// gdcmElementSet.cxx
//-----------------------------------------------------------------------------
//
#include "gdcmElementSet.h"
#include "gdcmTS.h"


//-----------------------------------------------------------------------------
// Constructor / Destructor
/**
 * \ingroup gdcmElementSet
 * \brief   Constructor from a given gdcmElementSet
 */
gdcmDocEntrySet::gdcmDocEntrySet() {

}

/**
 * \ingroup gdcmElementSet
 * \brief   Canonical destructor.
 */
gdcmElementSet::~gdcmElementSet() 
{
/*   for(tous les DocEntry)
   {
      delete *cc;
   }
   */
}


//-----------------------------------------------------------------------------
// Public


//-----------------------------------------------------------------------------
// Protected

//-----------------------------------------------------------------------------
// Private

/**
 * \brief  Find the value Length of the passed Header Entry
 * @param  Entry Header Entry whose length of the value shall be loaded. 
 */
 void gdcmElementSet::FindDocEntryLength (gdcmDocEntry *Entry) {
   guint16 element = Entry->GetElement();
   //guint16 group   = Entry->GetGroup(); //FIXME
   std::string  vr = Entry->GetVR();
   guint16 length16;
       
   
   if ( (filetype == ExplicitVR) && (! Entry->IsImplicitVR()) ) 
   {
      if ( (vr=="OB") || (vr=="OW") || (vr=="SQ") || (vr=="UN") ) 
      {
         // The following reserved two bytes (see PS 3.5-2001, section
         // 7.1.2 Data element structure with explicit vr p27) must be
         // skipped before proceeding on reading the length on 4 bytes.
         fseek(fp, 2L, SEEK_CUR);
         guint32 length32 = ReadInt32();

         if ( (vr == "OB") && (length32 == 0xffffffff) ) 
         {
            Entry->SetLength(FindHeaderEntryLengthOB());
            return;
         }
         FixHeaderEntryFoundLength(Entry, length32); 
         return;
      }

      // Length is encoded on 2 bytes.
      length16 = ReadInt16();
      
      // We can tell the current file is encoded in big endian (like
      // Data/US-RGB-8-epicard) when we find the "Transfer Syntax" tag
      // and it's value is the one of the encoding of a big endian file.
      // In order to deal with such big endian encoded files, we have
      // (at least) two strategies:
      // * when we load the "Transfer Syntax" tag with value of big endian
      //   encoding, we raise the proper flags. Then we wait for the end
      //   of the META group (0x0002) among which is "Transfer Syntax",
      //   before switching the swap code to big endian. We have to postpone
      //   the switching of the swap code since the META group is fully encoded
      //   in little endian, and big endian coding only starts at the next
      //   group. The corresponding code can be hard to analyse and adds
      //   many additional unnecessary tests for regular tags.
      // * the second strategy consists in waiting for trouble, that shall
      //   appear when we find the first group with big endian encoding. This
      //   is easy to detect since the length of a "Group Length" tag (the
      //   ones with zero as element number) has to be of 4 (0x0004). When we
      //   encounter 1024 (0x0400) chances are the encoding changed and we
      //   found a group with big endian encoding.
      // We shall use this second strategy. In order to make sure that we
      // can interpret the presence of an apparently big endian encoded
      // length of a "Group Length" without committing a big mistake, we
      // add an additional check: we look in the already parsed elements
      // for the presence of a "Transfer Syntax" whose value has to be "big
      // endian encoding". When this is the case, chances are we have got our
      // hands on a big endian encoded file: we switch the swap code to
      // big endian and proceed...
      if ( (element  == 0x0000) && (length16 == 0x0400) ) 
      {
         if ( ! IsExplicitVRBigEndianTransferSyntax() ) 
         {
            dbg.Verbose(0, "gdcmDocument::FindLength", "not explicit VR");
            errno = 1;
            return;
         }
         length16 = 4;
         SwitchSwapToBigEndian();
         // Restore the unproperly loaded values i.e. the group, the element
         // and the dictionary entry depending on them.
         guint16 CorrectGroup   = SwapShort(Entry->GetGroup());
         guint16 CorrectElem    = SwapShort(Entry->GetElement());
         gdcmDictEntry * NewTag = GetDictEntryByNumber(CorrectGroup,
                                                       CorrectElem);
         if (!NewTag) 
         {
            // This correct tag is not in the dictionary. Create a new one.
            NewTag = NewVirtualDictEntry(CorrectGroup, CorrectElem);
         }
         // FIXME this can create a memory leaks on the old entry that be
         // left unreferenced.
         Entry->SetDictEntry(NewTag);
      }
       
      // Heuristic: well some files are really ill-formed.
      if ( length16 == 0xffff) 
      {
         length16 = 0;
         //dbg.Verbose(0, "gdcmDocument::FindLength",
         //            "Erroneous element length fixed.");
         // Actually, length= 0xffff means that we deal with
         // Unknown Sequence Length 
      }
      FixHeaderEntryFoundLength(Entry, (guint32)length16);
      return;
   }
   else
   {
      // Either implicit VR or a non DICOM conformal (see note below) explicit
      // VR that ommited the VR of (at least) this element. Farts happen.
      // [Note: according to the part 5, PS 3.5-2001, section 7.1 p25
      // on Data elements "Implicit and Explicit VR Data Elements shall
      // not coexist in a Data Set and Data Sets nested within it".]
      // Length is on 4 bytes.
      
      FixHeaderEntryFoundLength(Entry, ReadInt32());
      return;
   }
}