Better use of async functions for API

- Use local_preferences for storing data

lib/api.dart

@@ -8,6 +8,8 @@ import 'package:http/http.dart' as http;
 
 class InvenTreeAPI {
 
+  static const _URL_GET_TOKEN = "user/token/";
+
   // Ensure we only ever create a single instance of the API class
   static final InvenTreeAPI _api = new InvenTreeAPI._internal();
 
@@ -56,6 +58,11 @@ class InvenTreeAPI {
 
   // Construct an API URL
   String _makeUrl(String url) {
+
+    if (url.startsWith('/')) {
+      url = url.substring(1);
+    }
+
     return path.join(_base_url, url);
   }
 
@@ -65,27 +72,36 @@ class InvenTreeAPI {
 
   // Request the raw /api/ endpoing to see if there is an InvenTree server listening
   void _tryConnection() async {
-    final response = get("");
+
+    print("Testing connection to server");
+
+    final response = await get("").then((http.Response response) {
+      print("response!");
+      print(response.body);
+    }).catchError((error) {
+      print("Error trying connection");
+    });
+
+    // TODO - Add timeout handler
   }
 
   // Request an API token from the server.
   // A valid username/password combination must be provided
   void _secureToken() async {
-
     if (_token.isNotEmpty) {
       print("Discarding old token - " + _token);
     }
     _token = "";
 
-    var _url = _makeUrl("user/token/");
-    final response = await http.post(_url,
+    var response = post(_URL_GET_TOKEN,
         body: {
           "username": _username,
-          "password": _password
+          "password": _password,
         });
 
+    response.then((http.Response response) {
       if (response.statusCode != 200) {
-      print("Invalid status code:" + String.fromCharCode(response.statusCode));
+        print("Invalid status code: " + response.statusCode.toString());
       } else {
         var _json = json.decode(response.body);
 
@@ -94,21 +110,75 @@ class InvenTreeAPI {
           print("Received token: " + _token);
         }
       }
+    }).catchError((error) {
+      print("Error retrieving token");
+    });
   }
 
-  Future<http.Response> get(String url) async {
+  // Perform a PATCH request
+  Future<http.Response> patch(String url, {Map<String, String> body}) async {
+
     var _url = _makeUrl(url);
-    final response = await http.get(_url,
-      headers: {
-          HttpHeaders.authorizationHeader: "Token: " + _token
-        }
-    );
+    var _headers = _defaultHeaders();
+    var _body = Map<String, String>();
 
-    print("Making request to " + _url);
-    print(response.statusCode);
-    print(response.body);
+    // Copy across provided data
+    body.forEach((K, V) => _body[K] = V);
+
+    print("PATCH: " + _url);
+
+    final response = await http.patch(_url,
+      headers: _headers,
+      body: _body,
+    );
 
     return response;
   }
 
+  // Perform a POST request
+  Future<http.Response> post(String url, {Map<String, String> body}) async {
+
+    var _url = _makeUrl(url);
+    var _headers = _defaultHeaders();
+    var _body = Map<String, String>();
+
+    // Copy across provided data
+    body.forEach((K, V) => _body[K] = V);
+
+    print("POST: " + _url);
+
+    final response = await http.post(_url,
+      headers: _headers,
+      body: _body,
+    );
+
+    return response;
+  }
+
+  // Perform a GET request
+  Future<http.Response> get(String url) async {
+
+    var _url = _makeUrl(url);
+    var _headers = _defaultHeaders();
+
+    print("GET: " + _url);
+
+    final response = await http.get(_url,
+      headers: _headers,
+    );
+
+    return response;
+  }
+
+  Map<String, String> _defaultHeaders() {
+
+    var headers = Map<String, String>();
+
+    if (_token.isNotEmpty) {
+      headers[HttpHeaders.authorizationHeader] = "Token " + _token;
+    }
+
+    return headers;
+  }
+
 }

lib/login_settings.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 import 'api.dart';
+import 'preferences.dart';
 
 class InvenTreeLoginSettingsWidget extends StatefulWidget {
 
@@ -133,13 +134,9 @@ class _InvenTreeLoginSettingsState extends State<InvenTreeLoginSettingsWidget> {
     if (_formKey.currentState.validate()) {
       _formKey.currentState.save();
 
-      SharedPreferences prefs = await SharedPreferences.getInstance();
+      await InvenTreeUserPreferences().saveLoginDetails(_addr, _user, _pass);
 
-      await prefs.setString('server', _addr);
-      await prefs.setString('username', _user);
-      await prefs.setString('password', _pass);
-
-      InvenTreeAPI().connect(_addr, _user, _pass);
+      print("Saved");
     }
   }
 }

lib/main.dart

@@ -2,11 +2,13 @@ import 'package:flutter/material.dart';
 
 import 'settings.dart';
 import 'api.dart';
+import 'preferences.dart';
 
 void main() => runApp(MyApp());
 
 class MyApp extends StatelessWidget {
   // This widget is the root of your application.
+
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
@@ -21,7 +23,7 @@ class MyApp extends StatelessWidget {
         // or simply save your changes to "hot reload" in a Flutter IDE).
         // Notice that the counter didn't reset back to zero; the application
         // is not restarted.
-        primarySwatch: Colors.blue,
+        primarySwatch: Colors.lightGreen,
       ),
       home: MyHomePage(title: 'InvenTree'),
     );

lib/preferences.dart

@@ -0,0 +1,41 @@
+import 'package:shared_preferences/shared_preferences.dart';
+import 'api.dart';
+
+
+class InvenTreeUserPreferences {
+
+  static const String _SERVER = 'server';
+  static const String _USERNAME = 'username';
+  static const String _PASSWORD = 'password';
+
+  // Ensure we only ever create a single instance of the preferences class
+  static final InvenTreeUserPreferences _api = new InvenTreeUserPreferences._internal();
+
+  factory InvenTreeUserPreferences() {
+    return _api;
+  }
+
+  InvenTreeUserPreferences._internal();
+
+  // Load saved login details, and attempt connection
+  void loadLoginDetails() async {
+    SharedPreferences prefs = await SharedPreferences.getInstance();
+
+    var server = prefs.getString(_SERVER);
+    var username = prefs.getString(_USERNAME);
+    var password = prefs.getString(_PASSWORD);
+
+    await InvenTreeAPI().connect(server, username, password);
+  }
+
+  void saveLoginDetails(String server, String username, String password) async {
+    SharedPreferences prefs = await SharedPreferences.getInstance();
+
+    await prefs.setString(_SERVER, server);
+    await prefs.setString(_USERNAME, username);
+    await prefs.setString(_PASSWORD, password);
+
+    // Reconnect the API
+    await InvenTreeAPI().connect(server, username, password);
+  }
+}