001package org.cpsolver.studentsct.heuristics.selection;
002
003import java.util.ArrayList;
004import java.util.Collections;
005import java.util.LinkedList;
006import java.util.List;
007import java.util.Queue;
008
009import org.cpsolver.ifs.assignment.Assignment;
010import org.cpsolver.ifs.heuristics.ValueSelection;
011import org.cpsolver.ifs.heuristics.VariableSelection;
012import org.cpsolver.ifs.solution.Solution;
013import org.cpsolver.ifs.solver.Solver;
014import org.cpsolver.ifs.util.DataProperties;
015import org.cpsolver.studentsct.filter.StudentFilter;
016import org.cpsolver.studentsct.model.Enrollment;
017import org.cpsolver.studentsct.model.Request;
018import org.cpsolver.studentsct.model.Request.RequestPriority;
019
020/**
021 * Use the standard IFS search for the unassigned critical course requests.
022 * This selection is based on {@link StandardSelection} using
023 * {@link UnassignedCriticalCourseRequestSelection} as variable selection.
024 * Unlike {@link StandardSelection}, it allows for a critical course request to be
025 * unassigned.
026 * 
027 * @version StudentSct 1.3 (Student Sectioning)<br>
028 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
029 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
030 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
031 * <br>
032 *          This library is free software; you can redistribute it and/or modify
033 *          it under the terms of the GNU Lesser General Public License as
034 *          published by the Free Software Foundation; either version 3 of the
035 *          License, or (at your option) any later version. <br>
036 * <br>
037 *          This library is distributed in the hope that it will be useful, but
038 *          WITHOUT ANY WARRANTY; without even the implied warranty of
039 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
040 *          Lesser General Public License for more details. <br>
041 * <br>
042 *          You should have received a copy of the GNU Lesser General Public
043 *          License along with this library; if not see
044 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
045 */
046public class CriticalStandardSelection extends StandardSelection {
047    private RequestPriority iPriority;
048    private boolean iAllowCriticalUnassignment = false;
049    
050    public CriticalStandardSelection(DataProperties properties, VariableSelection<Request, Enrollment> variableSelection, ValueSelection<Request, Enrollment> valueSelection, RequestPriority priority) {
051        super(properties, variableSelection, valueSelection);
052        iPriority = priority;
053        iAllowCriticalUnassignment = properties.getPropertyBoolean("Neighbour.AllowCriticalUnassignment", iAllowCriticalUnassignment);
054        iCanWorsen = properties.getPropertyBoolean("Neighbour.CriticalStandardCanWorsen", false);
055    }
056    
057    public CriticalStandardSelection(DataProperties properties, ValueSelection<Request, Enrollment> valueSelection, RequestPriority priority) {
058        this(properties, new UnassignedCriticalCourseRequestSelection(priority), valueSelection, priority);
059    }
060    
061    public CriticalStandardSelection(DataProperties properties, ValueSelection<Request, Enrollment> valueSelection) {
062        this(properties, valueSelection, RequestPriority.Critical);
063    }
064    
065    @Override
066    public void init(Solver<Request, Enrollment> solver) {
067        StudentFilter filter = null;
068        if (iVariableSelection instanceof UnassignedRequestSelection)
069            filter = ((UnassignedRequestSelection)iVariableSelection).getFilter();
070        init(solver, iPriority.name() + " Ifs" + (filter == null ? "" : " (" + filter.getName().toLowerCase() + " students)") + "...");
071    }
072    
073    @Override
074    public boolean canUnassign(Enrollment enrollment, Enrollment conflict, Assignment<Request, Enrollment> assignment) {
075        if (!iAllowCriticalUnassignment) return super.canUnassign(enrollment, conflict, assignment);
076        if (!iCanConflict) return false;
077        if (!iCanHigherPriorityConflict && conflict.getRequest().getPriority() < enrollment.getRequest().getPriority()) return false;
078        if (conflict.getRequest().isMPP() && conflict.equals(conflict.getRequest().getInitialAssignment())) return false;
079        if (iPreferPriorityStudents || conflict.getRequest().getRequestPriority().isSame(enrollment.getRequest())) {
080            if (conflict.getStudent().getPriority().isHigher(enrollment.getStudent())) return false;
081        }
082        // Override to allow unassignment of critical course requests
083        return true;
084    }
085    
086    /**
087     * Returns the unassigned critical course requests in a random order.
088     */
089    static class UnassignedCriticalCourseRequestSelection implements VariableSelection<Request, Enrollment>{
090        protected int iNrRounds = 0;
091        protected Queue<Request> iRequests = null;
092        private RequestPriority iPriority;
093        
094        public UnassignedCriticalCourseRequestSelection(RequestPriority priority) {
095            iPriority = priority;
096        }
097        
098        @Override
099        public void init(Solver<Request, Enrollment> solver) {
100            iRequests = new LinkedList<Request>();
101            iNrRounds = solver.getProperties().getPropertyInt("Neighbour.CriticalRounds", 10);
102        }
103
104        @Override
105        public Request selectVariable(Solution<Request, Enrollment> solution) {
106            return nextRequest(solution);
107        }
108        
109        protected synchronized Request nextRequest(Solution<Request, Enrollment> solution) {
110            if (iRequests.isEmpty() && iNrRounds > 0) {
111                iNrRounds --;
112                List<Request> variables = new ArrayList<Request>();
113                for (Request r: solution.getModel().unassignedVariables(solution.getAssignment()))
114                    if (iPriority.isCritical(r)) variables.add(r);
115                Collections.shuffle(variables);
116                iRequests.addAll(variables);
117            }
118            return iRequests.poll();
119        }
120    }
121}