/***************************************************************************
 * gh_heap.c -- heap based priority queue.                                 *
 *                                                                         *
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/* $Id: gh_heap.c 38790 2024-02-28 18:46:45Z dmiller $ */

#ifdef HAVE_CONFIG_H
#include "nsock_config.h"
#include "nbase_config.h"
#endif

#ifdef WIN32
#include "nbase_winconfig.h"
#endif

#include <nbase.h>
#include "gh_heap.h"

#define GH_SLOTS   128


static gh_hnode_t **hnode_ptr(gh_heap_t *heap, unsigned int index) {
  assert(index <= heap->count);
  gh_hnode_t **ptr = &(heap->slots[index]);
  assert(index == heap->count || (*ptr)->index == index);
  return ptr;
}

gh_hnode_t *gh_heap_find(gh_heap_t *heap, unsigned int index) {
  if (index >= heap->count)
    return NULL;

  return *hnode_ptr(heap, index);
}

static int hnode_up(gh_heap_t *heap, gh_hnode_t *hnode)
{
  unsigned int cur_idx = hnode->index;
  gh_hnode_t **cur_ptr = hnode_ptr(heap, cur_idx);
  unsigned int parent_idx;
  gh_hnode_t **parent_ptr;
  int action = 0;

  assert(*cur_ptr == hnode);

  while (cur_idx > 0) {
    parent_idx = (cur_idx - 1) >> 1;

    parent_ptr = hnode_ptr(heap, parent_idx);

    if (heap->cmp_op(*parent_ptr, hnode))
      break;

    (*parent_ptr)->index = cur_idx;
    *cur_ptr = *parent_ptr;
    cur_ptr = parent_ptr;
    cur_idx = parent_idx;
    action = 1;
  }

  hnode->index = cur_idx;
  *cur_ptr = hnode;

  return action;
}

static int hnode_down(gh_heap_t *heap, gh_hnode_t *hnode)
{
  unsigned int count = heap->count;
  unsigned int ch1_idx, ch2_idx, cur_idx;
  gh_hnode_t **ch1_ptr, **ch2_ptr, **cur_ptr;
  gh_hnode_t  *ch1, *ch2;
  int action = 0;

  cur_idx = hnode->index;
  cur_ptr = hnode_ptr(heap, cur_idx);
  assert(*cur_ptr == hnode);

  while (cur_idx < count) {
    ch1_idx = (cur_idx << 1) + 1;
    if (ch1_idx >= count)
      break;

    ch1_ptr = hnode_ptr(heap, ch1_idx);
    ch1 = *ch1_ptr;

    ch2_idx = ch1_idx + 1;
    if (ch2_idx < count) {
      ch2_ptr = hnode_ptr(heap, ch2_idx);
      ch2 = *ch2_ptr;

      if (heap->cmp_op(ch2, ch1)) {
        ch1_idx = ch2_idx;
        ch1_ptr = ch2_ptr;
        ch1 = ch2;
      }
    }

    assert(ch1->index == ch1_idx);

    if (heap->cmp_op(hnode, ch1))
      break;

    ch1->index = cur_idx;
    *cur_ptr = ch1;
    cur_ptr = ch1_ptr;
    cur_idx = ch1_idx;
    action = 1;
  }

  hnode->index = cur_idx;
  *cur_ptr = hnode;

  return action;
}

static int heap_grow(gh_heap_t *heap) {
  int newsize;

  /* Do we really need to grow? */
  assert(heap->count == heap->highwm);

  newsize = heap->count + GH_SLOTS;
  heap->slots = (gh_hnode_t **)safe_realloc(heap->slots,
                                            newsize * sizeof(gh_hnode_t *));
  heap->highwm += GH_SLOTS;
  memset(heap->slots + heap->count, 0, GH_SLOTS * sizeof(gh_hnode_t *));
  return 0;
}

int gh_heap_init(gh_heap_t *heap, gh_heap_cmp_t cmp_op) {
  int rc;

  if (!cmp_op)
      return -1;

  heap->cmp_op = cmp_op;
  heap->count  = 0;
  heap->highwm = 0;
  heap->slots  = NULL;

  rc = heap_grow(heap);
  if (rc)
    gh_heap_free(heap);

  return rc;
}

void gh_heap_free(gh_heap_t *heap) {
  if (heap->highwm) {
    assert(heap->slots);
    free(heap->slots);
  }
  memset(heap, 0, sizeof(gh_heap_t));
}

int gh_heap_push(gh_heap_t *heap, gh_hnode_t *hnode) {
  gh_hnode_t **new_ptr;
  unsigned int new_index = heap->count;

  assert(!gh_hnode_is_valid(hnode));

  if (new_index == heap->highwm)
    heap_grow(heap);

  hnode->index = new_index;
  new_ptr = hnode_ptr(heap, new_index);
  assert(*new_ptr == NULL);
  heap->count++;
  *new_ptr = hnode;

  hnode_up(heap, hnode);
  return 0;
}

int gh_heap_remove(gh_heap_t *heap, gh_hnode_t *hnode)
{
  unsigned int count = heap->count;
  unsigned int cur_idx = hnode->index;
  gh_hnode_t **cur_ptr;
  gh_hnode_t *last;

  assert(gh_hnode_is_valid(hnode));
  assert(cur_idx < count);

  cur_ptr = hnode_ptr(heap, cur_idx);
  assert(*cur_ptr == hnode);

  count--;
  last = *hnode_ptr(heap, count);
  heap->count = count;
  if (last != hnode)
  {
    last->index = cur_idx;
    *cur_ptr = last;
    if (!hnode_up(heap, *cur_ptr))
      hnode_down(heap, *cur_ptr);
  }

  gh_hnode_invalidate(hnode);
  cur_ptr = hnode_ptr(heap, count);
  *cur_ptr = NULL;
  return 0;
}
