Add: Create collection backup before overwriting osu collection

Closes #51

App/SidePanelActionsHandler.cs

@@ -26,6 +26,7 @@
 using Common;
 using GuiComponents.Interfaces;
 using System.ComponentModel;
+using System.Security.Cryptography;
 
 namespace App
 {
@@ -523,14 +524,15 @@ private async void SaveDefaultCollection(object sender, object data = null)
                 // access denied
                 if (ex.NativeErrorCode != 5)
                     throw;
-                
+
                 _userDialogs.OkMessageBox("Could not determine if osu! is running due to a permissions error.", "Warning", MessageBoxType.Warning);
             }
 
             if (_userDialogs.YesNoMessageBox("Are you sure that you want to overwrite your existing osu! collection?",
                 "Are you sure?", MessageBoxType.Question))
             {
                 await BeforeCollectionSave(Initalizer.LoadedCollections);
+                BackupOsuCollection();
                 _osuFileIo.CollectionLoader.SaveOsuCollection(Initalizer.LoadedCollections, fileLocation);
                 _userDialogs.OkMessageBox("Collections saved.", "Info", MessageBoxType.Success);
             }
@@ -540,6 +542,53 @@ private async void SaveDefaultCollection(object sender, object data = null)
             }
         }
 
+        private void BackupOsuCollection()
+        {
+            var backupFolder = Path.Combine(Initalizer.OsuDirectory, "collectionBackups");
+            if (!Directory.Exists(backupFolder))
+                Directory.CreateDirectory(backupFolder);
+
+            var sourceCollectionFile = Path.Combine(Initalizer.OsuDirectory, "collection.db");
+            if (!File.Exists(sourceCollectionFile))
+                return;
+
+            var destinationCollectionFile = Path.Combine(Initalizer.OsuDirectory, "collectionBackups", $"collection_{CalculateMD5(sourceCollectionFile)}.db");
+            if (File.Exists(destinationCollectionFile))
+            {
+                //Just update file save date to indicate latest collection version
+                File.SetLastWriteTime(destinationCollectionFile, DateTime.Now);
+                return;
+            }
+
+            CleanupBackups();
+            File.Copy(sourceCollectionFile, destinationCollectionFile);
+
+            string CalculateMD5(string filename)
+            {
+                using (var md5 = MD5.Create())
+                {
+                    using (var stream = File.OpenRead(filename))
+                    {
+                        var hash = md5.ComputeHash(stream);
+                        return BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
+                    }
+                }
+            }
+
+            void CleanupBackups()
+            {
+                var deleteDateThreshold = DateTime.UtcNow.AddDays(-30);
+                var collectionFilePaths = Directory.GetFiles(backupFolder, "*.db", SearchOption.TopDirectoryOnly);
+                var collectionFiles = collectionFilePaths.Select(f => new FileInfo(f))
+                    .Where(f => f.LastWriteTimeUtc < deleteDateThreshold);
+
+                foreach (var collectionFile in collectionFiles)
+                {
+                    collectionFile.Delete();
+                }
+            }
+        }
+
         private void ClearCollections(object sender, object data = null)
         {
             _collectionEditor.EditCollection(CollectionEditArgs.ClearCollections());