How to do a switchmap or any better way to replace values in RxDart - dart

Question

I have a collection with chatroom information. Something like this:
{
chatroomid: 59,
members: [2,3]
}
Now what I want to do is, get the collection stream, in the course of doing that be able to replace the members string ids with a corresponding firestore document based on member id.
End result should look something like this:
{
chatroomid: 59,
members: [{
id: 2,
username: Johndoe1
},
{
id: 3,
username: Jennydoe1
}]
}
Is this possible with Dart RxDart?
Trying something like this fails:
getChatroomStream(chatroomid)
.switchMap((i) {
return Stream.value(i.members.map((e) => i.members.add(Document(path: 'Global.userRef/$e').streamData())));
})
.listen((event) {print(event);});
[VERBOSE-2:ui_dart_state.cc(177)] Unhandled Exception: Concurrent
modification during iteration: Instance of
'MappedListIterable<dynamic, void>'.
#0 ListIterator.moveNext (dart:_internal/iterable.dart:337:7)

Answer 1

class MemberInfo {
final int id;
final String? username;
final bool isLoading;
}
class Room {
final int chatroomid;
final List<int> members;
}
class RoomWithMemberInfos {
final int chatroomid;
final List<MemberInfo> infos;
factory RoomWithMemberInfos.initial(Room room) {
return RoomWithMemberInfos(
room.chatroomid,
room.members
.map((id) => MemberInfo(id, null, true))
.toList(growable: false)
);
}
RoomWithMemberInfos withInfo(MemberInfo info) {
return RoomWithMemberInfos(
chatroomid,
infos
.map((e) => e.id == info.id ? MemberInfo(e.id, info.name, false) : e)
.toList(growable: false)
);
}
}
Stream<MemberInfo> getMemberInfo(int id) { ... }
getChatroomStream()
.switchMap((Room room) {
final initial = RoomWithMemberInfos.initial(room);
return Stream
.fromIterable(room.members)
.flatMap(getMemberInfo)
.scan<RoomWithMemberInfos>(
(acc, info) => acc!.withInfo(info),
initial,
)
.startWith(initial);
});