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

import Combine
import Foundation
import GRDB
import Martin

@MainActor
final class MessagesStore: ObservableObject {
    @Published private(set) var messages: [Message] = []
    @Published var replyText = ""

    private(set) var roster: Roster
    private let client: Client

    private var messagesCancellable: AnyCancellable?
    private let archiver = ArchiveMessageFetcher()

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

// MARK: - Send message
extension MessagesStore {
    func sendMessage(_ message: String) {
        Task {
            var msg = Message.blank
            msg.from = roster.bareJid
            msg.to = roster.contactBareJid
            msg.body = message

            // store as pending on db, and send
            do {
                try await msg.save()
                try await client.sendMessage(msg)
                try await msg.setStatus(.sent)
            } catch {
                try? await msg.setStatus(.error)
            }
        }
    }

    func sendContact(_ jidStr: String) {
        sendMessage("contact:\(jidStr)")
    }

    func sendLocation(_ lat: Double, _ lon: Double) {
        sendMessage("geo:\(lat),\(lon)")
    }
}

// MARK: - Subscriptions
private extension MessagesStore {
    func subscribe() {
        messagesCancellable = ValueObservation.tracking(Message
            .filter(
                (Column("to") == roster.bareJid && Column("from") == roster.contactBareJid) ||
                    (Column("from") == roster.bareJid && Column("to") == roster.contactBareJid)
            )
            .order(Column("date").desc)
            .fetchAll
        )
        .publisher(in: Database.shared.dbQueue, scheduling: .immediate)
        .receive(on: DispatchQueue.main)
        .sink { _ in
        } receiveValue: { [weak self] messages in
            guard let self else { return }
            self.messages = messages
            Task {
                await self.archiver.initialFetch(messages, self.roster, self.client)
            }
        }
    }
}

// MARK: - Archived messages
extension MessagesStore {
    func scrolledMessage(_ messageId: String) {
        if messageId == messages.last?.id {
            Task {
                await archiver.fetchBackward(roster, client)
            }
        } else if messageId == messages.first?.id {
            Task {
                await archiver.fetchForward(roster, client)
            }
        }
    }
}

private actor ArchiveMessageFetcher {
    private var initFetchStarted = false
    private var forwardRsm: RSM.Query?
    private var backwardRsm: RSM.Query?
    private var fetchInProgress = false

    func initialFetch(_ messages: [Message], _ roster: Roster, _ client: Client) async {
        if initFetchStarted { return }
        initFetchStarted = true
        fetchInProgress = true

        do {
            if let firstExistId = messages.first?.id {
                let result = try await client.fetchArchiveMessages(for: roster, query: .init(before: firstExistId, max: Const.mamRequestPageSize))
                result.complete ? forwardRsm = nil : (forwardRsm = .init(after: result.rsm?.last, max: Const.mamRequestPageSize))
                result.complete ? backwardRsm = nil : (backwardRsm = .init(before: result.rsm?.first, max: Const.mamRequestPageSize))
            } else {
                let result = try await client.fetchArchiveMessages(for: roster, query: .init(lastItems: Const.mamRequestPageSize))
                result.complete ? backwardRsm = nil : (backwardRsm = .init(before: result.rsm?.first, max: Const.mamRequestPageSize))
            }
        } catch {
            logIt(.error, "Error requesting archived messages: \(error)")
            initFetchStarted = false
        }

        fetchInProgress = false
    }

    func fetchForward(_ roster: Roster, _ client: Client) async {
        while !initFetchStarted {
            await Task.yield()
        }
        guard let rsm = forwardRsm else { return }
        if fetchInProgress { return }

        fetchInProgress = true
        Task {
            let result = try await client.fetchArchiveMessages(for: roster, query: rsm)
            result.complete ? (forwardRsm = nil) : (forwardRsm = .init(after: result.rsm?.last, max: Const.mamRequestPageSize))
            fetchInProgress = false
        }
    }

    func fetchBackward(_ roster: Roster, _ client: Client) async {
        while !initFetchStarted {
            await Task.yield()
        }
        guard let rsm = backwardRsm else { return }
        if fetchInProgress { return }

        fetchInProgress = true
        Task {
            let result = try await client.fetchArchiveMessages(for: roster, query: rsm)
            result.complete ? (backwardRsm = nil) : (backwardRsm = .init(before: result.rsm?.first, max: Const.mamRequestPageSize))
            fetchInProgress = false
        }
    }
}