Implement mania invert mod

osu.Game.Rulesets.Mania/Mods/ManiaModInvert.cs

@@ -0,0 +1,68 @@
+// 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.Collections.Generic;
+using System.Linq;
+using osu.Game.Audio;
+using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Mania.Beatmaps;
+using osu.Game.Rulesets.Mania.Objects;
+using osu.Game.Rulesets.Mods;
+
+namespace osu.Game.Rulesets.Mania.Mods
+{
+    public class ManiaModInvert : Mod, IApplicableAfterBeatmapConversion
+    {
+        public override string Name => "Invert";
+
+        public override string Acronym => "IN";
+        public override double ScoreMultiplier => 1;
+
+        public override string Description => "Hold the keys. To the beat.";
+
+        public override ModType Type => ModType.Conversion;
+
+        public void ApplyToBeatmap(IBeatmap beatmap)
+        {
+            var maniaBeatmap = (ManiaBeatmap)beatmap;
+
+            var newObjects = new List<ManiaHitObject>();
+
+            foreach (var column in maniaBeatmap.HitObjects.GroupBy(h => h.Column))
+            {
+                var newColumnObjects = new List<ManiaHitObject>();
+
+                var locations = column.OfType<Note>().Select(n => (startTime: n.StartTime, samples: n.Samples))
+                                      .Concat(column.OfType<HoldNote>().SelectMany(h => new[]
+                                      {
+                                          (startTime: h.StartTime, samples: h.GetNodeSamples(0)),
+                                          (startTime: h.EndTime, samples: h.GetNodeSamples(1))
+                                      }))
+                                      .OrderBy(h => h.startTime).ToList();
+
+                for (int i = 0; i < locations.Count - 1; i += 2)
+                {
+                    newColumnObjects.Add(new HoldNote
+                    {
+                        Column = column.Key,
+                        StartTime = locations[i].startTime,
+                        Duration = locations[i + 1].startTime - locations[i].startTime,
+                        Samples = locations[i].samples,
+                        NodeSamples = new List<IList<HitSampleInfo>>
+                        {
+                            locations[i].samples,
+                            locations[i + 1].samples
+                        }
+                    });
+                }
+
+                newObjects.AddRange(newColumnObjects);
+            }
+
+            maniaBeatmap.HitObjects = newObjects.OrderBy(h => h.StartTime).ToList();
+
+            // No breaks
+            maniaBeatmap.Breaks.Clear();
+        }
+    }
+}