Musubi/Packages/MusubiKit/Sources/Remote/NodeBrowser.swift

import Foundation
import MusubiCore
import Network
import Observation
import OSLog

/// Control side: finds nodes via Bonjour and keeps a connection to each of them.
@MainActor @Observable
public final class NodeBrowser {
    @MainActor @Observable
    public final class Node: Identifiable {
        public nonisolated let id: String // Bonjour service name = node name
        public fileprivate(set) var isConnected = false
        public fileprivate(set) var status: NodeStatus?
        fileprivate var link: Link?
        fileprivate var endpoint: NWEndpoint?
        fileprivate var retryTask: Task<Void, Never>?

        init(name: String) { id = name }

        public var name: String { id }

        public func send(_ message: RemoteMessage) {
            link?.send(message)
        }
    }

    public private(set) var nodes: [Node] = []
    public private(set) var error: String?

    /// A node said hello (first contact or after a reconnect).
    public var onNodeConnected: ((Node) -> Void)?

    private let name: String
    private var browser: NWBrowser?
    private var interface: NWInterface?
    private let queue = DispatchQueue(label: "studio.zielke.musubi.remote.control")
    private let log = Logger(subsystem: "studio.zielke.musubi", category: "remote")

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

    public func start(interfaceName: String) async {
        stop()
        guard let interface = await NetworkInterfaces.interface(named: interfaceName) else {
            error = "Technik-Schnittstelle \(interfaceName) nicht gefunden."
            return
        }
        self.interface = interface
        let browser = NWBrowser(for: .bonjour(type: RemoteProtocol.serviceType, domain: nil), using: .musubi(interface: interface))
        browser.browseResultsChangedHandler = { [weak self] results, _ in
            let found = results.compactMap { result -> (String, NWEndpoint)? in
                guard case .service(let name, _, _, _) = result.endpoint else { return nil }
                return (name, result.endpoint)
            }
            Task { @MainActor in self?.update(found) }
        }
        browser.stateUpdateHandler = { [weak self] state in
            if case .failed(let failure) = state {
                Task { @MainActor in self?.error = "Knotensuche gestört: \(failure.localizedDescription)" }
            }
        }
        browser.start(queue: queue)
        self.browser = browser
        error = nil
        log.info("Control: browsing on \(interfaceName, privacy: .public)")
    }

    public func stop() {
        browser?.cancel()
        browser = nil
        for node in nodes {
            node.retryTask?.cancel()
            node.link?.cancel()
        }
        nodes = []
    }

    public func node(named name: String) -> Node? {
        nodes.first { $0.id == name }
    }

    private func update(_ found: [(String, NWEndpoint)]) {
        for (name, endpoint) in found where name != self.name {
            let node = self.node(named: name) ?? {
                let node = Node(name: name)
                nodes.append(node)
                nodes.sort { $0.id.localizedStandardCompare($1.id) == .orderedAscending }
                return node
            }()
            node.endpoint = endpoint
            if node.link == nil { connect(node) }
        }
        // Nodes that vanished from Bonjour stay listed while connected; the connection decides.
    }

    private func connect(_ node: Node) {
        guard let endpoint = node.endpoint else { return }
        node.retryTask?.cancel()
        let link = Link(connection: NWConnection(to: endpoint, using: .musubi(interface: interface)), queue: queue)
        link.onMessage = { [weak self, weak node] message in
            guard let self, let node, node.link === link else { return }
            received(message, from: node)
        }
        link.onState = { [weak self, weak node] state in
            guard let self, let node, node.link === link else { return }
            switch state {
            case .ready:
                link.send(.hello(name: self.name, role: .control, version: RemoteProtocol.version))
            case .failed, .cancelled:
                if node.isConnected { log.notice("Control: lost \(node.id, privacy: .public)") }
                node.isConnected = false
                node.link = nil
                scheduleRetry(node)
            case .waiting:
                link.cancel()
            default:
                break
            }
        }
        node.link = link
        link.start()
    }

    private func scheduleRetry(_ node: Node) {
        node.retryTask = Task { [weak self, weak node] in
            try? await Task.sleep(for: .seconds(3))
            guard !Task.isCancelled, let self, let node, node.link == nil else { return }
            connect(node)
        }
    }

    private func received(_ message: RemoteMessage, from node: Node) {
        switch message {
        case .hello(let name, let role, _):
            guard role == .node else { return }
            node.isConnected = true
            log.info("Control: connected to \(name, privacy: .public)")
            onNodeConnected?(node)
        case .status(let status):
            node.status = status
        case .apply, .show, .stop:
            break
        }
    }
}