namespace ZB.MOM.WW.OtOpcUa.OpcUaServer;

/// <summary>How <see cref="AddressSpaceApplier"/> must mutate the address space for a given
/// <see cref="AddressSpacePlan"/>. A pure policy classification OVER the planner's diff (the planner stays
/// a pure diff; the kind is the applier's routing policy over that diff — see R2-07 03/P1).</summary>
public enum AddressSpaceChangeKind
{
    /// <summary><see cref="AddressSpacePlan.IsEmpty"/> — nothing to do.</summary>
    Empty,

    /// <summary>Only surgical-eligible changed tags, node-irrelevant vtag changes, folder renames, and/or
    /// node-inert driver deltas — the existing F10b in-place path. No adds, no removes.</summary>
    AttributeOnly,

    /// <summary>Only additions (any mix of Equipment/Alarms/Tags/VirtualTags) on top of at-most-AttributeOnly
    /// changes — no removals, no node-affecting changes. Phase 1: the idempotent Materialise passes create
    /// exactly the added nodes with no teardown, so every client subscription survives.</summary>
    PureAdd,

    /// <summary>Only removals on top of at-most-AttributeOnly changes — no additions, no node-affecting
    /// changes. Phase 2: scoped in-place teardown of only the removed subtree.</summary>
    PureRemove,

    /// <summary>Additions AND removals, still no node-affecting changes. Phase 3 applies removes-then-adds
    /// surgically; until Phase 3 it maps to a full rebuild.</summary>
    AddRemoveMix,

    /// <summary>Anything with a node-affecting change (ChangedEquipment, ChangedAlarms, non-surgical
    /// ChangedEquipmentTags, node-relevant ChangedEquipmentVirtualTags) — the unclassifiable-safe default.
    /// Full rebuild.</summary>
    Rebuild,
}

/// <summary>
///     Pure static classifier over an <see cref="AddressSpacePlan"/> — names the delta class the applier
///     routes each plan through, so a pure-add deploy no longer tears down and recreates every node on the
///     server (03/P1). First-match-wins per the plan's classification table; the default-closed
///     <see cref="AddressSpaceChangeKind.Rebuild"/> catches every node-affecting change (including any future
///     plan field that makes a changed record unequal), so the worst outcome of any misclassification is
///     today's full-rebuild behaviour.
/// </summary>
public static class AddressSpaceChangeClassifier
{
    /// <summary>Classify <paramref name="plan"/> into the delta class the applier routes it through.</summary>
    /// <param name="plan">The plan to classify.</param>
    /// <returns>The <see cref="AddressSpaceChangeKind"/> for the plan.</returns>
    public static AddressSpaceChangeKind Classify(AddressSpacePlan plan)
    {
        ArgumentNullException.ThrowIfNull(plan);

        // 1 — nothing to do.
        if (plan.IsEmpty) return AddressSpaceChangeKind.Empty;

        // 2 — any node-affecting CHANGE forces a full rebuild (default-closed). ChangedEquipment /
        // ChangedAlarms are always node-affecting; a changed tag is node-affecting UNLESS it is
        // surgical-eligible, and a changed vtag is node-affecting UNLESS it is node-irrelevant. The v3
        // Batch-4 Raw/UNS Changed sets (container re-shape, raw-tag attribute/alarm edit, UNS re-point /
        // display-name-override) route to Rebuild as the safe default — WP3's applier owns any surgical
        // in-place refinement for them. Evaluated BEFORE the add/remove split so a non-surgical change
        // alongside pure adds still rebuilds.
        //
        // WP4 BINDING GUARD (Wave C review M3): ChangedRawTags → Rebuild is what keeps native-alarm notifier
        // wiring correct today. A native alarm's set of referencing equipment lives in
        // RawTagPlan.ReferencingEquipmentPaths (part of its record equality), so ADDING/DROPPING a reference
        // makes the raw tag a ChangedRawTag → full rebuild → OtOpcUaNodeManager clears + re-wires the notifiers
        // cleanly. ANY future surgical (non-rebuild) ChangedRawTags path MUST also re-wire/unwire the alarm
        // notifiers (WireAlarmNotifiers is a reconcile — pass the tag's COMPLETE current referencing set — plus
        // an explicit unwire on removal), else a de-referenced equipment keeps receiving the alarm's events.
        if (plan.ChangedEquipment.Count > 0 ||
            plan.ChangedAlarms.Count > 0 ||
            plan.ChangedRawContainers.Count > 0 ||
            plan.ChangedRawTags.Count > 0 ||
            plan.ChangedUnsReferenceVariables.Count > 0 ||
            plan.ChangedEquipmentTags.Any(d => !TagDeltaIsSurgicalEligible(d)) ||
            plan.ChangedEquipmentVirtualTags.Any(d => !VtagDeltaIsNodeIrrelevant(d)))
        {
            return AddressSpaceChangeKind.Rebuild;
        }

        // Driver deltas (Added/Removed/ChangedDrivers) are node-INERT — they never touch the address-space
        // topology (they route to DriverHostActor's spawn plan in Runtime), so they are excluded from the
        // add/remove split below and leave a driver-only plan classified AttributeOnly.
        var hasAdds =
            plan.AddedEquipment.Count + plan.AddedAlarms.Count +
            plan.AddedEquipmentTags.Count + plan.AddedEquipmentVirtualTags.Count +
            plan.AddedRawContainers.Count + plan.AddedRawTags.Count +
            plan.AddedUnsReferenceVariables.Count > 0;
        var hasRemoves =
            plan.RemovedEquipment.Count + plan.RemovedAlarms.Count +
            plan.RemovedEquipmentTags.Count + plan.RemovedEquipmentVirtualTags.Count +
            plan.RemovedRawContainers.Count + plan.RemovedRawTags.Count +
            plan.RemovedUnsReferenceVariables.Count > 0;

        // 3 — additions AND removals.
        if (hasAdds && hasRemoves) return AddressSpaceChangeKind.AddRemoveMix;
        // 4 — additions only.
        if (hasAdds) return AddressSpaceChangeKind.PureAdd;
        // 5 — removals only.
        if (hasRemoves) return AddressSpaceChangeKind.PureRemove;
        // 6 — only surgical tag deltas / node-irrelevant vtag deltas / folder renames / driver deltas.
        return AddressSpaceChangeKind.AttributeOnly;
    }

    // A VirtualTag's materialised OPC UA node (MaterialiseEquipmentVirtualTags) is derived ONLY from
    // {EquipmentId, FolderPath, Name, DataType}. Expression/DependencyRefs/Historize are engine/write-side
    // only and are adopted by VirtualTagHostActor's INDEPENDENT respawn (DriverHostActor → ApplyVirtualTags),
    // so a delta changing ONLY those three leaves a byte-identical node and needs no address-space rebuild.
    // Whitelist-of-may-differ via `with` + the record's custom Equals: any OTHER field difference (current
    // or future) makes the override unequal → falls back to a full rebuild (safe default).
    internal static bool VtagDeltaIsNodeIrrelevant(AddressSpacePlan.EquipmentVirtualTagDelta d) =>
        (d.Previous with
        {
            Expression = d.Current.Expression,
            DependencyRefs = d.Current.DependencyRefs,
            Historize = d.Current.Historize,
        }).Equals(d.Current);

    // F10b: a CHANGED equipment tag whose ONLY differences are Writable / IsHistorized /
    // HistorianTagname / DataType / IsArray / ArrayLength (a plain value variable — no alarm condition node)
    // can be updated IN PLACE on the existing node via ISurgicalAddressSpaceSink.UpdateTagAttributes,
    // avoiding a full rebuild (preserving subscriptions). The presentation-shape fields (DataType / IsArray /
    // ArrayLength) join the whitelist now that the surgical sink swaps DataType + ValueRank + ArrayDimensions
    // in place (and raises a GeneralModelChangeEvent). FullName / DriverInstanceId / Name / identity / alarm
    // differences still fall through to a rebuild — FullName/DriverInstanceId re-route the node to a different
    // driver point, Name re-derives the NodeId, and an alarm flip turns the node into a Part 9 condition. The
    // override-unequal default also covers any future field.
    // REACH (live-verified): the shape path only fires for drivers whose TagConfig carries a stable
    // top-level "FullName" (Galaxy = tag_name.AttributeName; OpcUaClient = the node id) — there a DataType/array
    // edit leaves FullName untouched ⇒ surgical. For structured-TagConfig protocol drivers (Modbus/S7/AbCip/…)
    // TagConfigIntent.Parse falls back to the RAW TagConfig blob as FullName, so a DataType/
    // array edit also mutates that blob ⇒ FullName differs ⇒ this returns false ⇒ full rebuild. That is the
    // correct safe default (a protocol driver's subscription needs re-spawning for a new shape anyway).
    internal static bool TagDeltaIsSurgicalEligible(AddressSpacePlan.EquipmentTagDelta d) =>
        d.Previous.Alarm is null && d.Current.Alarm is null &&
        (d.Previous with
        {
            Writable = d.Current.Writable,
            IsHistorized = d.Current.IsHistorized,
            HistorianTagname = d.Current.HistorianTagname,
            DataType = d.Current.DataType,
            IsArray = d.Current.IsArray,
            ArrayLength = d.Current.ArrayLength,
        }).Equals(d.Current);
}