using GenHTTP.Api.Content;
using GenHTTP.Api.Infrastructure;
using GenHTTP.Api.Protocol;
using GenHTTP.Engine;
using GenHTTP.Modules.Practices;
using InABox.API;
using InABox.Core;
using NPOI.SS.Formula.Functions;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Linq;
using System.Net;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Threading.Tasks;
using System.Timers;
using Timer = System.Timers.Timer;

namespace PRSServices;

public abstract class Handler<TProperties> : IHandler
{
    public IHandler Parent { get; set; }

    public abstract void Init(TProperties properties);

    public IAsyncEnumerable<ContentElement> GetContentAsync(IRequest request)
    {
        throw new NotImplementedException();
    }

    public abstract ValueTask<IResponse?> HandleAsync(IRequest request);

    public ValueTask PrepareAsync()
    {
        return new ValueTask();
    }

    public IEnumerable<ContentElement> GetContent(IRequest request)
    {
        return Enumerable.Empty<ContentElement>();
    }
}

public class HandlerBuilder<THandler, TProperties> : IHandlerBuilder<HandlerBuilder<THandler, TProperties>> 
    where THandler : Handler<TProperties>, new()
{
    private readonly List<IConcernBuilder> _Concerns = new();

    public HandlerBuilder(TProperties properties)
    {
        Properties = properties;
    }

    private TProperties Properties;

    public HandlerBuilder<THandler, TProperties> Add(IConcernBuilder concern)
    {
        _Concerns.Add(concern);
        return this;
    }

    public IHandler Build(IHandler parent)
    {
        return Concerns.Chain(parent, _Concerns, p => {
            var handler = new THandler { Parent = p };
            handler.Init(Properties);
            return handler;
        });
    }
}

public class Listener<THandler, TProperties> 
    where THandler : Handler<TProperties>, new()
    where TProperties : notnull
{
    private X509Certificate2? certificate;

    private Timer? CertificateRefreshTimer;
    private Timer? CertificateHaltTimer;
    private string? CertificateFile;
    private ushort Port;

    private IServerHost host;
    private TProperties Properties;

    public Listener(TProperties properties)
    {
        Init(properties);
    }

    [MemberNotNull("host", "Properties")]
    public void Init(TProperties properties)
    {
        Properties = properties;
        host = Host.Create()
            .Console()
            .Handler(new HandlerBuilder<THandler, TProperties>(properties))
            .Defaults();
    }

    public void InitCertificate(ushort port, X509Certificate2 certificate)
    {
        this.certificate = certificate;
        host.Bind(IPAddress.Any, port, certificate);
    }

    public void InitPort(ushort port)
    {
        Port = port;
        host.Bind(IPAddress.Any, port);
    }

    public void InitHTTPS(ushort port, string certificateFile)
    {
        Port = port;

        var useHTTP = true;
        if (File.Exists(certificateFile))
        {
            Logger.Send(LogType.Information, "", "Certificate found; verifying HTTPS Certificate");
            try
            {
                var certificate = new X509Certificate2(certificateFile);
                if (certificate.NotAfter > DateTime.Now)
                {
                    var names = certificate.GetNameInfo(X509NameType.DnsName, false);
                    Logger.Send(LogType.Information, "", $"Certificate valid for {names}");

                    CertificateFile = certificateFile;
                    InitCertificate(port, certificate);
                    useHTTP = false;
                }
                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");
            }
        }
        if (useHTTP)
        {
            InitPort(port);
        }
        else
        {
            if (CertificateRefreshTimer == null)
            {
                CertificateRefreshTimer = new Timer(1000 * 60 * 60 * 24);
                CertificateRefreshTimer.Elapsed += CertificateTimer_Elapsed;
                CertificateRefreshTimer.AutoReset = true;
            }
            CertificateRefreshTimer.Start();
        }
    }

    public void Start()
    {
        host.Start();
    }

    public void Stop()
    {
        host.Stop();
    }
    private void Restart()
    {
        Clear();
        Init(Properties);
        if(CertificateFile != null)
        {
            InitHTTPS(Port, CertificateFile);
        }
        else
        {
            InitPort(Port);
        }
        Start();
    }

    /// <summary>
    /// Clears certificate and host information, and stops the listener.
    /// </summary>
    private void Clear()
    {
        host?.Stop();
        certificate = null;
    }

    #region Certificate Management

    private void CertificateTimer_Elapsed(object? sender, ElapsedEventArgs e)
    {
        if (certificate != null)
        {
            X509Certificate2? cert = null;
            if (File.Exists(CertificateFile))
            {
                cert = new X509Certificate2(CertificateFile);
            }

            if (cert != null && cert.NotAfter > certificate.NotAfter && cert.NotAfter > DateTime.Now)
            {
                Logger.Send(LogType.Information, "", "HTTPS Certificate with greater expiry date found; restarting HTTPS listener...");
                Restart();
            }

            var expiry = certificate.NotAfter;
            var untilExpiry = expiry - DateTime.Now;
            if (untilExpiry.TotalDays <= 7)
            {
                SendCertificateExpiryNotification(expiry);
                if (untilExpiry.TotalDays <= 1)
                {
                    CertificateRefreshTimer?.Stop();

                    CertificateHaltTimer = new Timer(untilExpiry.TotalMilliseconds);
                    CertificateHaltTimer.Elapsed += HTTPS_Halt_Elapsed;
                    CertificateHaltTimer.AutoReset = false;
                    CertificateHaltTimer.Start();
                }
            }
        }
    }

    private void SendCertificateExpiryNotification(DateTime expiry)
    {
        string message;
        if (expiry.Date == DateTime.Now.Date)
        {
            message = $"HTTPS Certificate will expire today at {expiry.TimeOfDay:hh\\:mm}";
        }
        else
        {
            message = $"HTTPS Certificate will expire in {(expiry - DateTime.Now).Days} at {expiry:dd/MM/yyyy hh:mm}";
        }
        Logger.Send(LogType.Information, "", message);
    }

    /// <summary>
    /// Restarts listener in HTTP mode
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void HTTPS_Halt_Elapsed(object? sender, ElapsedEventArgs e)
    {
        CertificateHaltTimer?.Dispose();
        CertificateHaltTimer = null;

        Logger.Send(LogType.Information, "", "Expiry of certificate reached; restarting HTTPS listener...");
        Restart();
    }

    #endregion
}