add StationTrackerComponent (#36803)

* maybe I am cooking

* logmissing

* copy paste oops

* add some stuff

* review

* fix

* rerun tests

---------

Co-authored-by: slarticodefast <161409025+slarticodefast@users.noreply.github.com>

Content.Shared/Station/SharedStationSystem.cs

@@ -0,0 +1,111 @@
+using Content.Shared.Station.Components;
+using JetBrains.Annotations;
+using Robust.Shared.Map;
+
+namespace Content.Shared.Station;
+
+public abstract partial class SharedStationSystem : EntitySystem
+{
+    [Dependency] private readonly MetaDataSystem _meta = default!;
+
+    private EntityQuery<TransformComponent> _xformQuery;
+    private EntityQuery<StationMemberComponent> _stationMemberQuery;
+
+    /// <inheritdoc/>
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        _xformQuery = GetEntityQuery<TransformComponent>();
+        _stationMemberQuery = GetEntityQuery<StationMemberComponent>();
+
+        SubscribeLocalEvent<StationTrackerComponent, MapInitEvent>(OnTrackerMapInit);
+        SubscribeLocalEvent<StationTrackerComponent, ComponentRemove>(OnTrackerRemove);
+        SubscribeLocalEvent<StationTrackerComponent, GridUidChangedEvent>(OnTrackerGridChanged);
+        SubscribeLocalEvent<StationTrackerComponent, MetaFlagRemoveAttemptEvent>(OnMetaFlagRemoveAttempt);
+    }
+
+    private void OnTrackerMapInit(Entity<StationTrackerComponent> ent, ref MapInitEvent args)
+    {
+        _meta.AddFlag(ent, MetaDataFlags.ExtraTransformEvents);
+        UpdateStationTracker(ent.AsNullable());
+    }
+
+    private void OnTrackerRemove(Entity<StationTrackerComponent> ent, ref ComponentRemove args)
+    {
+        _meta.RemoveFlag(ent, MetaDataFlags.ExtraTransformEvents);
+    }
+
+    private void OnTrackerGridChanged(Entity<StationTrackerComponent> ent, ref GridUidChangedEvent args)
+    {
+        UpdateStationTracker((ent, ent.Comp, args.Transform));
+    }
+
+    private void OnMetaFlagRemoveAttempt(Entity<StationTrackerComponent> ent, ref MetaFlagRemoveAttemptEvent args)
+    {
+        if ((args.ToRemove & MetaDataFlags.ExtraTransformEvents) != 0 &&
+            ent.Comp.LifeStage <= ComponentLifeStage.Running)
+        {
+            args.ToRemove &= ~MetaDataFlags.ExtraTransformEvents;
+        }
+    }
+
+    /// <summary>
+    /// Updates the station tracker component based on entity's current location.
+    /// </summary>
+    [PublicAPI]
+    public void UpdateStationTracker(Entity<StationTrackerComponent?, TransformComponent?> ent)
+    {
+        if (!Resolve(ent, ref ent.Comp1))
+            return;
+
+        var xform = ent.Comp2;
+
+        if (!_xformQuery.Resolve(ent, ref xform))
+            return;
+
+        // Entity is in nullspace or not on a grid
+        if (xform.MapID == MapId.Nullspace || xform.GridUid == null)
+        {
+            SetStation(ent, null);
+            return;
+        }
+
+        // Check if the grid is part of a station
+        if (!_stationMemberQuery.TryGetComponent(xform.GridUid.Value, out var stationMember))
+        {
+            SetStation(ent, null);
+            return;
+        }
+
+        SetStation(ent, stationMember.Station);
+    }
+
+    /// <summary>
+    /// Sets the station for a StationTrackerComponent.
+    /// </summary>
+    [PublicAPI]
+    public void SetStation(Entity<StationTrackerComponent?> ent, EntityUid? station)
+    {
+        if (!Resolve(ent, ref ent.Comp))
+            return;
+
+        if (ent.Comp.Station == station)
+            return;
+
+        ent.Comp.Station = station;
+        Dirty(ent);
+    }
+
+    /// <summary>
+    /// Gets the station an entity is currently on, if any.
+    /// </summary>
+    [PublicAPI]
+    public EntityUid? GetCurrentStation(Entity<StationTrackerComponent?> ent)
+    {
+        if (!Resolve(ent, ref ent.Comp, logMissing: false))
+            return null;
+
+        return ent.Comp.Station;
+    }
+}