/*
  $Id$

  Copyright (C) 2007 by The Regents of the University of California

  Redistribution of this file is permitted under the terms of the BSD license

  Date: 05/14/2007
  Author: Chen Li <chenli (at) ics.uci.edu>

*/

#include <iostream>
#include <vector>
#include <queue>
#include <assert.h>

#include "listmerger.h"
#include "util/array.h"

// http://support.microsoft.com/kb/837697
typedef pair<Array<unsigned>*, unsigned> ArrayWithPosition;

// Overload the < operator.
bool operator< (const ArrayWithPosition &awp1, const ArrayWithPosition &awp2)
{
  return awp1.first->at(awp1.second) < awp2.first->at(awp2.second);
}

// Overload the > operator.
bool operator> (const ArrayWithPosition& awp1, const ArrayWithPosition &awp2)
{
  return awp1.first->at(awp1.second) > awp2.first->at(awp2.second);
}

void HeapMerger::merge(const vector<Array<unsigned>*> &arrays,
		       const unsigned threshold,
		       const unsigned maxObjectID,
		       vector<unsigned> &results)
{
  // build a heap. Each element is a list with its current position (0)
  priority_queue<ArrayWithPosition> pq;
  for (unsigned i = 0; i < arrays.size(); i ++)
    pq.push((make_pair(arrays.at(i),0)));

  // remove any leftover in the results
  results.clear();

  // iterate over the queue
  unsigned prevObjectId = 0;
  unsigned objFreqency = 0;
  while (!pq.empty()) {
    // remove the head
    ArrayWithPosition awp = pq.top();
    pq.pop();

    // check the object id of the current element
    //assert(awp.first != NULL);
    //assert(awp.first->size() > awp.second);

    unsigned newObjectId = awp.first->at(awp.second);
    if (newObjectId == prevObjectId) {
      objFreqency ++;
    }
    else {
      prevObjectId = newObjectId; // a new object id
      objFreqency = 1;
    }

    if (objFreqency >= threshold) // found a new candidate
      if (!results.empty() && results.back() != newObjectId) // ignore duplcates in the results
	results.push_back(newObjectId); // insert this candidate

    // increment the position of the list by one
    awp.second ++;
    if (awp.second < awp.first->size()) // the list has more elments
      pq.push(awp);
  }

  // return the results
}