//------------------------------------------------------------------------------
// <copyright file="FileEnumerator.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>                                                                
//------------------------------------------------------------------------------

/*
 * FileEnumerator class
 * 
 * Copyright (c) 2003 Microsoft Corporation
 *
 * Class to efficiently enumerate the files in a directory.  The only thing the framework provides
 * to do this is Directory.GetFiles(), which is unusable on large directories because it returns an
 * array containing all the file names at once (huge memory allocation).
 *
 * An efficient alternative is to use FindFirstFile/FindNextFile, which works but requires a lot
 * more code.  Also, it makes our code base harder to port to non-windows platforms.
 *
 * This FileEnumerator class solves both problem, by providing a simple and efficient wrapper.
 * By working with a single object, it is almost as efficient as calling FindFirstFile/FindNextFile,
 * but is much easier to use.  e.g. instead of:
 *
 *      UnsafeNativeMethods.WIN32_FIND_DATA wfd;
 *      IntPtr hFindFile = UnsafeNativeMethods.FindFirstFile(physicalDir + @"\*.*", out wfd);
 *
 *      if (hFindFile == INVALID_HANDLE_VALUE)
 *          return;
 *
 *      try {
 *          for (bool more=true; more; more=UnsafeNativeMethods.FindNextFile(hFindFile, out wfd)) {
 *
 *              // Skip false directories
 *              if (wfd.cFileName == "." || wfd.cFileName == "..")
 *                  continue;
 *              
 *              string fullPath = Path.Combine(physicalDir, wfd.cFileName);
 *
 *              ProcessFile(fullPath);
 *          }
 *      }
 *      finally {
 *          UnsafeNativeMethods.FindClose(hFindFile);
 *      }
 *
 * we can simply write
 *
 *      foreach (FileData fileData in FileEnumerator.Create(physicalDir)) {
 *          ProcessFile(fileData.FullName);
 *      }
 */


namespace System.Web.Util {

using System.IO;
using System.Collections;

/*
 * This is a somewhat artificial base class for FileEnumerator.  The main reason
 * for it is to allow user code to be more readable, by looking like:
 *      foreach (FileData fileData in FileEnumerator.Create(path)) { ... }
 * instead of
 *      foreach (FileEnumerator fileData in FileEnumerator.Create(path)) { ... }
 */
internal abstract class FileData {

    protected string _path;
    protected UnsafeNativeMethods.WIN32_FIND_DATA _wfd;

    internal string Name {
        get { return _wfd.cFileName; }
    }

    internal string FullName {
        get { return _path + @"\" + _wfd.cFileName; }
    }

    internal bool IsDirectory {
        get { return (_wfd.dwFileAttributes & UnsafeNativeMethods.FILE_ATTRIBUTE_DIRECTORY) != 0; }
    }

    internal bool IsHidden {
        get { return (_wfd.dwFileAttributes & UnsafeNativeMethods.FILE_ATTRIBUTE_HIDDEN) != 0; }
    }

    internal FindFileData GetFindFileData() {
        return new FindFileData(ref _wfd);
    }
}

internal class FileEnumerator: FileData, IEnumerable, IEnumerator, IDisposable {
    private IntPtr _hFindFile = UnsafeNativeMethods.INVALID_HANDLE_VALUE;

    internal static FileEnumerator Create(string path) {
        return new FileEnumerator(path);
    }

    private FileEnumerator(string path) {
        _path = Path.GetFullPath(path);
    }

    ~FileEnumerator() {
        ((IDisposable)this).Dispose();
    }

    // Should the current file be excluded from the enumeration
    private bool SkipCurrent() {
    
        // Skip false directories
        if (_wfd.cFileName == "." || _wfd.cFileName == "..")
            return true;

        return false;
    }

    // We just return ourselves for the enumerator, to avoid creating a new object
    IEnumerator IEnumerable.GetEnumerator() {
        return this;
    }

    bool IEnumerator.MoveNext() {

        for (;;) {
            if (_hFindFile == UnsafeNativeMethods.INVALID_HANDLE_VALUE) {
                _hFindFile = UnsafeNativeMethods.FindFirstFile(_path + @"\*.*", out _wfd);
                
                // Empty enumeration case
                if (_hFindFile == UnsafeNativeMethods.INVALID_HANDLE_VALUE)
                    return false;
            }
            else {
                bool hasMoreFiles = UnsafeNativeMethods.FindNextFile(_hFindFile, out _wfd);
                if (!hasMoreFiles)
                    return false;
            }
            
            if (!SkipCurrent())
                return true;
        }
    }

    // The current object of the enumeration is always ourselves.  No new object created.
    object IEnumerator.Current {
        get { return this; }
    }

    void IEnumerator.Reset() {
        // We don't support reset, though it would be easy to add if needed
        throw new InvalidOperationException();
    }

    void IDisposable.Dispose() {
        if (_hFindFile != UnsafeNativeMethods.INVALID_HANDLE_VALUE) {
            UnsafeNativeMethods.FindClose(_hFindFile);
            _hFindFile = UnsafeNativeMethods.INVALID_HANDLE_VALUE;
        }
        System.GC.SuppressFinalize(this);
    }
}

}