Clhp map

app/lib/pages/marker_handler/get_relation.dart

 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
-import '../consts.dart';
 import 'dart:typed_data';
+import 'package:path_provider/path_provider.dart';
+
+import '../consts.dart';
 
 /// Fetch relation data from server
 Future<Uint8List> fetchRelation() async {
@@ -21,16 +23,38 @@ Future<Uint8List> fetchRelation() async {
       var responseBody = await response.transform(utf8.decoder).join();
 
       if (responseBody.isNotEmpty) {
+        Directory appDocumentsDirectory = await getApplicationDocumentsDirectory();
+        String filePath = '${appDocumentsDirectory.path}/last_relation.json';
+
+        try { // Write most recent time of update to file
+          await File(filePath).writeAsString(responseBody, mode: FileMode.write);
+          print('Relation written to file');
+        } catch (error) { print('Error in writing to file: $error');}
+
         // Return relation data from the response body
         return Uint8List.fromList(utf8.encode(responseBody));
-      } else {
-        throw Exception('Response body is empty');
       }
-    } else {
-      throw Exception('Failed to fetch relation data: Status code ${response.statusCode}');
     }
+    return loadSavedRelation();
   } catch (e) {
-    throw Exception('Failed to fetch relation data: ${e.toString()}');
+    return loadSavedRelation();
+  }
+}
+
+Future<Uint8List> loadSavedRelation() async {
+  // Get latest saved relation from file if the server does not respond
+  Directory appDocumentsDirectory = await getApplicationDocumentsDirectory();
+  String filePath = '${appDocumentsDirectory.path}/last_relation.json';
+
+  // Read file contents
+  File file = File(filePath);
+  if (await file.exists()) {
+    String contents = await file.readAsString();
+    List<dynamic> jsonData = json.decode(contents); // Parse JSON string from file
+    Uint8List relation = Uint8List.fromList(utf8.encode(jsonData.toString()));
+    return relation;
+  } else {
+    throw Exception('File does not exist');
   }
 }