using System.Net;
using System.Net.Security;
using System.Net.Sockets;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using Microsoft.Extensions.Logging.Abstractions;
using NATS.Server;
using NATS.Server.Protocol;
using NATS.Server.TestUtilities;
using NATS.Server.Tls;

namespace NATS.Server.Transport.Tests;

public class TlsConnectionWrapperTests
{
    [Fact]
    public async Task NoTls_returns_plain_stream()
    {
        var (serverSocket, clientSocket) = await CreateSocketPairAsync();
        using var serverStream = new NetworkStream(serverSocket, ownsSocket: true);
        using var clientStream = new NetworkStream(clientSocket, ownsSocket: true);

        var opts = new NatsOptions(); // No TLS configured
        var serverInfo = CreateServerInfo();

        var (stream, infoSent) = await TlsConnectionWrapper.NegotiateAsync(
            serverSocket, serverStream, opts, null, serverInfo, NullLogger.Instance, CancellationToken.None);

        stream.ShouldBe(serverStream); // Same stream, no wrapping
        infoSent.ShouldBeFalse();
    }

    [Fact]
    public async Task TlsRequired_upgrades_to_ssl()
    {
        var (cert, _) = TestCertHelper.GenerateTestCert();

        var (serverSocket, clientSocket) = await CreateSocketPairAsync();
        using var clientNetStream = new NetworkStream(clientSocket, ownsSocket: true);

        var opts = new NatsOptions { TlsCert = "dummy", TlsKey = "dummy" };
        var sslOpts = new SslServerAuthenticationOptions
        {
            ServerCertificate = cert,
        };
        var serverInfo = CreateServerInfo();

        // Client side: read INFO then start TLS
        var clientTask = Task.Run(async () =>
        {
            // Read INFO line
            var buf = new byte[4096];
            var read = await clientNetStream.ReadAsync(buf);
            var info = System.Text.Encoding.ASCII.GetString(buf, 0, read);
            info.ShouldStartWith("INFO ");

            // Upgrade to TLS
            var sslClient = new SslStream(clientNetStream, true,
                (_, _, _, _) => true); // Trust all for testing
            await sslClient.AuthenticateAsClientAsync("localhost");
            return sslClient;
        });

        var serverNetStream = new NetworkStream(serverSocket, ownsSocket: true);
        var (stream, infoSent) = await TlsConnectionWrapper.NegotiateAsync(
            serverSocket, serverNetStream, opts, sslOpts, serverInfo, NullLogger.Instance, CancellationToken.None);

        stream.ShouldBeOfType<SslStream>();
        infoSent.ShouldBeTrue();

        var clientSsl = await clientTask;

        // Verify encrypted communication works
        await stream.WriteAsync("PING\r\n"u8.ToArray());
        await stream.FlushAsync();

        var readBuf = new byte[64];
        var bytesRead = await clientSsl.ReadAsync(readBuf);
        var msg = System.Text.Encoding.ASCII.GetString(readBuf, 0, bytesRead);
        msg.ShouldBe("PING\r\n");

        stream.Dispose();
        clientSsl.Dispose();
    }

    [Fact]
    public async Task MixedMode_allows_plaintext_when_AllowNonTls()
    {
        var (cert, _) = TestCertHelper.GenerateTestCert();

        var (serverSocket, clientSocket) = await CreateSocketPairAsync();
        using var clientNetStream = new NetworkStream(clientSocket, ownsSocket: true);

        var opts = new NatsOptions
        {
            TlsCert = "dummy",
            TlsKey = "dummy",
            AllowNonTls = true,
            TlsTimeout = TimeSpan.FromSeconds(2),
        };
        var sslOpts = new SslServerAuthenticationOptions
        {
            ServerCertificate = cert,
        };
        var serverInfo = CreateServerInfo();

        // Client side: read INFO then send plaintext (not TLS)
        var clientTask = Task.Run(async () =>
        {
            var buf = new byte[4096];
            var read = await clientNetStream.ReadAsync(buf);
            var info = System.Text.Encoding.ASCII.GetString(buf, 0, read);
            info.ShouldStartWith("INFO ");

            // Send plaintext CONNECT (not a TLS handshake)
            var connectLine = System.Text.Encoding.ASCII.GetBytes("CONNECT {}\r\n");
            await clientNetStream.WriteAsync(connectLine);
            await clientNetStream.FlushAsync();
        });

        var serverNetStream = new NetworkStream(serverSocket, ownsSocket: true);
        var (stream, infoSent) = await TlsConnectionWrapper.NegotiateAsync(
            serverSocket, serverNetStream, opts, sslOpts, serverInfo, NullLogger.Instance, CancellationToken.None);

        await clientTask;

        // In mixed mode with plaintext client, we get a PeekableStream, not SslStream
        stream.ShouldBeOfType<PeekableStream>();
        infoSent.ShouldBeTrue();

        stream.Dispose();
    }

    [Fact]
    public async Task TlsRequired_rejects_plaintext()
    {
        var (cert, _) = TestCertHelper.GenerateTestCert();

        var (serverSocket, clientSocket) = await CreateSocketPairAsync();
        using var clientNetStream = new NetworkStream(clientSocket, ownsSocket: true);

        var opts = new NatsOptions
        {
            TlsCert = "dummy",
            TlsKey = "dummy",
            AllowNonTls = false,
            TlsTimeout = TimeSpan.FromSeconds(2),
        };
        var sslOpts = new SslServerAuthenticationOptions
        {
            ServerCertificate = cert,
        };
        var serverInfo = CreateServerInfo();

        // Client side: read INFO then send plaintext
        var clientTask = Task.Run(async () =>
        {
            var buf = new byte[4096];
            var read = await clientNetStream.ReadAsync(buf);
            var info = System.Text.Encoding.ASCII.GetString(buf, 0, read);
            info.ShouldStartWith("INFO ");

            // Send plaintext data (first byte is 'C', not 0x16 TLS marker)
            var connectLine = System.Text.Encoding.ASCII.GetBytes("CONNECT {}\r\n");
            await clientNetStream.WriteAsync(connectLine);
            await clientNetStream.FlushAsync();
        });

        var serverNetStream = new NetworkStream(serverSocket, ownsSocket: true);

        await Should.ThrowAsync<InvalidOperationException>(async () =>
        {
            await TlsConnectionWrapper.NegotiateAsync(
                serverSocket, serverNetStream, opts, sslOpts, serverInfo, NullLogger.Instance, CancellationToken.None);
        });

        await clientTask;
        serverNetStream.Dispose();
    }

    [Fact]
    public async Task TlsFirst_handshakes_before_sending_info()
    {
        var (cert, _) = TestCertHelper.GenerateTestCert();

        var (serverSocket, clientSocket) = await CreateSocketPairAsync();
        using var clientNetStream = new NetworkStream(clientSocket, ownsSocket: true);

        var opts = new NatsOptions { TlsCert = "dummy", TlsKey = "dummy", TlsHandshakeFirst = true };
        var sslOpts = new SslServerAuthenticationOptions
        {
            ServerCertificate = cert,
        };
        var serverInfo = CreateServerInfo();

        // Client side: immediately start TLS (no INFO first)
        var clientTask = Task.Run(async () =>
        {
            var sslClient = new SslStream(clientNetStream, true, (_, _, _, _) => true);
            await sslClient.AuthenticateAsClientAsync("localhost");

            // After TLS, read INFO over encrypted stream
            var buf = new byte[4096];
            var read = await sslClient.ReadAsync(buf);
            var info = System.Text.Encoding.ASCII.GetString(buf, 0, read);
            info.ShouldStartWith("INFO ");

            return sslClient;
        });

        var serverNetStream = new NetworkStream(serverSocket, ownsSocket: true);
        var (stream, infoSent) = await TlsConnectionWrapper.NegotiateAsync(
            serverSocket, serverNetStream, opts, sslOpts, serverInfo, NullLogger.Instance, CancellationToken.None);

        stream.ShouldBeOfType<SslStream>();
        infoSent.ShouldBeTrue();

        var clientSsl = await clientTask;

        // Verify encrypted communication works
        await stream.WriteAsync("PING\r\n"u8.ToArray());
        await stream.FlushAsync();

        var readBuf = new byte[64];
        var bytesRead = await clientSsl.ReadAsync(readBuf);
        var msg = System.Text.Encoding.ASCII.GetString(readBuf, 0, bytesRead);
        msg.ShouldBe("PING\r\n");

        stream.Dispose();
        clientSsl.Dispose();
    }

    private static ServerInfo CreateServerInfo() => new()
    {
        ServerId = "TEST",
        ServerName = "test",
        Version = NatsProtocol.Version,
        Host = "127.0.0.1",
        Port = 4222,
    };

    private static async Task<(Socket server, Socket client)> CreateSocketPairAsync()
    {
        using var listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        listener.Bind(new IPEndPoint(IPAddress.Loopback, 0));
        listener.Listen(1);
        var port = ((IPEndPoint)listener.LocalEndPoint!).Port;

        var client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await client.ConnectAsync(new IPEndPoint(IPAddress.Loopback, port));
        var server = await listener.AcceptAsync();

        return (server, client);
    }
}