using System.Runtime.CompilerServices;
using Google.Protobuf;
using Grpc.Core;
using AVEVA.Historian.Client.Models;
using AVEVA.Historian.Client.Wcf;
using GrpcHistory = ArchestrA.Grpc.Contract.History;
using GrpcRetrieval = ArchestrA.Grpc.Contract.Retrieval;
using GrpcStatus = ArchestrA.Grpc.Contract.Status;
using GrpcTransaction = ArchestrA.Grpc.Contract.Transaction;

namespace AVEVA.Historian.Client.Grpc;

/// <summary>
/// 2023 R2 gRPC event-read orchestrator. Mirrors <see cref="HistorianWcfEventOrchestrator"/> over the
/// gRPC transport: the same CM_EVENT registration sequence and the same event request/row buffers
/// travel inside protobuf <c>bytes</c> fields, reusing the proven WCF serializers/parsers verbatim.
///
/// Operation mapping (2020 WCF → 2023 R2 gRPC):
///   Hist.UpdateClientStatus3 → HistoryService.UpdateClientStatus
///   Hist.RegisterTags2 → HistoryService.RegisterTags
///   Hist.EnsureTags2 → HistoryService.EnsureTags
///   Stat.GetHistorianInfo → StatusService.GetHistorianInfo
///   Stat.GetSystemParameter → StatusService.GetSystemParameter
///   Retr.StartEventQuery → RetrievalService.StartEventQuery
///   Retr.GetNextEventQueryResultBuffer (loop) → RetrievalService.GetNextEventQueryResultBuffer
///   Retr.EndEventQuery → RetrievalService.EndEventQuery
///
/// <para>
/// The CM_EVENT registration replay (<see cref="RegisterCmEventTag"/>) is the hard part: without it
/// the server returns native error type=4 code=85 from GetNextEventQueryResultBuffer. The captured
/// registration buffers are shared with the WCF path via
/// <see cref="HistorianEventRegistrationProtocol"/> so the two transports cannot drift. The gRPC
/// RetrievalService event ops do NOT need the WCF <c>Retr.GetV</c>/<c>IsOriginalAllowed</c> prime
/// (the read path proved the front-door session is sufficient over gRPC).
/// </para>
/// <para>
/// <b>Live status (2026-06-22):</b> the chain runs end-to-end and <c>StartEventQuery</c> succeeds, but
/// <c>GetNextEventQueryResultBuffer</c> <b>long-polls</b> when the query has no rows — it blocks to the
/// call deadline instead of returning the synchronous 5-byte code-85 terminal the 2020 WCF op returns.
/// A poll-deadline expiry is therefore treated as the no-data terminal (see the loop). The idle dev box
/// holds no events, so <b>row-level retrieval is not yet live-verified</b>; verifying parsed rows over
/// gRPC awaits an event-bearing 2023 R2 server. This is tooled + completes cleanly, NOT proven to
/// return rows.
/// </para>
/// </summary>
internal sealed class HistorianGrpcEventOrchestrator
{
    private readonly HistorianClientOptions _options;

    public HistorianGrpcEventOrchestrator(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;

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

        cancellationToken.ThrowIfCancellationRequested();

        // Hard overall cap. The per-call gRPC-Web deadlines are NOT honored reliably over a tunnelled
        // link (observed live 2026-06-22: a chain with 4s per-call deadlines still ran >90s because the
        // server stalls several registration RPCs and long-polls GetNext). gRPC DOES honor token
        // cancellation, so a linked CTS firing at OverallBudget bounds the whole read deterministically.
        // A budget timeout on the unverified no-row path is surfaced as ProtocolEvidenceMissing, not as
        // a raw cancellation, so callers get the same honest "not row-verified over gRPC" signal.
        using CancellationTokenSource linked = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        linked.CancelAfter(OverallBudget);

        IReadOnlyList<HistorianEvent> events;
        try
        {
            events = await Task.Run(
                () => RunEventChain(startUtc, endUtc, filter, linked.Token),
                linked.Token).ConfigureAwait(false);
        }
        catch (Exception ex) when (IsBudgetCancellation(ex, linked, cancellationToken))
        {
            throw new ProtocolEvidenceMissingException(
                $"ReadEvents over gRPC did not return rows within {OverallBudget.TotalSeconds:0}s: StartEventQuery " +
                "succeeds but the CM_EVENT registration replay stalls and GetNextEventQueryResultBuffer long-polls " +
                "(no synchronous code-85 terminal over gRPC). Row-level retrieval is not yet verified over gRPC " +
                "(the dev box holds no events) — use the WCF transport for event reads.");
        }

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

    /// <summary>
    /// Hard wall-clock budget for the entire gRPC event read. Bounds the chain deterministically since
    /// per-call gRPC-Web deadlines are unreliable over a tunnel. Scaled off the request timeout but
    /// capped so a long default timeout cannot make the (currently row-unverified) read stall for minutes.
    /// </summary>
    private TimeSpan OverallBudget
    {
        get
        {
            TimeSpan cap = TimeSpan.FromSeconds(30);
            return _options.RequestTimeout < cap ? _options.RequestTimeout : cap;
        }
    }

    /// <summary>
    /// True when an exception was caused by the overall-budget linked CTS firing (not by the caller's
    /// own cancellation). The budget surfaces either as an <see cref="OperationCanceledException"/>
    /// (Task.Run / token checks) or a gRPC <see cref="RpcException"/> with
    /// <see cref="StatusCode.Cancelled"/> from an in-flight RPC.
    /// </summary>
    private static bool IsBudgetCancellation(Exception ex, CancellationTokenSource linked, CancellationToken caller)
    {
        if (caller.IsCancellationRequested || !linked.IsCancellationRequested)
        {
            return false;
        }

        return ex is OperationCanceledException
            || (ex is RpcException rpc && rpc.StatusCode is StatusCode.Cancelled or StatusCode.DeadlineExceeded);
    }

    private List<HistorianEvent> RunEventChain(DateTime startUtc, DateTime endUtc, HistorianEventFilter? filter, CancellationToken cancellationToken)
    {
        using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(_options);
        HistorianGrpcHandshake.Session session = HistorianGrpcHandshake.OpenSession(connection, _options, cancellationToken);

        RegisterCmEventTag(connection, session, cancellationToken);

        List<HistorianEvent> events = RunEventQuery(connection, session, startUtc, endUtc, filter, cancellationToken);

        // Honest no-data handling: when the query returns real rows, hand them back. When it instead
        // reaches the no-data terminal with ZERO rows (the gRPC server long-polls GetNext rather than
        // returning the WCF code-85 terminal), we cannot distinguish "genuinely no events in range"
        // from "the CM_EVENT registration replay didn't fully land over gRPC" — so we refuse to return
        // a possibly-false empty list and surface the unverified state instead. An event-bearing 2023 R2
        // server will return rows here and exercise the parse path; flip this once that is captured.
        if (events.Count == 0)
        {
            throw new ProtocolEvidenceMissingException(
                "ReadEvents over gRPC: the chain completes and StartEventQuery succeeds, but " +
                "GetNextEventQueryResultBuffer returns no rows (it long-polls to the no-data terminal " +
                $"after the CM_EVENT registration replay; last={LastErrorBufferDescription}). Row-level " +
                "retrieval is not yet verified over gRPC (the dev box holds no events) — use the WCF " +
                "transport for event reads until a capture against an event-bearing 2023 R2 server confirms it.");
        }

        return events;
    }

    private DateTime Deadline() => DateTime.UtcNow.Add(_options.RequestTimeout);

    /// <summary>
    /// Deadline for the GetNextEventQueryResultBuffer long-poll. Bounded to at most 10s (or the
    /// configured <see cref="HistorianClientOptions.RequestTimeout"/> if shorter) so the no-data
    /// terminal — a deadline expiry over gRPC — is reached promptly instead of stalling the read for
    /// the full request timeout. When rows are available the server returns them well before this.
    /// </summary>
    private DateTime EventPollDeadline()
    {
        TimeSpan cap = TimeSpan.FromSeconds(10);
        TimeSpan poll = _options.RequestTimeout < cap ? _options.RequestTimeout : cap;
        return DateTime.UtcNow.Add(poll);
    }

    /// <summary>
    /// Deadline for the best-effort registration RPCs. Bounded to at most 5s: several of these
    /// (RegisterTags / EnsureTags / GetHistorianInfo) <b>stall server-side</b> on the remote 2023 R2
    /// box (observed live 2026-06-22) and only return at their deadline, so an unbounded
    /// <see cref="RequestTimeout"/> would make the registration phase dominate the read. They are
    /// swallowed via <see cref="TryRun"/> regardless of outcome.
    /// </summary>
    private DateTime RegistrationDeadline()
    {
        TimeSpan cap = TimeSpan.FromSeconds(5);
        TimeSpan d = _options.RequestTimeout < cap ? _options.RequestTimeout : cap;
        return DateTime.UtcNow.Add(d);
    }

    /// <summary>
    /// Replays the native event-tag registration sequence (UpdC3 → 6 system params → RTag2 → 1 more
    /// system param → cross-service GetV probes → EnsT2) over the gRPC services. Best-effort: each
    /// call is wrapped so an individual rejection on this server does not abort the chain — the goal
    /// is to drive the server-side session into the state StartEventQuery / GetNextEventQueryResultBuffer
    /// expect. Buffers come from <see cref="HistorianEventRegistrationProtocol"/>.
    /// </summary>
    private void RegisterCmEventTag(HistorianGrpcConnection connection, HistorianGrpcHandshake.Session session, CancellationToken cancellationToken)
    {
        var historyClient = new GrpcHistory.HistoryService.HistoryServiceClient(connection.Channel);
        var statusClient = new GrpcStatus.StatusService.StatusServiceClient(connection.Channel);
        var retrievalClient = new GrpcRetrieval.RetrievalService.RetrievalServiceClient(connection.Channel);
        var transactionClient = new GrpcTransaction.TransactionService.TransactionServiceClient(connection.Channel);

        // Discovery dance the native event flow runs between Open2 and EnsT2. All bounded by the
        // short RegistrationDeadline (several stall server-side on the remote box).
        TryRun(() => statusClient.GetStatusInterfaceVersion(new GrpcStatus.GetStatusInterfaceVersionRequest(), connection.Metadata, RegistrationDeadline(), cancellationToken));
        TryRun(() => statusClient.GetStatusInterfaceVersion(new GrpcStatus.GetStatusInterfaceVersionRequest(), connection.Metadata, RegistrationDeadline(), cancellationToken));

        byte[] historianVersionRequest = HistorianEventRegistrationProtocol.BuildGetHistorianInfoRequest("HistorianVersion");
        TryRun(() => statusClient.GetHistorianInfo(
            new GrpcStatus.GetHistorianInfoRequest { StrHandle = session.StringHandle, BtRequest = ByteString.CopyFrom(historianVersionRequest) },
            connection.Metadata, RegistrationDeadline(), cancellationToken));
        TryRun(() => statusClient.GetHistorianInfo(
            new GrpcStatus.GetHistorianInfoRequest { StrHandle = session.StringHandle, BtRequest = ByteString.CopyFrom(historianVersionRequest) },
            connection.Metadata, RegistrationDeadline(), cancellationToken));

        byte[] clientStatus = HistorianEventRegistrationProtocol.BuildUpdateClientStatusBlob();
        TryRun(() => historyClient.UpdateClientStatus(
            new GrpcHistory.UpdateClientStatusRequest { StrHandle = session.StringHandle, BtClientStatus = ByteString.CopyFrom(clientStatus) },
            connection.Metadata, RegistrationDeadline(), cancellationToken));

        // Records 11-16: 6 system-parameter queries before RTag2.
        foreach (string parameterName in HistorianEventRegistrationProtocol.StatusParametersBeforeRegister)
        {
            TryRun(() => statusClient.GetSystemParameter(
                new GrpcStatus.GetSystemParameterRequest { UiHandle = session.ClientHandle, StrParameterName = parameterName },
                connection.Metadata, RegistrationDeadline(), cancellationToken));
        }

        byte[] registerBuffer = HistorianEventRegistrationProtocol.BuildRegisterCmEventInputBuffer();
        TryRun(() => historyClient.RegisterTags(
            new GrpcHistory.RegisterTagsRequest { StrHandle = session.StringHandle, BtTagInfos = ByteString.CopyFrom(registerBuffer) },
            connection.Metadata, RegistrationDeadline(), cancellationToken));

        // Record 18: one more system-parameter query after RTag2 before EnsT2.
        TryRun(() => statusClient.GetSystemParameter(
            new GrpcStatus.GetSystemParameterRequest { UiHandle = session.ClientHandle, StrParameterName = "AllowRenameTags" },
            connection.Metadata, RegistrationDeadline(), cancellationToken));

        // Records 19-21: cross-service version probes between RTag2 and EnsT2 (session-table registration).
        TryRun(() => transactionClient.GetTransactionInterfaceVersion(new GrpcTransaction.GetTransactionInterfaceVersionRequest(), connection.Metadata, RegistrationDeadline(), cancellationToken));
        TryRun(() => statusClient.GetStatusInterfaceVersion(new GrpcStatus.GetStatusInterfaceVersionRequest(), connection.Metadata, RegistrationDeadline(), cancellationToken));
        TryRun(() => retrievalClient.GetRetrievalInterfaceVersion(new GrpcRetrieval.GetRetrievalInterfaceVersionRequest(), connection.Metadata, RegistrationDeadline(), cancellationToken));

        byte[] payload = HistorianAddTagsProtocol.SerializeCmEventCTagMetadata(DateTime.UtcNow);
        TryRun(() => historyClient.EnsureTags(
            new GrpcHistory.EnsureTagsRequest { StrHandle = session.StringHandle, BtTagInfos = ByteString.CopyFrom(payload), ElementCount = 1 },
            connection.Metadata, RegistrationDeadline(), cancellationToken));
    }

    private List<HistorianEvent> RunEventQuery(
        HistorianGrpcConnection connection,
        HistorianGrpcHandshake.Session session,
        DateTime startUtc,
        DateTime endUtc,
        HistorianEventFilter? filter,
        CancellationToken cancellationToken)
    {
        var retrievalClient = new GrpcRetrieval.RetrievalService.RetrievalServiceClient(connection.Channel);
        GrpcRetrieval.GetRetrievalInterfaceVersionResponse retrievalVersion = retrievalClient.GetRetrievalInterfaceVersion(
            new GrpcRetrieval.GetRetrievalInterfaceVersionRequest(), connection.Metadata, Deadline(), cancellationToken);
        HistorianServerVersionGate.Validate(HistorianServiceInterface.Retrieval, retrievalVersion.UiVersion, _options);

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

        GrpcRetrieval.StartEventQueryResponse startResponse = retrievalClient.StartEventQuery(
            new GrpcRetrieval.StartEventQueryRequest
            {
                UiHandle = session.ClientHandle,
                UiQueryRequestType = HistorianEventQueryProtocol.QueryRequestTypeEvent,
                BtRequest = ByteString.CopyFrom(requestBuffer)
            },
            connection.Metadata,
            Deadline(),
            cancellationToken);

        byte[] startError = startResponse.Status?.BtError?.ToByteArray() ?? [];
        if (!(startResponse.Status?.BSuccess ?? false))
        {
            throw new InvalidOperationException(
                $"gRPC StartEventQuery failed (errorLen={startError.Length}, error5={HistorianEventRegistrationProtocol.DescribeNativeError(startError)}).");
        }

        uint queryHandle = startResponse.UiQueryHandle;
        try
        {
            List<HistorianEvent> events = [];
            while (true)
            {
                cancellationToken.ThrowIfCancellationRequested();

                GrpcRetrieval.GetNextEventQueryResultBufferResponse nextResponse;
                try
                {
                    nextResponse = retrievalClient.GetNextEventQueryResultBuffer(
                        new GrpcRetrieval.GetNextEventQueryResultBufferRequest { UiHandle = session.ClientHandle, UiQueryHandle = queryHandle },
                        connection.Metadata,
                        EventPollDeadline(),
                        cancellationToken);
                }
                catch (RpcException ex) when (ex.StatusCode == StatusCode.DeadlineExceeded)
                {
                    // No-data terminal. Over gRPC the 2023 R2 server LONG-POLLS GetNextEventQueryResultBuffer
                    // when the query has no (more) rows to hand back, rather than returning the 5-byte
                    // type=4 code=85 terminal the 2020 WCF op returns synchronously. A poll-deadline
                    // expiry is therefore the gRPC equivalent of that soft terminal: stop reading and
                    // return whatever rows were already collected. (Confirmed live 2026-06-22: the chain
                    // runs and StartEventQuery succeeds, but GetNext blocks to the deadline on the idle
                    // dev box, which holds no events.) See class remarks.
                    LastErrorBufferDescription = "GetNext long-poll deadline (no-data terminal)";
                    return events;
                }

                byte[] resultBuffer = nextResponse.BtResult?.ToByteArray() ?? [];
                byte[] errorBuffer = nextResponse.Status?.BtError?.ToByteArray() ?? [];
                bool nextSuccess = nextResponse.Status?.BSuccess ?? false;

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

                // Any 5-byte type=4 error is a soft terminal (code 30 NoMoreData is canonical; code
                // 85 / 0x55 is the missing-registration signal seen on early runs). Mirror the WCF
                // orchestrator: stop reading and surface the diagnostic rather than throw.
                if (errorBuffer.Length == 5 && errorBuffer[0] == 4)
                {
                    return events;
                }

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

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

                if (resultBuffer.Length == 0 && errorBuffer.Length == 0)
                {
                    return events;
                }
            }
        }
        finally
        {
            EndEventQuerySafely(retrievalClient, connection, session.ClientHandle, queryHandle);
        }
    }

    private void EndEventQuerySafely(
        GrpcRetrieval.RetrievalService.RetrievalServiceClient client,
        HistorianGrpcConnection connection,
        uint clientHandle,
        uint queryHandle)
    {
        try
        {
            client.EndEventQuery(
                new GrpcRetrieval.EndEventQueryRequest { UiHandle = clientHandle, UiQueryHandle = queryHandle },
                connection.Metadata,
                Deadline(),
                CancellationToken.None);
        }
        catch
        {
            // Best-effort cleanup; the read result is already collected.
        }
    }

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