using System.Buffers.Binary;
using System.Runtime.CompilerServices;
using System.Runtime.Versioning;
using System.ServiceModel;
using System.ServiceModel.Channels;
using AVEVA.Historian.Client.Models;
using AVEVA.Historian.Client.Wcf.Contracts;

namespace AVEVA.Historian.Client.Wcf;

/// <remarks>
/// Mirrors HistorianWcfReadOrchestrator but targets IRetrievalServiceContract4 for the event flow.
/// Event row buffer layout is undecoded as of this pass — when StartEventQuery succeeds, this
/// orchestrator returns an empty enumeration but logs the row-buffer length via the
/// <see cref="LastResultBufferLength"/> diagnostic so a follow-up capture can decode the wire shape.
/// </remarks>
[SupportedOSPlatform("windows")]
internal sealed class HistorianWcfEventOrchestrator
{
    private const int OpenConnection3MinResponseLength = 5;
    private const int CredentialBlockSizeBytes = 1026;
    private const int MaxValClRounds = 8;
    private const string ClientNodeNameFallback = "AVEVA.Historian.Client";
    private const string ClientDataSourceId = "2020.406.2652.2";
    private const string ClientDllVersionString = "2020.406.2652.2";
    private const byte NativeClientType = 4;
    private const uint NativeIntegratedReadOnlyConnectionMode = 0x402;
    private const byte NativeClientCommonInfoFormatVersion = 4;
    private const ushort NativeHcalVersion = 17;
    private const uint NativeClientVersionInt = 999_999;
    private const ushort NativeOpen2ClientVersion = 9;

    /// <summary>
    /// Documented native CM_EVENT default tag id used by aahClientManaged.dll
    /// CreateDefaultEventTag → ConvertEventTagToTagMetadata. Registering this tag via
    /// IHistoryServiceContract2.RegisterTags2 before StartEventQuery causes the server
    /// to subscribe the session to CM_EVENT events; without it,
    /// GetNextEventQueryResultBuffer returns native error type=4 code=85 (0x55).
    /// </summary>
    private static readonly Guid CmEventTagId = new("353b8145-5df0-4d46-a253-871aef49b321");

    private readonly HistorianClientOptions _options;

    public HistorianWcfEventOrchestrator(HistorianClientOptions options)
    {
        _options = options ?? throw new ArgumentNullException(nameof(options));
    }

    /// <summary>Diagnostic: length of the most recent event-row result buffer the server sent.</summary>
    public int LastResultBufferLength { get; private set; }

    /// <summary>Diagnostic: type+code description of the most recent error/terminal buffer.</summary>
    public string LastErrorBufferDescription { get; private set; } = string.Empty;

    /// <summary>Diagnostic: handle string passed to EnsT2.</summary>
    public static string LastEnsT2Handle { get; private set; } = string.Empty;

    /// <summary>Diagnostic: SHA256 of the CTagMetadata payload sent to EnsT2.</summary>
    public static string LastEnsT2PayloadSha256 { get; private set; } = string.Empty;

    /// <summary>Diagnostic: native return code from the prerequisite UpdC3 call.</summary>
    public static uint LastUpdC3ReturnCode { get; private set; }

    /// <summary>Diagnostic: native return code from the prerequisite RTag2 call.</summary>
    public static uint LastRTag2ReturnCode { get; private set; }

    public async IAsyncEnumerable<HistorianEvent> ReadEventsAsync(
        DateTime startUtc,
        DateTime endUtc,
        [EnumeratorCancellation] CancellationToken cancellationToken)
    {
        if (!_options.IntegratedSecurity && string.IsNullOrEmpty(_options.UserName))
        {
            throw new ProtocolEvidenceMissingException(
                "Managed event flow currently requires IntegratedSecurity or an explicit UserName + Password.");
        }

        cancellationToken.ThrowIfCancellationRequested();

        IReadOnlyList<HistorianEvent> events = await Task.Run(
            () => RunEventChain(startUtc, endUtc, cancellationToken),
            cancellationToken).ConfigureAwait(false);

        foreach (HistorianEvent evt in events)
        {
            cancellationToken.ThrowIfCancellationRequested();
            yield return evt;
        }
    }

    private List<HistorianEvent> RunEventChain(DateTime startUtc, DateTime endUtc, CancellationToken cancellationToken)
    {
        Guid contextKey = Guid.NewGuid();
        var (histBinding, histEndpoint, retrBinding, retrEndpoint) = HistorianWcfBindingFactory.CreateBindingPair(_options);
        Binding auxBinding = HistorianWcfBindingFactory.CreateAuxiliaryBinding(_options);
        EndpointAddress statusEndpoint = HistorianWcfBindingFactory.CreateAuxiliaryEndpointAddress(_options, HistorianWcfServiceNames.Status);
        EndpointAddress transactionEndpoint = HistorianWcfBindingFactory.CreateAuxiliaryEndpointAddress(_options, HistorianWcfServiceNames.Transaction);
        uint clientHandle = HistorianWcfAuthChainHelper.OpenAuthenticatedConnection(
            _options, histBinding, histEndpoint, contextKey, cancellationToken,
            connectionMode: HistorianWcfAuthChainHelper.NativeIntegratedReadOnlyConnectionMode,
            additionalSetup: (historyChannel, context) =>
                AddCmEventTagViaAddT(historyChannel, context, auxBinding, statusEndpoint, transactionEndpoint, retrBinding, retrEndpoint));
        return RunEventQuery(retrBinding, retrEndpoint, clientHandle, startUtc, endUtc, cancellationToken);
    }

    private List<HistorianEvent> RunEventQuery(
        Binding binding,
        EndpointAddress retrievalEndpoint,
        uint clientHandle,
        DateTime startUtc,
        DateTime endUtc,
        CancellationToken cancellationToken)
    {
        ChannelFactory<IRetrievalServiceContract4> factory = new(binding, retrievalEndpoint);

        try
        {
            IRetrievalServiceContract4 channel = factory.CreateChannel();
            ICommunicationObject channelCo = (ICommunicationObject)channel;
            try
            {
                channel.GetInterfaceVersion(out _);

                uint isAllowedReturn = channel.IsOriginalAllowed(clientHandle, out bool isAllowed);
                if (isAllowedReturn != 0 || !isAllowed)
                {
                    throw new InvalidOperationException(
                        $"Retr.IsOriginalAllowed denied the connection (return={isAllowedReturn}, isAllowed={isAllowed}).");
                }

                IReadOnlyList<HistorianEventQueryAttempt> attempts = HistorianEventQueryProtocol.CreateStartEventQueryAttempts(
                    startUtc.ToUniversalTime(),
                    endUtc.ToUniversalTime(),
                    eventCount: 5);
                byte[] requestBuffer = attempts[0].RequestBuffer;

                uint queryHandle = 0;
                bool startSuccess = channel.StartEventQuery(
                    clientHandle,
                    HistorianEventQueryProtocol.QueryRequestTypeEvent,
                    checked((uint)requestBuffer.Length),
                    requestBuffer,
                    out _,
                    out _,
                    ref queryHandle,
                    out _,
                    out byte[] startError);
                startError ??= [];
                if (!startSuccess)
                {
                    throw new InvalidOperationException(
                        $"Retr.StartEventQuery failed (errorLen={startError.Length}, error5={DescribeNativeError(startError)}).");
                }

                List<HistorianEvent> events = [];
                while (true)
                {
                    cancellationToken.ThrowIfCancellationRequested();

                    bool nextSuccess = channel.GetNextEventQueryResultBuffer(
                        clientHandle,
                        queryHandle,
                        out _,
                        out byte[] resultBuffer,
                        out _,
                        out byte[] errorBuffer);
                    resultBuffer ??= [];
                    errorBuffer ??= [];

                    LastResultBufferLength = resultBuffer.Length;
                    LastErrorBufferDescription = DescribeNativeError(errorBuffer);

                    // Any 5-byte type=4 error is treated as a soft terminal so the chain can
                    // surface evidence even when an unfamiliar code (e.g. 85 / 0x55 observed
                    // on first end-to-end runs without an event-tag registration step) blocks
                    // row enumeration. Code 30 (NoMoreData) is the canonical terminal; other
                    // codes mean "stop reading and let the caller see the diagnostic". When
                    // nextSuccess is false the server signaled hard failure; if there is also
                    // a 5-byte type=4 error buffer we still return the buffer length as
                    // evidence and surface via LastErrorBufferDescription rather than throw.
                    if (errorBuffer.Length == 5 && errorBuffer[0] == 4)
                    {
                        return events;
                    }

                    if (!nextSuccess)
                    {
                        throw new InvalidOperationException(
                            $"Retr.GetNextEventQueryResultBuffer failed (errorLen={errorBuffer.Length}, error5={DescribeNativeError(errorBuffer)}).");
                    }

                    if (resultBuffer.Length > 0)
                    {
                        events.AddRange(HistorianEventRowProtocol.Parse(resultBuffer));
                    }

                    if (resultBuffer.Length == 0 && errorBuffer.Length == 0)
                    {
                        return events;
                    }
                }
            }
            finally
            {
                CloseChannelSafely(channelCo);
            }
        }
        finally
        {
            CloseFactorySafely(factory);
        }
    }

    /// <summary>Diagnostic: native return code from the last AddT(CM_EVENT) call.</summary>
    public static uint LastAddReturnCode { get; private set; }

    /// <summary>Diagnostic: byte length of the AddT response output buffer.</summary>
    public static int LastAddOutputLength { get; private set; }

    /// <remarks>
    /// Calls <c>IHistoryServiceContract.AddTags</c> with the documented CM_EVENT CTagMetadata
    /// payload. The chain now reaches the server's AddT handler (a real WCF response is
    /// returned rather than the previous parameter-binding failure) but currently receives
    /// native return code 76 against this Historian. Combined with code 85 from
    /// <c>GetNextEventQueryResultBuffer</c>, two specific server rejections remain to decode
    /// before live event reads return rows. The orchestrator continues regardless so the
    /// caller can see the chain outcome via <see cref="LastAddReturnCode"/>,
    /// <see cref="LastResultBufferLength"/>, and <see cref="LastErrorBufferDescription"/>.
    /// Next concrete step: instrument <c>Wcf.AddT.Request</c> on a successful native event
    /// run and compare byte-for-byte against this serialiser's output.
    /// </remarks>
    /// <remarks>
    /// Replays the native event-tag registration sequence captured via the
    /// instrument-wcf-writemessage IL-rewrite tool: UpdC3 (UpdateClientStatus3) → RTag2
    /// (RegisterTags2 with the CM_EVENT tag id) → EnsT2 (EnsureTags2 with the full
    /// CTagMetadata blob). The 81-byte UpdC3 status blob and 24-byte RTag2 buffer are
    /// captured byte-for-byte from a successful native event read; the EnsT2 payload is
    /// regenerated by <see cref="HistorianAddTagsProtocol.SerializeCmEventCTagMetadata"/>.
    /// The Stat-service queries the native client also issues (Stat/GetV, Stat/GETHI,
    /// Stat/GetSystemParameter for AllowOriginals/HistorianPartner/HistorianVersion/
    /// MaxCyclicStorageTimeout/RealTimeWindow/FutureTimeThreshold/AllowRenameTags) appear
    /// informational and are skipped here.
    /// </remarks>
    private static void AddCmEventTagViaAddT(
        IHistoryServiceContract2 historyChannel,
        HistorianWcfAuthChainHelper.OpenConnectionContext context,
        Binding statusBinding,
        EndpointAddress statusEndpoint,
        EndpointAddress transactionEndpoint,
        Binding retrievalBinding,
        EndpointAddress retrievalEndpoint)
    {
        string handle = context.StorageSessionId.ToString("D").ToUpperInvariant();
        LastEnsT2Handle = handle;

        ChannelFactory<IStatusServiceContract2> statusFactory = new(statusBinding, statusEndpoint);
        IStatusServiceContract2 statusChannel = statusFactory.CreateChannel();
        ICommunicationObject statusCo = (ICommunicationObject)statusChannel;

        ChannelFactory<ITransactionServiceContract> transactionFactory = new(statusBinding, transactionEndpoint);
        ITransactionServiceContract transactionChannel = transactionFactory.CreateChannel();
        ICommunicationObject transactionCo = (ICommunicationObject)transactionChannel;

        ChannelFactory<IRetrievalServiceContract4> retrievalFactory = new(retrievalBinding, retrievalEndpoint);
        IRetrievalServiceContract4 retrievalChannel = retrievalFactory.CreateChannel();
        ICommunicationObject retrievalCo = (ICommunicationObject)retrievalChannel;

        try
        {
            // Replays the discovery dance the native event flow runs between Open2 and EnsT2,
            // captured byte-for-byte via instrument-wcf-{write,read}message. Best-effort —
            // individual calls may fail on this server; the chain continues regardless because
            // the goal is to put the server-side session into the state EnsT2 expects.
            TryRun(() => statusChannel.GetInterfaceVersion(out _));
            TryRun(() => statusChannel.GetInterfaceVersion(out _));

            byte[] historianVersionRequest = BuildGetHistorianInfoRequest("HistorianVersion");
            TryRun(() => statusChannel.GetHistorianInfo(handle, historianVersionRequest, out _, out _));
            TryRun(() => statusChannel.GetHistorianInfo(handle, historianVersionRequest, out _, out _));

            byte[] clientStatus = BuildUpdC3ClientStatusBlob();
            bool updSuccess = historyChannel.UpdateClientStatus3(
                handle: handle,
                clientStatusSize: (uint)clientStatus.Length,
                clientStatus: ref clientStatus,
                serverStatusSize: out _,
                serverStatus: out _,
                errorSize: out _,
                errorBuffer: out _);
            LastUpdC3ReturnCode = updSuccess ? 0u : 1u;

            // Records 11-16: 6 system-parameter queries before RTag2.
            foreach (string parameterName in NativeStatusParametersBeforeRTag2)
            {
                TryRun(() => statusChannel.GetSystemParameter(context.ClientHandle, parameterName, out _, out _, out _));
            }

            byte[] registerBuffer = BuildRTag2CmEventInputBuffer();
            bool registerSuccess = historyChannel.RegisterTags2(
                handle: handle,
                elementCount: 1,
                inputBuffer: registerBuffer,
                outputBuffer: out _,
                errorBuffer: out _);
            LastRTag2ReturnCode = registerSuccess ? 0u : 1u;

            // Record 18: one more system-parameter query after RTag2 before EnsT2.
            TryRun(() => statusChannel.GetSystemParameter(context.ClientHandle, "AllowRenameTags", out _, out _, out _));

            // Records 19-21: cross-service version probes the native client makes between
            // RTag2 and EnsT2. They likely register the client with each service's session
            // table; without them EnsT2 may reject the session.
            TryRun(() => transactionChannel.GetInterfaceVersion(out _));
            TryRun(() => statusChannel.GetInterfaceVersion(out _));
            TryRun(() => retrievalChannel.GetInterfaceVersion(out _));

            byte[] payload = HistorianAddTagsProtocol.SerializeCmEventCTagMetadata(DateTime.UtcNow);
            using (var sha = System.Security.Cryptography.SHA256.Create())
            {
                byte[] hash = sha.ComputeHash(payload);
                LastEnsT2PayloadSha256 = BitConverter.ToString(hash).Replace("-", string.Empty).ToLowerInvariant();
            }

            bool ensureSuccess = historyChannel.EnsureTags2(
                handle: handle,
                elementCount: 1,
                inputBuffer: payload,
                outputBuffer: out byte[] addOutput,
                errorBuffer: out _);

            LastAddReturnCode = ensureSuccess ? 0u : 1u;
            LastAddOutputLength = addOutput?.Length ?? 0;
        }
        catch (Exception ex)
        {
            LastAddReturnCode = 0xFFFFFFFFu;
            LastAddOutputLength = 0;
            _ = ex;
        }
        finally
        {
            CloseChannelSafely(retrievalCo);
            CloseFactorySafely(retrievalFactory);
            CloseChannelSafely(transactionCo);
            CloseFactorySafely(transactionFactory);
            CloseChannelSafely(statusCo);
            CloseFactorySafely(statusFactory);
        }
    }

    private static readonly string[] NativeStatusParametersBeforeRTag2 =
    [
        "AllowOriginals",
        "HistorianPartner",
        "HistorianVersion",
        "MaxCyclicStorageTimeout",
        "RealTimeWindow",
        "FutureTimeThreshold",
    ];

    private static void TryRun(Action action)
    {
        try { action(); }
        catch { }
    }

    /// <summary>
    /// Native GETHI pRequestBuff layout for a parameter-name query: 8-byte header
    /// (UInt16 0x6753 + UInt16 0x0002 + UInt32 nameLength) + UTF-16 LE chars (no
    /// trailing null byte — observed truncated by 1 byte vs full UTF-16 in the
    /// captured native bytes). Layout taken from
    /// writemessage-capture-event-latest.ndjson record 8.
    /// </summary>
    private static byte[] BuildGetHistorianInfoRequest(string parameterName)
    {
        byte[] nameBytes = System.Text.Encoding.Unicode.GetBytes(parameterName);
        // Native truncates the trailing high byte of the last UTF-16 char.
        int payloadLength = nameBytes.Length > 0 ? nameBytes.Length - 1 : 0;
        byte[] buffer = new byte[8 + payloadLength];
        BinaryPrimitives.WriteUInt16LittleEndian(buffer.AsSpan(0, 2), 0x6753);
        BinaryPrimitives.WriteUInt16LittleEndian(buffer.AsSpan(2, 2), 0x0002);
        BinaryPrimitives.WriteUInt32LittleEndian(buffer.AsSpan(4, 4), (uint)parameterName.Length);
        Buffer.BlockCopy(nameBytes, 0, buffer, 8, payloadLength);
        return buffer;
    }

    /// <summary>
    /// 81-byte UpdC3 clientStatus blob captured from a native event read (record 10 of
    /// writemessage-capture-event-latest.ndjson). Layout: 0x02 0x01 + 76 zero bytes +
    /// uint32(0x0000001E). The trailing 30 is likely an interval / timeout in seconds; all
    /// other observed fields are zero for a fresh session.
    /// </summary>
    private static byte[] BuildUpdC3ClientStatusBlob()
    {
        byte[] blob = new byte[81];
        blob[0] = 0x02;
        blob[1] = 0x01;
        blob[77] = 0x1E;
        return blob;
    }

    /// <summary>
    /// 24-byte RTag2 pInBuff captured from a native event read (record 17). Layout:
    /// 8-byte header (0x50 0x67 0x02 0x00 + uint32 element count = 1) + 16-byte tag id GUID.
    /// </summary>
    private static byte[] BuildRTag2CmEventInputBuffer()
    {
        byte[] buffer = new byte[24];
        buffer[0] = 0x50;
        buffer[1] = 0x67;
        buffer[2] = 0x02;
        buffer[3] = 0x00;
        BinaryPrimitives.WriteUInt32LittleEndian(buffer.AsSpan(4, 4), 1u);
        CmEventTagId.ToByteArray().CopyTo(buffer.AsSpan(8, 16));
        return buffer;
    }

    private static string DescribeNativeError(byte[] errorBuffer)
    {
        if (errorBuffer.Length < 5)
        {
            return "<short>";
        }

        byte type = errorBuffer[0];
        uint code = BinaryPrimitives.ReadUInt32LittleEndian(errorBuffer.AsSpan(1, 4));
        return $"type={type} code={code} (0x{code:X})";
    }

    private static void CloseChannelSafely(ICommunicationObject channel)
    {
        try
        {
            if (channel.State == CommunicationState.Faulted) channel.Abort();
            else channel.Close();
        }
        catch { try { channel.Abort(); } catch { } }
    }

    private static void CloseFactorySafely<TChannel>(ChannelFactory<TChannel> factory)
    {
        try
        {
            if (factory.State == CommunicationState.Faulted) factory.Abort();
            else factory.Close();
        }
        catch { try { factory.Abort(); } catch { } }
    }
}