before deleting Rules

Gameboard.ShogiUI.Rules/PlanarCollection.cs

@@ -0,0 +1,59 @@
+using PathFinding;
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace Gameboard.ShogiUI.Rules
+{
+  public class PlanarCollection<T> : IPlanarCollection<T>, IEnumerable<T> where T : IPlanarElement
+  {
+    public delegate void ForEachDelegate(T element, int x, int y);
+    private readonly T?[] array;
+    private readonly int width;
+    private readonly int height;
+
+    public PlanarCollection(int width, int height)
+    {
+      this.width = width;
+      this.height = height;
+      array = new T[width * height];
+    }
+
+    public T? this[int x, int y]
+    {
+      get => array[y * width + x];
+      set => array[y * width + x] = value;
+    }
+    public T? this[float x, float y]
+    {
+      get => array[(int)y * width + (int)x];
+      set => array[(int)y * width + (int)x] = value;
+    }
+
+    public int GetLength(int dimension) => dimension switch
+    {
+      0 => width,
+      1 => height,
+      _ => throw new IndexOutOfRangeException()
+    };
+
+    public void ForEachNotNull(ForEachDelegate callback)
+    {
+      for (var x = 0; x < width; x++)
+      {
+        for (var y = 0; y < height; y++)
+        {
+          if (this[x, y] != null)
+            callback(this[x, y], x, y);
+        }
+      }
+    }
+
+    public IEnumerator<T> GetEnumerator()
+    {
+      foreach (var item in array) yield return item;
+    }
+
+    IEnumerator IEnumerable.GetEnumerator() => array.GetEnumerator();
+  }
+}