Station alert levels (#8226)

Content.Client/AlertLevel/AlertLevelDisplaySystem.cs

@@ -0,0 +1,46 @@
+using System.Linq;
+using Content.Shared.AlertLevel;
+using Robust.Client.GameObjects;
+using Robust.Client.Graphics;
+using Robust.Shared.Utility;
+
+namespace Content.Client.AlertLevel;
+
+public sealed class AlertLevelDisplaySystem : EntitySystem
+{
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        SubscribeLocalEvent<AlertLevelDisplayComponent, AppearanceChangeEvent>(OnAppearanceChange);
+    }
+
+    private void OnAppearanceChange(EntityUid uid, AlertLevelDisplayComponent component, ref AppearanceChangeEvent args)
+    {
+        if (args.Sprite == null)
+        {
+            return;
+        }
+
+        if (!args.Sprite.LayerMapTryGet(AlertLevelDisplay.Layer, out _))
+        {
+            var layer = args.Sprite.AddLayer(new RSI.StateId(component.AlertVisuals.Values.First()));
+            args.Sprite.LayerMapSet(AlertLevelDisplay.Layer, layer);
+        }
+
+        if (!args.AppearanceData.TryGetValue(AlertLevelDisplay.CurrentLevel, out var level))
+        {
+            args.Sprite.LayerSetState(AlertLevelDisplay.Layer, new RSI.StateId(component.AlertVisuals.Values.First()));
+            return;
+        }
+
+        if (component.AlertVisuals.TryGetValue((string) level, out var visual))
+        {
+            args.Sprite.LayerSetState(AlertLevelDisplay.Layer, new RSI.StateId(visual));
+        }
+        else
+        {
+            args.Sprite.LayerSetState(AlertLevelDisplay.Layer, new RSI.StateId(component.AlertVisuals.Values.First()));
+        }
+    }
+}