// ZipStorer, by Jaime Olivares
// Website: zipstorer.codeplex.com
// Version: 2.35 (March 14, 2010)

// Simplified to extract-only by Nikse - August 18, 2010

using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;
using System.Text;

namespace Nikse.SubtitleEdit.Core
{
    /// <summary>
    /// Zip archive decompression. Represents a Zip file.
    /// </summary>
    public class ZipExtractor : 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 Public fields

        #region Private fields

        // Stream object of storage file
        private Stream ZipFileStream;
        // Central dir image
        private byte[] CentralDirImage = null;
        // Static CRC32 Table
        private static UInt32[] CrcTable = null;
        // Default filename encoder
        private static Encoding DefaultEncoding = Encoding.GetEncoding(437);

        #endregion Private fields

        #region Public methods

        // Static constructor. Just invoked once in order to create the CRC32 lookup table.
        static ZipExtractor()
        {
            // 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 open an existing storage file
        /// </summary>
        /// <param name="filename">Full path of Zip file to open</param>
        /// <returns>A valid ZipStorer object</returns>
        public static ZipExtractor Open(string filename)
        {
            Stream stream = new FileStream(filename, FileMode.Open, FileAccess.Read);
            ZipExtractor zip = Open(stream);
            return zip;
        }

        /// <summary>
        /// Method to open an existing storage from stream
        /// </summary>
        /// <param name="stream">Already opened stream with zip contents</param>
        /// <returns>A valid ZipStorer object</returns>
        public static ZipExtractor Open(Stream stream)
        {
            ZipExtractor zip = new ZipExtractor();
            zip.ZipFileStream = stream;

            if (zip.ReadFileInfo())
                return zip;

            throw new System.IO.InvalidDataException();
        }

        /// <summary>
        /// Close the Zip storage
        /// </summary>
        /// <remarks>This is a required step, unless automatic dispose is used</remarks>
        public void Close()
        {
            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;

            bool result = false;
            using (Stream output = new FileStream(filename, FileMode.Create, FileAccess.Write))
            {
                result = ExtractFile(zfe, output);
            }
            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;
        }

        #endregion Public methods

        #region Private methods

        /// <summary>
        /// Calculate the file offset by reading the corresponding local header
        /// </summary>
        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)
        */

        /* 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)

         *
        /* 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)
        */

        /* 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 (1–31)
                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 (0–59)
                11-15 Hour (0–23 on a 24-hour clock)
        */

        private static 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);
        }

        // 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.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 Private methods

        #region IDisposable Members

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                this.Close();
            }
        }

        #endregion IDisposable Members
    }
}