/*
 *  Copyright © 2004 Peter Harvey <pah06@uow.edu.au>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "config.h"

#include "ephy-nodes-cover.h"

/* Count the number of node entries which are children of parent. */
gint
ephy_nodes_count_covered (EphyNode *parent, const GPtrArray *children)
{
  guint i, len = 0;
  EphyNode *child;

  for (i = 0; i < children->len; i++) {
    child = g_ptr_array_index (children, i);
    if (ephy_node_has_child (parent, child)) {
      len++;
    }
  }
  return len;
}

/* Removes from the array of children those which are children of the given parent. */
gint
ephy_nodes_remove_covered (EphyNode *parent, GPtrArray *children)
{
  guint i, len = children->len;
  EphyNode *child;

  for (i = 0; i < children->len; i++) {
    child = g_ptr_array_index (children, i);
    if (ephy_node_has_child (parent, child)) {
      g_ptr_array_remove_index_fast (children, i);
      i--;
    }
  }
  return len - children->len;
}

/* Removes from the array of children those which are children of the given parent. */
gint
ephy_nodes_remove_not_covered (EphyNode *parent, GPtrArray *children)
{
  guint i, len = children->len;
  EphyNode *child;

  for (i = 0; i < children->len; i++) {
    child = g_ptr_array_index (children, i);
    if (!ephy_node_has_child (parent, child)) {
      g_ptr_array_remove_index_fast (children, i);
      i--;
    }
  }
  return len - children->len;
}

/* Returns the subset of children which are childs of the given parent.
 * Stores the result in the given _covered array if non-null. */
GPtrArray *
ephy_nodes_get_covered (EphyNode *parent, const GPtrArray *children, GPtrArray *_covered)
{
  GPtrArray *covered = _covered ? _covered : g_ptr_array_sized_new (children->len);
  EphyNode *child;
  guint i;

  covered->len = 0;
  for (i = 0; i < children->len; i++) {
    child = g_ptr_array_index (children, i);
    if (ephy_node_has_child (parent, child)) {
      g_ptr_array_add (covered, child);
    }
  }

  return covered;
}

/* Returns true if the parent covers all the children. */
gboolean
ephy_nodes_covered (EphyNode *parent, const GPtrArray *children)
{
  EphyNode *child;
  guint i;

  for (i = 0; i < children->len; i++) {
    child = g_ptr_array_index (children, i);
    if (!ephy_node_has_child (parent, child)) {
      return FALSE;
    }
  }

  return TRUE;
}

static gint
compare_chosen (const guint *a, const guint *b, guint *count_c)
{
  return (count_c[*b] - count_c[*a]);
}

/* Returns the subset of parents which provide a covering of children.
 * Arguments other than parents and children arguments are only used if non-null.
 * Uses the _covering array to store the subset of parents.
 * Uses the _uncovered array to store those children which couldn't be covered.
 * Uses the _sizes array to store the number of children covered by each parent. */
GPtrArray *
ephy_nodes_get_covering (const GPtrArray *parents, const GPtrArray *children,
                         GPtrArray *_covering, GPtrArray *_uncovered, GArray *_sizes)
{
  GPtrArray *uncovered = _uncovered ? _uncovered : g_ptr_array_sized_new (children->len);
  GPtrArray *covering = _covering ? _covering : g_ptr_array_sized_new (parents->len);
  GArray *chosen = g_array_sized_new (FALSE, FALSE, sizeof (guint), parents->len);
  GArray *sizes = _sizes;

  /* Create arrays to store the number of children each parent has which
   * are currently not covered, and the number of children it has total. */
  guint *count_u = g_malloc (sizeof (guint) * parents->len);
  guint *count_c = g_malloc (sizeof (guint) * parents->len);

  EphyNode *parent;
  guint i, p;

  /* Empty all the returning arrays. */
  uncovered->len = 0;
  covering->len = 0;
  if (sizes) sizes->len = 0;

  /* Initialise the array of uncovered bookmarks. */
  for (i = 0; i < children->len; i++) {
    g_ptr_array_add (uncovered, g_ptr_array_index (children, i));
  }

  /* Initialise the count_u and count_c arrays.
   * NB: count_u[0] is set to 0 if the parent node
     covers the entire set of children. */
  for (i = 0, p = 0; i < parents->len; i++) {
    parent = g_ptr_array_index (parents, i);
    count_c[i] = ephy_nodes_count_covered (parent, children);
    count_u[i] = (count_c[i] < children->len) ? count_c[i] : 0;
    if (count_u[i] > count_u[p]) p = i;
  }

  /* While there are more suitable topics... */
  while (p < parents->len && count_u[p]) {
    /* Update the arrays of uncovered bookmarks and covering topics. */
    parent = g_ptr_array_index (parents, p);
    ephy_nodes_remove_covered (parent, uncovered);
    g_array_append_val (chosen, p);

    /* Find the next most suitable topic. */
    count_u[p] = 0;
    for (i = 0; i < parents->len; i++) {
      /* Lazy update the count_u[i] array. */
      if (count_u[i] > count_u[p] || (count_u[i] == count_u[p] && count_c[i] < count_c[p])) {
        parent = g_ptr_array_index (parents, i);
        count_u[i] = ephy_nodes_count_covered (parent, uncovered);
      }

      if (count_u[i] > count_u[p] || (count_u[i] == count_u[p] && count_c[i] < count_c[p])) {
        p = i;
      }
    }
  }

  g_array_sort_with_data (chosen, (GCompareDataFunc)compare_chosen, count_c);

  for (i = 0; i < chosen->len; i++) {
    p = g_array_index (chosen, guint, i);
    g_ptr_array_add (covering, g_ptr_array_index (parents, p));
    if (sizes) g_array_append_val (sizes, count_c[p]);
  }

  if (_uncovered != uncovered) g_ptr_array_free (uncovered, TRUE);
  g_array_free (chosen, TRUE);
  g_free (count_u);
  g_free (count_c);

  return covering;
}
