using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using Grpc.Core;
using Grpc.Net.Client;
using Grpc.Net.Client.Web;

namespace AVEVA.Historian.Client.Grpc;

/// <summary>
/// Builds a <see cref="GrpcChannel"/> for the 2023 R2 Historian Client Access Point,
/// replicating the stock <c>Archestra.Historian.GrpcClient.GrpcClientBase.InitializeBase</c>
/// transport shape: gRPC-Web (binary) over HTTP/1.1, optional TLS with an
/// untrusted-certificate bypass, and gzip request encoding.
/// </summary>
internal static class HistorianGrpcChannelFactory
{
    /// <summary>
    /// Resolves the effective gRPC port: when the caller left <see cref="HistorianClientOptions.Port"/>
    /// at the WCF default (32568), the 2023 R2 gRPC default (32565) is substituted; otherwise the
    /// explicit value is honoured.
    /// </summary>
    internal static int ResolvePort(HistorianClientOptions options) =>
        options.Port == HistorianClientOptions.DefaultPort ? HistorianClientOptions.DefaultGrpcPort : options.Port;

    /// <summary>
    /// Builds the channel address. TLS uses <c>https://{ServerDnsIdentity|Host}:{port}</c> (the
    /// DNS-identity override lets the URL match the server certificate name when connecting by IP);
    /// plaintext uses <c>http://{Host}:{port}</c>.
    /// </summary>
    internal static string ResolveAddress(HistorianClientOptions options)
    {
        int port = ResolvePort(options);
        if (options.GrpcUseTls)
        {
            string tlsHost = !string.IsNullOrEmpty(options.ServerDnsIdentity) ? options.ServerDnsIdentity! : options.Host;
            return $"https://{tlsHost}:{port}";
        }

        return $"http://{options.Host}:{port}";
    }

    public static HistorianGrpcConnection Create(HistorianClientOptions options)
    {
        string address = ResolveAddress(options);

        var httpHandler = new HttpClientHandler();
        if (options.AllowUntrustedServerCertificate)
        {
            httpHandler.ServerCertificateCustomValidationCallback = AcceptAnyCertificate;
        }

        // gRPC-Web binary mode over HTTP/1.1 — matches the stock client (GrpcWebMode.GrpcWeb,
        // HttpVersion 1.1). The 2023 R2 HCAP endpoint speaks gRPC-Web, not bare HTTP/2 gRPC.
        var webHandler = new GrpcWebHandler(GrpcWebMode.GrpcWeb, httpHandler)
        {
            HttpVersion = new Version(1, 1)
        };

        var channelOptions = new GrpcChannelOptions
        {
            HttpHandler = webHandler
        };

        GrpcChannel channel = GrpcChannel.ForAddress(address, channelOptions);

        // The stock client always advertises gzip request encoding; honour the option so
        // bandwidth-limited links can disable it.
        var metadata = new Metadata();
        if (options.Compression)
        {
            metadata.Add("grpc-internal-encoding-request", "gzip");
        }

        return new HistorianGrpcConnection(channel, metadata);
    }

    private static bool AcceptAnyCertificate(
        HttpRequestMessage request,
        X509Certificate2? certificate,
        X509Chain? chain,
        SslPolicyErrors errors) => true;
}

/// <summary>A live gRPC channel plus the per-call metadata header set.</summary>
internal sealed class HistorianGrpcConnection(GrpcChannel channel, Metadata metadata) : IDisposable
{
    public GrpcChannel Channel { get; } = channel;

    public Metadata Metadata { get; } = metadata;

    public void Dispose() => Channel.Dispose();
}