using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using MessagePack;
using Serilog;
using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;

namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;

/// <summary>
///     Sidecar-side dispatcher. Each post-Hello frame routes by <see cref="MessageKind"/> to
///     the right historian operation and the result frame is written back through the same
///     pipe. Per-call exceptions are caught and surfaced as <c>Success=false, Error=...</c>
///     replies so a single bad request doesn't kill the connection.
/// </summary>
public sealed class HistorianFrameHandler : IFrameHandler
{
    // WriteAlarmEventsReply.PerEventStatus byte semantics: 0=Ack, 1=Retry, 2=Permanent.
    private const byte StatusAck = 0;
    private const byte StatusRetry = 1;
    private const byte StatusPermanent = 2;

    private readonly IHistorianDataSource _historian;
    private readonly IAlarmEventWriter? _alarmWriter;
    private readonly ILogger _logger;

    /// <summary>Initializes a new instance of the HistorianFrameHandler class.</summary>
    /// <param name="historian">The historian data source to query.</param>
    /// <param name="logger">The logger instance.</param>
    /// <param name="alarmWriter">Optional alarm event writer for writebacks.</param>
    public HistorianFrameHandler(
        IHistorianDataSource historian,
        ILogger logger,
        IAlarmEventWriter? alarmWriter = null)
    {
        _historian = historian ?? throw new ArgumentNullException(nameof(historian));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _alarmWriter = alarmWriter;
    }

    /// <summary>Handles an incoming frame by dispatching to the appropriate historian operation.</summary>
    /// <param name="kind">The frame message kind.</param>
    /// <param name="body">The frame body bytes.</param>
    /// <param name="writer">The frame writer for sending responses.</param>
    /// <param name="ct">Cancellation token.</param>
    public Task HandleAsync(MessageKind kind, byte[] body, FrameWriter writer, CancellationToken ct)
        => kind switch
        {
            MessageKind.ReadRawRequest => HandleReadRawAsync(body, writer, ct),
            MessageKind.ReadProcessedRequest => HandleReadProcessedAsync(body, writer, ct),
            MessageKind.ReadAtTimeRequest => HandleReadAtTimeAsync(body, writer, ct),
            MessageKind.ReadEventsRequest => HandleReadEventsAsync(body, writer, ct),
            MessageKind.WriteAlarmEventsRequest => HandleWriteAlarmEventsAsync(body, writer, ct),
            _ => UnknownAsync(kind),
        };

    private Task UnknownAsync(MessageKind kind)
    {
        _logger.Warning("Sidecar received unsupported frame kind {Kind}; dropping", kind);
        return Task.CompletedTask;
    }

    private async Task HandleReadRawAsync(byte[] body, FrameWriter writer, CancellationToken ct)
    {
        var req = MessagePackSerializer.Deserialize<ReadRawRequest>(body);
        var reply = new ReadRawReply { CorrelationId = req.CorrelationId };
        try
        {
            var samples = await _historian.ReadRawAsync(
                req.TagName,
                new DateTime(req.StartUtcTicks, DateTimeKind.Utc),
                new DateTime(req.EndUtcTicks, DateTimeKind.Utc),
                req.MaxValues,
                ct).ConfigureAwait(false);

            reply.Success = true;
            reply.Samples = ToWire(samples);
        }
        catch (Exception ex)
        {
            _logger.Warning(ex, "Sidecar ReadRaw failed for {Tag}", req.TagName);
            reply.Success = false;
            reply.Error = ex.Message;
        }

        await writer.WriteAsync(MessageKind.ReadRawReply, reply, ct).ConfigureAwait(false);
    }

    private async Task HandleReadProcessedAsync(byte[] body, FrameWriter writer, CancellationToken ct)
    {
        var req = MessagePackSerializer.Deserialize<ReadProcessedRequest>(body);
        var reply = new ReadProcessedReply { CorrelationId = req.CorrelationId };
        try
        {
            var buckets = await _historian.ReadAggregateAsync(
                req.TagName,
                new DateTime(req.StartUtcTicks, DateTimeKind.Utc),
                new DateTime(req.EndUtcTicks, DateTimeKind.Utc),
                req.IntervalMs,
                req.AggregateColumn,
                ct).ConfigureAwait(false);

            reply.Success = true;
            reply.Buckets = ToWire(buckets);
        }
        catch (Exception ex)
        {
            _logger.Warning(ex, "Sidecar ReadProcessed failed for {Tag}", req.TagName);
            reply.Success = false;
            reply.Error = ex.Message;
        }

        await writer.WriteAsync(MessageKind.ReadProcessedReply, reply, ct).ConfigureAwait(false);
    }

    private async Task HandleReadAtTimeAsync(byte[] body, FrameWriter writer, CancellationToken ct)
    {
        var req = MessagePackSerializer.Deserialize<ReadAtTimeRequest>(body);
        var reply = new ReadAtTimeReply { CorrelationId = req.CorrelationId };
        try
        {
            var timestamps = new DateTime[req.TimestampsUtcTicks.Length];
            for (var i = 0; i < timestamps.Length; i++)
                timestamps[i] = new DateTime(req.TimestampsUtcTicks[i], DateTimeKind.Utc);

            var samples = await _historian.ReadAtTimeAsync(req.TagName, timestamps, ct).ConfigureAwait(false);
            reply.Success = true;
            reply.Samples = ToWire(samples);
        }
        catch (Exception ex)
        {
            _logger.Warning(ex, "Sidecar ReadAtTime failed for {Tag}", req.TagName);
            reply.Success = false;
            reply.Error = ex.Message;
        }

        await writer.WriteAsync(MessageKind.ReadAtTimeReply, reply, ct).ConfigureAwait(false);
    }

    private async Task HandleReadEventsAsync(byte[] body, FrameWriter writer, CancellationToken ct)
    {
        var req = MessagePackSerializer.Deserialize<ReadEventsRequest>(body);
        var reply = new ReadEventsReply { CorrelationId = req.CorrelationId };
        try
        {
            var events = await _historian.ReadEventsAsync(
                req.SourceName,
                new DateTime(req.StartUtcTicks, DateTimeKind.Utc),
                new DateTime(req.EndUtcTicks, DateTimeKind.Utc),
                req.MaxEvents,
                ct).ConfigureAwait(false);

            reply.Success = true;
            reply.Events = ToWire(events);
        }
        catch (Exception ex)
        {
            _logger.Warning(ex, "Sidecar ReadEvents failed for source {Source}", req.SourceName);
            reply.Success = false;
            reply.Error = ex.Message;
        }

        await writer.WriteAsync(MessageKind.ReadEventsReply, reply, ct).ConfigureAwait(false);
    }

    private async Task HandleWriteAlarmEventsAsync(byte[] body, FrameWriter writer, CancellationToken ct)
    {
        var req = MessagePackSerializer.Deserialize<WriteAlarmEventsRequest>(body);

        // MessagePack deserializes an absent or explicit-nil array as null, not Array.Empty.
        // Normalise here so every path below can safely dereference .Length without an NRE.
        req.Events ??= Array.Empty<AlarmHistorianEventDto>();

        var reply = new WriteAlarmEventsReply { CorrelationId = req.CorrelationId };

        if (_alarmWriter is null)
        {
            reply.Success = false;
            reply.Error = "Sidecar not configured with an alarm-event writer.";
            reply.PerEventOk = new bool[req.Events.Length];
            reply.PerEventStatus = AllStatus(req.Events.Length, StatusRetry);
            await writer.WriteAsync(MessageKind.WriteAlarmEventsReply, reply, ct).ConfigureAwait(false);
            return;
        }

        try
        {
            // Classify each event before touching the writer: structurally-malformed
            // (poison) events can never be persisted, so mark them Permanent and exclude
            // them from the writer batch. Only the well-formed remainder is handed to the
            // writer, whose bool[] result is mapped back onto the original indices.
            var status = new byte[req.Events.Length];
            var writable = new List<AlarmHistorianEventDto>(req.Events.Length);
            var originalIndex = new List<int>(req.Events.Length);
            for (var i = 0; i < req.Events.Length; i++)
            {
                if (IsStructurallyMalformed(req.Events[i]))
                {
                    status[i] = StatusPermanent;
                }
                else
                {
                    originalIndex.Add(i);
                    writable.Add(req.Events[i]);
                }
            }

            // Aligned 1:1 to `writable`; empty when every event was poison (writer skipped).
            var perEvent = writable.Count == 0
                ? Array.Empty<bool>()
                : await _alarmWriter.WriteAsync(writable.ToArray(), ct).ConfigureAwait(false);

            for (var i = 0; i < originalIndex.Count; i++)
            {
                var ok = i < perEvent.Length && perEvent[i];
                status[originalIndex[i]] = ok ? StatusAck : StatusRetry;
            }

            reply.PerEventStatus = status;
            reply.PerEventOk = StatusToOk(status);
            reply.Success = true;
            // Whole-batch Success stays true even when some events failed — per-event
            // PerEventStatus slots carry the granular result (Ack / Retry / Permanent);
            // the SQLite drain worker acks 0, retries 1, and dead-letters 2. PerEventOk
            // is kept populated for rolling-deploy back-compat with an older client.
        }
        catch (Exception ex)
        {
            _logger.Warning(ex, "Sidecar WriteAlarmEvents failed");
            reply.Success = false;
            reply.Error = ex.Message;
            reply.PerEventOk = new bool[req.Events.Length];
            reply.PerEventStatus = AllStatus(req.Events.Length, StatusRetry);
        }

        await writer.WriteAsync(MessageKind.WriteAlarmEventsReply, reply, ct).ConfigureAwait(false);
    }

    /// <summary>
    ///     Classifies an alarm event as structurally malformed (poison): an event the historian
    ///     event store can never persist regardless of retries. Such events are marked Permanent
    ///     so the store-and-forward sink dead-letters them immediately instead of looping to the
    ///     retry cap. A blank source name or alarm type, or a non-positive event timestamp, are
    ///     the structural invariants the historian write requires.
    /// </summary>
    /// <param name="e">The candidate alarm event.</param>
    /// <returns><c>true</c> when the event is structurally malformed; otherwise <c>false</c>.</returns>
    internal static bool IsStructurallyMalformed(AlarmHistorianEventDto e) =>
        e is null
        || string.IsNullOrWhiteSpace(e.SourceName)
        || string.IsNullOrWhiteSpace(e.AlarmType)
        || e.EventTimeUtcTicks <= 0;

    private static byte[] AllStatus(int length, byte value)
    {
        var status = new byte[length];
        for (var i = 0; i < length; i++) status[i] = value;
        return status;
    }

    private static bool[] StatusToOk(byte[] status)
    {
        var ok = new bool[status.Length];
        for (var i = 0; i < status.Length; i++) ok[i] = status[i] == StatusAck;
        return ok;
    }

    private static HistorianSampleDto[] ToWire(List<HistorianSample> samples)
    {
        var dtos = new HistorianSampleDto[samples.Count];
        for (var i = 0; i < samples.Count; i++)
        {
            var s = samples[i];
            dtos[i] = new HistorianSampleDto
            {
                ValueBytes = s.Value is null ? null : MessagePackSerializer.Serialize(s.Value),
                Quality = s.Quality,
                TimestampUtcTicks = s.TimestampUtc.Ticks,
            };
        }
        return dtos;
    }

    private static HistorianAggregateSampleDto[] ToWire(List<HistorianAggregateSample> samples)
    {
        var dtos = new HistorianAggregateSampleDto[samples.Count];
        for (var i = 0; i < samples.Count; i++)
        {
            dtos[i] = new HistorianAggregateSampleDto
            {
                Value = samples[i].Value,
                TimestampUtcTicks = samples[i].TimestampUtc.Ticks,
            };
        }
        return dtos;
    }

    private static HistorianEventDto[] ToWire(List<Backend.HistorianEventDto> events)
    {
        var dtos = new HistorianEventDto[events.Count];
        for (var i = 0; i < events.Count; i++)
        {
            var e = events[i];
            dtos[i] = new HistorianEventDto
            {
                EventId = e.Id.ToString(),
                Source = e.Source,
                EventTimeUtcTicks = e.EventTime.Ticks,
                ReceivedTimeUtcTicks = e.ReceivedTime.Ticks,
                DisplayText = e.DisplayText,
                Severity = e.Severity,
            };
        }
        return dtos;
    }
}

/// <summary>
///     Strategy for persisting alarm events into the Wonderware Alarm &amp; Events log. PR 3.W
///     supplies a real implementation that drives the aahClient SDK; PR 3.3 ships the
///     contract + a default null implementation so the sidecar can boot without one.
/// </summary>
public interface IAlarmEventWriter
{
    /// <summary>
    ///     Writes a batch of alarm events. Returns one boolean per input event indicating
    ///     persisted vs. retry-please. The SQLite store-and-forward sink retries failed
    ///     slots on the next drain tick.
    /// </summary>
    /// <param name="events">Alarm events to write.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    Task<bool[]> WriteAsync(AlarmHistorianEventDto[] events, CancellationToken cancellationToken);
}