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    }
055    
056    public CriticalStandardSelection(DataProperties properties, ValueSelection<Request, Enrollment> valueSelection, RequestPriority priority) {
057        this(properties, new UnassignedCriticalCourseRequestSelection(priority), valueSelection, priority);
058    }
059    
060    public CriticalStandardSelection(DataProperties properties, ValueSelection<Request, Enrollment> valueSelection) {
061        this(properties, valueSelection, RequestPriority.Critical);
062    }
063    
064    @Override
065    public void init(Solver<Request, Enrollment> solver) {
066        StudentFilter filter = null;
067        if (iVariableSelection instanceof UnassignedRequestSelection)
068            filter = ((UnassignedRequestSelection)iVariableSelection).getFilter();
069        init(solver, iPriority.name() + " Ifs" + (filter == null ? "" : " (" + filter.getName().toLowerCase() + " students)") + "...");
070    }
071    
072    @Override
073    public boolean canUnassign(Enrollment enrollment, Enrollment conflict, Assignment<Request, Enrollment> assignment) {
074        if (!iAllowCriticalUnassignment) return super.canUnassign(enrollment, conflict, assignment);
075        if (!iCanConflict) return false;
076        if (!iCanHigherPriorityConflict && conflict.getRequest().getPriority() < enrollment.getRequest().getPriority()) return false;
077        if (conflict.getRequest().isMPP() && conflict.equals(conflict.getRequest().getInitialAssignment())) return false;
078        if (iPreferPriorityStudents || conflict.getRequest().getRequestPriority().isSame(enrollment.getRequest())) {
079            if (conflict.getStudent().getPriority().isHigher(enrollment.getStudent())) return false;
080        }
081        // Override to allow unassignment of critical course requests
082        return true;
083    }
084    
085    /**
086     * Returns the unassigned critical course requests in a random order.
087     */
088    static class UnassignedCriticalCourseRequestSelection implements VariableSelection<Request, Enrollment>{
089        protected int iNrRounds = 0;
090        protected Queue<Request> iRequests = null;
091        private RequestPriority iPriority;
092        
093        public UnassignedCriticalCourseRequestSelection(RequestPriority priority) {
094            iPriority = priority;
095        }
096        
097        @Override
098        public void init(Solver<Request, Enrollment> solver) {
099            iRequests = new LinkedList<Request>();
100            iNrRounds = solver.getProperties().getPropertyInt("Neighbour.CriticalRounds", 10);
101        }
102
103        @Override
104        public Request selectVariable(Solution<Request, Enrollment> solution) {
105            return nextRequest(solution);
106        }
107        
108        protected synchronized Request nextRequest(Solution<Request, Enrollment> solution) {
109            if (iRequests.isEmpty() && iNrRounds > 0) {
110                iNrRounds --;
111                List<Request> variables = new ArrayList<Request>();
112                for (Request r: solution.getModel().unassignedVariables(solution.getAssignment()))
113                    if (iPriority.isCritical(r)) variables.add(r);
114                Collections.shuffle(variables);
115                iRequests.addAll(variables);
116            }
117            return iRequests.poll();
118        }
119    }
120}