using Google.Protobuf;
using AVEVA.Historian.Client.Models;
using AVEVA.Historian.Client.Protocol;
using AVEVA.Historian.Client.Wcf;
using GrpcRetrieval = ArchestrA.Grpc.Contract.Retrieval;

namespace AVEVA.Historian.Client.Grpc;

/// <summary>
/// Executes SQL commands over the 2023 R2 gRPC transport (HCAL R1.1), mirroring
/// <see cref="HistorianWcfSqlClient"/>'s two-op <c>ExeC</c>/<c>GetR</c> flow. The 2020 WCF path uses a
/// dedicated <c>GetRecordSetByteStream</c> op; the gRPC front door has no such RPC, so the NRBF
/// recordset stream would be fetched through the generic <c>RetrievalService.GetNextQueryResultBuffer</c>
/// keyed by the query handle <c>ExecuteSqlCommand</c> returns. <c>ExecuteSqlCommand</c> takes the
/// uppercase string session handle; the result-buffer fetch takes the transient <c>uint</c> client
/// handle (both come from the one Open2 session).
/// <para>
/// <b>SERVER-WALLED (captured 2026-06-22).</b> The 2023 R2 front-door
/// <c>RetrievalService.ExecuteSqlCommand</c> faults server-side before returning a query handle:
/// the response carries native error 38 wrapping a managed
/// <c>System.IndexOutOfRangeException ... at aahClientAccessPoint.CSrvDbConnection.ExecuteSqlCommand</c>.
/// This is a server-side <c>CSrvDbConnection</c> (SQL DB-connection) precondition that the pure
/// managed gRPC session does not establish — the same class of wall as
/// <c>StorageService.OpenStorageConnection</c>. Priming <c>Retr.GetV</c> does not clear it, and
/// <b>a <c>HistoryService.RegisterTags</c> prime does NOT clear it either</b> (tried live 2026-06-22 on
/// both read-only <c>0x402</c> and write-enabled <c>0x401</c> sessions: <c>RegisterTags</c> itself
/// returned false and <c>ExecuteSqlCommand</c> faulted with the identical native-38 IndexOutOfRange) —
/// so unlike the OpenStorageConnection wall, the SQL DB-connection context is not established by the
/// RegisterTags family. The request framing here is the captured/expected shape; the op stays bounded
/// behind <see cref="ProtocolEvidenceMissingException"/> until the DB-connection registration is
/// reproduced. Use the WCF transport for SQL.
/// </para>
/// </summary>
internal static class HistorianGrpcSqlClient
{
    // GetNextQueryResultBuffer is byte-stream-paged; a small record set returns in one page. Runaway guard.
    private const int MaxPages = 4096;

    public static Task<HistorianSqlResult> ExecuteSqlCommandAsync(
        HistorianClientOptions options,
        string command,
        HistorianSqlExecuteOption option,
        CancellationToken cancellationToken)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(command);
        return Task.Run(() => ExecuteSqlCommand(options, command, option, cancellationToken), cancellationToken);
    }

    private static HistorianSqlResult ExecuteSqlCommand(
        HistorianClientOptions options,
        string command,
        HistorianSqlExecuteOption option,
        CancellationToken cancellationToken)
    {
        using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(options);
        HistorianGrpcHandshake.Session session = HistorianGrpcHandshake.OpenSession(connection, options, cancellationToken);
        var retrievalClient = new GrpcRetrieval.RetrievalService.RetrievalServiceClient(connection.Channel);
        DateTime Deadline() => DateTime.UtcNow.Add(options.RequestTimeout);

        // Prime the Retrieval service version handshake (Retr.GetV) before the string-handle SQL op, as
        // the native WCF SQL path does — the server-side ExecuteSqlCommand otherwise faults.
        retrievalClient.GetRetrievalInterfaceVersion(
            new GrpcRetrieval.GetRetrievalInterfaceVersionRequest(), connection.Metadata, Deadline(), cancellationToken);

        GrpcRetrieval.ExecuteSqlCommandResponse exec = retrievalClient.ExecuteSqlCommand(
            new GrpcRetrieval.ExecuteSqlCommandRequest
            {
                StrHandle = session.StringHandle,
                StrCommand = command,
                UiOption = (uint)option,
                UiQueryHandle = 0
            },
            connection.Metadata,
            Deadline(),
            cancellationToken);

        if (!(exec.Status?.BSuccess ?? false))
        {
            // Captured 2026-06-22: the server-side CSrvDbConnection.ExecuteSqlCommand throws
            // IndexOutOfRange (native error 38) — a DB-connection precondition the pure managed gRPC
            // session doesn't establish. Surface the SDK's evidence-missing signal rather than a raw
            // server fault. See the class remarks.
            throw new ProtocolEvidenceMissingException(
                "ExecuteSqlCommand over gRPC: server-side CSrvDbConnection.ExecuteSqlCommand faults " +
                "(IndexOutOfRange / native error 38) — an unmet DB-connection precondition (gRPC transport). Use WCF.");
        }

        int returnValue = exec.IRetValue;
        uint queryHandle = exec.UiQueryHandle;

        using MemoryStream accumulated = new();
        for (int page = 0; page < MaxPages; page++)
        {
            cancellationToken.ThrowIfCancellationRequested();
            GrpcRetrieval.GetNextQueryResultBufferResponse buffer = retrievalClient.GetNextQueryResultBuffer(
                new GrpcRetrieval.GetNextQueryResultBufferRequest { UiHandle = session.ClientHandle, UiQueryHandle = queryHandle },
                connection.Metadata,
                Deadline(),
                cancellationToken);

            byte[] resultBuffer = buffer.BtQueryResult?.ToByteArray() ?? [];

            // GetR is false-even-on-success: the final page returns false with the data still in the
            // buffer, so always consume the buffer first, then stop on a false status or an empty page.
            if (resultBuffer.Length > 0)
            {
                accumulated.Write(resultBuffer, 0, resultBuffer.Length);
            }

            if (!(buffer.Status?.BSuccess ?? false) || resultBuffer.Length == 0)
            {
                break;
            }
        }

        return HistorianSqlResultProtocol.Parse(accumulated.ToArray(), returnValue);
    }
}