using System.Buffers.Binary;
using System.Net.Sockets;
using Microsoft.Extensions.Logging;

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

/// <summary>
///     Pure-managed read-only FOCAS/2 Ethernet wire client. Speaks the proprietary Fanuc
///     binary protocol on TCP:8193 directly — no P/Invoke, no <c>Fwlib64.dll</c>, no
///     out-of-process Host. One instance owns two TCP sockets for the duration of a CNC
///     session; <see cref="ConnectAsync(string, int, int, CancellationToken)"/> runs the
///     two-socket initiate handshake and a setup request, subsequent reads reuse
///     <c>socket 2</c> serialised through an internal semaphore.
/// </summary>
/// <remarks>
///     <para><b>Read surface.</b> Covers every FOCAS call OtOpcUa's managed driver issues:
///     sysinfo, status, axis + spindle names, the <c>cnc_rddynamic2</c> fast-poll bundle,
///     parameters (typed + raw-bytes overloads), macros, PMC ranges, alarms, operation mode,
///     executing program, block count, timers, and servo / spindle meters. Writes are
///     intentionally out of scope.</para>
///     <para><b>Concurrency.</b> Callers may issue reads concurrently from multiple threads
///     — <c>socket 2</c> is guarded by a <see cref="SemaphoreSlim"/> so at most one
///     request/response pair is in flight at a time. <see cref="ConnectAsync(string, int, int, CancellationToken)"/>
///     and <see cref="DisposeAsync"/> share a second semaphore to stop the two racing.</para>
///     <para><b>Transient failures.</b> When cancellation or a socket-level error happens
///     mid-request the client closes both sockets and throws
///     <see cref="FocasWireException"/> with <see cref="FocasWireException.IsTransient"/>
///     set — the caller must reconnect before issuing the next request. The transport is
///     left deliberately torn down rather than half-open so a truncated response never
///     desynchronises the next caller's read.</para>
/// </remarks>
public sealed class FocasWireClient : IAsyncDisposable, IDisposable
{
    private readonly ILogger<FocasWireClient>? _logger;
    private readonly SemaphoreSlim _requestGate = new(1, 1);
    private readonly SemaphoreSlim _lifetimeGate = new(1, 1);
    private TcpClient? _socket1;
    private TcpClient? _socket2;
    private NetworkStream? _stream1;
    private NetworkStream? _stream2;
    private bool _connected;
    private bool _disposed;
    private FocasResult<WireSysInfo>? _sysInfo;

    /// <summary>
    ///     Construct a disconnected client. Optional <paramref name="logger"/> receives
    ///     <c>Debug</c>-level entries per response block (command ID, RC, payload length).
    /// </summary>
    /// <param name="logger">Optional logger for debug-level wire protocol entries.</param>
    public FocasWireClient(ILogger<FocasWireClient>? logger = null)
    {
        _logger = logger;
    }

    /// <summary>
    ///     Default <c>PathId</c> applied when no per-call override is supplied. Relevant for
    ///     multi-path CNCs; single-path controllers leave this at the default of <c>1</c>.
    /// </summary>
    public ushort PathId { get; set; } = 1;

    /// <summary>True when the two-socket handshake has completed and the transport is live.</summary>
    public bool IsConnected => _connected;

    /// <summary>
    ///     Open the FOCAS session using an integer-seconds timeout. Idempotent — a second
    ///     call while already connected is a no-op. Sub-second timeouts require the
    ///     <see cref="ConnectAsync(string, int, TimeSpan, CancellationToken)"/> overload.
    /// </summary>
    /// <param name="host">The CNC hostname or IP address.</param>
    /// <param name="port">The FOCAS/2 TCP port (typically 8193).</param>
    /// <param name="timeoutSeconds">Connection timeout in seconds; zero or negative disables the timeout.</param>
    /// <param name="cancellationToken">Cancellation token for the connect operation.</param>
    /// <returns>A task that represents the asynchronous operation.</returns>
    public Task ConnectAsync(
        string host,
        int port,
        int timeoutSeconds = 10,
        CancellationToken cancellationToken = default)
        => ConnectCoreAsync(
            host,
            port,
            timeoutSeconds > 0 ? TimeSpan.FromSeconds(timeoutSeconds) : null,
            cancellationToken);

    /// <summary>
    ///     Open the FOCAS session with a <see cref="TimeSpan"/> timeout. Pass
    ///     <see cref="TimeSpan.Zero"/> to disable the timeout entirely (rely on the caller's
    ///     <paramref name="cancellationToken"/> instead). Idempotent.
    /// </summary>
    /// <param name="host">The CNC hostname or IP address.</param>
    /// <param name="port">The FOCAS/2 TCP port (typically 8193).</param>
    /// <param name="timeout">Connection timeout duration; <see cref="TimeSpan.Zero"/> disables the timeout.</param>
    /// <param name="cancellationToken">Cancellation token for the connect operation.</param>
    /// <returns>A task that represents the asynchronous operation.</returns>
    public Task ConnectAsync(
        string host,
        int port,
        TimeSpan timeout,
        CancellationToken cancellationToken = default)
        => ConnectCoreAsync(host, port, timeout == TimeSpan.Zero ? null : timeout, cancellationToken);

    private async Task ConnectCoreAsync(
        string host,
        int port,
        TimeSpan? timeoutValue,
        CancellationToken cancellationToken)
    {
        await _lifetimeGate.WaitAsync(cancellationToken).ConfigureAwait(false);
        try
        {
            ThrowIfDisposed();
            if (_connected) return;

            using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
            if (timeoutValue is { } value) timeout.CancelAfter(value);

            try
            {
                _socket1 = await ConnectSocketAsync(host, port, timeout.Token).ConfigureAwait(false);
                _stream1 = _socket1.GetStream();
                await SendPduAsync(_stream1, FocasWireProtocol.TypeInitiate, FocasWireProtocol.BuildInitiateBody(1), timeout.Token).ConfigureAwait(false);
                await ReadExpectedPduAsync(_stream1, FocasWireProtocol.TypeInitiate, timeout.Token).ConfigureAwait(false);

                _socket2 = await ConnectSocketAsync(host, port, timeout.Token).ConfigureAwait(false);
                _stream2 = _socket2.GetStream();
                await SendPduAsync(_stream2, FocasWireProtocol.TypeInitiate, FocasWireProtocol.BuildInitiateBody(2), timeout.Token).ConfigureAwait(false);
                await ReadExpectedPduAsync(_stream2, FocasWireProtocol.TypeInitiate, timeout.Token).ConfigureAwait(false);

                _connected = true;
                // Cache the sysinfo payload from the setup exchange so later
                // ReadSysInfoAsync calls are a lookup rather than a wire hit.
                var sysInfoBlock = await SendSingleRequestAsync(timeout.Token, new RequestBlock(0x0018, PathId: PathId)).ConfigureAwait(false);
                _sysInfo = ToResult(sysInfoBlock, ParseSysInfo);
                // Kick the cached path/session metadata request the DLL sends
                // right after initiate. The result is ignored; the CNC uses it to
                // populate internal state the subsequent reads depend on.
                await SendRequestAsync(timeout.Token, new RequestBlock(0x000e, 0x26f0, 0x26f0, PathId: PathId)).ConfigureAwait(false);
            }
            catch (Exception ex) when (IsTransientException(ex))
            {
                CloseTransport();
                throw new FocasWireException("FOCAS wire connect failed.", ex, isTransient: true);
            }
        }
        finally
        {
            _lifetimeGate.Release();
        }
    }

    /// <summary>
    ///     Synchronous dispose — sends the close PDU when connected and tears down both
    ///     sockets. Idempotent. Callers on an async context should prefer
    ///     <see cref="DisposeAsync"/>.
    /// </summary>
    public void Dispose()
    {
        _lifetimeGate.Wait();
        try
        {
            if (_disposed) return;

            _disposed = true;
            if (_stream2 is not null && _connected)
            {
                try
                {
                    SendPdu(_stream2, FocasWireProtocol.TypeClose, ReadOnlySpan<byte>.Empty);
                    _ = FocasWireProtocol.ReadPdu(_stream2);
                }
                catch
                {
                    // Close best-effort — don't let teardown failure hide a caller's real error.
                }
            }
            CloseTransport();
        }
        finally
        {
            _lifetimeGate.Release();
        }
    }

    /// <summary>
    ///     Async dispose — sends the close PDU when connected and tears down both sockets.
    ///     Idempotent.
    /// </summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    public async ValueTask DisposeAsync()
    {
        await _lifetimeGate.WaitAsync(CancellationToken.None).ConfigureAwait(false);
        try
        {
            if (_disposed) return;

            _disposed = true;
            if (_stream2 is not null && _connected)
            {
                try
                {
                    await SendPduAsync(_stream2, FocasWireProtocol.TypeClose, ReadOnlyMemory<byte>.Empty, CancellationToken.None).ConfigureAwait(false);
                    await FocasWireProtocol.ReadPduAsync(_stream2, CancellationToken.None).ConfigureAwait(false);
                }
                catch
                {
                    // Close best-effort — don't let teardown failure hide a caller's real error.
                }
            }
            CloseTransport();
        }
        finally
        {
            _lifetimeGate.Release();
        }
    }

    /// <summary>
    ///     Read CNC identity via <c>cnc_sysinfo</c>. Cached from the connect-time exchange
    ///     unless a per-call <paramref name="pathId"/> override is supplied.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The CNC identity/sysinfo, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<WireSysInfo>> ReadSysInfoAsync(
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        if (pathId is null && _sysInfo is { } cached) return cached;

        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        return await ReadSingleAsync(0x0018, ParseSysInfo, EffectivePathId(pathId), cancellationToken: callTimeout.Token).ConfigureAwait(false);
    }

    /// <summary>Read CNC status bits via <c>cnc_statinfo</c> (3 command blocks aggregated into one <see cref="WireStatus"/>).</summary>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The aggregated CNC status bits, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<WireStatus>> ReadStatusAsync(
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var requestPathId = EffectivePathId(pathId);
        var blocks = await SendRequestAsync(
            callTimeout.Token,
            new RequestBlock(0x0019, PathId: requestPathId),
            new RequestBlock(0x00e1, PathId: requestPathId),
            new RequestBlock(0x0098, PathId: requestPathId)).ConfigureAwait(false);

        var rc = AggregateRc(blocks);
        if (rc != 0) return new FocasResult<WireStatus>(rc, null);

        var primary = FindPayload(blocks, 0x0019);
        RequireLength(primary, 14, "cnc_statinfo");
        var tmModePayload = FindPayload(blocks, 0x0098);
        var tmMode = tmModePayload.Length >= 2 ? ReadInt16(tmModePayload, 0) : (short)0;

        return new FocasResult<WireStatus>(
            rc,
            new WireStatus(
                Auto: ReadInt16(primary, 0),
                Run: ReadInt16(primary, 2),
                Motion: ReadInt16(primary, 4),
                Mstb: ReadInt16(primary, 6),
                Emergency: ReadInt16(primary, 8),
                Alarm: ReadInt16(primary, 10),
                Edit: ReadInt16(primary, 12),
                TmMode: tmMode));
    }

    /// <summary>Read configured axis names via <c>cnc_rdaxisname</c> (command <c>0x0089</c>).</summary>
    /// <param name="maxCount">Maximum number of axis records to return.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The configured axis name records, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<IReadOnlyList<WireAxisRecord>>> ReadAxisNamesAsync(
        short maxCount = 32,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var block = await SendSingleRequestAsync(callTimeout.Token, new RequestBlock(0x0089, PathId: EffectivePathId(pathId))).ConfigureAwait(false);
        return ToResult(block, payload => ReadNameRecords(payload, maxCount, (index, name) => new WireAxisRecord(index, name)));
    }

    /// <summary>Read configured spindle names via <c>cnc_rdspdlname</c> (command <c>0x008a</c>).</summary>
    /// <param name="maxCount">Maximum number of spindle records to return.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The configured spindle name records, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<IReadOnlyList<WireSpindleRecord>>> ReadSpindleNamesAsync(
        short maxCount = 8,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var block = await SendSingleRequestAsync(callTimeout.Token, new RequestBlock(0x008a, PathId: EffectivePathId(pathId))).ConfigureAwait(false);
        return ToResult(block, payload => ReadNameRecords(payload, maxCount, (index, name) => new WireSpindleRecord(index, name)));
    }

    /// <summary>
    ///     Fast-poll bundle for one axis via <c>cnc_rddynamic2</c>. Sends 9 request blocks in
    ///     one PDU and aggregates the replies — alarm flags, program/sequence numbers, feed
    ///     and spindle actuals, plus the four-slot position quadruple.
    /// </summary>
    /// <param name="axis">The axis number to read from.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The fast-poll dynamic snapshot for the axis, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<WireDynamic>> ReadDynamic2Async(
        short axis = 1,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var requestPathId = EffectivePathId(pathId);
        var blocks = await SendRequestAsync(
            callTimeout.Token,
            new RequestBlock(0x001a, PathId: requestPathId),
            new RequestBlock(0x001c, PathId: requestPathId),
            new RequestBlock(0x001d, PathId: requestPathId),
            new RequestBlock(0x0024, PathId: requestPathId),
            new RequestBlock(0x0025, PathId: requestPathId),
            new RequestBlock(0x0026, 4, axis, PathId: requestPathId),
            new RequestBlock(0x0026, 1, axis, PathId: requestPathId),
            new RequestBlock(0x0026, 6, axis, PathId: requestPathId),
            new RequestBlock(0x0026, 7, axis, PathId: requestPathId)).ConfigureAwait(false);

        var rc = AggregateRc(blocks);
        if (rc != 0) return new FocasResult<WireDynamic>(rc, null);

        var programPayload = FindPayload(blocks, 0x001c);
        return new FocasResult<WireDynamic>(
            rc,
            new WireDynamic(
                ReadFirstInt32(blocks, 0x001a),
                programPayload.Length >= 4 ? ReadInt32(programPayload, 0) : 0,
                programPayload.Length >= 8 ? ReadInt32(programPayload, 4) : 0,
                ReadFirstInt32(blocks, 0x001d),
                ReadFirstInt32(blocks, 0x0024),
                ReadFirstInt32(blocks, 0x0025),
                new WireAxisPosition(
                    ReadSelectorPosition(blocks, 0x0026, 0),
                    ReadSelectorPosition(blocks, 0x0026, 1),
                    ReadSelectorPosition(blocks, 0x0026, 2),
                    ReadSelectorPosition(blocks, 0x0026, 3))));
    }

    /// <summary>Read servo-meter load percentages via <c>cnc_rdsvmeter</c> (command <c>0x0056</c>).</summary>
    /// <param name="maxCount">Maximum number of servo meter records to return.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The servo-meter load percentages, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<IReadOnlyList<WireServoMeter>>> ReadServoMeterAsync(
        short maxCount = 32,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var requestPathId = EffectivePathId(pathId);
        var blocks = await SendRequestAsync(
            callTimeout.Token,
            new RequestBlock(0x0056, 1, PathId: requestPathId),
            new RequestBlock(0x0089, PathId: requestPathId)).ConfigureAwait(false);

        var rc = AggregateRc(blocks);
        if (rc != 0) return new FocasResult<IReadOnlyList<WireServoMeter>>(rc, null);

        var result = ParseServoMeters(FindPayload(blocks, 0x0056), FindPayload(blocks, 0x0089), maxCount);
        return new FocasResult<IReadOnlyList<WireServoMeter>>(rc, result);
    }

    /// <summary>
    ///     Read the per-axis position decimal-place figures via <c>cnc_getfigure</c>
    ///     (command <c>0x00d3</c>). The response payload is a self-delimiting sequence of
    ///     big-endian <c>short</c> decimal-place counts — one per configured axis — which the
    ///     driver applies as a <c>10^figure</c> scale on raw position reads.
    /// </summary>
    /// <remarks>
    ///     The <c>0x00d3</c> command id is co-designed with the in-tree <c>focas_mock</c> sim and
    ///     validated against it; like the rest of this managed wire backend the binary shape is
    ///     sim-consistent and has not been validated against a real Fanuc CNC (bench-CNC-gated).
    /// </remarks>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The per-axis position decimal-place figures, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<IReadOnlyList<int>>> ReadPositionFiguresAsync(
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var requestPathId = EffectivePathId(pathId);
        var block = await SendSingleRequestAsync(
            callTimeout.Token,
            new RequestBlock(0x00d3, PathId: requestPathId)).ConfigureAwait(false);

        if (block.Rc != 0) return new FocasResult<IReadOnlyList<int>>(block.Rc, null);

        var payload = block.Payload;
        var figures = new List<int>(payload.Length / 2);
        for (var offset = 0; offset + 2 <= payload.Length; offset += 2)
            figures.Add(ReadInt16(payload, offset));

        return new FocasResult<IReadOnlyList<int>>(block.Rc, figures);
    }

    /// <summary>Read per-spindle load percentages via <c>cnc_rdspload</c> (command <c>0x0040</c> with arg1=0).</summary>
    /// <param name="spindleSelector">Spindle selector; -1 selects all spindles.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The per-spindle load percentages, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<IReadOnlyList<WireSpindleMetric>>> ReadSpindleLoadAsync(
        short spindleSelector = -1,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadSpindleMetricAsync(0, spindleSelector, cancellationToken, timeout, pathId);

    /// <summary>Read per-spindle maximum RPMs via <c>cnc_rdspmaxrpm</c> (command <c>0x0040</c> with arg1=1).</summary>
    /// <param name="spindleSelector">Spindle selector; -1 selects all spindles.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The per-spindle maximum RPMs, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<IReadOnlyList<WireSpindleMetric>>> ReadSpindleMaxRpmAsync(
        short spindleSelector = -1,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadSpindleMetricAsync(1, spindleSelector, cancellationToken, timeout, pathId);

    /// <summary>
    ///     Raw-bytes parameter read via <c>cnc_rdparam</c>. Caller marshals the returned
    ///     payload to the type declared in the per-series parameter catalog. <paramref name="axis"/>
    ///     selects an axis-scoped parameter; <c>0</c> means global.
    /// </summary>
    /// <param name="dataNumber">The parameter data number.</param>
    /// <param name="axis">Axis selector; zero means a global parameter.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The raw parameter payload bytes, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<byte[]>> ReadParameterBytesAsync(
        short dataNumber,
        short axis = 0,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var secondArg = axis == 0 ? dataNumber : axis;
        var block = await SendSingleRequestAsync(callTimeout.Token, new RequestBlock(0x000e, dataNumber, secondArg, PathId: EffectivePathId(pathId))).ConfigureAwait(false);
        return ToResult(block, payload => payload);
    }

    /// <summary>Typed Int32 parameter read — convenience over <see cref="ReadParameterBytesAsync"/>.</summary>
    /// <param name="dataNumber">The parameter data number.</param>
    /// <param name="type">The FOCAS parameter type code.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The typed parameter value, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<WireParameter>> ReadParameterAsync(
        short dataNumber,
        short type = 0,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        var result = await ReadParameterBytesAsync(dataNumber, cancellationToken: cancellationToken, timeout: timeout, pathId: pathId).ConfigureAwait(false);
        if (!result.IsOk || result.Value is null) return new FocasResult<WireParameter>(result.Rc, null);
        return new FocasResult<WireParameter>(
            result.Rc,
            new WireParameter(dataNumber, type, result.Value.Length >= 4 ? ReadInt32(result.Value, 0) : 0));
    }

    /// <summary>Typed 8-bit parameter read.</summary>
    /// <param name="dataNumber">The parameter data number.</param>
    /// <param name="axis">Axis selector; zero means a global parameter.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The typed 8-bit parameter value, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<byte>> ReadParameterByteAsync(short dataNumber, short axis = 0, CancellationToken cancellationToken = default, TimeSpan? timeout = null, ushort? pathId = null)
    {
        var result = await ReadParameterBytesAsync(dataNumber, axis, cancellationToken, timeout, pathId).ConfigureAwait(false);
        return !result.IsOk || result.Value is null
            ? new FocasResult<byte>(result.Rc, default)
            : new FocasResult<byte>(result.Rc, result.Value.Length >= 1 ? result.Value[0] : default);
    }

    /// <summary>Typed 16-bit parameter read.</summary>
    /// <param name="dataNumber">The parameter data number.</param>
    /// <param name="axis">Axis selector; zero means a global parameter.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The typed 16-bit parameter value, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<short>> ReadParameterInt16Async(short dataNumber, short axis = 0, CancellationToken cancellationToken = default, TimeSpan? timeout = null, ushort? pathId = null)
    {
        var result = await ReadParameterBytesAsync(dataNumber, axis, cancellationToken, timeout, pathId).ConfigureAwait(false);
        return !result.IsOk || result.Value is null
            ? new FocasResult<short>(result.Rc, default)
            : new FocasResult<short>(result.Rc, result.Value.Length >= 2 ? ReadInt16(result.Value, 0) : default);
    }

    /// <summary>Typed 32-bit parameter read.</summary>
    /// <param name="dataNumber">The parameter data number.</param>
    /// <param name="axis">Axis selector; zero means a global parameter.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The typed 32-bit parameter value, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<int>> ReadParameterInt32Async(short dataNumber, short axis = 0, CancellationToken cancellationToken = default, TimeSpan? timeout = null, ushort? pathId = null)
    {
        var result = await ReadParameterBytesAsync(dataNumber, axis, cancellationToken, timeout, pathId).ConfigureAwait(false);
        return !result.IsOk || result.Value is null
            ? new FocasResult<int>(result.Rc, default)
            : new FocasResult<int>(result.Rc, result.Value.Length >= 4 ? ReadInt32(result.Value, 0) : default);
    }

    /// <summary>Typed IEEE-754 single-precision parameter read.</summary>
    /// <param name="dataNumber">The parameter data number.</param>
    /// <param name="axis">Axis selector; zero means a global parameter.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The typed single-precision parameter value, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<float>> ReadParameterFloat32Async(short dataNumber, short axis = 0, CancellationToken cancellationToken = default, TimeSpan? timeout = null, ushort? pathId = null)
    {
        var result = await ReadParameterBytesAsync(dataNumber, axis, cancellationToken, timeout, pathId).ConfigureAwait(false);
        return !result.IsOk || result.Value is null || result.Value.Length < 4
            ? new FocasResult<float>(result.Rc, default)
            : new FocasResult<float>(result.Rc, BitConverter.Int32BitsToSingle(ReadInt32(result.Value, 0)));
    }

    /// <summary>Typed IEEE-754 double-precision parameter read.</summary>
    /// <param name="dataNumber">The parameter data number.</param>
    /// <param name="axis">Axis selector; zero means a global parameter.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The typed double-precision parameter value, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<double>> ReadParameterFloat64Async(short dataNumber, short axis = 0, CancellationToken cancellationToken = default, TimeSpan? timeout = null, ushort? pathId = null)
    {
        var result = await ReadParameterBytesAsync(dataNumber, axis, cancellationToken, timeout, pathId).ConfigureAwait(false);
        return !result.IsOk || result.Value is null || result.Value.Length < 8
            ? new FocasResult<double>(result.Rc, default)
            : new FocasResult<double>(result.Rc, BitConverter.Int64BitsToDouble(BinaryPrimitives.ReadInt64BigEndian(result.Value.AsSpan(0, 8))));
    }

    /// <summary>Read a single macro variable via <c>cnc_rdmacro</c> (command <c>0x0015</c>).</summary>
    /// <param name="number">The macro variable number.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The macro variable value, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<WireMacro>> ReadMacroAsync(
        short number,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadSingleWithTimeoutAsync(
            0x0015,
            payload => new WireMacro(number, payload.Length >= 4 ? ReadInt32(payload, 0) : 0, payload.Length >= 6 ? ReadInt16(payload, 4) : (short)0),
            cancellationToken, timeout, EffectivePathId(pathId), number, number);

    /// <summary>
    ///     Read a PMC range via <c>pmc_rdpmcrng</c>. <paramref name="area"/> is the numeric
    ///     address-letter code (see <see cref="FocasPmcArea"/>); <paramref name="dataType"/>
    ///     is the width code (see <see cref="FocasPmcDataType"/>). Payload is decoded into
    ///     <see cref="WirePmcRange.Values"/> — one entry per slot of the requested width.
    /// </summary>
    /// <param name="area">The PMC address-letter code numeric value.</param>
    /// <param name="dataType">The PMC data width code numeric value.</param>
    /// <param name="start">The starting address.</param>
    /// <param name="end">The ending address; must be greater than or equal to start.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The decoded PMC range values, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<WirePmcRange>> ReadPmcRangeAsync(
        short area,
        short dataType,
        ushort start,
        ushort end,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        if (end < start)
            throw new ArgumentOutOfRangeException(nameof(end), "PMC end address must be greater than or equal to start.");

        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var block = await SendSingleRequestAsync(
            callTimeout.Token,
            new RequestBlock(0x8001, start, end, area, dataType, RequestClass: 2, PathId: EffectivePathId(pathId))).ConfigureAwait(false);

        return ToResult(block, payload => ParsePmcRange(area, dataType, start, end, payload));
    }

    /// <summary>Typed overload for <see cref="ReadPmcRangeAsync(short, short, ushort, ushort, CancellationToken, TimeSpan?, ushort?)"/>.</summary>
    /// <param name="area">The PMC address-letter code.</param>
    /// <param name="dataType">The PMC data width code.</param>
    /// <param name="start">The starting address.</param>
    /// <param name="end">The ending address; must be greater than or equal to start.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The decoded PMC range values, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<WirePmcRange>> ReadPmcRangeAsync(
        FocasPmcArea area,
        FocasPmcDataType dataType,
        ushort start,
        ushort end,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadPmcRangeAsync((short)area, (short)dataType, start, end, cancellationToken, timeout, pathId);

    /// <summary>
    ///     Read active alarms via <c>cnc_rdalmmsg2</c> (command <c>0x0023</c>). Parses both
    ///     the 76-byte vendor <c>ODBALMMSG2_data</c> layout and the 80-byte legacy wire
    ///     shape so the same managed surface works across firmware revisions.
    /// </summary>
    /// <param name="type">Alarm type filter; -1 reads all active alarms.</param>
    /// <param name="count">Maximum number of alarms to return.</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The active alarm list, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public async Task<FocasResult<IReadOnlyList<WireAlarm>>> ReadAlarmsAsync(
        short type = -1,
        short count = 32,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var block = await SendSingleRequestAsync(
            callTimeout.Token,
            new RequestBlock(0x0023, type, count, 2, 0x40, PathId: EffectivePathId(pathId))).ConfigureAwait(false);

        return ToResult(block, payload => ParseAlarms(payload, count));
    }

    /// <summary>Read operation mode via <c>cnc_rdopmode</c>, returned as the typed <see cref="FocasOperationMode"/>.</summary>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The current operation mode, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<FocasOperationMode>> ReadOperationModeAsync(
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadSingleWithTimeoutAsync(
            0x0057,
            payload => (FocasOperationMode)(payload.Length >= 2 ? ReadInt16(payload, 0) : (short)0),
            cancellationToken, timeout, EffectivePathId(pathId));

    /// <summary>
    ///     Raw-code variant of <see cref="ReadOperationModeAsync"/> — returns the underlying
    ///     FOCAS <c>short</c> so callers storing the raw mode code (e.g. OtOpcUa's
    ///     <c>FocasProgramInfo.Mode</c> int field) don't have to cast the enum.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The raw operation mode code, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<short>> ReadOperationModeCodeAsync(
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadSingleWithTimeoutAsync(
            0x0057,
            payload => payload.Length >= 2 ? ReadInt16(payload, 0) : (short)0,
            cancellationToken, timeout, EffectivePathId(pathId));

    /// <summary>Read the currently-executing program name + O-number via <c>cnc_exeprgname2</c> (command <c>0x00fc</c>).</summary>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The executing program name and O-number, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<WireProgramName>> ReadExecutingProgramNameAsync(
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadSingleWithTimeoutAsync(0x00fc, ParseProgramName, cancellationToken, timeout, EffectivePathId(pathId));

    /// <summary>Read the executed block count via <c>cnc_rdblkcount</c>.</summary>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The executed block count, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<int>> ReadBlockCountAsync(
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadSingleWithTimeoutAsync(
            0x0035,
            payload => payload.Length >= 4 ? ReadInt32(payload, 0) : 0,
            cancellationToken, timeout, EffectivePathId(pathId));

    /// <summary>
    ///     Read one cumulative timer via <c>cnc_rdtimer</c>. <paramref name="type"/> selects
    ///     PowerOn / Operating / Cutting / Cycle per the FOCAS spec (0..3).
    /// </summary>
    /// <param name="type">Timer type selector (0=PowerOn, 1=Operating, 2=Cutting, 3=Cycle).</param>
    /// <param name="cancellationToken">Cancellation token for the read operation.</param>
    /// <param name="timeout">Optional per-call timeout override.</param>
    /// <param name="pathId">Optional path ID override; defaults to <see cref="PathId"/>.</param>
    /// <returns>The cumulative timer value, wrapped in a <see cref="FocasResult{T}"/>.</returns>
    public Task<FocasResult<WireTimer>> ReadTimerAsync(
        short type,
        CancellationToken cancellationToken = default,
        TimeSpan? timeout = null,
        ushort? pathId = null)
        => ReadSingleWithTimeoutAsync(
            0x0120,
            payload => ParseTimer(type, payload),
            cancellationToken, timeout, EffectivePathId(pathId), type);

    // ---- internal plumbing ------------------------------------------------------------

    private async Task<FocasResult<IReadOnlyList<WireSpindleMetric>>> ReadSpindleMetricAsync(
        int metric, short spindleSelector, CancellationToken cancellationToken, TimeSpan? timeout, ushort? pathId)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        var block = await SendSingleRequestAsync(
            callTimeout.Token,
            new RequestBlock(0x0040, metric, spindleSelector, PathId: EffectivePathId(pathId))).ConfigureAwait(false);

        return ToResult<IReadOnlyList<WireSpindleMetric>>(block, payload =>
        {
            var values = new List<WireSpindleMetric>();
            for (var offset = 0; offset + 8 <= payload.Length; offset += 8)
                values.Add(new WireSpindleMetric((short)(values.Count + 1), ReadInt32(payload, offset)));
            return values;
        });
    }

    private async Task<FocasResult<T>> ReadSingleAsync<T>(
        ushort command,
        Func<byte[], T> parser,
        ushort? pathId = null,
        int arg1 = 0,
        int arg2 = 0,
        int arg3 = 0,
        int arg4 = 0,
        CancellationToken cancellationToken = default)
    {
        var block = await SendSingleRequestAsync(cancellationToken, new RequestBlock(command, arg1, arg2, arg3, arg4, PathId: EffectivePathId(pathId))).ConfigureAwait(false);
        return ToResult(block, parser);
    }

    private async Task<FocasResult<T>> ReadSingleWithTimeoutAsync<T>(
        ushort command,
        Func<byte[], T> parser,
        CancellationToken cancellationToken,
        TimeSpan? timeout,
        ushort pathId,
        int arg1 = 0,
        int arg2 = 0,
        int arg3 = 0,
        int arg4 = 0)
    {
        using var callTimeout = CreateCallTimeout(cancellationToken, timeout);
        return await ReadSingleAsync(command, parser, pathId, arg1, arg2, arg3, arg4, callTimeout.Token).ConfigureAwait(false);
    }

    private async Task<ResponseBlock> SendSingleRequestAsync(CancellationToken cancellationToken, RequestBlock block)
    {
        var blocks = await SendRequestAsync(cancellationToken, block).ConfigureAwait(false);
        return blocks.Count == 0 ? new ResponseBlock(block.Command, 0, Array.Empty<byte>()) : blocks[0];
    }

    private async Task<IReadOnlyList<ResponseBlock>> SendRequestAsync(CancellationToken cancellationToken, params RequestBlock[] blocks)
    {
        EnsureConnected();
        await _requestGate.WaitAsync(cancellationToken).ConfigureAwait(false);
        var requestStarted = false;
        try
        {
            var body = FocasWireProtocol.BuildRequestBody(blocks);
            requestStarted = true;
            await SendPduAsync(_stream2!, FocasWireProtocol.TypeData, body, cancellationToken).ConfigureAwait(false);
            var response = await ReadExpectedPduAsync(_stream2!, FocasWireProtocol.TypeData, cancellationToken).ConfigureAwait(false);
            var responseBlocks = FocasWireProtocol.ParseResponseBlocks(response.Body);
            foreach (var block in responseBlocks)
                _logger?.LogDebug("FOCAS response command=0x{Command:x4} rc={Rc} payloadLength={PayloadLength}", block.Command, block.Rc, block.Payload.Length);
            return responseBlocks;
        }
        catch (Exception ex) when (requestStarted && IsTransientException(ex))
        {
            // A cancelled or failed mid-request write leaves the wire in an undefined state —
            // tear the connection down so the next caller reconnects cleanly instead of
            // consuming a stale response.
            CloseTransport();
            throw new FocasWireException("FOCAS wire request failed; connection was closed to avoid response desynchronization.", ex, isTransient: true);
        }
        finally
        {
            _requestGate.Release();
        }
    }

    private static async Task<TcpClient> ConnectSocketAsync(string host, int port, CancellationToken cancellationToken)
    {
        var socket = new TcpClient { NoDelay = true };
        try
        {
            await WithCancellation(socket.ConnectAsync(host, port), cancellationToken).ConfigureAwait(false);
            return socket;
        }
        catch
        {
            socket.Dispose();
            throw;
        }
    }

    private static async Task SendPduAsync(NetworkStream stream, byte type, ReadOnlyMemory<byte> body, CancellationToken cancellationToken)
    {
        var pdu = FocasWireProtocol.BuildPdu(type, FocasWireProtocol.DirectionRequest, body.Span);
        await stream.WriteAsync(pdu, 0, pdu.Length, cancellationToken).ConfigureAwait(false);
        await stream.FlushAsync(cancellationToken).ConfigureAwait(false);
    }

    private static void SendPdu(NetworkStream stream, byte type, ReadOnlySpan<byte> body)
    {
        var pdu = FocasWireProtocol.BuildPdu(type, FocasWireProtocol.DirectionRequest, body);
        stream.Write(pdu, 0, pdu.Length);
        stream.Flush();
    }

    private void ThrowIfDisposed()
    {
        if (_disposed) throw new ObjectDisposedException(nameof(FocasWireClient));
    }

    private static async Task WithCancellation(Task task, CancellationToken cancellationToken)
    {
        if (!cancellationToken.CanBeCanceled)
        {
            await task.ConfigureAwait(false);
            return;
        }

        var cancellation = new TaskCompletionSource<bool>();
        using var registration = cancellationToken.Register(static state => ((TaskCompletionSource<bool>)state!).TrySetResult(true), cancellation);
        if (task != await Task.WhenAny(task, cancellation.Task).ConfigureAwait(false))
            throw new OperationCanceledException(cancellationToken);
        await task.ConfigureAwait(false);
    }

    private static CancellationTokenSource CreateCallTimeout(CancellationToken cancellationToken, TimeSpan? timeout)
    {
        var source = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        if (timeout is { } value) source.CancelAfter(value);
        return source;
    }

    private static async Task<Pdu> ReadExpectedPduAsync(NetworkStream stream, byte expectedType, CancellationToken cancellationToken)
    {
        var pdu = await FocasWireProtocol.ReadPduAsync(stream, cancellationToken).ConfigureAwait(false);
        if (pdu.Type != expectedType || pdu.Direction != FocasWireProtocol.DirectionResponse)
            throw new FocasWireException($"Unexpected FOCAS PDU type 0x{pdu.Type:x2}, direction 0x{pdu.Direction:x2}.", rc: null);
        return pdu;
    }

    private void EnsureConnected()
    {
        ThrowIfDisposed();
        if (!_connected || _stream2 is null)
            throw new FocasWireException("FOCAS wire client is not connected.", rc: null, isTransient: true);
    }

    private void CloseTransport()
    {
        _connected = false;
        _sysInfo = null;
        _stream1?.Dispose();
        _stream2?.Dispose();
        _socket1?.Dispose();
        _socket2?.Dispose();
        _stream1 = null;
        _stream2 = null;
        _socket1 = null;
        _socket2 = null;
    }

    private ushort EffectivePathId(ushort? pathId) => pathId ?? PathId;

    private static FocasResult<T> ToResult<T>(ResponseBlock block, Func<byte[], T> parser)
        => block.Rc != 0
            ? new FocasResult<T>(block.Rc, default)
            : new FocasResult<T>(block.Rc, parser(block.Payload));

    private static short AggregateRc(IReadOnlyList<ResponseBlock> blocks)
        => blocks.FirstOrDefault(block => block.Rc != 0)?.Rc ?? 0;

    /// <summary>
    ///     Decode a <c>cnc_rdtimer</c> (0x0120) payload into <see cref="WireTimer"/>. The 8-byte
    ///     data block is two 32-bit fields {minute, msec}, and they are <b>little-endian</b> on the
    ///     wire — unlike the big-endian block envelope and every other payload (sysinfo / dynamic /
    ///     macro). Validated against a live FANUC 31i-B (2026-06-25): the msec field only falls in
    ///     valid range (0..59999) under little-endian; big-endian decoded it as ~2.4e9. Captured
    ///     cutting-time payload <c>ac f2 10 00 90 a3 00 00</c> → minute=1110188, msec=41872. See
    ///     <c>docs/plans/2026-06-25-focas-pdu-v3-30i-b-support.md</c>.
    /// </summary>
    /// <param name="type">Timer type selector, carried through into the returned <see cref="WireTimer"/>.</param>
    /// <param name="payload">The raw 8-byte <c>cnc_rdtimer</c> response payload.</param>
    /// <returns>The decoded minute/msec timer value.</returns>
    internal static WireTimer ParseTimer(short type, byte[] payload) => new(
        type,
        payload.Length >= 4 ? BinaryPrimitives.ReadInt32LittleEndian(payload.AsSpan(0, 4)) : 0,
        payload.Length >= 8 ? BinaryPrimitives.ReadInt32LittleEndian(payload.AsSpan(4, 4)) : 0);

    /// <summary>
    ///     Decode a <c>cnc_rdsvmeter</c> response into <see cref="WireServoMeter"/> records. On the
    ///     31i-B (v3) each per-axis LOADELM is <b>8 bytes</b> — {int32 data; int16 dec; int16 unit}
    ///     — NOT the 12-byte shape the original parser assumed. The 12-byte stride misaligned after
    ///     the first record (it read the dec/unit shorts of the prior record as the next record's
    ///     data → wild values like 655360). Axis NAMES are not in the svmeter payload; they come
    ///     from the <c>cnc_rdaxisname</c> (0x0089) block requested alongside it and are correlated
    ///     by index. Validated against a live 31i-B 2026-06-25.
    ///     <para><b>Scaling caveat:</b> downstream applies LoadPercent = data / 10^dec; on the 31i-B
    ///     <c>dec</c> read as 10, which makes idle loads vanishingly small. The data/dec/unit field
    ///     semantics for servo load are inferred from the wire and not yet confirmed against the
    ///     machine's servo-meter screen — confirm magnitude at commissioning. The alignment + name
    ///     fix here is what removes the gross misaligned garbage.</para>
    /// </summary>
    /// <param name="svPayload">The raw <c>cnc_rdsvmeter</c> response payload.</param>
    /// <param name="axisNamePayload">The raw <c>cnc_rdaxisname</c> response payload used to correlate axis names by index.</param>
    /// <param name="maxCount">Maximum number of servo meter records to return.</param>
    /// <returns>The decoded servo-meter records.</returns>
    internal static IReadOnlyList<WireServoMeter> ParseServoMeters(byte[] svPayload, byte[] axisNamePayload, int maxCount)
    {
        var result = new List<WireServoMeter>();
        for (var offset = 0; offset + 8 <= svPayload.Length && result.Count < maxCount; offset += 8)
        {
            var index = result.Count;
            var nameOffset = index * 4;
            var name = nameOffset + 4 <= axisNamePayload.Length
                ? FocasWireProtocol.ReadNameRecord(axisNamePayload.AsSpan(nameOffset, 4))
                : string.Empty;
            result.Add(new WireServoMeter(
                (short)(index + 1),
                name,
                ReadInt32(svPayload, offset),
                ReadInt16(svPayload, offset + 4),
                ReadInt16(svPayload, offset + 6)));
        }
        return result;
    }

    /// <summary>Byte width of one PMC slot for a FOCAS data-type code: Byte=1, Word=2, Long/Real=4, Double=8.</summary>
    /// <param name="dataType">The PMC data width code.</param>
    /// <returns>The byte width of one slot for the given data-type code.</returns>
    internal static int PmcByteWidth(short dataType) => dataType switch
    {
        1 => 2,
        2 or 4 => 4,
        5 => 8,
        _ => 1,
    };

    /// <summary>
    ///     Decode a <c>pmc_rdpmcrng</c> payload into <see cref="WirePmcRange"/>. The CNC returns
    ///     (end-start+1) BYTES; this slices them into width-sized big-endian slots. Callers must
    ///     size the request range to <c>width</c> bytes per value (see
    ///     <c>WireFocasClient.ReadPmcAsync</c>) or a trailing partial slot is dropped — which on the
    ///     31i-B surfaced as a spurious <c>BadOutOfRange</c> for a single Word read. 2026-06-25.
    /// </summary>
    /// <param name="area">The PMC address-letter code numeric value.</param>
    /// <param name="dataType">The PMC data width code numeric value.</param>
    /// <param name="start">The starting address.</param>
    /// <param name="end">The ending address.</param>
    /// <param name="payload">The raw <c>pmc_rdpmcrng</c> response payload.</param>
    /// <returns>The decoded PMC range values.</returns>
    internal static WirePmcRange ParsePmcRange(short area, short dataType, ushort start, ushort end, byte[] payload)
    {
        var width = PmcByteWidth(dataType);
        var values = new List<long>();
        for (var offset = 0; offset + width <= payload.Length; offset += width)
        {
            values.Add(width switch
            {
                1 => payload[offset],
                2 => ReadInt16(payload, offset),
                4 => ReadInt32(payload, offset),
                8 => BinaryPrimitives.ReadInt64BigEndian(payload.AsSpan(offset, 8)),
                _ => 0,
            });
        }
        return new WirePmcRange(area, dataType, start, end, values);
    }

    private static byte[] FindPayload(IReadOnlyList<ResponseBlock> blocks, ushort command)
        => blocks.FirstOrDefault(block => block.Command == command)?.Payload ?? Array.Empty<byte>();

    private static int ReadFirstInt32(IReadOnlyList<ResponseBlock> blocks, ushort command)
    {
        var payload = FindPayload(blocks, command);
        return payload.Length >= 4 ? ReadInt32(payload, 0) : 0;
    }

    private static int ReadSelectorPosition(IReadOnlyList<ResponseBlock> blocks, ushort command, int selectorIndex)
    {
        var seen = 0;
        foreach (var block in blocks)
        {
            if (block.Command != command) continue;
            if (seen == selectorIndex)
                return block.Payload.Length >= 4 ? ReadInt32(block.Payload, 0) : 0;
            seen++;
        }
        return 0;
    }

    private static WireSysInfo ParseSysInfo(byte[] payload)
    {
        RequireLength(payload, 16, "cnc_sysinfo");
        return new WireSysInfo(
            ReadInt16(payload, 0),
            ReadInt16(payload, 2),
            FocasWireProtocol.ReadAscii(payload.AsSpan(4, 2)),
            FocasWireProtocol.ReadAscii(payload.AsSpan(6, 2)),
            FocasWireProtocol.ReadAscii(payload.AsSpan(8, 4)),
            FocasWireProtocol.ReadAscii(payload.AsSpan(12, 4)),
            payload.Length >= 18 ? FocasWireProtocol.ReadAscii(payload.AsSpan(16, 2)) : string.Empty);
    }

    private static WireProgramName ParseProgramName(byte[] payload)
    {
        var nameLength = payload.Length >= 40 ? 36 : payload.Length;
        var name = FocasWireProtocol.ReadAscii(payload.AsSpan(0, nameLength));
        var number = payload.Length >= 40 ? ReadInt32(payload, 36) : (int?)null;
        return new WireProgramName(name, number);
    }

    private static IReadOnlyList<WireAlarm> ParseAlarms(byte[] payload, short count)
        => payload.Length % 76 == 0
            ? ParseVendorAlarms(payload, count)
            : ParseLegacyWireAlarms(payload, count);

    private static IReadOnlyList<WireAlarm> ParseVendorAlarms(byte[] payload, short count)
    {
        var alarms = new List<WireAlarm>();
        for (var offset = 0; offset + 76 <= payload.Length && alarms.Count < count; offset += 76)
        {
            var messageLength = ReadInt16(payload, offset + 10);
            alarms.Add(new WireAlarm(
                ReadInt32(payload, offset),
                ReadInt16(payload, offset + 4),
                ReadInt16(payload, offset + 6),
                messageLength,
                FocasWireProtocol.ReadAscii(payload.AsSpan(offset + 12, 64))));
        }
        return alarms;
    }

    private static IReadOnlyList<WireAlarm> ParseLegacyWireAlarms(byte[] payload, short count)
    {
        var alarms = new List<WireAlarm>();
        for (var offset = 0; offset + 80 <= payload.Length && alarms.Count < count; offset += 80)
        {
            alarms.Add(new WireAlarm(
                ReadInt32(payload, offset),
                (short)ReadInt32(payload, offset + 4),
                (short)ReadInt32(payload, offset + 8),
                (short)ReadInt32(payload, offset + 12),
                FocasWireProtocol.ReadAscii(payload.AsSpan(offset + 16, 64))));
        }
        return alarms;
    }

    private static IReadOnlyList<T> ReadNameRecords<T>(byte[] payload, short maxCount, Func<short, string, T> factory)
    {
        var names = new List<T>();
        for (var offset = 0; offset + 4 <= payload.Length && offset / 4 < maxCount; offset += 4)
        {
            var name = FocasWireProtocol.ReadNameRecord(payload.AsSpan(offset, 4));
            if (!string.IsNullOrWhiteSpace(name))
                names.Add(factory((short)((offset / 4) + 1), name));
        }
        return names;
    }

    private static void RequireLength(byte[] payload, int length, string call)
    {
        if (payload.Length < length)
            throw new FocasWireException($"{call} returned {payload.Length} bytes; expected at least {length}.", rc: null);
    }

    private static bool IsTransientException(Exception exception)
        => exception is IOException or SocketException or TimeoutException or OperationCanceledException
            || exception.InnerException is IOException or SocketException or TimeoutException or OperationCanceledException;

    private static short ReadInt16(byte[] bytes, int offset)
        => BinaryPrimitives.ReadInt16BigEndian(bytes.AsSpan(offset, 2));

    private static int ReadInt32(byte[] bytes, int offset)
        => BinaryPrimitives.ReadInt32BigEndian(bytes.AsSpan(offset, 4));
}
