another.im-ios/ConversationsClassic/AppCore/Middlewares/MessagesMiddleware.swift

import Combine
import Foundation

final class MessagesMiddleware {
    static let shared = MessagesMiddleware()

    func middleware(state: AppState, action: AppAction) -> AnyPublisher<AppAction, Never> {
        switch action {
        case .conversationAction(.makeConversationActive(let chat, let roster)):
            return Deferred {
                Future<AppAction, Never> { promise in
                    if let currentClient = state.accountsState.accounts.first(where: { $0.bareJid == chat.account }) {
                        let features = state.accountsState.discoFeatures[currentClient.bareJid] ?? []
                        if features.map({ $0.xep }).contains("XEP-0313") {
                            let oldestMessageDate = state.conversationsState.currentMessages.first?.date ?? Date()
                            let archivesRequestDate = Calendar.current.date(byAdding: .day, value: -Const.mamRequestLength, to: oldestMessageDate) ?? Date()
                            promise(.success(.xmppAction(.xmppLoadArchivedMessages(jid: currentClient.bareJid, to: roster?.bareJid, fromDate: archivesRequestDate))))
                        } else {
                            promise(.success(.info("MessageMiddleware: XEP-0313 not supported for client \(currentClient.bareJid)")))
                        }
                    } else {
                        promise(.success(.info("MessageMiddleware: No client found for account \(chat.account), probably some error here")))
                    }
                }
            }
            .eraseToAnyPublisher()

        default:
            return Empty().eraseToAnyPublisher()
        }
    }
}