🧹 [code health improvement] Prevent deletion of problems referenced by assignments

apps/server/db/query/problem.sql

@@ -135,3 +135,15 @@ LIMIT $1 OFFSET $2;
 -- name: CountAllProblems :one
 SELECT COUNT(*) FROM problems
 WHERE archived_at IS NULL;
+-- name: CheckProblemInActiveAssignments :one
+SELECT COUNT(*)
+FROM assignment_problems ap
+JOIN assignments a ON ap.assignment_id = a.id
+WHERE ap.problem_id = $1
+  AND a.status = 'active'
+  AND a.archived_at IS NULL;
+
+-- name: CheckProblemInAssignmentGroups :one
+SELECT COUNT(*)
+FROM assignment_group_problems
+WHERE problem_id = $1;

apps/server/go.mod

@@ -1,6 +1,6 @@
 module github.com/coderz-space/coderz.space
 
-go 1.24.3
+go 1.25.0
 
 require (
 	github.com/go-playground/validator/v10 v10.30.1

apps/server/internal/modules/problem/service.go

@@ -128,8 +128,24 @@ func (s *Service) UpdateProblem(ctx context.Context, req UpdateProblemRequest, p
 }
 
 func (s *Service) DeleteProblem(ctx context.Context, problemID pgtype.UUID) error {
-	// TODO: Check if problem is referenced by assignments (requires assignment queries)
-	// For now, just archive the problem
+	// Check if problem is referenced by active assignments
+	activeCount, err := s.queries.CheckProblemInActiveAssignments(ctx, problemID)
+	if err != nil {
+		return err
+	}
+	if activeCount > 0 {
+		return errors.New("cannot delete problem: referenced by active assignments")
+	}
+
+	// Check if problem is referenced by assignment groups
+	groupCount, err := s.queries.CheckProblemInAssignmentGroups(ctx, problemID)
+	if err != nil {
+		return err
+	}
+	if groupCount > 0 {
+		return errors.New("cannot delete problem: referenced by assignment groups")
+	}
+
 	return s.queries.ArchiveProblem(ctx, problemID)
 }