Started on implementing a spinner gap check for catch

.idea/.idea.osu.Desktop/.idea/indexLayout.xml

@@ -1,5 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="ContentModelUserStore">
+    <attachedFolders />
+    <explicitIncludes />
+    <explicitExcludes />
+  </component>
   <component name="UserContentModel">
     <attachedFolders />
     <explicitIncludes />

osu.Game.Rulesets.Catch/CatchRuleset.cs

@@ -188,5 +188,7 @@ namespace osu.Game.Rulesets.Catch
         public override IConvertibleReplayFrame CreateConvertibleReplayFrame() => new CatchReplayFrame();
 
         public override HitObjectComposer CreateHitObjectComposer() => new CatchHitObjectComposer(this);
+
+        public override IBeatmapVerifier CreateBeatmapVerifier() => new CatchBeatmapVerifier();
     }
 }

osu.Game.Rulesets.Catch/Edit/CatchBeatmapVerifier.cs

@@ -0,0 +1,24 @@
+// 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.Rulesets.Catch.Edit.Checks;
+using osu.Game.Rulesets.Edit;
+using osu.Game.Rulesets.Edit.Checks.Components;
+
+namespace osu.Game.Rulesets.Catch.Edit
+{
+    public class CatchBeatmapVerifier : IBeatmapVerifier
+    {
+        private readonly List<ICheck> checks = new List<ICheck>
+        {
+            new CheckTooShortSpinnerGap()
+        };
+
+        public IEnumerable<Issue> Run(BeatmapVerifierContext context)
+        {
+            return checks.SelectMany(check => check.Run(context));
+        }
+    }
+}

osu.Game.Rulesets.Catch/Edit/Checks/CheckTooShortSpinnerGap.cs

@@ -0,0 +1,91 @@
+// 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 System.Collections.Generic;
+using osu.Game.Rulesets.Catch.Objects;
+using osu.Game.Rulesets.Edit;
+using osu.Game.Rulesets.Edit.Checks.Components;
+using osu.Game.Rulesets.Objects;
+
+namespace osu.Game.Rulesets.Catch.Edit.Checks
+{
+    public class CheckTooShortSpinnerGap : ICheck
+    {
+        private static readonly int[] spinner_start_delta_threshold = { 250, 250, 125, 125, 62, 62 };
+        private static readonly int[] spinner_end_delta_threshold = { 250, 250, 250, 125, 125, 125 };
+
+        public CheckMetadata Metadata { get; } = new CheckMetadata(CheckCategory.Compose, "Too short spinner gap");
+
+        public IEnumerable<IssueTemplate> PossibleTemplates => new IssueTemplate[]
+        {
+            new IssueTemplateSpinnerStartGap(this),
+            new IssueTemplateSpinnerEndGap(this)
+        };
+
+        public IEnumerable<Issue> Run(BeatmapVerifierContext context)
+        {
+            var hitObjects = context.Beatmap.HitObjects;
+            int interpretedDifficulty = (int)context.InterpretedDifficulty;
+            int expectedStartDelta = spinner_start_delta_threshold[interpretedDifficulty];
+            int expectedEndDelta = spinner_end_delta_threshold[interpretedDifficulty];
+
+            for (int i = 0; i < hitObjects.Count - 1; ++i)
+            {
+                if (!(hitObjects[i] is BananaShower bananaShower))
+                    continue;
+
+                if (i != 0 && hitObjects[i - 1] is CatchHitObject previousHitObject && !(previousHitObject is BananaShower))
+                {
+                    double spinnerStartDelta = bananaShower.StartTime - previousHitObject.GetEndTime();
+
+                    if (spinnerStartDelta < expectedStartDelta)
+                    {
+                        yield return new IssueTemplateSpinnerStartGap(this)
+                            .Create(spinnerStartDelta, expectedStartDelta, bananaShower, previousHitObject);
+                    }
+                }
+
+                if (hitObjects[i + 1] is CatchHitObject nextHitObject && !(nextHitObject is BananaShower))
+                {
+                    double spinnerEndDelta = nextHitObject.StartTime - bananaShower.EndTime;
+
+                    if (spinnerEndDelta < expectedEndDelta)
+                    {
+                        yield return new IssueTemplateSpinnerEndGap(this)
+                            .Create(spinnerEndDelta, expectedEndDelta, bananaShower, nextHitObject);
+                    }
+                }
+            }
+        }
+
+        public abstract class IssueTemplateSpinnerGap : IssueTemplate
+        {
+            protected IssueTemplateSpinnerGap(ICheck check, IssueType issueType, string unformattedMessage)
+                : base(check, issueType, unformattedMessage)
+            {
+            }
+
+            public Issue Create(double deltaTime, int expectedDeltaTime, params HitObject[] hitObjects)
+            {
+                return new Issue(hitObjects, this, Math.Floor(deltaTime), expectedDeltaTime);
+            }
+        }
+
+        public class IssueTemplateSpinnerStartGap : IssueTemplateSpinnerGap
+        {
+            public IssueTemplateSpinnerStartGap(ICheck check)
+                : base(check, IssueType.Problem, "There is only {0} ms apart between the start of the spinner and the last object, there should be {1} ms or more.")
+            {
+            }
+        }
+
+        public class IssueTemplateSpinnerEndGap : IssueTemplateSpinnerGap
+        {
+            public IssueTemplateSpinnerEndGap(ICheck check)
+                : base(check, IssueType.Problem, "There is only {0} ms apart between the end of the spinner and the next object, there should be {1} ms or more.")
+            {
+            }
+        }
+    }
+}