/**
  @file

  @ingroup nanotrav

  @brief Functions for heap-based priority queues.

  @details The functions in this file manage a priority queue
  implemented as a heap. The first element of the heap is the one with
  the smallest key.  The queue stores generic pointers, but the key
  must be an int.  Refer to Chapter 7 of Cormen, Leiserson, and Rivest
  for the theory.

  @author Fabio Somenzi

  @copyright@parblock
  Copyright (c) 1995-2015, Regents of the University of Colorado

  All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:

  Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.

  Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.

  Neither the name of the University of Colorado nor the names of its
  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE.
  @endparblock

*/

#include "ntr.h"

/*---------------------------------------------------------------------------*/
/* Constant declarations                                                     */
/*---------------------------------------------------------------------------*/


/*---------------------------------------------------------------------------*/
/* Stucture declarations                                                     */
/*---------------------------------------------------------------------------*/

/**
   @brief Entry of NtrHeap.
*/
struct NtrHeapSlot {
    void *item;
    int key;
};

/**
   @brief Heap-based priority queue.
*/
struct NtrHeap {
    int size;
    int nslots;
    NtrHeapSlot *slots;
};

/*---------------------------------------------------------------------------*/
/* Type declarations                                                         */
/*---------------------------------------------------------------------------*/

/*---------------------------------------------------------------------------*/
/* Variable declarations                                                     */
/*---------------------------------------------------------------------------*/


/*---------------------------------------------------------------------------*/
/* Macro declarations                                                        */
/*---------------------------------------------------------------------------*/

#define PARENT(i)	(((i)-1)>>1)
#define RIGHT(i)	(((i)+1)<<1)
#define LEFT(i)		(((i)<<1)|1)
#define ITEM(p,i)	((p)[i].item)
#define KEY(p,i)	((p)[i].key)

/** \cond */

/*---------------------------------------------------------------------------*/
/* Static function prototypes                                                */
/*---------------------------------------------------------------------------*/

static void ntrHeapify (NtrHeap *heap, int i);
static int ntrHeapResize (NtrHeap *heap);

/** \endcond */


/*---------------------------------------------------------------------------*/
/* Definition of exported functions                                          */
/*---------------------------------------------------------------------------*/


/**
  @brief Initializes a priority queue.

  @return a pointer to the heap if successful; NULL otherwise.

  @sideeffect None

  @see Ntr_FreeHeap

*/
NtrHeap *
Ntr_InitHeap(
  int size)
{
    NtrHeap *heap;

    heap = ALLOC(NtrHeap,1);
    if (heap == NULL) return(NULL);
    heap->size = size;
    heap->nslots = 0;
    heap->slots = ALLOC(NtrHeapSlot,size);
    if (heap->slots == NULL) {
	FREE(heap);
	return(NULL);
    }
    return(heap);

} /* end of Ntr_InitHeap */


/**
  @brief Frees a priority queue.

  @sideeffect None

  @see Ntr_InitHeap

*/
void
Ntr_FreeHeap(
  NtrHeap *heap)
{
    FREE(heap->slots);
    FREE(heap);
    return;

} /* end of Ntr_FreeHeap */


/**
  @brief Inserts an item in a priority queue.

  @return 1 if successful; 0 otherwise.

  @sideeffect None

  @see Ntr_HeapExtractMin

*/
int
Ntr_HeapInsert(
  NtrHeap *heap,
  void *item,
  int key)
{
    NtrHeapSlot *slots;
    int i = heap->nslots;

    if (i == heap->size && !ntrHeapResize(heap)) return(0);
    slots = heap->slots;
    heap->nslots++;
    while (i > 0 && KEY(slots,PARENT(i)) > key) {
	ITEM(slots,i) = ITEM(slots,PARENT(i));
	KEY(slots,i) = KEY(slots,PARENT(i));
	i = PARENT(i);
    }
    ITEM(slots,i) = item;
    KEY(slots,i) = key;
    return(1);

} /* end of Ntr_HeapInsert */


/**
  @brief Extracts the element with the minimum key from a priority
  queue.

  @return 1 if successful; 0 otherwise.

  @sideeffect The minimum key and the associated item are returned as
  side effects.

  @see Ntr_HeapInsert

*/
int
Ntr_HeapExtractMin(
  NtrHeap *heap,
  void *item,
  int *key)
{
    NtrHeapSlot *slots = heap->slots;

    if (heap->nslots == 0) return(0);
    *(void **)item = ITEM(slots,0);
    *key = KEY(slots,0);
    heap->nslots--;
    ITEM(slots,0) = ITEM(slots,heap->nslots);
    KEY(slots,0) = KEY(slots,heap->nslots);
    ntrHeapify(heap,0);

    return(1);

} /* end of Ntr_HeapExtractMin */


/**
  @brief Returns the number of items in a priority queue.

  @sideeffect None

*/
int
Ntr_HeapCount(
  NtrHeap *heap)
{
    return(heap->nslots);

} /* end of Ntr_HeapCount */


/**
  @brief Clones a priority queue.

  @sideeffect None

  @see Ntr_InitHeap

*/
NtrHeap *
Ntr_HeapClone(
  NtrHeap *source)
{
    NtrHeap *dest;
    int i;
    int nslots = source->nslots;
    NtrHeapSlot *sslots = source->slots;
    NtrHeapSlot *dslots;

    dest = Ntr_InitHeap(source->size);
    if (dest == NULL) return(NULL);
    dest->nslots = nslots;
    dslots = dest->slots;
    for (i = 0; i < nslots; i++) {
	KEY(dslots,i) = KEY(sslots,i);
	ITEM(dslots,i) = ITEM(sslots,i);
    }
    return(dest);

} /* end of Ntr_HeapClone */


/**
  @brief Calls a function on all items in a heap.
*/
void
Ntr_HeapForeach(
  NtrHeap *heap,
  void (*f)(void * e, void * arg),
  void * arg)
{
    int i;

    for (i = 0; i < heap->nslots; i++) {
        f(heap->slots[i].item, arg);
    }

} /* end of Ntr_HeapForeach */


/**
  @brief Tests the heap property of a priority queue.

  @return 1 if Successful; 0 otherwise.

  @sideeffect None

*/
int
Ntr_TestHeap(
  NtrHeap *heap,
  int i)
{
    NtrHeapSlot *slots = heap->slots;
    int nslots = heap->nslots;

    if (i > 0 && KEY(slots,i) < KEY(slots,PARENT(i)))
	return(0);
    if (LEFT(i) < nslots) {
	if (!Ntr_TestHeap(heap,LEFT(i)))
	    return(0);
    }
    if (RIGHT(i) < nslots) {
	if (!Ntr_TestHeap(heap,RIGHT(i)))
	    return(0);
    }
    return(1);

} /* end of Ntr_TestHeap */


/*---------------------------------------------------------------------------*/
/* Definition of static functions                                            */
/*---------------------------------------------------------------------------*/


/**
  @brief Maintains the heap property of a priority queue.

  @sideeffect None

  @see Ntr_HeapExtractMin

*/
static void
ntrHeapify(
  NtrHeap *heap,
  int i)
{
    int smallest;
    int left = LEFT(i);
    int right = RIGHT(i);
    int nslots = heap->nslots;
    NtrHeapSlot *slots = heap->slots;
    int key = KEY(slots,i);

    if (left < nslots && KEY(slots,left) < key) {
	smallest = left;
    } else {
	smallest = i;
    }
    if (right < nslots && KEY(slots,right) < KEY(slots,smallest)) {
	smallest = right;
    }
    if (smallest != i) {
	void *item = ITEM(slots,i);
	KEY(slots,i) = KEY(slots,smallest);
	ITEM(slots,i) = ITEM(slots,smallest);
	KEY(slots,smallest) = key;
	ITEM(slots,smallest) = item;
	ntrHeapify(heap,smallest);
    }

    return;

} /* end of ntrHeapify */


/**
  @brief Resizes a priority queue.

  @details Resizes a priority queue by doubling the number of
  available slots.

  @return 1 if successful; 0 otherwise.

  @sideeffect None

  @see Ntr_HeapInsert

*/
static int
ntrHeapResize(
  NtrHeap *heap)
{
  int oldlength = heap->size;
  int newlength = 2 * oldlength;
  NtrHeapSlot *oldslots = heap->slots;
  NtrHeapSlot *newslots = REALLOC(NtrHeapSlot, oldslots, newlength);
  if (newslots == NULL) return 0;
  heap->size = newlength;
  heap->slots = newslots;
  assert(Ntr_TestHeap(heap, 0));
  return 1;

} /* end of ntrHeapResize */