using System.Buffers.Binary;
using System.Text.Json;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

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

/// <summary>
///     Modbus TCP implementation of <see cref="IDriver"/> + <see cref="ITagDiscovery"/> +
///     <see cref="IReadable"/> + <see cref="IWritable"/>. First native-protocol greenfield
///     driver for the v2 stack — validates the driver-agnostic <c>IAddressSpaceBuilder</c> +
///     <c>IReadable</c>/<c>IWritable</c> abstractions generalize beyond Galaxy.
/// </summary>
/// <remarks>
///     Scope limits: synchronous Read/Write only, no subscriptions (Modbus has no push model;
///     subscriptions would need a polling loop over the declared tags — additive PR). Historian
///     + alarm capabilities are out of scope (the protocol doesn't express them).
/// </remarks>
public sealed class ModbusDriver(ModbusDriverOptions options, string driverInstanceId,
    Func<ModbusDriverOptions, IModbusTransport>? transportFactory = null)
    : IDriver, ITagDiscovery, IReadable, IWritable, IDisposable, IAsyncDisposable
{
    private readonly ModbusDriverOptions _options = options;
    private readonly Func<ModbusDriverOptions, IModbusTransport> _transportFactory =
        transportFactory ?? (o => new ModbusTcpTransport(o.Host, o.Port, o.Timeout));

    private IModbusTransport? _transport;
    private DriverHealth _health = new(DriverState.Unknown, null, null);
    private readonly Dictionary<string, ModbusTagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);

    public string DriverInstanceId => driverInstanceId;
    public string DriverType => "Modbus";

    public async Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
    {
        _health = new DriverHealth(DriverState.Initializing, null, null);
        try
        {
            _transport = _transportFactory(_options);
            await _transport.ConnectAsync(cancellationToken).ConfigureAwait(false);
            foreach (var t in _options.Tags) _tagsByName[t.Name] = t;
            _health = new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null);
        }
        catch (Exception ex)
        {
            _health = new DriverHealth(DriverState.Faulted, null, ex.Message);
            throw;
        }
    }

    public async Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
    {
        await ShutdownAsync(cancellationToken);
        await InitializeAsync(driverConfigJson, cancellationToken);
    }

    public async Task ShutdownAsync(CancellationToken cancellationToken)
    {
        if (_transport is not null) await _transport.DisposeAsync().ConfigureAwait(false);
        _transport = null;
        _health = new DriverHealth(DriverState.Unknown, _health.LastSuccessfulRead, null);
    }

    public DriverHealth GetHealth() => _health;
    public long GetMemoryFootprint() => 0;
    public Task FlushOptionalCachesAsync(CancellationToken cancellationToken) => Task.CompletedTask;

    // ---- ITagDiscovery ----

    public Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(builder);
        var folder = builder.Folder("Modbus", "Modbus");
        foreach (var t in _options.Tags)
        {
            folder.Variable(t.Name, t.Name, new DriverAttributeInfo(
                FullName: t.Name,
                DriverDataType: MapDataType(t.DataType),
                IsArray: false,
                ArrayDim: null,
                SecurityClass: t.Writable ? SecurityClassification.Operate : SecurityClassification.ViewOnly,
                IsHistorized: false,
                IsAlarm: false));
        }
        return Task.CompletedTask;
    }

    // ---- IReadable ----

    public async Task<IReadOnlyList<DataValueSnapshot>> ReadAsync(
        IReadOnlyList<string> fullReferences, CancellationToken cancellationToken)
    {
        var transport = RequireTransport();
        var now = DateTime.UtcNow;
        var results = new DataValueSnapshot[fullReferences.Count];
        for (var i = 0; i < fullReferences.Count; i++)
        {
            if (!_tagsByName.TryGetValue(fullReferences[i], out var tag))
            {
                results[i] = new DataValueSnapshot(null, StatusBadNodeIdUnknown, null, now);
                continue;
            }
            try
            {
                var value = await ReadOneAsync(transport, tag, cancellationToken).ConfigureAwait(false);
                results[i] = new DataValueSnapshot(value, 0u, now, now);
                _health = new DriverHealth(DriverState.Healthy, now, null);
            }
            catch (Exception ex)
            {
                results[i] = new DataValueSnapshot(null, StatusBadInternalError, null, now);
                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
            }
        }
        return results;
    }

    private async Task<object> ReadOneAsync(IModbusTransport transport, ModbusTagDefinition tag, CancellationToken ct)
    {
        switch (tag.Region)
        {
            case ModbusRegion.Coils:
            {
                var pdu = new byte[] { 0x01, (byte)(tag.Address >> 8), (byte)(tag.Address & 0xFF), 0x00, 0x01 };
                var resp = await transport.SendAsync(_options.UnitId, pdu, ct).ConfigureAwait(false);
                return (resp[2] & 0x01) == 1;
            }
            case ModbusRegion.DiscreteInputs:
            {
                var pdu = new byte[] { 0x02, (byte)(tag.Address >> 8), (byte)(tag.Address & 0xFF), 0x00, 0x01 };
                var resp = await transport.SendAsync(_options.UnitId, pdu, ct).ConfigureAwait(false);
                return (resp[2] & 0x01) == 1;
            }
            case ModbusRegion.HoldingRegisters:
            case ModbusRegion.InputRegisters:
            {
                var quantity = RegisterCount(tag.DataType);
                var fc = tag.Region == ModbusRegion.HoldingRegisters ? (byte)0x03 : (byte)0x04;
                var pdu = new byte[] { fc, (byte)(tag.Address >> 8), (byte)(tag.Address & 0xFF),
                                       (byte)(quantity >> 8), (byte)(quantity & 0xFF) };
                var resp = await transport.SendAsync(_options.UnitId, pdu, ct).ConfigureAwait(false);
                // resp = [fc][byte-count][data...]
                var data = new ReadOnlySpan<byte>(resp, 2, resp[1]);
                return DecodeRegister(data, tag.DataType);
            }
            default:
                throw new InvalidOperationException($"Unknown region {tag.Region}");
        }
    }

    // ---- IWritable ----

    public async Task<IReadOnlyList<WriteResult>> WriteAsync(
        IReadOnlyList<WriteRequest> writes, CancellationToken cancellationToken)
    {
        var transport = RequireTransport();
        var results = new WriteResult[writes.Count];
        for (var i = 0; i < writes.Count; i++)
        {
            var w = writes[i];
            if (!_tagsByName.TryGetValue(w.FullReference, out var tag))
            {
                results[i] = new WriteResult(StatusBadNodeIdUnknown);
                continue;
            }
            if (!tag.Writable || tag.Region is ModbusRegion.DiscreteInputs or ModbusRegion.InputRegisters)
            {
                results[i] = new WriteResult(StatusBadNotWritable);
                continue;
            }
            try
            {
                await WriteOneAsync(transport, tag, w.Value, cancellationToken).ConfigureAwait(false);
                results[i] = new WriteResult(0u);
            }
            catch (Exception)
            {
                results[i] = new WriteResult(StatusBadInternalError);
            }
        }
        return results;
    }

    private async Task WriteOneAsync(IModbusTransport transport, ModbusTagDefinition tag, object? value, CancellationToken ct)
    {
        switch (tag.Region)
        {
            case ModbusRegion.Coils:
            {
                var on = Convert.ToBoolean(value);
                var pdu = new byte[] { 0x05, (byte)(tag.Address >> 8), (byte)(tag.Address & 0xFF),
                                       on ? (byte)0xFF : (byte)0x00, 0x00 };
                await transport.SendAsync(_options.UnitId, pdu, ct).ConfigureAwait(false);
                return;
            }
            case ModbusRegion.HoldingRegisters:
            {
                var bytes = EncodeRegister(value, tag.DataType);
                if (bytes.Length == 2)
                {
                    var pdu = new byte[] { 0x06, (byte)(tag.Address >> 8), (byte)(tag.Address & 0xFF),
                                           bytes[0], bytes[1] };
                    await transport.SendAsync(_options.UnitId, pdu, ct).ConfigureAwait(false);
                }
                else
                {
                    // FC 16 (Write Multiple Registers) for 32-bit types
                    var qty = (ushort)(bytes.Length / 2);
                    var pdu = new byte[6 + 1 + bytes.Length];
                    pdu[0] = 0x10;
                    pdu[1] = (byte)(tag.Address >> 8); pdu[2] = (byte)(tag.Address & 0xFF);
                    pdu[3] = (byte)(qty >> 8); pdu[4] = (byte)(qty & 0xFF);
                    pdu[5] = (byte)bytes.Length;
                    Buffer.BlockCopy(bytes, 0, pdu, 6, bytes.Length);
                    await transport.SendAsync(_options.UnitId, pdu, ct).ConfigureAwait(false);
                }
                return;
            }
            default:
                throw new InvalidOperationException($"Writes not supported for region {tag.Region}");
        }
    }

    // ---- codec ----

    internal static ushort RegisterCount(ModbusDataType t) => t switch
    {
        ModbusDataType.Int16 or ModbusDataType.UInt16 => 1,
        ModbusDataType.Int32 or ModbusDataType.UInt32 or ModbusDataType.Float32 => 2,
        _ => throw new InvalidOperationException($"Non-register data type {t}"),
    };

    internal static object DecodeRegister(ReadOnlySpan<byte> data, ModbusDataType t) => t switch
    {
        ModbusDataType.Int16 => BinaryPrimitives.ReadInt16BigEndian(data),
        ModbusDataType.UInt16 => BinaryPrimitives.ReadUInt16BigEndian(data),
        ModbusDataType.Int32 => BinaryPrimitives.ReadInt32BigEndian(data),
        ModbusDataType.UInt32 => BinaryPrimitives.ReadUInt32BigEndian(data),
        ModbusDataType.Float32 => BinaryPrimitives.ReadSingleBigEndian(data),
        _ => throw new InvalidOperationException($"Non-register data type {t}"),
    };

    internal static byte[] EncodeRegister(object? value, ModbusDataType t)
    {
        switch (t)
        {
            case ModbusDataType.Int16:
            {
                var v = Convert.ToInt16(value);
                var b = new byte[2];
                BinaryPrimitives.WriteInt16BigEndian(b, v);
                return b;
            }
            case ModbusDataType.UInt16:
            {
                var v = Convert.ToUInt16(value);
                var b = new byte[2];
                BinaryPrimitives.WriteUInt16BigEndian(b, v);
                return b;
            }
            case ModbusDataType.Int32:
            {
                var v = Convert.ToInt32(value);
                var b = new byte[4];
                BinaryPrimitives.WriteInt32BigEndian(b, v);
                return b;
            }
            case ModbusDataType.UInt32:
            {
                var v = Convert.ToUInt32(value);
                var b = new byte[4];
                BinaryPrimitives.WriteUInt32BigEndian(b, v);
                return b;
            }
            case ModbusDataType.Float32:
            {
                var v = Convert.ToSingle(value);
                var b = new byte[4];
                BinaryPrimitives.WriteSingleBigEndian(b, v);
                return b;
            }
            default:
                throw new InvalidOperationException($"Non-register data type {t}");
        }
    }

    private static DriverDataType MapDataType(ModbusDataType t) => t switch
    {
        ModbusDataType.Bool => DriverDataType.Boolean,
        ModbusDataType.Int16 or ModbusDataType.Int32 => DriverDataType.Int32,
        ModbusDataType.UInt16 or ModbusDataType.UInt32 => DriverDataType.Int32,
        ModbusDataType.Float32 => DriverDataType.Float32,
        _ => DriverDataType.Int32,
    };

    private IModbusTransport RequireTransport() =>
        _transport ?? throw new InvalidOperationException("ModbusDriver not initialized");

    private const uint StatusBadInternalError = 0x80020000u;
    private const uint StatusBadNodeIdUnknown = 0x80340000u;
    private const uint StatusBadNotWritable = 0x803B0000u;

    public void Dispose() => DisposeAsync().AsTask().GetAwaiter().GetResult();
    public async ValueTask DisposeAsync()
    {
        if (_transport is not null) await _transport.DisposeAsync().ConfigureAwait(false);
        _transport = null;
    }
}