Define the concept of patterns + additional comments.

osu.Game.Rulesets.Mania/Beatmaps/Patterns/Pattern.cs

@@ -0,0 +1,61 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System.Collections.Generic;
+using System.Linq;
+using osu.Framework.Extensions.IEnumerableExtensions;
+using osu.Game.Rulesets.Mania.Objects;
+
+namespace osu.Game.Rulesets.Mania.Beatmaps.Patterns
+{
+    /// <summary>
+    /// Creates a pattern containing hit objects.
+    /// </summary>
+    internal class Pattern
+    {
+        private readonly List<ManiaHitObject> hitObjects = new List<ManiaHitObject>();
+
+        /// <summary>
+        /// All the hit objects contained in this pattern.
+        /// </summary>
+        public IEnumerable<ManiaHitObject> HitObjects => hitObjects;
+
+        /// <summary>
+        /// Whether this pattern already contains a hit object in a code.
+        /// </summary>
+        /// <param name="column">The column index.</param>
+        /// <returns>Whether this pattern already contains a hit object in <paramref name="column"/></returns>
+        public bool IsFilled(int column) => hitObjects.Exists(h => h.Column == column);
+
+        /// <summary>
+        /// Amount of columns taken up by hit objects in this pattern.
+        /// </summary>
+        public int ColumnsFilled => HitObjects.GroupBy(h => h.Column).Count();
+
+        /// <summary>
+        /// Adds a hit object to this pattern.
+        /// </summary>
+        /// <param name="hitObject">The hit object to add.</param>
+        public void Add(ManiaHitObject hitObject) => hitObjects.Add(hitObject);
+
+        /// <summary>
+        /// Copies hit object from another pattern to this one.
+        /// </summary>
+        /// <param name="other">The other pattern.</param>
+        public void Add(Pattern other)
+        {
+            other.HitObjects.ForEach(Add);
+        }
+
+        /// <summary>
+        /// Clears this pattern, removing all hit objects.
+        /// </summary>
+        public void Clear() => hitObjects.Clear();
+
+        /// <summary>
+        /// Removes a hit object from this pattern.
+        /// </summary>
+        /// <param name="hitObject">The hit object to remove.</param>
+        public bool Remove(ManiaHitObject hitObject) => hitObjects.Remove(hitObject);
+    }
+}