another.im-ios/ConversationsClassic/AppData/Store/ConversationStore.swift

import Collections
import Combine
import Foundation
import GRDB

@MainActor
final class ConversationStore: ObservableObject {
    @Published private(set) var messages: Deque<Message> = []
    private(set) var roster: Roster

    private let client: Client
    private let blockSize = Const.messagesPageSize
    private let messagesMax = Const.messagesMaxSize

    private var messagesCancellable: AnyCancellable?

    init(roster: Roster, client: Client) {
        self.client = client
        self.roster = roster
    }
}

extension ConversationStore {
    func loadMoreBackward() async {
        let earliestDate = messages.last?.date ?? Date()
        resubscribe(.before(earliestDate))
        // let fetchedMessages = await fetchBlock(earliestDate, nil)
        // messages.append(contentsOf: fetchedMessages)
        // if messages.count > messagesMax {
        //     messages.removeFirst(messages.count - messagesMax)
        // }

        // guard let lastMessage = messages.last else { return }
        // let messages = await fetchBlock(lastMessage.date, nil)
        // self.messages.append(contentsOf: messages)
    }

    func loadMoreForward() async {
        // guard let firstMessage = messages.first else { return }
        // let messages = await fetchBlock(nil, firstMessage.date)
        // self.messages.insert(contentsOf: messages, at: 0)
    }
}

private extension ConversationStore {
    enum FetchDirection {
        case before(Date)
        case after(Date)
    }

    func resubscribe(_ side: FetchDirection) {
        switch side {
        case .before(let date):
            messagesCancellable = ValueObservation.tracking(Message
                .filter(
                    (Column("to") == roster.bareJid && Column("from") == roster.contactBareJid) ||
                        (Column("from") == roster.bareJid && Column("to") == roster.contactBareJid)
                )
                .filter(Column("date") < date)
                .limit(blockSize)
                .order(Column("date").desc)
                .fetchAll
            )
            .publisher(in: Database.shared.dbQueue, scheduling: .immediate)
            .sink { _ in
            } receiveValue: { [weak self] messages in
                self?.processFetched(messages, side)
            }

        case .after(let date):
            messagesCancellable = ValueObservation.tracking(Message
                .filter(
                    (Column("to") == roster.bareJid && Column("from") == roster.contactBareJid) ||
                        (Column("from") == roster.bareJid && Column("to") == roster.contactBareJid)
                )
                .filter(Column("date") > date)
                .limit(blockSize)
                .order(Column("date").desc)
                .fetchAll
            )
            .publisher(in: Database.shared.dbQueue, scheduling: .immediate)
            .sink { _ in
            } receiveValue: { [weak self] messages in
                self?.processFetched(messages, side)
            }
        }
    }

    func processFetched(_ messages: [Message], _ side: FetchDirection) {
        switch side {
        case .before:
            self.messages.append(contentsOf: messages)

        case .after:
            self.messages.insert(contentsOf: messages, at: 0)
        }

        Task {
            await processAttachments(messages)
        }
    }

    func processAttachments(_ messages: [Message]) async {
        // load attachment here
        print(messages.count)
    }
}