Add base legacy skin transformer

osu.Game/Skinning/LegacySkinTransformer.cs

@@ -0,0 +1,35 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Audio.Sample;
+using osu.Framework.Bindables;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Textures;
+using osu.Game.Audio;
+
+namespace osu.Game.Skinning
+{
+    /// <summary>
+    /// Transformer used to handle support of legacy features for individual rulesets.
+    /// </summary>
+    public abstract class LegacySkinTransformer : ISkin
+    {
+        /// <summary>
+        /// Source of the <see cref="ISkin"/> which is being transformed.
+        /// </summary>
+        protected ISkinSource Source { get; }
+
+        protected LegacySkinTransformer(ISkinSource source)
+        {
+            Source = source;
+        }
+
+        public abstract Drawable GetDrawableComponent(ISkinComponent component);
+
+        public Texture GetTexture(string componentName) => Source.GetTexture(componentName);
+
+        public virtual SampleChannel GetSample(ISampleInfo sampleInfo) => Source.GetSample(sampleInfo);
+
+        public abstract IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup);
+    }
+}