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

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

/// <summary>
///     <see cref="IFocasClient"/> implementation backed by Fanuc's licensed
///     <c>Fwlib32.dll</c> via <see cref="FwlibNative"/> P/Invoke. The DLL is NOT shipped with
///     OtOpcUa; the deployment places it next to the server executable or on <c>PATH</c>
///     (per Fanuc licensing — see <c>docs/v2/focas-deployment.md</c>).
/// </summary>
/// <remarks>
///     <para>Construction is licence-safe — .NET P/Invoke is lazy, so instantiating this class
///     does NOT load <c>Fwlib32.dll</c>. The DLL only loads on the first wire call (Connect /
///     Read / Write / Probe). When missing, those calls throw <see cref="DllNotFoundException"/>
///     which the driver surfaces as <c>BadCommunicationError</c> through the normal exception
///     mapping.</para>
///
///     <para>Session-scoped handle — <c>cnc_allclibhndl3</c> opens one FWLIB handle per CNC;
///     all PMC / parameter / macro reads on that device go through the same handle. Dispose
///     calls <c>cnc_freelibhndl</c>.</para>
/// </remarks>
internal sealed class FwlibFocasClient : IFocasClient
{
    private ushort _handle;
    private bool _connected;

    // Per-PMC-byte RMW lock registry. Bit writes to the same byte get serialised so two
    // concurrent bit updates don't lose one another's modification. Key = "{addrType}:{byteAddr}".
    private readonly ConcurrentDictionary<string, SemaphoreSlim> _rmwLocks = new();

    private SemaphoreSlim GetRmwLock(short addrType, int byteAddr) =>
        _rmwLocks.GetOrAdd($"{addrType}:{byteAddr}", _ => new SemaphoreSlim(1, 1));

    public bool IsConnected => _connected;

    public Task ConnectAsync(FocasHostAddress address, TimeSpan timeout, CancellationToken cancellationToken)
    {
        if (_connected) return Task.CompletedTask;

        var timeoutMs = (int)Math.Max(1, timeout.TotalMilliseconds);
        var ret = FwlibNative.AllcLibHndl3(address.Host, (ushort)address.Port, timeoutMs, out var handle);
        if (ret != 0)
            throw new InvalidOperationException(
                $"FWLIB cnc_allclibhndl3 failed with EW_{ret} connecting to {address}.");
        _handle = handle;
        _connected = true;
        return Task.CompletedTask;
    }

    public Task<(object? value, uint status)> ReadAsync(
        FocasAddress address, FocasDataType type, CancellationToken cancellationToken)
    {
        if (!_connected) return Task.FromResult<(object?, uint)>((null, FocasStatusMapper.BadCommunicationError));
        cancellationToken.ThrowIfCancellationRequested();

        return address.Kind switch
        {
            FocasAreaKind.Pmc => Task.FromResult(ReadPmc(address, type)),
            FocasAreaKind.Parameter => Task.FromResult(ReadParameter(address, type)),
            FocasAreaKind.Macro => Task.FromResult(ReadMacro(address)),
            _ => Task.FromResult<(object?, uint)>((null, FocasStatusMapper.BadNotSupported)),
        };
    }

    public async Task<uint> WriteAsync(
        FocasAddress address, FocasDataType type, object? value, CancellationToken cancellationToken)
    {
        if (!_connected) return FocasStatusMapper.BadCommunicationError;
        cancellationToken.ThrowIfCancellationRequested();

        return address.Kind switch
        {
            FocasAreaKind.Pmc when type == FocasDataType.Bit && address.BitIndex is int =>
                await WritePmcBitAsync(address, Convert.ToBoolean(value), cancellationToken).ConfigureAwait(false),
            FocasAreaKind.Pmc => WritePmc(address, type, value),
            FocasAreaKind.Parameter => WriteParameter(address, type, value),
            FocasAreaKind.Macro => WriteMacro(address, value),
            _ => FocasStatusMapper.BadNotSupported,
        };
    }

    /// <summary>
    ///     Read-modify-write one bit within a PMC byte. Acquires a per-byte semaphore so
    ///     concurrent bit writes against the same byte serialise and neither loses its update.
    /// </summary>
    private async Task<uint> WritePmcBitAsync(
        FocasAddress address, bool newValue, CancellationToken cancellationToken)
    {
        var addrType = FocasPmcAddrType.FromLetter(address.PmcLetter ?? "") ?? (short)0;
        var bit = address.BitIndex ?? 0;
        if (bit is < 0 or > 7)
            throw new InvalidOperationException(
                $"PMC bit index {bit} out of range (0-7) for {address.Canonical}.");

        var rmwLock = GetRmwLock(addrType, address.Number);
        await rmwLock.WaitAsync(cancellationToken).ConfigureAwait(false);
        try
        {
            // Read the parent byte.
            var readBuf = new FwlibNative.IODBPMC { Data = new byte[40] };
            var readRet = FwlibNative.PmcRdPmcRng(
                _handle, addrType, FocasPmcDataType.Byte,
                (ushort)address.Number, (ushort)address.Number, 8 + 1, ref readBuf);
            if (readRet != 0) return FocasStatusMapper.MapFocasReturn(readRet);

            var current = readBuf.Data[0];
            var updated = newValue
                ? (byte)(current | (1 << bit))
                : (byte)(current & ~(1 << bit));

            // Write the updated byte.
            var writeBuf = new FwlibNative.IODBPMC
            {
                TypeA = addrType,
                TypeD = FocasPmcDataType.Byte,
                DatanoS = (ushort)address.Number,
                DatanoE = (ushort)address.Number,
                Data = new byte[40],
            };
            writeBuf.Data[0] = updated;

            var writeRet = FwlibNative.PmcWrPmcRng(_handle, 8 + 1, ref writeBuf);
            return writeRet == 0 ? FocasStatusMapper.Good : FocasStatusMapper.MapFocasReturn(writeRet);
        }
        finally
        {
            rmwLock.Release();
        }
    }

    public Task<bool> ProbeAsync(CancellationToken cancellationToken)
    {
        if (!_connected) return Task.FromResult(false);
        var buf = new FwlibNative.ODBST();
        var ret = FwlibNative.StatInfo(_handle, ref buf);
        return Task.FromResult(ret == 0);
    }

    // ---- PMC ----

    private (object? value, uint status) ReadPmc(FocasAddress address, FocasDataType type)
    {
        var addrType = FocasPmcAddrType.FromLetter(address.PmcLetter ?? "")
            ?? throw new InvalidOperationException($"Unknown PMC letter '{address.PmcLetter}'.");
        var dataType = FocasPmcDataType.FromFocasDataType(type);
        var length = PmcReadLength(type);

        var buf = new FwlibNative.IODBPMC { Data = new byte[40] };
        var ret = FwlibNative.PmcRdPmcRng(
            _handle, addrType, dataType,
            (ushort)address.Number, (ushort)address.Number, (ushort)length, ref buf);
        if (ret != 0) return (null, FocasStatusMapper.MapFocasReturn(ret));

        var value = type switch
        {
            FocasDataType.Bit => ExtractBit(buf.Data[0], address.BitIndex ?? 0),
            FocasDataType.Byte => (object)(sbyte)buf.Data[0],
            FocasDataType.Int16 => (object)BinaryPrimitives.ReadInt16LittleEndian(buf.Data),
            FocasDataType.Int32 => (object)BinaryPrimitives.ReadInt32LittleEndian(buf.Data),
            FocasDataType.Float32 => (object)BinaryPrimitives.ReadSingleLittleEndian(buf.Data),
            FocasDataType.Float64 => (object)BinaryPrimitives.ReadDoubleLittleEndian(buf.Data),
            _ => (object)buf.Data[0],
        };
        return (value, FocasStatusMapper.Good);
    }

    private uint WritePmc(FocasAddress address, FocasDataType type, object? value)
    {
        var addrType = FocasPmcAddrType.FromLetter(address.PmcLetter ?? "") ?? (short)0;
        var dataType = FocasPmcDataType.FromFocasDataType(type);
        var length = PmcWriteLength(type);

        var buf = new FwlibNative.IODBPMC
        {
            TypeA = addrType,
            TypeD = dataType,
            DatanoS = (ushort)address.Number,
            DatanoE = (ushort)address.Number,
            Data = new byte[40],
        };
        EncodePmcValue(buf.Data, type, value, address.BitIndex);

        var ret = FwlibNative.PmcWrPmcRng(_handle, (ushort)length, ref buf);
        return ret == 0 ? FocasStatusMapper.Good : FocasStatusMapper.MapFocasReturn(ret);
    }

    private (object? value, uint status) ReadParameter(FocasAddress address, FocasDataType type)
    {
        var buf = new FwlibNative.IODBPSD { Data = new byte[32] };
        var length = ParamReadLength(type);
        var ret = FwlibNative.RdParam(_handle, (ushort)address.Number, axis: 0, (short)length, ref buf);
        if (ret != 0) return (null, FocasStatusMapper.MapFocasReturn(ret));

        var value = type switch
        {
            FocasDataType.Bit when address.BitIndex is int bit => ExtractBit(buf.Data[0], bit),
            FocasDataType.Byte => (object)(sbyte)buf.Data[0],
            FocasDataType.Int16 => (object)BinaryPrimitives.ReadInt16LittleEndian(buf.Data),
            FocasDataType.Int32 => (object)BinaryPrimitives.ReadInt32LittleEndian(buf.Data),
            _ => (object)BinaryPrimitives.ReadInt32LittleEndian(buf.Data),
        };
        return (value, FocasStatusMapper.Good);
    }

    private uint WriteParameter(FocasAddress address, FocasDataType type, object? value)
    {
        var buf = new FwlibNative.IODBPSD
        {
            Datano = (short)address.Number,
            Type = 0,
            Data = new byte[32],
        };
        var length = ParamReadLength(type);
        EncodeParamValue(buf.Data, type, value);
        var ret = FwlibNative.WrParam(_handle, (short)length, ref buf);
        return ret == 0 ? FocasStatusMapper.Good : FocasStatusMapper.MapFocasReturn(ret);
    }

    private (object? value, uint status) ReadMacro(FocasAddress address)
    {
        var buf = new FwlibNative.ODBM();
        var ret = FwlibNative.RdMacro(_handle, (short)address.Number, length: 8, ref buf);
        if (ret != 0) return (null, FocasStatusMapper.MapFocasReturn(ret));

        // Macro value = mcr_val / 10^dec_val. Convert to double so callers get the correct
        // scaled value regardless of the decimal-point count the CNC reports.
        var scaled = buf.McrVal / Math.Pow(10.0, buf.DecVal);
        return (scaled, FocasStatusMapper.Good);
    }

    private uint WriteMacro(FocasAddress address, object? value)
    {
        // Write as integer + 0 decimal places — callers that need decimal precision can extend
        // this via a future WriteMacroScaled overload. Consistent with what most HMIs do today.
        var intValue = Convert.ToInt32(value);
        var ret = FwlibNative.WrMacro(_handle, (short)address.Number, length: 8, intValue, decimalPointCount: 0);
        return ret == 0 ? FocasStatusMapper.Good : FocasStatusMapper.MapFocasReturn(ret);
    }

    public void Dispose()
    {
        if (_connected)
        {
            try { FwlibNative.FreeLibHndl(_handle); } catch { }
            _connected = false;
        }
    }

    // ---- helpers ----

    private static int PmcReadLength(FocasDataType type) => type switch
    {
        FocasDataType.Bit or FocasDataType.Byte => 8 + 1,    // 8-byte header + 1 byte payload
        FocasDataType.Int16 => 8 + 2,
        FocasDataType.Int32 => 8 + 4,
        FocasDataType.Float32 => 8 + 4,
        FocasDataType.Float64 => 8 + 8,
        _ => 8 + 1,
    };

    private static int PmcWriteLength(FocasDataType type) => PmcReadLength(type);
    private static int ParamReadLength(FocasDataType type) => type switch
    {
        FocasDataType.Bit or FocasDataType.Byte => 4 + 1,
        FocasDataType.Int16 => 4 + 2,
        FocasDataType.Int32 => 4 + 4,
        _ => 4 + 4,
    };

    private static bool ExtractBit(byte word, int bit) => (word & (1 << bit)) != 0;

    internal static void EncodePmcValue(byte[] data, FocasDataType type, object? value, int? bitIndex)
    {
        switch (type)
        {
            case FocasDataType.Bit:
                // PMC Bit writes with a non-null bitIndex go through WritePmcBitAsync's RMW path
                // upstream. This branch only fires when a caller passes Bit with no bitIndex —
                // treat the value as a whole-byte boolean (non-zero / zero).
                data[0] = Convert.ToBoolean(value) ? (byte)1 : (byte)0;
                break;
            case FocasDataType.Byte:
                data[0] = (byte)(sbyte)Convert.ToSByte(value);
                break;
            case FocasDataType.Int16:
                BinaryPrimitives.WriteInt16LittleEndian(data, Convert.ToInt16(value));
                break;
            case FocasDataType.Int32:
                BinaryPrimitives.WriteInt32LittleEndian(data, Convert.ToInt32(value));
                break;
            case FocasDataType.Float32:
                BinaryPrimitives.WriteSingleLittleEndian(data, Convert.ToSingle(value));
                break;
            case FocasDataType.Float64:
                BinaryPrimitives.WriteDoubleLittleEndian(data, Convert.ToDouble(value));
                break;
            default:
                throw new NotSupportedException($"FocasDataType {type} not writable via PMC.");
        }
        _ = bitIndex; // bit-in-byte handled above
    }

    internal static void EncodeParamValue(byte[] data, FocasDataType type, object? value)
    {
        switch (type)
        {
            case FocasDataType.Byte:
                data[0] = (byte)(sbyte)Convert.ToSByte(value);
                break;
            case FocasDataType.Int16:
                BinaryPrimitives.WriteInt16LittleEndian(data, Convert.ToInt16(value));
                break;
            case FocasDataType.Int32:
                BinaryPrimitives.WriteInt32LittleEndian(data, Convert.ToInt32(value));
                break;
            default:
                BinaryPrimitives.WriteInt32LittleEndian(data, Convert.ToInt32(value));
                break;
        }
    }
}

/// <summary>Default <see cref="IFocasClientFactory"/> — produces a fresh <see cref="FwlibFocasClient"/> per device.</summary>
public sealed class FwlibFocasClientFactory : IFocasClientFactory
{
    public IFocasClient Create() => new FwlibFocasClient();
}