using Org.BouncyCastle.Crypto.Tls;
using Org.BouncyCastle.Security;
using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography.X509Certificates;

namespace AIK.Service.Service
{
    /// <summary>
    /// BouncyCastle 纯托管 TLS 1.2 握手封装，供 HTTP（BouncyCastleTlsHandler）与
    /// WebSocket（BouncyCastleWebSocketClient）共用。完全绕过 Win7 SChannel 对 TLS 1.2 的限制。
    /// </summary>
    internal static class BouncyCastleTlsHelper
    {
        /// <summary>
        /// 在已建立的 TCP 流上执行 BouncyCastle TLS 1.2 握手（含 SNI 与证书链校验），
        /// 返回可读写的 TLS 流。握手为阻塞操作，调用方可在后台线程执行。
        /// </summary>
        public static Stream ConnectTlsStream(Stream innerStream, string host)
        {
            var protocol = new TlsClientProtocol(innerStream, new SecureRandom());
            protocol.Connect(new BouncyTlsClient(host));
            return protocol.Stream;
        }

        /// <summary>
        /// BouncyCastle TLS 1.2 客户端，支持 SNI（server_name 扩展）。
        /// 证书验证：使用 .NET X509Chain 校验，RevocationMode=NoCheck 以兼容 Win7 离线环境。
        /// </summary>
        private sealed class BouncyTlsClient : DefaultTlsClient
        {
            private readonly string _host;

            public BouncyTlsClient(string host)
                : base()
            {
                _host = host;
            }

            public override IDictionary GetClientExtensions()
            {
                var extensions = base.GetClientExtensions() ?? new Hashtable();
                // SNI：多域名虚拟主机（CDN/nginx）必须带 server_name，否则握手被拒
                var serverNames = new ServerNameList(new List<ServerName> { new ServerName(0, _host) });
                TlsExtensionsUtilities.AddServerNameExtension(extensions, serverNames);
                return extensions;
            }

            public override TlsAuthentication GetAuthentication() => new BouncyTlsAuthentication();
        }

        private sealed class BouncyTlsAuthentication : TlsAuthentication
        {
            public void NotifyServerCertificate(Certificate serverCertificate)
            {
                if (serverCertificate == null || serverCertificate.Length == 0)
                {
                    throw new TlsFatalAlert(AlertDescription.bad_certificate);
                }

                // 将 BouncyCastle 证书转为 .NET X509Certificate2 并做链校验
                var chain = new X509Chain { ChainPolicy = { RevocationMode = X509RevocationMode.NoCheck } };
                var certs = new List<X509Certificate2>();
                try
                {
                    for (int i = 0; i < serverCertificate.Length; i++)
                    {
                        certs.Add(new X509Certificate2(serverCertificate.GetCertificateAt(i).GetEncoded()));
                    }
                    foreach (var extra in certs.Skip(1))
                    {
                        chain.ChainPolicy.ExtraStore.Add(extra);
                    }
                    bool valid = chain.Build(certs[0]);
                    if (!valid)
                    {
                        var errors = string.Join("; ", chain.ChainStatus.Select(s => s.StatusInformation.Trim()));
                        throw new TlsFatalAlert(AlertDescription.bad_certificate, new Exception($"证书链校验失败: {errors}"));
                    }
                }
                finally
                {
                    foreach (var c in certs) c.Dispose();
                }
            }

            public TlsCredentials GetClientCredentials(Org.BouncyCastle.Crypto.Tls.CertificateRequest certificateRequest) => null;
        }
    }
}