using System.Net;
using Makaretu.Dns;

namespace MusicBridge.Agent.Network;

// All lifecycle calls run on the console loop, not on network-change callback threads.
internal sealed class MdnsPublisher(string fingerprint, int port) : IDisposable
{
    private MulticastService? multicast;
    private ServiceDiscovery? discovery;
    private ServiceProfile? profile;
    private string addressesKey = "";
    private DateTimeOffset nextAnnouncement;
    private DateTimeOffset lastRefresh;
    public string Status { get; private set; } = "mDNS: ожидание локальной сети.";

    public static ServiceProfile CreateProfile(string fingerprint, int port, IPAddress[] addresses)
    {
        if (port is < 1 or > 65535 || addresses.Length == 0 || addresses.Any(a => !LocalAddresses.IsEligible(a)))
            throw new ArgumentException("Неверный порт или адрес объявления mDNS.");
        var descriptor = DiscoveryDescriptor.Create(fingerprint);
        var result = new ServiceProfile(descriptor.InstanceName, "_musicbridge._tcp", (ushort)port, addresses);
        foreach (var pair in descriptor.TxtRecords()) result.AddProperty(pair.Key, pair.Value);
        foreach (var record in result.Resources) record.TTL = TimeSpan.FromSeconds(120);
        return result;
    }

    public void Refresh(IPAddress[] addresses)
    {
        try
        {
            // Rebind after a long pause (sleep/resume), even if Windows kept the same IP.
            var now = DateTimeOffset.UtcNow;
            if (lastRefresh != default && (now - lastRefresh > TimeSpan.FromSeconds(20) || now < lastRefresh)) Stop();
            lastRefresh = now;
            var key = string.Join(",", addresses.Select(a => a.ToString()));
            if (discovery is null || key != addressesKey)
            {
                Stop();
                if (addresses.Length == 0) { Status = "mDNS: нет адреса домашней сети."; return; }
                multicast = new MulticastService(nics => nics.Where(nic => nic.GetIPProperties().UnicastAddresses.Any(a => addresses.Contains(a.Address))))
                {
                    UseIpv4 = true, UseIpv6 = false
                };
                profile = CreateProfile(fingerprint, port, addresses);
                discovery = new ServiceDiscovery(multicast);
                discovery.Advertise(profile);
                multicast.Start();
                addressesKey = key;
                nextAnnouncement = DateTimeOffset.MinValue;
            }
            if (DateTimeOffset.UtcNow >= nextAnnouncement)
            {
                var message = new Makaretu.Dns.Message { QR = true, AA = true };
                message.Answers.Add(new PTRRecord
                {
                    Name = profile!.QualifiedServiceName, DomainName = profile.FullyQualifiedName, TTL = TimeSpan.FromSeconds(120)
                });
                foreach (var record in profile.Resources) message.Answers.Add(record);
                multicast!.SendAnswer(message, checkDuplicate: false);
                nextAnnouncement = DateTimeOffset.UtcNow.AddSeconds(30);
            }
            Status = $"mDNS: объявляется {profile!.FullyQualifiedName}";
        }
        catch (Exception ex)
        {
            Stop();
            Status = $"mDNS недоступен: {ex.Message}";
        }
    }

    private void Stop()
    {
        try { if (profile is not null) discovery?.Unadvertise(profile); }
        catch (Exception) { /* Best-effort goodbye when a network has disappeared. */ }
        discovery?.Dispose();
        multicast?.Dispose();
        discovery = null;
        multicast = null;
        profile = null;
        addressesKey = "";
    }

    public void Dispose() => Stop();
}