Add IReadOnlyList extensions

src/Jellyfin.Extensions/ReadOnlyListExtension.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+
+namespace Jellyfin.Extensions
+{
+    /// <summary>
+    /// Static extensions for the <see cref="IReadOnlyList{T}"/> interface.
+    /// </summary>
+    public static class ReadOnlyListExtension
+    {
+        /// <summary>
+        /// Finds the index of the desired item.
+        /// </summary>
+        /// <param name="source">The source list.</param>
+        /// <param name="value">The value to fine.</param>
+        /// <typeparam name="T">The type of item to find.</typeparam>
+        /// <returns>Index if found, else -1.</returns>
+        public static int IndexOf<T>(this IReadOnlyList<T> source, T value)
+        {
+            if (source is IList<T> list)
+            {
+                return list.IndexOf(value);
+            }
+
+            for (int i = 0; i < source.Count; i++)
+            {
+                if (Equals(value, source[i]))
+                {
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+
+        /// <summary>
+        /// Finds the index of the predicate.
+        /// </summary>
+        /// <param name="source">The source list.</param>
+        /// <param name="match">The value to find.</param>
+        /// <typeparam name="T">The type of item to find.</typeparam>
+        /// <returns>Index if found, else -1.</returns>
+        public static int FindIndex<T>(this IReadOnlyList<T> source, Predicate<T> match)
+        {
+            if (source is List<T> list)
+            {
+                return list.FindIndex(match);
+            }
+
+            for (int i = 0; i < source.Count; i++)
+            {
+                if (match(source[i]))
+                {
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+    }
+}