using System;
using System.Drawing.Printing;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace RichTextBoxPrint
{
    /// <summary>
    /// Класс, добавляющий возможность печати из RichTextBox
    /// </summary>
    internal static class RichTextBoxPrint
    {
        public static void Print(this RichTextBox rtf, PrintDocument prn)
        {
            new PrintRtf(rtf, prn);
        }
        public static void Print(this RichTextBox rtf)
        {
            Print(rtf, new PrintDocument());
        }

        private class PrintRtf
        {
            public PrintRtf(RichTextBox rtf, PrintDocument prn)
            {
                Rtf = rtf;
                Prn = prn;
                Cnt = 0;
                Prn.PrintPage += DoPrintPage;
                Prn.EndPrint += DoEndPrint;
                Prn.Print();
            }

            private RichTextBox Rtf;
            private PrintDocument Prn;
            private int Cnt;

            #region Служебные определения

            // Convert the unit that is used by the .NET framework (1/100 inch) 
            // and the unit that is used by Win32 API calls (twips 1/1440 inch)
            private const double AnInch = 14.4;

            [StructLayout(LayoutKind.Sequential)]
            private struct RECT
            {
                public int Left;
                public int Top;
                public int Right;
                public int Bottom;
            }

            [StructLayout(LayoutKind.Sequential)]
            private struct CHARRANGE
            {
                public int cpMin; // First character of range (0 for start of doc)
                public int cpMax; // Last character of range (-1 for end of doc)
            }

            [StructLayout(LayoutKind.Sequential)]
            private struct FORMATRANGE
            {
                public IntPtr hdc; // Actual DC to draw on
                public IntPtr hdcTarget; // Target DC for determining text formatting
                public RECT rc; // Region of the DC to draw to (in twips)
                public RECT rcPage; // Region of the whole DC (page size) (in twips)
                public CHARRANGE chrg; // Range of text to draw (see above declaration)
            }

            private const int WM_USER = 0x0400;
            private const int EM_FORMATRANGE = WM_USER + 57;

            [DllImport("User32.dll")]
            private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);

            #endregion

            private int PrintChars(int charFrom, int charTo, PrintPageEventArgs e)
            {
                #region Mark starting and ending character
                CHARRANGE cRange;
                cRange.cpMin = charFrom;
                cRange.cpMax = charTo;
                #endregion
                #region Calculate the area to render and print
                RECT rectToPrint;
                rectToPrint.Top = (int)(e.MarginBounds.Top * AnInch);
                rectToPrint.Bottom = (int)(e.MarginBounds.Bottom * AnInch);
                rectToPrint.Left = (int)(e.MarginBounds.Left * AnInch);
                rectToPrint.Right = (int)(e.MarginBounds.Right * AnInch);
                #endregion
                #region Calculate the size of the page
                RECT rectPage;
                rectPage.Top = (int)(e.PageBounds.Top * AnInch);
                rectPage.Bottom = (int)(e.PageBounds.Bottom * AnInch);
                rectPage.Left = (int)(e.PageBounds.Left * AnInch);
                rectPage.Right = (int)(e.PageBounds.Right * AnInch);
                #endregion
                #region SendMessage
                IntPtr hdc = e.Graphics.GetHdc();

                FORMATRANGE fmtRange;
                fmtRange.chrg = cRange;                 // Indicate character from to character to 
                fmtRange.hdc = hdc;                     // Use the same DC for measuring and rendering
                fmtRange.hdcTarget = hdc;               // Point at printer hDC
                fmtRange.rc = rectToPrint;              // Indicate the area on page to print
                fmtRange.rcPage = rectPage;             // Indicate whole size of page

                IntPtr res = IntPtr.Zero;
                IntPtr wparam = new IntPtr(1);

                // Move the pointer to the FORMATRANGE structure in memory
                IntPtr lparam = Marshal.AllocCoTaskMem(Marshal.SizeOf(fmtRange));
                Marshal.StructureToPtr(fmtRange, lparam, false);

                // Send the rendered data for printing 
                res = SendMessage(Rtf.Handle, EM_FORMATRANGE, wparam, lparam);

                // Free the block of memory allocated
                Marshal.FreeCoTaskMem(lparam);

                // Release the device context handle obtained by a previous call
                e.Graphics.ReleaseHdc(hdc);
                #endregion
                // Return last + 1 character printer
                return res.ToInt32();
            }

            private void DoPrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
            {
                //Print the content of the RichTextBox. Store the last character printed.
                Cnt = PrintChars(Cnt, Rtf.TextLength, e);

                // Look for more pages
                e.HasMorePages = (Cnt < Rtf.TextLength);
            }
            private void DoEndPrint(object sender, System.Drawing.Printing.PrintEventArgs e)
            {
                Prn.PrintPage -= DoPrintPage;
                Prn.EndPrint -= DoEndPrint;
            }
        }
    }
}