info_tren/lib/api/train_data.dart

import 'package:http/http.dart' as http;
import 'package:info_tren/api/common.dart';
import 'package:info_tren/models.dart';

Future<TrainData> getTrain(String trainNumber, {DateTime? date}) async {
  date ??= DateTime.now();
  final response = await http.get(Uri.https(authority, 'v3/trains/$trainNumber', {
    'date': date.toUtc().toIso8601String(),
  }),);
  return trainDataFromJson(response.body);
}