Station alert levels (#8226)

Content.Server/AlertLevel/AlertLevelDisplaySystem.cs

@@ -0,0 +1,35 @@
+using Content.Server.Station.Systems;
+using Content.Shared.AlertLevel;
+
+namespace Content.Server.AlertLevel;
+
+public sealed class AlertLevelDisplaySystem : EntitySystem
+{
+    [Dependency] private readonly StationSystem _stationSystem = default!;
+
+    public override void Initialize()
+    {
+        SubscribeLocalEvent<AlertLevelChangedEvent>(OnAlertChanged);
+        SubscribeLocalEvent<AlertLevelDisplayComponent, ComponentInit>(OnDisplayInit);
+    }
+
+    private void OnAlertChanged(AlertLevelChangedEvent args)
+    {
+        foreach (var (_, appearance) in EntityManager.EntityQuery<AlertLevelDisplayComponent, AppearanceComponent>())
+        {
+            appearance.SetData(AlertLevelDisplay.CurrentLevel, args.AlertLevel);
+        }
+    }
+
+    private void OnDisplayInit(EntityUid uid, AlertLevelDisplayComponent component, ComponentInit args)
+    {
+        if (TryComp(uid, out AppearanceComponent? appearance))
+        {
+            var stationUid = _stationSystem.GetOwningStation(uid);
+            if (stationUid != null && TryComp(stationUid, out AlertLevelComponent? alert))
+            {
+                appearance.SetData(AlertLevelDisplay.CurrentLevel, alert.CurrentLevel);
+            }
+        }
+    }
+}