// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Collections.Generic;
using System.IO.Pipelines;
using System.Linq;
using System.Net;
using System.Net.Security;
using System.Security.Authentication;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Connections;
using Microsoft.AspNetCore.Connections.Features;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Server.Kestrel.Core.Internal;
using Microsoft.AspNetCore.Server.Kestrel.Https.Internal;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Microsoft.AspNetCore.Http2Cat
{
    internal class Http2CatHostedService : IHostedService
    {
        private readonly IConnectionFactory _connectionFactory;
        private readonly ILogger<Http2CatHostedService> _logger;
        private readonly CancellationTokenSource _stopTokenSource = new CancellationTokenSource();
        private Task _backgroundTask;

        public Http2CatHostedService(IConnectionFactory connectionFactory, ILogger<Http2CatHostedService> logger,
            IOptions<Http2CatOptions> options, IHostApplicationLifetime hostApplicationLifetime)
        {
            _connectionFactory = connectionFactory;
            _logger = logger;
            HostApplicationLifetime = hostApplicationLifetime;
            Options = options.Value;
        }

        public IHostApplicationLifetime HostApplicationLifetime { get; }
        private Http2CatOptions Options { get; }

        public Task StartAsync(CancellationToken cancellationToken)
        {
            _backgroundTask = RunAsync();
            return Task.CompletedTask;
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            _stopTokenSource.Cancel();
            return _backgroundTask;
        }

        private async Task RunAsync()
        {
            try
            {
                var address = BindingAddress.Parse(Options.Url);

                if (!IPAddress.TryParse(address.Host, out var ip))
                {
                    ip = Dns.GetHostEntry(address.Host).AddressList.First();
                }

                var endpoint = new IPEndPoint(ip, address.Port);

                _logger.LogInformation($"Connecting to '{endpoint}'.");

                await using var context = await _connectionFactory.ConnectAsync(endpoint);

                _logger.LogInformation($"Connected to '{endpoint}'.");

                var originalTransport = context.Transport;
                IAsyncDisposable sslState = null;
                if (address.Scheme.Equals("https", StringComparison.OrdinalIgnoreCase))
                {
                    _logger.LogInformation("Starting TLS handshake.");

                    var memoryPool = context.Features.Get<IMemoryPoolFeature>()?.MemoryPool;
                    var inputPipeOptions = new StreamPipeReaderOptions(memoryPool, memoryPool.GetMinimumSegmentSize(), memoryPool.GetMinimumAllocSize(), leaveOpen: true);
                    var outputPipeOptions = new StreamPipeWriterOptions(pool: memoryPool, leaveOpen: true);

                    var sslDuplexPipe = new SslDuplexPipe(context.Transport, inputPipeOptions, outputPipeOptions);
                    var sslStream = sslDuplexPipe.Stream;
                    sslState = sslDuplexPipe;

                    context.Transport = sslDuplexPipe;

                    await sslStream.AuthenticateAsClientAsync(new SslClientAuthenticationOptions
                    {
                        TargetHost = address.Host,
                        RemoteCertificateValidationCallback = (_, __, ___, ____) => true,
                        ApplicationProtocols = new List<SslApplicationProtocol> { SslApplicationProtocol.Http2 },
                        EnabledSslProtocols = SslProtocols.Tls12,
                    }, CancellationToken.None);

                    _logger.LogInformation($"TLS handshake completed successfully.");
                }

                var http2Utilities = new Http2Utilities(context, _logger, _stopTokenSource.Token);

                try
                {
                    await Options.Scenaro(http2Utilities);
                }
                catch (Exception ex)
                {
                    _logger.LogError(ex, "App error");
                    throw;
                }
                finally
                {
                    // Unwind Https for shutdown. This must happen before the context goes out of scope or else DisposeAsync will never complete
                    context.Transport = originalTransport;

                    if (sslState != null)
                    {
                        await sslState.DisposeAsync();
                    }
                }
            }
            finally
            {
                HostApplicationLifetime.StopApplication();
            }
        }
    }
}
