterative Forward Search)<br>
021 *          Copyright (C) 2014 Tomáš Müller<br>
022 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
023 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
024 * <br>
025 *          This library is free software; you can redistribute it and/or modify
026 *          it under the terms of the GNU Lesser General Public License as
027 *          published by the Free Software Foundation; either version 3 of the
028 *          License, or (at your option) any later version. <br>
029 * <br>
030 *          This library is distributed in the hope that it will be useful, but
031 *          WITHOUT ANY WARRANTY; without even the implied warranty of
032 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
033 *          Lesser General Public License for more details. <br>
034 * <br>
035 *          You should have received a copy of the GNU Lesser General Public
036 *          License along with this library; if not see <a href='http://www.gnu.org/licenses'>http://www.gnu.org/licenses</a>.
037 * @param <V> Variable
038 * @param <T> Value
039 * @param <C> Assignment Context
040 **/
041public abstract class NeighbourSelectionWithContext<V extends Variable<V, T>, T extends Value<V, T>, C extends AssignmentContext> implements NeighbourSelection<V, T>, HasAssignmentContext<V, T, C>, CanHoldContext {
042    private AssignmentContextReference<V, T, C> iContextReference = null;
043    private AssignmentContext[] iContext = new AssignmentContext[CanHoldContext.sMaxSize];
044    protected C iContextOverride = null;
045
046    @Override
047    public void init(Solver<V, T> solver) {
048        iContextReference = solver.currentSolution().getModel().createReference(this);
049        if (isSingleContextSolver(solver))
050            iContextOverride = createAssignmentContext(solver.currentSolution().getAssignment());
051    }
052    
053    /**
054     * Returns true if there should be only one context for this neighbourhood selection.
055     * @param solver current solver
056     * @return {@link Solver#hasSingleSolution()}
057     */
058    protected boolean isSingleContextSolver(Solver<V, T> solver) {
059        return solver.hasSingleSolution();
060    }
061    
062    /**
063     * Returns an assignment context associated with this selection. If there is no 
064     * assignment context associated with this selection yet, one is created using the
065     * {@link ConstraintWithContext#createAssignmentContext(Assignment)} method. From that time on,
066     * this context is kept with the assignment.
067     * @param assignment given assignment
068     * @return assignment context associated with this selection and the given assignment
069     */
070    @Override
071    public C getContext(Assignment<V, T> assignment) {
072        if (iContextOverride != null)
073            return iContextOverride;
074        return AssignmentContextHelper.getContext(this, assignment);
075    }
076    
077    @Override
078    public AssignmentContextReference<V, T, C> getAssignmentContextReference() { return iContextReference; }
079
080    @Override
081    public void setAssignmentContextReference(AssignmentContextReference<V, T, C> reference) { iContextReference = reference; }
082
083    @Override
084    public AssignmentContext[] getContext() { return iContext; }
085    
086    /**
087     * Has context override
088     * @return true if all threads are using the same context
089     */
090    public boolean hasContextOverride() {
091        return iContextOverride != null;
092    }
093}