ansi-fahrplan/InputHandler.cs

using System.Security.Principal;
using Mindmagma.Curses;

namespace ANSI_Fahrplan;

public class InputHandler {
	/// <summary>
	/// Handler called by the input handler routine when a key is pressed
	/// </summary>
	/// <param name="sender">Sender object of event callback</param>
	/// <param name="e">Event arguments with details like the pressed key code</param>
	public delegate	void KeypressEventHandler (object sender, NCursesKeyPressEventArgs e);

	// Event fired when key is pressed
	public event KeypressEventHandler? OnKeyPress;

	// Similar to OnKeyPress, but called before any regular OnKeyPress event handlers are called
	public event KeypressEventHandler? OnKeyPressPrivileged;

	// When this variable is set, no event handlers will be called except this one
	// Once e.CancelNextEvent is true from this event, it will be set to null again
	private KeypressEventHandler? _rawKeyPressHandler;
	public KeypressEventHandler? RawKeyPressHandler { get { return _rawKeyPressHandler; }}

	private nint _targetWindow;
	public nint TargetWindow { get { return _targetWindow; }}

	private CancellationTokenSource? listeningRoutineCts;

	private Task? listeningTask;

	/// <summary>
	/// Class constructor
	/// </summary>
	/// <param name="targetWindow">Window for which to listen to key presses</param>
	public InputHandler (nint targetWindow) {
		_targetWindow = targetWindow;
	}

	/// <summary>
	/// Start listening to key presses and call registered callbacks
	/// <paramref name="window">Window to listen to key presses in<param/>
	/// </summary>
	public void StartListening () {
		if (IsListening ()) return;

		listeningRoutineCts = new CancellationTokenSource ();

		listeningTask = Task.Run (_ListeningRoutine);
		while (listeningTask.Status == TaskStatus.WaitingToRun) Thread.Sleep (50);
	}

	/// <summary>
	/// Stop listening to key presses
	/// </summary>
	public void StopListening () {
		if (! IsListening ()) return;
		if (listeningRoutineCts is null) return;
		if (listeningTask is null) return;

		listeningRoutineCts.Cancel ();
		listeningTask.Wait ();
		listeningTask = null;

		NCurses.Keypad (TargetWindow, false);
	}

	/// <summary>
	/// Returns the current listening status of the input event handler
	/// </summary>
	/// <returns>True if the event handler routine is listening to key presses</returns>
	public bool IsListening () {
		return listeningTask is not null && (
			listeningTask.Status == TaskStatus.Running ||
			listeningTask.Status == TaskStatus.WaitingForActivation
		);
	}

	/// <summary>
	/// Enable temporary raw keypress event handler to forward
	/// all keypressed directly to a specific function
	/// </summary>
	/// <param name="eventHandler">Event handler to pass key presses to</param>
	/// <param name="screen">Screen to pass key char duty to</param>
	public void EnableRawEventHandler (KeypressEventHandler eventHandler, nint? window = null) {
		if (window is not null) {
			StopListening ();
			_targetWindow = (nint) window;
			StartListening ();
		}

		_rawKeyPressHandler = eventHandler;
	}

	/// <summary>
	/// Disables the temporary raw keypress event handler
	/// <param name="screen">Screen to pass key char duty back to</param>
	/// </summary>
	public void DisableRawEventHandler (nint? screen = null) {
		if (RawKeyPressHandler is null) return;

		if (screen is not null) {
			StopListening ();
			_targetWindow = (nint) screen;
			StartListening ();
		}

		_rawKeyPressHandler = null;
	}

	/// <summary>
	/// Prepares the window for proper key press reading
	/// </summary>
	private void WindowSetup () {
		NCurses.Keypad (TargetWindow, true);
		NCurses.NoDelay (TargetWindow, false);
	}

	/// <summary>
	/// Actual keypress handler being called as Task by StartListening ()
	/// </summary>
	private void _ListeningRoutine () {
		if (listeningRoutineCts is null) return;

		WindowSetup ();

		while (!listeningRoutineCts.Token.IsCancellationRequested) {
			int keyCode = NCurses.WindowGetChar (TargetWindow);

			// Do nothing until the key code is larger than -1
			if (keyCode < 0) continue;

			var eventArgs = new NCursesKeyPressEventArgs (keyCode, TargetWindow);

			// If enabled, forward all key pressed directly to raw keypress event handler
			if (RawKeyPressHandler is not null) {
				RawKeyPressHandler (this, eventArgs);
				continue;
			}

			var skipRegularEventHandlers = false;

			// Handle any registered privileged key handlers
			if (OnKeyPressPrivileged is not null) {
				foreach (KeypressEventHandler h in OnKeyPressPrivileged.GetInvocationList ()) {
					h (this, eventArgs);
					if (eventArgs.CancelNextEvent == true) {
						skipRegularEventHandlers = true;
						break;
					}
				}
			}

			// Handle any regular registered key handlers
			if (OnKeyPress is not null && !skipRegularEventHandlers) {
				foreach (KeypressEventHandler h in OnKeyPress.GetInvocationList ()) {
					h (this, eventArgs);
					if (eventArgs.CancelNextEvent == true) continue ;
				}
			}
		}

		listeningRoutineCts.Dispose ();
		listeningRoutineCts = null;
	}
}

public class NCursesKeyPressEventArgs : EventArgs {
	private int _keyCode;
	public int KeyCode { get { return _keyCode; }}
	
	private nint _targetWindow;
	public nint TargetWindow { get { return _targetWindow; }}

	public bool CancelNextEvent { get; set; } = false;

	public NCursesKeyPressEventArgs (int keyCode, nint targetWindow) {
		_keyCode = keyCode;
		_targetWindow = targetWindow;
	}
}