Restore SEBPatch

SafeExamBrowser.UserInterface.Shared/Activators/KeyboardActivator.cs

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+/*
+ * 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 System.Windows.Input;
+using SafeExamBrowser.WindowsApi.Contracts;
+using SafeExamBrowser.WindowsApi.Contracts.Events;
+
+namespace SafeExamBrowser.UserInterface.Shared.Activators
+{
+	public abstract class KeyboardActivator
+	{
+		private Guid? hookId;
+		private INativeMethods nativeMethods;
+		private bool paused;
+
+		protected KeyboardActivator(INativeMethods nativeMethods)
+		{
+			this.nativeMethods = nativeMethods;
+		}
+
+		protected abstract bool Process(Key key, KeyModifier modifier, KeyState state);
+
+		public void Pause()
+		{
+			OnBeforePause();
+			paused = true;
+		}
+
+		public void Resume()
+		{
+			OnBeforeResume();
+			paused = false;
+		}
+
+		public void Start()
+		{
+			hookId = nativeMethods.RegisterKeyboardHook(KeyboardHookCallback);
+		}
+
+		public void Stop()
+		{
+			if (hookId.HasValue)
+			{
+				nativeMethods.DeregisterKeyboardHook(hookId.Value);
+			}
+		}
+
+		protected virtual void OnBeforePause()
+		{
+		}
+
+		protected virtual void OnBeforeResume()
+		{
+		}
+
+		private bool KeyboardHookCallback(int keyCode, KeyModifier modifier, KeyState state)
+		{
+			if (!paused)
+			{
+				return Process(KeyInterop.KeyFromVirtualKey(keyCode), modifier, state);
+			}
+
+			return false;
+		}
+	}
+}