How to modify Groovy script to send notification (bell) only wen the HD User send a message via WEB?

Summary:

Hello, I have this groovy script that send notification to the agent (AssigneeResourceId) when a new message is send/add to the service request via web, this happen when the user send the message but also when the agent send a message; in second case is unnecessary since notification of a new message comes to the agent who responded.

How can I modify it to send the notification only when the user (and not the agent) send a new message?

Trigger: Before Update

try {

    def recipientPartyId = AssigneeResourceId

def newMessageReceived = true

    def messageText = 'Hai ricevuto un messaggio da una richiesta di servizio.'