/afs/cs.wisc.edu/u/m/o/mohan/private/cs564/btree/btree/src/filescan.cpp

#include "filescan.h"
#include "exceptions/end_of_file_exception.h"

namespace badgerdb { 

FileScan::FileScan(const std::string &name, BufMgr *bufferMgr)
{
  file = new PageFile(name, false); //dont create new file
  bufMgr = bufferMgr;
  curDirtyFlag = false;
  curPage = NULL;
  filePageIter = file->begin();
}

FileScan::~FileScan()
{
  // generally must unpin last page of the scan
  if (curPage != NULL)
  {
    bufMgr->unPinPage(file, (*filePageIter).page_number(), curDirtyFlag);
    curPage = NULL;
    curDirtyFlag = false;
    filePageIter = file->begin();
  }
  delete file;
}

void FileScan::scanNext(RecordId& outRid)
{
  std::string rec;

  if (filePageIter == file->end())
  {
    throw EndOfFileException();
  }

  // special case of the first record of the first page of the file
  if (curPage == NULL)
  {
    // need to get the first page of the file
    filePageIter = file->begin();
    if(filePageIter == file->end())
    {
      throw EndOfFileException();
    }
   
    // read the first page of the file
    bufMgr->readPage(file, (*filePageIter).page_number(), curPage); 
    curDirtyFlag = false;

    // get the first record off the page
    pageRecordIter = curPage->begin(); 

    if(pageRecordIter != curPage->end()) 
    {
      // get pointer to record
      rec = *pageRecordIter;

      outRid = pageRecordIter.getCurrentRecord();
      return;
    }
  }

  // Loop, looking for a record that satisfied the predicate.
  // First try and get the next record off the current page
  pageRecordIter++;

  while (pageRecordIter == curPage->end())
  {
    // unpin the current page
    bufMgr->unPinPage(file, (*filePageIter).page_number(), curDirtyFlag);
    curPage = NULL;
    curDirtyFlag = false;

    filePageIter++;
    if (filePageIter == file->end())
    {
      curPage = NULL;
      throw EndOfFileException();
    }

    // read the next page of the file
    bufMgr->readPage(file, (*filePageIter).page_number(), curPage);

    // get the first record off the page
    pageRecordIter = curPage->begin(); 
  }

  // curRec points at a valid record
  // see if the record satisfies the scan's predicate 
  // get a pointer to the record
  rec = *pageRecordIter;

  // return rid of the record
  outRid = pageRecordIter.getCurrentRecord();
  return;
}

// returns pointer to the current record.  page is left pinned
// and the scan logic is required to unpin the page 
std::string FileScan::getRecord()
{
  return *pageRecordIter;
}

// mark current page of scan dirty
void FileScan::markDirty()
{
  curDirtyFlag = true;
}

}