resolves #163 🔨🔬✨

SonghayCore.Tests/Extensions/MenuDisplayItemModelExtensionsTests.cs

@@ -0,0 +1,43 @@
+using Songhay.Models;
+
+namespace Songhay.Tests.Extensions;
+
+public class MenuDisplayItemModelExtensionsTests
+{
+    // ReSharper disable once InconsistentNaming
+    public static IEnumerable<object[]> GetAllByData =
+        new[]
+        {
+            new object[]
+            {
+                new MenuDisplayItemModel
+                {
+                    GroupId = "g-42",
+                    ChildItems = 
+                        new []
+                        {
+                            new MenuDisplayItemModel(),
+                            new MenuDisplayItemModel { GroupId = "g-42" },
+                            new MenuDisplayItemModel
+                            {
+                                ChildItems = new []
+                                {
+                                    new MenuDisplayItemModel { GroupId = "g-42" },
+                                }
+                            }
+                        }
+                },
+                (MenuDisplayItemModel i) => i.HasGroupId("g-42"), // predicate
+                3 // expectedNumberOfItems
+            }
+        };
+
+    [Theory]
+    [MemberData(nameof(GetAllByData))]
+    public void GetAllBy_Test(MenuDisplayItemModel data, Func<MenuDisplayItemModel, bool> predicate, int expectedNumberOfItems)
+    {
+        var actual = data.GetAllBy(predicate).ToArray();
+        Assert.NotEmpty(actual);
+        Assert.Equal(expectedNumberOfItems, actual.Length);
+    }
+}

SonghayCore/Extensions/MenuDisplayItemModelExtensions.cs

@@ -5,13 +5,34 @@
 /// </summary>
 public static class MenuDisplayItemModelExtensions
 {
+    /// <summary>
+    /// Gets all <see cref="MenuDisplayItemModel"/>
+    /// by the specified predicate.
+    /// </summary>
+    /// <param name="data">the <see cref="MenuDisplayItemModel"/></param>
+    /// <param name="predicate">the predicate</param>
+    public static IEnumerable<MenuDisplayItemModel> GetAllBy(this MenuDisplayItemModel? data,
+        Func<MenuDisplayItemModel, bool> predicate)
+    {
+        var items1 = data != null ?
+            new[] {data}.Where(predicate)
+            :
+             Enumerable.Empty<MenuDisplayItemModel>();
+        var items2 = data?
+            .ChildItems.SelectMany(i => i.GetAllBy(predicate))
+             ??
+             Enumerable.Empty<MenuDisplayItemModel>();
+
+        return items1.Union(items2);
+    }
+
     /// <summary>
     /// Returns <c>true</c> when the grouping has the specified identifier.
     /// </summary>
-    /// <param name="data"></param>
-    /// <param name="groupId"></param>
+    /// <param name="data">the <see cref="MenuDisplayItemModel"/></param>
+    /// <param name="groupId">the <see cref="MenuDisplayItemModel.GroupId"/></param>
     public static bool HasGroupId(this MenuDisplayItemModel? data, string groupId) => data != null &&
-        (!string.IsNullOrWhiteSpace(groupId) && data.GroupId.EqualsInvariant(groupId));
+        !string.IsNullOrWhiteSpace(groupId) && data.GroupId.EqualsInvariant(groupId);
 
     /// <summary>
     /// Returns the Default Selection