/*
 * sorts.c:   all sorts of sorts
 *
 * ====================================================================
 *    Licensed to the Apache Software Foundation (ASF) under one
 *    or more contributor license agreements.  See the NOTICE file
 *    distributed with this work for additional information
 *    regarding copyright ownership.  The ASF licenses this file
 *    to you under the Apache License, Version 2.0 (the
 *    "License"); you may not use this file except in compliance
 *    with the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing,
 *    software distributed under the License is distributed on an
 *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *    KIND, either express or implied.  See the License for the
 *    specific language governing permissions and limitations
 *    under the License.
 * ====================================================================
 */


#include <apr_pools.h>
#include <apr_hash.h>
#include <apr_tables.h>
#include <stdlib.h>       /* for qsort()   */
#include <assert.h>
#include "svn_hash.h"
#include "svn_path.h"
#include "svn_sorts.h"
#include "svn_error.h"


/*** svn_sort__hash() ***/

/* (Should this be a permanent part of APR?)

   OK, folks, here's what's going on.  APR hash tables hash on
   key/klen objects, and store associated generic values.  They work
   great, but they have no ordering.

   The point of this exercise is to somehow arrange a hash's keys into
   an "ordered list" of some kind -- in this case, a nicely sorted
   one.

   We're using APR arrays, therefore, because that's what they are:
   ordered lists.  However, what "keys" should we put in the array?
   Clearly, (const char *) objects aren't general enough.  Or rather,
   they're not as general as APR's hash implementation, which stores
   (void *)/length as keys.  We don't want to lose this information.

   Therefore, it makes sense to store pointers to {void *, size_t}
   structures in our array.  No such apr object exists... BUT... if we
   can use a new type svn_sort__item_t which contains {char *, size_t, void
   *}.  If store these objects in our array, we get the hash value
   *for free*.  When looping over the final array, we don't need to
   call apr_hash_get().  Major bonus!
 */


int
svn_sort_compare_items_as_paths(const svn_sort__item_t *a,
                                const svn_sort__item_t *b)
{
  const char *astr, *bstr;

  astr = a->key;
  bstr = b->key;
  assert(astr[a->klen] == '\0');
  assert(bstr[b->klen] == '\0');
  return svn_path_compare_paths(astr, bstr);
}


int
svn_sort_compare_items_lexically(const svn_sort__item_t *a,
                                 const svn_sort__item_t *b)
{
  int val;
  apr_size_t len;

  /* Compare bytes of a's key and b's key up to the common length. */
  len = (a->klen < b->klen) ? a->klen : b->klen;
  val = memcmp(a->key, b->key, len);
  if (val != 0)
    return val;

  /* They match up until one of them ends; whichever is longer is greater. */
  return (a->klen < b->klen) ? -1 : (a->klen > b->klen) ? 1 : 0;
}


int
svn_sort_compare_revisions(const void *a, const void *b)
{
  svn_revnum_t a_rev = *(const svn_revnum_t *)a;
  svn_revnum_t b_rev = *(const svn_revnum_t *)b;

  if (a_rev == b_rev)
    return 0;

  return a_rev < b_rev ? 1 : -1;
}


int
svn_sort_compare_paths(const void *a, const void *b)
{
  const char *item1 = *((const char * const *) a);
  const char *item2 = *((const char * const *) b);

  return svn_path_compare_paths(item1, item2);
}


int
svn_sort_compare_ranges(const void *a, const void *b)
{
  const svn_merge_range_t *item1 = *((const svn_merge_range_t * const *) a);
  const svn_merge_range_t *item2 = *((const svn_merge_range_t * const *) b);

  if (item1->start == item2->start
      && item1->end == item2->end)
    return 0;

  if (item1->start == item2->start)
    return item1->end < item2->end ? -1 : 1;

  return item1->start < item2->start ? -1 : 1;
}

apr_array_header_t *
svn_sort__hash(apr_hash_t *ht,
               int (*comparison_func)(const svn_sort__item_t *,
                                      const svn_sort__item_t *),
               apr_pool_t *pool)
{
  apr_hash_index_t *hi;
  apr_array_header_t *ary;
  svn_boolean_t sorted;
  svn_sort__item_t *prev_item;

  /* allocate an array with enough elements to hold all the keys. */
  ary = apr_array_make(pool, apr_hash_count(ht), sizeof(svn_sort__item_t));

  /* loop over hash table and push all keys into the array */
  sorted = TRUE;
  prev_item = NULL;
  for (hi = apr_hash_first(pool, ht); hi; hi = apr_hash_next(hi))
    {
      svn_sort__item_t *item = apr_array_push(ary);

      apr_hash_this(hi, &item->key, &item->klen, &item->value);

      if (prev_item == NULL)
        {
          prev_item = item;
          continue;
        }

      if (sorted)
        {
          sorted = (comparison_func(prev_item, item) < 0);
          prev_item = item;
        }
    }

  /* quicksort the array if it isn't already sorted.  */
  if (!sorted)
    qsort(ary->elts, ary->nelts, ary->elt_size,
          (int (*)(const void *, const void *))comparison_func);

  return ary;
}

/* Return the lowest index at which the element *KEY should be inserted into
   the array at BASE which has NELTS elements of size ELT_SIZE bytes each,
   according to the ordering defined by COMPARE_FUNC.
   0 <= NELTS <= INT_MAX, 1 <= ELT_SIZE <= INT_MAX.
   The array must already be sorted in the ordering defined by COMPARE_FUNC.
   COMPARE_FUNC is defined as for the C stdlib function bsearch().
   Note: This function is modeled on bsearch() and on lower_bound() in the
   C++ STL.
 */
static int
bsearch_lower_bound(const void *key,
                    const void *base,
                    int nelts,
                    int elt_size,
                    int (*compare_func)(const void *, const void *))
{
  int lower = 0;
  int upper = nelts - 1;

  /* Binary search for the lowest position at which to insert KEY. */
  while (lower <= upper)
    {
      int try = lower + (upper - lower) / 2;  /* careful to avoid overflow */
      int cmp = compare_func((const char *)base + try * elt_size, key);

      if (cmp < 0)
        lower = try + 1;
      else
        upper = try - 1;
    }
  assert(lower == upper + 1);

  return lower;
}

int
svn_sort__bsearch_lower_bound(const void *key,
                              const apr_array_header_t *array,
                              int (*compare_func)(const void *, const void *))
{
  return bsearch_lower_bound(key,
                             array->elts, array->nelts, array->elt_size,
                             compare_func);
}

void
svn_sort__array_insert(const void *new_element,
                       apr_array_header_t *array,
                       int insert_index)
{
  int elements_to_move;
  char *new_position;

  assert(0 <= insert_index && insert_index <= array->nelts);
  elements_to_move = array->nelts - insert_index;  /* before bumping nelts */

  /* Grow the array, allocating a new space at the end. Note: this can
     reallocate the array's "elts" at a different address. */
  apr_array_push(array);

  /* Move the elements after INSERT_INDEX along. (When elements_to_move == 0,
     this is a no-op.) */
  new_position = (char *)array->elts + insert_index * array->elt_size;
  memmove(new_position + array->elt_size, new_position,
          array->elt_size * elements_to_move);

  /* Copy in the new element */
  memcpy(new_position, new_element, array->elt_size);
}

void
svn_sort__array_delete(apr_array_header_t *arr,
                       int delete_index,
                       int elements_to_delete)
{
  /* Do we have a valid index and are there enough elements? */
  if (delete_index >= 0
      && delete_index < arr->nelts
      && elements_to_delete > 0
      && (elements_to_delete + delete_index) <= arr->nelts)
    {
      /* If we are not deleting a block of elements that extends to the end
         of the array, then we need to move the remaining elements to keep
         the array contiguous. */
      if ((elements_to_delete + delete_index) < arr->nelts)
        memmove(
          arr->elts + arr->elt_size * delete_index,
          arr->elts + (arr->elt_size * (delete_index + elements_to_delete)),
          arr->elt_size * (arr->nelts - elements_to_delete - delete_index));

      /* Delete the last ELEMENTS_TO_DELETE elements. */
      arr->nelts -= elements_to_delete;
    }
}

void
svn_sort__array_reverse(apr_array_header_t *array,
                        apr_pool_t *scratch_pool)
{
  int i;

  if (array->elt_size == sizeof(void *))
    {
      for (i = 0; i < array->nelts / 2; i++)
        {
          int swap_index = array->nelts - i - 1;
          void *tmp = APR_ARRAY_IDX(array, i, void *);

          APR_ARRAY_IDX(array, i, void *) =
            APR_ARRAY_IDX(array, swap_index, void *);
          APR_ARRAY_IDX(array, swap_index, void *) = tmp;
        }
    }
  else
    {
      apr_size_t sz = array->elt_size;
      char *tmp = apr_palloc(scratch_pool, sz);

      for (i = 0; i < array->nelts / 2; i++)
        {
          int swap_index = array->nelts - i - 1;
          char *x = array->elts + (sz * i);
          char *y = array->elts + (sz * swap_index);

          memcpy(tmp, x, sz);
          memcpy(x, y, sz);
          memcpy(y, tmp, sz);
        }
    }
}