Add references support

lib/helpers/virtual_directory_helper.dart

@@ -0,0 +1,52 @@
+import 'package:comunic/models/api_request.dart';
+import 'package:flutter/material.dart';
+
+/// Virtual directory helper
+///
+/// @author Pierre Hubert
+
+enum VirtualDirectoryType { USER, GROUP, NONE }
+
+class VirtualDirectoryResult {
+  final VirtualDirectoryType type;
+  final int id;
+
+  const VirtualDirectoryResult({
+    @required this.type,
+    this.id,
+  }) : assert(type != null);
+}
+
+class VirtualDirectoryHelper {
+  /// Find a virtual directory
+  Future<VirtualDirectoryResult> find(String directory) async {
+    final response = await APIRequest(
+        uri: "virtualDirectory/find",
+        needLogin: true,
+        args: {"directory": directory}).exec();
+
+    switch (response.code) {
+      case 404:
+        return VirtualDirectoryResult(type: VirtualDirectoryType.NONE);
+
+      case 200:
+        final id = response.getObject()["id"];
+        final kind = response.getObject()["kind"];
+        switch (kind) {
+          case "user":
+            return VirtualDirectoryResult(
+                type: VirtualDirectoryType.USER, id: id);
+          case "group":
+            return VirtualDirectoryResult(
+                type: VirtualDirectoryType.GROUP, id: id);
+
+          default:
+            throw Exception("Unsupported virtual directory kind: $kind");
+        }
+        break;
+
+      default:
+        throw new Exception("Could not get virtual directory!");
+    }
+  }
+}