////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Dr. Frank Celler
////////////////////////////////////////////////////////////////////////////////

#include "datafile.h"
#include "ApplicationFeatures/PageSizeFeature.h"
#include "Basics/FileUtils.h"
#include "Basics/StaticStrings.h"
#include "Basics/StringUtils.h"
#include "Basics/files.h"
#include "Basics/hashes.h"
#include "Basics/memory-map.h"
#include "Basics/tri-strings.h"
#include "Logger/Logger.h"
#include "VocBase/DatafileHelper.h"
#include "VocBase/ticks.h"

#include <sstream>

// #define DEBUG_DATAFILE 1

using namespace arangodb;
using namespace arangodb::basics;

namespace {

/// @brief check if a marker appears to be created by ArangoDB 28
static TRI_voc_crc_t Crc28(TRI_voc_crc_t crc, void const* data, size_t length) {
  static TRI_voc_crc_t const CrcPolynomial = 0xEDB88320; 
  unsigned char* current = (unsigned char*) data;   
  while (length--) {
    crc ^= *current++;

    for (unsigned int i = 0; i < 8; ++i) {
      if (crc & 1) {
        crc = (crc >> 1) ^ CrcPolynomial;
      } else {
        crc = crc >> 1;         
      }
    }
  }   
  return crc;
}

static bool IsMarker28 (void const* marker) {
  struct Marker28 {
    TRI_voc_size_t       _size; 
    TRI_voc_crc_t        _crc;     
    uint32_t             _type;   
#ifdef TRI_PADDING_32
    char _padding_df_marker[4];
#endif
    TRI_voc_tick_t _tick;     
  };

  TRI_voc_size_t zero = 0;
  off_t o = offsetof(Marker28, _crc);
  size_t n = sizeof(TRI_voc_crc_t);

  char const* ptr = static_cast<char const*>(marker);
  Marker28 const* m = static_cast<Marker28 const*>(marker);

  TRI_voc_crc_t crc = TRI_InitialCrc32();

  crc = Crc28(crc, ptr, o);
  crc = Crc28(crc, (char*) &zero, n);
  crc = Crc28(crc, ptr + o + n, m->_size - o - n);

  crc = TRI_FinalCrc32(crc);

  return crc == m->_crc;
}

/// @brief calculates the actual CRC of a marker, without bounds checks
static TRI_voc_crc_t CalculateCrcValue(TRI_df_marker_t const* marker) {
  TRI_voc_size_t zero = 0;
  off_t o = marker->offsetOfCrc();
  size_t n = sizeof(TRI_voc_crc_t);

  char const* ptr = reinterpret_cast<char const*>(marker);

  TRI_voc_crc_t crc = TRI_InitialCrc32();

  crc = TRI_BlockCrc32(crc, ptr, o);
  crc = TRI_BlockCrc32(crc, (char*)&zero, n);
  crc = TRI_BlockCrc32(crc, ptr + o + n, marker->getSize() - o - n);

  crc = TRI_FinalCrc32(crc);

  return crc;
}

/// @brief checks a CRC of a marker, with bounds checks
static bool CheckCrcMarker(TRI_df_marker_t const* marker, char const* end) {
  TRI_voc_size_t const size = marker->getSize();

  if (size < sizeof(TRI_df_marker_t)) {
    return false;
  }

  if (reinterpret_cast<char const*>(marker) + size > end) {
    return false;
  }

  auto expected = CalculateCrcValue(marker);
  return marker->getCrc() == expected;
}

}

////////////////////////////////////////////////////////////////////////////////
/// @brief creates a new datafile
///
/// returns the file descriptor or -1 if the file cannot be created
////////////////////////////////////////////////////////////////////////////////

static int CreateDatafile(std::string const& filename, TRI_voc_size_t maximalSize) {
  TRI_ERRORBUF;

  // open the file
  int fd = TRI_CREATE(filename.c_str(), O_CREAT | O_EXCL | O_RDWR | TRI_O_CLOEXEC,
                      S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);

  TRI_IF_FAILURE("CreateDatafile1") {
    // intentionally fail
    TRI_CLOSE(fd);
    fd = -1;
    errno = ENOSPC;
  }

  if (fd < 0) {
    if (errno == ENOSPC) {
      TRI_set_errno(TRI_ERROR_ARANGO_FILESYSTEM_FULL);
      LOG(ERR) << "cannot create datafile '" << filename << "': " << TRI_last_error();
    } else {
      TRI_SYSTEM_ERROR();

      TRI_set_errno(TRI_ERROR_SYS_ERROR);
      LOG(ERR) << "cannot create datafile '" << filename << "': " << TRI_GET_ERRORBUF;
    }
    return -1;
  }

  // fill file with zeros from FileNullBuffer
  size_t writeSize = TRI_GetNullBufferSizeFiles();
  size_t written = 0;
  while (written < maximalSize) {
    if (writeSize + written > maximalSize) {
      writeSize = maximalSize - written;
    }

    ssize_t writeResult =
        TRI_WRITE(fd, TRI_GetNullBufferFiles(), static_cast<TRI_write_t>(writeSize));

    TRI_IF_FAILURE("CreateDatafile2") {
      // intentionally fail
      writeResult = -1;
      errno = ENOSPC;
    }

    if (writeResult < 0) {
      if (errno == ENOSPC) {
        TRI_set_errno(TRI_ERROR_ARANGO_FILESYSTEM_FULL);
        LOG(ERR) << "cannot create datafile '" << filename << "': " << TRI_last_error();
      } else {
        TRI_SYSTEM_ERROR();
        TRI_set_errno(TRI_ERROR_SYS_ERROR);
        LOG(ERR) << "cannot create datafile '" << filename << "': " << TRI_GET_ERRORBUF;
      }

      TRI_CLOSE(fd);
      TRI_UnlinkFile(filename.c_str());

      return -1;
    }

    written += static_cast<size_t>(writeResult);
  }

  // go back to offset 0
  TRI_lseek_t offset = TRI_LSEEK(fd, (TRI_lseek_t)0, SEEK_SET);

  if (offset == (TRI_lseek_t)-1) {
    TRI_SYSTEM_ERROR();
    TRI_set_errno(TRI_ERROR_SYS_ERROR);
    TRI_CLOSE(fd);

    // remove empty file
    TRI_UnlinkFile(filename.c_str());

    LOG(ERR) << "cannot seek in datafile '" << filename << "': '" << TRI_GET_ERRORBUF << "'";
    return -1;
  }

  return fd;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief truncates a datafile
///
/// Create a truncated datafile, seal it and rename the old.
////////////////////////////////////////////////////////////////////////////////

static int TruncateAndSealDatafile(TRI_datafile_t* datafile,
                                   TRI_voc_size_t vocSize) {
  TRI_ERRORBUF;
  void* data;
  void* mmHandle;

  // this function must not be called for non-physical datafiles
  TRI_ASSERT(datafile->isPhysical());
  size_t pageSize = PageSizeFeature::getPageSize();

  // use multiples of page-size
  size_t maximalSize =
      ((vocSize + sizeof(TRI_df_footer_marker_t) + pageSize - 1) / pageSize) *
      pageSize;

  // sanity check
  if (sizeof(TRI_df_header_marker_t) + sizeof(TRI_df_footer_marker_t) >
      maximalSize) {
    LOG(ERR) << "cannot create datafile '" << datafile->getName() << "', maximal size " << maximalSize << " is too small";
    return TRI_set_errno(TRI_ERROR_ARANGO_MAXIMAL_SIZE_TOO_SMALL);
  }

  // open the file
  std::string filename = arangodb::basics::FileUtils::buildFilename(datafile->_filename, ".new");

  int fd =
      TRI_CREATE(filename.c_str(), O_CREAT | O_EXCL | O_RDWR | TRI_O_CLOEXEC,
                 S_IRUSR | S_IWUSR);

  if (fd < 0) {
    TRI_SYSTEM_ERROR();
    LOG(ERR) << "cannot create new datafile '" << filename << "': " << TRI_GET_ERRORBUF;

    return TRI_set_errno(TRI_ERROR_SYS_ERROR);
  }

  // go back to the beginning of the file
  TRI_lseek_t offset = TRI_LSEEK(fd, (TRI_lseek_t)(maximalSize - 1), SEEK_SET);

  if (offset == (TRI_lseek_t)-1) {
    TRI_SYSTEM_ERROR();
    TRI_set_errno(TRI_ERROR_SYS_ERROR);
    TRI_CLOSE(fd);

    // remove empty file
    TRI_UnlinkFile(filename.c_str());

    LOG(ERR) << "cannot seek in new datafile '" << filename << "': " << TRI_GET_ERRORBUF;

    return TRI_ERROR_SYS_ERROR;
  }

  char zero = 0;
  int res = TRI_WRITE(fd, &zero, 1);

  if (res < 0) {
    TRI_SYSTEM_ERROR();
    TRI_set_errno(TRI_ERROR_SYS_ERROR);
    TRI_CLOSE(fd);

    // remove empty file
    TRI_UnlinkFile(filename.c_str());

    LOG(ERR) << "cannot create datafile '" << filename << "': " << TRI_GET_ERRORBUF;

    return TRI_ERROR_SYS_ERROR;
  }

  // memory map the data
  res = TRI_MMFile(0, maximalSize, PROT_WRITE | PROT_READ, MAP_SHARED, fd,
                   &mmHandle, 0, &data);

  if (res != TRI_ERROR_NO_ERROR) {
    TRI_SYSTEM_ERROR();
    TRI_set_errno(res);
    TRI_CLOSE(fd);

    // remove empty file
    TRI_UnlinkFile(filename.c_str());

    LOG(ERR) << "cannot memory map file '" << filename << "': " << TRI_GET_ERRORBUF;
    LOG(ERR) << "The database directory might reside on a shared folder "
                "(VirtualBox, VMWare) or an NFS "
                "mounted volume which does not allow memory mapped files.";

    return TRI_errno();
  }

  // copy the data
  memcpy(data, datafile->_data, vocSize);

  // patch the datafile structure
  res = TRI_UNMMFile(datafile->_data, datafile->_initSize, datafile->_fd,
                     &datafile->_mmHandle);

  if (res < 0) {
    TRI_CLOSE(datafile->_fd);
    LOG(ERR) << "munmap failed with: " << res;
    return res;
  }

  // .............................................................................................
  // For windows: Mem mapped files use handles
  // the datafile->_mmHandle handle object has been closed in the underlying
  // TRI_UNMMFile(...) call above so we do not need to close it for the
  // associated file below
  // .............................................................................................

  TRI_CLOSE(datafile->_fd);

  datafile->_data = static_cast<char*>(data);
  datafile->_next = (char*)(data) + vocSize;
  datafile->_currentSize = vocSize;
  // do not change _initSize!
  TRI_ASSERT(datafile->_initSize == datafile->_maximalSize);
  datafile->_maximalSize = static_cast<TRI_voc_size_t>(maximalSize);
  datafile->_fd = fd;
  datafile->_mmHandle = mmHandle;
  datafile->_state = TRI_DF_STATE_CLOSED;
  datafile->_full = false;
  datafile->_isSealed = false;
  datafile->_synced = static_cast<char*>(data);
  datafile->_written = datafile->_next;

  // rename files
  std::string oldname = arangodb::basics::FileUtils::buildFilename(datafile->_filename, ".corrupted");

  res = TRI_RenameFile(datafile->_filename.c_str(), oldname.c_str());

  if (res != TRI_ERROR_NO_ERROR) {
    return res;
  }

  res = TRI_RenameFile(filename.c_str(), datafile->_filename.c_str());

  if (res != TRI_ERROR_NO_ERROR) {
    return res;
  }

  // need to reset the datafile state here to write, otherwise the following
  // call will return an error
  datafile->_state = TRI_DF_STATE_WRITE;

  return datafile->seal();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tries to repair a datafile
////////////////////////////////////////////////////////////////////////////////

static bool TryRepairDatafile(TRI_datafile_t* datafile) {
  // this function must not be called for non-physical datafiles
  TRI_ASSERT(datafile->isPhysical());

  char* ptr = datafile->_data;
  char* end = datafile->_data + datafile->_currentSize;

  if (datafile->_currentSize == 0) {
    end = datafile->_data + datafile->_maximalSize;
  }

  TRI_voc_size_t currentSize = 0;

  while (ptr < end) {
    TRI_df_marker_t* marker = reinterpret_cast<TRI_df_marker_t*>(ptr);
    TRI_voc_size_t const size = marker->getSize();

    if (size == 0) {
      // reached end
      return true;
    }

    if (size < sizeof(TRI_df_marker_t) || ptr + size > end) {
      // marker too small or too big
      return false;
    }

    if (!TRI_IsValidMarkerDatafile(marker)) {
      // unknown marker type
      return false;
    }

    if (marker->getType() != 0) {
      if (!CheckCrcMarker(marker, end)) {
        // CRC mismatch!
        auto next = reinterpret_cast<char const*>(marker) + size;
        auto p = next;

        if (p < end) {
          // check if the rest of the datafile is only followed by NULL bytes
          bool isFollowedByNullBytes = true;
          while (p < end) {
            if (*p != '\0') {
              isFollowedByNullBytes = false;
              break;
            }
            ++p;
          }

          if (isFollowedByNullBytes) {
            // only last marker in datafile was corrupt. fix the datafile in
            // place
            LOG(INFO) << "truncating datafile '" << datafile->getName() << "' at position " << currentSize;
            int res = TruncateAndSealDatafile(datafile, currentSize);
            return (res == TRI_ERROR_NO_ERROR);
          }

          // there is some other stuff following. now inspect it...
          TRI_ASSERT(next <= end);

          if (next < end) {
            // there is a next marker
            auto nextMarker = reinterpret_cast<TRI_df_marker_t const*>(next);

            if (nextMarker->getType() != 0 &&
                nextMarker->getSize() >= sizeof(TRI_df_marker_t) &&
                next + nextMarker->getSize() <= end &&
                TRI_IsValidMarkerDatafile(nextMarker) &&
                CheckCrcMarker(nextMarker, end)) {
              // next marker looks good.

              // create a temporary buffer
              auto buffer = std::unique_ptr<char[]>(new char[size]);

              // create a new marker in the temporary buffer
              auto temp = reinterpret_cast<TRI_df_marker_t*>(buffer.get());
              DatafileHelper::InitMarker(
                  reinterpret_cast<TRI_df_marker_t*>(buffer.get()), TRI_DF_MARKER_BLANK,
                  static_cast<uint32_t>(size));
              temp->setCrc(CalculateCrcValue(temp));

              // all done. now copy back the marker into the file
              memcpy(static_cast<void*>(ptr), buffer.get(),
                     static_cast<size_t>(size));

              buffer.reset(); // don't need the buffer anymore
              bool ok = datafile->sync(ptr, (ptr + size));

              if (ok) {
                LOG(INFO) << "zeroed single invalid marker in datafile '" << datafile->getName() << "' at position " << currentSize;
              } else {
                LOG(ERR) << "could not zero single invalid marker in datafile '" << datafile->getName() << "' at position " << currentSize;
                return false;
              }
            } else {
              // next marker looks broken, too.
              int res = TruncateAndSealDatafile(datafile, currentSize);
              return (res == TRI_ERROR_NO_ERROR);
            }
          }
        }
      }
    }

    size_t alignedSize = DatafileHelper::AlignedMarkerSize<TRI_voc_size_t>(marker);
    currentSize += static_cast<TRI_voc_size_t>(alignedSize);

    if (marker->getType() == TRI_DF_MARKER_FOOTER) {
      return true;
    }

    ptr += alignedSize;
  }

  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief fixes a corrupted datafile
////////////////////////////////////////////////////////////////////////////////

static bool FixDatafile(TRI_datafile_t* datafile, TRI_voc_size_t currentSize) {
  LOG(WARN) << "datafile '" << datafile->getName() << "' is corrupted at position " << currentSize;

  LOG(WARN) << "setting datafile '" << datafile->getName() << "' to read-only and ignoring all data from this file beyond this position";

  datafile->_currentSize = currentSize;
  TRI_ASSERT(datafile->_initSize == datafile->_maximalSize);
  datafile->_maximalSize = static_cast<TRI_voc_size_t>(currentSize);
  datafile->_next = datafile->_data + datafile->_currentSize;
  datafile->_full = true;
  datafile->_state = TRI_DF_STATE_READ;
  datafile->_isSealed = true;

  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checks a datafile
////////////////////////////////////////////////////////////////////////////////

static bool CheckDatafile(TRI_datafile_t* datafile, bool ignoreFailures) {
  // this function must not be called for non-physical datafiles
  TRI_ASSERT(datafile->isPhysical());

  char* ptr = datafile->_data;
  char* end = datafile->_data + datafile->_currentSize;
  TRI_voc_size_t currentSize = 0;

  if (datafile->_currentSize == 0) {
    LOG(WARN) << "current size is 0 in read-only datafile '" << datafile->getName() << "', trying to fix";

    end = datafile->_data + datafile->_maximalSize;
  }

  TRI_voc_tick_t maxTick = 0;

  auto updateTick =
      [](TRI_voc_tick_t maxTick) -> void { TRI_UpdateTickServer(maxTick); };

  while (ptr < end) {
    TRI_df_marker_t* marker = reinterpret_cast<TRI_df_marker_t*>(ptr);
    TRI_voc_size_t const size = marker->getSize();
    TRI_voc_tick_t const tick = marker->getTick();
    TRI_df_marker_type_t const type = marker->getType();

#ifdef DEBUG_DATAFILE
    LOG(TRACE) << "MARKER: size " << size << ", tick " << tick << ", crc " << marker->getCrc() << ", type " << type;
#endif

    if (size == 0) {
      LOG(DEBUG) << "reached end of datafile '" << datafile->getName() << "' data, current size " << currentSize;

      datafile->_currentSize = currentSize;
      datafile->_next = datafile->_data + datafile->_currentSize;

      updateTick(maxTick);

      return true;
    }

    if (size < sizeof(TRI_df_marker_t)) {
      if (ignoreFailures) {
        return FixDatafile(datafile, currentSize);
      }
       
      datafile->_lastError =
          TRI_set_errno(TRI_ERROR_ARANGO_CORRUPTED_DATAFILE);
      datafile->_currentSize = currentSize;
      datafile->_next = datafile->_data + datafile->_currentSize;
      datafile->_state = TRI_DF_STATE_OPEN_ERROR;

      LOG(WARN) << "marker in datafile '" << datafile->getName() << "' too small, size " << size << ", should be at least " << sizeof(TRI_df_marker_t);

      updateTick(maxTick);

      return false;
    }

    // prevent reading over the end of the file
    if (ptr + size > end) {
      if (ignoreFailures) {
        return FixDatafile(datafile, currentSize);
      }
       
      datafile->_lastError =
          TRI_set_errno(TRI_ERROR_ARANGO_CORRUPTED_DATAFILE);
      datafile->_currentSize = currentSize;
      datafile->_next = datafile->_data + datafile->_currentSize;
      datafile->_state = TRI_DF_STATE_OPEN_ERROR;

      LOG(WARN) << "marker in datafile '" << datafile->getName() << "' points with size " << size << " beyond end of file";

      updateTick(maxTick);

      return false;
    }

    // the following sanity check offers some, but not 100% crash-protection
    // when reading
    // totally corrupted datafiles
    if (!TRI_IsValidMarkerDatafile(marker)) {
      if (type == 0 && size < 128) {
        // ignore markers with type 0 and a small size
        LOG(WARN) << "ignoring suspicious marker in datafile '" << datafile->getName() << "': type: " << type << ", size: " << size;
      } else {
        if (ignoreFailures) {
          return FixDatafile(datafile, currentSize);
        }
         
        datafile->_lastError =
            TRI_set_errno(TRI_ERROR_ARANGO_CORRUPTED_DATAFILE);
        datafile->_currentSize = currentSize;
        datafile->_next = datafile->_data + datafile->_currentSize;
        datafile->_state = TRI_DF_STATE_OPEN_ERROR;

        LOG(WARN) << "marker in datafile '" << datafile->getName() << "' is corrupt: type: " << type << ", size: " << size;

        updateTick(maxTick);

        return false;
      }
    }

    if (type != 0) {
      bool ok = CheckCrcMarker(marker, end);

      if (!ok) {
        // CRC mismatch!
        bool nextMarkerOk = false;

        if (size > 0) {
          auto next = reinterpret_cast<char const*>(marker) + size;
          auto p = next;

          if (p < end) {
            // check if the rest of the datafile is only followed by NULL bytes
            bool isFollowedByNullBytes = true;
            while (p < end) {
              if (*p != '\0') {
                isFollowedByNullBytes = false;
                break;
              }
              ++p;
            }

            if (isFollowedByNullBytes) {
              // only last marker in datafile was corrupt. fix the datafile in
              // place
              LOG(WARN) << "datafile '" << datafile->getName() << "' automatically truncated at last marker";
              ignoreFailures = true;
            } else {
              // there is some other stuff following. now inspect it...
              TRI_ASSERT(next <= end);

              if (next < end) {
                // there is a next marker
                auto nextMarker =
                    reinterpret_cast<TRI_df_marker_t const*>(next);

                if (nextMarker->getType() != 0 &&
                    nextMarker->getSize() >= sizeof(TRI_df_marker_t) &&
                    next + nextMarker->getSize() <= end &&
                    TRI_IsValidMarkerDatafile(nextMarker) &&
                    CheckCrcMarker(nextMarker, end)) {
                  // next marker looks good.
                  nextMarkerOk = true;
                }
              } else {
                // EOF
                nextMarkerOk = true;
              }
            }
          }
        }

        if (ignoreFailures) {
          return FixDatafile(datafile, currentSize);
        }
         
        datafile->_lastError =
            TRI_set_errno(TRI_ERROR_ARANGO_CORRUPTED_DATAFILE);
        datafile->_currentSize = currentSize;
        datafile->_next = datafile->_data + datafile->_currentSize;
        datafile->_state = TRI_DF_STATE_OPEN_ERROR;

        LOG(WARN) << "crc mismatch found in datafile '" << datafile->getName() << "' at position " << currentSize << ". expected crc: " << CalculateCrcValue(marker) << ", actual crc: " << marker->getCrc();

        if (nextMarkerOk) {
          LOG(INFO) << "data directly following this marker looks ok so repairing the marker may recover it";
        } else {
          LOG(WARN) << "data directly following this marker cannot be analyzed";
        }

        updateTick(maxTick);

        return false;
      }
    }

    if (tick > maxTick) {
      maxTick = tick;
    }

    size_t alignedSize = DatafileHelper::AlignedMarkerSize<size_t>(marker);
    currentSize += static_cast<TRI_voc_size_t>(alignedSize);

    if (marker->getType() == TRI_DF_MARKER_FOOTER) {
      LOG(DEBUG) << "found footer, reached end of datafile '" << datafile->getName() << "', current size " << currentSize;

      datafile->_isSealed = true;
      datafile->_currentSize = currentSize;
      datafile->_next = datafile->_data + datafile->_currentSize;

      updateTick(maxTick);
      return true;
    }

    ptr += alignedSize;
  }

  updateTick(maxTick);
  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief extract the numeric part from a filename
/// the filename must look like this: /.*type-abc\.ending$/, where abc is
/// a number, and type and ending are arbitrary letters
////////////////////////////////////////////////////////////////////////////////

static uint64_t GetNumericFilenamePart(char const* filename) {
  char const* pos1 = strrchr(filename, '.');

  if (pos1 == nullptr) {
    return 0;
  }

  char const* pos2 = strrchr(filename, '-');

  if (pos2 == nullptr || pos2 > pos1) {
    return 0;
  }

  return StringUtils::uint64(pos2 + 1, pos1 - pos2 - 1);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief create the initial datafile header marker
////////////////////////////////////////////////////////////////////////////////

static int WriteInitialHeaderMarker(TRI_datafile_t* datafile, TRI_voc_fid_t fid,
                                    TRI_voc_size_t maximalSize) {
  // create the header
  TRI_df_header_marker_t header = DatafileHelper::CreateHeaderMarker(
    maximalSize, static_cast<TRI_voc_tick_t>(fid));

  // reserve space and write header to file
  TRI_df_marker_t* position;
  int res =
      TRI_ReserveElementDatafile(datafile, header.base.getSize(), &position, 0);

  if (res == TRI_ERROR_NO_ERROR) {
    TRI_ASSERT(position != nullptr);
    res = TRI_WriteCrcElementDatafile(datafile, position, &header.base, false);
  }

  return res;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief creates a new anonymous datafile
///
/// this is only supported on certain platforms (Linux, MacOS)
////////////////////////////////////////////////////////////////////////////////

#ifdef TRI_HAVE_ANONYMOUS_MMAP

static TRI_datafile_t* CreateAnonymousDatafile(TRI_voc_fid_t fid,
                                               TRI_voc_size_t maximalSize) {
#ifdef TRI_MMAP_ANONYMOUS
  // fd -1 is required for "real" anonymous regions
  int fd = -1;
  int flags = TRI_MMAP_ANONYMOUS | MAP_SHARED;
#else
  // ugly workaround if MAP_ANONYMOUS is not available
  int fd = TRI_OPEN("/dev/zero", O_RDWR | TRI_O_CLOEXEC);

  if (fd == -1) {
    return nullptr;
  }

  int flags = MAP_PRIVATE;
#endif

  // memory map the data
  void* data;
  void* mmHandle;
  ssize_t res = TRI_MMFile(nullptr, maximalSize, PROT_WRITE | PROT_READ, flags,
                           fd, &mmHandle, 0, &data);

#ifdef MAP_ANONYMOUS
// nothing to do
#else
  // close auxilliary file
  TRI_CLOSE(fd);
  fd = -1;
#endif

  if (res != TRI_ERROR_NO_ERROR) {
    TRI_set_errno(res);

    LOG(ERR) << "cannot memory map anonymous region: " << TRI_last_error();
    LOG(ERR) << "The database directory might reside on a shared folder "
                "(VirtualBox, VMWare) or an NFS "
                "mounted volume which does not allow memory mapped files.";
    return nullptr;
  }

  return new TRI_datafile_t(StaticStrings::Empty, fd, mmHandle, maximalSize, 0, fid, static_cast<char*>(data));
}

#endif

////////////////////////////////////////////////////////////////////////////////
/// @brief creates a new physical datafile
////////////////////////////////////////////////////////////////////////////////

static TRI_datafile_t* CreatePhysicalDatafile(std::string const& filename,
                                              TRI_voc_fid_t fid,
                                              TRI_voc_size_t maximalSize) {
  TRI_ASSERT(!filename.empty());

  int fd = CreateDatafile(filename, maximalSize);

  if (fd < 0) {
    // an error occurred
    return nullptr;
  }

  // memory map the data
  void* data;
  void* mmHandle;
  int flags = MAP_SHARED;
#ifdef __linux__
  // try populating the mapping already
  flags |= MAP_POPULATE;
#endif
  ssize_t res = TRI_MMFile(0, maximalSize, PROT_WRITE | PROT_READ, flags, fd,
                           &mmHandle, 0, &data);

  if (res != TRI_ERROR_NO_ERROR) {
    TRI_set_errno(res);
    TRI_CLOSE(fd);

    // remove empty file
    TRI_UnlinkFile(filename.c_str());

    LOG(ERR) << "cannot memory map file '" << filename << "': '" << TRI_errno_string((int)res) << "'";
    LOG(ERR) << "The database directory might reside on a shared folder "
                "(VirtualBox, VMWare) or an NFS "
                "mounted volume which does not allow memory mapped files.";
    return nullptr;
  }

  // create datafile structure
  try {
    return new TRI_datafile_t(filename, fd, mmHandle, maximalSize, 0, fid, static_cast<char*>(data));
  } catch (...) {
    TRI_CLOSE(fd);
    return nullptr;
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief opens a datafile
////////////////////////////////////////////////////////////////////////////////

static TRI_datafile_t* OpenDatafile(std::string const& filename, bool ignoreErrors) {
  TRI_ERRORBUF;
  void* data;
  TRI_stat_t status;
  void* mmHandle;

  // this function must not be called for non-physical datafiles
  TRI_ASSERT(!filename.empty());
  TRI_voc_fid_t fid = GetNumericFilenamePart(filename.c_str());

  // ..........................................................................
  // attempt to open a datafile file
  // ..........................................................................

  int fd = TRI_OPEN(filename.c_str(), O_RDWR | TRI_O_CLOEXEC);

  if (fd < 0) {
    TRI_SYSTEM_ERROR();
    TRI_set_errno(TRI_ERROR_SYS_ERROR);

    LOG(ERR) << "cannot open datafile '" << filename << "': '" << TRI_GET_ERRORBUF << "'";

    return nullptr;
  }

  // compute the size of the file
  int res = TRI_FSTAT(fd, &status);

  if (res < 0) {
    TRI_SYSTEM_ERROR();
    TRI_set_errno(TRI_ERROR_SYS_ERROR);
    TRI_CLOSE(fd);

    LOG(ERR) << "cannot get status of datafile '" << filename << "': " << TRI_GET_ERRORBUF;

    return nullptr;
  }

  // check that file is not too small
  TRI_voc_size_t size = static_cast<TRI_voc_size_t>(status.st_size);

  if (size < sizeof(TRI_df_header_marker_t) + sizeof(TRI_df_footer_marker_t)) {
    TRI_set_errno(TRI_ERROR_ARANGO_CORRUPTED_DATAFILE);
    TRI_CLOSE(fd);

    LOG(ERR) << "datafile '" << filename << "' is corrupt, size is only " << (unsigned int)size;

    return nullptr;
  }

  // read header from file
  char buffer[128];
  memset(&buffer[0], 0, sizeof(buffer)); 

  ssize_t len = sizeof(TRI_df_header_marker_t);

  ssize_t toRead = sizeof(buffer);
  if (toRead > static_cast<ssize_t>(status.st_size)) {
    toRead = static_cast<ssize_t>(status.st_size);
  }

  bool ok = TRI_ReadPointer(fd, &buffer[0], toRead);

  if (!ok) {
    LOG(ERR) << "cannot read datafile header from '" << filename << "': " << TRI_last_error();

    TRI_CLOSE(fd);
    return nullptr;
  }

  char const* ptr = reinterpret_cast<char*>(&buffer[0]);
  char const* end = static_cast<char const*>(ptr) + len;
  TRI_df_header_marker_t const* header = reinterpret_cast<TRI_df_header_marker_t const*>(&buffer[0]);

  // check CRC
  ok = CheckCrcMarker(reinterpret_cast<TRI_df_marker_t const*>(ptr), end);

  if (!ok) {
    if (IsMarker28(ptr)) {
      LOG(ERR) << "datafile found from older version of ArangoDB. "
               << "Please dump data from that version with arangodump "
               << "and reload it into this ArangoDB instance with arangorestore";
      TRI_CLOSE(fd);
      TRI_set_errno(TRI_ERROR_NOT_IMPLEMENTED);
      FATAL_ERROR_EXIT();
    }

    TRI_set_errno(TRI_ERROR_ARANGO_CORRUPTED_DATAFILE);

    LOG(ERR) << "corrupted datafile header read from '" << filename << "'";

    if (!ignoreErrors) {
      TRI_CLOSE(fd);
      return nullptr;
    }
  }

  // check the datafile version
  if (ok) {
    if (header->_version != TRI_DF_VERSION) {
      TRI_set_errno(TRI_ERROR_ARANGO_CORRUPTED_DATAFILE);

      LOG(ERR) << "unknown datafile version '" << header->_version << "' in datafile '" << filename << "'";

      if (!ignoreErrors) {
        TRI_CLOSE(fd);
        return nullptr;
      }
    }
  }

  // check the maximal size
  if (size > header->_maximalSize) {
    LOG(DEBUG) << "datafile '" << filename << "' has size '" << size << "', but maximal size is '" << header->_maximalSize << "'";
  }

  // map datafile into memory
  res = TRI_MMFile(0, size, PROT_READ, MAP_SHARED, fd, &mmHandle, 0, &data);

  if (res != TRI_ERROR_NO_ERROR) {
    TRI_set_errno(res);
    TRI_CLOSE(fd);

    LOG(ERR) << "cannot memory map datafile '" << filename << "': " << TRI_errno_string(res);
    LOG(ERR) << "The database directory might reside on a shared folder "
                "(VirtualBox, VMWare) or an NFS "
                "mounted volume which does not allow memory mapped files.";
    return nullptr;
  }

  // create datafile structure
  try {
    return new TRI_datafile_t(filename, fd, mmHandle, size, size, fid, static_cast<char*>(data));
  } catch (...) {
    TRI_UNMMFile(data, size, fd, &mmHandle);
    TRI_CLOSE(fd);

    return nullptr;
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief creates either an anonymous or a physical datafile
////////////////////////////////////////////////////////////////////////////////

TRI_datafile_t* TRI_CreateDatafile(std::string const& filename, TRI_voc_fid_t fid,
                                   TRI_voc_size_t maximalSize,
                                   bool withInitialMarkers) {
  TRI_datafile_t* datafile;
  size_t pageSize = PageSizeFeature::getPageSize();

  TRI_ASSERT(pageSize >= 256);

  // use multiples of page-size
  maximalSize =
      (TRI_voc_size_t)(((maximalSize + pageSize - 1) / pageSize) * pageSize);

  // sanity check maximal size
  if (sizeof(TRI_df_header_marker_t) + sizeof(TRI_df_footer_marker_t) >
      maximalSize) {
    LOG(ERR) << "cannot create datafile, maximal size '" << (unsigned int)maximalSize << "' is too small";
    TRI_set_errno(TRI_ERROR_ARANGO_MAXIMAL_SIZE_TOO_SMALL);

    return nullptr;
  }

  // create either an anonymous or a physical datafile
  if (filename.empty()) {
#ifdef TRI_HAVE_ANONYMOUS_MMAP
    datafile = CreateAnonymousDatafile(fid, maximalSize);
#else
    // system does not support anonymous mmap
    return nullptr;
#endif
  } else {
    datafile = CreatePhysicalDatafile(filename, fid, maximalSize);
  }

  if (datafile == nullptr) {
    // an error occurred during creation
    return nullptr;
  }

  datafile->_state = TRI_DF_STATE_WRITE;

  if (withInitialMarkers) {
    int res = WriteInitialHeaderMarker(datafile, fid, maximalSize);

    if (res != TRI_ERROR_NO_ERROR) {
      LOG(ERR) << "cannot write header to datafile '" << datafile->getName() << "'";
      TRI_UNMMFile(datafile->_data, datafile->_maximalSize, datafile->_fd,
                   &datafile->_mmHandle);

      datafile->close();
      delete datafile;

      return nullptr;
    }
  }

  LOG(DEBUG) << "created datafile '" << datafile->getName() << "' of size " << maximalSize << " and page-size " << pageSize;

  return datafile;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief returns the name for a marker
////////////////////////////////////////////////////////////////////////////////

char const* TRI_NameMarkerDatafile(TRI_df_marker_t const* marker) {
  switch (marker->getType()) {
    // general markers
    case TRI_DF_MARKER_HEADER:
      return "datafile header";
    case TRI_DF_MARKER_FOOTER:
      return "footer";
    case TRI_DF_MARKER_BLANK:
      return "blank marker (used when repairing datafiles)";
    case TRI_DF_MARKER_COL_HEADER:
      return "collection header";
    case TRI_DF_MARKER_PROLOGUE:
      return "prologue";
    case TRI_DF_MARKER_VPACK_DOCUMENT:
      return "document";
    case TRI_DF_MARKER_VPACK_REMOVE:
      return "remove document";
    case TRI_DF_MARKER_VPACK_CREATE_COLLECTION:
      return "create collection";
    case TRI_DF_MARKER_VPACK_DROP_COLLECTION:
      return "drop collection";
    case TRI_DF_MARKER_VPACK_RENAME_COLLECTION:
      return "rename collection";
    case TRI_DF_MARKER_VPACK_CHANGE_COLLECTION:
      return "change collection";
    case TRI_DF_MARKER_VPACK_CREATE_INDEX:
      return "create index";
    case TRI_DF_MARKER_VPACK_DROP_INDEX:
      return "drop index";
    case TRI_DF_MARKER_VPACK_CREATE_DATABASE:
      return "create database";
    case TRI_DF_MARKER_VPACK_DROP_DATABASE:
      return "drop database";
    case TRI_DF_MARKER_VPACK_BEGIN_TRANSACTION:
      return "begin transaction";
    case TRI_DF_MARKER_VPACK_COMMIT_TRANSACTION:
      return "commit transaction";
    case TRI_DF_MARKER_VPACK_ABORT_TRANSACTION:
      return "abort transaction";

    default:
      return "unused/unknown";
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checks whether a marker is valid
////////////////////////////////////////////////////////////////////////////////

bool TRI_IsValidMarkerDatafile(TRI_df_marker_t const* marker) {
  if (marker == nullptr) {
    return false;
  }

  // check marker type
  TRI_df_marker_type_t const type = marker->getType();

  if (type <= TRI_DF_MARKER_MIN) {
    // marker type is less than minimum allowed type value
    return false;
  }

  if (type >= TRI_DF_MARKER_MAX) {
    // marker type is greater than maximum allowed type value
    return false;
  }

  if (marker->getSize() >= DatafileHelper::MaximalMarkerSize()) {
    // a single marker bigger than 256 MB seems unreasonable
    // note: this is an arbitrary limit
    return false;
  }

  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief reserves room for an element, advances the pointer
///
/// note: maximalJournalSize is the collection's maximalJournalSize property,
/// which may be different from the size of the current datafile
/// some callers do not set the value of maximalJournalSize
////////////////////////////////////////////////////////////////////////////////

int TRI_ReserveElementDatafile(TRI_datafile_t* datafile, TRI_voc_size_t size,
                               TRI_df_marker_t** position,
                               TRI_voc_size_t maximalJournalSize) {
  *position = nullptr;
  size = DatafileHelper::AlignedSize<TRI_voc_size_t>(size);

  if (datafile->_state != TRI_DF_STATE_WRITE) {
    if (datafile->_state == TRI_DF_STATE_READ) {
      LOG(ERR) << "cannot reserve marker, datafile is read-only";

      return TRI_set_errno(TRI_ERROR_ARANGO_READ_ONLY);
    }

    return TRI_set_errno(TRI_ERROR_ARANGO_ILLEGAL_STATE);
  }

  // check the maximal size
  if (size + DatafileHelper::JournalOverhead() > datafile->_maximalSize) {
    // marker is bigger than journal size.
    // adding the marker to this datafile will not work

    if (maximalJournalSize <= datafile->_maximalSize) {
      // the collection property 'maximalJournalSize' is equal to
      // or smaller than the size of this datafile
      // creating a new file and writing the marker into it will not work either
      return TRI_set_errno(TRI_ERROR_ARANGO_DOCUMENT_TOO_LARGE);
    }

    // if we get here, the collection's 'maximalJournalSize' property is
    // higher than the size of this datafile.
    // maybe the marker will fit into a new datafile with the bigger size?
    if (size + DatafileHelper::JournalOverhead() > maximalJournalSize) {
      // marker still won't fit
      return TRI_set_errno(TRI_ERROR_ARANGO_DOCUMENT_TOO_LARGE);
    }

    // fall-through intentional
  }

  // add the marker, leave enough room for the footer
  if (datafile->_currentSize + size + datafile->_footerSize >
      datafile->_maximalSize) {
    datafile->_lastError = TRI_set_errno(TRI_ERROR_ARANGO_DATAFILE_FULL);
    datafile->_full = true;

    LOG(TRACE) << "cannot write marker, not enough space";

    return TRI_ERROR_ARANGO_DATAFILE_FULL;
  }

  *position = reinterpret_cast<TRI_df_marker_t*>(datafile->_next);

  TRI_ASSERT(*position != nullptr);

  datafile->_next += size;
  datafile->_currentSize += size;

  return TRI_ERROR_NO_ERROR;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief writes a marker to the datafile
/// this function will write the marker as-is, without any CRC or tick updates
////////////////////////////////////////////////////////////////////////////////

int TRI_WriteElementDatafile(TRI_datafile_t* datafile, void* position,
                             TRI_df_marker_t const* marker, bool forceSync) {
  TRI_ASSERT(marker->getTick() > 0);
  TRI_ASSERT(marker->getSize() > 0);

  TRI_UpdateTicksDatafile(datafile, marker);

  if (datafile->_state != TRI_DF_STATE_WRITE) {
    if (datafile->_state == TRI_DF_STATE_READ) {
      LOG(ERR) << "cannot write marker, datafile is read-only";

      return TRI_set_errno(TRI_ERROR_ARANGO_READ_ONLY);
    }

    return TRI_set_errno(TRI_ERROR_ARANGO_ILLEGAL_STATE);
  }

  TRI_ASSERT(position != nullptr);

  // out of bounds check for writing into a datafile
  if (position == nullptr || position < (void*)datafile->_data ||
      position >= (void*)(datafile->_data + datafile->_maximalSize)) {
    LOG(ERR) << "logic error. writing out of bounds of datafile '" << datafile->getName() << "'";
    return TRI_set_errno(TRI_ERROR_ARANGO_ILLEGAL_STATE);
  }

  memcpy(position, marker, static_cast<size_t>(marker->getSize()));

  if (forceSync) {
    bool ok = datafile->sync(static_cast<char const*>(position),
                             reinterpret_cast<char const*>(position) + marker->getSize());

    if (!ok) {
      datafile->_state = TRI_DF_STATE_WRITE_ERROR;

      if (errno == ENOSPC) {
        datafile->_lastError = TRI_set_errno(TRI_ERROR_ARANGO_FILESYSTEM_FULL);
      } else {
        datafile->_lastError = TRI_set_errno(TRI_ERROR_SYS_ERROR);
      }

      LOG(ERR) << "msync failed with: " << TRI_last_error();

      return datafile->_lastError;
    } else {
      LOG(TRACE) << "msync succeeded " << (void*) position << ", size " << marker->getSize();
    }
  }

  return TRI_ERROR_NO_ERROR;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief update tick values for a datafile
////////////////////////////////////////////////////////////////////////////////

void TRI_UpdateTicksDatafile(TRI_datafile_t* datafile,
                             TRI_df_marker_t const* marker) {
  TRI_df_marker_type_t const type = marker->getType();

  if (type != TRI_DF_MARKER_HEADER && type != TRI_DF_MARKER_FOOTER &&
      type != TRI_DF_MARKER_COL_HEADER) {
    // every marker but headers / footers counts

    TRI_voc_tick_t tick = marker->getTick();

    if (datafile->_tickMin == 0) {
      datafile->_tickMin = tick;
    }

    if (datafile->_tickMax < tick) {
      datafile->_tickMax = tick;
    }

    if (datafile->_dataMin == 0) {
      datafile->_dataMin = tick;
    }

    if (datafile->_dataMax < tick) {
      datafile->_dataMax = tick;
    }
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checksums and writes a marker to the datafile
////////////////////////////////////////////////////////////////////////////////

int TRI_WriteCrcElementDatafile(TRI_datafile_t* datafile, void* position,
                                TRI_df_marker_t* marker, bool forceSync) {
  TRI_ASSERT(marker->getTick() != 0);

  if (datafile->isPhysical()) {
    TRI_voc_crc_t crc = TRI_InitialCrc32();

    crc = TRI_BlockCrc32(crc, (char const*)marker, marker->getSize());
    marker->setCrc(TRI_FinalCrc32(crc));
  }

  return TRI_WriteElementDatafile(datafile, position, marker, forceSync);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief iterates over a datafile
/// also may set datafile's min/max tick values
/// deprecated
////////////////////////////////////////////////////////////////////////////////

bool TRI_IterateDatafile(TRI_datafile_t* datafile,
                         bool (*iterator)(TRI_df_marker_t const*, void*,
                                          TRI_datafile_t*),
                         void* data) {
  TRI_ASSERT(iterator != nullptr);

  LOG(TRACE) << "iterating over datafile '" << datafile->getName() << "', fid: " << datafile->_fid;

  char const* ptr = datafile->_data;
  char const* end = datafile->_data + datafile->_currentSize;

  if (datafile->_state != TRI_DF_STATE_READ &&
      datafile->_state != TRI_DF_STATE_WRITE) {
    TRI_set_errno(TRI_ERROR_ARANGO_ILLEGAL_STATE);
    return false;
  }

  while (ptr < end) {
    auto const* marker = reinterpret_cast<TRI_df_marker_t const*>(ptr);

    if (marker->getSize() == 0) {
      return true;
    }

    // update the tick statistics
    TRI_UpdateTicksDatafile(datafile, marker);

    if (!iterator(marker, data, datafile)) {
      return false;
    }

    ptr += DatafileHelper::AlignedMarkerSize<size_t>(marker);
  }

  return true;
}

/// @brief iterates over a datafile
/// also may set datafile's min/max tick values
bool TRI_IterateDatafile(TRI_datafile_t* datafile,
                         std::function<bool(TRI_df_marker_t const*, TRI_datafile_t*)> const& cb) {
  LOG(TRACE) << "iterating over datafile '" << datafile->getName() << "', fid: " << datafile->_fid;

  char const* ptr = datafile->_data;
  char const* end = datafile->_data + datafile->_currentSize;

  if (datafile->_state != TRI_DF_STATE_READ &&
      datafile->_state != TRI_DF_STATE_WRITE) {
    TRI_set_errno(TRI_ERROR_ARANGO_ILLEGAL_STATE);
    return false;
  }

  while (ptr < end) {
    auto const* marker = reinterpret_cast<TRI_df_marker_t const*>(ptr);

    if (marker->getSize() == 0) {
      return true;
    }

    // update the tick statistics
    TRI_UpdateTicksDatafile(datafile, marker);

    if (!cb(marker, datafile)) {
      return false;
    }

    ptr += DatafileHelper::AlignedMarkerSize<size_t>(marker);
  }

  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief opens an existing datafile
///
/// The datafile will be opened read-only if a footer is found
////////////////////////////////////////////////////////////////////////////////

TRI_datafile_t* TRI_OpenDatafile(std::string const& filename, bool ignoreFailures) {
  // this function must not be called for non-physical datafiles
  TRI_ASSERT(!filename.empty());

  TRI_datafile_t* datafile = OpenDatafile(filename, false);

  if (datafile == nullptr) {
    return nullptr;
  }

  // check the datafile by scanning markers
  bool ok = CheckDatafile(datafile, ignoreFailures);

  if (!ok) {
    TRI_UNMMFile(datafile->_data, datafile->_maximalSize, datafile->_fd,
                 &datafile->_mmHandle);
    TRI_CLOSE(datafile->_fd);

    LOG(ERR) << "datafile '" << datafile->getName() << "' is corrupt";
    // must free datafile here
    delete datafile;

    return nullptr;
  }

  // change to read-write if no footer has been found
  if (!datafile->_isSealed) {
    datafile->_state = TRI_DF_STATE_WRITE;
    TRI_ProtectMMFile(datafile->_data, datafile->_maximalSize,
                      PROT_READ | PROT_WRITE, datafile->_fd,
                      &datafile->_mmHandle);
  }

  // Advise on sequential use:
  TRI_MMFileAdvise(datafile->_data, datafile->_maximalSize,
                   TRI_MADVISE_SEQUENTIAL);
  TRI_MMFileAdvise(datafile->_data, datafile->_maximalSize,
                   TRI_MADVISE_WILLNEED);

  return datafile;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief renames a datafile
////////////////////////////////////////////////////////////////////////////////

int TRI_RenameDatafile(TRI_datafile_t* datafile, char const* filename) {
  // this function must not be called for non-physical datafiles
  TRI_ASSERT(datafile->isPhysical());
  TRI_ASSERT(filename != nullptr);

  if (TRI_ExistsFile(filename)) {
    LOG(ERR) << "cannot overwrite datafile '" << filename << "'";

    datafile->_lastError =
        TRI_set_errno(TRI_ERROR_ARANGO_DATAFILE_ALREADY_EXISTS);
    return TRI_ERROR_ARANGO_DATAFILE_ALREADY_EXISTS;
  }

  int res = TRI_RenameFile(datafile->_filename.c_str(), filename);

  if (res != TRI_ERROR_NO_ERROR) {
    datafile->_state = TRI_DF_STATE_RENAME_ERROR;
    datafile->_lastError = TRI_set_errno(TRI_ERROR_SYS_ERROR);

    return res;
  }

  datafile->_filename = filename;

  return TRI_ERROR_NO_ERROR;
}

/// @brief seals a datafile, writes a footer, sets it to read-only
int TRI_datafile_t::seal() {
  if (_state == TRI_DF_STATE_READ) {
    return TRI_ERROR_ARANGO_READ_ONLY;
  }

  if (_state != TRI_DF_STATE_WRITE) {
    return TRI_ERROR_ARANGO_ILLEGAL_STATE;
  }

  if (_isSealed) {
    return TRI_ERROR_ARANGO_DATAFILE_SEALED;
  }

  // set a proper tick value
  if (_tickMax == 0) {
    _tickMax = TRI_NewTickServer();
  }

  // create the footer
  TRI_df_footer_marker_t footer = DatafileHelper::CreateFooterMarker(_tickMax);

  // reserve space and write footer to file
  _footerSize = 0;

  TRI_df_marker_t* position;
  int res =
      TRI_ReserveElementDatafile(this, footer.base.getSize(), &position, 0);

  if (res == TRI_ERROR_NO_ERROR) {
    TRI_ASSERT(position != nullptr);
    res = TRI_WriteCrcElementDatafile(this, position, &footer.base, false);
  }

  if (res != TRI_ERROR_NO_ERROR) {
    return res;
  }

  // sync file
  bool ok = sync(_synced, reinterpret_cast<char const*>(_data) + _currentSize);

  if (!ok) {
    _state = TRI_DF_STATE_WRITE_ERROR;

    if (errno == ENOSPC) {
      _lastError = TRI_set_errno(TRI_ERROR_ARANGO_FILESYSTEM_FULL);
    } else {
      _lastError = TRI_errno();
    }

    LOG(ERR) << "msync failed with: " << TRI_last_error();
  }

  // everything is now synced
  _synced = _written;

  TRI_ProtectMMFile(_data, _maximalSize, PROT_READ,
                    _fd, &_mmHandle);

  // seal datafile
  if (ok) {
    _isSealed = true;
    _state = TRI_DF_STATE_READ;
    // note: _initSize must remain constant
    TRI_ASSERT(_initSize == _maximalSize);
    _maximalSize = _currentSize;
  }

  if (!ok) {
    return _lastError;
  }

  if (isPhysical()) {
    // From now on we predict random access (until collection or compaction):
    TRI_MMFileAdvise(_data, _maximalSize, TRI_MADVISE_RANDOM);
  }

  return TRI_ERROR_NO_ERROR;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief truncates a datafile and seals it
/// this is called from the recovery procedure only
////////////////////////////////////////////////////////////////////////////////

int TRI_TruncateDatafile(std::string const& path, TRI_voc_size_t position) {
  // this function must not be called for non-physical datafiles
  TRI_ASSERT(!path.empty());

  TRI_datafile_t* datafile = OpenDatafile(path, true);

  if (datafile == nullptr) {
    return TRI_ERROR_ARANGO_DATAFILE_UNREADABLE;
  }

  int res = TruncateAndSealDatafile(datafile, position);
  delete datafile;

  return res;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief try to repair a datafile
////////////////////////////////////////////////////////////////////////////////

bool TRI_TryRepairDatafile(char const* path) {
  // this function must not be called for non-physical datafiles
  TRI_ASSERT(path != nullptr);

  TRI_datafile_t* datafile = OpenDatafile(path, true);

  if (datafile == nullptr) {
    return false;
  }

  // set to read/write access
  TRI_ProtectMMFile(datafile->_data, datafile->_maximalSize,
                    PROT_READ | PROT_WRITE, datafile->_fd,
                    &datafile->_mmHandle);

  bool result = TryRepairDatafile(datafile);
  delete datafile;

  return result;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief diagnoses a marker
////////////////////////////////////////////////////////////////////////////////

static std::string DiagnoseMarker(TRI_df_marker_t const* marker,
                                  char const* end) {
  std::ostringstream result;

  if (marker == nullptr) {
    return "marker is undefined. should not happen";
  }

  // check marker type
  TRI_df_marker_type_t type = marker->getType();

  if (type <= TRI_DF_MARKER_MIN) {
    // marker type is less than minimum allowed type value
    result << "marker type value (" << static_cast<int>(type)
           << ") is wrong. expecting value higher than " << TRI_DF_MARKER_MIN;
    return result.str();
  }

  if (type >= TRI_DF_MARKER_MAX) {
    // marker type is greater than maximum allowed type value
    result << "marker type value (" << static_cast<int>(type)
           << ") is wrong. expecting value less than " << TRI_DF_MARKER_MAX;
    return result.str();
  }

  TRI_voc_size_t size = marker->getSize();

  if (size >= DatafileHelper::MaximalMarkerSize()) {
    // a single marker bigger than this size seems unreasonable
    // note: this is an arbitrary limit
    result << "marker size value (" << size
           << ") is wrong. expecting value less than "
           << DatafileHelper::MaximalMarkerSize();
    return result.str();
  }

  if (size < sizeof(TRI_df_marker_t)) {
    result << "marker size is too small (" << size
           << "). expecting at least " << sizeof(TRI_df_marker_t) << " bytes";
    return result.str();
  }

  if (reinterpret_cast<char const*>(marker) + size > end) {
    return "marker size is beyond end of datafile";
  }

  TRI_voc_crc_t crc = CalculateCrcValue(marker);

  if (marker->getCrc() == crc) {
    return "crc checksum is correct";
  }
   
  result << "crc checksum (hex " << std::hex << marker->getCrc()
         << ") is wrong. expecting (hex " << std::hex << crc << ")";

  return result.str();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief scans a datafile
////////////////////////////////////////////////////////////////////////////////

static DatafileScan ScanDatafile(TRI_datafile_t const* datafile) {
  // this function must not be called for non-physical datafiles
  TRI_ASSERT(datafile->isPhysical());

  char* ptr = datafile->_data;
  char* end = datafile->_data + datafile->_currentSize;
  TRI_voc_size_t currentSize = 0;

  DatafileScan scan;

  scan.currentSize = datafile->_currentSize;
  scan.maximalSize = datafile->_maximalSize;

  if (datafile->_currentSize == 0) {
    end = datafile->_data + datafile->_maximalSize;
  }

  while (ptr < end) {
    TRI_df_marker_t* marker = reinterpret_cast<TRI_df_marker_t*>(ptr);

    DatafileScanEntry entry;
    entry.position = static_cast<TRI_voc_size_t>(ptr - datafile->_data);
    entry.size = marker->getSize();
    entry.realSize = static_cast<TRI_voc_size_t>(DatafileHelper::AlignedMarkerSize<size_t>(marker));
    entry.tick = marker->getTick();
    entry.type = marker->getType();
    entry.status = 1;
    entry.typeName = TRI_NameMarkerDatafile(marker);

    if (marker->getSize() == 0 && marker->getCrc() == 0 && marker->getType() == 0 &&
        marker->getTick() == 0) {
      entry.status = 2;

      scan.endPosition = currentSize;
      scan.entries.emplace_back(entry);
      return scan;
    }

    ++scan.numberMarkers;

    if (marker->getSize() == 0) {
      entry.status = 3;

      scan.status = 2;
      scan.endPosition = currentSize;
      scan.entries.emplace_back(entry);
      return scan;
    }

    if (marker->getSize() < sizeof(TRI_df_marker_t)) {
      entry.status = 4;

      entry.diagnosis = DiagnoseMarker(marker, end);
      scan.endPosition = currentSize;
      scan.status = 3;

      scan.entries.emplace_back(entry);
      return scan;
    }

    if (!TRI_IsValidMarkerDatafile(marker)) {
      entry.status = 4;

      entry.diagnosis = DiagnoseMarker(marker, end);
      scan.endPosition = currentSize;
      scan.status = 3;

      scan.entries.emplace_back(entry);
      return scan;
    }

    bool ok = CheckCrcMarker(marker, end);

    if (!ok) {
      entry.status = 5;

      entry.diagnosis = DiagnoseMarker(marker, end);
      scan.status = 4;
    }

    TRI_df_marker_type_t const type = marker->getType();

    if (type == TRI_DF_MARKER_VPACK_DOCUMENT ||
        type == TRI_DF_MARKER_VPACK_REMOVE) {
      VPackSlice const slice(reinterpret_cast<char const*>(marker) + DatafileHelper::VPackOffset(type));
      TRI_ASSERT(slice.isObject());
      entry.key = slice.get(StaticStrings::KeyString).copyString();
    }

    scan.entries.emplace_back(entry);

    size_t size = DatafileHelper::AlignedMarkerSize<size_t>(marker);
    currentSize += static_cast<TRI_voc_size_t>(size);

    if (marker->getType() == TRI_DF_MARKER_FOOTER) {
      scan.endPosition = currentSize;
      scan.isSealed = true;
      return scan;
    }

    ptr += size;
  }

  return scan;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief returns information about the datafile
////////////////////////////////////////////////////////////////////////////////

DatafileScan TRI_ScanDatafile(char const* path) {
  DatafileScan scan;

  // this function must not be called for non-physical datafiles
  TRI_ASSERT(path != nullptr);

  TRI_datafile_t* datafile = OpenDatafile(path, true);

  if (datafile != nullptr) {
    scan = ScanDatafile(datafile);
    delete datafile;
  } else {
    scan.currentSize = 0;
    scan.maximalSize = 0;
    scan.endPosition = 0;
    scan.numberMarkers = 0;

    scan.status = 5;
    scan.isSealed = false;
  }

  return scan;
}


TRI_datafile_t::TRI_datafile_t(std::string const& filename, int fd, void* mmHandle, TRI_voc_size_t maximalSize,
                               TRI_voc_size_t currentSize, TRI_voc_fid_t fid, char* data)
        : _fid(fid),
          _state(TRI_DF_STATE_READ),
          _fd(fd),
          _mmHandle(mmHandle),
          _initSize(maximalSize), 
          _maximalSize(maximalSize), 
          _currentSize(currentSize),
          _footerSize(sizeof(TRI_df_footer_marker_t)),
          _data(data),
          _next(data + currentSize),
          _tickMin(0),
          _tickMax(0),
          _dataMin(0),
          _dataMax(0),
          _filename(filename),
          _lastError(TRI_ERROR_NO_ERROR),
          _full(false),
          _isSealed(false),
          _synced(data),
          _written(nullptr) {
  // filename is a string for physical datafiles, and NULL for anonymous regions
  // fd is a positive value for physical datafiles, and -1 for anonymous regions
  if (filename.empty()) {
    TRI_ASSERT(fd == -1);
  } else {
    TRI_ASSERT(fd >= 0);

    // Advise OS that sequential access is going to happen:
    TRI_MMFileAdvise(_data, _maximalSize, TRI_MADVISE_SEQUENTIAL);
  }
}
  
TRI_datafile_t::~TRI_datafile_t() {
  try {
    this->close();
  } catch (...) {
    // silently continue as this is the destructor
  }
}

/// @brief return the name of a datafile
std::string TRI_datafile_t::getName() const {
  if (_filename.empty()) {
    // anonymous regions do not have a filename
    return "anonymous region";
  }

  // return name of the physical file
  return _filename;
}

/// @brief close a datafile
int TRI_datafile_t::close() {
  if (_state == TRI_DF_STATE_READ ||
      _state == TRI_DF_STATE_WRITE) {
    int res = TRI_UNMMFile(_data, _initSize, _fd, &_mmHandle);

    if (res != TRI_ERROR_NO_ERROR) {
      LOG(ERR) << "munmap failed with: " << res;
      _state = TRI_DF_STATE_WRITE_ERROR;
      _lastError = res;
      return res;
    }

    if (isPhysical()) {
      int res = TRI_CLOSE(_fd);

      if (res != TRI_ERROR_NO_ERROR) {
        LOG(ERR) << "unable to close datafile '" << getName() << "': " << res;
      }
    }

    _state = TRI_DF_STATE_CLOSED;
    _data = nullptr;
    _next = nullptr;
    _fd = -1;

    return TRI_ERROR_NO_ERROR;
  } 
  
  if (_state == TRI_DF_STATE_CLOSED) {
    LOG(WARN) << "closing an already closed datafile '" << getName() << "'";
    return TRI_ERROR_NO_ERROR;
  } 
  
  return TRI_ERROR_ARANGO_ILLEGAL_STATE;
}

/// @brief sync the data of a datafile
bool TRI_datafile_t::sync(char const* begin, char const* end) {
  if (!isPhysical()) {
    // anonymous regions do not need to be synced
    return true;
  }

  TRI_ASSERT(_fd >= 0);

  if (begin == end) {
    // no need to sync
    return true;
  }

  return TRI_MSync(_fd, begin, end);
}