another.im-ios/AnotherIM/xmpp/XMPPClient.swift

import Foundation

// MARK: Events
enum Event {
    case startClientLogin(jid: JID, credsId: UUID)

    case resolveDomain
    case domainResolved([SRVRecord])
    case domainResolvingError(SRVResolverError)

    case tryConnect
    case socketConnected(SocketType)
    case socketDisconnected
    case socketError(Error)
    case socketReceived(Data)
    case allRecordsUnreachable

    case startStream
    case streamStarted(args: [String: String])
    case streamEnded
    case parserError(Error)

    case xmlInbound(XMLElement)
    case xmlOutbound(XMLElement)

    case startTls
    case startTlsDone
    case startTlsFailed(Error)

    case gotAuthError(AuthorizationError)
    case startAuth(XMLElement)
    case challengeAuth(XMLElement)
    case authDone(sasl: SaslType, args: [String: String])

    case stanzaInbound(Stanza)
    case stanzaOutbound(Stanza)

    case bindStream
    case bindStreamDone(String)
    case bindStreamError

    // stream established, RFC-6120 procedure done
    case streamReady

    case requestRoster
    // case gotRoster // by request or by server push
}

// MARK: State
struct ClientState: Codable & Equatable {
    var jid: JID
    var credentialsId: UUID
    var userAgent: UserAgent
    var sessionState: SessionState
    var srvRecords: [SRVRecord]
    var srvRecordIndex: Int
    var socketType: SocketType
    var isSocketSecured: Bool
    var streamId: String

    // for allow self-signed or expired certificates
    // not secure, but sometimes needed
    var allowInsecure: Bool
    var allowPlainAuth: Bool

    var authorizationStep: AuthorizationStep
    var isStreamBound: Bool

    static var initial: ClientState {
        // swiftlint:disable:next force_try
        let initJid = try! JID("need@initiali.ze")

        return .init(
            jid: initJid,
            credentialsId: UUID(),
            userAgent: .init(uuid: "", software: "", device: ""),
            sessionState: .waitingSRVRecords,
            srvRecords: [],
            srvRecordIndex: -1,
            socketType: .startTls,
            isSocketSecured: false,
            streamId: "",
            allowInsecure: false,
            allowPlainAuth: false,
            authorizationStep: .notAuthorized,
            isStreamBound: false
        )
    }
}

// MARK: Client
final class XMPPClient {
    private var state = ClientState.initial
    private let logger = ClientLogger()
    private let storage: XMPPClientStorageProtocol
    private lazy var modules: [any XmppModule] = [
        SRVResolverModule(),
        ConnectionModule(self.fire),
        ParserModule(self.fire),
        SessionModule(),
        AuthorizationModule(self.storage),
        StanzaModule(self.storage),
        DiscoveryModule(),
        RosterModule()
    ]

    init(storage: any XMPPClientStorageProtocol, userAgent: UserAgent) {
        self.storage = storage
        state.userAgent = userAgent
    }

    func tryLogin(jid: JID, credentialsId: UUID) {
        logger.update(jid.full)
        Task {
            await fire(.startClientLogin(jid: jid, credsId: credentialsId))
        }
    }
}

// MARK: Private part
private extension XMPPClient {
    private func fire(_ event: Event) async {
        // log
        logger.logEvent(event)

        // apply reducing
        let newState = modules.reduce(state) { result, next in
            next.reduce(oldState: result, with: event)
        }
        logger.logState(state, newState)
        state = newState

        // apply side effects
        await withTaskGroup(of: Event?.self) { [state] group in
            for mod in modules {
                group.addTask { await mod.process(state: state, with: event) }
            }

            for await case let nextEvent? in group {
                await fire(nextEvent)
            }
        }
    }
}