Sending Email notification conditionally

Summary:

I need to send Email notification on update.

Content (required):

The notification on update should be conditionally. but on criteria I could not find a way to do it.

The condition:

if (updated by task creator) then send Email to assignee.

if (update by assignee of the task) then send Email to creator.

How to do this?

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):