using System.Diagnostics.CodeAnalysis;
using System.Net;
using CoreFoundation;
using CoreTelephony;
using SystemConfiguration;

namespace Blahblah.Library.Network;

[SuppressMessage("Interoperability", "CA1416:Validate platform compatibility", Justification = "<Pending>")]
partial class Connectivity
{
    static readonly Lazy<CTCellularData> cellularData = new(() => new CTCellularData());

    static ReachabilityListener? listener;

    private static partial NetworkStatus PlatformGetStatus()
    {
        var restricted = cellularData.Value.RestrictedState == CTCellularDataRestrictedState.Restricted;

        var internetStatus = InternetConnectionStatus();
        if (internetStatus == NetworkStatus.ReachableViaCarrierDataNetwork && !restricted)
        {
            return NetworkStatus.ReachableViaCarrierDataNetwork;
        }
        if (internetStatus == NetworkStatus.ReachableViaWiFiNetwork)
        {
            return NetworkStatus.ReachableViaWiFiNetwork;
        }

        var remoteStatus = RemoteHostStatus();
        if (remoteStatus == NetworkStatus.ReachableViaCarrierDataNetwork && !restricted)
        {
            return NetworkStatus.ReachableViaCarrierDataNetwork;
        }
        if (remoteStatus == NetworkStatus.ReachableViaWiFiNetwork)
        {
            return NetworkStatus.ReachableViaWiFiNetwork;
        }

        return NetworkStatus.NotReachable;
    }

    static NetworkStatus RemoteHostStatus()
    {
        using var remote = new NetworkReachability(hostName);

        if (!remote.TryGetFlags(out var flags))
        {
            return NetworkStatus.NotReachable;
        }

        if (!IsReachableWithoutRequiringConnection(flags))
        {
            return NetworkStatus.NotReachable;
        }

        if ((flags & NetworkReachabilityFlags.IsWWAN) != 0)
        {
            return NetworkStatus.ReachableViaCarrierDataNetwork;
        }

        return NetworkStatus.ReachableViaWiFiNetwork;

    }

    static bool IsReachableWithoutRequiringConnection(NetworkReachabilityFlags flags)
    {
        // Is it reachable with the current network configuration?
        var isReachable = (flags & NetworkReachabilityFlags.Reachable) != 0;

        // Do we need a connection to reach it?
        var noConnectionRequired = (flags & NetworkReachabilityFlags.ConnectionRequired) == 0;

        // Since the network stack will automatically try to get the WAN up,
        // probe that
        if ((flags & NetworkReachabilityFlags.IsWWAN) != 0)
        {
            noConnectionRequired = true;
        }

        return isReachable && noConnectionRequired;
    }

    static NetworkStatus InternetConnectionStatus()
    {
        var status = NetworkStatus.NotReachable;

        var defaultNetworkAvailable = IsNetworkAvailable(out var flags);

        // If the connection is reachable and no connection is required, then assume it's WiFi
        if (defaultNetworkAvailable)
        {
            status = NetworkStatus.ReachableViaWiFiNetwork;
        }
        else if ((flags & NetworkReachabilityFlags.IsWWAN) != 0)
        {
            // If it's a WWAN connection..
            status = NetworkStatus.ReachableViaCarrierDataNetwork;
        }

        // If the connection is on-demand or on-traffic and no user intervention
        // is required, then assume WiFi.
        if (((flags & NetworkReachabilityFlags.ConnectionOnDemand) != 0 || (flags & NetworkReachabilityFlags.ConnectionOnTraffic) != 0) &&
             (flags & NetworkReachabilityFlags.InterventionRequired) == 0)
        {
            status = NetworkStatus.ReachableViaWiFiNetwork;
        }

        return status;
    }

    private static bool IsNetworkAvailable(out NetworkReachabilityFlags flags)
    {
        var ip = new IPAddress(0);
        using var route = new NetworkReachability(ip);

        if (!route.TryGetFlags(out flags))
        {
            return false;
        }

        return IsReachableWithoutRequiringConnection(flags);
    }

    private static partial void StartListeners()
    {
        StopListeners();

        listener = new ReachabilityListener();
        listener.ReachabilityChanged += OnConnectivityChanged;
    }

    private static partial void StopListeners()
    {
        if (listener == null)
        {
            return;
        }
        listener.ReachabilityChanged -= OnConnectivityChanged;
        listener.Dispose();
        listener = null;
    }

    class ReachabilityListener : IDisposable
    {
        NetworkReachability? routeReachability;
        NetworkReachability? remoteReachability;

        public event Action? ReachabilityChanged;

        public ReachabilityListener()
        {
            var ip = new IPAddress(0);
            routeReachability = new NetworkReachability(ip);
            routeReachability.SetNotification(OnChange);
            routeReachability.Schedule(CFRunLoop.Main, CFRunLoop.ModeDefault);

            remoteReachability = new NetworkReachability(hostName);

            // Need to probe before we queue, or we wont get any meaningful values
            // this only happens when you create NetworkReachability from a hostname
            remoteReachability.TryGetFlags(out var flags);

            remoteReachability.SetNotification(OnChange);
            remoteReachability.Schedule(CFRunLoop.Main, CFRunLoop.ModeDefault);

            cellularData.Value.RestrictionDidUpdateNotifier = new(OnRestrictedStateChanged);
        }

        public void Dispose()
        {
            routeReachability?.Dispose();
            routeReachability = null;
            remoteReachability?.Dispose();
            remoteReachability = null;

            cellularData.Value.RestrictionDidUpdateNotifier = null;
        }

        void OnRestrictedStateChanged(CTCellularDataRestrictedState state)
        {
            ReachabilityChanged?.Invoke();
        }

        async void OnChange(NetworkReachabilityFlags flags)
        {
            // Add in artificial delay so the connection status has time to change
            // else it will return true no matter what.
            await Task.Delay(100);

            ReachabilityChanged?.Invoke();
        }
    }
}