//    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/>.

#pragma once

#include <cstdint> // for std::uint32_t, uint64_t, etc.

#include <lz4.h>

#include <openvpn/common/exception.hpp>
#include <openvpn/common/socktypes.hpp> // for ntohl/htonl
#include <openvpn/buffer/buffer.hpp>

namespace openvpn {
  namespace LZ4 {
    OPENVPN_EXCEPTION(lz4_error);

    inline BufferPtr compress(const ConstBuffer& src,
			      const size_t headroom,
			      const size_t tailroom)
    {
      // sanity check
      if (src.size() > LZ4_MAX_INPUT_SIZE)
	OPENVPN_THROW(lz4_error, "compress buffer size=" << src.size() << " exceeds LZ4_MAX_INPUT_SIZE=" << LZ4_MAX_INPUT_SIZE);

      // allocate dest buffer
      BufferPtr dest = new BufferAllocated(sizeof(std::uint32_t) + headroom + tailroom + LZ4_COMPRESSBOUND(src.size()), 0);
      dest->init_headroom(headroom);

      // as a hint to receiver, write the decompressed size
      {
	const std::uint32_t size = htonl(src.size());
	dest->write(&size, sizeof(size));
      }

      // compress
      const int comp_size = ::LZ4_compress_default((const char *)src.c_data(), (char *)dest->data_end(),
						   (int)src.size(), (int)dest->remaining(tailroom));
      if (comp_size <= 0)
	OPENVPN_THROW(lz4_error, "LZ4_compress_default returned error status=" << comp_size);
      dest->inc_size(comp_size);
      return dest;
    }

    inline BufferPtr decompress(const ConstBuffer& source,
				const size_t headroom,
				const size_t tailroom,
				size_t max_decompressed_size=LZ4_MAX_INPUT_SIZE)
    {
      // get the decompressed size
      ConstBuffer src(source);
      if (src.size() < sizeof(std::uint32_t))
	OPENVPN_THROW(lz4_error, "decompress buffer size=" << src.size() << " is too small");
      std::uint32_t size;
      src.read(&size, sizeof(size));
      size = ntohl(size);
      if (max_decompressed_size > LZ4_MAX_INPUT_SIZE)
	max_decompressed_size = LZ4_MAX_INPUT_SIZE;
      if (max_decompressed_size && size > max_decompressed_size)
	OPENVPN_THROW(lz4_error, "decompress expansion size=" << size << " is too large (must be <= " << max_decompressed_size << ')');

      // allocate dest buffer
      BufferPtr dest = new BufferAllocated(headroom + tailroom + size, 0);
      dest->init_headroom(headroom);

      // decompress
      const int decomp_size = LZ4_decompress_safe((const char *)src.c_data(), (char *)dest->data(),
						  (int)src.size(), size);
      if (decomp_size <= 0)
	OPENVPN_THROW(lz4_error, "LZ4_decompress_safe returned error status=" << decomp_size);
      if (static_cast<unsigned int>(decomp_size) != size)
	OPENVPN_THROW(lz4_error, "decompress size inconsistency expected_size=" << size << " actual_size=" << decomp_size);
      dest->inc_size(decomp_size);
      return dest;
    }

  }
}