From b87a5956dd62de3fb77532073022ee6ac0a08e21 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Sun, 6 Jun 2021 12:17:55 +0900
Subject: [PATCH] Add fallback logic to `SkinManager`

---
 osu.Game/Skinning/SkinManager.cs | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/osu.Game/Skinning/SkinManager.cs b/osu.Game/Skinning/SkinManager.cs
index d373618232..9aa2d90064 100644
--- a/osu.Game/Skinning/SkinManager.cs
+++ b/osu.Game/Skinning/SkinManager.cs
@@ -204,16 +204,34 @@ namespace osu.Game.Skinning
 
         public event Action SourceChanged;
 
-        public Drawable GetDrawableComponent(ISkinComponent component) => CurrentSkin.Value.GetDrawableComponent(component);
+        public Drawable GetDrawableComponent(ISkinComponent component) => lookupWithFallback(s => s.GetDrawableComponent(component));
 
-        public Texture GetTexture(string componentName, WrapMode wrapModeS, WrapMode wrapModeT) => CurrentSkin.Value.GetTexture(componentName, wrapModeS, wrapModeT);
+        public Texture GetTexture(string componentName, WrapMode wrapModeS, WrapMode wrapModeT) => lookupWithFallback(s => s.GetTexture(componentName, wrapModeS, wrapModeT));
 
-        public ISample GetSample(ISampleInfo sampleInfo) => CurrentSkin.Value.GetSample(sampleInfo);
+        public ISample GetSample(ISampleInfo sampleInfo) => lookupWithFallback(s => s.GetSample(sampleInfo));
 
-        public IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup) => CurrentSkin.Value.GetConfig<TLookup, TValue>(lookup);
+        public IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup) => lookupWithFallback(s => s.GetConfig<TLookup, TValue>(lookup));
 
         public ISkin FindProvider(Func<ISkin, bool> lookupFunction) => lookupFunction(CurrentSkin.Value) ? CurrentSkin.Value : null;
 
+        private Skin defaultLegacySkin;
+
+        private T lookupWithFallback<T>(Func<ISkin, T> func)
+            where T : class
+        {
+            var selectedSkin = func(CurrentSkin.Value);
+
+            if (selectedSkin != null)
+                return selectedSkin;
+
+            defaultLegacySkin ??= new DefaultLegacySkin(this);
+
+            if (CurrentSkin.Value is LegacySkin)
+                return func(defaultLegacySkin);
+
+            return null;
+        }
+
         #region IResourceStorageProvider
 
         AudioManager IStorageResourceProvider.AudioManager => audio;