using System.Net;
using System.Net.Sockets;

namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests;

/// <summary>
///     Reachability gate for the shared opc-plc fixture (<c>OPCUA_SIM_ENDPOINT</c>, default
///     <c>opc.tcp://10.100.0.35:50000</c>). A small copy of the probe in
///     <c>Driver.OpcUaClient.IntegrationTests/OpcPlcFixture</c> rather than a cross-project reference —
///     that project drags the whole driver in. Tests call <see cref="SkipUnlessReachable"/> first, so a
///     machine without the simulator reports Skipped instead of a connect failure.
/// </summary>
internal static class OpcPlcProbe
{
    private const string EndpointEnvVar = "OPCUA_SIM_ENDPOINT";
    private const string DefaultEndpoint = "opc.tcp://10.100.0.35:50000";

    /// <summary>The simulator endpoint the tests should connect to.</summary>
    public static string Endpoint =>
        Environment.GetEnvironmentVariable(EndpointEnvVar) is { Length: > 0 } e ? e : DefaultEndpoint;

    private static readonly Lazy<string?> Reason = new(Probe);

    /// <summary>Skips the calling test when opc-plc does not accept a TCP connection (probed once per run).</summary>
    public static void SkipUnlessReachable()
    {
        if (Reason.Value is { } reason) Xunit.Assert.Skip(reason);
    }

    private static string? Probe()
    {
        var body = Endpoint.StartsWith("opc.tcp://", StringComparison.OrdinalIgnoreCase)
            ? Endpoint["opc.tcp://".Length..]
            : Endpoint;
        var slash = body.IndexOf('/');
        if (slash >= 0) body = body[..slash];
        var colon = body.LastIndexOf(':');
        var host = colon >= 0 ? body[..colon] : body;
        var port = colon >= 0 && int.TryParse(body[(colon + 1)..], out var p) ? p : 4840;
        try
        {
            using var client = new TcpClient(AddressFamily.InterNetwork);
            var addr = Dns.GetHostAddresses(host).FirstOrDefault(a => a.AddressFamily == AddressFamily.InterNetwork)
                       ?? IPAddress.Loopback;
            if (client.ConnectAsync(addr, port).Wait(TimeSpan.FromSeconds(2)) && client.Connected) return null;
            return $"opc-plc simulator at {host}:{port} did not accept a TCP connection within 2s. Start it or override {EndpointEnvVar}.";
        }
        catch (Exception ex)
        {
            return $"opc-plc simulator at {host}:{port} unreachable: {ex.GetType().Name}: {ex.Message}. Start it or override {EndpointEnvVar}.";
        }
    }
}