// GzipInputStream.cs
//
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;
using System.IO;

using ICSharpCode.SharpZipLib.Checksums;
using ICSharpCode.SharpZipLib.Zip.Compression;
using ICSharpCode.SharpZipLib.Zip.Compression.Streams;

namespace ICSharpCode.SharpZipLib.GZip 
{
	
	/// <summary>
	/// This filter stream is used to decompress a "GZIP" format stream.
	/// The "GZIP" format is described baseInputStream RFC 1952.
	/// 
	/// author of the original java version : John Leuner
	/// </summary>
	/// <example> This sample shows how to unzip a gzipped file
	/// <code>
	/// using System;
	/// using System.IO;
	/// 
	/// using ICSharpCode.SharpZipLib.Core;
	/// using ICSharpCode.SharpZipLib.GZip;
	/// 
	/// class MainClass
	/// {
	/// 	public static void Main(string[] args)
	/// 	{
	///			using (Stream inStream = new GZipInputStream(File.OpenRead(args[0])))
	///			using (FileStream outStream = File.Create(Path.GetFileNameWithoutExtension(args[0]))) {
	///				byte[] buffer = new byte[4096];
	///				StreamUtils.Copy(inStream, outStream, buffer);
	/// 		}
	/// 	}
	/// }	
	/// </code>
	/// </example>
	public class GZipInputStream : InflaterInputStream
	{
		#region Instance Fields
		/// <summary>
		/// CRC-32 value for uncompressed data
		/// </summary>
		protected Crc32 crc = new Crc32();
		
		/// <summary>
		/// Indicates end of stream
		/// </summary>
		protected bool eos;
		
		// Have we read the GZIP header yet?
		bool readGZIPHeader;
		#endregion

		#region Constructors
		/// <summary>
		/// Creates a GZipInputStream with the default buffer size
		/// </summary>
		/// <param name="baseInputStream">
		/// The stream to read compressed data from (baseInputStream GZIP format)
		/// </param>
		public GZipInputStream(Stream baseInputStream)
			: this(baseInputStream, 4096)
		{
		}
		
		/// <summary>
		/// Creates a GZIPInputStream with the specified buffer size
		/// </summary>
		/// <param name="baseInputStream">
		/// The stream to read compressed data from (baseInputStream GZIP format)
		/// </param>
		/// <param name="size">
		/// Size of the buffer to use
		/// </param>
		public GZipInputStream(Stream baseInputStream, int size)
			: base(baseInputStream, new Inflater(true), size)
		{
		}
		#endregion	

		#region Stream overrides
		/// <summary>
		/// Reads uncompressed data into an array of bytes
		/// </summary>
		/// <param name="buffer">
		/// The buffer to read uncompressed data into
		/// </param>
		/// <param name="offset">
		/// The offset indicating where the data should be placed
		/// </param>
		/// <param name="count">
		/// The number of uncompressed bytes to be read
		/// </param>
		/// <returns>Returns the number of bytes actually read.</returns>
		public override int Read(byte[] buffer, int offset, int count) 
		{
			// We first have to read the GZIP header, then we feed all the
			// rest of the data to the base class.
			//
			// As we do that we continually update the CRC32. Once the data is
			// finished, we check the CRC32
			//
			// This means we don't need our own buffer, as everything is done
			// in baseInputStream the superclass.
			if (!readGZIPHeader) {
				ReadHeader();
			}
			
			if (eos) {
				return 0;
			}
			
			// We don't have to read the header, so we just grab data from the superclass
			int bytesRead = base.Read(buffer, offset, count);
			if (bytesRead > 0) {
				crc.Update(buffer, offset, bytesRead);
			}
			
			if (inf.IsFinished) {
				ReadFooter();
			}
			return bytesRead;
		}
		#endregion	

		#region Support routines
		void ReadHeader() 
		{
			// 1. Check the two magic bytes
			Crc32 headCRC = new Crc32();
			int magic = baseInputStream.ReadByte();

			if (magic < 0) {
				throw new EndOfStreamException("EOS reading GZIP header");
			}

			headCRC.Update(magic);
			if (magic != (GZipConstants.GZIP_MAGIC >> 8)) {
				throw new GZipException("Error GZIP header, first magic byte doesn't match");
			}
				
			magic = baseInputStream.ReadByte();

			if (magic < 0) {
				throw new EndOfStreamException("EOS reading GZIP header");
			}
			
			if (magic != (GZipConstants.GZIP_MAGIC & 0xFF)) {
				throw new GZipException("Error GZIP header,  second magic byte doesn't match");
			}

			headCRC.Update(magic);
			
			// 2. Check the compression type (must be 8)
			int compressionType = baseInputStream.ReadByte();

			if ( compressionType < 0 ) {
				throw new EndOfStreamException("EOS reading GZIP header");
			}
		
			if ( compressionType != 8 ) {
				throw new GZipException("Error GZIP header, data not in deflate format");
			}
			headCRC.Update(compressionType);
			
			// 3. Check the flags
			int flags = baseInputStream.ReadByte();
			if (flags < 0) {
				throw new EndOfStreamException("EOS reading GZIP header");
			}
			headCRC.Update(flags);
			
			/*    This flag byte is divided into individual bits as follows:
				
				bit 0   FTEXT
				bit 1   FHCRC
				bit 2   FEXTRA
				bit 3   FNAME
				bit 4   FCOMMENT
				bit 5   reserved
				bit 6   reserved
				bit 7   reserved
			*/
				
			// 3.1 Check the reserved bits are zero
			
			if ((flags & 0xd0) != 0) {
				throw new GZipException("Reserved flag bits in GZIP header != 0");
			}
			
			// 4.-6. Skip the modification time, extra flags, and OS type
			for (int i=0; i< 6; i++) {
				int readByte = baseInputStream.ReadByte();
				if (readByte < 0) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}
				headCRC.Update(readByte);
			}
			
			// 7. Read extra field
			if ((flags & GZipConstants.FEXTRA) != 0) {
				// Skip subfield id
				for (int i=0; i< 2; i++) {
					int readByte = baseInputStream.ReadByte();
					if (readByte < 0) {
						throw new EndOfStreamException("EOS reading GZIP header");
					}
					headCRC.Update(readByte);
				}

				if (baseInputStream.ReadByte() < 0 || baseInputStream.ReadByte() < 0) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}
				
				int len1, len2;
				len1 = baseInputStream.ReadByte();
				len2 = baseInputStream.ReadByte();
				if ((len1 < 0) || (len2 < 0)) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}
				headCRC.Update(len1);
				headCRC.Update(len2);
				
				int extraLen = (len1 << 8) | len2;
				for (int i = 0; i < extraLen;i++) {
					int readByte = baseInputStream.ReadByte();
					if (readByte < 0) 
					{
						throw new EndOfStreamException("EOS reading GZIP header");
					}
					headCRC.Update(readByte);
				}
			}
			
			// 8. Read file name
			if ((flags & GZipConstants.FNAME) != 0) {
				int readByte;
				while ( (readByte = baseInputStream.ReadByte()) > 0) {
					headCRC.Update(readByte);
				}
				
				if (readByte < 0) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}
				headCRC.Update(readByte);
			}
			
			// 9. Read comment
			if ((flags & GZipConstants.FCOMMENT) != 0) {
				int readByte;
				while ( (readByte = baseInputStream.ReadByte()) > 0) {
					headCRC.Update(readByte);
				}
				
				if (readByte < 0) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}

				headCRC.Update(readByte);
			}
			
			// 10. Read header CRC
			if ((flags & GZipConstants.FHCRC) != 0) {
				int tempByte;
				int crcval = baseInputStream.ReadByte();
				if (crcval < 0) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}
				
				tempByte = baseInputStream.ReadByte();
				if (tempByte < 0) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}
				
				crcval = (crcval << 8) | tempByte;
				if (crcval != ((int) headCRC.Value & 0xffff)) {
					throw new GZipException("Header CRC value mismatch");
				}
			}
			
			readGZIPHeader = true;
		}
		
		void ReadFooter() 
		{
			byte[] footer = new byte[8];
			int avail = inf.RemainingInput;
			
			if (avail > 8) {
				avail = 8;
			}
			
			System.Array.Copy(inputBuffer.RawData, inputBuffer.RawLength - inf.RemainingInput, footer, 0, avail);
			int needed = 8 - avail;
			
			while (needed > 0) {
				int count = baseInputStream.Read(footer, 8 - needed, needed);
				if (count <= 0) {
					throw new EndOfStreamException("EOS reading GZIP footer");
				}
				needed -= count; // Jewel Jan 16
			}

			int crcval = (footer[0] & 0xff) | ((footer[1] & 0xff) << 8) | ((footer[2] & 0xff) << 16) | (footer[3] << 24);
			if (crcval != (int) crc.Value) {
				throw new GZipException("GZIP crc sum mismatch, theirs \"" + crcval + "\" and ours \"" + (int) crc.Value);
			}
			
			// NOTE The total here is the original total modulo 2 ^ 32.
			uint total = 
				(uint)((uint)footer[4] & 0xff) |
				(uint)(((uint)footer[5] & 0xff) << 8) |
				(uint)(((uint)footer[6] & 0xff) << 16) |
				(uint)((uint)footer[7] << 24);

			if ((inf.TotalOut & 0xffffffff) != total) {
				throw new GZipException("Number of bytes mismatch in footer");
			}
			
			// Should we support multiple gzip members.
			// Difficult, since there may be some bytes still in baseInputStream dataBuffer
			eos = true;
		}
		#endregion
	}
}