/*=========================================================================

  Program: GDCM (Grassroots DICOM). A DICOM library

  Copyright (c) 2006-2011 Mathieu Malaterre
  All rights reserved.
  See Copyright.txt or http://gdcm.sourceforge.net/Copyright.html for details.

     This software is distributed WITHOUT ANY WARRANTY; without even
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notice for more information.

=========================================================================*/
#include "gdcmReader.h"
#include "gdcmTrace.h"
#include "gdcmVR.h"
#include "gdcmFileMetaInformation.h"
#include "gdcmSwapper.h"

#include "gdcmDeflateStream.h"
#include "gdcmSystem.h"

#include "gdcmExplicitDataElement.h"
#include "gdcmImplicitDataElement.h"

#ifdef _MSC_VER
#include <windows.h> // MultiByteToWideChar
#endif

#ifdef GDCM_SUPPORT_BROKEN_IMPLEMENTATION
#include "gdcmUNExplicitDataElement.h"
#include "gdcmCP246ExplicitDataElement.h"
#include "gdcmExplicitImplicitDataElement.h"
#include "gdcmUNExplicitImplicitDataElement.h"
#include "gdcmVR16ExplicitDataElement.h"
#endif


namespace gdcm_ns
{

Reader::Reader():F(new File)
{
  Stream = nullptr;
  Ifstream = nullptr;
}

Reader::~Reader()
{
  if (Ifstream)
    {
    Ifstream->close();
    delete Ifstream;
    Ifstream = nullptr;
    Stream = nullptr;
    }
}

/// \brief tells us if "DICM" is found as position 128
///        (i.e. the file is a 'true dicom' one)
/// If not found then seek back at beginning of file (could be Mallinckrodt
/// or old ACRNEMA with no preamble)
/// \precondition we are at the beginning of file
/// \postcondition we are at the beginning of the DataSet or
/// Meta Information Header
bool Reader::ReadPreamble()
{
 return true;
}

/// \brief read the DICOM Meta Information Header
/// Find out the TransferSyntax used (default: Little Endian Explicit)
/// \precondition we are at the start of group 0x0002 (well after preamble)
/// \postcondition we are at the beginning of the DataSet
bool Reader::ReadMetaInformation()
{
  return true;
}

bool Reader::ReadDataSet()
{
  return true;
}

TransferSyntax Reader::GuessTransferSyntax()
{
  // Don't call this function if you have a meta file info
  //assert( Header->GetTransferSyntaxType() == TransferSyntax::TS_END );
  std::streampos start = Stream->tellg();
  SwapCode sc = SwapCode::Unknown;
  TransferSyntax::NegociatedType nts = TransferSyntax::Unknown;
  TransferSyntax ts (TransferSyntax::TS_END);
  Tag t;
  t.Read<SwapperNoOp>(*Stream);
  if( ! (t.GetGroup() % 2) )
    {
    switch( t.GetGroup() )
      {
    case 0x0008:
      sc = SwapCode::LittleEndian;
      break;
    case 0x0800:
      sc = SwapCode::BigEndian;
      break;
    default:
      assert(0);
      }
    // Purposely not Re-use ReadVR since we can read VR_END
    char vr_str[3];
    Stream->read(vr_str, 2);
    vr_str[2] = '\0';
    // Cannot use GetVRTypeFromFile since is assert ...
    VR::VRType vr = VR::GetVRType(vr_str);
    if( vr != VR::VR_END )
      {
      nts = TransferSyntax::Explicit;
      }
    else
      {
      assert( !(VR::IsSwap(vr_str)));
      Stream->seekg(-2, std::ios::cur); // Seek back
      if( t.GetElement() == 0x0000 )
        {
        VL gl; // group length
        gl.Read<SwapperNoOp>(*Stream);
        switch(gl)
          {
        case 0x00000004 :
          sc = SwapCode::LittleEndian;    // 1234
          break;
        case 0x04000000 :
          sc = SwapCode::BigEndian;       // 4321
          break;
        case 0x00040000 :
          sc = SwapCode::BadLittleEndian; // 3412
          gdcmWarningMacro( "Bad Little Endian" );
          break;
        case 0x00000400 :
          sc = SwapCode::BadBigEndian;    // 2143
          gdcmWarningMacro( "Bad Big Endian" );
          break;
        default:
          assert(0);
          }
        }
      nts = TransferSyntax::Implicit;
      }
    }
  else
    {
    gdcmWarningMacro( "Start with a private tag creator" );
    assert( t.GetGroup() > 0x0002 );
    switch( t.GetElement() )
      {
    case 0x0010:
      sc = SwapCode::LittleEndian;
      break;
    default:
      assert(0);
      }
    // Purposely not Re-use ReadVR since we can read VR_END
    char vr_str[3];
    Stream->read(vr_str, 2);
    vr_str[2] = '\0';
    // Cannot use GetVRTypeFromFile since is assert ...
    VR::VRType vr = VR::GetVRType(vr_str);
    if( vr != VR::VR_END )
      {
      nts = TransferSyntax::Explicit;
      }
    else
      {
      nts = TransferSyntax::Implicit;
      // We are reading a private creator (0x0010) so it's LO, it's
      // difficult to come up with something to check, maybe that
      // VL < 256 ...
      gdcmWarningMacro( "Very dangerous assertion needs some work" );
      }
    }
  assert( nts != TransferSyntax::Unknown );
  assert( sc != SwapCode::Unknown );
  if( nts == TransferSyntax::Implicit )
    {
    if( sc == SwapCode::BigEndian )
      {
      ts = TransferSyntax::ImplicitVRBigEndianACRNEMA;
      }
    else if ( sc == SwapCode::LittleEndian )
      {
      ts = TransferSyntax::ImplicitVRLittleEndian;
      }
    else
      {
      assert(0);
      }
    }
  else
    {
    assert(0);
    }
  Stream->seekg( start, std::ios::beg );
  assert( ts != TransferSyntax::TS_END );
  return ts;
}

namespace details
{
  class DefaultCaller
  {
  private:
    DataSet & m_dataSet;
  public:
    DefaultCaller(DataSet &ds): m_dataSet(ds){}
    template<class T1, class T2>
      void ReadCommon(std::istream & is) const
        {
        m_dataSet.template Read<T1,T2>(is);
        }
    template<class T1, class T2>
      void ReadCommonWithLength(std::istream & is, VL & length) const
        {
        m_dataSet.template ReadWithLength<T1,T2>(is,length);
        // manually set eofbit:
        // https://groups.google.com/forum/?fromgroups#!topic/comp.lang.c++/yTW4ESh1IL8
        is.setstate( std::ios::eofbit );
        }
    static void Check(bool b, std::istream &stream)
      {
      (void)stream;
      if( b ) assert( stream.eof() );
      }
  };

  class ReadUpToTagCaller
  {
  private:
    DataSet & m_dataSet;
    const Tag & m_tag;
    std::set<Tag> const & m_skipTags;
  public:
    ReadUpToTagCaller(DataSet &ds,const Tag & tag, std::set<Tag> const & skiptags)
    :
    m_dataSet(ds),m_tag(tag),m_skipTags(skiptags)
    {
    }

    template<class T1, class T2>
      void ReadCommon(std::istream & is) const
        {
        m_dataSet.template ReadUpToTag<T1,T2>(is,m_tag,m_skipTags);
        }
    template<class T1, class T2>
      void ReadCommonWithLength(std::istream & is, VL & length) const
        {
        m_dataSet.template ReadUpToTagWithLength<T1,T2>(is,m_tag,m_skipTags,length);
        }
    static void Check(bool , std::istream &)  {}
  };

  class ReadSelectedTagsCaller
  {
  private:
    DataSet & m_dataSet;
    std::set<Tag> const & m_tags;
    bool m_readvalues;
  public:
    ReadSelectedTagsCaller(DataSet &ds, std::set<Tag> const & tags, const bool readvalues)
      :
    m_dataSet(ds),m_tags(tags),m_readvalues(readvalues)
    {
    }

    template<class T1, class T2>
    void ReadCommon(std::istream & is) const
    {
      m_dataSet.template ReadSelectedTags<T1,T2>(is,m_tags,m_readvalues);
    }
    template<class T1, class T2>
    void ReadCommonWithLength(std::istream & is, VL & length) const
    {
      m_dataSet.template ReadSelectedTagsWithLength<T1,T2>(is,m_tags,length,m_readvalues);
    }
    static void Check(bool , std::istream &)  {}
  };

  class ReadSelectedPrivateTagsCaller
  {
  private:
    DataSet & m_dataSet;
    std::set<PrivateTag> const & m_groups;
    bool m_readvalues;
  public:
    ReadSelectedPrivateTagsCaller(DataSet &ds, std::set<PrivateTag> const & groups, const bool readvalues)
      :
    m_dataSet(ds),m_groups(groups),m_readvalues(readvalues)
    {
    }

    template<class T1, class T2>
    void ReadCommon(std::istream & is) const
    {
      m_dataSet.template ReadSelectedPrivateTags<T1,T2>(is,m_groups,m_readvalues);
    }
    template<class T1, class T2>
    void ReadCommonWithLength(std::istream & is, VL & length) const
    {
      m_dataSet.template ReadSelectedPrivateTagsWithLength<T1,T2>(is,m_groups,length,m_readvalues);
    }
    static void Check(bool , std::istream &)  {}
  };
}

bool Reader::Read()
{
  details::DefaultCaller caller(F->GetDataSet());
  return InternalReadCommon(caller);
}

bool Reader::ReadUpToTag(const Tag & tag, std::set<Tag> const & skiptags)
{
  details::ReadUpToTagCaller caller(F->GetDataSet(),tag,skiptags);
  return InternalReadCommon(caller);
}

bool Reader::ReadSelectedTags( std::set<Tag> const & selectedTags, bool readvalues )
{
  details::ReadSelectedTagsCaller caller(F->GetDataSet(), selectedTags,readvalues);
  return InternalReadCommon(caller);
}

bool Reader::ReadSelectedPrivateTags( std::set<PrivateTag> const & selectedPTags, bool readvalues )
{
  details::ReadSelectedPrivateTagsCaller caller(F->GetDataSet(), selectedPTags,readvalues);
  return InternalReadCommon(caller);
}

template <typename T_Caller>
bool Reader::InternalReadCommon(const T_Caller &caller)
{
  if( !Stream || !*Stream )
    {
    gdcmErrorMacro( "No File" );
    return false;
    }
  bool success = true;

  try
    {
    std::istream &is = *Stream;

    bool haspreamble = true;
    try
      {
      F->GetHeader().GetPreamble().Read( is );
      }
    catch( std::exception & )
      {
      // return to beginning of file, hopefully this file is simply missing preamble
      is.clear();
      is.seekg(0, std::ios::beg);
      haspreamble = false;
      }
    catch( ... )
      {
      assert(0);
      }

    bool hasmetaheader = false;
    try
      {
      if( haspreamble )
        {
        try
          {
          F->GetHeader().Read( is );
          hasmetaheader = true;
          assert( !F->GetHeader().IsEmpty() );
          }
        catch( std::exception &ex )
          {
          (void)ex;  //to avoid unreferenced variable warning on release
          gdcmWarningMacro(ex.what());
          // Weird implicit meta header:
          is.seekg(128+4, std::ios::beg );
          assert( is.good() );
          try
            {
            F->GetHeader().ReadCompat(is);
            }
          catch( std::exception &ex2 )
            {
            (void)ex2;  //to avoid unreferenced variable warning on release
            // Ok I get it now... there is absolutely no meta header, giving up
            //hasmetaheader = false;
            gdcmErrorMacro(ex2.what());
            }
          }
        }
      else
        {
        F->GetHeader().ReadCompat(is);
        }
      }
    catch( std::exception & )
      {
      // Same player play again:
      is.seekg(0, std::ios::beg );
      hasmetaheader = false;
      }
    catch( ... )
      {
      // Ooops..
      assert(0);
      }
    if( F->GetHeader().IsEmpty() )
      {
      hasmetaheader = false;
      gdcmDebugMacro( "no file meta info found" );
      }

    const TransferSyntax &ts = F->GetHeader().GetDataSetTransferSyntax();
    if( !ts.IsValid() )
      {
      throw Exception( "Meta Header issue" );
      }

  // Special case where the dataset was compressed using the deflate
  // algorithm
  if( ts == TransferSyntax::DeflatedExplicitVRLittleEndian )
    {

    zlib_stream::zip_istream gzis( is );
    // FIXME: we also know in this case that we are dealing with Explicit:
    assert( ts.GetNegociatedType() == TransferSyntax::Explicit );
    //F->GetDataSet().ReadUpToTag<ExplicitDataElement,SwapperNoOp>(gzis,tag, skiptags);
    caller.template ReadCommon<ExplicitDataElement,SwapperNoOp>(gzis);
    // I need the following hack to read: srwithgraphdeflated.dcm
    //is.clear();
    // well not anymore, see special handling of trailing \0 in:
    // basic_unzip_streambuf<charT, traits>::fill_input_buffer(void)
    return is.good();
    }

  try
    {
    if( ts.GetSwapCode() == SwapCode::BigEndian )
      {
      //US-RGB-8-epicard.dcm is big endian
      if( ts.GetNegociatedType() == TransferSyntax::Implicit )
        {
        // There is no such thing as Implicit Big Endian... oh well
        // LIBIDO-16-ACR_NEMA-Volume.dcm
        //F->GetDataSet().ReadUpToTag<ImplicitDataElement,SwapperDoOp>(is,tag, skiptags);
        //caller.template ReadCommon<ImplicitDataElement,SwapperDoOp>(is);
        gdcmErrorMacro( "VirtualBigEndianNotHandled" );
        throw "Virtual Big Endian Implicit is not defined by DICOM";
        }
      else
        {
        //F->GetDataSet().ReadUpToTag<ExplicitDataElement,SwapperDoOp>(is,tag, skiptags);
        caller.template ReadCommon<ExplicitDataElement,SwapperDoOp>(is);
        }
      }
    else // LittleEndian
      {
      if( ts.GetNegociatedType() == TransferSyntax::Implicit )
        {
        if( hasmetaheader && haspreamble )
          {
          //F->GetDataSet().ReadUpToTag<ImplicitDataElement,SwapperNoOp>(is,tag, skiptags);
          caller.template ReadCommon<ImplicitDataElement,SwapperNoOp>(is);
          }
        else
          {
          std::streampos start = is.tellg();
          is.seekg( 0, std::ios::end);
          std::streampos end = is.tellg();
          assert( !is.eof() );
          assert( is.good() );
          std::streamoff theOffset = end-start;
          assert (theOffset > 0 || (uint32_t)theOffset < std::numeric_limits<uint32_t>::max());
          VL l = (uint32_t)(theOffset);
          is.seekg( start, std::ios::beg );
          assert( is.good() );
          assert( !is.eof() );
          caller.template ReadCommonWithLength<ImplicitDataElement,SwapperNoOp>(is,l);
          }
        }
      else
        {
        caller.template ReadCommon<ExplicitDataElement,SwapperNoOp>(is);
        }
      }
    }
  // Only catch parse exception at this point
  catch( ParseException &ex )
    {
#ifdef GDCM_SUPPORT_BROKEN_IMPLEMENTATION
    if( ex.GetLastElement().GetVR() == VR::UN && ex.GetLastElement().IsUndefinedLength() )
      {
      // non CP 246
      // P.Read( is );
      is.clear();
      if( haspreamble )
        {
        is.seekg(128+4, std::ios::beg);
        }
      else
        {
        is.seekg(0, std::ios::beg);
        }
      if( hasmetaheader )
        {
        // FIXME: we are reading twice the same meta-header, we succedeed the first time...
        // We should be able to seek to proper place instead of re-reading
        FileMetaInformation header;
        header.Read(is);
        }

      // GDCM 1.X
      gdcmWarningMacro( "Attempt to read non CP 246" );
      F->GetDataSet().Clear(); // remove garbage from 1st attempt...
      //F->GetDataSet().ReadUpToTag<CP246ExplicitDataElement,SwapperNoOp>(is,tag, skiptags);
      caller.template ReadCommon<CP246ExplicitDataElement,SwapperNoOp>(is);
      }
    else if( ex.GetLastElement().GetVR() == VR::UN )
      {
      // P.Read( is );
      is.clear();
      if( haspreamble )
        {
        is.seekg(128+4, std::ios::beg);
        }
      else
        {
        is.seekg(0, std::ios::beg);
        }
      if( hasmetaheader )
        {
        // FIXME: we are reading twice the same meta-header, we succedeed the first time...
        // We should be able to seek to proper place instead of re-reading
        FileMetaInformation header;
        header.Read(is);
        }

      // GDCM 1.X
      gdcmWarningMacro( "Attempt to read GDCM 1.X wrongly encoded");
      F->GetDataSet().Clear(); // remove garbage from 1st attempt...
      //F->GetDataSet().ReadUpToTag<UNExplicitDataElement,SwapperNoOp>(is,tag, skiptags);
      caller.template ReadCommon<UNExplicitDataElement,SwapperNoOp>(is);
      // This file can only be rewritten as implicit...
      }
    else if ( ex.GetLastElement().GetTag() == Tag(0xfeff,0x00e0) )
      {
      // Famous philips where some private sequence were byteswapped !
      // eg. PHILIPS_Intera-16-MONO2-Uncompress.dcm
      // P.Read( is );
      is.clear();
      if( haspreamble )
        {
        is.seekg(128+4, std::ios::beg);
        }
      else
        {
        is.seekg(0, std::ios::beg);
        }
      if( hasmetaheader )
        {
        // FIXME: we are reading twice the same meta-header, we succedeed the first time...
        // We should be able to seek to proper place instead of re-reading
        FileMetaInformation header;
        header.Read(is);
        }

      //
      gdcmWarningMacro( "Attempt to read Philips with ByteSwap private sequence wrongly encoded");
      F->GetDataSet().Clear(); // remove garbage from 1st attempt...
      assert(0);  // TODO FIXME
      }
    else if( ex.GetLastElement().GetVR() == VR::INVALID )
      {
      if( ts.GetNegociatedType() == TransferSyntax::Explicit )
        {
        try
          {
          gdcmWarningMacro( "Attempt to read file with VR16bits" );
          // We could not read the VR in an explicit dataset
          // seek back tag + vr:
          is.seekg( -6, std::ios::cur );
          VR16ExplicitDataElement ide;
          ide.template Read<SwapperNoOp>( is );
          // If we are here it means we succeeded in reading the implicit data element:
          F->GetDataSet().Insert( ide );
          //F->GetDataSet().template Read<VR16ExplicitDataElement,SwapperNoOp>(is);
          caller.template ReadCommon<VR16ExplicitDataElement,SwapperNoOp>(is);
          // This file can only be rewritten as implicit...
          }
        catch ( Exception & )
          {
          try
            {
            // Ouch ! the file is neither:
            // 1. An Explicit encoded
            // 2. I could not reread it using the VR16Explicit reader, last option is
            // that the file is explicit/implicit
            is.clear();
            if( haspreamble )
              {
              is.seekg(128+4, std::ios::beg);
              }
            else
              {
              is.seekg(0, std::ios::beg);
              }
            if( hasmetaheader )
              {
              // FIXME: we are reading twice the same meta-header, we succedeed the first time...
              // We should be able to seek to proper place instead of re-reading
              FileMetaInformation header;
              header.Read(is);
              }

            // Explicit/Implicit
            // gdcmData/c_vf1001.dcm falls into that category, while in fact the fmi could simply
            // be inverted and all would be perfect...
            gdcmWarningMacro( "Attempt to read file with explicit/implicit" );
            F->GetDataSet().Clear(); // remove garbage from 1st attempt...
            //F->GetDataSet().template Read<ExplicitImplicitDataElement,SwapperNoOp>(is);
            caller.template ReadCommon<ExplicitImplicitDataElement,SwapperNoOp>(is);
            }
          catch ( Exception &ex2 )
            {
            (void)ex2;
            // Mon Jan 24 10:59:25 CET 2011
            // MM: UNExplicitImplicitDataElement does not seems to be used anymore to read
            // gdcmData/TheralysGDCM120Bug.dcm, instead the code path goes into
            // ExplicitImplicitDataElement class instead.
            // Simply rethrow the exception for now.
            throw;
            }
          }
        }
      }
    else
      {
      gdcmWarningMacro( "Attempt to read the file as mixture of explicit/implicit");
      // Let's try again with an ExplicitImplicitDataElement:
      if( ts.GetSwapCode() == SwapCode::LittleEndian &&
        ts.GetNegociatedType() == TransferSyntax::Explicit )
        {
        // P.Read( is );
        if( haspreamble )
          {
          is.seekg(128+4, std::ios::beg);
          }
        else
          {
          is.seekg(0, std::ios::beg);
          }
        if( hasmetaheader )
          {
          // FIXME: we are reading twice the same meta-header, we succedeed the first time...
          // We should be able to seek to proper place instead of re-reading
          FileMetaInformation header;
          header.ReadCompat(is);
          }

        // Philips
        F->GetDataSet().Clear(); // remove garbage from 1st attempt...
        //F->GetDataSet().ReadUpToTag<ExplicitImplicitDataElement,SwapperNoOp>(is,tag, skiptags);
        caller.template ReadCommon<ExplicitImplicitDataElement,SwapperNoOp>(is);
        // This file can only be rewritten as implicit...
        }
      else
        {
        gdcmDebugMacro( "No way this is DICOM" );
        success = false;
        }
      }
#else
    gdcmDebugMacro( ex.what() ); (void)ex;
    success = false;
#endif /* GDCM_SUPPORT_BROKEN_IMPLEMENTATION */
    }
  catch( Exception &ex )
    {
    (void)ex;  //to avoid unreferenced variable warning on release
    gdcmDebugMacro( ex.what() );
    success = false;
    }
  catch( ... )
    {
    gdcmWarningMacro( "Unknown exception" );
    success = false;
    }

  //if( success ) assert( Stream->eof() );
  caller.Check(success, *Stream );
    }
  catch( Exception &ex )
    {
    (void)ex;  //to avoid unreferenced variable warning on release
    gdcmDebugMacro( ex.what() );
    success = false;
    }
  catch( ... )
    {
    gdcmWarningMacro( "Unknown exception" );
    success = false;
    }

  // FIXME : call this function twice...
  if (Ifstream && Ifstream->is_open())
    {
    //Ifstream->close();
    //delete Ifstream;
    //Ifstream = NULL;
    //Stream = NULL;
    }

  return success;
}

static inline bool isasciiupper( char c ) {
  return c >= 'A' && c <= 'Z';
}

// This function re-implements code from:
// http://www.dclunie.com/medical-image-faq/html/part2.html#DICOMTransferSyntaxDetermination
// The above code does not work well for random file. It implicitly assumes we
// are trying to read a DICOM file in the first place, while our goal is indeed
// to detect whether or not the file can be assimilated as DICOM. So we
// extended it.  Of course this function only returns a 'maybe DICOM', since we
// are not guaranteed that the stream is not truncated, but this is outside the
// scope of this function.
bool Reader::CanRead() const
{
  if( !Stream ) return false;

  // fastpath
  std::istream &is = *Stream;
  if( is.bad() ) return false;
  if( is.tellg() != std::streampos(0) ) return false;
    {
    is.seekg( 128, std::ios::beg ); // we ignore return value as we test is.good()
    char b[4];
    if (is.good() && is.read(b,4) && strncmp(b,"DICM",4) == 0)
      {
      is.seekg(0, std::ios::beg);
      return true;
      }
    }

  // Start overhead for backward compatibility
  bool bigendian = false;
  bool explicitvr = false;
  is.clear();
  is.seekg(0, std::ios::beg);

  char b[8];
  if (is.good() && is.read(b,8))
    {
    // examine probable group number ... assume <= 0x00ff
    if (b[0] < b[1]) bigendian=true;
    else if (b[0] == 0 && b[1] == 0)
      {
      // blech ... group number is zero
      // no point in looking at element number
      // as it will probably be zero too (group length)
      // try the 32 bit value length of implicit vr
      if (b[4] < b[7]) bigendian=true;
      }
    // else littleendian
    if (isasciiupper(b[4]) && isasciiupper(b[5])) explicitvr=true;
    }
  SwapCode sc = SwapCode::Unknown;
  TransferSyntax::NegociatedType nts = TransferSyntax::Unknown;

  std::stringstream ss( std::string(b, 8) );

  Tag t;
  if (bigendian)
    {
    t.Read<SwapperDoOp>(ss);
    //assert( t.GetGroup() != 0x2 );
    if( t.GetGroup() <= 0xff )
      sc = SwapCode::BigEndian;
    }
  else
    {
    t.Read<SwapperNoOp>(ss);
    //assert( t.GetGroup() != 0x2 );
    if( t.GetGroup() <= 0xff )
      sc = SwapCode::LittleEndian;
    }

  VL vl;
  VR::VRType vr = VR::VR_END;
  if (explicitvr)
    {
    char vr_str[3];
    vr_str[0] = b[4];
    vr_str[1] = b[5];
    vr_str[2] = '\0';
    vr = VR::GetVRType(vr_str);
    if( vr != VR::VR_END )
      nts = TransferSyntax::Explicit;
    }
  else
    {
    if( bigendian )
      vl.Read<SwapperDoOp>( ss );
    else
      vl.Read<SwapperNoOp>( ss );
    if( vl < 0xff )
      nts = TransferSyntax::Implicit;
    }

  // reset in all other cases:
  is.clear();
  is.seekg(0, std::ios::beg);

  // Implicit Little Endian
  if( nts == TransferSyntax::Implicit && sc == SwapCode::LittleEndian ) return true;
  if( nts == TransferSyntax::Implicit && sc == SwapCode::BigEndian ) return false;
  if( nts == TransferSyntax::Explicit && sc == SwapCode::LittleEndian ) return true;
  if( nts == TransferSyntax::Explicit && sc == SwapCode::BigEndian ) return true;

  return false;
}

void Reader::SetFileName(const char *utf8path)
{
  if(Ifstream) delete Ifstream;
  Ifstream = new std::ifstream();
  if (utf8path && *utf8path) {
#ifdef _MSC_VER
    const std::wstring uncpath = System::ConvertToUNC(utf8path);
    Ifstream->open(uncpath.c_str(), std::ios::binary);
#else
    Ifstream->open( utf8path, std::ios::binary);
#endif
  }
  if( Ifstream->is_open() )
    {
    Stream = Ifstream;
    assert( Stream && *Stream );
    }
  else
    {
    delete Ifstream;
    Ifstream = nullptr;
    Stream = nullptr;
    }
}

size_t Reader::GetStreamCurrentPosition() const
{
  return static_cast<size_t>(GetStreamPtr()->tellg());
}


} // end namespace gdcm_ns