// Copyright (C) 2002-2012 Nikolaus Gebhardt
// This file is part of the "Irrlicht Engine".
// For conditions of distribution and use, see copyright notice in irrlicht.h

#ifndef __IRR_HEAPSORT_H_INCLUDED__
#define __IRR_HEAPSORT_H_INCLUDED__

#include "irrTypes.h"

namespace irr
{
namespace core
{

//! Function object which can be used for sorting (default)
template<class T>
inline bool sortless(const T& a, const T& b)
{
	return a < b;
}

//! Sinks an element into the heap with a custom compare function
template<class T, class Compare>
inline void heapsink(T*array, s32 element, s32 max, Compare cmp)
{
	while ((element<<1) < max) // there is a left child
	{
		s32 j = (element<<1);

		if (j+1 < max && cmp(array[j], array[j+1]))
			j = j+1; // take right child

		if (cmp(array[element], array[j]))
		{
			T t = array[j]; // swap elements
			array[j] = array[element];
			array[element] = t;
			element = j;
		}
		else
			return;
	}
}

//! Sorts an array with size 'size' using heapsort with a custom compare function
template<class T, class Compare>
inline void heapsort(T* array_, s32 size, Compare cmp)
{
	// for heapsink we pretent this is not c++, where
	// arrays start with index 0. So we decrease the array pointer,
	// the maximum always +2 and the element always +1

	T* virtualArray = array_ - 1;
	s32 virtualSize = size + 2;
	s32 i;

	// build heap

	for (i=((size-1)/2); i>=0; --i)
		heapsink(virtualArray, i+1, virtualSize-1, cmp);

	// sort array, leave out the last element (0)
	for (i=size-1; i>0; --i)
	{
		T t = array_[0];
		array_[0] = array_[i];
		array_[i] = t;
		heapsink(virtualArray, 1, i + 1, cmp);
	}
}

} // end namespace core
} // end namespace irr

#endif