loading state and error handling refactor

lib/api/mhsl/mhslApi.dart

@@ -1,9 +1,14 @@
+import 'dart:async';
 import 'dart:convert';
+import 'dart:io';
 
 import 'package:http/http.dart' as http;
 import 'package:jiffy/jiffy.dart';
-import '../apiError.dart';
+
 import '../apiRequest.dart';
+import '../errors/network_exception.dart';
+import '../errors/parse_exception.dart';
+import '../errors/server_exception.dart';
 
 abstract class MhslApi<T> extends ApiRequest {
   String subpath;
@@ -15,18 +20,38 @@ abstract class MhslApi<T> extends ApiRequest {
   T assemble(String raw);
 
   Future<T> run() async {
-    var endpoint = Uri.parse('https://mhsl.eu/marianum/marianummobile/$subpath');
+    final endpoint = Uri.parse('https://mhsl.eu/marianum/marianummobile/$subpath');
 
-    var data = await request(endpoint);
-    if(data == null) {
-      throw ApiError('Request could not be dispatched!');
+    final http.Response data;
+    try {
+      final raw = await request(endpoint);
+      if (raw == null) {
+        throw const NetworkException(
+          userMessage: 'Keine Antwort vom MHSL-Dienst erhalten.',
+          technicalDetails: 'mhsl request returned null',
+        );
+      }
+      data = raw;
+    } on SocketException catch (e) {
+      throw NetworkException(technicalDetails: 'mhsl $subpath: ${e.message}');
+    } on TimeoutException catch (e) {
+      throw NetworkException.timeout(technicalDetails: 'mhsl $subpath: $e');
+    } on http.ClientException catch (e) {
+      throw NetworkException(technicalDetails: 'mhsl $subpath: ${e.message}');
     }
 
-    if(data.statusCode > 299) {
-      throw ApiError('Non 200 Status code from mhsl services: $subpath: ${data.statusCode}');
+    if (data.statusCode > 299) {
+      throw ServerException(
+        statusCode: data.statusCode,
+        technicalDetails: 'mhsl $subpath HTTP ${data.statusCode}',
+      );
     }
 
-    return assemble(utf8.decode(data.bodyBytes));
+    try {
+      return assemble(utf8.decode(data.bodyBytes));
+    } catch (e) {
+      throw ParseException(technicalDetails: 'mhsl $subpath assemble: $e');
+    }
   }
 
   static String dateTimeToJson(DateTime time) => Jiffy.parseFromDateTime(time).format(pattern: 'yyyy-MM-dd HH:mm:ss');