Associated Icons Image Control

using System;
using System.IO;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Collections;
using System.Web;
using System.Web.UI;
using System.Runtime.InteropServices;

namespace AssociatedIcons.Controls
{
	public sealed class IconExtractor
	{
		private IconExtractor()
		{
		}

		internal static string GetUrlToIcon(string extensionOrFile, bool large)
		{
			//let's extract the extension from the given argument
			string extension = GetExtension(extensionOrFile);
			string url = GetIconVirtualPath(extension, large);
			return ((Page)HttpContext.Current.Handler).ResolveUrl(url);
		}

		private static string GetIconVirtualPath(string extension, bool large)
		{
			string fileName = string.Format("ext.{0}{1}.png", large?"32":"16", extension);

			//--if you decide to use GIF, use the following line instead
			//string fileName = string.Format("ext.{0}{1}.gif", large?"32":"16", extension);

			string path = Path.Combine(GetStubFilesPhysicalFolder(), fileName);

			//we will ensure the image file with the icon exists
			if(!File.Exists(path))
			{
				//the icon file has not been created yet. Let's do it
				using(Icon icon = ExtractIconForExtension(extension, large))
				using(Bitmap bmp = icon.ToBitmap())
				using(Graphics g = Graphics.FromImage(bmp))
				{
					//we will paint the backgound in HotPink (praying that
					// nobody in their rightful mind would use this color 
					// in their icons) and make it the transparent color
					bmp.MakeTransparent(Color.HotPink);
					g.Clear(Color.HotPink);

					//--alternatively you can choose to paint it in a regular
					//-- color, like plain white, and forget transparency altogether.
					//--  you cand do that by replacing those two lines
					//--  above with the following one
					//g.Clear(Color.White);

					//Paint the icon
					g.DrawIcon(icon, new Rectangle(0, 0, icon.Width, icon.Height));
					
					//save the image in a PNG file
					bmp.Save(path, ImageFormat.Png);

					//--save the image in a GIF file
					//---- if you decide to save as GIF, use the following line instead
					//bmp.Save(path, ImageFormat.Gif);
				}
			}

			string vpath = Path.Combine(GetStubFilesVirtualFolder(), fileName);
			return vpath;
		}

		#region Icon Extraction Code


		private static Icon ExtractIconForExtension(string extension, bool large)
		{
			if(extension != null)
			{
				//let's just make up a file name with that extension
				string fictitiousFile = "0" + extension; 
				//now get the icon for that file
				return GetAssociatedIcon(fictitiousFile, large);
			}
			else
			{
				throw new ArgumentException("Invalid file or extension.", "fileOrExtension");
			}

		}

		private static string GetExtension(string extensionOrFile)
		{
			try
			{
				string ext = System.IO.Path.GetExtension(extensionOrFile);
				ext = ext.Replace("#", "_");
				ext = ext.Replace("&", "_");
				return ext;
			}
			catch{/**/}

			return "";
		}

		private static string GetStubFilesVirtualFolder()
		{
			//TODO: You should make this folder path
			//  be derived of a config value
			//  instead of just hardcoding like in 
			//  the following line
			return "~/IconStubs";
		}

		private static string GetStubFilesPhysicalFolder()
		{
			//TODO: You should make this folder path
			//  be derived of a config value
			//  instead of just hardcoding like in 
			//  the following line
			return HttpContext.Current.Server.MapPath(GetStubFilesVirtualFolder());
		}


		private static Icon GetAssociatedIcon(string stubPath, bool large)
		{
			SHFILEINFO info = new SHFILEINFO(true);
			int cbFileInfo = Marshal.SizeOf(info);
			SHGFI flags;

			if (large)
				flags = SHGFI.Icon|SHGFI.LargeIcon|SHGFI.UseFileAttributes;
			else
				flags = SHGFI.Icon|SHGFI.SmallIcon|SHGFI.UseFileAttributes;

			
			SHGetFileInfo(stubPath, 256, out info,(uint)cbFileInfo, flags);
			return (Icon)Icon.FromHandle(info.hIcon);
		}

		



		#endregion

		#region Win32 API imports 



		[DllImport("shell32.dll", CharSet=CharSet.Auto)]
		private static extern int  SHGetFileInfo(
			string pszPath     ,
			int    dwFileAttributes,
			out    SHFILEINFO psfi ,
			uint   cbfileInfo      ,
			SHGFI  uFlags );

		private const int MAX_PATH = 260;
		private const int MAX_TYPE = 80 ;

		private struct SHFILEINFO
		{
			public SHFILEINFO(bool b)
			{
				hIcon=IntPtr.Zero;
				iIcon=0;
				dwAttributes=0;
				szDisplayName="";
				szTypeName="";
			}


			public IntPtr hIcon;
			public int iIcon;
			public uint dwAttributes;
			[MarshalAs(UnmanagedType.ByValTStr, SizeConst=MAX_PATH)]
			public string szDisplayName;
			[MarshalAs(UnmanagedType.ByValTStr, SizeConst=MAX_TYPE)]
			public string szTypeName;
		};

		[Flags]
			enum SHGFI : int
		{
			/// <summary>get icon</summary>
			Icon         = 0x000000100,   

			/// <summary>get display name</summary>
			DisplayName      = 0x000000200, 

			/// <summary>get type name</summary>
			TypeName     = 0x000000400, 

			/// <summary>get attributes</summary>
			Attributes       = 0x000000800, 

			/// <summary>get icon location</summary>
			IconLocation     = 0x000001000, 
 
			/// <summary>return exe type</summary>
			ExeType      = 0x000002000,  

			/// <summary>get system icon index</summary>
			SysIconIndex     = 0x000004000,  

			/// <summary>put a link overlay on icon</summary>
			LinkOverlay      = 0x000008000,  

			/// <summary>show icon in selected state</summary>
			Selected     = 0x000010000,  

			/// <summary>get only specified attributes</summary>
			Attr_Specified   = 0x000020000, 
 
			/// <summary>get large icon</summary>
			LargeIcon    = 0x000000000,  

			/// <summary>get small icon</summary>
			SmallIcon    = 0x000000001,  

			/// <summary>get open icon</summary>
			OpenIcon     = 0x000000002,  

			/// <summary>get shell size icon</summary>
			ShellIconize     = 0x000000004,  

			/// <summary>pszPath is a pidl</summary>
			PIDL         = 0x000000008,  

			/// <summary>use passed dwFileAttribute</summary>
			UseFileAttributes= 0x000000010,  

			/// <summary>apply the appropriate overlays</summary>
			AddOverlays      = 0x000000020,  

			/// <summary>Get the index of the overlay in the upper 8 bits of the iIcon</summary>
			OverlayIndex     = 0x000000040,  
		}   

		#endregion
	}
}