Redmine

I would like create (or use, if one exists already) a plugin that adds a custom field to issue comments. I just simply want a boolean to indicate whether the comment is public or not. As far as I can see, here's what I'd need to do.

• add field to issue comment record
• add a permission so I can administer who can set that field
• modify the comment form on issues to include checkbox for field
• change issue rest api to include field when generating the comments (or even include it when querying for issues)

Is there a plugin like this that I could copy?