/* Refreshes the stack of parent pointers in |trav|
   and updates its generation number. */
static void
trav_refresh (struct bst_traverser *trav)
{
  assert (trav != NULL);

  trav->bst_generation = trav->bst_table->bst_generation;

  if (trav->bst_node != NULL)
    {
      bst_comparison_func *cmp = trav->bst_table->bst_compare;
      void *param = trav->bst_table->bst_param;
      struct bst_node *node = trav->bst_node;
      struct bst_node *i;

      trav->bst_height = 0;
      for (i = trav->bst_table->bst_root; i != node; )
        {
          assert (trav->bst_height < BST_MAX_HEIGHT);
          assert (i != NULL);

          trav->bst_stack[trav->bst_height++] = i;
          i = i->bst_link[cmp (node->bst_data, i->bst_data, param) > 0];
        }
    }
}

/* Initializes |trav| for use with |tree|
   and selects the null node. */
void
bst_t_init (struct bst_traverser *trav, struct bst_table *tree)
{
  trav->bst_table = tree;
  trav->bst_node = NULL;
  trav->bst_height = 0;
  trav->bst_generation = tree->bst_generation;
}

/* Initializes |trav| for |tree|
   and selects and returns a pointer to its least-valued item.
   Returns |NULL| if |tree| contains no nodes. */
void *
bst_t_first (struct bst_traverser *trav, struct bst_table *tree)
{
  struct bst_node *x;

  assert (tree != NULL && trav != NULL);

  trav->bst_table = tree;
  trav->bst_height = 0;
  trav->bst_generation = tree->bst_generation;

  x = tree->bst_root;
  if (x != NULL)
    while (x->bst_link[0] != NULL)
      {
        if (trav->bst_height >= BST_MAX_HEIGHT)
          {
            bst_balance (tree);
            return bst_t_first (trav, tree);
          }

        trav->bst_stack[trav->bst_height++] = x;
        x = x->bst_link[0];
      }
  trav->bst_node = x;

  return x != NULL ? x->bst_data : NULL;
}

/* Initializes |trav| for |tree|
   and selects and returns a pointer to its greatest-valued item.
   Returns |NULL| if |tree| contains no nodes. */
void *
bst_t_last (struct bst_traverser *trav, struct bst_table *tree)
{
  struct bst_node *x;

  assert (tree != NULL && trav != NULL);

  trav->bst_table = tree;
  trav->bst_height = 0;
  trav->bst_generation = tree->bst_generation;

  x = tree->bst_root;
  if (x != NULL)
    while (x->bst_link[1] != NULL)
      {
        if (trav->bst_height >= BST_MAX_HEIGHT)
          {
            bst_balance (tree);
            return bst_t_last (trav, tree);
          }

        trav->bst_stack[trav->bst_height++] = x;
        x = x->bst_link[1];
      }
  trav->bst_node = x;

  return x != NULL ? x->bst_data : NULL;
}

/* Searches for |item| in |tree|.
   If found, initializes |trav| to the item found and returns the item
   as well.
   If there is no matching item, initializes |trav| to the null item
   and returns |NULL|. */
void *
bst_t_find (struct bst_traverser *trav, struct bst_table *tree, void *item)
{
  struct bst_node *p, *q;

  assert (trav != NULL && tree != NULL && item != NULL);
  trav->bst_table = tree;
  trav->bst_height = 0;
  trav->bst_generation = tree->bst_generation;
  for (p = tree->bst_root; p != NULL; p = q)
    {
      int cmp = tree->bst_compare (item, p->bst_data, tree->bst_param);

      if (cmp < 0)
        q = p->bst_link[0];
      else if (cmp > 0)
        q = p->bst_link[1];
      else /* |cmp == 0| */
        {
          trav->bst_node = p;
          return p->bst_data;
        }

      if (trav->bst_height >= BST_MAX_HEIGHT)
        {
          bst_balance (trav->bst_table);
          return bst_t_find (trav, tree, item);
        }
      trav->bst_stack[trav->bst_height++] = p;
    }

  trav->bst_height = 0;
  trav->bst_node = NULL;
  return NULL;
}

/* Attempts to insert |item| into |tree|.
   If |item| is inserted successfully, it is returned and |trav| is
   initialized to its location.
   If a duplicate is found, it is returned and |trav| is initialized to
   its location.  No replacement of the item occurs.
   If a memory allocation failure occurs, |NULL| is returned and |trav|
   is initialized to the null item. */
void *
bst_t_insert (struct bst_traverser *trav, struct bst_table *tree, void *item)
{
  struct bst_node **q;

  assert (tree != NULL && item != NULL);

  trav->bst_table = tree;
  trav->bst_height = 0;

  q = &tree->bst_root;
  while (*q != NULL)
    {
      int cmp = tree->bst_compare (item, (*q)->bst_data, tree->bst_param);
      if (cmp == 0)
        {
          trav->bst_node = *q;
          trav->bst_generation = tree->bst_generation;
          return (*q)->bst_data;
        }

      if (trav->bst_height >= BST_MAX_HEIGHT)
        {
          bst_balance (tree);
          return bst_t_insert (trav, tree, item);
        }
      trav->bst_stack[trav->bst_height++] = *q;

      q = &(*q)->bst_link[cmp > 0];
    }

  trav->bst_node = *q = tree->bst_alloc->libavl_malloc (tree->bst_alloc,
                                                        sizeof **q);
  if (*q == NULL)
    {
      trav->bst_node = NULL;
      trav->bst_generation = tree->bst_generation;
      return NULL;
    }

  (*q)->bst_link[0] = (*q)->bst_link[1] = NULL;
  (*q)->bst_data = item;
  tree->bst_count++;
  trav->bst_generation = tree->bst_generation;
  return (*q)->bst_data;
}

/* Initializes |trav| to have the same current node as |src|. */
void *
bst_t_copy (struct bst_traverser *trav, const struct bst_traverser *src)
{
  assert (trav != NULL && src != NULL);

  if (trav != src)
    {
      trav->bst_table = src->bst_table;
      trav->bst_node = src->bst_node;
      trav->bst_generation = src->bst_generation;
      if (trav->bst_generation == trav->bst_table->bst_generation)
        {
          trav->bst_height = src->bst_height;
          memcpy (trav->bst_stack, (const void *) src->bst_stack,
                  sizeof *trav->bst_stack * trav->bst_height);
        }
    }

  return trav->bst_node != NULL ? trav->bst_node->bst_data : NULL;
}

/* Returns the next data item in inorder
   within the tree being traversed with |trav|,
   or if there are no more data items returns |NULL|. */
void *
bst_t_next (struct bst_traverser *trav)
{
  struct bst_node *x;

  assert (trav != NULL);

  if (trav->bst_generation != trav->bst_table->bst_generation)
    trav_refresh (trav);

  x = trav->bst_node;
  if (x == NULL)
    {
      return bst_t_first (trav, trav->bst_table);
    }
  else if (x->bst_link[1] != NULL)
    {
      if (trav->bst_height >= BST_MAX_HEIGHT)
        {
          bst_balance (trav->bst_table);
          return bst_t_next (trav);
        }

      trav->bst_stack[trav->bst_height++] = x;
      x = x->bst_link[1];

      while (x->bst_link[0] != NULL)
        {
          if (trav->bst_height >= BST_MAX_HEIGHT)
            {
              bst_balance (trav->bst_table);
              return bst_t_next (trav);
            }

          trav->bst_stack[trav->bst_height++] = x;
          x = x->bst_link[0];
        }
    }
  else
    {
      struct bst_node *y;

      do
        {
          if (trav->bst_height == 0)
            {
              trav->bst_node = NULL;
              return NULL;
            }

          y = x;
          x = trav->bst_stack[--trav->bst_height];
        }
      while (y == x->bst_link[1]);
    }
  trav->bst_node = x;

  return x->bst_data;
}

/* Returns the previous data item in inorder
   within the tree being traversed with |trav|,
   or if there are no more data items returns |NULL|. */
void *
bst_t_prev (struct bst_traverser *trav)
{
  struct bst_node *x;

  assert (trav != NULL);

  if (trav->bst_generation != trav->bst_table->bst_generation)
    trav_refresh (trav);

  x = trav->bst_node;
  if (x == NULL)
    {
      return bst_t_last (trav, trav->bst_table);
    }
  else if (x->bst_link[0] != NULL)
    {
      if (trav->bst_height >= BST_MAX_HEIGHT)
        {
          bst_balance (trav->bst_table);
          return bst_t_prev (trav);
        }

      trav->bst_stack[trav->bst_height++] = x;
      x = x->bst_link[0];

      while (x->bst_link[1] != NULL)
        {
          if (trav->bst_height >= BST_MAX_HEIGHT)
            {
              bst_balance (trav->bst_table);
              return bst_t_prev (trav);
            }

          trav->bst_stack[trav->bst_height++] = x;
          x = x->bst_link[1];
        }
    }
  else
    {
      struct bst_node *y;

      do
        {
          if (trav->bst_height == 0)
            {
              trav->bst_node = NULL;
              return NULL;
            }

          y = x;
          x = trav->bst_stack[--trav->bst_height];
        }
      while (y == x->bst_link[0]);
    }
  trav->bst_node = x;

  return x->bst_data;
}

/* Returns |trav|'s current item. */
void *
bst_t_cur (struct bst_traverser *trav)
{
  assert (trav != NULL);

  return trav->bst_node != NULL ? trav->bst_node->bst_data : NULL;
}

/* Replaces the current item in |trav| by |new| and returns the item replaced.
   |trav| must not have the null item selected.
   The new item must not upset the ordering of the tree. */
void *
bst_t_replace (struct bst_traverser *trav, void *new)
{
  void *old;

  assert (trav != NULL && trav->bst_node != NULL && new != NULL);
  old = trav->bst_node->bst_data;
  trav->bst_node->bst_data = new;
  return old;
}