Ensure peer with requested peer name is disconnected (#139)

## Description

Ensures a peer with requested peer name is disconnected.

## Motivation and Context

This resolves the issue of peer name collision by returning a 409 when
user asks for a taken peer name.

## Types of changes

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to
      not work as expected)

Author: czerwiukk

examples/room-manager/src/plugins/fishjam.ts

@@ -2,6 +2,7 @@ import fastifyPlugin from 'fastify-plugin';
 import { type FastifyInstance } from 'fastify';
 import {
   FishjamClient,
+  PeerId,
   Room,
   RoomConfigRoomTypeEnum,
   RoomId,
@@ -58,6 +59,8 @@ export const fishjamPlugin = fastifyPlugin(async (fastify: FastifyInstance): Pro
       return createPeer(roomName, peerName);
     }
 
+    await ensurePeerIsDisconnected(room.id, peer.id);
+
     if (!peerAccess?.peerToken) throw new RoomManagerError('Missing peer token in room');
 
     peerAccess.peerToken = await fishjamClient.refreshPeerToken(room.id, peer.id);
@@ -172,6 +175,15 @@ export const fishjamPlugin = fastifyPlugin(async (fastify: FastifyInstance): Pro
     return newRoom;
   }
 
+  async function ensurePeerIsDisconnected(roomId: RoomId, peerId: PeerId) {
+    const room = await fishjamClient.getRoom(roomId);
+    const isPeerConnected = room.peers.some((peer) => peer.id === peerId && peer.status === 'connected');
+
+    if (isPeerConnected) {
+      throw new RoomManagerError('Peer is already connected', 409);
+    }
+  }
+
   function getBroadcastViewerToken(roomName: string) {
     const roomId = roomNameToRoomIdMap.get(roomName);
     if (!roomId) throw new RoomManagerError('Room not found', 404);