using System;
using System.Windows.Forms;

namespace WeifenLuo.WinFormsUI.Docking
{
	// Inspired by Chris Sano's article:
	// http://msdn.microsoft.com/smartclient/default.aspx?pull=/library/en-us/dnwinforms/html/colorpicker.asp
	// In Sano's article, the DragForm needs to meet the following criteria:
	// (1) it was not to show up in the task bar;
	//     ShowInTaskBar = false
	// (2) it needed to be the top-most window;
	//     TopMost = true (not necessary here)
	// (3) its icon could not show up in the ALT+TAB window if the user pressed ALT+TAB during a drag-and-drop;
	//     FormBorderStyle = FormBorderStyle.None;
	//     Create with WS_EX_TOOLWINDOW window style.
	//     Compares with the solution in the artile by setting FormBorderStyle as FixedToolWindow,
	//     and then clip the window caption and border, this way is much simplier.
	// (4) it was not to steal focus from the application when displayed.
	//     User Win32 ShowWindow API with SW_SHOWNOACTIVATE
	// In addition, this form should only for display and therefore should act as transparent, otherwise
	// WindowFromPoint will return this form, instead of the control beneath. Need BOTH of the following to
	// achieve this (don't know why, spent hours to try it out :( ):
	//  1. Enabled = false;
	//  2. WM_NCHITTEST returns HTTRANSPARENT
	internal class DragForm : Form
	{
		public DragForm()
		{
			FormBorderStyle = FormBorderStyle.None;
			ShowInTaskbar = false;
			SetStyle(ControlStyles.Selectable, false);
			Enabled = false;
		}

		protected override CreateParams CreateParams
		{
			get
			{
				CreateParams createParams = base.CreateParams;
				createParams.ExStyle |= (int)Win32.WindowExStyles.WS_EX_TOOLWINDOW;
				return createParams;
			}
		}

		protected override void WndProc(ref Message m)
		{
			if (m.Msg == (int)Win32.Msgs.WM_NCHITTEST)
			{
				m.Result = (IntPtr)Win32.HitTest.HTTRANSPARENT;
				return;
			}

			base.WndProc (ref m);
		}

		public virtual void Show(bool bActivate)
		{
			if (bActivate)
				Show();
			else
				NativeMethods.ShowWindow(Handle, (int)Win32.ShowWindowStyles.SW_SHOWNOACTIVATE);
		}
	}
}