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The constraint solver library contains a local search based framework that allows modeling of a problem using constraint programming primitives (variables, values, constraints).
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package org.cpsolver.studentsct;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.cpsolver.ifs.assignment.Assignment;
import org.cpsolver.ifs.assignment.DefaultSingleAssignment;
import org.cpsolver.ifs.model.Model;
import org.cpsolver.ifs.model.Neighbour;
import org.cpsolver.ifs.solution.Solution;
import org.cpsolver.ifs.util.DataProperties;
import org.cpsolver.studentsct.constraint.SectionLimit;
import org.cpsolver.studentsct.constraint.StudentConflict;
import org.cpsolver.studentsct.heuristics.selection.BranchBoundSelection;
import org.cpsolver.studentsct.model.Course;
import org.cpsolver.studentsct.model.CourseRequest;
import org.cpsolver.studentsct.model.Enrollment;
import org.cpsolver.studentsct.model.Request;
import org.cpsolver.studentsct.model.Student;


/**
 * Online student sectioning test (using {@link BranchBoundSelection}
 * selection). This class is used by the online student sectioning mock-up page. 

 * 

 * Usage:
 * 
 * StudentSctBBTest test = new StudentSctBBTest(student); //student already has all his/her requests defined

 * Solution sectioningSolution = test.getSolution(); //solution contains only one student (the given one) with his/her schedule

 * Vector sectioningMessages = test.getMessages(); //sectioning messages (to be printed in the GUI).
 * 
 * 
 * @author  Tomas Muller
 * @version StudentSct 1.3 (Student Sectioning)

 *          Copyright (C) 2007 - 2014 Tomas Muller

 *          [email protected]

 *          http://muller.unitime.org

 * 

 *          This library is free software; you can redistribute it and/or modify
 *          it under the terms of the GNU Lesser General Public License as
 *          published by the Free Software Foundation; either version 3 of the
 *          License, or (at your option) any later version. 

 * 

 *          This library is distributed in the hope that it will be useful, but
 *          WITHOUT ANY WARRANTY; without even the implied warranty of
 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 *          Lesser General Public License for more details. 

 * 

 *          You should have received a copy of the GNU Lesser General Public
 *          License along with this library; if not see
 *          http://www.gnu.org/licenses/.
 */
public class StudentSctBBTest extends Model {
    private Student iStudent = null;
    private Solution iSolution = null;
    private long iTime;
    private boolean iTimeoutReached = false;

    /**
     * Constructor
     * 
     * @param student
     *            a student to be sectioned
     */
    public StudentSctBBTest(Student student) {
        iStudent = student;
        for (Request request : iStudent.getRequests())
            addVariable(request);
        addGlobalConstraint(new SectionLimit(new DataProperties()));
        addConstraint(new StudentConflict(student));
    }

    /** Return the given student 
     * @return selected student
     **/
    public Student getStudent() {
        return iStudent;
    }

    /**
     * Compute and return the sectioning solution. It contains only the given
     * student with his/her schedule
     * @return current solution
     */
    public Solution getSolution() {
        if (iSolution == null) {
            iSolution = new Solution(this, new DefaultSingleAssignment());
            BranchBoundSelection.Selection selection = new BranchBoundSelection(new DataProperties()).getSelection(iSolution.getAssignment(), getStudent());
            Neighbour neighbour = selection.select();
            if (neighbour != null)
                neighbour.assign(iSolution.getAssignment(), 0);
            iTime = selection.getTime();
            iTimeoutReached = selection.isTimeoutReached();
        }
        return iSolution;
    }

    /**
     * Return a list of messages ({@link Message} objects) from the sectioning
     * of the given student
     * @return enrollment messages
     */
    public List getMessages() {
        Assignment assignment = getSolution().getAssignment();
        List ret = new ArrayList();
        ret.add(new Message(Message.sMsgLevelInfo, null, "Solution found in " + iTime + " ms."));
        if (iTimeoutReached)
            ret.add(new Message(Message.sMsgLevelInfo, null,
                    "
Time out reached, solution optimality can not be guaranteed."));
        for (Request request : getStudent().getRequests()) {
            if (!request.isAlternative() && assignment.getValue(request) == null) {
                ret.add(new Message(Message.sMsgLevelWarn, request,
                        "Unable to enroll to " + request + ", " + (request instanceof CourseRequest ? ((CourseRequest) request).getCourses().size() == 1 ? "course is" : "courses are" : "time is") + " not available."));
                Collection values = (request instanceof CourseRequest ? (Collection) ((CourseRequest) request).getAvaiableEnrollmentsSkipSameTime(assignment) : request.computeEnrollments(assignment));
                for (Iterator f = values.iterator(); f.hasNext();) {
                    Enrollment enrollment = f.next();
                    Set conf = conflictValues(assignment, enrollment);
                    if (conf != null && !conf.isEmpty()) {
                        Enrollment conflict = conf.iterator().next();
                        if (conflict.equals(enrollment))
                            ret.add(new Message(Message.sMsgLevelInfo, request, "Assignment of " + enrollment.getName().replaceAll("\n", "
    ") + "
 is not available."));
                        else
                            ret.add(new Message(Message.sMsgLevelInfo, request, "Assignment of " + enrollment.getName().replaceAll("\n", "
    ") +
                                    "
 conflicts with " + conflict.getName().replaceAll("\n", "
    ") + ""));
                    }
                }
            }
            if (request instanceof CourseRequest && assignment.getValue(request) != null) {
                CourseRequest courseRequest = (CourseRequest) request;
                Enrollment enrollment = assignment.getValue(request);
                List selectedEnrollments = courseRequest.getSelectedEnrollments(assignment, false);
                if (selectedEnrollments != null && !selectedEnrollments.isEmpty()
                        && !selectedEnrollments.contains(enrollment)) {
                    Course course = (courseRequest.getSelectedChoices().iterator().next()).getOffering().getCourse(
                            getStudent());
                    Enrollment selected = selectedEnrollments.get(0);
                    Set conf = conflictValues(assignment, selected);
                    if (conf != null && !conf.isEmpty()) {
                        ret.add(new Message(Message.sMsgLevelWarn, request,
                                "Unable to enroll selected enrollment for " + course.getName() + ", seleted " + (courseRequest.getSelectedChoices().size() == 1 ? "class is" : "classes are") +
                                " conflicting with other choices."));
                        Enrollment conflict = conf.iterator().next();
                        if (conflict.equals(selected))
                            ret.add(new Message(Message.sMsgLevelInfo, request, "Assignment of " + selected.getName().replaceAll("\n", "
    ") + "
 is not available."));
                        else
                            ret.add(new Message(Message.sMsgLevelInfo, request, "Assignment of " + selected.getName().replaceAll("\n", "
    ") +
                                    "
 conflicts with " + conflict.getName().replaceAll("\n", "
    ") + ""));
                    } else {
                        ret.add(new Message(Message.sMsgLevelWarn, request, "Unable to enroll selected enrollment for " + course.getName() + "."));
                    }
                }
            }
        }
        return ret;
    }

    /** Sectioning message */
    public static class Message {
        /** Message levels */
        public static String[] sMsgLevels = { "INFO", "WARN", "ERROR" };
        /** Info message level */
        public static int sMsgLevelInfo = 0;
        /** Warning message level */
        public static int sMsgLevelWarn = 1;
        /** Error message level */
        public static int sMsgLevelError = 2;

        private int iLevel;
        private Request iRequest;
        private String iMessage;

        /**
         * Constructor
         * 
         * @param level
         *            message level (one of
         *            {@link StudentSctBBTest.Message#sMsgLevelInfo},
         *            {@link StudentSctBBTest.Message#sMsgLevelWarn}, and
         *            {@link StudentSctBBTest.Message#sMsgLevelError})
         * @param request
         *            related course / free time request
         * @param message
         *            a message
         */
        public Message(int level, Request request, String message) {
            iLevel = level;
            iRequest = request;
            iMessage = message;
        }

        /**
         * Message level (one of {@link StudentSctBBTest.Message#sMsgLevelInfo},
         * {@link StudentSctBBTest.Message#sMsgLevelWarn}, and
         * {@link StudentSctBBTest.Message#sMsgLevelError})
         * @return message level
         */
        public int getLevel() {
            return iLevel;
        }

        /** Message level as string 
         * @return message level
         **/
        public String getLevelString() {
            return sMsgLevels[iLevel];
        }

        /** Related course / free time request 
         * @return associated student request
         **/
        public Request getRequest() {
            return iRequest;
        }

        /** Message 
         * @return message text
         **/
        public String getMessage() {
            return iMessage;
        }

        /** String representation (message level: message) */
        @Override
        public String toString() {
            return getLevelString() + ":" + getMessage();
        }
    }
}