Add: Difference of collections

App/CollectionEditor.cs

@@ -48,7 +48,7 @@ public void EditCollection(CollectionEditArgs e)
                         break;
                 }
             }
-            else if (e.Action == CollectionEdit.Intersect)
+            else if (e.Action == CollectionEdit.Intersect || e.Action == CollectionEdit.Difference)
             {
                 if (e.Collections.Count < 2)
                     return;

App/Presenters/Controls/CollectionListingPresenter.cs

@@ -85,6 +85,11 @@ private void _view_RightClick(object sender, Gui.Misc.StringEventArgs e)
                         return;
                     args = CollectionEditArgs.InverseCollections(selectedCollections, selectedCollections[0].Name);
                     break;
+                case "Difference":
+                    if (selectedCollections == null)
+                        return;
+                    args = CollectionEditArgs.DifferenceCollections(selectedCollections, selectedCollections[0].Name);
+                    break;
                 case "Create":
                     args = CollectionEditArgs.AddCollections(null);
                     break;

CollectionManagerDll/Enums/CollectionEdit.cs

@@ -13,5 +13,6 @@ public enum CollectionEdit
         Duplicate=8,
         Intersect=9,
         Inverse=10,
+        Difference=11,
     }
 }

CollectionManagerDll/Modules/CollectionsManager/CollectionEditArgs.cs

@@ -88,6 +88,16 @@ public static CollectionEditArgs InverseCollections(Collections collections, str
             };
         }
         #endregion
+        #region Difference Collections
+        public static CollectionEditArgs DifferenceCollections(Collections collections, string newName)
+        {
+            return new CollectionEditArgs(CollectionEdit.Difference)
+            {
+                Collections = collections,
+                NewName = newName
+            };
+        }
+        #endregion
         #region Clear Collections
         public static CollectionEditArgs ClearCollections()
         {

CollectionManagerDll/Modules/CollectionsManager/CollectionsManager.cs

@@ -23,6 +23,7 @@ edit collection name
          merge x collections
          intersect x collections
          inverse map sum of x collections
+         difference x collections
          clear collections
          add beatmaps to collection
          remove beatmaps from collection
@@ -121,6 +122,25 @@ private void EditCollection(CollectionEditArgs args, bool suspendRefresh = false
 
                 EditCollection(CollectionEditArgs.AddCollections(new Collections() { targetCollection }), true);
             }
+            else if (action == CollectionEdit.Difference)
+            {
+                var targetCollection = args.Collections.Last();
+                args.Collections.RemoveAt(args.Collections.Count - 1);
+                var mainCollection = args.Collections[0];
+                args.Collections.RemoveAt(0);
+                var beatmaps = mainCollection.AllBeatmaps();
+                foreach (var collection in args.Collections)
+                {
+                    beatmaps = beatmaps.Except(collection.AllBeatmaps(), new CollectionBeatmapComparer()).Union(collection.AllBeatmaps().Except(beatmaps, new CollectionBeatmapComparer()));
+                }
+
+                foreach (var beatmap in beatmaps)
+                {
+                    targetCollection.AddBeatmap(beatmap);
+                }
+
+                EditCollection(CollectionEditArgs.AddCollections(new Collections() { targetCollection }), true);
+            }
             else if (action == CollectionEdit.Clear)
             {
                 LoadedCollections.Clear();

README.md

@@ -106,6 +106,10 @@ The following opinions are made available by right clicking in the left panel:
 
   The new collection is named using the selected collection closest to the top of the listing, with `_0` appended to its name.
 
+- Difference: Differentiates all selected collections by making a new collection with only maps that are present in only one selected collection.
+
+  The new collection is named using the selected collection closest to the top of the listing, with `_0` appended to its name.
+
 - Inverse: Inverses all selected collections by making a new collection with only maps that are not present in any of the selected collections but are present in your osu! songs folder.
 
   The new collection is named using the selected collection closest to the top of the listing, with `_0` appended to its name.