Move logic to AndroidImportTask and add delete mechanism

osu.Android/AndroidImportTask.cs

@@ -0,0 +1,57 @@
+// 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 System.IO;
+using System.Threading.Tasks;
+using Android.Content;
+using Android.Net;
+using Android.Provider;
+using osu.Game.Database;
+
+namespace osu.Android
+{
+    public class AndroidImportTask : ImportTask
+    {
+        private readonly ContentResolver contentResolver;
+
+        private readonly Uri uri;
+
+        private AndroidImportTask(Stream stream, string filename, ContentResolver contentResolver, Uri uri)
+            : base(stream, filename)
+        {
+            this.contentResolver = contentResolver;
+            this.uri = uri;
+        }
+
+        public override void DeleteFile()
+        {
+            contentResolver.Delete(uri, null, null);
+        }
+
+        public static async Task<AndroidImportTask?> Create(ContentResolver contentResolver, Uri uri)
+        {
+            // there are more performant overloads of this method, but this one is the most backwards-compatible
+            // (dates back to API 1).
+
+            var cursor = contentResolver.Query(uri, null, null, null, null);
+
+            if (cursor == null)
+                return null;
+
+            cursor.MoveToFirst();
+
+            int filenameColumn = cursor.GetColumnIndex(IOpenableColumns.DisplayName);
+            string filename = cursor.GetString(filenameColumn);
+
+            // SharpCompress requires archive streams to be seekable, which the stream opened by
+            // OpenInputStream() seems to not necessarily be.
+            // copy to an arbitrary-access memory stream to be able to proceed with the import.
+            var copy = new MemoryStream();
+
+            using (var stream = contentResolver.OpenInputStream(uri))
+                await stream.CopyToAsync(copy).ConfigureAwait(false);
+
+            return new AndroidImportTask(copy, filename, contentResolver, uri);
+        }
+    }
+}