another.im-ios/ConversationsClassic/AppData/Client/Client+MartinMAM.swift

import Combine
import Foundation
import GRDB
import Martin

private typealias ArchMsg = Martin.MessageArchiveManagementModule.ArchivedMessageReceived

final class ClientMartinMAM {
    private var cancellables: Set<AnyCancellable> = []
    private var processor = ArchiveMessageProcessor()

    init(_ xmppConnection: XMPPClient) {
        // subscribe to archived messages
        xmppConnection.module(.mam).archivedMessagesPublisher
            .sink(receiveValue: { [weak self] archived in
                guard let self = self else { return }
                Task {
                    await self.processor.append(archived)
                }
            })
            .store(in: &cancellables)
    }
}

private actor ArchiveMessageProcessor {
    private var accumulator: [ArchMsg] = []

    init() {
        Task {
            while true {
                try? await Task.sleep(nanoseconds: 700 * NSEC_PER_MSEC)
                await process()
            }
        }
    }

    func append(_ msg: ArchMsg) async {
        accumulator.append(msg)
        if accumulator.count >= Const.mamRequestPageSize {
            await process()
        }
    }

    func process() async {
        if accumulator.isEmpty { return }
        await handleMessages(accumulator)
        accumulator.removeAll()
    }

    private func handleMessages(_ received: [ArchMsg]) async {
        if received.isEmpty { return }
        try? await Database.shared.dbQueue.write { db in
            for recv in received {
                let message = recv.message
                let date = recv.timestamp
                if let msgId = message.id {
                    if try Message.fetchOne(db, key: msgId) != nil {
                        #if DEBUG
                            print("---")
                            print("Skipping archived message with id \(msgId) (message exists)")
                            print("---")
                        #endif
                    } else {
                        #if DEBUG
                            print("---")
                            print("Archive message received: \(message)")
                            print("Date: \(date)")
                            print("---")
                        #endif
                        if var msg = Message.map(message, context: nil) {
                            msg.date = date
                            try msg.insert(db)
                        }
                    }
                }
            }
        }
    }
}