/*

 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")

 *

 * This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/.

 *

 * See the COPYRIGHT file distributed with this work for additional

 * information regarding copyright ownership.

 */

/*! \file

 * Heap implementation of priority queues adapted from the following:

 *

 *	\li "Introduction to Algorithms," Cormen, Leiserson, and Rivest,

 *	MIT Press / McGraw Hill, 1990, ISBN 0-262-03141-8, chapter 7.

 *

 *	\li "Algorithms," Second Edition, Sedgewick, Addison-Wesley, 1988,

 *	ISBN 0-201-06673-4, chapter 11.

 */

#include <config.h>

#include <stdbool.h>

#include <isc/heap.h>

#include <isc/magic.h>

#include <isc/mem.h>

#include <isc/string.h>		/* Required for memmove. */

#include <isc/util.h>

/*@{*/

/*%

 * Note: to make heap_parent and heap_left easy to compute, the first

 * element of the heap array is not used; i.e. heap subscripts are 1-based,

 * not 0-based.  The parent is index/2, and the left-child is index*2.

 * The right child is index*2+1.

 */

#define heap_parent(i)			((i) >> 1)

#define heap_left(i)			((i) << 1)

/*@}*/

#define SIZE_INCREMENT			1024

#define HEAP_MAGIC			ISC_MAGIC('H', 'E', 'A', 'P')

#define VALID_HEAP(h)			ISC_MAGIC_VALID(h, HEAP_MAGIC)

/*%

 * When the heap is in a consistent state, the following invariant

 * holds true: for every element i > 1, heap_parent(i) has a priority

 * higher than or equal to that of i.

 */

#define HEAPCONDITION(i) ((i) == 1 || \

			  ! heap->compare(heap->array[(i)], \

					  heap->array[heap_parent(i)]))

/*% ISC heap structure. */

struct isc_heap {

	unsigned int			magic;

	isc_mem_t *			mctx;

	unsigned int			size;

	unsigned int			size_increment;

	unsigned int			last;

	void				**array;

	isc_heapcompare_t		compare;

	isc_heapindex_t			index;

};

#ifdef ISC_HEAP_CHECK

static void

heap_check(isc_heap_t *heap) {

	unsigned int i;

	for (i = 1; i <= heap->last; i++) {

		INSIST(HEAPCONDITION(i));

	}

}

#else

#define heap_check(x) (void)0

#endif

isc_result_t

isc_heap_create(isc_mem_t *mctx, isc_heapcompare_t compare,

		isc_heapindex_t idx, unsigned int size_increment,

		isc_heap_t **heapp)

{

	isc_heap_t *heap;

	REQUIRE(heapp != NULL && *heapp == NULL);

	REQUIRE(compare != NULL);

	heap = isc_mem_get(mctx, sizeof(*heap));

	if (heap == NULL)

		return (ISC_R_NOMEMORY);

	heap->magic = HEAP_MAGIC;

	heap->size = 0;

	heap->mctx = NULL;

	isc_mem_attach(mctx, &heap->mctx);

	if (size_increment == 0)

		heap->size_increment = SIZE_INCREMENT;

	else

		heap->size_increment = size_increment;

	heap->last = 0;

	heap->array = NULL;

	heap->compare = compare;

	heap->index = idx;

	*heapp = heap;

	return (ISC_R_SUCCESS);

}

void

isc_heap_destroy(isc_heap_t **heapp) {

	isc_heap_t *heap;

	REQUIRE(heapp != NULL);

	REQUIRE(VALID_HEAP((*heapp)));

	heap = *heapp;

	if (heap->array != NULL)

		isc_mem_put(heap->mctx, heap->array,

			    heap->size * sizeof(void *));

	heap->magic = 0;

	isc_mem_putanddetach(&heap->mctx, heap, sizeof(*heap));

	*heapp = NULL;

}

static bool

resize(isc_heap_t *heap) {

	void **new_array;

	unsigned int new_size;

	REQUIRE(VALID_HEAP(heap));

	new_size = heap->size + heap->size_increment;

	new_array = isc_mem_get(heap->mctx, new_size * sizeof(void *));

	if (new_array == NULL)

		return (false);

	if (heap->array != NULL) {

		memmove(new_array, heap->array, heap->size * sizeof(void *));

		isc_mem_put(heap->mctx, heap->array,

			    heap->size * sizeof(void *));

	}

	heap->size = new_size;

	heap->array = new_array;

	return (true);

}

static void

float_up(isc_heap_t *heap, unsigned int i, void *elt) {

	unsigned int p;

	for (p = heap_parent(i) ;

	     i > 1 && heap->compare(elt, heap->array[p]) ;

	     i = p, p = heap_parent(i)) {

		heap->array[i] = heap->array[p];

		if (heap->index != NULL)

			(heap->index)(heap->array[i], i);

	}

	heap->array[i] = elt;

	if (heap->index != NULL)

		(heap->index)(heap->array[i], i);

	INSIST(HEAPCONDITION(i));

	heap_check(heap);

}

static void

sink_down(isc_heap_t *heap, unsigned int i, void *elt) {

	unsigned int j, size, half_size;

	size = heap->last;

	half_size = size / 2;

	while (i <= half_size) {

		/* Find the smallest of the (at most) two children. */

		j = heap_left(i);

		if (j < size && heap->compare(heap->array[j+1],

					      heap->array[j]))

			j++;

		if (heap->compare(elt, heap->array[j]))

			break;

		heap->array[i] = heap->array[j];

		if (heap->index != NULL)

			(heap->index)(heap->array[i], i);

		i = j;

	}

	heap->array[i] = elt;

	if (heap->index != NULL)

		(heap->index)(heap->array[i], i);

	INSIST(HEAPCONDITION(i));

	heap_check(heap);

}

isc_result_t

isc_heap_insert(isc_heap_t *heap, void *elt) {

	unsigned int new_last;

	REQUIRE(VALID_HEAP(heap));

	heap_check(heap);

	new_last = heap->last + 1;

	RUNTIME_CHECK(new_last > 0); /* overflow check */

	if (new_last >= heap->size && !resize(heap))

		return (ISC_R_NOMEMORY);

	heap->last = new_last;

	float_up(heap, new_last, elt);

	return (ISC_R_SUCCESS);

}

void

isc_heap_delete(isc_heap_t *heap, unsigned int idx) {

	void *elt;

	bool less;

	REQUIRE(VALID_HEAP(heap));

	REQUIRE(idx >= 1 && idx <= heap->last);

	heap_check(heap);

	if (heap->index != NULL)

		(heap->index)(heap->array[idx], 0);

	if (idx == heap->last) {

		heap->array[heap->last] = NULL;

		heap->last--;

		heap_check(heap);

	} else {

		elt = heap->array[heap->last];

		heap->array[heap->last] = NULL;

		heap->last--;

		less = heap->compare(elt, heap->array[idx]);

		heap->array[idx] = elt;

		if (less)

			float_up(heap, idx, heap->array[idx]);

		else

			sink_down(heap, idx, heap->array[idx]);

	}

}

void

isc_heap_increased(isc_heap_t *heap, unsigned int idx) {

	REQUIRE(VALID_HEAP(heap));

	REQUIRE(idx >= 1 && idx <= heap->last);

	float_up(heap, idx, heap->array[idx]);

}

void

isc_heap_decreased(isc_heap_t *heap, unsigned int idx) {

	REQUIRE(VALID_HEAP(heap));

	REQUIRE(idx >= 1 && idx <= heap->last);

	sink_down(heap, idx, heap->array[idx]);

}

void *

isc_heap_element(isc_heap_t *heap, unsigned int idx) {

	REQUIRE(VALID_HEAP(heap));

	REQUIRE(idx >= 1);

	heap_check(heap);

	if (idx <= heap->last)

		return (heap->array[idx]);

	return (NULL);

}

void

isc_heap_foreach(isc_heap_t *heap, isc_heapaction_t action, void *uap) {

	unsigned int i;

	REQUIRE(VALID_HEAP(heap));

	REQUIRE(action != NULL);

	for (i = 1 ; i <= heap->last ; i++)

		(action)(heap->array[i], uap);

}