Frontend first draft

frontend/pshared/lib/api/responses/error/server.dart

@@ -0,0 +1,43 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'server.g.dart';
+
+
+@JsonSerializable()
+class ErrorResponse implements Exception {
+  final int code;
+  final String details;
+  final String source;
+  final String error;
+
+  const ErrorResponse({
+    required this.code, 
+    required this.details, 
+    required this.error,
+    required this.source,
+  });
+
+  @override
+  String toString() {
+    final buffer = StringBuffer('Error response (code: $code');
+
+    if (details.isNotEmpty) {
+      buffer.write(', details: $details');
+    }
+
+    if (error.isNotEmpty) {
+      buffer.write(', error: $error');
+    }
+
+    if (source.isNotEmpty) {
+      buffer.write(', source: $source');
+    }
+
+    buffer.write(')');
+
+    return buffer.toString();
+  }
+
+  factory ErrorResponse.fromJson(Map<String, dynamic> json) => _$ErrorResponseFromJson(json);
+  Map<String, dynamic> toJson() => _$ErrorResponseToJson(this);
+}