using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;

/// <summary>
///     Issue #267 (plan PR F3-a) — projects FANUC CNC alarms onto the OPC UA alarm surface
///     via <see cref="IAlarmSource"/>. Two modes:
///     <list type="bullet">
///         <item><see cref="FocasAlarmProjectionMode.ActiveOnly"/> (default) — only
///             currently-active alarms surface. Subscribe / unsubscribe / acknowledge wire up,
///             but no history poll runs. This is the conservative mode operators get when
///             they don't explicitly opt into history.</item>
///         <item><see cref="FocasAlarmProjectionMode.ActivePlusHistory"/> — additionally
///             polls <c>cnc_rdalmhistry</c> on connect and on every
///             <see cref="FocasAlarmProjectionOptions.HistoryPollInterval"/> tick. Each
///             previously-unseen entry fires an <c>OnAlarmEvent</c> with
///             <c>SourceTimestampUtc</c> set from the CNC's reported timestamp (not Now)
///             so OPC UA dashboards see the real occurrence time.</item>
///     </list>
/// </summary>
/// <remarks>
///     <para><b>Dedup</b> — an in-memory <see cref="HashSet{T}"/> keyed on
///     <c>(OccurrenceTime, AlarmNumber, AlarmType)</c> tracks every entry the projection has
///     emitted. The same triple across two polls only emits once. The set resets on reconnect
///     — first poll after reconnect re-emits everything in the ring buffer; OPC UA clients
///     that care about exactly-once semantics dedupe on their side via the
///     timestamp + number + type tuple.</para>
///
///     <para><b>HistoryDepth clamp</b> — user-supplied depth is bounded to
///     <c>[1..<see cref="FocasAlarmProjectionOptions.MaxHistoryDepth"/>]</c> so an operator
///     who types <c>10000</c> by accident doesn't blow up the wire session. The clamp lives
///     in <see cref="ResolveDepth"/>.</para>
///
///     <para><b>Active alarms</b> — first cut surfaces history only. Active alarms (raise +
///     clear via <c>cnc_rdalmmsg</c>/<c>cnc_rdalmmsg2</c>) are a follow-up; this projection's
///     subscribe path returns a handle but does not poll for active alarms today. The
///     ActiveOnly mode therefore is functionally a no-op subscribe — the IAlarmSource
///     contract still wires up so capability negotiation works + a future PR can add the
///     active-alarm poll without reshaping the projection. The plan deliberately scopes F3-a
///     to the history extension; the active poll lands as F3-b.</para>
/// </remarks>
internal sealed class FocasAlarmProjection : IAsyncDisposable
{
    private readonly Func<CancellationToken, Task<IFocasClient?>> _connectAsync;
    private readonly Action<AlarmEventArgs> _emit;
    private readonly FocasAlarmProjectionOptions _options;
    private readonly string _diagnosticPrefix;

    private readonly Dictionary<long, Subscription> _subs = new();
    private readonly Lock _subsLock = new();
    private long _nextId;

    /// <summary>
    ///     Dedup set across the entire projection — alarm history is per-CNC, not
    ///     per-subscription, so a single set across all subscriptions matches operator
    ///     intent (one CNC, one ring buffer, one set of history events even if multiple
    ///     OPC UA clients have subscribed).
    /// </summary>
    private readonly HashSet<DedupKey> _seen = new();
    private readonly Lock _seenLock = new();

    public FocasAlarmProjection(
        FocasAlarmProjectionOptions options,
        Func<CancellationToken, Task<IFocasClient?>> connectAsync,
        Action<AlarmEventArgs> emit,
        string diagnosticPrefix = "focas-alarm-sub")
    {
        ArgumentNullException.ThrowIfNull(options);
        ArgumentNullException.ThrowIfNull(connectAsync);
        ArgumentNullException.ThrowIfNull(emit);
        _options = options;
        _connectAsync = connectAsync;
        _emit = emit;
        _diagnosticPrefix = diagnosticPrefix;
    }

    public Task<IAlarmSubscriptionHandle> SubscribeAsync(
        IReadOnlyList<string> sourceNodeIds, CancellationToken cancellationToken)
    {
        var id = Interlocked.Increment(ref _nextId);
        var handle = new FocasAlarmSubscriptionHandle(id, _diagnosticPrefix);

        if (_options.Mode != FocasAlarmProjectionMode.ActivePlusHistory)
        {
            // ActiveOnly — return the handle so capability negotiation works, but skip the
            // history poll entirely. The active-alarm poll lands as a follow-up PR.
            return Task.FromResult<IAlarmSubscriptionHandle>(handle);
        }

        var cts = new CancellationTokenSource();
        var sub = new Subscription(handle, [..sourceNodeIds], cts);
        lock (_subsLock) _subs[id] = sub;
        sub.Loop = Task.Run(() => RunHistoryPollAsync(sub, cts.Token), cts.Token);
        return Task.FromResult<IAlarmSubscriptionHandle>(handle);
    }

    public async Task UnsubscribeAsync(IAlarmSubscriptionHandle handle, CancellationToken cancellationToken)
    {
        if (handle is not FocasAlarmSubscriptionHandle h) return;
        Subscription? sub;
        lock (_subsLock)
        {
            if (!_subs.Remove(h.Id, out sub)) return;
        }
        try { await sub.Cts.CancelAsync().ConfigureAwait(false); } catch { }
        try { await sub.Loop.ConfigureAwait(false); } catch { }
        sub.Cts.Dispose();
    }

    /// <summary>
    ///     Acknowledge stub — FANUC's history surface is read-only (the ring buffer only
    ///     records what the CNC has cleared internally), so per-history-entry ack is a no-op.
    ///     A future PR may extend the active-alarm flow with a per-CNC reset call.
    /// </summary>
    public Task AcknowledgeAsync(
        IReadOnlyList<AlarmAcknowledgeRequest> acknowledgements, CancellationToken cancellationToken)
        => Task.CompletedTask;

    public async ValueTask DisposeAsync()
    {
        List<Subscription> snap;
        lock (_subsLock) { snap = _subs.Values.ToList(); _subs.Clear(); }
        foreach (var sub in snap)
        {
            try { await sub.Cts.CancelAsync().ConfigureAwait(false); } catch { }
            try { await sub.Loop.ConfigureAwait(false); } catch { }
            sub.Cts.Dispose();
        }
    }

    /// <summary>
    ///     Reset the dedup set — used after reconnect so the next history poll re-emits
    ///     everything in the ring buffer. Public for tests + the driver's reconnect hook.
    /// </summary>
    public void ResetDedup()
    {
        lock (_seenLock) _seen.Clear();
    }

    /// <summary>
    ///     Pull one history snapshot + emit unseen entries. Extracted from the timer loop so
    ///     unit tests can drive a single tick without standing up Task.Run.
    /// </summary>
    internal async Task<int> PollOnceAsync(Subscription sub, CancellationToken ct)
    {
        var client = await _connectAsync(ct).ConfigureAwait(false);
        if (client is null) return 0;

        var depth = ResolveDepth(_options.HistoryDepth);
        IReadOnlyList<FocasAlarmHistoryEntry> entries;
        try
        {
            entries = await client.ReadAlarmHistoryAsync(depth, ct).ConfigureAwait(false);
        }
        catch (OperationCanceledException) when (ct.IsCancellationRequested)
        {
            throw;
        }
        catch
        {
            // Per-tick failure — leave dedup intact, next tick retries. Matches the
            // AbCip alarm projection's "non-fatal per-tick" pattern (#177).
            return 0;
        }

        var emitted = 0;
        foreach (var entry in entries)
        {
            var key = new DedupKey(entry.OccurrenceTime, entry.AlarmNumber, entry.AlarmType);
            bool added;
            lock (_seenLock) added = _seen.Add(key);
            if (!added) continue;

            // Each subscription gets its own copy of the event — multiple OPC UA clients
            // can subscribe + each sees the historic events through their own subscription
            // handle. Source node id is the first declared id (sub.SourceNodeIds[0]) when
            // present; empty subscriptions get a synthetic "alarm-history" id so the
            // event still threads through the IAlarmSource contract cleanly.
            var sourceNodeId = sub.SourceNodeIds.Count > 0 ? sub.SourceNodeIds[0] : "alarm-history";

            _emit(new AlarmEventArgs(
                SubscriptionHandle: sub.Handle,
                SourceNodeId: sourceNodeId,
                ConditionId: $"focas-history#{entry.AlarmType}-{entry.AlarmNumber}-{entry.OccurrenceTime:O}",
                AlarmType: $"FOCAS_T{entry.AlarmType}",
                Message: BuildMessage(entry),
                Severity: AlarmSeverity.High,
                SourceTimestampUtc: entry.OccurrenceTime.UtcDateTime));
            emitted++;
        }
        return emitted;
    }

    private async Task RunHistoryPollAsync(Subscription sub, CancellationToken ct)
    {
        // First poll fires immediately on subscribe (== "on connect" per F3-a) so operators
        // get history dashboard data without waiting for the cadence to elapse.
        try { await PollOnceAsync(sub, ct).ConfigureAwait(false); }
        catch (OperationCanceledException) when (ct.IsCancellationRequested) { return; }
        catch { /* swallowed in PollOnceAsync; defensive double-catch */ }

        var interval = _options.HistoryPollInterval > TimeSpan.Zero
            ? _options.HistoryPollInterval
            : FocasAlarmProjectionOptions.DefaultHistoryPollInterval;

        while (!ct.IsCancellationRequested)
        {
            try { await Task.Delay(interval, ct).ConfigureAwait(false); }
            catch (OperationCanceledException) { break; }

            try { await PollOnceAsync(sub, ct).ConfigureAwait(false); }
            catch (OperationCanceledException) when (ct.IsCancellationRequested) { break; }
            catch { /* per-tick failures are non-fatal */ }
        }
    }

    /// <summary>
    ///     Bound user-requested depth to <c>[1..MaxHistoryDepth]</c>. <c>0</c>/negative
    ///     values fall back to <see cref="FocasAlarmProjectionOptions.DefaultHistoryDepth"/>
    ///     so misconfigured options still pull a reasonable batch.
    /// </summary>
    internal static int ResolveDepth(int requested)
    {
        if (requested <= 0) return FocasAlarmProjectionOptions.DefaultHistoryDepth;
        return Math.Min(requested, FocasAlarmProjectionOptions.MaxHistoryDepth);
    }

    private static string BuildMessage(FocasAlarmHistoryEntry entry)
    {
        if (string.IsNullOrEmpty(entry.Message))
            return $"FOCAS alarm T{entry.AlarmType} #{entry.AlarmNumber}";
        return $"FOCAS T{entry.AlarmType} #{entry.AlarmNumber}: {entry.Message}";
    }

    /// <summary>Composite dedup key — see class-level remarks.</summary>
    private readonly record struct DedupKey(DateTimeOffset OccurrenceTime, int AlarmNumber, int AlarmType);

    internal sealed class Subscription
    {
        public Subscription(FocasAlarmSubscriptionHandle handle, IReadOnlyList<string> sourceNodeIds, CancellationTokenSource cts)
        {
            Handle = handle; SourceNodeIds = sourceNodeIds; Cts = cts;
        }
        public FocasAlarmSubscriptionHandle Handle { get; }
        public IReadOnlyList<string> SourceNodeIds { get; }
        public CancellationTokenSource Cts { get; }
        public Task Loop { get; set; } = Task.CompletedTask;
    }
}

/// <summary>Handle returned by <see cref="FocasAlarmProjection.SubscribeAsync"/>.</summary>
public sealed record FocasAlarmSubscriptionHandle(long Id, string DiagnosticPrefix) : IAlarmSubscriptionHandle
{
    public string DiagnosticId => $"{DiagnosticPrefix}-{Id}";
}