using System;
using System.Drawing;
using System.Runtime.InteropServices;

namespace PRSDesktop
{
    /// <summary>
    ///     Provides functions to capture the entire screen, or a particular window, and save it to a file.
    /// </summary>
    public class ScreenCapture
    {
        /// <summary>
        ///     Creates an Image object containing a screen shot of the entire desktop
        /// </summary>
        /// <returns></returns>
        public Bitmap CaptureScreen()
        {
            return CaptureWindow(User32.GetDesktopWindow());
        }

        /// <summary>
        ///     Creates an Image object containing a screen shot of a section of the desktop
        /// </summary>
        /// <returns></returns>
        public Bitmap CaptureScreen(int x, int y, int w, int h)
        {
            return CaptureWindow(User32.GetDesktopWindow(), x, y, w, h);
        }

        public Bitmap CaptureWindow(IntPtr handle)
        {
            var windowRect = new User32.RECT();
            User32.GetWindowRect(handle, ref windowRect);
            var width = windowRect.right - windowRect.left;
            var height = windowRect.bottom - windowRect.top;
            return CaptureWindow(handle, 0, 0, width, height);
        }

        /// <summary>
        ///     Creates an Image object containing a screen shot of a specific window
        /// </summary>
        /// <param name="handle">The handle to the window. (In windows forms, this is obtained by the Handle property)</param>
        /// <returns></returns>
        public Bitmap CaptureWindow(IntPtr handle, int x, int y, int w, int h)
        {
            // get te hDC of the target window
            var hdcSrc = User32.GetWindowDC(handle);
            // get the size

            var windowRect = new User32.RECT { left = x, top = y, right = x + w, bottom = y + h };
            //User32.GetWindowRect(handle, ref windowRect);
            //int width = windowRect.right - windowRect.left;
            //int height = windowRect.bottom - windowRect.top;

            // create a device context we can copy to
            var hdcDest = GDI32.CreateCompatibleDC(hdcSrc);
            // create a bitmap we can copy it to,
            // using GetDeviceCaps to get the width/height
            var hBitmap = GDI32.CreateCompatibleBitmap(hdcSrc, w, h);
            // select the bitmap object
            var hOld = GDI32.SelectObject(hdcDest, hBitmap);
            // bitblt over
            GDI32.BitBlt(hdcDest, 0, 0, w, h, hdcSrc, x, y, GDI32.SRCCOPY);
            // restore selection
            GDI32.SelectObject(hdcDest, hOld);
            // clean up 
            GDI32.DeleteDC(hdcDest);
            User32.ReleaseDC(handle, hdcSrc);
            // get a .NET image object for it
            var img = Image.FromHbitmap(hBitmap);
            // free up the Bitmap object
            GDI32.DeleteObject(hBitmap);
            return img;
        }

        /// <summary>
        ///     Helper class containing Gdi32 API functions
        /// </summary>
        private class GDI32
        {
            public const int SRCCOPY = 0x00CC0020; // BitBlt dwRop parameter

            [DllImport("gdi32.dll")]
            public static extern bool BitBlt(IntPtr hObject, int nXDest, int nYDest,
                int nWidth, int nHeight, IntPtr hObjectSource,
                int nXSrc, int nYSrc, int dwRop);

            [DllImport("gdi32.dll")]
            public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC, int nWidth,
                int nHeight);

            [DllImport("gdi32.dll")]
            public static extern IntPtr CreateCompatibleDC(IntPtr hDC);

            [DllImport("gdi32.dll")]
            public static extern bool DeleteDC(IntPtr hDC);

            [DllImport("gdi32.dll")]
            public static extern bool DeleteObject(IntPtr hObject);

            [DllImport("gdi32.dll")]
            public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
        }

        /// <summary>
        ///     Helper class containing User32 API functions
        /// </summary>
        private class User32
        {
            [DllImport("user32.dll")]
            public static extern IntPtr GetDesktopWindow();

            [DllImport("user32.dll")]
            public static extern IntPtr GetWindowDC(IntPtr hWnd);

            [DllImport("user32.dll")]
            public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);

            [DllImport("user32.dll")]
            public static extern IntPtr GetWindowRect(IntPtr hWnd, ref RECT rect);

            [StructLayout(LayoutKind.Sequential)]
            public struct RECT
            {
                public int left;
                public int top;
                public int right;
                public int bottom;
            }
        }
    }
}