using System.Diagnostics;
using System.Net.Sockets;
using System.Text.Json;
using System.Text.Json.Serialization;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;

/// <summary>
///     Cheap TCP-connect probe for the <see cref="ModbusDriverOptions"/>-shaped driver config.
///     Opens a socket to the configured endpoint and closes immediately. Surfaces a green
///     tick + latency on success; red chip + SocketError on failure; "timed out" on the
///     caller's cancellation. Does NOT exchange any protocol bytes — richer per-driver
///     handshakes are a documented follow-up.
/// </summary>
public sealed class ModbusDriverProbe : IDriverProbe
{
    private static readonly JsonSerializerOptions _opts = new()
    {
        PropertyNameCaseInsensitive = true,
        UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip,
    };

    /// <inheritdoc />
    public string DriverType => "ModbusTcp";

    /// <inheritdoc />
    public async Task<DriverProbeResult> ProbeAsync(string configJson, TimeSpan timeout, CancellationToken ct)
    {
        ModbusDriverOptions? opts;
        try { opts = JsonSerializer.Deserialize<ModbusDriverOptions>(configJson, _opts); }
        catch (Exception ex) { return new(false, $"Config JSON is invalid: {ex.Message}", null); }
        if (opts is null) return new(false, "Config JSON deserialized to null.", null);

        var (host, port) = ExtractTarget(opts);
        if (string.IsNullOrWhiteSpace(host) || port <= 0)
            return new(false, "Config has no host/port to probe.", null);

        var sw = Stopwatch.StartNew();
        try
        {
            using var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            await socket.ConnectAsync(host, port, ct);
            sw.Stop();
            return new(true, null, sw.Elapsed);
        }
        catch (SocketException ex)
        {
            return new(false, $"Connect failed: {ex.SocketErrorCode}", null);
        }
        catch (OperationCanceledException)
        {
            return new(false, $"Probe timed out after {timeout.TotalSeconds:F0}s.", null);
        }
        catch (Exception ex)
        {
            return new(false, ex.Message, null);
        }
    }

    private static (string host, int port) ExtractTarget(ModbusDriverOptions opts)
        => (opts.Host, opts.Port);
}
