ansi-fahrplan/CursesWrapper/ScrollWindow.cs

using System.Drawing;
using Mindmagma.Curses;

namespace SCI.CursesWrapper;

public class ScrollWindow : Window {
	private nint _innerPadId;
	public nint InnerPadId { get { return _innerPadId; }}

	private Point _scrollPosition;
	public Point ScrollPosition { get { return _scrollPosition; }}

	private Size _padSize;
	public Size PadSize { get { return _padSize; }}

	public ScrollWindow (Window parentWindow, InputHandler inputHandler, int innerHeight = -1) :
		base (0, 0, 0, 0, inputHandler, parentWindow)
	{
		var padWidth  = GetUsableWidth ();
		var padHeight = innerHeight;
		
		if (padHeight == -1) {
			padHeight = parentWindow.GetUsableHeight ();
		}

		_innerPadId = NCurses.NewPad (padHeight, padWidth);

		_padSize = new Size (padWidth, padHeight);

		NCurses.WindowBackground (InnerPadId, ColorSchemes.TextInputField ());
		ShowPad ();

		OnKeyPress += ScrollKeyHandler;
	}

	/// <summary>
	/// Scrolls the window up or down on up key or down key
	/// </summary>
	/// <param name="sender"></param>
	/// <param name="e"></param>
	private void ScrollKeyHandler (object sender, NCursesKeyPressEventArgs e) {
		if (e.SourceWindow is null || e.SourceWindow != this) return;

		if (e.KeyCode == CursesKey.UP) {
			ScrollTo (ScrollPosition.X, ScrollPosition.Y - 1);
		} else if (e.KeyCode == CursesKey.DOWN) {
			ScrollTo (ScrollPosition.X, ScrollPosition.Y + 1);
		}
	}

	/// <summary>
	/// Scrolls the pad to the specified coordinates
	/// </summary>
	/// <param name="scrollX"></param>
	/// <param name="scrollY"></param>
	public void ScrollTo (int scrollX, int scrollY) {
		if (ParentWindow is null) return;

		_scrollPosition = new Point (scrollX, scrollY);
		ShowPad ();
	}

	/// <summary>
	/// Shows the pad the current scroll location
	/// </summary>
	public void ShowPad () {
		if (ParentWindow is null) return;

		var scrollToX = ScrollPosition.X;
		var scrollToY = ScrollPosition.Y;

		var viewableWidth  = GetUsableWidth ();
		var viewableHeight = GetUsableHeight ();

		// Check for unnecessary scrolling due to small Pad size
		if (PadSize.Width <= viewableWidth) {
			scrollToX = 0;
		}
		if (PadSize.Height <= viewableHeight) {
			scrollToY = 0;
		}

		// Check values for upper bounds
		if (scrollToX > PadSize.Width - viewableWidth)   scrollToX = PadSize.Width - viewableWidth;
		if (scrollToY > PadSize.Height - viewableHeight) scrollToY = PadSize.Height - viewableHeight;

		// Check values for lower bounds
		if (scrollToX < 0) scrollToX = 0;
		if (scrollToY < 0) scrollToY = 0;

		// Store potentially updated scroll coordinates
		_scrollPosition = new Point (scrollToX, scrollToY);

		var fromY = Position.Y;
		var fromX = Position.X;
		var toY   = viewableHeight;
		var toX   = viewableWidth - 2; // TODO: Why the two? How is the geometry this wong?!

		NCurses.PadRefresh (
			_innerPadId,
			scrollToY, scrollToX,
			fromY,
			fromX,
			toY,
			toX
		);
	}
}