Development: Add server functionality for simple exam seat distribution

src/main/java/de/tum/cit/aet/artemis/exam/dto/room/ExamRoomDTO.java

@@ -7,5 +7,6 @@
 import com.fasterxml.jackson.annotation.JsonInclude;
 
 @JsonInclude(JsonInclude.Include.NON_EMPTY)
-public record ExamRoomDTO(@NotNull String roomNumber, @NotNull String name, @NotNull String building, int numberOfSeats, @NotNull Set<ExamRoomLayoutStrategyDTO> layoutStrategies) {
+public record ExamRoomDTO(long id, @NotNull String roomNumber, @NotNull String name, @NotNull String building, int numberOfSeats,
+        @NotNull Set<ExamRoomLayoutStrategyDTO> layoutStrategies) {
 }

src/main/java/de/tum/cit/aet/artemis/exam/repository/ExamRoomExamAssignmentRepository.java

@@ -0,0 +1,24 @@
+package de.tum.cit.aet.artemis.exam.repository;
+
+import org.springframework.context.annotation.Conditional;
+import org.springframework.context.annotation.Lazy;
+import org.springframework.data.jpa.repository.Modifying;
+import org.springframework.stereotype.Repository;
+import org.springframework.transaction.annotation.Transactional;
+
+import de.tum.cit.aet.artemis.core.repository.base.ArtemisJpaRepository;
+import de.tum.cit.aet.artemis.exam.config.ExamEnabled;
+import de.tum.cit.aet.artemis.exam.domain.room.ExamRoomExamAssignment;
+
+/**
+ * Spring Data JPA repository for the {@link de.tum.cit.aet.artemis.exam.domain.room.ExamRoomExamAssignment} entity.
+ */
+@Conditional(ExamEnabled.class)
+@Lazy
+@Repository
+public interface ExamRoomExamAssignmentRepository extends ArtemisJpaRepository<ExamRoomExamAssignment, Long> {
+
+    @Transactional
+    @Modifying
+    void deleteAllByExamId(long examId);
+}

src/main/java/de/tum/cit/aet/artemis/exam/repository/ExamRoomRepository.java

@@ -4,6 +4,7 @@
 
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Lazy;
+import org.springframework.data.jpa.repository.EntityGraph;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.stereotype.Repository;
 
@@ -49,7 +50,32 @@ HAVING COUNT(*) > 1
                 ON examRoom.roomNumber = latestRoom.roomNumber
                 AND examRoom.name = latestRoom.name
                 AND examRoom.createdDate < latestRoom.maxCreatedDate
-            WHERE examRoom.id NOT IN ( SELECT DISTINCT erea.examRoom.id FROM ExamRoomExamAssignment erea )
+            WHERE NOT EXISTS (
+                SELECT 1
+                FROM ExamRoomExamAssignment erea
+                WHERE erea.examRoom.id = examRoom.id
+            )
             """)
     Set<Long> findAllIdsOfOutdatedAndUnusedExamRooms();
+
+    /**
+     * Returns IDs of the current (latest) version of each unique exam room (roomNumber, name).
+     *
+     * @return All IDs of the current exam rooms
+     */
+    @Query("""
+            SELECT id
+            FROM (
+                SELECT er.id AS id, er.roomNumber AS roomNumber, er.name AS name, er.createdDate AS createdDate, ROW_NUMBER() OVER (
+                    PARTITION BY er.roomNumber, er.name
+                    ORDER BY er.createdDate DESC, er.id DESC
+                ) AS rowNumber
+                FROM ExamRoom er
+            )
+            WHERE rowNumber = 1
+            """)
+    Set<Long> findAllIdsOfCurrentExamRooms();
+
+    @EntityGraph(type = EntityGraph.EntityGraphType.LOAD, attributePaths = { "layoutStrategies" })
+    Set<ExamRoom> findAllWithEagerLayoutStrategiesByIdIn(Set<Long> ids);
 }

src/main/java/de/tum/cit/aet/artemis/exam/service/ExamRoomDistributionService.java

@@ -0,0 +1,121 @@
+package de.tum.cit.aet.artemis.exam.service;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import jakarta.validation.constraints.NotEmpty;
+
+import org.springframework.context.annotation.Conditional;
+import org.springframework.context.annotation.Lazy;
+import org.springframework.stereotype.Service;
+
+import de.tum.cit.aet.artemis.core.exception.BadRequestAlertException;
+import de.tum.cit.aet.artemis.exam.config.ExamEnabled;
+import de.tum.cit.aet.artemis.exam.domain.Exam;
+import de.tum.cit.aet.artemis.exam.domain.ExamUser;
+import de.tum.cit.aet.artemis.exam.domain.room.ExamRoom;
+import de.tum.cit.aet.artemis.exam.domain.room.ExamRoomExamAssignment;
+import de.tum.cit.aet.artemis.exam.dto.room.ExamSeatDTO;
+import de.tum.cit.aet.artemis.exam.repository.ExamRepository;
+import de.tum.cit.aet.artemis.exam.repository.ExamRoomExamAssignmentRepository;
+import de.tum.cit.aet.artemis.exam.repository.ExamRoomRepository;
+import de.tum.cit.aet.artemis.exam.repository.ExamUserRepository;
+
+/**
+ * Service Implementation for managing distributions of exam users to exam rooms in an exam.
+ */
+@Conditional(ExamEnabled.class)
+@Lazy
+@Service
+public class ExamRoomDistributionService {
+
+    private static final String ENTITY_NAME = "examRoomDistributionService";
+
+    private final ExamRepository examRepository;
+
+    private final ExamRoomRepository examRoomRepository;
+
+    private final ExamRoomService examRoomService;
+
+    private final ExamRoomExamAssignmentRepository examRoomExamAssignmentRepository;
+
+    private final ExamUserRepository examUserRepository;
+
+    public ExamRoomDistributionService(ExamRepository examRepository, ExamRoomRepository examRoomRepository, ExamRoomService examRoomService,
+            ExamRoomExamAssignmentRepository examRoomExamAssignmentRepository, ExamUserRepository examUserRepository) {
+        this.examRepository = examRepository;
+        this.examRoomRepository = examRoomRepository;
+        this.examRoomService = examRoomService;
+        this.examRoomExamAssignmentRepository = examRoomExamAssignmentRepository;
+        this.examUserRepository = examUserRepository;
+    }
+
+    /**
+     * Distribute all students who are registered for a given exam across a selection of rooms.
+     * Existing planned seats and room assignments are replaced.
+     *
+     * @param examId      The exam
+     * @param examRoomIds The ids of the rooms to distribute to
+     * @implNote Currently only the "default" layout strategy is used.
+     */
+    public void distributeRegisteredStudents(long examId, @NotEmpty Set<Long> examRoomIds) {
+        final Exam exam = examRepository.findByIdWithExamUsersElseThrow(examId);
+        final Set<ExamRoom> examRoomsForExam = examRoomRepository.findAllWithEagerLayoutStrategiesByIdIn(examRoomIds);
+
+        final int numberOfUsableSeats = examRoomsForExam.stream().mapToInt(examRoom -> examRoomService.getDefaultLayoutStrategyOrElseThrow(examRoom).getCapacity()).sum();
+        final int numberOfExamUsers = exam.getExamUsers().size();
+
+        if (numberOfUsableSeats < numberOfExamUsers) {
+            throw new BadRequestAlertException("Not enough seats available in the selected rooms", ENTITY_NAME, "notEnoughExamSeats",
+                    Map.of("numberOfUsableSeats", numberOfUsableSeats, "numberOfExamUsers", numberOfExamUsers));
+        }
+
+        examRoomExamAssignmentRepository.deleteAllByExamId(examId);
+        List<ExamRoomExamAssignment> examRoomExamAssignments = new ArrayList<>();
+        for (ExamRoom examRoom : examRoomsForExam) {
+            var examRoomExamAssignment = new ExamRoomExamAssignment();
+            examRoomExamAssignment.setExamRoom(examRoom);
+            examRoomExamAssignment.setExam(exam);
+            examRoomExamAssignments.add(examRoomExamAssignment);
+        }
+        examRoomExamAssignmentRepository.saveAll(examRoomExamAssignments);
+
+        distributeExamUsersToUsableSeatsInRooms(exam, examRoomsForExam);
+    }
+
+    private void distributeExamUsersToUsableSeatsInRooms(Exam exam, Set<ExamRoom> examRoomsForExam) {
+        Map<String, List<ExamSeatDTO>> roomNumberToUsableSeatsDefaultLayout = new HashMap<>();
+        for (ExamRoom examRoom : examRoomsForExam) {
+            roomNumberToUsableSeatsDefaultLayout.put(examRoom.getRoomNumber(), examRoomService.getDefaultUsableSeats(examRoom));
+        }
+
+        setPlannedRoomAndPlannedSeatForExamUsersRandomly(exam, roomNumberToUsableSeatsDefaultLayout);
+
+        examUserRepository.saveAll(exam.getExamUsers());
+        examRepository.save(exam);
+    }
+
+    private void setPlannedRoomAndPlannedSeatForExamUsersRandomly(Exam exam, Map<String, List<ExamSeatDTO>> roomNumberToUsableSeats) {
+        Iterator<ExamUser> examUsersIterator = exam.getExamUsers().iterator();
+
+        for (var roomNumberToUsableSeatsEntry : roomNumberToUsableSeats.entrySet()) {
+            final String roomNumber = roomNumberToUsableSeatsEntry.getKey();
+            final List<ExamSeatDTO> usableSeatsForThisRoom = roomNumberToUsableSeatsEntry.getValue();
+
+            for (ExamSeatDTO seat : usableSeatsForThisRoom) {
+                if (!examUsersIterator.hasNext()) {
+                    return;
+                }
+
+                ExamUser nextExamUser = examUsersIterator.next();
+                nextExamUser.setPlannedRoom(roomNumber);
+                nextExamUser.setPlannedSeat(seat.name());
+                exam.addExamUser(nextExamUser);
+            }
+        }
+    }
+}