using System.Buffers.Binary;
using System.Collections.Concurrent;
using System.Text;

namespace ZB.MOM.WW.OtOpcUa.Driver.Heidenhain.Tests.Simulator;

public enum SimReplyKind { Frame, Drop, Stall }

/// <summary>What the simulated control does with one request.</summary>
public sealed record SimReply(SimReplyKind Kind, string? Command = null, byte[]? Payload = null)
{
    public static SimReply Ok(string command, byte[] payload) => new(SimReplyKind.Frame, command, payload);
    public static SimReply Refuse(int code, int type = 1) => new(SimReplyKind.Frame, "T_ER", [(byte)type, (byte)code]);
    public static SimReply Drop() => new(SimReplyKind.Drop);
    public static SimReply Stall() => new(SimReplyKind.Stall);

    /// <summary>Parses a reference fixture value <c>S_RI:0004</c> / <c>T_ER:0117</c>.</summary>
    public static SimReply FromFixture(string value)
    {
        var parts = value.Split(':', 2);
        return Ok(parts[0], Convert.FromHexString(parts[1]));
    }
}

/// <summary>
///     A small, mutable model of an iTNC 530 speaking the six allowlisted LSV2 requests. Anything else is
///     recorded as a <see cref="Violations">violation</see> and refused — the driver must never produce one.
/// </summary>
public sealed class SimulatedControl
{
    private readonly ConcurrentQueue<string> _violations = new();

    public byte[] Version { get; set; } = Encoding.Latin1.GetBytes("iTNC 530\0NC 340490 04\0PLC\0OPT\0");
    public byte[]? Layout { get; set; } = LayoutBytes(10);
    public Func<string, string, SimReply?>? Login { get; set; }
    public ConcurrentDictionary<int, Func<SimReply>> Runtime { get; } = new();
    public ConcurrentDictionary<string, SimReply> DataPaths { get; } = new(StringComparer.Ordinal);
    public Func<long, int, SimReply>? Memory { get; set; }
    public List<(string Role, string Password)> Logins { get; } = [];

    /// <summary>Requests the control refused as not-allowlisted (must stay empty).</summary>
    public IReadOnlyList<string> Violations => _violations.ToArray();

    /// <summary>Optional hook to override any reply (fault injection).</summary>
    public Func<Lsv2Request, SimReply?>? Intercept { get; set; }

    public SimReply Handle(Lsv2Request req)
    {
        if (Intercept?.Invoke(req) is { } forced) return forced;
        switch (req.Command)
        {
            case "A_LG":
            {
                var fields = req.Text.Split('\0');
                var role = fields[0];
                var password = fields.Length > 2 ? fields[1] : "";
                lock (Logins) Logins.Add((role, password));
                return Login?.Invoke(role, password) ?? SimReply.Ok("T_OK", []);
            }
            case "R_VR" when req.Payload.Length == 0:
                return SimReply.Ok("S_VR", Version);
            case "R_PR" when req.Payload.Length == 0:
                return Layout is null ? SimReply.Refuse(24) : SimReply.Ok("S_PR", Layout);
            case "R_RI" when req.Payload.Length == 2:
                return Runtime.TryGetValue(req.Selector, out var f) ? f() : SimReply.Refuse(24);
            case "R_MB" when req.Payload.Length == 5:
                var address = BinaryPrimitives.ReadUInt32BigEndian(req.Payload);
                return Memory?.Invoke(address, req.Payload[4]) ?? SimReply.Refuse(23);
            case "R_DP" when req.Payload.Length > 5:
            {
                var path = Encoding.Latin1.GetString(req.Payload, 4, req.Payload.Length - 5).Replace('\\', '/');
                return DataPaths.TryGetValue(path, out var r) ? r : SimReply.Refuse(24);
            }
            default:
                _violations.Enqueue(req.Command);
                return SimReply.Refuse(22);
        }
    }

    /// <summary>The reference test layout: words at 1000 with the given byte count, strings at 2000 (width 16), IW 3000, OW 4000.</summary>
    public static byte[] LayoutBytes(int wordBytes)
    {
        var b = new byte[120];
        BinaryPrimitives.WriteInt32BigEndian(b.AsSpan(40), 1000);
        BinaryPrimitives.WriteInt32BigEndian(b.AsSpan(44), wordBytes);
        BinaryPrimitives.WriteInt32BigEndian(b.AsSpan(48), 2000);
        BinaryPrimitives.WriteInt32BigEndian(b.AsSpan(52), 10);
        b[56] = 16;
        BinaryPrimitives.WriteInt32BigEndian(b.AsSpan(64), 3000);
        BinaryPrimitives.WriteInt32BigEndian(b.AsSpan(68), 10);
        BinaryPrimitives.WriteInt32BigEndian(b.AsSpan(72), 4000);
        BinaryPrimitives.WriteInt32BigEndian(b.AsSpan(76), 10);
        return b;
    }

    /// <summary>Two-byte uint16be runtime reply.</summary>
    public static SimReply U16(int v)
    {
        var p = new byte[2];
        BinaryPrimitives.WriteUInt16BigEndian(p, (ushort)v);
        return SimReply.Ok("S_RI", p);
    }
}

/// <summary>Loads the ported Java <c>.properties</c> golden vectors.</summary>
public static class Fixtures
{
    public static IReadOnlyDictionary<string, string> Load(string name)
    {
        var path = Path.Combine(AppContext.BaseDirectory, "Fixtures", name);
        var map = new Dictionary<string, string>(StringComparer.Ordinal);
        foreach (var line in File.ReadAllLines(path))
        {
            if (line.Length == 0 || line[0] == '#') continue;
            var eq = line.IndexOf('=');
            map[line[..eq]] = line[(eq + 1)..];
        }

        return map;
    }
}