Ambient music rules refactor (#29921)

* refactor

* dutypo

Content.Shared/Random/Rules/RulesSystem.cs

@@ -0,0 +1,39 @@
+using Robust.Shared.Prototypes;
+
+namespace Content.Shared.Random.Rules;
+
+/// <summary>
+/// Rules-based item selection. Can be used for any sort of conditional selection
+/// Every single condition needs to be true for this to be selected.
+/// e.g. "choose maintenance audio if 90% of tiles nearby are maintenance tiles"
+/// </summary>
+[Prototype("rules")]
+public sealed partial class RulesPrototype : IPrototype
+{
+    [IdDataField] public string ID { get; } = string.Empty;
+
+    [DataField("rules", required: true)]
+    public List<RulesRule> Rules = new();
+}
+
+[ImplicitDataDefinitionForInheritors]
+public abstract partial class RulesRule
+{
+    [DataField]
+    public bool Inverted;
+    public abstract bool Check(EntityManager entManager, EntityUid uid);
+}
+
+public sealed class RulesSystem : EntitySystem
+{
+    public bool IsTrue(EntityUid uid, RulesPrototype rules)
+    {
+        foreach (var rule in rules.Rules)
+        {
+            if (!rule.Check(EntityManager, uid))
+                return false;
+        }
+
+        return true;
+    }
+}