Add cloud variable api

lib/apis/cloud_variable_api.dart

@@ -0,0 +1,27 @@
+import 'dart:convert';
+
+import 'package:contacts_plus_plus/clients/api_client.dart';
+import 'package:contacts_plus_plus/models/cloud_variable.dart';
+
+class CloudVariableApi {
+  static Future<CloudVariable> readCloudVariable(ApiClient client,
+      {required String ownerId, required String path,}) async {
+    final response = await client.get("/${ownerId.isEmpty ? "globalvars" : "users/$ownerId/vars"}/$path");
+    client.checkResponse(response);
+    final body = jsonDecode(response.body);
+    return CloudVariable.fromMap(body);
+  }
+
+  static Future<CloudVariable> readGlobalCloudVariable(ApiClient client, {required String path}) async =>
+      await readCloudVariable(client, ownerId: "", path: path);
+
+  static Future<void> deleteCloudVariable(ApiClient client, {required String ownerId, required String path}) async {
+    final response = await client.delete("/users/vars/$path");
+    client.checkResponse(response);
+  }
+
+  static Future<void> writeCloudVariable(ApiClient client, {required String ownerId, required String path, required String value}) async {
+    final response = await client.put("/users/$ownerId/vars/$path", body: value);
+    client.checkResponse(response);
+  }
+}

lib/models/cloud_variable.dart

@@ -0,0 +1,33 @@
+import 'package:contacts_plus_plus/auxiliary.dart';
+
+class CloudVariable {
+  final String ownerId;
+  final String path;
+  final String value;
+  final String partitionKey;
+  final String rowKey;
+  final DateTime timestamp;
+  final String eTag;
+
+  const CloudVariable({
+    required this.ownerId,
+    required this.path,
+    required this.value,
+    required this.partitionKey,
+    required this.rowKey,
+    required this.timestamp,
+    required this.eTag,
+  });
+
+  factory CloudVariable.fromMap(Map map) {
+    return CloudVariable(
+      ownerId: map["ownerId"],
+      path: map["path"],
+      value: map["value"],
+      partitionKey: map["partitionKey"],
+      rowKey: map["rowKey"],
+      timestamp: DateTime.tryParse(map["timestamp"]) ?? DateTimeX.epoch,
+      eTag: map["eTag"],
+    );
+  }
+}