class ViewController: UIViewController {

    let networkStatus: UILabel = {
        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.font = UIFont.systemFont(ofSize: 21)
        label.textColor = .black
        label.numberOfLines = 0
        label.sizeToFit()
        label.text ="Status"
        label.textAlignment = .center
        return label
    }()

    let hostNameLabel: UILabel = {
        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.font = UIFont.systemFont(ofSize: 21)
        label.textColor = .black
        label.numberOfLines = 0
        label.sizeToFit()
        label.text ="Host"
        label.textAlignment = .center
        return label
    }()

    var reachability: Reachability?
    let hostNames = [nil,"google.com","invalidhost"]
    var hostIndex = 0

    override func viewDidLoad() {
        super.viewDidLoad()

        setConstraints()
        startHost(at: 0)
    }

    func startHost(at index: Int) {
        stopNotifier()
        setupReachability(hostNames[index], useClosures: true)
        startNotifier()
        DispatchQueue.main.asyncAfter(deadline: .now() + 5) {
            self.startHost(at: (index + 1) % 3)
        }
    }

    func setupReachability(_ hostName: String?, useClosures: Bool) {
        let reachability: Reachability?
        if let hostName = hostName {
            reachability = Reachability(hostname: hostName)
            hostNameLabel.text = hostName
        } else {
            reachability = Reachability()
            hostNameLabel.text ="No host name"
        }
        self.reachability = reachability
        print("--- set up with host name: \\(hostNameLabel.text!)")

        if useClosures {
            reachability?.whenReachable = { reachability in
                self.updateLabelColourWhenReachable(reachability)
            }
            reachability?.whenUnreachable = { reachability in
                self.updateLabelColourWhenNotReachable(reachability)
            }
        } else {
            NotificationCenter.default.addObserver(
                self,
                selector: #selector(reachabilityChanged(_:)),
                name: .reachabilityChanged,
                object: reachability
            )
        }
    }

    func startNotifier() {
        print("--- start notifier")
        do {
            try reachability?.startNotifier()
        } catch {
            networkStatus.textColor = .red
            networkStatus.text ="Unable to start\
notifier"
            return
        }
    }

    func stopNotifier() {
        print("--- stop notifier")
        reachability?.stopNotifier()
        NotificationCenter.default.removeObserver(self, name: .reachabilityChanged, object: nil)
        reachability = nil
    }

    func updateLabelColourWhenReachable(_ reachability: Reachability) {
        print("\\(reachability.description) - \\(reachability.connection)")
        if reachability.connection == .wifi {
            self.networkStatus.textColor = .green
        } else {
            self.networkStatus.textColor = .blue
        }

        self.networkStatus.text ="\\(reachability.connection)"
    }

    func updateLabelColourWhenNotReachable(_ reachability: Reachability) {
        print("\\(reachability.description) - \\(reachability.connection)")

        self.networkStatus.textColor = .red

        self.networkStatus.text ="\\(reachability.connection)"
    }

    @objc func reachabilityChanged(_ note: Notification) {
        let reachability = note.object as! Reachability

        if reachability.connection != .none {
            updateLabelColourWhenReachable(reachability)
        } else {
            updateLabelColourWhenNotReachable(reachability)
        }
    }

    func setConstraints(){
        view.addSubview(networkStatus)
        view.addSubview(hostNameLabel)

        networkStatus.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 8).isActive = true
        networkStatus.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -8).isActive = true
        networkStatus.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true

        hostNameLabel.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 8).isActive = true
        hostNameLabel.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -8).isActive = true
        hostNameLabel.topAnchor.constraint(equalTo: networkStatus.bottomAnchor, constant: 20).isActive = true
    }

    deinit {
        stopNotifier()
    }
}

import SystemConfiguration
import Foundation

public enum ReachabilityError: Error {
    case FailedToCreateWithAddress(sockaddr_in)
    case FailedToCreateWithHostname(String)
    case UnableToSetCallback
    case UnableToSetDispatchQueue
}

@available(*, unavailable, renamed:"Notification.Name.reachabilityChanged")
public let ReachabilityChangedNotification = NSNotification.Name("ReachabilityChangedNotification")

extension Notification.Name {
    public static let reachabilityChanged = Notification.Name("reachabilityChanged")
}

func callback(reachability: SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutableRawPointer?) {
    guard let info = info else { return }

    let reachability = Unmanaged<Reachability>.fromOpaque(info).takeUnretainedValue()
    reachability.reachabilityChanged()
}

public class Reachability {

    public typealias NetworkReachable = (Reachability) -> ()
    public typealias NetworkUnreachable = (Reachability) -> ()

    @available(*, unavailable, renamed:"Connection")
    public enum NetworkStatus: CustomStringConvertible {
        case notReachable, reachableViaWiFi, reachableViaWWAN
        public var description: String {
            switch self {
            case .reachableViaWWAN: return"Cellular"
            case .reachableViaWiFi: return"WiFi"
            case .notReachable: return"No Connection"
            }
        }
    }

    public enum Connection: CustomStringConvertible {
        case none, wifi, cellular
        public var description: String {
            switch self {
            case .cellular: return"Cellular"
            case .wifi: return"WiFi"
            case .none: return"No Connection"
            }
        }
    }

    public var whenReachable: NetworkReachable?
    public var whenUnreachable: NetworkUnreachable?

    @available(*, deprecated: 4.0, renamed:"allowsCellularConnection")
    public let reachableOnWWAN: Bool = true

    /// Set to `false` to force Reachability.connection to .none when on cellular connection (default value `true`)
    public var allowsCellularConnection: Bool

    // The notification center on which"reachability changed" events are being posted
    public var notificationCenter: NotificationCenter = NotificationCenter.default

    @available(*, deprecated: 4.0, renamed:"connection.description")
    public var currentReachabilityString: String {
        return"\\(connection)"
    }

    @available(*, unavailable, renamed:"connection")
    public var currentReachabilityStatus: Connection {
        return connection
    }

    public var connection: Connection {
        guard isReachableFlagSet else { return .none }

        // If we're reachable, but not on an iOS device (i.e. simulator), we must be on WiFi
        guard isRunningOnDevice else { return .wifi }

        var connection = Connection.none

        if !isConnectionRequiredFlagSet {
            connection = .wifi
        }

        if isConnectionOnTrafficOrDemandFlagSet {
            if !isInterventionRequiredFlagSet {
                connection = .wifi
            }
        }

        if isOnWWANFlagSet {
            if !allowsCellularConnection {
                connection = .none
            } else {
                connection = .cellular
            }
        }

        return connection
    }

    fileprivate var previousFlags: SCNetworkReachabilityFlags?

    fileprivate var isRunningOnDevice: Bool = {
        #if targetEnvironment(simulator)
        return false
        #else
        return true
        #endif
    }()

    fileprivate var notifierRunning = false
    fileprivate let reachabilityRef: SCNetworkReachability

    fileprivate let reachabilitySerialQueue = DispatchQueue(label:"uk.co.ashleymills.reachability")

    fileprivate var usingHostname = false

    required public init(reachabilityRef: SCNetworkReachability, usingHostname: Bool = false) {
        allowsCellularConnection = true
        self.reachabilityRef = reachabilityRef
        self.usingHostname = usingHostname
    }

    public convenience init?(hostname: String) {
        guard let ref = SCNetworkReachabilityCreateWithName(nil, hostname) else { return nil }
        self.init(reachabilityRef: ref, usingHostname: true)
    }

    public convenience init?() {
        var zeroAddress = sockaddr()
        zeroAddress.sa_len = UInt8(MemoryLayout<sockaddr>.size)
        zeroAddress.sa_family = sa_family_t(AF_INET)

        guard let ref = SCNetworkReachabilityCreateWithAddress(nil, &zeroAddress) else { return nil }

        self.init(reachabilityRef: ref)
    }

    deinit {
        stopNotifier()
    }
}

public extension Reachability {

    // MARK: - *** Notifier methods ***
    func startNotifier() throws {
        guard !notifierRunning else { return }

        var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
        context.info = UnsafeMutableRawPointer(Unmanaged<Reachability>.passUnretained(self).toOpaque())
        if !SCNetworkReachabilitySetCallback(reachabilityRef, callback, &context) {
            stopNotifier()
            throw ReachabilityError.UnableToSetCallback
        }

        if !SCNetworkReachabilitySetDispatchQueue(reachabilityRef, reachabilitySerialQueue) {
            stopNotifier()
            throw ReachabilityError.UnableToSetDispatchQueue
        }

        // Perform an initial check
        reachabilitySerialQueue.async {
            self.reachabilityChanged()
        }

        notifierRunning = true
    }

    func stopNotifier() {
        defer { notifierRunning = false }

        SCNetworkReachabilitySetCallback(reachabilityRef, nil, nil)
        SCNetworkReachabilitySetDispatchQueue(reachabilityRef, nil)
    }

    // MARK: - *** Connection test methods ***
    @available(*, deprecated: 4.0, message:"Please use `connection != .none`")
    var isReachable: Bool {
        guard isReachableFlagSet else { return false }

        if isConnectionRequiredAndTransientFlagSet {
            return false
        }

        if isRunningOnDevice {
            if isOnWWANFlagSet && !reachableOnWWAN {
                // We don't want to connect when on cellular connection
                return false
            }
        }

        return true
    }

    @available(*, deprecated: 4.0, message:"Please use `connection == .cellular`")
    var isReachableViaWWAN: Bool {
        // Check we're not on the simulator, we're REACHABLE and check we're on WWAN
        return isRunningOnDevice && isReachableFlagSet && isOnWWANFlagSet
    }

    @available(*, deprecated: 4.0, message:"Please use `connection == .wifi`")
    var isReachableViaWiFi: Bool {
        // Check we're reachable
        guard isReachableFlagSet else { return false }

        // If reachable we're reachable, but not on an iOS device (i.e. simulator), we must be on WiFi
        guard isRunningOnDevice else { return true }

        // Check we're NOT on WWAN
        return !isOnWWANFlagSet
    }

    var description: String {
        let W = isRunningOnDevice ? (isOnWWANFlagSet ?"W" :"-") :"X"
        let R = isReachableFlagSet ?"R" :"-"
        let c = isConnectionRequiredFlagSet ?"c" :"-"
        let t = isTransientConnectionFlagSet ?"t" :"-"
        let i = isInterventionRequiredFlagSet ?"i" :"-"
        let C = isConnectionOnTrafficFlagSet ?"C" :"-"
        let D = isConnectionOnDemandFlagSet ?"D" :"-"
        let l = isLocalAddressFlagSet ?"l" :"-"
        let d = isDirectFlagSet ?"d" :"-"

        return"\\(W)\\(R) \\(c)\\(t)\\(i)\\(C)\\(D)\\(l)\\(d)"
    }
}

fileprivate extension Reachability {
    func reachabilityChanged() {
        guard previousFlags != flags else { return }

        let block = connection != .none ? whenReachable : whenUnreachable

        DispatchQueue.main.async {
            if self.usingHostname {
                print("USING HOSTNAME ABOUT TO CALL BLOCK")
            }
            block?(self)
            self.notificationCenter.post(name: .reachabilityChanged, object:self)
        }

        previousFlags = flags
    }

    var isOnWWANFlagSet: Bool {
        #if os(iOS)
        return flags.contains(.isWWAN)
        #else
        return false
        #endif
    }
    var isReachableFlagSet: Bool {
        return flags.contains(.reachable)
    }
    var isConnectionRequiredFlagSet: Bool {
        return flags.contains(.connectionRequired)
    }
    var isInterventionRequiredFlagSet: Bool {
        return flags.contains(.interventionRequired)
    }
    var isConnectionOnTrafficFlagSet: Bool {
        return flags.contains(.connectionOnTraffic)
    }
    var isConnectionOnDemandFlagSet: Bool {
        return flags.contains(.connectionOnDemand)
    }
    var isConnectionOnTrafficOrDemandFlagSet: Bool {
        return !flags.intersection([.connectionOnTraffic, .connectionOnDemand]).isEmpty
    }
    var isTransientConnectionFlagSet: Bool {
        return flags.contains(.transientConnection)
    }
    var isLocalAddressFlagSet: Bool {
        return flags.contains(.isLocalAddress)
    }
    var isDirectFlagSet: Bool {
        return flags.contains(.isDirect)
    }
    var isConnectionRequiredAndTransientFlagSet: Bool {
        return flags.intersection([.connectionRequired, .transientConnection]) == [.connectionRequired, .transientConnection]
    }

    var flags: SCNetworkReachabilityFlags {
        var flags = SCNetworkReachabilityFlags()
        if SCNetworkReachabilityGetFlags(reachabilityRef, &flags) {
            print("Returning flags \\(flags)")
            return flags
        } else {
            return SCNetworkReachabilityFlags()
        }
    }
}

func startHost(at index: Int) {
        stopNotifier()
        setupReachability(hostNames[index], useClosures: true)
        startNotifier()

        // Timer is HERE
        DispatchQueue.main.asyncAfter(deadline: .now() + 5) {
            self.startHost(at: (index + 1) % 3)
        }
    }