using System;
using System.Threading;
using System.Threading.Tasks;
using Serilog;
using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;

namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
{
    /// <summary>
    ///     IPC-side <see cref="IAlarmEventWriter"/> implementation that delegates to an
    ///     <see cref="IAlarmHistorianWriteBackend"/> (production: aahClientManaged-bound)
    ///     and maps the trinary <see cref="AlarmHistorianWriteOutcome"/> down to the
    ///     <c>bool[]</c> the IPC reply contract carries. Per-event outcomes:
    ///     <list type="bullet">
    ///       <item><description><see cref="AlarmHistorianWriteOutcome.Ack"/> → <c>true</c> (drop from sender's queue).</description></item>
    ///       <item><description><see cref="AlarmHistorianWriteOutcome.RetryPlease"/> → <c>false</c> (sender retries on next drain tick).</description></item>
    ///       <item><description><see cref="AlarmHistorianWriteOutcome.PermanentFail"/> → <c>false</c> (sender's B.4 widens the IPC bool back into the trinary outcome by inspecting structured diagnostics; this slot intentionally collapses to "not-ok" at the wire).</description></item>
    ///     </list>
    /// </summary>
    public sealed class AahClientManagedAlarmEventWriter : IAlarmEventWriter
    {
        private static readonly ILogger Log = Serilog.Log.ForContext<AahClientManagedAlarmEventWriter>();

        private readonly IAlarmHistorianWriteBackend _backend;

        /// <summary>
        /// Initializes a new instance of the AahClientManagedAlarmEventWriter class.
        /// </summary>
        /// <param name="backend">The alarm historian write backend to delegate to.</param>
        public AahClientManagedAlarmEventWriter(IAlarmHistorianWriteBackend backend)
        {
            _backend = backend ?? throw new ArgumentNullException(nameof(backend));
        }

        /// <summary>
        /// Writes an array of alarm historian events asynchronously.
        /// </summary>
        /// <param name="events">The alarm events to write.</param>
        /// <param name="cancellationToken">Cancellation token.</param>
        public async Task<bool[]> WriteAsync(AlarmHistorianEventDto[] events, CancellationToken cancellationToken)
        {
            if (events is null || events.Length == 0)
            {
                return new bool[0];
            }

            AlarmHistorianWriteOutcome[] outcomes;
            try
            {
                outcomes = await _backend.WriteBatchAsync(events, cancellationToken).ConfigureAwait(false);
            }
            catch (OperationCanceledException)
            {
                throw;
            }
            catch (Exception ex)
            {
                // Backend-level failure (cluster unreachable, transport error). Treat the
                // whole batch as RetryPlease so the sender's queue holds the rows for
                // the next drain tick — preferable to dropping them on a transient.
                Log.Warning(ex,
                    "Alarm historian backend WriteBatchAsync threw — marking entire {Count}-event batch RetryPlease.",
                    events.Length);
                var fallback = new bool[events.Length];
                return fallback;
            }

            if (outcomes.Length != events.Length)
            {
                // Backend contract violation — defensive degrade so a bug in the backend
                // doesn't desync the sender's queue accounting. Treat as RetryPlease.
                Log.Warning(
                    "Alarm historian backend returned {ReturnedCount} outcomes for a batch of {InputCount} events; degrading to RetryPlease for the whole batch.",
                    outcomes.Length, events.Length);
                return new bool[events.Length];
            }

            var perEventOk = new bool[outcomes.Length];
            for (var i = 0; i < outcomes.Length; i++)
            {
                perEventOk[i] = outcomes[i] == AlarmHistorianWriteOutcome.Ack;
            }
            return perEventOk;
        }

        /// <summary>
        ///     Translate the outcome of a single SDK call (raw HRESULT + diagnostic) into the
        ///     trinary <see cref="AlarmHistorianWriteOutcome"/>. Exposed for the production
        ///     <see cref="SdkAlarmHistorianWriteBackend"/> to share the mapping with tests.
        /// </summary>
        /// <param name="hresult">The HRESULT code from the SDK call.</param>
        /// <param name="isCommunicationError">Indicates whether the error is a communication-class error.</param>
        /// <param name="isMalformedInput">Indicates whether the input was malformed.</param>
        public static AlarmHistorianWriteOutcome MapOutcome(int hresult, bool isCommunicationError, bool isMalformedInput)
        {
            // Order matters: malformed input is permanent regardless of HRESULT pattern;
            // communication-class errors are transient regardless of which specific
            // HRESULT bit fired.
            if (isMalformedInput)
            {
                return AlarmHistorianWriteOutcome.PermanentFail;
            }
            if (hresult == 0)
            {
                return AlarmHistorianWriteOutcome.Ack;
            }
            if (isCommunicationError)
            {
                return AlarmHistorianWriteOutcome.RetryPlease;
            }
            // Default: unknown HRESULT failure — be conservative and let the sender retry.
            // The sender's drain worker has its own dead-letter cap so a permanently-broken
            // event won't loop forever.
            return AlarmHistorianWriteOutcome.RetryPlease;
        }
    }
}