//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2020 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    as published by the Free Software Foundation.
//
//    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 Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

#ifndef OPENVPN_BUFFER_ZLIB_H
#define OPENVPN_BUFFER_ZLIB_H

#ifdef HAVE_ZLIB

#include <cstring> // for std::memset

#include <zlib.h>

#include <openvpn/common/exception.hpp>
#include <openvpn/buffer/buffer.hpp>
#include <openvpn/buffer/buflist.hpp>

namespace openvpn {
  namespace ZLib {
    OPENVPN_EXCEPTION(zlib_error);

    class ZStreamBase // used internally by compress_gzip/decompress_gzip
    {
    public:
      z_stream s;
    protected:
      ZStreamBase()  { std::memset(&s, 0, sizeof(s)); }
    private:
      ZStreamBase(const ZStreamBase&) = delete;
      ZStreamBase& operator=(const ZStreamBase&) = delete;
    };

    inline BufferPtr compress_gzip(BufferPtr src,
				   const size_t headroom,
				   const size_t tailroom,
				   const int level,
				   const int window_bits=15,
				   const int mem_level=8)
    {
      constexpr int GZIP_ENCODING = 16;

      struct ZStream : public ZStreamBase {
	~ZStream() { ::deflateEnd(&s); }
      };

      if (src)
	{
	  int status;
	  ZStream zs;
	  zs.s.next_in = src->data();
	  zs.s.avail_in = src->size();
	  status = ::deflateInit2(&zs.s,
				  level,
				  Z_DEFLATED,
				  GZIP_ENCODING + window_bits,
				  mem_level,
				  Z_DEFAULT_STRATEGY);
	  if (status != Z_OK)
	    OPENVPN_THROW(zlib_error, "zlib deflateinit2 failed, error=" << status);
	  const uLong outcap = ::deflateBound(&zs.s, src->size());
	  BufferPtr b = new BufferAllocated(outcap + headroom + tailroom, 0);
	  b->init_headroom(headroom);
	  zs.s.next_out = b->data();
	  zs.s.avail_out = outcap;
	  status = ::deflate(&zs.s, Z_FINISH);
	  if (status != Z_STREAM_END)
	    OPENVPN_THROW(zlib_error, "zlib deflate failed, error=" << status);
	  b->set_size(zs.s.total_out);
	  return b;
	}
      else
	return BufferPtr();
    }

    inline BufferPtr decompress_gzip(BufferPtr src,
				     const size_t headroom,
				     const size_t tailroom,
				     const size_t max_size,
				     const size_t block_size=4096,
				     const int window_bits=15)
    {
      constexpr int GZIP_ENCODING = 16;

      struct ZStream : public ZStreamBase {
	~ZStream() { ::inflateEnd(&s); }
      };

      if (src)
	{
	  int status;
	  ZStream zs;
	  zs.s.next_in = src->data();
	  zs.s.avail_in = src->size();
	  status = ::inflateInit2(&zs.s, GZIP_ENCODING + window_bits);
	  if (status != Z_OK)
	    OPENVPN_THROW(zlib_error, "zlib inflateinit2 failed, error=" << status);

	  BufferList blist;
	  size_t hr = headroom;
	  size_t tr = tailroom;
	  do {
	    // use headroom/tailroom on first block to take advantage
	    // of BufferList::join() optimization for one-block lists
	    BufferPtr b = new BufferAllocated(block_size + hr + tr, 0);
	    b->init_headroom(hr);
	    const size_t avail = b->remaining(tr);
	    zs.s.next_out = b->data();
	    zs.s.avail_out = avail;
	    status = ::inflate(&zs.s, Z_SYNC_FLUSH);
	    if (status != Z_OK && status != Z_STREAM_END)
	      OPENVPN_THROW(zlib_error, "zlib inflate failed, error=" << status);
	    b->set_size(avail - zs.s.avail_out);
	    blist.push_back(std::move(b));
	    if (max_size && zs.s.total_out > max_size)
	      OPENVPN_THROW(zlib_error, "zlib inflate max_size " << max_size << " exceeded");
	    hr = tr = 0;
	  } while (status == Z_OK);
	  return blist.join(headroom, tailroom, true);
	}
      else
	return BufferPtr();
    }

  }
}

#endif
#endif