/*

 * glade-tsort.c: a topological sorting algorithm implementation

 *

 * Copyright (C) 2013 Juan Pablo Ugarte.

 *

 * 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, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 *

 * Authors:

 *   Juan Pablo Ugarte <juanpablougarte@gmail.com>

 */

#include "glade-tsort.h"

/**

 * _node_edge_prepend:

 * @node: a _NodeEdge pointer or NULL

 * @predecessor:

 * @successor:

 * 

 * Adds a new node with the values @predecessor and @successor to the start of

 * @node list.

 * 

 * Returns: the new start of the node list.

 */

GList *

_node_edge_prepend  (GList *list,

                     gpointer predecessor,

                     gpointer successor)

{

  _NodeEdge *edge = g_slice_new (_NodeEdge);

  edge->predecessor = predecessor;

  edge->successor = successor;

  return g_list_prepend (list, edge);

}

static void

_node_edge_free (gpointer data)

{

  g_slice_free (_NodeEdge, data);

}

void

_node_edge_list_free (GList *list)

{

  g_list_free_full (list, _node_edge_free);

}

static inline void

tsort_remove_non_start_nodes (GList **nodes, GList *edges)

{

  GList *l;

  for (l = edges; l; l = g_list_next (l))

    {

      _NodeEdge *edge = l->data;

      *nodes = g_list_remove (*nodes, edge->successor);

    }

}

static inline gboolean

tsort_node_has_no_incoming_edge (gpointer node, GList *edges)

{

  GList *l;

  for (l = edges; l; l = g_list_next (l))

    {

      _NodeEdge *edge = l->data;

      if (node == edge->successor)

        return FALSE;

    }

  return TRUE;

}

/**

 * _glade_tsort:

 * @nodes: list of pointers to sort

 * @edges: pointer to the list of #_NodeEdge that conform the dependency 

 *         graph of @nodes.

 * 

 * Topological sorting implementation.

 * After calling this funtion only graph cycles (circular dependencies) are left

 * in @edges list. So if @edges is NULL it means the returned list has all the 

 * elements topologically sorted if not it means there are at least one

 * circular dependency.

 *

 * L ← Empty list that will contain the sorted elements

 * S ← Set of all nodes with no incoming edges

 * while S is non-empty do

 *     remove a node n from S

 *     insert n into L

 *     for each node m with an edge e from n to m do

 *         remove edge e from the graph

 *         if m has no other incoming edges then

 *             insert m into S

 * return L (a topologically sorted order if graph has no edges)

 *

 * see: http://en.wikipedia.org/wiki/Topological_sorting

 * 

 * Returns: a new list sorted by dependency including nodes only present in @edges

 */

GList *

_glade_tsort (GList **nodes, GList **edges)

{

  GList *sorted_nodes;

  /* L ← Empty list that will contain the sorted elements */

  sorted_nodes = NULL;

  /* S ← Set of all nodes with no incoming edges */

  tsort_remove_non_start_nodes (nodes, *edges);

  /* while S is non-empty do */

  while (*nodes)

    {

      GList *l, *next;

      gpointer n;

      /* remove a node n from S */

      n = (*nodes)->data;

      *nodes = g_list_delete_link (*nodes, *nodes);

      /* insert n into L */

      /*if (!glade_widget_get_parent (n)) this would be a specific optimization */

      sorted_nodes = g_list_prepend (sorted_nodes, n);

      /* for each node m ... */

      for (l = *edges; l; l = next)

        {

          _NodeEdge *edge = l->data;

          next = g_list_next (l);

          /* ... with an edge e from n to m do */

          if (edge->predecessor == n)

            {

              /* remove edge e from the graph */

              *edges = g_list_delete_link (*edges, l);

              /* if m has no other incoming edges then */

              if (tsort_node_has_no_incoming_edge (edge->successor, *edges))

                /* insert m into S */

                *nodes = g_list_prepend (*nodes, edge->successor);

              g_slice_free (_NodeEdge, edge);

            }

        }

    }

  /* if graph has edges then return error (graph has at least one cycle) */

#if 0   /* We rather not return NULL, caller must check if edge */

  if (*edges)

    {      

      g_list_free (sorted_nodes);

      _node_edge_list_free (*edges);

      *edges = NULL;

      return NULL;

    }

#endif  

  /* return L (a topologically sorted order if edge is NULL) */

  return g_list_reverse (sorted_nodes);

}