acdream/src/AcDream.App/Physics/LiveEntityPvpBitfieldSync.cs

using AcDream.App.World;
using AcDream.Core.Items;
using AcDream.Core.Physics;

namespace AcDream.App.Physics;

/// <summary>
/// #297 second edge: keeps a live entity's collision-shadow
/// <see cref="EntityCollisionFlags"/> synced with its
/// <see cref="ClientObject.PublicWeenieBitfield"/> after a live
/// PropertyInt(PlayerKillerStatus) update.
///
/// <para>
/// The MOVER side of the retail PvP exemption already refreshes for free:
/// <see cref="EntityCollisionFlagsExt.ResolveMoverPvpState"/> reads
/// <see cref="ClientObject.PublicWeenieBitfield"/> straight from the table on
/// every call, so once <c>ClientObjectTable.UpdateIntProperty</c> rewrites
/// that field (see <see cref="PlayerKillerStatusBitfield"/>) the next mover
/// query already sees it. The TARGET side is different: <c>CollisionExemption
/// .ShouldSkip</c> reads a decoded <see cref="EntityCollisionFlags"/> value
/// cached on the <see cref="ShadowObjectRegistry"/> entry at registration
/// time (<c>LiveEntityCollisionBuilder.Build</c>).
/// </para>
///
/// <para>
/// This class is the IMMEDIATE fix — it makes the shadow-registry flags
/// track a PK-status change the moment PropertyInt 134 arrives, with no wait
/// for any other event. It is NOT sufficient by itself: review round 2 (F1)
/// found that the same <c>LiveEntityCollisionBuilder.Build</c> registration
/// path re-runs on every ObjDesc/appearance change (any equip/dequip) and
/// rebuilds the shadow flags from <c>spawn.ObjectDescriptionFlags</c> — the
/// canonical Runtime snapshot, NOT this class's write target — so without a
/// companion fix a later equip would silently revert the flags this class
/// just wrote. <see cref="AcDream.Runtime.Entities.RuntimeEntityPvpBitfieldSnapshotSync"/>
/// closes that gap by keeping the snapshot itself live, so every rebuild
/// (and the placement/teleport mover-flags path, which reads the snapshot
/// directly) reproduces the same correct value instead of a stale one. The
/// two classes write to two different stores (this one: the shadow
/// registry's cached per-cell flags; that one: the canonical wire snapshot)
/// and are not a duplicate-authority pair — removing either reopens a
/// distinct symptom.
/// </para>
///
/// <para>
/// Subscribes to every <see cref="ClientObjectTable.ObjectUpdated"/> rather
/// than filtering to PropertyInt 134 alone: the recompute is a cheap
/// dictionary lookup plus a bitmask merge
/// (<see cref="ShadowObjectRegistry.UpdatePwdBitfieldFlags"/>, which
/// short-circuits on an unchanged result — see its own remarks for why that
/// guard is load-bearing), it is a no-op for any object without a live
/// shadow registration, and it stays correct for any future
/// PWD-bitfield-affecting property without another wiring change.
/// </para>
/// </summary>
internal sealed class LiveEntityPvpBitfieldSync : IDisposable
{
    private readonly ClientObjectTable _objects;
    private readonly LiveEntityRuntime _liveEntities;
    private readonly ShadowObjectRegistry _shadows;
    private bool _disposed;

    public LiveEntityPvpBitfieldSync(
        ClientObjectTable objects,
        LiveEntityRuntime liveEntities,
        ShadowObjectRegistry shadows)
    {
        _objects = objects ?? throw new ArgumentNullException(nameof(objects));
        _liveEntities = liveEntities ?? throw new ArgumentNullException(nameof(liveEntities));
        _shadows = shadows ?? throw new ArgumentNullException(nameof(shadows));
        _objects.ObjectUpdated += OnObjectUpdated;
    }

    private void OnObjectUpdated(ClientObject item)
    {
        if (item.PublicWeenieBitfield is not { } bitfield)
            return;
        if (!_liveEntities.TryGetRecord(item.ObjectId, out LiveEntityRecord record)
            || record.WorldEntity is not { } entity)
        {
            return;
        }
        _shadows.UpdatePwdBitfieldFlags(entity.Id, bitfield);
    }

    public void Dispose()
    {
        if (_disposed) return;
        _disposed = true;
        _objects.ObjectUpdated -= OnObjectUpdated;
    }
}