Made a storage provider interface and both classic and avalonia impl.

Progrart.Core/Storage/ClassicStorageProvider.cs

@@ -0,0 +1,36 @@
+namespace Progrart.Core.Storage
+{
+    public class ClassicStorageProvider : IStorageProvider
+    {
+        public DirectoryInfo BaseDirectory;
+
+        public ClassicStorageProvider(DirectoryInfo baseDirectory)
+        {
+            BaseDirectory = baseDirectory;
+        }
+
+        public async Task<Stream?> TryOpenRead(string path)
+        {
+            try
+            {
+				return File.OpenRead(Path.Combine(BaseDirectory.FullName, path));
+			}
+            catch (Exception)
+            {
+                return null;
+            }
+        }
+
+        public async Task<Stream?> TryOpenWrite(string path)
+		{
+            try
+			{
+				return File.OpenWrite(Path.Combine(BaseDirectory.FullName, path));
+			}
+            catch (Exception)
+			{
+				return null;
+			}
+		}
+    }
+}