Wunderlist completed task remover written in Dart

gistfile1.dart

import 'dart:convert';
import 'package:http/http.dart' as http;

void main() {
  var url = 'https://a.wunderlist.com/api/v1/';
  var client_id = 'blabla';

  var client = new http.Client();
  client.post(url + "authenticate", body: {
    "email": "bla@blabla.net",
    "password": "blabla",
    "client_id": client_id
  }).then((response) {
    var access_token = JSON.decode(response.body)['access_token'];
    var headers = {
      'X-Access-Token': access_token,
      'X-Client-ID': client_id
    };

    //lists(client, url, headers); // use this to get the list id
    deleteCompleted(client, url, headers, "142033354"); // insert the list id you wanna clean up here

  });
  //.whenComplete(client.close);;
}

void deleteCompleted(http.Client client, String url, Map headers, String list_id) {
  client.get(url + "tasks?list_id=" + list_id + "&completed=true", headers: headers).then((response) {
    List<String> tasks = JSON.decode(response.body);
    for (var task in tasks) {
      if (task['completed']) {
        var delURL = url + "tasks/" + task['id'].toString() + "?revision=" + task['revision'].toString();
        print(delURL);
        client.delete(delURL, headers: headers).then((r) => print(r.body)).catchError((error) {
          print('Something went wrong.');
          print(error);
        });
      }
    }
  });
}

void lists(http.Client client, String url, Map headers) {
  client.get(url + "lists", headers: headers).then((response) {
    List<String> lists = JSON.decode(response.body);
    for (var list in lists) {
      print("${list['id']} | ${list['title']} | ${list['list_type']}");
    }
  });
}