session-ios/SessionMessagingKit/Sending & Receiving/Pollers/GroupPoller.swift

// Copyright © 2022 Rangeproof Pty Ltd. All rights reserved.

import Foundation
import Combine
import GRDB
import SessionSnodeKit
import SessionUtilitiesKit

// MARK: - Cache

public extension Cache {
    static let groupPollers: CacheConfig<GroupPollerCacheType, GroupPollerImmutableCacheType> = Dependencies.create(
        identifier: "groupPollers",
        createInstance: { dependencies in GroupPoller.Cache(using: dependencies) },
        mutableInstance: { $0 },
        immutableInstance: { $0 }
    )
}

// MARK: - GroupPoller

public final class GroupPoller: SwarmPoller {
    private let minPollInterval: Double = 3
    private let maxPollInterval: Double = 30
    
    public static func namespaces(swarmPublicKey: String) -> [SnodeAPI.Namespace] {
        guard (try? SessionId.Prefix(from: swarmPublicKey)) == .group else {
            return [.legacyClosedGroup]
        }
        
        return [
            .groupMessages,
            .configGroupInfo,
            .configGroupMembers,
            .configGroupKeys,
            .revokedRetrievableGroupMessages
        ]
    }

    // MARK: - Abstract Methods

    override public func nextPollDelay() -> TimeInterval {
        // Get the received date of the last message in the thread. If we don't have
        // any messages yet, pick some reasonable fake time interval to use instead
        let lastMessageDate: Date = dependencies[singleton: .storage]
            .read { [pollerDestination] db in
                try Interaction
                    .filter(Interaction.Columns.threadId == pollerDestination.target)
                    .select(.receivedAtTimestampMs)
                    .order(Interaction.Columns.timestampMs.desc)
                    .asRequest(of: Int64.self)
                    .fetchOne(db)
            }
            .map { receivedAtTimestampMs -> Date? in
                guard receivedAtTimestampMs > 0 else { return nil }
                
                return Date(timeIntervalSince1970: TimeInterval(Double(receivedAtTimestampMs) / 1000))
            }
            .defaulting(to: dependencies.dateNow.addingTimeInterval(-5 * 60))
        
        let timeSinceLastMessage: TimeInterval = dependencies.dateNow.timeIntervalSince(lastMessageDate)
        let limit: Double = (12 * 60 * 60)
        let a: TimeInterval = ((maxPollInterval - minPollInterval) / limit)
        let nextPollInterval: TimeInterval = a * min(timeSinceLastMessage, limit) + minPollInterval
        
        return nextPollInterval
    }

    override public func handlePollError(_ error: Error, _ lastError: Error?) -> PollerErrorResponse {
        return .continuePolling
    }
}

// MARK: - GroupPoller Cache

public extension GroupPoller {
    class Cache: GroupPollerCacheType {
        private let dependencies: Dependencies
        private var _pollers: [String: GroupPoller] = [:] // One for each swarm
        
        // MARK: - Initialization
        
        public init(using dependencies: Dependencies) {
            self.dependencies = dependencies
        }
        
        deinit {
            _pollers.forEach { _, poller in poller.stop() }
            _pollers.removeAll()
        }
        
        // MARK: - Functions
        
        public func startAllPollers() {
            // On the group poller queue fetch all closed groups which should poll and start the pollers
            Threading.groupPollerQueue.async(using: dependencies) { [dependencies] in
                dependencies[singleton: .storage]
                    .read { db -> Set<String> in
                        try ClosedGroup
                            .select(.threadId)
                            .filter(ClosedGroup.Columns.shouldPoll == true)
                            .asRequest(of: String.self)
                            .fetchSet(db)
                    }?
                    .forEach { [weak self] swarmPublicKey in
                        // If legacy groups have been deprecated then don't start pollers for them
                        guard
                            !dependencies[feature: .legacyGroupsDeprecated] ||
                            (try? SessionId.Prefix(from: swarmPublicKey)) != .standard
                        else { return }
                        
                        self?.getOrCreatePoller(for: swarmPublicKey).startIfNeeded()
                    }
            }
        }
        
        @discardableResult public func getOrCreatePoller(for swarmPublicKey: String) -> SwarmPollerType {
            guard let poller: GroupPoller = _pollers[swarmPublicKey.lowercased()] else {
                let poller: GroupPoller = GroupPoller(
                    pollerName: "Closed group poller with public key: \(swarmPublicKey)", // stringlint:ignore
                    pollerQueue: Threading.groupPollerQueue,
                    pollerDestination: .swarm(swarmPublicKey),
                    pollerDrainBehaviour: .alwaysRandom,
                    namespaces: GroupPoller.namespaces(swarmPublicKey: swarmPublicKey),
                    shouldStoreMessages: true,
                    logStartAndStopCalls: false,
                    using: dependencies
                )
                _pollers[swarmPublicKey.lowercased()] = poller
                return poller
            }
            
            return poller
        }
        
        public func stopAndRemovePoller(for swarmPublicKey: String) {
            _pollers[swarmPublicKey.lowercased()]?.stop()
            _pollers[swarmPublicKey.lowercased()] = nil
        }
        
        public func stopAndRemoveAllPollers() {
            _pollers.forEach { _, poller in poller.stop() }
            _pollers.removeAll()
        }
    }
}

// MARK: - GroupPollerCacheType

/// This is a read-only version of the Cache designed to avoid unintentionally mutating the instance in a non-thread-safe way
public protocol GroupPollerImmutableCacheType: ImmutableCacheType {}

public protocol GroupPollerCacheType: GroupPollerImmutableCacheType, MutableCacheType {
    func startAllPollers()
    @discardableResult func getOrCreatePoller(for swarmPublicKey: String) -> SwarmPollerType
    func stopAndRemovePoller(for swarmPublicKey: String)
    func stopAndRemoveAllPollers()
}