// ZipStorer, by Jaime Olivares

// Website: zipstorer.codeplex.com

// Version: 2.35 (March 14, 2010)



using System.Collections.Generic;

using System.Text;



namespace System.IO.Compression

{

    /// <summary>

    /// Unique class for compression/decompression file. Represents a Zip file.

    /// </summary>

    public class ZipStorer : IDisposable

    {

        /// <summary>

        /// Compression method enumeration

        /// </summary>

        public enum Compression : ushort { 

            /// <summary>Uncompressed storage</summary> 

            Store = 0, 

            /// <summary>Deflate compression method</summary>

            Deflate = 8 }



        /// <summary>

        /// Represents an entry in Zip file directory

        /// </summary>

        public struct ZipFileEntry

        {

            /// <summary>Compression method</summary>

            public Compression Method; 

            /// <summary>Full path and filename as stored in Zip</summary>

            public string FilenameInZip;

            /// <summary>Original file size</summary>

            public uint FileSize;

            /// <summary>Compressed file size</summary>

            public uint CompressedSize;

            /// <summary>Offset of header information inside Zip storage</summary>

            public uint HeaderOffset;

            /// <summary>Offset of file inside Zip storage</summary>

            public uint FileOffset;

            /// <summary>Size of header information</summary>

            public uint HeaderSize;

            /// <summary>32-bit checksum of entire file</summary>

            public uint Crc32;

            /// <summary>Last modification time of file</summary>

            public DateTime ModifyTime;

            /// <summary>User comment for file</summary>

            public string Comment;

            /// <summary>True if UTF8 encoding for filename and comments, false if default (CP 437)</summary>

            public bool EncodeUTF8;



            /// <summary>Overriden method</summary>

            /// <returns>Filename in Zip</returns>

            public override string ToString()

            {

                return this.FilenameInZip;

            }

        }



        #region Public fields

        /// <summary>True if UTF8 encoding for filename and comments, false if default (CP 437)</summary>

        public bool EncodeUTF8 = false;

        /// <summary>Force deflate algotithm even if it inflates the stored file. Off by default.</summary>

        public bool ForceDeflating = false;

        #endregion



        #region Private fields

        // List of files to store

        private List<ZipFileEntry> Files = new List<ZipFileEntry>();

        // Filename of storage file

        private string FileName;

        // Stream object of storage file

        private Stream ZipFileStream;

        // General comment

        private string Comment = "";

        // Central dir image

        private byte[] CentralDirImage = null;

        // Existing files in zip

        private ushort ExistingFiles = 0;

        // File access for Open method

        private FileAccess Access;

        // Static CRC32 Table

        private static UInt32[] CrcTable = null;

        // Default filename encoder

        private static Encoding DefaultEncoding = Encoding.GetEncoding(437);

        #endregion



        #region Public methods

        // Static constructor. Just invoked once in order to create the CRC32 lookup table.

        static ZipStorer()

        {

            // Generate CRC32 table

            CrcTable = new UInt32[256];

            for (int i = 0; i < CrcTable.Length; i++)

            {

                UInt32 c = (UInt32)i;

                for (int j = 0; j < 8; j++)

                {

                    if ((c & 1) != 0)

                        c = 3988292384 ^ (c >> 1);

                    else

                        c >>= 1;

                }

                CrcTable[i] = c;

            }

        }

        /// <summary>

        /// Method to create a new storage file

        /// </summary>

        /// <param name="_filename">Full path of Zip file to create</param>

        /// <param name="_comment">General comment for Zip file</param>

        /// <returns>A valid ZipStorer object</returns>

        public static ZipStorer Create(string _filename, string _comment)

        {

            Stream stream = new FileStream(_filename, FileMode.Create, FileAccess.ReadWrite);



            ZipStorer zip = Create(stream, _comment);

            zip.Comment = _comment;

            zip.FileName = _filename;



            return zip;

        }

        /// <summary>

        /// Method to create a new zip storage in a stream

        /// </summary>

        /// <param name="_stream"></param>

        /// <param name="_comment"></param>

        /// <returns>A valid ZipStorer object</returns>

        public static ZipStorer Create(Stream _stream, string _comment)

        {

            ZipStorer zip = new ZipStorer();

            zip.Comment = _comment;

            zip.ZipFileStream = _stream;

            zip.Access = FileAccess.Write;



            return zip;

        }

        /// <summary>

        /// Method to open an existing storage file

        /// </summary>

        /// <param name="_filename">Full path of Zip file to open</param>

        /// <param name="_access">File access mode as used in FileStream constructor</param>

        /// <returns>A valid ZipStorer object</returns>

        public static ZipStorer Open(string _filename, FileAccess _access)

        {

            Stream stream = (Stream)new FileStream(_filename, FileMode.Open, _access == FileAccess.Read ? FileAccess.Read : FileAccess.ReadWrite);



            ZipStorer zip = Open(stream, _access);

            zip.FileName = _filename;



            return zip;

        }

        /// <summary>

        /// Method to open an existing storage from stream

        /// </summary>

        /// <param name="_stream">Already opened stream with zip contents</param>

        /// <param name="_access">File access mode for stream operations</param>

        /// <returns>A valid ZipStorer object</returns>

        public static ZipStorer Open(Stream _stream, FileAccess _access)

        {

            if (!_stream.CanSeek && _access != FileAccess.Read)

                throw new InvalidOperationException("Stream cannot seek");



            ZipStorer zip = new ZipStorer();

            //zip.FileName = _filename;

            zip.ZipFileStream = _stream;

            zip.Access = _access;



            if (zip.ReadFileInfo())

                return zip;



            throw new System.IO.InvalidDataException();

        }

        /// <summary>

        /// Add full contents of a file into the Zip storage

        /// </summary>

        /// <param name="_method">Compression method</param>

        /// <param name="_pathname">Full path of file to add to Zip storage</param>

        /// <param name="_filenameInZip">Filename and path as desired in Zip directory</param>

        /// <param name="_comment">Comment for stored file</param>        

        public void AddFile(Compression _method, string _pathname, string _filenameInZip, string _comment)

        {

            if (Access == FileAccess.Read)

                throw new InvalidOperationException("Writing is not alowed");



            FileStream stream = new FileStream(_pathname, FileMode.Open, FileAccess.Read);

            AddStream(_method, _filenameInZip, stream, File.GetLastWriteTime(_pathname), _comment);

            stream.Close();

        }

        /// <summary>

        /// Add full contents of a stream into the Zip storage

        /// </summary>

        /// <param name="_method">Compression method</param>

        /// <param name="_filenameInZip">Filename and path as desired in Zip directory</param>

        /// <param name="_source">Stream object containing the data to store in Zip</param>

        /// <param name="_modTime">Modification time of the data to store</param>

        /// <param name="_comment">Comment for stored file</param>

        public void AddStream(Compression _method, string _filenameInZip, Stream _source, DateTime _modTime, string _comment)

        {

            if (Access == FileAccess.Read)

                throw new InvalidOperationException("Writing is not alowed");



            long offset;

            if (this.Files.Count==0)

                offset = 0;

            else

            {

                ZipFileEntry last = this.Files[this.Files.Count-1];

                offset = last.HeaderOffset + last.HeaderSize;

            }



            // Prepare the fileinfo

            ZipFileEntry zfe = new ZipFileEntry();

            zfe.Method = _method;

            zfe.EncodeUTF8 = this.EncodeUTF8;

            zfe.FilenameInZip = NormalizedFilename(_filenameInZip);

            zfe.Comment = (_comment == null ? "" : _comment);



            // Even though we write the header now, it will have to be rewritten, since we don't know compressed size or crc.

            zfe.Crc32 = 0;  // to be updated later

            zfe.HeaderOffset = (uint)this.ZipFileStream.Position;  // offset within file of the start of this local record

            zfe.ModifyTime = _modTime;



            // Write local header

            WriteLocalHeader(ref zfe);

            zfe.FileOffset = (uint)this.ZipFileStream.Position;



            // Write file to zip (store)

            Store(ref zfe, _source);

            _source.Close();



            this.UpdateCrcAndSizes(ref zfe);



            Files.Add(zfe);

        }

        /// <summary>

        /// Updates central directory (if pertinent) and close the Zip storage

        /// </summary>

        /// <remarks>This is a required step, unless automatic dispose is used</remarks>

        public void Close()

        {

            if (this.Access != FileAccess.Read)

            {

                uint centralOffset = (uint)this.ZipFileStream.Position;

                uint centralSize = 0;



                if (this.CentralDirImage != null)

                    this.ZipFileStream.Write(CentralDirImage, 0, CentralDirImage.Length);



                for (int i = 0; i < Files.Count; i++)

                {

                    long pos = this.ZipFileStream.Position;

                    this.WriteCentralDirRecord(Files[i]);

                    centralSize += (uint)(this.ZipFileStream.Position - pos);

                }



                if (this.CentralDirImage != null)

                    this.WriteEndRecord(centralSize + (uint)CentralDirImage.Length, centralOffset);

                else

                    this.WriteEndRecord(centralSize, centralOffset);

            }



            if (this.ZipFileStream != null)

            {

                this.ZipFileStream.Flush();

                this.ZipFileStream.Dispose();

                this.ZipFileStream = null;

            }

        }

        /// <summary>

        /// Read all the file records in the central directory 

        /// </summary>

        /// <returns>List of all entries in directory</returns>

        public List<ZipFileEntry> ReadCentralDir()

        {

            if (this.CentralDirImage == null)

                throw new InvalidOperationException("Central directory currently does not exist");



            List<ZipFileEntry> result = new List<ZipFileEntry>();



            for (int pointer = 0; pointer < this.CentralDirImage.Length; )

            {

                uint signature = BitConverter.ToUInt32(CentralDirImage, pointer);

                if (signature != 0x02014b50)

                    break;



                bool encodeUTF8 = (BitConverter.ToUInt16(CentralDirImage, pointer + 8) & 0x0800) != 0;

                ushort method = BitConverter.ToUInt16(CentralDirImage, pointer + 10);

                uint modifyTime = BitConverter.ToUInt32(CentralDirImage, pointer + 12);

                uint crc32 = BitConverter.ToUInt32(CentralDirImage, pointer + 16);

                uint comprSize = BitConverter.ToUInt32(CentralDirImage, pointer + 20);

                uint fileSize = BitConverter.ToUInt32(CentralDirImage, pointer + 24);

                ushort filenameSize = BitConverter.ToUInt16(CentralDirImage, pointer + 28);

                ushort extraSize = BitConverter.ToUInt16(CentralDirImage, pointer + 30);

                ushort commentSize = BitConverter.ToUInt16(CentralDirImage, pointer + 32);

                uint headerOffset = BitConverter.ToUInt32(CentralDirImage, pointer + 42);

                uint headerSize = (uint)( 46 + filenameSize + extraSize + commentSize);



                Encoding encoder = encodeUTF8 ? Encoding.UTF8 : DefaultEncoding;



                ZipFileEntry zfe = new ZipFileEntry();

                zfe.Method = (Compression)method;

                zfe.FilenameInZip = encoder.GetString(CentralDirImage, pointer + 46, filenameSize);

                zfe.FileOffset = GetFileOffset(headerOffset);

                zfe.FileSize = fileSize;

                zfe.CompressedSize = comprSize;

                zfe.HeaderOffset = headerOffset;

                zfe.HeaderSize = headerSize;

                zfe.Crc32 = crc32;

                zfe.ModifyTime = DosTimeToDateTime(modifyTime);

                if (commentSize > 0)

                    zfe.Comment = encoder.GetString(CentralDirImage, pointer + 46 + filenameSize + extraSize, commentSize);



                result.Add(zfe);

                pointer += (46 + filenameSize + extraSize + commentSize);

            }



            return result;

        }

        /// <summary>

        /// Copy the contents of a stored file into a physical file

        /// </summary>

        /// <param name="_zfe">Entry information of file to extract</param>

        /// <param name="_filename">Name of file to store uncompressed data</param>

        /// <returns>True if success, false if not.</returns>

        /// <remarks>Unique compression methods are Store and Deflate</remarks>

        public bool ExtractFile(ZipFileEntry _zfe, string _filename)

        {

            // Make sure the parent directory exist

            string path = System.IO.Path.GetDirectoryName(_filename);



            if (!Directory.Exists(path))

                Directory.CreateDirectory(path);

            // Check it is directory. If so, do nothing

            if (Directory.Exists(_filename))

                return true;



            Stream output = new FileStream(_filename, FileMode.Create, FileAccess.Write);

            bool result = ExtractFile(_zfe, output);

            if (result)

                output.Close();



            File.SetCreationTime(_filename, _zfe.ModifyTime);

            File.SetLastWriteTime(_filename, _zfe.ModifyTime);

            

            return result;

        }

        /// <summary>

        /// Copy the contents of a stored file into an opened stream

        /// </summary>

        /// <param name="_zfe">Entry information of file to extract</param>

        /// <param name="_stream">Stream to store the uncompressed data</param>

        /// <returns>True if success, false if not.</returns>

        /// <remarks>Unique compression methods are Store and Deflate</remarks>

        public bool ExtractFile(ZipFileEntry _zfe, Stream _stream)

        {

            if (!_stream.CanWrite)

                throw new InvalidOperationException("Stream cannot be written");



            // check signature

            byte[] signature = new byte[4];

            this.ZipFileStream.Seek(_zfe.HeaderOffset, SeekOrigin.Begin);

            this.ZipFileStream.Read(signature, 0, 4);

            if (BitConverter.ToUInt32(signature, 0) != 0x04034b50)

                return false;



            // Select input stream for inflating or just reading

            Stream inStream;

            if (_zfe.Method == Compression.Store)

                inStream = this.ZipFileStream;

            else if (_zfe.Method == Compression.Deflate)

                inStream = new DeflateStream(this.ZipFileStream, CompressionMode.Decompress, true);

            else

                return false;



            // Buffered copy

            byte[] buffer = new byte[16384];

            this.ZipFileStream.Seek(_zfe.FileOffset, SeekOrigin.Begin);

            uint bytesPending = _zfe.FileSize;

            while (bytesPending > 0)

            {

                int bytesRead = inStream.Read(buffer, 0, (int)Math.Min(bytesPending, buffer.Length));

                _stream.Write(buffer, 0, bytesRead);

                bytesPending -= (uint)bytesRead;

            }

            _stream.Flush();



            if (_zfe.Method == Compression.Deflate)

                inStream.Dispose();

            return true;

        }

        /// <summary>

        /// Removes one of many files in storage. It creates a new Zip file.

        /// </summary>

        /// <param name="_zip">Reference to the current Zip object</param>

        /// <param name="_zfes">List of Entries to remove from storage</param>

        /// <returns>True if success, false if not</returns>

        /// <remarks>This method only works for storage of type FileStream</remarks>

        public static bool RemoveEntries(ref ZipStorer _zip, List<ZipFileEntry> _zfes)

        {

            if (!(_zip.ZipFileStream is FileStream))

                throw new InvalidOperationException("RemoveEntries is allowed just over streams of type FileStream");





            //Get full list of entries

            List<ZipFileEntry> fullList = _zip.ReadCentralDir();



            //In order to delete we need to create a copy of the zip file excluding the selected items

            string tempZipName = Path.GetTempFileName();

            string tempEntryName = Path.GetTempFileName();



            try

            {

                ZipStorer tempZip = ZipStorer.Create(tempZipName, string.Empty);



                foreach (ZipFileEntry zfe in fullList)

                {

                    if (!_zfes.Contains(zfe))

                    {

                        if (_zip.ExtractFile(zfe, tempEntryName))

                        {

                            tempZip.AddFile(zfe.Method, tempEntryName, zfe.FilenameInZip, zfe.Comment);

                        }

                    }

                }

                _zip.Close();

                tempZip.Close();



                File.Delete(_zip.FileName);

                File.Move(tempZipName, _zip.FileName);



                _zip = ZipStorer.Open(_zip.FileName, _zip.Access);

            }

            catch

            {

                return false;

            }

            finally

            {

                if (File.Exists(tempZipName))

                    File.Delete(tempZipName);

                if (File.Exists(tempEntryName))

                    File.Delete(tempEntryName);

            }

            return true;

        }

        #endregion



        #region Private methods

        // Calculate the file offset by reading the corresponding local header

        private uint GetFileOffset(uint _headerOffset)

        {

            byte[] buffer = new byte[2];



            this.ZipFileStream.Seek(_headerOffset + 26, SeekOrigin.Begin);

            this.ZipFileStream.Read(buffer, 0, 2);

            ushort filenameSize = BitConverter.ToUInt16(buffer, 0);

            this.ZipFileStream.Read(buffer, 0, 2);

            ushort extraSize = BitConverter.ToUInt16(buffer, 0);



            return (uint)(30 + filenameSize + extraSize + _headerOffset);

        }

        /* Local file header:

            local file header signature     4 bytes  (0x04034b50)

            version needed to extract       2 bytes

            general purpose bit flag        2 bytes

            compression method              2 bytes

            last mod file time              2 bytes

            last mod file date              2 bytes

            crc-32                          4 bytes

            compressed size                 4 bytes

            uncompressed size               4 bytes

            filename length                 2 bytes

            extra field length              2 bytes



            filename (variable size)

            extra field (variable size)

        */

        private void WriteLocalHeader(ref ZipFileEntry _zfe)

        {

            long pos = this.ZipFileStream.Position;

            Encoding encoder = _zfe.EncodeUTF8 ? Encoding.UTF8 : DefaultEncoding;

            byte[] encodedFilename = encoder.GetBytes(_zfe.FilenameInZip);



            this.ZipFileStream.Write(new byte[] { 80, 75, 3, 4, 20, 0}, 0, 6); // No extra header

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)(_zfe.EncodeUTF8 ? 0x0800 : 0)), 0, 2); // filename and comment encoding 

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)_zfe.Method), 0, 2);  // zipping method

            this.ZipFileStream.Write(BitConverter.GetBytes(DateTimeToDosTime(_zfe.ModifyTime)), 0, 4); // zipping date and time

            this.ZipFileStream.Write(new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, 0, 12); // unused CRC, un/compressed size, updated later

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)encodedFilename.Length), 0, 2); // filename length

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)0), 0, 2); // extra length



            this.ZipFileStream.Write(encodedFilename, 0, encodedFilename.Length);

            _zfe.HeaderSize = (uint)(this.ZipFileStream.Position - pos);

        }

        /* Central directory's File header:

            central file header signature   4 bytes  (0x02014b50)

            version made by                 2 bytes

            version needed to extract       2 bytes

            general purpose bit flag        2 bytes

            compression method              2 bytes

            last mod file time              2 bytes

            last mod file date              2 bytes

            crc-32                          4 bytes

            compressed size                 4 bytes

            uncompressed size               4 bytes

            filename length                 2 bytes

            extra field length              2 bytes

            file comment length             2 bytes

            disk number start               2 bytes

            internal file attributes        2 bytes

            external file attributes        4 bytes

            relative offset of local header 4 bytes



            filename (variable size)

            extra field (variable size)

            file comment (variable size)

        */

        private void WriteCentralDirRecord(ZipFileEntry _zfe)

        {

            Encoding encoder = _zfe.EncodeUTF8 ? Encoding.UTF8 : DefaultEncoding;

            byte[] encodedFilename = encoder.GetBytes(_zfe.FilenameInZip);

            byte[] encodedComment = encoder.GetBytes(_zfe.Comment);



            this.ZipFileStream.Write(new byte[] { 80, 75, 1, 2, 23, 0xB, 20, 0 }, 0, 8);

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)(_zfe.EncodeUTF8 ? 0x0800 : 0)), 0, 2); // filename and comment encoding 

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)_zfe.Method), 0, 2);  // zipping method

            this.ZipFileStream.Write(BitConverter.GetBytes(DateTimeToDosTime(_zfe.ModifyTime)), 0, 4);  // zipping date and time

            this.ZipFileStream.Write(BitConverter.GetBytes(_zfe.Crc32), 0, 4); // file CRC

            this.ZipFileStream.Write(BitConverter.GetBytes(_zfe.CompressedSize), 0, 4); // compressed file size

            this.ZipFileStream.Write(BitConverter.GetBytes(_zfe.FileSize), 0, 4); // uncompressed file size

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)encodedFilename.Length), 0, 2); // Filename in zip

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)0), 0, 2); // extra length

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)encodedComment.Length), 0, 2);



            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)0), 0, 2); // disk=0

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)0), 0, 2); // file type: binary

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)0), 0, 2); // Internal file attributes

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)0x8100), 0, 2); // External file attributes (normal/readable)

            this.ZipFileStream.Write(BitConverter.GetBytes(_zfe.HeaderOffset), 0, 4);  // Offset of header



            this.ZipFileStream.Write(encodedFilename, 0, encodedFilename.Length);

            this.ZipFileStream.Write(encodedComment, 0, encodedComment.Length);

        }

        /* End of central dir record:

            end of central dir signature    4 bytes  (0x06054b50)

            number of this disk             2 bytes

            number of the disk with the

            start of the central directory  2 bytes

            total number of entries in

            the central dir on this disk    2 bytes

            total number of entries in

            the central dir                 2 bytes

            size of the central directory   4 bytes

            offset of start of central

            directory with respect to

            the starting disk number        4 bytes

            zipfile comment length          2 bytes

            zipfile comment (variable size)

        */

        private void WriteEndRecord(uint _size, uint _offset)

        {

            Encoding encoder = this.EncodeUTF8 ? Encoding.UTF8 : DefaultEncoding;

            byte[] encodedComment = encoder.GetBytes(this.Comment);



            this.ZipFileStream.Write(new byte[] { 80, 75, 5, 6, 0, 0, 0, 0 }, 0, 8);

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)Files.Count+ExistingFiles), 0, 2);

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)Files.Count+ExistingFiles), 0, 2);

            this.ZipFileStream.Write(BitConverter.GetBytes(_size), 0, 4);

            this.ZipFileStream.Write(BitConverter.GetBytes(_offset), 0, 4);

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)encodedComment.Length), 0, 2);

            this.ZipFileStream.Write(encodedComment, 0, encodedComment.Length);

        }

        // Copies all source file into storage file

        private void Store(ref ZipFileEntry _zfe, Stream _source)

        {

            byte[] buffer = new byte[16384];

            int bytesRead;

            uint totalRead = 0;

            Stream outStream;



            long posStart = this.ZipFileStream.Position;

            long sourceStart = _source.Position;



            if (_zfe.Method == Compression.Store)

                outStream = this.ZipFileStream;

            else

                outStream = new DeflateStream(this.ZipFileStream, CompressionMode.Compress, true);



            _zfe.Crc32 = 0 ^ 0xffffffff;

            

            do

            {

                bytesRead = _source.Read(buffer, 0, buffer.Length);

                totalRead += (uint)bytesRead;

                if (bytesRead > 0)

                {

                    outStream.Write(buffer, 0, bytesRead);



                    for (uint i = 0; i < bytesRead; i++)

                    {

                        _zfe.Crc32 = ZipStorer.CrcTable[(_zfe.Crc32 ^ buffer[i]) & 0xFF] ^ (_zfe.Crc32 >> 8);

                    }

                }

            } while (bytesRead == buffer.Length);

            outStream.Flush();



            if (_zfe.Method == Compression.Deflate)

                outStream.Dispose();



            _zfe.Crc32 ^= 0xffffffff;

            _zfe.FileSize = totalRead;

            _zfe.CompressedSize = (uint)(this.ZipFileStream.Position - posStart);



            // Verify for real compression

            if (_zfe.Method == Compression.Deflate && !this.ForceDeflating && _source.CanSeek && _zfe.CompressedSize > _zfe.FileSize)

            {

                // Start operation again with Store algorithm

                _zfe.Method = Compression.Store;

                this.ZipFileStream.Position = posStart;

                this.ZipFileStream.SetLength(posStart);

                _source.Position = sourceStart;

                this.Store(ref _zfe, _source);

            }

        }

        /* DOS Date and time:

            MS-DOS date. The date is a packed value with the following format. Bits Description 

                0-4 Day of the month (1&#x2013;31) 

                5-8 Month (1 = January, 2 = February, and so on) 

                9-15 Year offset from 1980 (add 1980 to get actual year) 

            MS-DOS time. The time is a packed value with the following format. Bits Description 

                0-4 Second divided by 2 

                5-10 Minute (0&#x2013;59) 

                11-15 Hour (0&#x2013;23 on a 24-hour clock) 

        */

        private uint DateTimeToDosTime(DateTime _dt)

        {

            return (uint)(

                (_dt.Second / 2) | (_dt.Minute << 5) | (_dt.Hour << 11) | 

                (_dt.Day<<16) | (_dt.Month << 21) | ((_dt.Year - 1980) << 25));

        }

        private DateTime DosTimeToDateTime(uint _dt)

        {

            return new DateTime(

                (int)(_dt >> 25) + 1980,

                (int)(_dt >> 21) & 15,

                (int)(_dt >> 16) & 31,

                (int)(_dt >> 11) & 31,

                (int)(_dt >> 5) & 63,

                (int)(_dt & 31) * 2);

        }



        /* CRC32 algorithm

          The 'magic number' for the CRC is 0xdebb20e3.  

          The proper CRC pre and post conditioning

          is used, meaning that the CRC register is

          pre-conditioned with all ones (a starting value

          of 0xffffffff) and the value is post-conditioned by

          taking the one's complement of the CRC residual.

          If bit 3 of the general purpose flag is set, this

          field is set to zero in the local header and the correct

          value is put in the data descriptor and in the central

          directory.

        */

        private void UpdateCrcAndSizes(ref ZipFileEntry _zfe)

        {

            long lastPos = this.ZipFileStream.Position;  // remember position



            this.ZipFileStream.Position = _zfe.HeaderOffset + 8;

            this.ZipFileStream.Write(BitConverter.GetBytes((ushort)_zfe.Method), 0, 2);  // zipping method



            this.ZipFileStream.Position = _zfe.HeaderOffset + 14;

            this.ZipFileStream.Write(BitConverter.GetBytes(_zfe.Crc32), 0, 4);  // Update CRC

            this.ZipFileStream.Write(BitConverter.GetBytes(_zfe.CompressedSize), 0, 4);  // Compressed size

            this.ZipFileStream.Write(BitConverter.GetBytes(_zfe.FileSize), 0, 4);  // Uncompressed size



            this.ZipFileStream.Position = lastPos;  // restore position

        }

        // Replaces backslashes with slashes to store in zip header

        private string NormalizedFilename(string _filename)

        {

            string filename = _filename.Replace('\\', '/');



            int pos = filename.IndexOf(':');

            if (pos >= 0)

                filename = filename.Remove(0, pos + 1);



            return filename.Trim('/');

        }

        // Reads the end-of-central-directory record

        private bool ReadFileInfo()

        {

            if (this.ZipFileStream.Length < 22)

                return false;



            try

            {

                this.ZipFileStream.Seek(-17, SeekOrigin.End);

                BinaryReader br = new BinaryReader(this.ZipFileStream);

                do

                {

                    this.ZipFileStream.Seek(-5, SeekOrigin.Current);

                    UInt32 sig = br.ReadUInt32();

                    if (sig == 0x06054b50)

                    {

                        this.ZipFileStream.Seek(6, SeekOrigin.Current);



                        UInt16 entries = br.ReadUInt16();

                        Int32 centralSize = br.ReadInt32();

                        UInt32 centralDirOffset = br.ReadUInt32();

                        UInt16 commentSize = br.ReadUInt16();



                        // check if comment field is the very last data in file

                        if (this.ZipFileStream.Position + commentSize != this.ZipFileStream.Length)

                            return false;



                        // Copy entire central directory to a memory buffer

                        this.ExistingFiles = entries;

                        this.CentralDirImage = new byte[centralSize];

                        this.ZipFileStream.Seek(centralDirOffset, SeekOrigin.Begin);

                        this.ZipFileStream.Read(this.CentralDirImage, 0, centralSize);



                        // Leave the pointer at the begining of central dir, to append new files

                        this.ZipFileStream.Seek(centralDirOffset, SeekOrigin.Begin);

                        return true;

                    }

                } while (this.ZipFileStream.Position > 0);

            }

            catch { }



            return false;

        }

        #endregion



        #region IDisposable Members

        /// <summary>

        /// Closes the Zip file stream

        /// </summary>

        public void Dispose()

        {

            this.Close();

        }

        #endregion

    }

}