Add beatmap minimum length checks

osu.Game/Rulesets/Edit/BeatmapVerifier.cs

@@ -34,6 +34,7 @@ namespace osu.Game.Rulesets.Edit
             new CheckUnsnappedObjects(),
             new CheckConcurrentObjects(),
             new CheckZeroLengthObjects(),
+            new CheckDrainTime(),
 
             // Timing
             new CheckPreviewTime(),

osu.Game/Rulesets/Edit/Checks/CheckDrainTime.cs

@@ -0,0 +1,38 @@
+// 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 osu.Game.Beatmaps;
+using osu.Game.Rulesets.Edit.Checks.Components;
+
+namespace osu.Game.Rulesets.Edit.Checks
+{
+    public class CheckDrainTime : ICheck
+    {
+        private const int min_drain_threshold = 30 * 1000;
+        public CheckMetadata Metadata => new CheckMetadata(CheckCategory.Compose, "Too short drain time");
+
+        public IEnumerable<IssueTemplate> PossibleTemplates => new IssueTemplate[]
+        {
+            new IssueTemplateTooShort(this)
+        };
+
+        public IEnumerable<Issue> Run(BeatmapVerifierContext context)
+        {
+            double drainTime = context.Beatmap.CalculatePlayableLength();
+
+            if (drainTime < min_drain_threshold)
+                yield return new IssueTemplateTooShort(this).Create((int)(drainTime / 1000));
+        }
+
+        public class IssueTemplateTooShort : IssueTemplate
+        {
+            public IssueTemplateTooShort(ICheck check)
+                : base(check, IssueType.Problem, "Less than 30 seconds of drain time, currently {0}.")
+            {
+            }
+
+            public Issue Create(int drainTimeSeconds) => new Issue(this, drainTimeSeconds);
+        }
+    }
+}