General refactorings

osu.Game/Collections/BeatmapCollection.cs

@@ -0,0 +1,47 @@
+// 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;
+using osu.Framework.Bindables;
+using osu.Game.Beatmaps;
+
+namespace osu.Game.Collections
+{
+    /// <summary>
+    /// A collection of beatmaps grouped by a name.
+    /// </summary>
+    public class BeatmapCollection
+    {
+        /// <summary>
+        /// Invoked whenever any change occurs on this <see cref="BeatmapCollection"/>.
+        /// </summary>
+        public event Action Changed;
+
+        /// <summary>
+        /// The collection's name.
+        /// </summary>
+        public readonly Bindable<string> Name = new Bindable<string>();
+
+        /// <summary>
+        /// The beatmaps contained by the collection.
+        /// </summary>
+        public readonly BindableList<BeatmapInfo> Beatmaps = new BindableList<BeatmapInfo>();
+
+        /// <summary>
+        /// The date when this collection was last modified.
+        /// </summary>
+        public DateTimeOffset LastModifyDate { get; private set; } = DateTimeOffset.UtcNow;
+
+        public BeatmapCollection()
+        {
+            Beatmaps.CollectionChanged += (_, __) => onChange();
+            Name.ValueChanged += _ => onChange();
+        }
+
+        private void onChange()
+        {
+            LastModifyDate = DateTimeOffset.Now;
+            Changed?.Invoke();
+        }
+    }
+}