Restore SEBPatch

SafeExamBrowser.Core/Operations/LazyInitializationOperation.cs

@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2024 ETH Zürich, IT Services
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using System;
+using SafeExamBrowser.Core.Contracts.OperationModel;
+using SafeExamBrowser.Core.Contracts.OperationModel.Events;
+
+namespace SafeExamBrowser.Core.Operations
+{
+	/// <summary>
+	/// A wrapper operation to allow for a lazy (just-in-time) instantiation of an operation, initialized on <see cref="Perform"/>.
+	/// Is useful when e.g. dependencies for a certain operation are not available during execution of the composition root, but rather
+	/// only after a preceding operation within an <see cref="IOperationSequence"/> has finished.
+	/// </summary>
+	public class LazyInitializationOperation : IOperation
+	{
+		private Func<IOperation> initialize;
+		private IOperation operation;
+
+		private event ActionRequiredEventHandler ActionRequiredImpl;
+		private event StatusChangedEventHandler StatusChangedImpl;
+
+		public event ActionRequiredEventHandler ActionRequired
+		{
+			add
+			{
+				ActionRequiredImpl += value;
+
+				if (operation != null)
+				{
+					operation.ActionRequired += value;
+				}
+			}
+			remove
+			{
+				ActionRequiredImpl -= value;
+
+				if (operation != null)
+				{
+					operation.ActionRequired -= value;
+				}
+			}
+		}
+
+		public event StatusChangedEventHandler StatusChanged
+		{
+			add
+			{
+				StatusChangedImpl += value;
+
+				if (operation != null)
+				{
+					operation.StatusChanged += value;
+				}
+			}
+			remove
+			{
+				StatusChangedImpl -= value;
+
+				if (operation != null)
+				{
+					operation.StatusChanged -= value;
+				}
+			}
+		}
+
+		public LazyInitializationOperation(Func<IOperation> initialize)
+		{
+			this.initialize = initialize;
+		}
+
+		public OperationResult Perform()
+		{
+			operation = initialize.Invoke();
+			operation.ActionRequired += ActionRequiredImpl;
+			operation.StatusChanged += StatusChangedImpl;
+
+			return operation.Perform();
+		}
+
+		public OperationResult Revert()
+		{
+			return operation.Revert();
+		}
+	}
+}