using System.Formats.Asn1;
using System.IO;
using System.Reflection;
using System.Security.Cryptography.X509Certificates;
using InABox.Clients;
using InABox.Core;
using InABox.IPC;
using InABox.Logging;
using InABox.Rpc;
using PRSServer;

namespace PRSServices;

public interface IEngine
{
    string ServiceName { get; set; }

    string Version { get; set; }
    void Run();
    void Stop();

    void Configure(Server settings);

    PortStatus[] PortStatusList();
}

public abstract class Engine<TProperties> : IEngine where TProperties : ServerProperties
{
    
    private RpcServerPipeTransport _enginemanager;
    
    protected  RpcClientPipeTransport? Transport;

    public TProperties Properties { get; private set; }
    public abstract void Run();
    public abstract void Stop();

    public virtual PortStatus[] PortStatusList()
    {
        return new PortStatus[] { };
    }

    public string ServiceName { get; set; }

    public string Version { get; set; }

    protected string AppDataFolder { get; set; }

    public virtual void Configure(Server server)
    {
        Properties = server.Properties as TProperties;

        AppDataFolder = GetPath(server.Key);
        MainLogger.AddLogger(new LogFileLogger(AppDataFolder));
        MainLogger.AddLogger(new NamedPipeLogger(server.Key));
        
        _enginemanager = new RpcServerPipeTransport($"{ServiceName}M");
        _enginemanager.AddHandler<IEngine, PortStatusCommand, PortStatusParameters, PortStatusResult>(new PortStatusHandler(this));
        _enginemanager.AfterMessage += (transport, args) => MainLogger.Send(LogType.Information,"",$"Engine Manager Message: {args.Message?.Command}", Guid.Empty);
        _enginemanager.Start();
    }

    private bool _connecting = false;

    protected void CheckConnection()
    {
        if (_connecting)
        {
            return;
        }

        _connecting = true;
        // Wait for server connection
        while (_connecting)
        {
            Logger.Send(LogType.Information, "", "Connecting to Database server...");
            if (Client.Ping())
                _connecting = false;
            else
            {
                Logger.Send(LogType.Error, "", "Database server unavailable. Trying again in 30 seconds...");
                Task.Delay(30_000).Wait();
            }
        }
        

        ClientFactory.SetBypass();

        return;
    }

    /// <summary>
    /// Initialise the client to the database server, and set up reconnection loop.
    /// </summary>
    protected void InitialiseConnection(string serverKey, Platform clientPlatform)
    {
        Transport = new RpcClientPipeTransport(DatabaseServerProperties.GetPipeName(serverKey, true));
        ClientFactory.SetClientType(typeof(RpcClient<>), clientPlatform, Version, Transport);
        Transport.OnClose += Transport_OnClose;
        CheckConnection();
    }

    private void Transport_OnClose(IRpcTransport transport, RpcTransportCloseArgs e)
    {
        // Try to reconnect when lost connection.
        Logger.Send(LogType.Error, "", "Database server connection lost.");
        CheckConnection();
    }

    public static string GetPath(string key)
    {
        if (Assembly.GetEntryAssembly() != null)
            return Path.Combine(
                Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
                Path.GetFileNameWithoutExtension(Assembly.GetEntryAssembly().Location),
                key
            );
        return Path.Combine(
            Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
            Path.GetFileNameWithoutExtension(Assembly.GetExecutingAssembly().Location),
            key
        );
    }
    
    public static X509Certificate2? LoadCertificate(string filename)
    {
        if (!String.IsNullOrWhiteSpace(filename))
        {
            Logger.Send(LogType.Information, "", $"Certificate FileName is {filename}");
            if (File.Exists(filename))
            {
                Logger.Send(LogType.Information, "", "Certificate found; verifying HTTPS Certificate");
                try
                {
                    var certificate = new X509Certificate2(filename);
                    if (certificate.NotAfter > DateTime.Now)
                    {
                        
                        var names = GetDnsNames(certificate);
                        Logger.Send(LogType.Information, "", $"Certificate valid for {string.Join(',', names)}");
                        return certificate;
                    }
                    else
                    {
                        Logger.Send(LogType.Error, "", "HTTPS Certificate has expired, using HTTP instead");
                    }
                }
                catch (Exception)
                {
                    Logger.Send(LogType.Error, "", "Error validating HTTPS Certificate, using HTTP instead");
                }
            }
            else
                Logger.Send(LogType.Error, "", "Certificate File does not exist!");
        }
        return null;
    }

    public static IEnumerable<string> GetDnsNames(X509Certificate2 certificate)
    {
        yield return certificate.GetNameInfo(X509NameType.DnsName, false);
        foreach (var name in DnsAlternateNames(certificate))
            yield return name;
    }

    public static IEnumerable<string> DnsAlternateNames(X509Certificate2 certificate)
    {
        // Adapted from https://stackoverflow.com/questions/16698307/how-do-you-parse-the-subject-alternate-names-from-an-x509certificate2/59382929#59382929

        // OID for SubjectAlternativeName X509 extension.
        const string SAN_OID = "2.5.29.17";

        var extension = certificate.Extensions[SAN_OID];
        if (extension is null) yield break;

        // Tag value "2" is defined by:
        //
        //    dNSName                         [2]     IA5String,
        //
        // in: https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.6
        var dnsNameTag = new Asn1Tag(TagClass.ContextSpecific, tagValue: 2, isConstructed: false);

        var asnReader = new AsnReader(extension.RawData, AsnEncodingRules.BER);
        var sequenceReader = asnReader.ReadSequence(Asn1Tag.Sequence);

        while (sequenceReader.HasData)
        {
            var tag = sequenceReader.PeekTag();
            if(tag != dnsNameTag)
            {
                sequenceReader.ReadEncodedValue();
                continue;
            }

            var dnsName = sequenceReader.ReadCharacterString(UniversalTagNumber.IA5String, dnsNameTag);
            yield return dnsName;
        }
    }

}