How to filter simpleChat messages (private chat)

Question

So I tried to find the solution, but after several hours, I can't find how to do it.
My use case:
There is one host for a room. Others users in the room can only talk to the host, and the users can only see their private discussion with the host. Users can see the chat component only when the host is connected.
The host use another application in which he can see the list of users who are talking to him. He can select a user in the list, and he see a simple chat with only the messages between him and the selected user.
What I have completed (I think it can help others in the future, and maybe there are better way to do it):
* In the user application: use the userManager property of your ConnectSessionContainer. It has an arrayCollection named hostCollection concerning the hosts who are currently connected.
In my case, I put the chat components into a container, and use a binding to the visible property:
visible="{connectSession.userManager.hostCollection.length>0}"
You can also add an event listener to the userManager and listen for UserEvent.USER_CREATE and USER_REMOVE and check if event.userDescriptor.role==100  or checking the hostCollection.length of the userManager again.
* If you subclass simpleClass, you can access to the _toCombo which is the combo box of the chat.
You can set its visible property to false, and set its selectedItem to the first object in its dataprovider which role is equal to 100 in order to force the chat to be private with the host.
* In the host application, you can create a list that use the ConnectSessionContainer.userManager.audienceCollection as dataProvider to have a list of the users.
It's easy to set the combobox of the simple chat to speak only to the selected user, but what I haven't been able to do is to filter the history to only show the conversation with the selected user, and not other messages, without creating several rooms.
I looked into the source code, but the history property of the simpleChatModel is just a string, and haven't find an easy way to filter it.
I looked for an arrayCollection of the history nodes, because I could have use the filter property of the collection, but I haven't find it.
So, where should I look, and what is the best way to filter the history using the recipient_Id?
Thank you for your help...
Sorry for the long post, but maybe it will help someone in the future...

Answer 1

Thank you for your response Hironmay,
I made some great progress by sub-classing both the simpleChat and simpleChatModel classes.
I read on Nigel twitter feed that he hates private, and I can thank him for his love of protected members, because it made my job so much easier!
I will explain what I did in the interest of other users, but I've got one last question: 
In the Room Console AIR app, there is an "retract all items" in the node details of the explore tab. 
I want to build the same button in my host chat application, but I haven't find a way to do it. 
There is a retractItem method on the CollectionNode class, but it requires the itemID and I haven't find a way to access every item in the chat history in order to get their itemID. 
I tried the clear() method of the chatModel, but it cleared only the current session, and leave the items in the server, and when the host logout, the items reappears when the host login again. 
On the bright side, here is what I use for my applications:
- Subsclassed the simpleChat in hostChat and clientChat classes, and the simpleChatModel in HostChatModel and ClientChatModel
- subclass the ChatMessageDescriptor ==> PrivateChatMessageDescriptor with 2 properties: userConcernedId and fromHost (boolean)
- override in the HostChatmodel the addMessage function to obtain  PrivateChatMessageDescriptor instances, and I add them in an ArrayCollection
- When the host select a user in the RosterList, a filter is used on the ArrayCollection, and the HistoryTextArea is updated to show only the thread between the host and the user. The _toCombo is updated to send private message to this user.
- I override the updateTypingIfNeeded method of HostChat to use a SharedProperty which contains the userId of the selected user when the host is typing or an empty string. This way, in the clientChat, I only show for the user when the host is typing a message for him, and not when other users are typing.
- I replace the TextInput by a TextArea to enable multiline input (well, this one opened lots of problems to fix, but I have)
- A lots of other tweaks  
So as you can see, I made it
But I look forward to a new set of sparks component, because it would have been much easier to extend the SimpleChat without rewritten half of it. 
And here are some of my feature requests: 
- In the SimpleChat class, add a protected getAndInitModel() , which would be called in the subscribe method. This way, one can switch the model without overriding the subscribe method of the Chat class.
- Have a "multilineInput" property in the SimpleChat class to chose a TextInput or a TextArea as the user input component.
- Provide a way to enable Host/Users interaction directly in the pods without having to create a new room for each user to "separate" them.
I think a lot of use cases for LCCS would be to implement solutions for Customer Experience, and that will need more focus on what the host can do (private chat, ...) 
Thank you again for your help, and thank the entire teams for this incredible service. 
Dimitri K.