import Foundation

import Network

final class ServiceChecker {
    static let statusDidChangeNotification = Notification.Name("ServiceChecker.statusDidChange")
    static let forceRefreshNotification = Notification.Name("ServiceChecker.forceRefresh")

    private let queue = DispatchQueue(label: "prole.status.checker")
    private var timer: DispatchSourceTimer?

    // Public reachability flags
    private(set) var svcReachable = false
    private(set) var raspberryReachable = false
    private(set) var piReachable = false
    private(set) var localReachable = false

    // Latency measurements (ms)
    private(set) var svcLatency: Int = -1
    private(set) var raspberryLatency: Int = -1
    private(set) var piLatency: Int = -1
    private(set) var localLatency: Int = -1

    // Last error messages (for tooltips when red)
    private(set) var svcError: String? = nil
    private(set) var raspberryError: String? = nil
    private(set) var piError: String? = nil
    private(set) var localError: String? = nil

    init() {
        NotificationCenter.default.addObserver(self, selector: #selector(forceRefresh), name: Self.forceRefreshNotification, object: nil)
    }

    func start(interval: TimeInterval = 15) {
        timer?.cancel()
        let t = DispatchSource.makeTimerSource(queue: queue)
        t.schedule(deadline: .now(), repeating: interval)
        t.setEventHandler { [weak self] in self?.refreshAll() }
        dlog("ServiceChecker: starting timer, interval=\(interval)s")
        t.resume()
        timer = t
    }

    @objc private func forceRefresh() { queue.async { self.refreshAll() } }

    private func refreshAll() {
        dlog("ServiceChecker: begin refresh round")
        let group = DispatchGroup()

        // clear previous errors before a new round
        svcError = nil; raspberryError = nil; piError = nil; localError = nil

        let cfg = Config.shared
        group.enter(); tcpPing(host: cfg.svcHost, port: UInt16(cfg.svcPort)) { [weak self] ok, ms, err in
            self?.svcReachable = ok; self?.svcLatency = ms; self?.svcError = err; group.leave()
        }
        group.enter(); tcpPing(host: cfg.retropieHost, port: UInt16(cfg.retropiePort)) { [weak self] ok, ms, err in
            self?.raspberryReachable = ok; self?.raspberryLatency = ms; self?.raspberryError = err; group.leave()
        }
        group.enter(); tcpPing(host: cfg.localHost, port: UInt16(cfg.localPort)) { [weak self] ok, ms, err in
            self?.localReachable = ok; self?.localLatency = ms; self?.localError = err; group.leave()
        }

        group.notify(queue: .main) {
            dlog("ServiceChecker: refresh round complete → posting statusDidChangeNotification")
            NotificationCenter.default.post(name: Self.statusDidChangeNotification, object: self)
        }
    }

    private func tcpPing(host: String, port: UInt16, timeout: TimeInterval = 2.0, completion: @escaping (Bool, Int, String?) -> Void) {
        dlog("tcpPing: attempting \(host):\(port) timeout=\(timeout)s")
        let start = DispatchTime.now()
        let params = NWParameters.tcp
        params.allowLocalEndpointReuse = true
        let endpoint = NWEndpoint.hostPort(host: .name(host, nil), port: .init(integerLiteral: port))
        let conn = NWConnection(to: endpoint, using: params)

        // Ensure completion is invoked exactly once
        var finished = false
        func finishOnce(_ ok: Bool, _ ms: Int, _ err: String?, reason: String) {
            // All state updates and timeout run on `queue` so this is serialized
            if finished { return }
            finished = true
            dlog("tcpPing: finishOnce(\(host):\(port)) reason=\(reason) ok=\(ok) ms=\(ms) err=\(err ?? "nil")")
            completion(ok, ms, err)
        }

        // Prepare timeout work item so we can cancel it on success/failure
        let timeoutWork = DispatchWorkItem { [weak conn] in
            if finished { return }
            dlog("tcpPing: timeout reached for \(host):\(port); cancelling connection")
            conn?.cancel()
            finishOnce(false, -1, "connection timed out", reason: "timeout")
        }

        conn.stateUpdateHandler = { state in
            switch state {
            case .ready:
                let elapsed = DispatchTime.now().uptimeNanoseconds - start.uptimeNanoseconds
                let ms = Int(Double(elapsed) / 1_000_000.0)
                dlog("tcpPing: READY \(host):\(port) in \(ms) ms")
                timeoutWork.cancel()
                finishOnce(true, ms, nil, reason: "ready")
                conn.cancel() // will emit .cancelled; ignored due to finished=true
            case .failed(let error):
                let msg = Self.describeNWError(error)
                dlog("tcpPing: FAILED \(host):\(port) — \(msg)")
                timeoutWork.cancel()
                finishOnce(false, -1, msg, reason: "failed")
                conn.cancel()
            case .cancelled:
                // If we already finished (e.g., due to .ready), this is expected; ignore.
                if finished {
                    dlog("tcpPing: CANCELLED \(host):\(port) after finish — ignoring")
                } else {
                    // Cancel without prior .ready/.failed implies timeout or external cancel
                    finishOnce(false, -1, "connection cancelled (possible timeout)", reason: "cancelled-before-finish")
                }
            default:
                break
            }
        }
        conn.start(queue: queue)
        // Schedule timeout on the same queue
        queue.asyncAfter(deadline: .now() + timeout, execute: timeoutWork)
    }

    // Tooltips
    func tooltipForSvc() -> String {
        let host = Config.shared.svcHost
        let port = Config.shared.svcPort
        if svcReachable { return "\(host):\(port)  —  reachable (\(svcLatency) ms)" }
        var s = "\(host):\(port)  —  unreachable"
        if let e = svcError { s += "\nError: \(e)" }
        return s
    }
    func tooltipForAggregateK3s() -> String {
        let rHost = Config.shared.retropieHost
        var r = raspberryReachable ? "\(rHost) ✓ (\(raspberryLatency) ms)" : "\(rHost) ✗"
        var p = piReachable ? "\(pHost) ✓ (\(piLatency) ms)" : "\(pHost) ✗"
        if !raspberryReachable, let e = raspberryError { r += " — \(e)" }
        if !piReachable, let e = piError { p += " — \(e)" }
        let overall: String
        switch (raspberryReachable, piReachable) {
        case (true, true): overall = "overall: green"
        case (true, false), (false, true): overall = "overall: yellow"
        default: overall = "overall: red"
        }
        return "k3s aggregate — \(overall)\n\(r)\n\(p)"
    }
    func tooltipForLocal() -> String {
        let host = Config.shared.localHost
        let port = Config.shared.localPort
        if localReachable { return "k3d \(host):\(port)  —  reachable (\(localLatency) ms)" }
        var s = "k3d \(host):\(port)  —  unreachable"
        if let e = localError { s += "\nError: \(e)" }
        return s
    }

    private static func describeNWError(_ error: NWError) -> String {
        switch error {
        case .posix(let code): return "POSIX \(code.rawValue): \(code)"
        case .dns(let code): return "DNS \(code): \(code)"
        case .tls(let status): return "TLS/OSStatus \(status)"
        case .wifiAware(let reason): return "Wi-Fi Aware: \(reason)"
        @unknown default: return "Unknown network error"
        }
    }
}