// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// Mobius Forensic Toolkit
// Copyright (C) 2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2018,2019,2020,2021,2022,2023,2024 Eduardo Aguiar
//
// 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, 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, see <http://www.gnu.org/licenses/>.
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
#include "reader_impl_aes.h"
#include "imagefile_impl.h"
#include <mobius/io/file.h>
#include <mobius/exception.inc>
#include <stdexcept>

namespace
{
//! \brief header size in bytes
constexpr int HEADER_SIZE = 16384;
} // namespace

// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
//! \brief Constructor
//! \param impl imagefile_impl object
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
reader_impl_aes::reader_impl_aes (const imagefile_impl& impl)
  : size_ (impl.get_size ()),
    cipher_ (mobius::crypt::new_cipher_ecb ("aes", impl.get_encryption_key ()))
{
  auto f = impl.get_file ();
  stream_ = f.new_reader ();
  stream_.seek (HEADER_SIZE);
}

// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
//! \brief set read position
//! \param offset offset in bytes
//! \param w either beginning, current or end
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
void
reader_impl_aes::seek (offset_type offset, whence_type w)
{
  // calculate offset from the beginning of data
  offset_type abs_offset;

  if (w == whence_type::beginning)
    abs_offset = offset;

  else if (w == whence_type::current)
    abs_offset = pos_ + offset;

  else if (w == whence_type::end)
    abs_offset = size_ - 1 + offset;

  else
    throw std::invalid_argument (mobius::MOBIUS_EXCEPTION_MSG ("Invalid whence_type"));

  // update current pos, if possible
  if (abs_offset < 0)
    throw std::invalid_argument (mobius::MOBIUS_EXCEPTION_MSG ("invalid offset"));
  
  else if (size_type (abs_offset) <= size_)  
    pos_ = abs_offset;
}

// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
//! \brief read bytes from reader
//! \param size size in bytes
//! \return bytearray containing data
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
mobius::bytearray
reader_impl_aes::read (size_type size)
{
  mobius::bytearray data;

  size = std::min (size_ - pos_, size);
  constexpr int CHUNK_SIZE = 512;

  while (size > 0)
    {
      size_type chunk_idx = pos_ / CHUNK_SIZE;

      if (chunk_idx != chunk_idx_)      // retrieve new data chunk, if necessary
        {
          stream_.seek (chunk_idx * CHUNK_SIZE + HEADER_SIZE);
          chunk_data_ = cipher_.decrypt (stream_.read (CHUNK_SIZE));
          chunk_idx_ = chunk_idx;
        }

      size_type slice_start = pos_ % CHUNK_SIZE;
      size_type slice_end = std::min (slice_start + size - 1, chunk_data_.size () - 1);
      data += chunk_data_.slice (slice_start, slice_end);
      pos_ += slice_end - slice_start + 1;
      size -= slice_end - slice_start + 1;
    }

  return data;
}
