Generic CollectionTransformer

src/Tgstation.Server.Host/Models/CollectionTransformer{TInput,TOutput,TTransformer}.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+
+namespace Tgstation.Server.Host.Models
+{
+	/// <summary>
+	/// <see cref="ITransformer{TInput, TOutput}"/> for transforming collections.
+	/// </summary>
+	/// <typeparam name="TInput">The input collection's underlying <see cref="Type"/>.</typeparam>
+	/// <typeparam name="TOutput">The output collection's underlying <see cref="Type"/>.</typeparam>
+	/// <typeparam name="TTransformer">The <see cref="ITransformer{TInput, TOutput}"/> <see cref="Type"/> from <typeparamref name="TInput"/> to <typeparamref name="TOutput"/>.</typeparam>
+	sealed class CollectionTransformer<TInput, TOutput, TTransformer> : TransformerBase<IEnumerable<TInput>, List<TOutput>>
+		where TTransformer : ITransformer<TInput, TOutput>, new()
+	{
+		/// <summary>
+		/// Build the <see cref="TransformerBase{TInput, TOutput}.Expression"/>.
+		/// </summary>
+		/// <returns>The <see cref="Expression{TDelegate}"/> for converting collections of <typeparamref name="TInput"/>s to <typeparamref name="TOutput"/>s.</returns>
+		private static Expression<Func<IEnumerable<TInput>, List<TOutput>>> BuildExpression()
+		{
+			var subTransformer = new TTransformer();
+			Expression<Func<IEnumerable<TInput>, Func<TInput, TOutput>, List<TOutput>>> expression = (model, subExpression) => model
+				.Select(subExpression)
+				.ToList();
+
+			var parameter = global::System.Linq.Expressions.Expression.Parameter(typeof(IEnumerable<TInput>), "collectionInput");
+			var invocation = global::System.Linq.Expressions.Expression.Invoke(expression, parameter, subTransformer.Expression);
+
+			var lambda = global::System.Linq.Expressions.Expression.Lambda<Func<IEnumerable<TInput>, List<TOutput>>>(invocation, parameter);
+
+			return lambda;
+		}
+
+		/// <summary>
+		/// Initializes a new instance of the <see cref="CollectionTransformer{TInput, TOutput, TTransformer}"/> class.
+		/// </summary>
+		public CollectionTransformer()
+			: base(BuildExpression())
+		{
+		}
+	}
+}