Ambient music rules refactor (#29921)

* refactor

* dutypo

Content.Shared/Random/Rules/NearbyEntities.cs

@@ -0,0 +1,58 @@
+using Content.Shared.Whitelist;
+
+namespace Content.Shared.Random.Rules;
+
+/// <summary>
+/// Checks for entities matching the whitelist in range.
+/// This is more expensive than <see cref="NearbyComponentsRule"/> so prefer that!
+/// </summary>
+public sealed partial class NearbyEntitiesRule : RulesRule
+{
+    /// <summary>
+    /// How many of the entity need to be nearby.
+    /// </summary>
+    [DataField]
+    public int Count = 1;
+
+    [DataField(required: true)]
+    public EntityWhitelist Whitelist = new();
+
+    [DataField]
+    public float Range = 10f;
+
+    public override bool Check(EntityManager entManager, EntityUid uid)
+    {
+        if (!entManager.TryGetComponent(uid, out TransformComponent? xform) ||
+            xform.MapUid == null)
+        {
+            return false;
+        }
+
+        var transform = entManager.System<SharedTransformSystem>();
+        var lookup = entManager.System<EntityLookupSystem>();
+        var whitelistSystem = entManager.System<EntityWhitelistSystem>();
+
+        var found = false;
+        var worldPos = transform.GetWorldPosition(xform);
+        var count = 0;
+
+        foreach (var ent in lookup.GetEntitiesInRange(xform.MapID, worldPos, Range))
+        {
+            if (whitelistSystem.IsWhitelistFail(Whitelist, ent))
+                continue;
+
+            count++;
+
+            if (count < Count)
+                continue;
+
+            found = true;
+            break;
+        }
+
+        if (!found)
+            return Inverted;
+
+        return !Inverted;
+    }
+}