using System;
using System.Drawing;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Win32;
using System.Runtime.InteropServices;

namespace FileExplorer
{
   public class GetSystemIcon
    {
        /// <summary>
        /// 依据文件名读取图标，若指定文件不存在，则返回空值。
        /// </summary>
        /// <param name="fileName"></param>
        /// <returns></returns>
        public static Icon GetIconByFileName(string fileName)
        {
            if (fileName == null || fileName.Equals(string.Empty)) return null;
            if (!File.Exists(fileName)) return null;

             SHFILEINFO shinfo = new SHFILEINFO();
            //Use this to get the small Icon
             Win32.SHGetFileInfo(fileName, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), Win32.SHGFI_ICON | Win32.SHGFI_LARGEICON);
            //The icon is returned in the hIcon member of the shinfo struct
             System.Drawing.Icon myIcon = System.Drawing.Icon.FromHandle(shinfo.hIcon);
            return myIcon;
        }

        /// <summary>
        /// 给出文件扩展名（.*），返回相应图标
        /// 若不以"."开头则返回文件夹的图标。
        /// </summary>
        /// <param name="fileType"></param>
        /// <param name="isLarge"></param>
        /// <returns></returns>
        public static Icon GetIconByFileType(string fileType, bool isLarge)
        {
            if (fileType == null || fileType.Equals(string.Empty)) return null;

             RegistryKey regVersion = null;
             string regFileType = null;
             string regIconString = null;
             string systemDirectory = Environment.SystemDirectory + "\\";

            if (fileType[0] == '.')
            {
                //读系统注册表中文件类型信息
                 regVersion = Registry.ClassesRoot.OpenSubKey(fileType, true);
                if (regVersion != null)
                {
                     regFileType = regVersion.GetValue("") as string;
                     regVersion.Close();
                     regVersion = Registry.ClassesRoot.OpenSubKey(regFileType + @"\DefaultIcon", true);
                    if (regVersion != null)
                    {
                         regIconString = regVersion.GetValue("") as string;
                         regVersion.Close();
                    }
                }
                if (regIconString == null)
                {
                    //没有读取到文件类型注册信息，指定为未知文件类型的图标
                     regIconString = systemDirectory + "shell32.dll,0";
                }
            }
            else
            {
                //直接指定为文件夹图标
                 regIconString = systemDirectory + "shell32.dll,3";
            }
             string[] fileIcon = regIconString.Split(new char[] { ',' });
            if (fileIcon.Length != 2)
            {
                //系统注册表中注册的标图不能直接提取，则返回可执行文件的通用图标
                 fileIcon = new string[] { systemDirectory + "shell32.dll", "2" };
            }
             Icon resultIcon = null;
            try
            {
                //调用API方法读取图标
                int[] phiconLarge = new int[1];
                int[] phiconSmall = new int[1];
                 uint count = Win32.ExtractIconEx(fileIcon[0], Int32.Parse(fileIcon[1]), phiconLarge, phiconSmall, 1);
                 IntPtr IconHnd = new IntPtr(isLarge ? phiconLarge[0] : phiconSmall[0]);
                 resultIcon = Icon.FromHandle(IconHnd);
            }
            catch(Exception err) 
            { 
                        LogNet.LogisTrac.WriteLog(typeof(GetSystemIcon), err);

            }
            return resultIcon;
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct SHFILEINFO
    {
        public IntPtr hIcon;
        public IntPtr iIcon;
        public uint dwAttributes;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
        public string szDisplayName;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
        public string szTypeName;
    };

    /// <summary>
    /// 定义调用的API方法
    /// </summary>
    class Win32
    {
        public const uint SHGFI_ICON = 0x100;
        public const uint SHGFI_LARGEICON = 0x0; // 'Large icon
        public const uint SHGFI_SMALLICON = 0x1; // 'Small icon

        [DllImport("shell32.dll")]
        public static extern IntPtr SHGetFileInfo(string pszPath, uint dwFileAttributes, ref SHFILEINFO psfi, uint cbSizeFileInfo, uint uFlags);
        [DllImport("shell32.dll")]
        public static extern uint ExtractIconEx(string lpszFile, int nIconIndex, int[] phiconLarge, int[] phiconSmall, uint nIcons);

    }

}