# include <ohana.h>
# include <gfitsio.h>
# include <zlib.h>

/** the two functions in this file re-implement the uncompress function of zlib.  
    For reasons I don't understand, it seems that I need to parse the header 
    segment of the compressed data myself rather than ship it to 'uncompress'.  
    It could be that CFITSIO is doing something bad, or it could be my 
    misunderstanding **/

/* zlib.h -- interface of the 'zlib' general purpose compression library
  version 1.2.3, July 18th, 2005

  Copyright (C) 1995-2005 Jean-loup Gailly and Mark Adler

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Jean-loup Gailly        Mark Adler
  jloup@gzip.org          madler@alumni.caltech.edu


  The data format used by the zlib library is described by RFCs (Request for
  Comments) 1950 to 1952 in the files http://www.ietf.org/rfc/rfc1950.txt
  (zlib format), rfc1951.txt (deflate format) and rfc1952.txt (gzip format).
*/

/*
     The 'zlib' compression library provides in-memory compression and
  decompression functions, including integrity checks of the uncompressed
  data.  This version of the library supports only one compression method
  (deflation) but other algorithms will be added later and will have the same
  stream interface.

     Compression can be done in a single step if the buffers are large
  enough (for example if an input file is mmap'ed), or can be done by
  repeated calls of the compression function.  In the latter case, the
  application must provide more input and/or consume the output
  (providing more output space) before each call.

     The compressed data format used by default by the in-memory functions is
  the zlib format, which is a zlib wrapper documented in RFC 1950, wrapped
  around a deflate stream, which is itself documented in RFC 1951.

     The library also supports reading and writing files in gzip (.gz) format
  with an interface similar to that of stdio using the functions that start
  with "gz".  The gzip format is different from the zlib format.  gzip is a
  gzip wrapper, documented in RFC 1952, wrapped around a deflate stream.

     This library can optionally read and write gzip streams in memory as well.

     The zlib format was designed to be compact and fast for use in memory
  and on communications channels.  The gzip format was designed for single-
  file compression on file systems, has a larger header than zlib to maintain
  directory information, and uses a different, slower check method than zlib.

     The library does not install any signal handler. The decoder checks
  the consistency of the compressed data, so the library should never
  crash even in case of corrupted input.
*/

// the header segments of a gzip file uses bytes and should not be swapped...
int gfits_gz_stripheader (unsigned char *data, int *ndata) {
  
  int nstart, Ndata;

  if (data[0] != 0x1f) return FALSE; // magic
  if (data[1] != 0x8b) return FALSE; // magic
  if (data[2] != 0x08) return FALSE; // DEFLATED
  if (data[3] &  0xe0) return FALSE; // uses reserved flags?
  
  // data[4] - data[9] : time, xflags, OS code

  nstart = 10; // data[nstart] is first byte after header

  // check for an extra field
  if (data[3] & 0x04) {
    nstart += data[10];
    nstart += (data[11] << 8); // data[10], data[11] are a single 2byte word that should be swapped
  }
  
  // check for filename
  if (data[3] & 0x08) {
    while (data[nstart]) nstart ++;
  }

  // check for comment
  if (data[3] & 0x10) {
    while (data[nstart]) nstart ++;
  }

  // check for CRC
  if (data[3] & 0x02) {
    nstart ++;
    nstart ++;
  }

  Ndata = *ndata - nstart;
  memmove (data, &data[nstart], Ndata);
  *ndata = Ndata;

  return TRUE;
}

// XXX ??? is cfitsio writing data which is incompatible with zlib ???
int gfits_uncompress (Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen)
{
    z_stream stream;
    int err;

    stream.next_in = (Bytef*)source;
    stream.avail_in = (uInt)sourceLen;
    /* Check for source > 64K on 16-bit machine: */
    if ((uLong)stream.avail_in != sourceLen) return Z_BUF_ERROR;

    stream.next_out = dest;
    stream.avail_out = (uInt)*destLen;
    if ((uLong)stream.avail_out != *destLen) return Z_BUF_ERROR;

    stream.zalloc = (alloc_func)0;
    stream.zfree = (free_func)0;

    // MAX_WBITS = 15
    err = inflateInit2(&stream, -15);
    if (err != Z_OK) return err;

    err = inflate(&stream, Z_FINISH);
    if (err != Z_STREAM_END) {
        inflateEnd(&stream);
        if (err == Z_NEED_DICT || (err == Z_BUF_ERROR && stream.avail_in == 0))
            return Z_DATA_ERROR;
        return err;
    }
    assert (stream.total_out <= *destLen);
    *destLen = stream.total_out;

    err = inflateEnd(&stream);
    return err;
}
