ansi-fahrplan/CursesWrapper/InputHandler.cs

using Mindmagma.Curses;

namespace SCI.CursesWrapper;

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);

	/// <summary>
	/// Event handlers for NCurses key presses
	/// </summary>
	public event KeypressEventHandler? OnKeyPress;

	/// <summary>
	/// Event Handlers called before the regular OnKeyPress handlers are called
	/// </summary>
	public event KeypressEventHandler? OnKeyPressPrivileged;

	/// <summary>
	/// Gets or sets the window this InputHandler is listening to
	/// </summary>
	private Window? _activeWindow;
	public Window? ActiveWindow {
		get {
			return _activeWindow;
		}
		set {
			_activeWindow = value;
		}
	}

	/// <summary>
	/// Root screen to fall back to when no window is active
	/// </summary>
	private nint rootScreen;

	/// <summary>
	/// Task running the endless input handler routine
	/// </summary>
	private Task? listeningTask;

	/// <summary>
	/// Cancellation Token Source to stop the listening task
	/// </summary>
	private CancellationTokenSource? listeningRoutineCts;

	/// <summary>
	/// Class constructor
	/// <paramref name="screen">Parent screen this InputHandler is attached to</paramref>
	/// </summary>
	public InputHandler (nint screen) {
		rootScreen = screen;
	}

	/// <summary>
	/// Start listening to key presses and call registered callbacks
	/// </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;

		if (ActiveWindow is not null) {
			NCurses.Keypad (ActiveWindow.WindowId, 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>
	/// Prepares the window for proper key press reading
	/// </summary>
	private void WindowSetup () {
		if (ActiveWindow is not null) {
			NCurses.Keypad (ActiveWindow.WindowId, true);
			NCurses.NoDelay (ActiveWindow.WindowId, false);
		} else {
			NCurses.Keypad (rootScreen, true);
			NCurses.NoDelay (rootScreen, false);
		}
	}

	/// <summary>
	/// Undoes any changes the setup routine configured for the active window
	/// </summary>
	private void WindowTeardown () {
		if (ActiveWindow is not null) {
			NCurses.Keypad (ActiveWindow.WindowId, false);
			NCurses.NoDelay (ActiveWindow.WindowId, true);
		} else {
			NCurses.Keypad (rootScreen, false);
			NCurses.NoDelay (rootScreen, true);
		}
	}

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

		WindowSetup ();

		int keyCode = -1;

		while (!listeningRoutineCts.Token.IsCancellationRequested) {
			if (OnKeyPress is null) {
				Console.Title = "No handlers";
			} else {
				Console.Title = $"Got {OnKeyPress.GetInvocationList ().Length} handlers";
			}
			
			if (ActiveWindow is not null) {
				keyCode = NCurses.WindowGetChar (ActiveWindow.WindowId);
			} else {
				keyCode = NCurses.GetChar ();
			}

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

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

			// Handle any regular registered key handlers
			if (OnKeyPress is not null) {
				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 Window? _sourceWindow;
	public Window? SourceWindow { get { return _sourceWindow; }}

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

	public NCursesKeyPressEventArgs (int keyCode, Window? sourceWindow) {
		_keyCode = keyCode;
		_sourceWindow = sourceWindow;
	}
}