import Foundation
import MusubiCore
import Network
import Observation
import OSLog

/// Node side: advertises itself via Bonjour on the technical interface and accepts one control at a time.
@MainActor @Observable
public final class NodeServer {
    public private(set) var controlName: String?
    public private(set) var error: String?
    public private(set) var isListening = false

    /// Called for `apply`, `show` and `stop` from the control.
    public var onCommand: ((RemoteMessage) -> Void)?

    private let name: String
    private var interfaceName: String?
    private var retryTask: Task<Void, Never>?
    private var listener: NWListener?
    private var link: Link?
    private let queue = DispatchQueue(label: "studio.zielke.musubi.remote.node")
    private let log = Logger(subsystem: "studio.zielke.musubi", category: "remote")

    public init(name: String) {
        self.name = name
    }

    public func start(interfaceName: String) async {
        stop()
        self.interfaceName = interfaceName
        guard let interface = await NetworkInterfaces.interface(named: interfaceName) else {
            error = "Technik-Schnittstelle \(interfaceName) nicht gefunden."
            log.error("Node: interface \(interfaceName, privacy: .public) not found")
            scheduleRetry()
            return
        }
        do {
            let listener = try NWListener(using: .musubi(interface: interface))
            listener.service = NWListener.Service(name: name, type: RemoteProtocol.serviceType)
            listener.newConnectionHandler = { [weak self] connection in
                Task { @MainActor in self?.accept(connection) }
            }
            listener.stateUpdateHandler = { [weak self] state in
                Task { @MainActor in self?.listenerChanged(state) }
            }
            listener.start(queue: queue)
            self.listener = listener
            log.info("Node: advertising \(self.name, privacy: .public) on \(interfaceName, privacy: .public)")
        } catch {
            self.error = "Fernsteuerung lässt sich nicht starten."
            log.error("Node: listener failed: \(error.localizedDescription, privacy: .public)")
        }
    }

    public func stop() {
        retryTask?.cancel()
        retryTask = nil
        link?.cancel()
        link = nil
        listener?.cancel()
        listener = nil
        isListening = false
        controlName = nil
    }

    public func send(_ status: NodeStatus) {
        guard controlName != nil else { return }
        link?.send(.status(status))
    }

    private func listenerChanged(_ state: NWListener.State) {
        switch state {
        case .ready:
            isListening = true
            error = nil
        case .failed(let failure):
            isListening = false
            if case .dns(let code) = failure, code == -65555 {
                // kDNSServiceErr_NoAuth: macOS has not (yet) allowed local network access.
                error = "macOS blockiert das lokale Netzwerk. Erlaube Musubi unter Systemeinstellungen › Datenschutz & Sicherheit › Lokales Netzwerk."
            } else {
                error = "Fernsteuerung gestört: \(failure.localizedDescription)"
            }
            log.error("Node: listener failed: \(failure.localizedDescription, privacy: .public)")
            scheduleRetry()
        case .cancelled: isListening = false
        default: break
        }
    }

    /// Tries again every 5 s, e.g. until local network access is granted or the cable is plugged in.
    private func scheduleRetry() {
        retryTask?.cancel()
        retryTask = Task { [weak self] in
            try? await Task.sleep(for: .seconds(5))
            guard !Task.isCancelled, let self, let interfaceName else { return }
            await start(interfaceName: interfaceName)
        }
    }

    /// The newest control wins; the previous connection is closed.
    private func accept(_ connection: NWConnection) {
        link?.cancel()
        controlName = nil
        let link = Link(connection: connection, queue: queue)
        link.onMessage = { [weak self] in self?.received($0, from: link) }
        link.onState = { [weak self] state in
            guard let self, self.link === link else { return }
            switch state {
            case .ready:
                link.send(.hello(name: self.name, role: .node, version: RemoteProtocol.version))
            case .failed, .cancelled:
                log.notice("Node: control \(self.controlName ?? "?", privacy: .public) disconnected")
                self.controlName = nil
                self.link = nil
            default: break
            }
        }
        self.link = link
        link.start()
    }

    private func received(_ message: RemoteMessage, from link: Link) {
        guard self.link === link else { return }
        switch message {
        case .hello(let name, _, _):
            controlName = name
            log.info("Node: controlled by \(name, privacy: .public)")
        case .apply, .show, .stop:
            onCommand?(message)
        case .status:
            break
        }
    }
}