Add support for contextual information in EntityTables (#37737)

* Add context support for entityTables

* fix build fail

* comments

* Update Content.Shared/EntityTable/EntityTableSystem.cs

---------

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

Content.Shared/EntityTable/EntityTableSystem.cs

@@ -1,4 +1,6 @@
+using System.Diagnostics.CodeAnalysis;
 using Content.Shared.EntityTable.EntitySelectors;
+using JetBrains.Annotations;
 using Robust.Shared.Prototypes;
 using Robust.Shared.Random;
 
@@ -9,18 +11,55 @@ public sealed class EntityTableSystem : EntitySystem
     [Dependency] private readonly IPrototypeManager _prototypeManager = default!;
     [Dependency] private readonly IRobustRandom _random = default!;
 
-    public IEnumerable<EntProtoId> GetSpawns(EntityTablePrototype entTableProto, System.Random? rand = null)
+    public IEnumerable<EntProtoId> GetSpawns(EntityTablePrototype entTableProto, System.Random? rand = null, EntityTableContext? ctx = null)
     {
         // convenient
-        return GetSpawns(entTableProto.Table, rand);
+        return GetSpawns(entTableProto.Table, rand, ctx);
     }
 
-    public IEnumerable<EntProtoId> GetSpawns(EntityTableSelector? table, System.Random? rand = null)
+    public IEnumerable<EntProtoId> GetSpawns(EntityTableSelector? table, System.Random? rand = null, EntityTableContext? ctx = null)
     {
         if (table == null)
             return new List<EntProtoId>();
 
         rand ??= _random.GetRandom();
-        return table.GetSpawns(rand, EntityManager, _prototypeManager);
+        ctx ??= new EntityTableContext();
+        return table.GetSpawns(rand, EntityManager, _prototypeManager, ctx);
+    }
+}
+
+/// <summary>
+/// Context used by selectors and conditions to evaluate in generic gamestate information.
+/// </summary>
+public sealed class EntityTableContext
+{
+    private readonly Dictionary<string, object> _data = new();
+
+    public EntityTableContext()
+    {
+
+    }
+
+    public EntityTableContext(Dictionary<string, object> data)
+    {
+        _data = data;
+    }
+
+    /// <summary>
+    /// Retrieves an arbitrary piece of data from the context based on a provided key.
+    /// </summary>
+    /// <param name="key">A string key that corresponds to the value we are searching for. </param>
+    /// <param name="value">The value we are trying to extract from the context object</param>
+    /// <typeparam name="T">The type of <see cref="value"/> that we are trying to retrieve</typeparam>
+    /// <returns>If <see cref="key"/> has a corresponding value of type <see cref="T"/></returns>
+    [PublicAPI]
+    public bool TryGetData<T>([ForbidLiteral] string key, [NotNullWhen(true)] out T? value)
+    {
+        value = default;
+        if (!_data.TryGetValue(key, out var valueData) || valueData is not T castValueData)
+            return false;
+
+        value = castValueData;
+        return true;
     }
 }