/**
 * collectd - src/utils_heap.c
 * Copyright (C) 2009       Florian octo Forster
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 * Authors:
 *   Florian octo Forster <octo at collectd.org>
 **/

#include "collectd.h"

#include <assert.h>
#include <errno.h>
#include <pthread.h>
#include <stdlib.h>

#include "utils/heap/heap.h"

struct c_heap_s {
  pthread_mutex_t lock;
  int (*compare)(const void *, const void *);

  void **list;
  size_t list_len;  /* # entries used */
  size_t list_size; /* # entries allocated */
};

enum reheap_direction { DIR_UP, DIR_DOWN };

static void reheap(c_heap_t *h, size_t root, enum reheap_direction dir) {
  size_t left;
  size_t right;
  size_t min;
  int status;

  /* Calculate the positions of the children */
  left = (2 * root) + 1;
  if (left >= h->list_len)
    left = 0;

  right = (2 * root) + 2;
  if (right >= h->list_len)
    right = 0;

  /* Check which one of the children is smaller. */
  if ((left == 0) && (right == 0))
    return;
  else if (left == 0)
    min = right;
  else if (right == 0)
    min = left;
  else {
    status = h->compare(h->list[left], h->list[right]);
    if (status > 0)
      min = right;
    else
      min = left;
  }

  status = h->compare(h->list[root], h->list[min]);
  if (status <= 0) {
    /* We didn't need to change anything, so the rest of the tree should be
     * okay now. */
    return;
  } else /* if (status > 0) */
  {
    void *tmp;

    tmp = h->list[root];
    h->list[root] = h->list[min];
    h->list[min] = tmp;
  }

  if ((dir == DIR_UP) && (root == 0))
    return;

  if (dir == DIR_UP)
    reheap(h, (root - 1) / 2, dir);
  else if (dir == DIR_DOWN)
    reheap(h, min, dir);
} /* void reheap */

c_heap_t *c_heap_create(int (*compare)(const void *, const void *)) {
  c_heap_t *h;

  if (compare == NULL)
    return NULL;

  h = calloc(1, sizeof(*h));
  if (h == NULL)
    return NULL;

  pthread_mutex_init(&h->lock, /* attr = */ NULL);
  h->compare = compare;

  h->list = NULL;
  h->list_len = 0;
  h->list_size = 0;

  return h;
} /* c_heap_t *c_heap_create */

void c_heap_destroy(c_heap_t *h) {
  if (h == NULL)
    return;

  h->list_len = 0;
  h->list_size = 0;
  free(h->list);
  h->list = NULL;

  pthread_mutex_destroy(&h->lock);

  free(h);
} /* void c_heap_destroy */

int c_heap_insert(c_heap_t *h, void *ptr) {
  size_t index;

  if ((h == NULL) || (ptr == NULL))
    return -EINVAL;

  pthread_mutex_lock(&h->lock);

  assert(h->list_len <= h->list_size);
  if (h->list_len == h->list_size) {
    void **tmp;

    tmp = realloc(h->list, (h->list_size + 16) * sizeof(*h->list));
    if (tmp == NULL) {
      pthread_mutex_unlock(&h->lock);
      return -ENOMEM;
    }

    h->list = tmp;
    h->list_size += 16;
  }

  /* Insert the new node as a leaf. */
  index = h->list_len;
  h->list[index] = ptr;
  h->list_len++;

  /* Reorganize the heap from bottom up. */
  reheap(h, /* parent of this node = */ (index - 1) / 2, DIR_UP);

  pthread_mutex_unlock(&h->lock);
  return 0;
} /* int c_heap_insert */

void *c_heap_get_root(c_heap_t *h) {
  void *ret = NULL;

  if (h == NULL)
    return NULL;

  pthread_mutex_lock(&h->lock);

  if (h->list_len == 0) {
    pthread_mutex_unlock(&h->lock);
    return NULL;
  } else if (h->list_len == 1) {
    ret = h->list[0];
    h->list[0] = NULL;
    h->list_len = 0;
  } else /* if (h->list_len > 1) */
  {
    ret = h->list[0];
    h->list[0] = h->list[h->list_len - 1];
    h->list[h->list_len - 1] = NULL;
    h->list_len--;

    reheap(h, /* root = */ 0, DIR_DOWN);
  }

  /* free some memory */
  if ((h->list_len + 32) < h->list_size) {
    void **tmp;

    tmp = realloc(h->list, (h->list_len + 16) * sizeof(*h->list));
    if (tmp != NULL) {
      h->list = tmp;
      h->list_size = h->list_len + 16;
    }
  }

  pthread_mutex_unlock(&h->lock);

  return ret;
} /* void *c_heap_get_root */