using System.Diagnostics.Metrics;
using System.IO;
using System.Net.Http;
using System.Net.Sockets;
using System.Threading;
using System.Threading.Tasks;

/*
    Copyright (c) 2021 ppy Pty Ltd <contact@ppy.sh>.
    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
*/

namespace Jellyfin.Networking.HappyEyeballs
{
    /// <summary>
    /// Defines the <see cref="HttpClientExtension"/> class.
    ///
    /// Implementation taken from https://github.com/ppy/osu-framework/pull/4191 .
    /// </summary>
    public static class HttpClientExtension
    {
        private const int ConnectionEstablishTimeout = 2000;

        /// <summary>
        /// Gets a value indicating whether the initial IPv6 check has been performed (to determine whether v6 is available or not).
        /// </summary>
        private static bool _hasResolvedIPv6Availability;

        /// <summary>
        /// Gets or sets a value indicating whether IPv6 should be preferred. Value may change based on runtime failures.
        /// </summary>
        public static bool? UseIPv6 { get; set; } = null;

        /// <summary>
        /// Implements the httpclient callback method.
        /// </summary>
        /// <param name="context">The <see cref="SocketsHttpConnectionContext"/> instance.</param>
        /// <param name="cancellationToken">The <see cref="CancellationToken"/> instance.</param>
        /// <returns>The http steam.</returns>
        public static async ValueTask<Stream> OnConnect(SocketsHttpConnectionContext context, CancellationToken cancellationToken)
        {
            // Until .NET supports an implementation of Happy Eyeballs (https://tools.ietf.org/html/rfc8305#section-2),
            // let's make IPv4 fallback work in a simple way. This issue is being tracked at https://github.com/dotnet/runtime/issues/26177
            // and expected to be fixed in .NET 6.
            if (UseIPv6 == true)
            {
                try
                {
                    var localToken = cancellationToken;

                    if (!_hasResolvedIPv6Availability)
                    {
                        // to make things move fast, use a very low timeout for the initial ipv6 attempt.
                        using var quickFailCts = new CancellationTokenSource(ConnectionEstablishTimeout);
                        using var linkedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, quickFailCts.Token);

                        localToken = linkedTokenSource.Token;
                    }

                    return await AttemptConnection(AddressFamily.InterNetworkV6, context, localToken).ConfigureAwait(false);
                }
#pragma warning disable CA1031 // Do not catch general exception types
                catch
#pragma warning restore CA1031 // Do not catch general exception types
                {
                    // very naively fallback to ipv4 permanently for this execution based on the response of the first connection attempt.
                    // Network manager will reset this value in the case of physical network changes / interruptions.
                    UseIPv6 = false;
                }
                finally
                {
                    _hasResolvedIPv6Availability = true;
                }
            }

            // fallback to IPv4.
            return await AttemptConnection(AddressFamily.InterNetwork, context, cancellationToken).ConfigureAwait(false);
        }

        private static async ValueTask<Stream> AttemptConnection(AddressFamily addressFamily, SocketsHttpConnectionContext context, CancellationToken cancellationToken)
        {
            // The following socket constructor will create a dual-mode socket on systems where IPV6 is available.
            var socket = new Socket(addressFamily, SocketType.Stream, ProtocolType.Tcp)
            {
                // Turn off Nagle's algorithm since it degrades performance in most HttpClient scenarios.
                NoDelay = true
            };

            try
            {
                await socket.ConnectAsync(context.DnsEndPoint, cancellationToken).ConfigureAwait(false);
                // The stream should take the ownership of the underlying socket,
                // closing it when it's disposed.
                return new NetworkStream(socket, ownsSocket: true);
            }
            catch
            {
                socket.Dispose();
                throw;
            }
        }
    }
}