Idris2: Dependent sum type discrimination - idris

Question

This is probably very basic dependently typed programming problem, but I cannot find anything about it. The problem is this: "I have a bunch of messages that I may or may not have to handle depending on some configuration. How do I discriminate between the messages that I need to handle and the messages I don't need to handle at the type level".
So for example, I have some configuration and some messages.
record Configuration where
constructor MkConfiguration
handlesOpenClose: Bool
handlesWillSave: Bool
config : Configuration
config = MkConfiguration { openClose: True, willSave: False }
data Message = FileOpened -- Handle when openClose = True
| FileClosed -- Handle when openClose = True
| WillSave -- Handle when willSave = True
I now want to be able to write something like this:
GetMessagesForConfig : Configuration -> Type
GetMessagesForConfig config = {-
config.openClose = true so FileOpened and FileClosed have to be handled,
config.willSave = false so WillSave does not have to be handled
-}
MessagesForConfig : Type
MessagesForConfig = GetMessagesForConfig config
handleMessage : MessagesForConfig -> Response
handleMessage FileOpened = {- do something -}
handleMessage FileClosed = {- do something -}
handleMessage WillSave impossible
Is this, or something like this possible?

Answer 1

One simple way to implement this without doing something like open unions is:
data Message : (openClose : Bool) -> (willSave : Bool) -> Type where
FileOpened : Message True a
FileClosed : Message True a
WillSave : Message a True
handleMessage : Messages True False -> Response
handleMessage FileOpened = {- do something -}
handleMessage FileClosed = {- do something -}
handleMessage WillSave impossible