#region PDFsharp - A .NET library for processing PDF
//
// Authors:
//   Stefan Lange (mailto:Stefan.Lange@pdfsharp.com)
//
// Copyright (c) 2005-2008 empira Software GmbH, Cologne (Germany)
//
// http://www.pdfsharp.com
// http://sourceforge.net/projects/pdfsharp
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
// DEALINGS IN THE SOFTWARE.
#endregion

using System;
using System.Diagnostics;
using System.Text;
using System.IO;
#if NET_ZIP
using System.IO.Compression;
#else
using PdfSharp.SharpZipLib.Zip.Compression;
using PdfSharp.SharpZipLib.Zip.Compression.Streams;
#endif

namespace PdfSharp.Pdf.Filters
{
  /// <summary>
  /// Implements the FlateDecode filter by wrapping SharpZipLib.
  /// </summary>
  public class FlateDecode : Filter
  {
    /// <summary>
    /// Encodes the specified data.
    /// </summary>
    public override byte[] Encode(byte[] data)
    {
      MemoryStream ms = new MemoryStream();

      // DeflateStream/GZipStream does not work immediately and I have not the leisure to work it out.
      // So I keep on using SharpZipLib even with .NET 2.0.
#if NET_ZIP
      // See http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=97064
      // 
      // Excerpt from the RFC 1950 specs for first byte:
      //
      // CMF (Compression Method and flags)
      //    This byte is divided into a 4-bit compression method and a 4-
      //    bit information field depending on the compression method.
      //
      //      bits 0 to 3  CM     Compression method
      //      bits 4 to 7  CINFO  Compression info
      //
      // CM (Compression method)
      //    This identifies the compression method used in the file. CM = 8
      //    denotes the "deflate" compression method with a window size up
      //    to 32K.  This is the method used by gzip and PNG (see
      //    references [1] and [2] in Chapter 3, below, for the reference
      //    documents).  CM = 15 is reserved.  It might be used in a future
      //    version of this specification to indicate the presence of an
      //    extra field before the compressed data.
      //
      // CINFO (Compression info)
      //    For CM = 8, CINFO is the base-2 logarithm of the LZ77 window
      //    size, minus eight (CINFO=7 indicates a 32K window size). Values
      //    of CINFO above 7 are not allowed in this version of the
      //    specification.  CINFO is not defined in this specification for
      //    CM not equal to 8.
      ms.WriteByte(0x78);

      // Excerpt from the RFC 1950 specs for second byte:
      //
      // FLG (FLaGs)
      //    This flag byte is divided as follows:
      //
      //       bits 0 to 4  FCHECK  (check bits for CMF and FLG)
      //       bit  5       FDICT   (preset dictionary)
      //       bits 6 to 7  FLEVEL  (compression level)
      //
      //    The FCHECK value must be such that CMF and FLG, when viewed as
      //    a 16-bit unsigned integer stored in MSB order (CMF*256 + FLG),
      //    is a multiple of 31.
      //
      // FDICT (Preset dictionary)
      //    If FDICT is set, a DICT dictionary identifier is present
      //    immediately after the FLG byte. The dictionary is a sequence of
      //    bytes which are initially fed to the compressor without
      //    producing any compressed output. DICT is the Adler-32 checksum
      //    of this sequence of bytes (see the definition of ADLER32
      //    below).  The decompressor can use this identifier to determine
      //    which dictionary has been used by the compressor.
      //
      // FLEVEL (Compression level)
      //    These flags are available for use by specific compression
      //    methods.  The "deflate" method (CM = 8) sets these flags as
      //    follows:
      //
      //       0 - compressor used fastest algorithm
      //       1 - compressor used fast algorithm
      //       2 - compressor used default algorithm
      //       3 - compressor used maximum compression, slowest algorithm
      //
      //    The information in FLEVEL is not needed for decompression; it
      //    is there to indicate if recompression might be worthwhile.
      ms.WriteByte(0x49);

      DeflateStream zip = new DeflateStream(ms, CompressionMode.Compress, true);
      zip.Write(data, 0, data.Length);
      zip.Close();
#else
      DeflaterOutputStream zip = new DeflaterOutputStream(ms, new Deflater(Deflater.DEFAULT_COMPRESSION, false));
      zip.Write(data, 0, data.Length);
      zip.Finish();
#endif
      ms.Capacity = (int)ms.Length;
      return ms.GetBuffer();
    }

    /// <summary>
    /// Decodes the specified data.
    /// </summary>
    public override byte[] Decode(byte[] data, FilterParms parms)
    {
      MemoryStream msInput = new MemoryStream(data);
      MemoryStream msOutput = new MemoryStream();
#if NET_ZIP
      // See http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=97064
      // It seems to work when skipping the first two bytes.
      byte header;   // 0x30 0x59
      header = (byte)msInput.ReadByte();
      //Debug.Assert(header == 48);
      header = (byte)msInput.ReadByte();
      //Debug.Assert(header == 89);
      DeflateStream zip = new DeflateStream(msInput, CompressionMode.Decompress, true);
      int cbRead;
      byte[] abResult = new byte[1024];
      do
      {
        cbRead = zip.Read(abResult, 0, abResult.Length);
        if (cbRead > 0)
          msOutput.Write(abResult, 0, cbRead);
      }
      while (cbRead > 0);
      zip.Close();
      msOutput.Flush();
      if (msOutput.Length >= 0)
      {
        msOutput.Capacity = (int)msOutput.Length;
        return msOutput.GetBuffer();
      }
      return null;
#else
      InflaterInputStream iis = new InflaterInputStream(msInput, new Inflater(false));
      int cbRead;
      byte[] abResult = new byte[32768];
      do
      {
        cbRead = iis.Read(abResult, 0, abResult.Length);
        if (cbRead > 0)
          msOutput.Write(abResult, 0, cbRead);
      }
      while (cbRead > 0);
      iis.Close();
      msOutput.Flush();
      if (msOutput.Length >= 0)
      {
        msOutput.Capacity = (int)msOutput.Length;
        return msOutput.GetBuffer();
      }
      return null;
#endif
    }
  }
}
