Do not leave group when following is active

back/src/Model/User.ts

@@ -25,6 +25,7 @@ export class User implements Movable {
         public readonly IPAddress: string,
         private position: PointInterface,
         public silent: boolean,
+        public following: string[],
         private positionNotifier: PositionNotifier,
         public readonly socket: UserSocket,
         public readonly tags: string[],
@@ -48,6 +49,21 @@ export class User implements Movable {
         this.positionNotifier.updatePosition(this, position, oldPosition);
     }
 
+    public addFollower(name: string): void {
+        if (this.following.includes(name)) {
+            return;
+        }
+        this.following.push(name);
+    }
+
+    public delFollower(name: string): void {
+        const idx = this.following.indexOf(name);
+        if (idx === -1) {
+            return;
+        }
+        this.following.splice(idx, 1);
+    }
+
     private batchedMessages: BatchMessage = new BatchMessage();
     private batchTimeout: NodeJS.Timeout | null = null;