another.im-ios/ConversationsClassic/AppData/Stores/RostersStore.swift

import Combine
import Foundation
import GRDB

@MainActor
final class RostersStore: ObservableObject {
    @Published private(set) var rosters: [Roster] = []

    private var cancellable: AnyCancellable?

    init(clientsPublisher: Published<[Client]>.Publisher) {
        subscribeToClientsStore(clientsPublisher: clientsPublisher)
    }

    private func subscribeToClientsStore(clientsPublisher: Published<[Client]>.Publisher) {
        let rostersPublisher = ValueObservation.tracking(Roster.fetchAll)
            .publisher(in: Database.shared.dbQueue)
            .receive(on: DispatchQueue.main)
            .catch { _ in Just([]) }

        cancellable = clientsPublisher
            .flatMap { clients in
                Publishers.MergeMany(clients.map { $0.$state })
                    .prepend(clients.map { $0.state })
                    .collect()
            }
            .combineLatest(rostersPublisher)
            .sink { [weak self] clientStates, rosters in
                self?.handleUpdates(clientStates: clientStates, rosters: rosters)
            }
    }

    private func handleUpdates(clientStates: [ClientState], rosters: [Roster]) {
        self.rosters = rosters
        print("Client States: \(clientStates.count), Rosters: \(rosters.count)")
    }
}