using System;
using System.Drawing;


namespace Roblox.Test
{
	/// <summary>
	/// This class shall keep all the functionality for capturing 
	/// the desktop.
	/// </summary>
	public class CaptureScreen
	{
		#region Public Class Functions
		public static Bitmap GetDesktopImage()
		{
			//In size variable we shall keep the size of the screen.
			SIZE size;
			
			//Variable to keep the handle to bitmap.
			IntPtr hBitmap;

			//Here we get the handle to the desktop device context.
			IntPtr 	hDC = PlatformInvokeUSER32.GetDC(PlatformInvokeUSER32.GetDesktopWindow()); 

			//Here we make a compatible device context in memory for screen device context.
			IntPtr hMemDC = PlatformInvokeGDI32.CreateCompatibleDC(hDC);
			
			//We pass SM_CXSCREEN constant to GetSystemMetrics to get the X coordinates of screen.
			size.cx = PlatformInvokeUSER32.GetSystemMetrics(PlatformInvokeUSER32.SM_CXSCREEN);

			//We pass SM_CYSCREEN constant to GetSystemMetrics to get the Y coordinates of screen.
			size.cy = PlatformInvokeUSER32.GetSystemMetrics(PlatformInvokeUSER32.SM_CYSCREEN);
			
			//We create a compatible bitmap of screen size using screen device context.
			hBitmap = PlatformInvokeGDI32.CreateCompatibleBitmap(hDC, size.cx, size.cy);

			//As hBitmap is IntPtr we can not check it against null. For this purspose IntPtr.Zero is used.
			if (hBitmap!=IntPtr.Zero)
			{
				//Here we select the compatible bitmap in memeory device context and keeps the refrence to Old bitmap.
				IntPtr hOld = (IntPtr) PlatformInvokeGDI32.SelectObject(hMemDC, hBitmap);
				//We copy the Bitmap to the memory device context.
				PlatformInvokeGDI32.BitBlt(hMemDC, 0, 0,size.cx,size.cy, hDC, 0, 0, PlatformInvokeGDI32.SRCCOPY);
				//We select the old bitmap back to the memory device context.
				PlatformInvokeGDI32.SelectObject(hMemDC, hOld);
				//We delete the memory device context.
				PlatformInvokeGDI32.DeleteDC(hMemDC);
				//We release the screen device context.
				PlatformInvokeUSER32.ReleaseDC(PlatformInvokeUSER32.GetDesktopWindow(), hDC);
				//Image is created by Image bitmap handle and stored in local variable.
				Bitmap bmp = System.Drawing.Image.FromHbitmap(hBitmap); 
				//Release the memory for compatible bitmap.
				PlatformInvokeGDI32.DeleteObject(hBitmap);
				//This statement runs the garbage collector manually.
				GC.Collect();
				//Return the bitmap 
				return bmp;
			}
		
			//If hBitmap is null retunrn null.
			return null;
		}
		#endregion
	}
}