Resolve "Add verification to not put person in two groups at once"

When you join a group, add members to a group, and create a group with set members, there is a check to see if those members are already a part of a group. An error message is shown to the user if that is the case. Closes #113 (closed)

src/main/java/nl/tudelft/submit/controller/StudentGroupController.java

@@ -30,6 +30,7 @@ import org.springframework.security.access.prepost.PreAuthorize;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.web.bind.annotation.*;
+import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 
 import nl.tudelft.labracore.api.dto.*;
 import nl.tudelft.labracore.lib.security.user.AuthenticatedPerson;
@@ -41,6 +42,7 @@ import nl.tudelft.submit.dto.create.note.GroupNoteCreateDTO;
 import nl.tudelft.submit.dto.create.note.SubmissionNoteCreateDTO;
 import nl.tudelft.submit.dto.id.SubmissionId;
 import nl.tudelft.submit.dto.view.labracore.SubmitGroupDetailsDTO;
+import nl.tudelft.submit.exception.GroupSwitchingException;
 import nl.tudelft.submit.model.Signature;
 import nl.tudelft.submit.security.AuthorizationService;
 import nl.tudelft.submit.service.*;
@@ -182,10 +184,16 @@ public class StudentGroupController {
 	@PostMapping
 	@PreAuthorize("@authorizationService.canCreateGroup(#create.getModule().getId())")
 	public String createGroup(@AuthenticatedPerson Person person,
-			@ModelAttribute("groupCreate") StudentGroupCreateDTO create) {
-		Long id = groupService.createGroup(create);
-
-		return "redirect:/group/" + id;
+			@ModelAttribute("groupCreate") StudentGroupCreateDTO create,
+			RedirectAttributes redirectAttributes) {
+		try {
+			Long id = groupService.createGroup(create);
+			return "redirect:/group/" + id;
+		} catch (GroupSwitchingException e) {
+			redirectAttributes.addFlashAttribute("error", e.getMessage());
+
+			return "redirect:/module/" + create.getModule().getId() + "/groups";
+		}
 	}
 
 	/**
@@ -246,10 +254,18 @@ public class StudentGroupController {
 	 */
 	@PostMapping("/{id}/join")
 	@PreAuthorize("@authorizationService.canJoinGroup(#id)")
-	public String joinGroup(@AuthenticatedPerson Person person, @PathVariable Long id) {
-		groupService.addPeopleToGroup(id, List.of(person.getUsername()));
-
+	public String joinGroup(@AuthenticatedPerson Person person, @PathVariable Long id,
+			RedirectAttributes redirectAttributes) {
 		ModuleDetailsDTO module = moduleService.getModuleById(groupService.getModuleIdFromGroup(id));
+		try {
+			groupService.addPeopleToGroup(id, List.of(person.getUsername()));
+
+		} catch (GroupSwitchingException e) {
+			redirectAttributes.addFlashAttribute("error", e.getMessage());
+
+			return "redirect:/module/" + module.getId() + "/groups";
+		}
+
 		return "redirect:/edition/" + module.getEdition().getId() + "/student?module=" + module.getId();
 	}
 
@@ -262,8 +278,13 @@ public class StudentGroupController {
 	 */
 	@PostMapping("/{id}/members")
 	@PreAuthorize("@authorizationService.canAddMembersToGroup(#id)")
-	public String addMembersToGroup(@PathVariable Long id, @RequestParam List<String> usernames) {
-		groupService.addPeopleToGroup(id, usernames);
+	public String addMembersToGroup(@PathVariable Long id, @RequestParam List<String> usernames,
+			RedirectAttributes redirectAttributes) {
+		try {
+			groupService.addPeopleToGroup(id, usernames);
+		} catch (GroupSwitchingException e) {
+			redirectAttributes.addFlashAttribute("error", e.getMessage());
+		}
 
 		return "redirect:/group/" + id;
 	}