/*

 * Copyright (c) 2020 Red Hat, Inc.

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 * 

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 * 

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

 * 02110-1301, USA. 

 *

 * $Id: //eng/vdo-releases/aluminum/src/c++/vdo/base/heap.h#2 $

 */

#ifndef HEAP_H

#define HEAP_H

#include "common.h"

/**

 * Prototype for functions which compare two array elements. All the time

 * complexity claims in this module assume this operation has O(1) time

 * complexity.

 *

 * @param item1  The first element to compare

 * @param item2  The second element to compare

 *

 * @return An integer which is less than, equal to, or greater than 0

 *         depending on whether item1 is less than, equal to, or greater

 *         than item2, respectively

 **/

typedef int HeapComparator(const void *item1, const void *item2);

/**

 * Prototype for functions which swap two array elements.

 *

 * @param item1  The first element to swap

 * @param item2  The second element to swap

 **/

typedef void HeapSwapper(void *item1, void *item2);

/**

 * A heap array can be any array of fixed-length elements in which the heap

 * invariant can be established. In a max-heap, every child of a node must be

 * at least as large as its children. Once that invariant is established in an

 * array by calling buildHeap(), all the other heap operations may be used on

 * that array.

 **/

typedef struct heap {

  /** the 1-based array of heap elements (nodes) */

  byte           *array;

  /** the function to use to compare two elements */

  HeapComparator *comparator;

  /** the function to use to swap two elements */

  HeapSwapper    *swapper;

  /** the maximum number of elements that can be stored */

  size_t          capacity;

  /** the size of every element (in bytes) */

  size_t          elementSize;

  /** the current number of elements in the heap */

  size_t          count;

} Heap;

/**

 * Initialize an binary heap by wrapping it around an array of elements.

 *

 * The heap will not own the array it wraps. Use buildHeap() subsequently to

 * arrange any elements contained in the array into a valid heap.

 *

 * @param heap          The heap to initialize

 * @param comparator    The function to use to compare two heap elements

 * @param swapper       The function to use to swap two heap elements

 * @param array         The array of elements (not modified by this call)

 * @param capacity      The maximum number of elements which fit in the array

 * @param elementSize   The size of every array element, in bytes

 **/

void initializeHeap(Heap           *heap,

                    HeapComparator *comparator,

                    HeapSwapper    *swapper,

                    void           *array,

                    size_t          capacity,

                    size_t          elementSize);

/**

 * Build a max-heap in place in an array (heapify it) by re-ordering the

 * elements to establish the heap invariant. Before calling this function,

 * first copy the elements to be arranged into a heap into the array that was

 * passed to initializeHeap(). This operation has O(N) time complexity in the

 * number of elements in the array.

 *

 * @param heap   The heap to build

 * @param count  The number of elements in the array to build into a heap

 **/

void buildHeap(Heap *heap, size_t count);

/**

 * Check whether the heap is currently empty.

 *

 * @param heap  The heap to query

 *

 * @return true if there are no elements in the heap

 **/

static inline bool isHeapEmpty(const Heap *heap)

{

  return (heap->count == 0);

}

/**

 * Remove the largest element from the top of the heap and restore the heap

 * invariant on the remaining elements. This operation has O(log2(N)) time

 * complexity.

 *

 * @param [in]  heap        The heap to modify

 * @param [out] elementPtr  A pointer to receive the largest element (may be

 *                          NULL if the caller just wishes to discard it)

 *

 * @return false if the heap was empty, so no element was removed

 **/

bool popMaxHeapElement(Heap *heap, void *elementPtr);

/**

 * Sort the elements contained in a heap.

 *

 * This function re-orders the elements contained in the heap to a sorted

 * array in-place by repeatedly popping the maximum element off the heap and

 * moving it to the spot vacated at the end of the heap array. When the

 * function returns, the heap will be empty and the array will contain the

 * elements in sorted order, from heap minimum to heap maximum. The sort is

 * unstable--relative ordering of equal keys is not preserved. This operation

 * has O(N*log2(N)) time complexity.

 *

 * @param heap  The heap containing the elements to sort

 *

 * @return the number of elements that were sorted

 **/

size_t sortHeap(Heap *heap);

/**

 * Gets the next sorted heap element and returns a pointer to it, in O(log2(N))

 * time.

 *

 * @param heap  The heap to sort one more step

 *

 * @return a pointer to the element sorted, or NULL if already fully sorted.

 **/

void *sortNextHeapElement(Heap *heap);

#endif /* HEAP_H */