gui-cs.Terminal.Gui/Terminal.Gui/Application.cs

using System;
using System.Collections.Generic;
using System.Threading;
using System.Linq;
using System.Globalization;
using System.Reflection;
using System.IO;
using System.Text.Json.Serialization;
using static Terminal.Gui.ConfigurationManager;

namespace Terminal.Gui {
	/// <summary>
	/// A static, singleton class representing the application. This class is the entry point for the application.
	/// </summary>
	/// <example>
	/// <code>
	/// // A simple Terminal.Gui app that creates a window with a frame and title with 
	/// // 5 rows/columns of padding.
	/// Application.Init();
	/// var win = new Window ($"Example App ({Application.QuitKey} to quit)") {
	///   X = 5,
	///   Y = 5,
	///   Width = Dim.Fill (5),
	///   Height = Dim.Fill (5)
	/// };
	/// Application.Top.Add(win);
	/// Application.Run();
	/// Application.Shutdown();
	/// </code>
	/// </example>
	/// <remarks>
	///  <para>
	///   Creates a instance of <see cref="Terminal.Gui.MainLoop"/> to process input events, handle timers and
	///   other sources of data. It is accessible via the <see cref="MainLoop"/> property.
	///  </para>
	///  <para>
	///   The <see cref="Iteration"/> event is invoked on each iteration of the <see cref="Terminal.Gui.MainLoop"/>.
	///  </para>
	///  <para>
	///   When invoked it sets the <see cref="SynchronizationContext"/> to one that is tied
	///   to the <see cref="MainLoop"/>, allowing user code to use async/await.
	///  </para>
	/// </remarks>
	public static partial class Application {

		/// <summary>
		/// The current <see cref="ConsoleDriver"/> in use.
		/// </summary>
		public static ConsoleDriver Driver;

		/// <summary>
		/// If <see langword="true"/>, forces the use of the System.Console-based (see <see cref="NetDriver"/>) driver. The default is <see langword="false"/>.
		/// </summary>
		[SerializableConfigurationProperty (Scope = typeof (SettingsScope))]
		public static bool UseSystemConsole { get; set; } = false;

		// For Unit testing - ignores UseSystemConsole
		internal static bool _forceFakeConsole;

		private static bool? _enableConsoleScrolling;
		/// <summary>
		/// The current <see cref="ConsoleDriver.EnableConsoleScrolling"/> used in the terminal.
		/// </summary>
		/// <remarks>
		/// <para>
		/// If <see langword="false"/> (the default) the height of the Terminal.Gui application (<see cref="ConsoleDriver.Rows"/>) 
		/// tracks to the height of the visible console view when the console is resized. In this case 
		/// scrolling in the console will be disabled and all <see cref="ConsoleDriver.Rows"/> will remain visible.
		/// </para>
		/// <para>
		/// If <see langword="true"/> then height of the Terminal.Gui application <see cref="ConsoleDriver.Rows"/> only tracks 
		/// the height of the visible console view when the console is made larger (the application will only grow in height, never shrink). 
		/// In this case console scrolling is enabled and the contents (<see cref="ConsoleDriver.Rows"/> high) will scroll
		/// as the console scrolls. 
		/// </para>
		/// This API was previously named 'HeightAsBuffer` but was renamed to make its purpose more clear.
		/// </remarks>
		[SerializableConfigurationProperty (Scope = typeof (SettingsScope))]
		public static bool EnableConsoleScrolling {
			get {
				if (Driver == null) {
					return _enableConsoleScrolling.HasValue && _enableConsoleScrolling.Value;
				}
				return Driver.EnableConsoleScrolling;
			}
			set {
				_enableConsoleScrolling = value;
				if (Driver == null) {
					return;
				}
				Driver.EnableConsoleScrolling = value;
			}
		}

		private static List<CultureInfo> _cachedSupportedCultures;

		/// <summary>
		/// Gets all cultures supported by the application without the invariant language.
		/// </summary>
		public static List<CultureInfo> SupportedCultures => _cachedSupportedCultures;

		private static List<CultureInfo> GetSupportedCultures ()
		{
			CultureInfo [] culture = CultureInfo.GetCultures (CultureTypes.AllCultures);

			// Get the assembly
			Assembly assembly = Assembly.GetExecutingAssembly ();

			//Find the location of the assembly
			string assemblyLocation = AppDomain.CurrentDomain.BaseDirectory;

			// Find the resource file name of the assembly
			string resourceFilename = $"{Path.GetFileNameWithoutExtension (assembly.Location)}.resources.dll";

			// Return all culture for which satellite folder found with culture code.
			return culture.Where (cultureInfo =>
			   assemblyLocation != null &&
			   Directory.Exists (Path.Combine (assemblyLocation, cultureInfo.Name)) &&
			   File.Exists (Path.Combine (assemblyLocation, cultureInfo.Name, resourceFilename))
			).ToList ();
		}

		#region Initialization (Init/Shutdown)

		/// <summary>
		/// Initializes a new instance of <see cref="Terminal.Gui"/> Application. 
		/// </summary>
		/// <para>
		/// Call this method once per instance (or after <see cref="Shutdown"/> has been called).
		/// </para>
		/// <para>
		/// This function loads the right <see cref="ConsoleDriver"/> for the platform, 
		/// Creates a <see cref="Toplevel"/>. and assigns it to <see cref="Top"/>
		/// </para>
		/// <para>
		/// <see cref="Shutdown"/> must be called when the application is closing (typically after <see cref="Run(Func{Exception, bool})"/> has 
		/// returned) to ensure resources are cleaned up and terminal settings restored.
		/// </para>
		/// <para>
		/// The <see cref="Run{T}(Func{Exception, bool}, ConsoleDriver, IMainLoopDriver)"/> function 
		/// combines <see cref="Init(ConsoleDriver, IMainLoopDriver)"/> and <see cref="Run(Toplevel, Func{Exception, bool})"/>
		/// into a single call. An applciation cam use <see cref="Run{T}(Func{Exception, bool}, ConsoleDriver, IMainLoopDriver)"/> 
		/// without explicitly calling <see cref="Init(ConsoleDriver, IMainLoopDriver)"/>.
		/// </para>
		/// <param name="driver">
		/// The <see cref="ConsoleDriver"/> to use. If not specified the default driver for the
		/// platform will be used (see <see cref="WindowsDriver"/>, <see cref="CursesDriver"/>, and <see cref="NetDriver"/>).</param>
		/// <param name="mainLoopDriver">
		/// Specifies the <see cref="MainLoop"/> to use. 
		/// Must not be <see langword="null"/> if <paramref name="driver"/> is not <see langword="null"/>.
		/// </param>
		public static void Init (ConsoleDriver driver = null, IMainLoopDriver mainLoopDriver = null) => InternalInit (() => Toplevel.Create (), driver, mainLoopDriver);

		internal static bool _initialized = false;
		internal static int _mainThreadId = -1;

		// INTERNAL function for initializing an app with a Toplevel factory object, driver, and mainloop.
		//
		// Called from:
		// 
		// Init() - When the user wants to use the default Toplevel. calledViaRunT will be false, causing all state to be reset.
		// Run<T>() - When the user wants to use a custom Toplevel. calledViaRunT will be true, enabling Run<T>() to be called without calling Init first.
		// Unit Tests - To initialize the app with a custom Toplevel, using the FakeDriver. calledViaRunT will be false, causing all state to be reset.
		// 
		// calledViaRunT: If false (default) all state will be reset. If true the state will not be reset.
		internal static void InternalInit (Func<Toplevel> topLevelFactory, ConsoleDriver driver = null, IMainLoopDriver mainLoopDriver = null, bool calledViaRunT = false)
		{
			if (_initialized && driver == null) return;

			if (_initialized) {
				throw new InvalidOperationException ("Init has already been called and must be bracketed by Shutdown.");
			}

			if (!calledViaRunT) {
				// Reset all class variables (Application is a singleton).
				ResetState ();
			}

			// For UnitTests
			if (driver != null) {
				Driver = driver;
			}

			// Start the process of configuration management.
			// Note that we end up calling LoadConfigurationFromAllSources
			// multiple times. We need to do this because some settings are only
			// valid after a Driver is loaded. In this cases we need just 
			// `Settings` so we can determine which driver to use.
			ConfigurationManager.Load (true);
			ConfigurationManager.Apply ();

			if (Driver == null) {
				var p = Environment.OSVersion.Platform;
				if (_forceFakeConsole) {
					// For Unit Testing only
					Driver = new FakeDriver ();
				} else if (UseSystemConsole) {
					Driver = new NetDriver ();
				} else if (p == PlatformID.Win32NT || p == PlatformID.Win32S || p == PlatformID.Win32Windows) {
					Driver = new WindowsDriver ();
				} else {
					Driver = new CursesDriver ();
				}
				if (Driver == null) {
					throw new InvalidOperationException ("Init could not determine the ConsoleDriver to use.");
				}
			}

			if (mainLoopDriver == null) {
				// TODO: Move this logic into ConsoleDriver
				if (Driver is FakeDriver) {
					mainLoopDriver = new FakeMainLoop (Driver);
				} else if (Driver is NetDriver) {
					mainLoopDriver = new NetMainLoop (Driver);
				} else if (Driver is WindowsDriver) {
					mainLoopDriver = new WindowsMainLoop (Driver);
				} else if (Driver is CursesDriver) {
					mainLoopDriver = new UnixMainLoop (Driver);
				}
				if (mainLoopDriver == null) {
					throw new InvalidOperationException ("Init could not determine the MainLoopDriver to use.");
				}
			}

			MainLoop = new MainLoop (mainLoopDriver);

			try {
				Driver.EnableConsoleScrolling = EnableConsoleScrolling;
				Driver.Init (OnTerminalResized);
			} catch (InvalidOperationException ex) {
				// This is a case where the driver is unable to initialize the console.
				// This can happen if the console is already in use by another process or
				// if running in unit tests.
				// In this case, we want to throw a more specific exception.
				throw new InvalidOperationException ("Unable to initialize the console. This can happen if the console is already in use by another process or in unit tests.", ex);
			}

			SynchronizationContext.SetSynchronizationContext (new MainLoopSyncContext (MainLoop));

			Top = topLevelFactory ();
			Current = Top;
			_cachedSupportedCultures = GetSupportedCultures ();
			_mainThreadId = Thread.CurrentThread.ManagedThreadId;
			_initialized = true;
		}


		/// <summary>
		/// Shutdown an application initialized with <see cref="Init(ConsoleDriver, IMainLoopDriver)"/>.
		/// </summary>
		/// <remarks>
		/// Shutdown must be called for every call to <see cref="Init(ConsoleDriver, IMainLoopDriver)"/> or <see cref="Application.Run(Toplevel, Func{Exception, bool})"/>
		/// to ensure all resources are cleaned up (Disposed) and terminal settings are restored.
		/// </remarks>
		public static void Shutdown ()
		{
			ResetState ();
			ConfigurationManager.PrintJsonErrors ();
		}

		// Encapsulate all setting of initial state for Application; Having
		// this in a function like this ensures we don't make mistakes in
		// guaranteeing that the state of this singleton is deterministic when Init
		// starts running and after Shutdown returns.
		static void ResetState ()
		{
			// Shutdown is the bookend for Init. As such it needs to clean up all resources
			// Init created. Apps that do any threading will need to code defensively for this.
			// e.g. see Issue #537
			foreach (var t in _toplevels) {
				t.Running = false;
				t.Dispose ();
			}
			_toplevels.Clear ();
			Current = null;
			Top?.Dispose ();
			Top = null;

			// BUGBUG: OverlappedTop is not cleared here, but it should be?

			MainLoop = null;
			Driver?.End ();
			Driver = null;
			Iteration = null;
			RootMouseEvent = null;
			RootKeyEvent = null;
			TerminalResized = null;
			_mainThreadId = -1;
			NotifyNewRunState = null;
			NotifyStopRunState = null;
			_initialized = false;
			_mouseGrabView = null;
			_enableConsoleScrolling = false;
			_lastMouseOwnerView = null;

			// Reset synchronization context to allow the user to run async/await,
			// as the main loop has been ended, the synchronization context from 
			// gui.cs does no longer process any callbacks. See #1084 for more details:
			// (https://github.com/gui-cs/Terminal.Gui/issues/1084).
			SynchronizationContext.SetSynchronizationContext (syncContext: null);
		}

		#endregion Initialization (Init/Shutdown)

		#region Run (Begin, Run, End)

		/// <summary>
		/// Notify that a new <see cref="RunState"/> was created (<see cref="Begin(Toplevel)"/> was called). The token is created in 
		/// <see cref="Begin(Toplevel)"/> and this event will be fired before that function exits.
		/// </summary>
		/// <remarks>
		///	If <see cref="ExitRunLoopAfterFirstIteration"/> is <see langword="true"/> callers to
		///	<see cref="Begin(Toplevel)"/> must also subscribe to <see cref="NotifyStopRunState"/>
		///	and manually dispose of the <see cref="RunState"/> token when the application is done.
		/// </remarks>
		public static event EventHandler<RunStateEventArgs> NotifyNewRunState;

		/// <summary>
		/// Notify that a existent <see cref="RunState"/> is stopping (<see cref="End(RunState)"/> was called).
		/// </summary>
		/// <remarks>
		///	If <see cref="ExitRunLoopAfterFirstIteration"/> is <see langword="true"/> callers to
		///	<see cref="Begin(Toplevel)"/> must also subscribe to <see cref="NotifyStopRunState"/>
		///	and manually dispose of the <see cref="RunState"/> token when the application is done.
		/// </remarks>
		public static event EventHandler<ToplevelEventArgs> NotifyStopRunState;

		/// <summary>
		/// The execution state for a <see cref="Toplevel"/> view.
		/// </summary>
		public class RunState : IDisposable {
			/// <summary>
			/// Initializes a new <see cref="RunState"/> class.
			/// </summary>
			/// <param name="view"></param>
			public RunState (Toplevel view)
			{
				Toplevel = view;
			}
			/// <summary>
			/// The <see cref="Toplevel"/> belonging to this <see cref="RunState"/>.
			/// </summary>
			public Toplevel Toplevel { get; internal set; }

#if DEBUG_IDISPOSABLE
			/// <summary>
			/// For debug (see DEBUG_IDISPOSABLE define) purposes to verify objects are being disposed properly
			/// </summary>
			public bool WasDisposed = false;

			/// <summary>
			/// For debug (see DEBUG_IDISPOSABLE define) purposes to verify objects are being disposed properly
			/// </summary>
			public int DisposedCount = 0;

			/// <summary>
			/// For debug (see DEBUG_IDISPOSABLE define) purposes; the runstate instances that have been created
			/// </summary>
			public static List<RunState> Instances = new List<RunState> ();

			/// <summary>
			/// Creates a new RunState object.
			/// </summary>
			public RunState ()
			{
				Instances.Add (this);
			}
#endif

			/// <summary>
			/// Releases all resource used by the <see cref="Application.RunState"/> object.
			/// </summary>
			/// <remarks>
			/// Call <see cref="Dispose()"/> when you are finished using the <see cref="Application.RunState"/>. 
			/// </remarks>
			/// <remarks>
			/// <see cref="Dispose()"/> method leaves the <see cref="Application.RunState"/> in an unusable state. After
			/// calling <see cref="Dispose()"/>, you must release all references to the
			/// <see cref="Application.RunState"/> so the garbage collector can reclaim the memory that the
			/// <see cref="Application.RunState"/> was occupying.
			/// </remarks>
			public void Dispose ()
			{
				Dispose (true);
				GC.SuppressFinalize (this);
#if DEBUG_IDISPOSABLE
				WasDisposed = true;
#endif
			}

			/// <summary>
			/// Releases all resource used by the <see cref="Application.RunState"/> object.
			/// </summary>
			/// <param name="disposing">If set to <see langword="true"/> we are disposing and should dispose held objects.</param>
			protected virtual void Dispose (bool disposing)
			{
				if (Toplevel != null && disposing) {
					throw new InvalidOperationException ("You must clean up (Dispose) the Toplevel before calling Application.RunState.Dispose");
				}
			}
		}

		/// <summary>
		/// Building block API: Prepares the provided <see cref="Toplevel"/> for execution.
		/// </summary>
		/// <returns>The <see cref="RunState"/> handle that needs to be passed to the <see cref="End(RunState)"/> method upon completion.</returns>
		/// <param name="Toplevel">The <see cref="Toplevel"/> to prepare execution for.</param>
		/// <remarks>
		/// This method prepares the provided <see cref="Toplevel"/> for running with the focus,
		/// it adds this to the list of <see cref="Toplevel"/>s, sets up the <see cref="MainLoop"/> to process the
		/// event, lays out the Subviews, focuses the first element, and draws the
		/// <see cref="Toplevel"/> in the screen. This is usually followed by executing
		/// the <see cref="RunLoop"/> method, and then the <see cref="End(RunState)"/> method upon termination which will
		///  undo these changes.
		/// </remarks>
		public static RunState Begin (Toplevel Toplevel)
		{
			if (Toplevel == null) {
				throw new ArgumentNullException (nameof (Toplevel));
			} else if (Toplevel.IsOverlappedContainer && OverlappedTop != Toplevel && OverlappedTop != null) {
				throw new InvalidOperationException ("Only one Overlapped Container is allowed.");
			}

			var rs = new RunState (Toplevel);

			// View implements ISupportInitializeNotification which is derived from ISupportInitialize
			if (!Toplevel.IsInitialized) {
				Toplevel.BeginInit ();
				Toplevel.EndInit ();
			}

			lock (_toplevels) {
				// If Top was already initialized with Init, and Begin has never been called
				// Top was not added to the Toplevels Stack. It will thus never get disposed.
				// Clean it up here:
				if (Top != null && Toplevel != Top && !_toplevels.Contains (Top)) {
					Top.Dispose ();
					Top = null;
				} else if (Top != null && Toplevel != Top && _toplevels.Contains (Top)) {
					Top.OnLeave (Toplevel);
				}
				if (string.IsNullOrEmpty (Toplevel.Id.ToString ())) {
					var count = 1;
					var id = (_toplevels.Count + count).ToString ();
					while (_toplevels.Count > 0 && _toplevels.FirstOrDefault (x => x.Id.ToString () == id) != null) {
						count++;
						id = (_toplevels.Count + count).ToString ();
					}
					Toplevel.Id = (_toplevels.Count + count).ToString ();

					_toplevels.Push (Toplevel);
				} else {
					var dup = _toplevels.FirstOrDefault (x => x.Id.ToString () == Toplevel.Id);
					if (dup == null) {
						_toplevels.Push (Toplevel);
					}
				}

				if (_toplevels.FindDuplicates (new ToplevelEqualityComparer ()).Count > 0) {
					throw new ArgumentException ("There are duplicates Toplevels Id's");
				}
			}
			if (Top == null || Toplevel.IsOverlappedContainer) {
				Top = Toplevel;
			}

			var refreshDriver = true;
			if (OverlappedTop == null || Toplevel.IsOverlappedContainer || (Current?.Modal == false && Toplevel.Modal)
				|| (Current?.Modal == false && !Toplevel.Modal) || (Current?.Modal == true && Toplevel.Modal)) {

				if (Toplevel.Visible) {
					Current = Toplevel;
					SetCurrentOverlappedAsTop ();
				} else {
					refreshDriver = false;
				}
			} else if ((OverlappedTop != null && Toplevel != OverlappedTop && Current?.Modal == true && !_toplevels.Peek ().Modal)
				|| (OverlappedTop != null && Toplevel != OverlappedTop && Current?.Running == false)) {
				refreshDriver = false;
				MoveCurrent (Toplevel);
			} else {
				refreshDriver = false;
				MoveCurrent (Current);
			}

			Driver.PrepareToRun (MainLoop, ProcessKeyEvent, ProcessKeyDownEvent, ProcessKeyUpEvent, ProcessMouseEvent);
			if (Toplevel.LayoutStyle == LayoutStyle.Computed) {
				Toplevel.SetRelativeLayout (new Rect (0, 0, Driver.Cols, Driver.Rows));
			}
			Toplevel.LayoutSubviews ();
			Toplevel.PositionToplevels ();
			Toplevel.FocusFirst ();
			if (refreshDriver) {
				OverlappedTop?.OnChildLoaded (Toplevel);
				Toplevel.OnLoaded ();
				Toplevel.SetNeedsDisplay ();
				Toplevel.Redraw (Toplevel.Bounds);
				Toplevel.PositionCursor ();
				Driver.Refresh ();
			}

			NotifyNewRunState?.Invoke (Toplevel, new RunStateEventArgs (rs));
			return rs;
		}

		/// <summary>
		/// Runs the application by calling <see cref="Run(Toplevel, Func{Exception, bool})"/> with the value of <see cref="Top"/>.
		/// </summary>
		/// <remarks>
		/// See <see cref="Run(Toplevel, Func{Exception, bool})"/> for more details.
		/// </remarks>
		public static void Run (Func<Exception, bool> errorHandler = null)
		{
			Run (Top, errorHandler);
		}

		/// <summary>
		/// Runs the application by calling <see cref="Run(Toplevel, Func{Exception, bool})"/> 
		/// with a new instance of the specified <see cref="Toplevel"/>-derived class.
		/// <para>
		/// Calling <see cref="Init(ConsoleDriver, IMainLoopDriver)"/> first is not needed as this function will initialize the application.
		/// </para>
		/// <para>
		/// <see cref="Shutdown"/> must be called when the application is closing (typically after Run> has 
		/// returned) to ensure resources are cleaned up and terminal settings restored.
		/// </para>
		/// </summary>
		/// <remarks>
		/// See <see cref="Run(Toplevel, Func{Exception, bool})"/> for more details.
		/// </remarks>
		/// <param name="errorHandler"></param>
		/// <param name="driver">The <see cref="ConsoleDriver"/> to use. If not specified the default driver for the
		/// platform will be used (<see cref="WindowsDriver"/>, <see cref="CursesDriver"/>, or <see cref="NetDriver"/>).
		/// Must be <see langword="null"/> if <see cref="Init(ConsoleDriver, IMainLoopDriver)"/> has already been called. 
		/// </param>
		/// <param name="mainLoopDriver">Specifies the <see cref="MainLoop"/> to use.</param>
		public static void Run<T> (Func<Exception, bool> errorHandler = null, ConsoleDriver driver = null, IMainLoopDriver mainLoopDriver = null) where T : Toplevel, new()
		{
			if (_initialized) {
				if (Driver != null) {
					// Init() has been called and we have a driver, so just run the app.
					var top = new T ();
					var type = top.GetType ().BaseType;
					while (type != typeof (Toplevel) && type != typeof (object)) {
						type = type.BaseType;
					}
					if (type != typeof (Toplevel)) {
						throw new ArgumentException ($"{top.GetType ().Name} must be derived from TopLevel");
					}
					Run (top, errorHandler);
				} else {
					// This codepath should be impossible because Init(null, null) will select the platform default driver
					throw new InvalidOperationException ("Init() completed without a driver being set (this should be impossible); Run<T>() cannot be called.");
				}
			} else {
				// Init() has NOT been called.
				InternalInit (() => new T (), driver, mainLoopDriver, calledViaRunT: true);
				Run (Top, errorHandler);
			}
		}

		/// <summary>
		///  Runs the main loop on the given <see cref="Toplevel"/> container.
		/// </summary>
		/// <remarks>
		///  <para>
		///   This method is used to start processing events
		///   for the main application, but it is also used to
		///   run other modal <see cref="View"/>s such as <see cref="Dialog"/> boxes.
		///  </para>
		///  <para>
		///   To make a <see cref="Run(Toplevel, Func{Exception, bool})"/> stop execution, call <see cref="Application.RequestStop"/>.
		///  </para>
		///  <para>
		///   Calling <see cref="Run(Toplevel, Func{Exception, bool})"/> is equivalent to calling <see cref="Begin(Toplevel)"/>, followed by <see cref="RunLoop(RunState, bool)"/>,
		///   and then calling <see cref="End(RunState)"/>.
		///  </para>
		///  <para>
		///   Alternatively, to have a program control the main loop and 
		///   process events manually, call <see cref="Begin(Toplevel)"/> to set things up manually and then
		///   repeatedly call <see cref="RunLoop(RunState, bool)"/> with the wait parameter set to false. By doing this
		///   the <see cref="RunLoop(RunState, bool)"/> method will only process any pending events, timers, idle handlers and
		///   then return control immediately.
		///  </para>
		///  <para>
		///   RELEASE builds only: When <paramref name="errorHandler"/> is <see langword="null"/> any exeptions will be rethrown. 
		///   Otherwise, if <paramref name="errorHandler"/> will be called. If <paramref name="errorHandler"/> 
		///   returns <see langword="true"/> the <see cref="RunLoop(RunState, bool)"/> will resume; otherwise 
		///   this method will exit.
		///  </para>
		/// </remarks>
		/// <param name="view">The <see cref="Toplevel"/> to run modally.</param>
		/// <param name="errorHandler">RELEASE builds only: Handler for any unhandled exceptions (resumes when returns true, rethrows when null).</param>
		public static void Run (Toplevel view, Func<Exception, bool> errorHandler = null)
		{
			var resume = true;
			while (resume) {
#if !DEBUG
				try {
#endif
				resume = false;
				var runToken = Begin (view);
				// If ExitRunLoopAfterFirstIteration is true then the user must dispose of the runToken
				// by using NotifyStopRunState event.
				RunLoop (runToken);
				if (!ExitRunLoopAfterFirstIteration) {
					End (runToken);
				}
#if !DEBUG
				}
				catch (Exception error)
				{
					if (errorHandler == null)
					{
						throw;
					}
					resume = errorHandler(error);
				}
#endif
			}
		}

		/// <summary>
		/// Triggers a refresh of the entire display.
		/// </summary>
		public static void Refresh ()
		{
			Driver.UpdateOffScreen ();
			View last = null;
			foreach (var v in _toplevels.Reverse ()) {
				if (v.Visible) {
					v.SetNeedsDisplay ();
					v.SetSubViewNeedsDisplay ();
					v.Redraw (v.Bounds);
				}
				last = v;
			}
			last?.PositionCursor ();
			Driver.Refresh ();
		}

		/// <summary>
		///  This event is raised on each iteration of the <see cref="MainLoop"/>. 
		/// </summary>
		/// <remarks>
		///  See also <see cref="Timeout"/>
		/// </remarks>
		public static Action Iteration;

		/// <summary>
		/// The <see cref="MainLoop"/> driver for the application
		/// </summary>
		/// <value>The main loop.</value>
		public static MainLoop MainLoop { get; private set; }

		/// <summary>
		/// Set to true to cause the RunLoop method to exit after the first iterations.
		/// Set to false (the default) to cause the RunLoop to continue running until Application.RequestStop() is called.
		/// </summary>
		public static bool ExitRunLoopAfterFirstIteration { get; set; } = false;

		//
		// provides the sync context set while executing code in Terminal.Gui, to let
		// users use async/await on their code
		//
		class MainLoopSyncContext : SynchronizationContext {
			readonly MainLoop mainLoop;

			public MainLoopSyncContext (MainLoop mainLoop)
			{
				this.mainLoop = mainLoop;
			}

			public override SynchronizationContext CreateCopy ()
			{
				return new MainLoopSyncContext (MainLoop);
			}

			public override void Post (SendOrPostCallback d, object state)
			{
				mainLoop.AddIdle (() => {
					d (state);
					return false;
				});
				//mainLoop.Driver.Wakeup ();
			}

			public override void Send (SendOrPostCallback d, object state)
			{
				if (Thread.CurrentThread.ManagedThreadId == _mainThreadId) {
					d (state);
				} else {
					var wasExecuted = false;
					mainLoop.Invoke (() => {
						d (state);
						wasExecuted = true;
					});
					while (!wasExecuted) {
						Thread.Sleep (15);
					}
				}
			}
		}

		/// <summary>
		///  Building block API: Runs the <see cref="MainLoop"/> for the created <see cref="Toplevel"/>.
		/// </summary>
		/// <remarks>
		///  Use the <paramref name="wait"/> parameter to control whether this is a blocking or non-blocking call.
		/// </remarks>
		/// <param name="state">The state returned by the <see cref="Begin(Toplevel)"/> method.</param>
		/// <param name="wait">By default this is <see langword="true"/> which will execute the loop waiting for events, 
		/// if set to <see langword="false"/>, a single iteration will execute.</param>
		public static void RunLoop (RunState state, bool wait = true)
		{
			if (state == null)
				throw new ArgumentNullException (nameof (state));
			if (state.Toplevel == null)
				throw new ObjectDisposedException ("state");

			bool firstIteration = true;
			for (state.Toplevel.Running = true; state.Toplevel.Running;) {
				if (ExitRunLoopAfterFirstIteration && !firstIteration) {
					return;
				}
				RunMainLoopIteration (ref state, wait, ref firstIteration);
			}
		}

		/// <summary>
		/// Run one iteration of the <see cref="MainLoop"/>.
		/// </summary>
		/// <param name="state">The state returned by <see cref="Begin(Toplevel)"/>.</param>
		/// <param name="wait">If <see langword="true"/> will execute the <see cref="MainLoop"/> waiting for events. If <see langword="true"/>
		/// will return after a single iteration.</param>
		/// <param name="firstIteration">Set to <see langword="true"/> if this is the first run loop iteration. Upon return,
		/// it will be set to <see langword="false"/> if at least one iteration happened.</param>
		public static void RunMainLoopIteration (ref RunState state, bool wait, ref bool firstIteration)
		{
			if (MainLoop.EventsPending (wait)) {
				// Notify Toplevel it's ready
				if (firstIteration) {
					state.Toplevel.OnReady ();
				}

				MainLoop.RunIteration ();
				Iteration?.Invoke ();

				EnsureModalOrVisibleAlwaysOnTop (state.Toplevel);
				if ((state.Toplevel != Current && Current?.Modal == true)
					|| (state.Toplevel != Current && Current?.Modal == false)) {
					OverlappedTop?.OnDeactivate (state.Toplevel);
					state.Toplevel = Current;
					OverlappedTop?.OnActivate (state.Toplevel);
					Top.SetSubViewNeedsDisplay ();
					Refresh ();
				}
				if (Driver.EnsureCursorVisibility ()) {
					state.Toplevel.SetNeedsDisplay ();
				}
			} else if (!wait) {
				return;
			}
			firstIteration = false;

			if (state.Toplevel != Top
				&& (!Top._needsDisplay.IsEmpty || Top._subViewNeedsDisplay || Top.LayoutNeeded)) {
				state.Toplevel.SetNeedsDisplay (state.Toplevel.Bounds);
				Top.Redraw (Top.Bounds);
				foreach (var top in _toplevels.Reverse ()) {
					if (top != Top && top != state.Toplevel) {
						top.SetNeedsDisplay ();
						top.Redraw (top.Bounds);
					}
				}
			}
			if (_toplevels.Count == 1 && state.Toplevel == Top
				&& (Driver.Cols != state.Toplevel.Frame.Width || Driver.Rows != state.Toplevel.Frame.Height)
				&& (!state.Toplevel._needsDisplay.IsEmpty || state.Toplevel._subViewNeedsDisplay || state.Toplevel.LayoutNeeded)) {

				Driver.SetAttribute (Colors.TopLevel.Normal);
				state.Toplevel.Clear (new Rect (0, 0, Driver.Cols, Driver.Rows));

			}

			if (!state.Toplevel._needsDisplay.IsEmpty || state.Toplevel._subViewNeedsDisplay || state.Toplevel.LayoutNeeded
				|| OverlappedChildNeedsDisplay ()) {
				state.Toplevel.Redraw (state.Toplevel.Bounds);
				//if (state.Toplevel.SuperView != null) {
				//	state.Toplevel.SuperView?.OnRenderLineCanvas ();
				//} else {
				//	state.Toplevel.OnRenderLineCanvas ();
				//}
				state.Toplevel.PositionCursor ();
				Driver.Refresh ();
			} else {
				Driver.UpdateCursor ();
			}
			if (state.Toplevel != Top && !state.Toplevel.Modal
				&& (!Top._needsDisplay.IsEmpty || Top._subViewNeedsDisplay || Top.LayoutNeeded)) {
				Top.Redraw (Top.Bounds);
			}
		}

		/// <summary>
		/// Wakes up the <see cref="MainLoop"/> that might be waiting on input; must be thread safe.
		/// </summary>
		public static void DoEvents ()
		{
			MainLoop.Driver.Wakeup ();
		}

		/// <summary>
		/// Stops running the most recent <see cref="Toplevel"/> or the <paramref name="top"/> if provided.
		/// </summary>
		/// <param name="top">The <see cref="Toplevel"/> to stop.</param>
		/// <remarks>
		///  <para>
		///  This will cause <see cref="Application.Run(Func{Exception, bool})"/> to return.
		///  </para>
		///  <para>
		///   Calling <see cref="Application.RequestStop"/> is equivalent to setting the <see cref="Toplevel.Running"/> property 
		///   on the currently running <see cref="Toplevel"/> to false.
		///  </para>
		/// </remarks>
		public static void RequestStop (Toplevel top = null)
		{
			if (OverlappedTop == null || top == null || (OverlappedTop == null && top != null)) {
				top = Current;
			}

			if (OverlappedTop != null && top.IsOverlappedContainer && top?.Running == true
				&& (Current?.Modal == false || (Current?.Modal == true && Current?.Running == false))) {

				OverlappedTop.RequestStop ();
			} else if (OverlappedTop != null && top != Current && Current?.Running == true && Current?.Modal == true
				&& top.Modal && top.Running) {

				var ev = new ToplevelClosingEventArgs (Current);
				Current.OnClosing (ev);
				if (ev.Cancel) {
					return;
				}
				ev = new ToplevelClosingEventArgs (top);
				top.OnClosing (ev);
				if (ev.Cancel) {
					return;
				}
				Current.Running = false;
				OnNotifyStopRunState (Current);
				top.Running = false;
				OnNotifyStopRunState (top);
			} else if ((OverlappedTop != null && top != OverlappedTop && top != Current && Current?.Modal == false
				&& Current?.Running == true && !top.Running)
				|| (OverlappedTop != null && top != OverlappedTop && top != Current && Current?.Modal == false
				&& Current?.Running == false && !top.Running && _toplevels.ToArray () [1].Running)) {

				MoveCurrent (top);
			} else if (OverlappedTop != null && Current != top && Current?.Running == true && !top.Running
				&& Current?.Modal == true && top.Modal) {
				// The Current and the top are both modal so needed to set the Current.Running to false too.
				Current.Running = false;
				OnNotifyStopRunState (Current);
			} else if (OverlappedTop != null && Current == top && OverlappedTop?.Running == true && Current?.Running == true && top.Running
				&& Current?.Modal == true && top.Modal) {
				// The OverlappedTop was requested to stop inside a modal Toplevel which is the Current and top,
				// both are the same, so needed to set the Current.Running to false too.
				Current.Running = false;
				OnNotifyStopRunState (Current);
			} else {
				Toplevel currentTop;
				if (top == Current || (Current?.Modal == true && !top.Modal)) {
					currentTop = Current;
				} else {
					currentTop = top;
				}
				if (!currentTop.Running) {
					return;
				}
				var ev = new ToplevelClosingEventArgs (currentTop);
				currentTop.OnClosing (ev);
				if (ev.Cancel) {
					return;
				}
				currentTop.Running = false;
				OnNotifyStopRunState (currentTop);
			}
		}

		static void OnNotifyStopRunState (Toplevel top)
		{
			if (ExitRunLoopAfterFirstIteration) {
				NotifyStopRunState?.Invoke (top, new ToplevelEventArgs (top));
			}
		}

		/// <summary>
		/// Building block API: completes the execution of a <see cref="Toplevel"/> that was started with <see cref="Begin(Toplevel)"/> .
		/// </summary>
		/// <param name="runState">The <see cref="RunState"/> returned by the <see cref="Begin(Toplevel)"/> method.</param>
		public static void End (RunState runState)
		{
			if (runState == null)
				throw new ArgumentNullException (nameof (runState));

			if (OverlappedTop != null) {
				OverlappedTop.OnChildUnloaded (runState.Toplevel);
			} else {
				runState.Toplevel.OnUnloaded ();
			}

			// End the RunState.Toplevel 
			// First, take it off the Toplevel Stack
			if (_toplevels.Count > 0) {
				if (_toplevels.Peek () != runState.Toplevel) {
					// If there the top of the stack is not the RunState.Toplevel then
					// this call to End is not balanced with the call to Begin that started the RunState
					throw new ArgumentException ("End must be balanced with calls to Begin");
				}
				_toplevels.Pop ();
			}

			// Notify that it is closing
			runState.Toplevel?.OnClosed (runState.Toplevel);

			// If there is a OverlappedTop that is not the RunState.Toplevel then runstate.TopLevel 
			// is a child of MidTop and we should notify the OverlappedTop that it is closing
			if (OverlappedTop != null && !(runState.Toplevel).Modal && runState.Toplevel != OverlappedTop) {
				OverlappedTop.OnChildClosed (runState.Toplevel);
			}

			// Set Current and Top to the next TopLevel on the stack
			if (_toplevels.Count == 0) {
				Current = null;
			} else {
				Current = _toplevels.Peek ();
				if (_toplevels.Count == 1 && Current == OverlappedTop) {
					OverlappedTop.OnAllChildClosed ();
				} else {
					SetCurrentOverlappedAsTop ();
					Current.OnEnter (Current);
				}
				Refresh ();
			}

			runState.Toplevel?.Dispose ();
			runState.Toplevel = null;
			runState.Dispose ();
		}

		#endregion Run (Begin, Run, End)

		#region Toplevel handling
		static readonly Stack<Toplevel> _toplevels = new Stack<Toplevel> ();

		/// <summary>
		/// The <see cref="Toplevel"/> object used for the application on startup (<seealso cref="Application.Top"/>)
		/// </summary>
		/// <value>The top.</value>
		public static Toplevel Top { get; private set; }

		/// <summary>
		/// The current <see cref="Toplevel"/> object. This is updated when <see cref="Application.Run(Func{Exception, bool})"/> 
		/// enters and leaves to point to the current <see cref="Toplevel"/> .
		/// </summary>
		/// <value>The current.</value>
		public static Toplevel Current { get; private set; }

		static void EnsureModalOrVisibleAlwaysOnTop (Toplevel Toplevel)
		{
			if (!Toplevel.Running || (Toplevel == Current && Toplevel.Visible) || OverlappedTop == null || _toplevels.Peek ().Modal) {
				return;
			}

			foreach (var top in _toplevels.Reverse ()) {
				if (top.Modal && top != Current) {
					MoveCurrent (top);
					return;
				}
			}
			if (!Toplevel.Visible && Toplevel == Current) {
				OverlappedMoveNext ();
			}
		}

		static View FindDeepestTop (Toplevel start, int x, int y, out int resx, out int resy)
		{
			var startFrame = start.Frame;

			if (!startFrame.Contains (x, y)) {
				resx = 0;
				resy = 0;
				return null;
			}

			if (_toplevels != null) {
				int count = _toplevels.Count;
				if (count > 0) {
					var rx = x - startFrame.X;
					var ry = y - startFrame.Y;
					foreach (var t in _toplevels) {
						if (t != Current) {
							if (t != start && t.Visible && t.Frame.Contains (rx, ry)) {
								start = t;
								break;
							}
						}
					}
				}
			}
			resx = x - startFrame.X;
			resy = y - startFrame.Y;
			return start;
		}

		static View FindTopFromView (View view)
		{
			View top = view?.SuperView != null && view?.SuperView != Top
				? view.SuperView : view;

			while (top?.SuperView != null && top?.SuperView != Top) {
				top = top.SuperView;
			}
			return top;
		}

		// Only return true if the Current has changed.
		static bool MoveCurrent (Toplevel top)
		{
			// The Current is modal and the top is not modal Toplevel then
			// the Current must be moved above the first not modal Toplevel.
			if (OverlappedTop != null && top != OverlappedTop && top != Current && Current?.Modal == true && !_toplevels.Peek ().Modal) {
				lock (_toplevels) {
					_toplevels.MoveTo (Current, 0, new ToplevelEqualityComparer ());
				}
				var index = 0;
				var savedToplevels = _toplevels.ToArray ();
				foreach (var t in savedToplevels) {
					if (!t.Modal && t != Current && t != top && t != savedToplevels [index]) {
						lock (_toplevels) {
							_toplevels.MoveTo (top, index, new ToplevelEqualityComparer ());
						}
					}
					index++;
				}
				return false;
			}
			// The Current and the top are both not running Toplevel then
			// the top must be moved above the first not running Toplevel.
			if (OverlappedTop != null && top != OverlappedTop && top != Current && Current?.Running == false && !top.Running) {
				lock (_toplevels) {
					_toplevels.MoveTo (Current, 0, new ToplevelEqualityComparer ());
				}
				var index = 0;
				foreach (var t in _toplevels.ToArray ()) {
					if (!t.Running && t != Current && index > 0) {
						lock (_toplevels) {
							_toplevels.MoveTo (top, index - 1, new ToplevelEqualityComparer ());
						}
					}
					index++;
				}
				return false;
			}
			if ((OverlappedTop != null && top?.Modal == true && _toplevels.Peek () != top)
				|| (OverlappedTop != null && Current != OverlappedTop && Current?.Modal == false && top == OverlappedTop)
				|| (OverlappedTop != null && Current?.Modal == false && top != Current)
				|| (OverlappedTop != null && Current?.Modal == true && top == OverlappedTop)) {
				lock (_toplevels) {
					_toplevels.MoveTo (top, 0, new ToplevelEqualityComparer ());
					Current = top;
				}
			}
			return true;
		}

		/// <summary>
		/// Invoked when the terminal was resized. The new size of the terminal is provided.
		/// </summary>
		public static Action<ResizedEventArgs> TerminalResized;

		static void OnTerminalResized ()
		{
			var full = new Rect (0, 0, Driver.Cols, Driver.Rows);
			TerminalResized?.Invoke (new ResizedEventArgs () { Cols = full.Width, Rows = full.Height });
			Driver.Clip = full;
			foreach (var t in _toplevels) {
				t.SetRelativeLayout (full);
				t.LayoutSubviews ();
				t.PositionToplevels ();
				t.OnTerminalResized (new SizeChangedEventArgs (full.Size));
			}
			Refresh ();
		}

		#endregion Toplevel handling

		#region Mouse handling
		/// <summary>
		/// Disable or enable the mouse. The mouse is enabled by default.
		/// </summary>
		[SerializableConfigurationProperty (Scope = typeof (SettingsScope))]
		public static bool IsMouseDisabled { get; set; }

		/// <summary>
		/// The current <see cref="View"/> object that wants continuous mouse button pressed events.
		/// </summary>
		public static View WantContinuousButtonPressedView { get; private set; }

		static View _mouseGrabView;

		/// <summary>
		/// The view that grabbed the mouse, to where mouse events will be routed to.
		/// </summary>
		public static View MouseGrabView => _mouseGrabView;

		/// <summary>
		/// Invoked when a view wants to grab the mouse; can be canceled.
		/// </summary>
		public static event EventHandler<GrabMouseEventArgs> GrabbingMouse;

		/// <summary>
		/// Invoked when a view wants ungrab the mouse; can be canceled.
		/// </summary>
		public static event EventHandler<GrabMouseEventArgs> UnGrabbingMouse;

		/// <summary>
		/// Invoked after a view has grabbed the mouse.
		/// </summary>
		public static event EventHandler<ViewEventArgs> GrabbedMouse;

		/// <summary>
		/// Invoked after a view has ungrabbed the mouse.
		/// </summary>
		public static event EventHandler<ViewEventArgs> UnGrabbedMouse;

		/// <summary>
		/// Grabs the mouse, forcing all mouse events to be routed to the specified view until <see cref="UngrabMouse"/> is called.
		/// </summary>
		/// <param name="view">View that will receive all mouse events until <see cref="UngrabMouse"/> is invoked.</param>
		public static void GrabMouse (View view)
		{
			if (view == null)
				return;
			if (!OnGrabbingMouse (view)) {
				OnGrabbedMouse (view);
				_mouseGrabView = view;
				Driver.UncookMouse ();
			}
		}

		/// <summary>
		/// Releases the mouse grab, so mouse events will be routed to the view on which the mouse is.
		/// </summary>
		public static void UngrabMouse ()
		{
			if (_mouseGrabView == null)
				return;
			if (!OnUnGrabbingMouse (_mouseGrabView)) {
				OnUnGrabbedMouse (_mouseGrabView);
				_mouseGrabView = null;
				Driver.CookMouse ();
			}
		}

		static bool OnGrabbingMouse (View view)
		{
			if (view == null)
				return false;
			var evArgs = new GrabMouseEventArgs (view);
			GrabbingMouse?.Invoke (view, evArgs);
			return evArgs.Cancel;
		}

		static bool OnUnGrabbingMouse (View view)
		{
			if (view == null)
				return false;
			var evArgs = new GrabMouseEventArgs (view);
			UnGrabbingMouse?.Invoke (view, evArgs);
			return evArgs.Cancel;
		}

		static void OnGrabbedMouse (View view)
		{
			if (view == null)
				return;
			GrabbedMouse?.Invoke (view, new ViewEventArgs (view));
		}

		static void OnUnGrabbedMouse (View view)
		{
			if (view == null)
				return;
			UnGrabbedMouse?.Invoke (view, new ViewEventArgs (view));
		}

		/// <summary>
		/// Merely a debugging aid to see the raw mouse events
		/// </summary>
		public static Action<MouseEvent> RootMouseEvent;

		static View _lastMouseOwnerView;

		static void ProcessMouseEvent (MouseEvent me)
		{
			bool OutsideFrame (Point p, Rect r)
			{
				return p.X < 0 || p.X > r.Width - 1 || p.Y < 0 || p.Y > r.Height - 1;
			}

			if (IsMouseDisabled) {
				return;
			}

			var view = View.FindDeepestView (Current, me.X, me.Y, out int rx, out int ry);

			if (view != null && view.WantContinuousButtonPressed) {
				WantContinuousButtonPressedView = view;
			} else {
				WantContinuousButtonPressedView = null;
			}
			if (view != null) {
				me.View = view;
			}
			RootMouseEvent?.Invoke (me);

			if (me.Handled) {
				return;
			}

			if (_mouseGrabView != null) {
				var newxy = _mouseGrabView.ScreenToView (me.X, me.Y);
				var nme = new MouseEvent () {
					X = newxy.X,
					Y = newxy.Y,
					Flags = me.Flags,
					OfX = me.X - newxy.X,
					OfY = me.Y - newxy.Y,
					View = view
				};
				if (OutsideFrame (new Point (nme.X, nme.Y), _mouseGrabView.Frame)) {
					_lastMouseOwnerView?.OnMouseLeave (me);
				}
				//System.Diagnostics.Debug.WriteLine ($"{nme.Flags};{nme.X};{nme.Y};{mouseGrabView}");
				if (_mouseGrabView?.OnMouseEvent (nme) == true) {
					return;
				}
			}

			if ((view == null || view == OverlappedTop) && !Current.Modal && OverlappedTop != null
				&& me.Flags != MouseFlags.ReportMousePosition && me.Flags != 0) {

				var top = FindDeepestTop (Top, me.X, me.Y, out _, out _);
				view = View.FindDeepestView (top, me.X, me.Y, out rx, out ry);

				if (view != null && view != OverlappedTop && top != Current) {
					MoveCurrent ((Toplevel)top);
				}
			}

			if (view != null) {
				var nme = new MouseEvent () {
					X = rx,
					Y = ry,
					Flags = me.Flags,
					OfX = 0,
					OfY = 0,
					View = view
				};

				if (_lastMouseOwnerView == null) {
					_lastMouseOwnerView = view;
					view.OnMouseEnter (nme);
				} else if (_lastMouseOwnerView != view) {
					_lastMouseOwnerView.OnMouseLeave (nme);
					view.OnMouseEnter (nme);
					_lastMouseOwnerView = view;
				}

				if (!view.WantMousePositionReports && me.Flags == MouseFlags.ReportMousePosition)
					return;

				if (view.WantContinuousButtonPressed)
					WantContinuousButtonPressedView = view;
				else
					WantContinuousButtonPressedView = null;

				// Should we bubbled up the event, if it is not handled?
				view.OnMouseEvent (nme);

				BringOverlappedTopToFront ();
			}
		}
		#endregion Mouse handling

		#region Keyboard handling


		static Key _alternateForwardKey = Key.PageDown | Key.CtrlMask;

		/// <summary>
		/// Alternative key to navigate forwards through views. Ctrl+Tab is the primary key.
		/// </summary>
		[SerializableConfigurationProperty (Scope = typeof (SettingsScope)), JsonConverter (typeof (KeyJsonConverter))]
		public static Key AlternateForwardKey {
			get => _alternateForwardKey;
			set {
				if (_alternateForwardKey != value) {
					var oldKey = _alternateForwardKey;
					_alternateForwardKey = value;
					OnAlternateForwardKeyChanged (new KeyChangedEventArgs (oldKey, value));
				}
			}
		}

		static void OnAlternateForwardKeyChanged (KeyChangedEventArgs e)
		{
			foreach (var top in _toplevels.ToArray ()) {
				top.OnAlternateForwardKeyChanged (e);
			}
		}

		static Key _alternateBackwardKey = Key.PageUp | Key.CtrlMask;

		/// <summary>
		/// Alternative key to navigate backwards through views. Shift+Ctrl+Tab is the primary key.
		/// </summary>
		[SerializableConfigurationProperty (Scope = typeof (SettingsScope)), JsonConverter (typeof (KeyJsonConverter))]
		public static Key AlternateBackwardKey {
			get => _alternateBackwardKey;
			set {
				if (_alternateBackwardKey != value) {
					var oldKey = _alternateBackwardKey;
					_alternateBackwardKey = value;
					OnAlternateBackwardKeyChanged (new KeyChangedEventArgs (oldKey, value));
				}
			}
		}

		static void OnAlternateBackwardKeyChanged (KeyChangedEventArgs oldKey)
		{
			foreach (var top in _toplevels.ToArray ()) {
				top.OnAlternateBackwardKeyChanged (oldKey);
			}
		}

		static Key _quitKey = Key.Q | Key.CtrlMask;

		/// <summary>
		/// Gets or sets the key to quit the application.
		/// </summary>
		[SerializableConfigurationProperty (Scope = typeof (SettingsScope)), JsonConverter (typeof (KeyJsonConverter))]
		public static Key QuitKey {
			get => _quitKey;
			set {
				if (_quitKey != value) {
					var oldKey = _quitKey;
					_quitKey = value;
					OnQuitKeyChanged (new KeyChangedEventArgs (oldKey, value));
				}
			}
		}
		static void OnQuitKeyChanged (KeyChangedEventArgs e)
		{
			// Duplicate the list so if it changes during enumeration we're safe
			foreach (var top in _toplevels.ToArray ()) {
				top.OnQuitKeyChanged (e);
			}
		}

		static void ProcessKeyEvent (KeyEvent ke)
		{
			if (RootKeyEvent?.Invoke (ke) ?? false) {
				return;
			}

			var chain = _toplevels.ToList ();
			foreach (var topLevel in chain) {
				if (topLevel.ProcessHotKey (ke))
					return;
				if (topLevel.Modal)
					break;
			}

			foreach (var topLevel in chain) {
				if (topLevel.ProcessKey (ke))
					return;
				if (topLevel.Modal)
					break;
			}

			foreach (var topLevel in chain) {
				// Process the key normally
				if (topLevel.ProcessColdKey (ke))
					return;
				if (topLevel.Modal)
					break;
			}
		}

		static void ProcessKeyDownEvent (KeyEvent ke)
		{
			var chain = _toplevels.ToList ();
			foreach (var topLevel in chain) {
				if (topLevel.OnKeyDown (ke))
					return;
				if (topLevel.Modal)
					break;
			}
		}

		static void ProcessKeyUpEvent (KeyEvent ke)
		{
			var chain = _toplevels.ToList ();
			foreach (var topLevel in chain) {
				if (topLevel.OnKeyUp (ke))
					return;
				if (topLevel.Modal)
					break;
			}
		}

		/// <summary>
		/// <para>
		/// Called for new KeyPress events before any processing is performed or
		/// views evaluate. Use for global key handling and/or debugging.
		/// </para>
		/// <para>Return true to suppress the KeyPress event</para>
		/// </summary>
		public static Func<KeyEvent, bool> RootKeyEvent;

		#endregion Keyboard handling
	}
}