add reorderable collection

src/Snap.Hutao/Snap.Hutao/Core/Database/IReorderable.cs

@@ -0,0 +1,9 @@
+// Copyright (c) DGP Studio. All rights reserved.
+// Licensed under the MIT license.
+
+namespace Snap.Hutao.Core.Database;
+
+internal interface IReorderable
+{
+    int Index { get; set; }
+}

src/Snap.Hutao/Snap.Hutao/Core/Database/ObservableReorderableDbCollection.cs

@@ -0,0 +1,66 @@
+// Copyright (c) DGP Studio. All rights reserved.
+// Licensed under the MIT license.
+
+using Microsoft.EntityFrameworkCore;
+using System.Collections.ObjectModel;
+using System.Collections.Specialized;
+using System.Runtime.InteropServices;
+
+namespace Snap.Hutao.Core.Database;
+
+internal sealed class ObservableReorderableDbCollection<T> : ObservableCollection<T>
+    where T : class, IReorderable
+{
+    private readonly DbContext dbContext;
+    private bool previousChangeIsRemoved;
+
+    public ObservableReorderableDbCollection(List<T> items, DbContext dbContext)
+        : base(AdjustIndex(items))
+    {
+        this.dbContext = dbContext;
+    }
+
+    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
+    {
+        base.OnCollectionChanged(e);
+
+        switch (e.Action)
+        {
+            case NotifyCollectionChangedAction.Remove:
+                previousChangeIsRemoved = true;
+                break;
+            case NotifyCollectionChangedAction.Add:
+                if (!previousChangeIsRemoved)
+                {
+                    return;
+                }
+
+                OnReorder();
+                previousChangeIsRemoved = false;
+                break;
+        }
+    }
+
+    private static List<T> AdjustIndex(List<T> list)
+    {
+        Span<T> span = CollectionsMarshal.AsSpan(list);
+        for (int i = 0; i < list.Count; i++)
+        {
+            ref readonly T item = ref span[i];
+            item.Index = i;
+        }
+
+        return list;
+    }
+
+    private void OnReorder()
+    {
+        AdjustIndex((List<T>)Items);
+
+        DbSet<T> dbSet = dbContext.Set<T>();
+        foreach (ref readonly T item in CollectionsMarshal.AsSpan((List<T>)Items))
+        {
+            dbSet.UpdateAndSave(item);
+        }
+    }
+}