feat(tester): extend ListProblems endpoint

internal/tester/repository/pg_problems_repository.go

@@ -67,3 +67,33 @@ func (r *ProblemRepository) DeleteProblem(ctx context.Context, id int32) error {
 
 	return nil
 }
+
+const (
+	ListProblemsQuery = `SELECT id, title, time_limit, memory_limit, created_at, updated_at
+FROM problems
+LIMIT ? OFFSET ?`
+	CountProblemsQuery = "SELECT COUNT(*) FROM problems"
+)
+
+func (r *ProblemRepository) ListProblems(ctx context.Context, page int32, pageSize int32) ([]*models.ProblemListItem, int32, error) {
+	const op = "ContestRepository.ListProblems"
+
+	if pageSize > 20 || pageSize < 1 {
+		pageSize = 1
+	}
+
+	var problems []*models.ProblemListItem
+	query := r.db.Rebind(ListProblemsQuery)
+	err := r.db.SelectContext(ctx, &problems, query, pageSize, (page-1)*pageSize)
+	if err != nil {
+		return nil, 0, handlePgErr(err, op)
+	}
+
+	var count int32
+	err = r.db.GetContext(ctx, &count, CountProblemsQuery)
+	if err != nil {
+		return nil, 0, handlePgErr(err, op)
+	}
+
+	return problems, count, nil
+}