using System;
using System.Drawing;
using System.Windows.Forms;

namespace Scatter
{
	public static class MouseWheelHandler
	{
		public static void Add(Control ctrl, Action<MouseEventArgs> onMouseWheel)
		{
			if (ctrl == null || onMouseWheel == null)
				throw new ArgumentNullException();

			var filter = new MouseWheelMessageFilter(ctrl, onMouseWheel);
			Application.AddMessageFilter(filter);
			ctrl.Disposed += (s, e) => Application.RemoveMessageFilter(filter);
		}

		private class MouseWheelMessageFilter
			: IMessageFilter
		{
			private readonly Control _ctrl;
			private readonly Action<MouseEventArgs> _onMouseWheel;

			public MouseWheelMessageFilter(Control ctrl, Action<MouseEventArgs> onMouseWheel)
			{
				_ctrl = ctrl;
				_onMouseWheel = onMouseWheel;
			}

			public bool PreFilterMessage(ref Message m)
			{
				var parent = _ctrl.Parent;
				if (parent != null && m.Msg == 0x20a) // WM_MOUSEWHEEL, find the control at screen position m.LParam
				{
					var pos = new Point(m.LParam.ToInt32() & 0xffff, m.LParam.ToInt32() >> 16);

					var clientPos = _ctrl.PointToClient(pos);

					if (_ctrl.ClientRectangle.Contains(clientPos)
					 && ReferenceEquals(_ctrl, parent.GetChildAtPoint(parent.PointToClient(pos))))
					{
						var wParam = m.WParam.ToInt32();
						Func<int, MouseButtons, MouseButtons> getButton =
							(flag, button) => ((wParam & flag) == flag) ? button : MouseButtons.None;

						var buttons = getButton(wParam & 0x0001, MouseButtons.Left)
									| getButton(wParam & 0x0010, MouseButtons.Middle)
									| getButton(wParam & 0x0002, MouseButtons.Right)
									| getButton(wParam & 0x0020, MouseButtons.XButton1)
									| getButton(wParam & 0x0040, MouseButtons.XButton2)
									; // Not matching for these /*MK_SHIFT=0x0004;MK_CONTROL=0x0008*/

						var delta = wParam >> 16;
						var e = new MouseEventArgs(buttons, 0, clientPos.X, clientPos.Y, delta);
						_onMouseWheel(e);

						return true;
					}
				}
				return false;
			}
		}
	}
}