using System;
using System.Collections.Generic;
using MxGateway.Contracts.Proto;

namespace MxGateway.Worker.MxAccess;

/// <summary>
///     In-process dispatcher that owns the lifetime of an
///     <see cref="IMxAccessAlarmConsumer"/> + <see cref="MxAccessAlarmEventSink"/>
///     pair, and wires the consumer's <c>AlarmTransitionEmitted</c> stream
///     onto the sink's <c>EnqueueTransition</c> path so transitions land on
///     the worker's <see cref="MxAccessEventQueue"/> as proto
///     <see cref="OnAlarmTransitionEvent"/> messages ready for IPC dispatch.
/// </summary>
/// <remarks>
///     <para>
///         This is the in-process slice of A.3 — it proves the
///         consumer→sink→queue pipeline end-to-end without touching the
///         worker's IPC command framing. The companion follow-up PR adds
///         <c>SubscribeAlarmsCommand</c> / <c>AcknowledgeAlarmCommand</c> /
///         <c>QueryActiveAlarmsCommand</c> proto entries plus the gateway-
///         side <c>WorkerAlarmRpcDispatcher</c> that issues them.
///     </para>
///     <para>
///         Threading: <see cref="WnWrapAlarmConsumer"/> polls on a
///         <see cref="System.Threading.Timer"/> thread today; production
///         hosting should marshal the consumer onto the worker's STA via
///         <c>StaRuntime.InvokeAsync</c>. The dispatcher itself is purely
///         a pass-through, so it inherits whatever thread the consumer's
///         event handler fires on. Fan-out into <c>EnqueueTransition</c>
///         uses <see cref="MxAccessEventQueue.Enqueue"/> which is
///         thread-safe.
///     </para>
/// </remarks>
public sealed class AlarmDispatcher : IDisposable
{
    private readonly IMxAccessAlarmConsumer consumer;
    private readonly MxAccessAlarmEventSink sink;
    private readonly string sessionId;
    private readonly EventHandler<MxAlarmTransitionEvent> handler;
    private bool disposed;

    public AlarmDispatcher(
        IMxAccessAlarmConsumer consumer,
        MxAccessAlarmEventSink sink,
        string sessionId)
    {
        this.consumer = consumer ?? throw new ArgumentNullException(nameof(consumer));
        this.sink = sink ?? throw new ArgumentNullException(nameof(sink));
        this.sessionId = sessionId ?? string.Empty;
        // Sink.Attach is the seam that propagates the session id onto the
        // proto SessionId field of every emitted MxEvent. Pass the consumer
        // as the "associated COM object" — sink ignores the object reference
        // for the alarm path, but the existing IMxAccessEventSink contract
        // requires a non-null first arg.
        this.sink.Attach(this.consumer, this.sessionId);
        this.handler = OnTransition;
        consumer.AlarmTransitionEmitted += handler;
    }

    /// <summary>
    ///     Begin polling the configured AVEVA alarm provider for
    ///     transitions. The supplied subscription expression follows the
    ///     canonical <c>\\&lt;machine&gt;\Galaxy!&lt;area&gt;</c> format.
    /// </summary>
    public void Subscribe(string subscription)
    {
        if (disposed) throw new ObjectDisposedException(nameof(AlarmDispatcher));
        consumer.Subscribe(subscription);
    }

    /// <summary>
    ///     Forward an <c>AcknowledgeAlarm</c> request to the underlying
    ///     consumer's <c>AlarmAckByGUID</c>. Returns the AVEVA-native
    ///     status code (0 = success).
    /// </summary>
    public int Acknowledge(
        Guid alarmGuid,
        string ackComment,
        string ackOperatorName,
        string ackOperatorNode,
        string ackOperatorDomain,
        string ackOperatorFullName)
    {
        if (disposed) throw new ObjectDisposedException(nameof(AlarmDispatcher));
        return consumer.AcknowledgeByGuid(
            alarmGuid,
            ackComment,
            ackOperatorName,
            ackOperatorNode,
            ackOperatorDomain,
            ackOperatorFullName);
    }

    /// <summary>
    ///     Acknowledge an alarm by its (name, provider, group) tuple.
    ///     Routes to the consumer's <c>AcknowledgeByName</c> path which
    ///     maps to <c>wwAlarmConsumerClass.AlarmAckByName</c>.
    /// </summary>
    public int AcknowledgeByName(
        string alarmName,
        string providerName,
        string groupName,
        string ackComment,
        string ackOperatorName,
        string ackOperatorNode,
        string ackOperatorDomain,
        string ackOperatorFullName)
    {
        if (disposed) throw new ObjectDisposedException(nameof(AlarmDispatcher));
        return consumer.AcknowledgeByName(
            alarmName,
            providerName,
            groupName,
            ackComment,
            ackOperatorName,
            ackOperatorNode,
            ackOperatorDomain,
            ackOperatorFullName);
    }

    /// <summary>
    ///     Snapshot the currently-active alarm set as
    ///     <see cref="ActiveAlarmSnapshot"/> protos for the
    ///     <c>QueryActiveAlarms</c> RPC's ConditionRefresh stream.
    /// </summary>
    public IReadOnlyList<ActiveAlarmSnapshot> SnapshotActiveAlarms()
    {
        if (disposed) throw new ObjectDisposedException(nameof(AlarmDispatcher));
        IReadOnlyList<MxAlarmSnapshotRecord> records = consumer.SnapshotActiveAlarms();
        if (records.Count == 0) return Array.Empty<ActiveAlarmSnapshot>();
        List<ActiveAlarmSnapshot> snapshots = new List<ActiveAlarmSnapshot>(records.Count);
        foreach (MxAlarmSnapshotRecord record in records)
        {
            snapshots.Add(MapToSnapshot(record));
        }
        return snapshots;
    }

    private void OnTransition(object? sender, MxAlarmTransitionEvent transition)
    {
        if (disposed) return;
        if (transition is null) return;

        MxAlarmSnapshotRecord record = transition.Record;
        AlarmTransitionKind kind = AlarmRecordTransitionMapper.MapTransition(
            transition.PreviousState, record.State);
        if (kind == AlarmTransitionKind.Unspecified) return;

        string fullReference = AlarmRecordTransitionMapper.ComposeFullReference(
            record.ProviderName, record.Group, record.TagName);

        sink.EnqueueTransition(
            alarmFullReference: fullReference,
            sourceObjectReference: record.TagName,
            alarmTypeName: record.Type,
            transitionKind: kind,
            severity: record.Priority,
            originalRaiseTimestampUtc: null,
            transitionTimestampUtc: record.TransitionTimestampUtc,
            operatorUser: record.OperatorName,
            operatorComment: record.AlarmComment,
            category: record.Group,
            description: string.Empty);
    }

    private static ActiveAlarmSnapshot MapToSnapshot(MxAlarmSnapshotRecord record)
    {
        ActiveAlarmSnapshot snapshot = new ActiveAlarmSnapshot
        {
            AlarmFullReference = AlarmRecordTransitionMapper.ComposeFullReference(
                record.ProviderName, record.Group, record.TagName),
            SourceObjectReference = record.TagName,
            AlarmTypeName = record.Type,
            CurrentState = MapConditionState(record.State),
            Severity = record.Priority,
            OperatorUser = record.OperatorName,
            OperatorComment = record.AlarmComment,
            Category = record.Group,
            Description = string.Empty,
        };
        if (record.TransitionTimestampUtc != DateTime.MinValue)
        {
            snapshot.LastTransitionTimestamp =
                Google.Protobuf.WellKnownTypes.Timestamp.FromDateTime(
                    DateTime.SpecifyKind(record.TransitionTimestampUtc, DateTimeKind.Utc));
        }
        return snapshot;
    }

    private static AlarmConditionState MapConditionState(MxAlarmStateKind state)
    {
        // The proto's AlarmConditionState only distinguishes Active /
        // ActiveAcked / Inactive — both Rtn states collapse to Inactive
        // (the ack-vs-unack distinction on a cleared alarm is not exposed
        // through OPC UA's Part 9 condition state model anyway).
        return state switch
        {
            MxAlarmStateKind.UnackAlm => AlarmConditionState.Active,
            MxAlarmStateKind.AckAlm => AlarmConditionState.ActiveAcked,
            MxAlarmStateKind.UnackRtn => AlarmConditionState.Inactive,
            MxAlarmStateKind.AckRtn => AlarmConditionState.Inactive,
            _ => AlarmConditionState.Unspecified,
        };
    }

    public string SessionId => sessionId;

    public void Dispose()
    {
        if (disposed) return;
        disposed = true;
        try { consumer.AlarmTransitionEmitted -= handler; } catch { /* swallow */ }
        try { sink.Detach(); } catch { /* swallow */ }
        try { consumer.Dispose(); } catch { /* swallow */ }
    }
}