A Quantum Immortal

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.Runtime.InteropServices;
using Microsoft.Win32.SafeHandles;
using NUnit.Framework;
using FILETIME=System.Runtime.InteropServices.ComTypes.FILETIME;
using IEnumerator=System.Collections.IEnumerator;
 
namespace Semingo.IntegrationTests.DirectoryUtils
{
    public static class DirectoryUtils
    {
        /// <summary>
        /// Efficiently get only some files from a dir
        /// </summary>
        /// <param name="directory"></param>
        /// <param name="limit"></param>
        /// <returns></returns>
        public static List<string> GetFiles(string directory, int limit)
        {
            Assert.IsTrue(limit > 0, "Limit should be positive");
            List<string> result = new List<string>(limit);
            FilesFinder filesFinder = new FilesFinder(directory + "\\*.*");
            foreach (FoundFileData foundFile in filesFinder)
            {
                string fullFilename = directory + "\\" + foundFile.FileName;
                if (!IsFile(fullFilename))
                    continue;
 
                limit--;
 
                result.Add(fullFilename);
 
                if (limit == 0)
                    return result;
            }
 
            return result;
        }
 
        /// <summary>
        /// Return a random set of count files from a directory. (note, this can be slow on huge directories!)
        /// </summary>
        /// <remarks>
        /// If the directory has less files, all of it is returned
        /// </remarks>
        /// <param name="directory"></param>
        /// <param name="limit"></param>
        /// <returns></returns>
        public static List<string> GetRandomizedFiles(string directory, int limit
        {
            string[] files = Directory.GetFiles(directory);
            if (files.Length <= limit)
                return new List<string>(files);
 
            // we don't have enough, so we have to randomize
            int[] permutation = GenerateRandomPermutation(files.Length);
 
            // take first count files
            List<string> result = new List<string>(count);
            for (int i = 0; i < count; ++i)
            {
                result.Add(files[permutation[i]]);
            }
            return result;
        }
 
        private static bool IsFile(string name)
        {
            return File.Exists(name);
        }
 
        private static int[] GenerateRandomPermutation(int count)
        {
            int[] array = new int[count];
            for (int i = 0; i < count; ++i)
                array[i] = i;
 
            // http://forums.msdn.microsoft.com/en-US/csharpgeneral/thread/8b489948-f1b5-46d0-8bc5-bd94c418e41d/
            Random random = new Random();  // i.e., Random Class.  
            int n = array.Length;       // The number of items left to shuffle (loop invariant).  
            while (n > 1)
            {
                int k = random.Next(n);  // 0 <= k < n.  
                n--;                     // n is now the last pertinent index;  
                int temp = array[n];     // swap array[n] with array[k] (does nothing if k == n).  
                array[n] = array[k];
                array[k] = temp;
            }
            return array;
        }
    }
 
    /// <summary>
    /// Taken from http://blogs.msdn.com/yvesdolc/archive/2005/08/06/448673.aspx and translated to C#
    /// </summary>
    public class FilesEnumerator : IEnumerator<FoundFileData>
    {
        #region Interop imports
 
        private const int ERROR_FILE_NOT_FOUND = 2;
        private const int ERROR_NO_MORE_FILES = 18;
 
        [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        private static extern IntPtr FindFirstFile(string lpFileName, out WIN32_FIND_DATA lpFindFileData);
 
        [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        private static extern bool FindNextFile(SafeHandle hFindFile, out WIN32_FIND_DATA lpFindFileData);
 
        #endregion
 
        #region Data Members
 
        private readonly string _fileName;
        private SafeHandle _findHandle;
        private WIN32_FIND_DATA _win32FindData;
 
        #endregion
 
        public FilesEnumerator(string fileName)
        {
            _fileName = fileName;
            _findHandle = null;
            _win32FindData = new WIN32_FIND_DATA();
        }
 
        #region IEnumerator<FoundFileData> Members
 
        public FoundFileData Current
        {
            get
            {
                if (_findHandle == null)
                    throw new InvalidOperationException("MoveNext() must be called first");
 
                return new FoundFileData(ref _win32FindData);
            }
        }
 
        object IEnumerator.Current
        {
            get { return Current; }
        }
 
        public bool MoveNext()
        {
            if (_findHandle == null)
            {
                _findHandle = new SafeFileHandle(FindFirstFile(_fileName, out _win32FindData), true);
                if (_findHandle.IsInvalid)
                {
                    int lastError = Marshal.GetLastWin32Error();
                    if (lastError == ERROR_FILE_NOT_FOUND)
                        return false;
 
                    throw new Win32Exception(lastError);
                }
            }
            else
            {
                if (!FindNextFile(_findHandle, out _win32FindData))
                {
                    int lastError = Marshal.GetLastWin32Error();
                    if (lastError == ERROR_NO_MORE_FILES)
                        return false;
 
                    throw new Win32Exception(lastError);
                }
            }
 
            return true;
        }
 
        public void Reset()
        {
            if (_findHandle.IsInvalid)
                return;
 
            _findHandle.Close();
            _findHandle.SetHandleAsInvalid();
        }
 
        public void Dispose()
        {
            _findHandle.Dispose();
        }
 
        #endregion
    }
 
    public class FilesFinder : IEnumerable<FoundFileData>
    {
        readonly string _fileName;
        public FilesFinder(string fileName)
        {
            _fileName = fileName;
        }
 
        public IEnumerator<FoundFileData> GetEnumerator()
        {
            return new FilesEnumerator(_fileName);
        }
 
        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }
    }
 
    public class FoundFileData
    {
        public string AlternateFileName;
        public FileAttributes Attributes;
        public DateTime CreationTime;
        public string FileName;
        public DateTime LastAccessTime;
        public DateTime LastWriteTime;
        public UInt64 Size;
 
        internal FoundFileData(ref WIN32_FIND_DATA win32FindData)
        {
            Attributes = (FileAttributes)win32FindData.dwFileAttributes;
            CreationTime = DateTime.FromFileTime((long)
                    (((UInt64)win32FindData.ftCreationTime.dwHighDateTime << 32) +
                     (UInt64)win32FindData.ftCreationTime.dwLowDateTime));
 
            LastAccessTime = DateTime.FromFileTime((long)
                    (((UInt64)win32FindData.ftLastAccessTime.dwHighDateTime << 32) +
                     (UInt64)win32FindData.ftLastAccessTime.dwLowDateTime));
 
            LastWriteTime = DateTime.FromFileTime((long)
                    (((UInt64)win32FindData.ftLastWriteTime.dwHighDateTime << 32) +
                     (UInt64)win32FindData.ftLastWriteTime.dwLowDateTime));
 
            Size = ((UInt64)win32FindData.nFileSizeHigh << 32) + win32FindData.nFileSizeLow;
            FileName = win32FindData.cFileName;
            AlternateFileName = win32FindData.cAlternateFileName;
        }
    }
 
    /// <summary>
    /// Safely wraps handles that need to be closed via FindClose() WIN32 method (obtained by FindFirstFile())
    /// </summary>
    public class SafeFindFileHandle : SafeHandleZeroOrMinusOneIsInvalid
    {
        [DllImport("kernel32.dll", SetLastError = true)]
        private static extern bool FindClose(SafeHandle hFindFile);
 
        public SafeFindFileHandle(bool ownsHandle)
            : base(ownsHandle)
        {
        }
 
        protected override bool ReleaseHandle()
        {
            return FindClose(this);
        }
    }
 
    // The CharSet must match the CharSet of the corresponding PInvoke signature
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    public struct WIN32_FIND_DATA
    {
        public uint dwFileAttributes;
        public FILETIME ftCreationTime;
        public FILETIME ftLastAccessTime;
        public FILETIME ftLastWriteTime;
        public uint nFileSizeHigh;
        public uint nFileSizeLow;
        public uint dwReserved0;
        public uint dwReserved1;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
        public string cFileName;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 14)]
        public string cAlternateFileName;
    }
}