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<?php

/* vim: set expandtab tabstop=4 shiftwidth=4 foldmethod=marker: */

// +-----------------------------------------------------------------------------+

// | Copyright (c) 2003 Sérgio Gonçalves Carvalho                                |

// +-----------------------------------------------------------------------------+

// | This file is part of Structures_Graph.                                      |

// |                                                                             |

// | Structures_Graph is free software; you can redistribute it and/or modify    |

// | it under the terms of the GNU Lesser General Public License as published by |

// | the Free Software Foundation; either version 2.1 of the License, or         |

// | (at your option) any later version.                                         |

// |                                                                             |

// | Structures_Graph 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 Lesser General Public License for more details.                         |

// |                                                                             |

// | You should have received a copy of the GNU Lesser General Public License    |

// | along with Structures_Graph; if not, write to the Free Software             |

// | Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA                    |

// | 02111-1307 USA                                                              |

// +-----------------------------------------------------------------------------+

// | Author: Sérgio Carvalho <sergio.carvalho@portugalmail.com>                  |

// +-----------------------------------------------------------------------------+

//

/**

 * This file contains the definition of the Structures_Graph_Manipulator_TopologicalSorter class.

 *

 * @see Structures_Graph_Manipulator_TopologicalSorter

 * @package Structures_Graph

 */

/* dependencies {{{ */

/** */

require_once 'PEAR.php';

/** */

require_once 'Structures/Graph.php';

/** */

require_once 'Structures/Graph/Node.php';

/** */

require_once 'Structures/Graph/Manipulator/AcyclicTest.php';

/* }}} */

/* class Structures_Graph_Manipulator_TopologicalSorter {{{ */

/**

 * The Structures_Graph_Manipulator_TopologicalSorter is a manipulator

 * which is able to return the set of nodes in a graph, sorted by topological

 * order.

 *

 * A graph may only be sorted topologically iff it's a DAG. You can test it

 * with the Structures_Graph_Manipulator_AcyclicTest.

 *

 * @author		Sérgio Carvalho <sergio.carvalho@portugalmail.com>

 * @copyright	(c) 2004 by Sérgio Carvalho

 * @see     Structures_Graph_Manipulator_AcyclicTest

 * @package Structures_Graph

 */

class Structures_Graph_Manipulator_TopologicalSorter {

    /* _nonVisitedInDegree {{{ */

    /**

    *

    * This is a variant of Structures_Graph::inDegree which does

    * not count nodes marked as visited.

    *

    * @access   private

    * @return	integer	 Number of non-visited nodes that link to this one

    */

    function _nonVisitedInDegree(&$node) {

        $result = 0;

        $graphNodes =& $node->_graph->getNodes();

        foreach (array_keys($graphNodes) as $key) {

            if ((!$graphNodes[$key]->getMetadata('topological-sort-visited')) && $graphNodes[$key]->connectsTo($node)) $result++;

        }

        return $result;

    }

    /* }}} */

    /* _sort {{{ */

    /**

    * @access   private

    */

    function _sort(&$graph) {

        // Mark every node as not visited

        $nodes =& $graph->getNodes();

        $nodeKeys = array_keys($nodes);

        $refGenerator = array();

        foreach($nodeKeys as $key) {

            $refGenerator[] = false;

            $nodes[$key]->setMetadata('topological-sort-visited', $refGenerator[sizeof($refGenerator) - 1]);

        }

        // Iteratively peel off leaf nodes

        $topologicalLevel = 0;

        do {

            // Find out which nodes are leafs (excluding visited nodes)

            $leafNodes = array();

            foreach($nodeKeys as $key) {

                if ((!$nodes[$key]->getMetadata('topological-sort-visited')) && Structures_Graph_Manipulator_TopologicalSorter::_nonVisitedInDegree($nodes[$key]) == 0) {

                    $leafNodes[] =& $nodes[$key];

                }

            }

            // Mark leafs as visited

            $refGenerator[] = $topologicalLevel;

            for ($i=sizeof($leafNodes) - 1; $i>=0; $i--) {

                $visited =& $leafNodes[$i]->getMetadata('topological-sort-visited');

                $visited = true;

                $leafNodes[$i]->setMetadata('topological-sort-visited', $visited);

                $leafNodes[$i]->setMetadata('topological-sort-level', $refGenerator[sizeof($refGenerator) - 1]);

            }

            $topologicalLevel++;

        } while (sizeof($leafNodes) > 0);

        // Cleanup visited marks

        foreach($nodeKeys as $key) $nodes[$key]->unsetMetadata('topological-sort-visited');

    }

    /* }}} */

    /* sort {{{ */

    /**

    *

    * sort returns the graph's nodes, sorted by topological order.

    *

    * The result is an array with

    * as many entries as topological levels. Each entry in this array is an array of nodes within

    * the given topological level.

    *

    * @return	array	 The graph's nodes, sorted by topological order.

    * @access	public

    */

    function sort(&$graph) {

        // We only sort graphs

        if (!is_a($graph, 'Structures_Graph')) return Pear::raiseError('Structures_Graph_Manipulator_TopologicalSorter::sort received an object that is not a Structures_Graph', STRUCTURES_GRAPH_ERROR_GENERIC);

        if (!Structures_Graph_Manipulator_AcyclicTest::isAcyclic($graph)) return Pear::raiseError('Structures_Graph_Manipulator_TopologicalSorter::sort received an graph that has cycles', STRUCTURES_GRAPH_ERROR_GENERIC);

        Structures_Graph_Manipulator_TopologicalSorter::_sort($graph);

        $result = array();

        // Fill out result array

        $nodes =& $graph->getNodes();

        $nodeKeys = array_keys($nodes);

        foreach($nodeKeys as $key) {

            if (!array_key_exists($nodes[$key]->getMetadata('topological-sort-level'), $result)) $result[$nodes[$key]->getMetadata('topological-sort-level')] = array();

            $result[$nodes[$key]->getMetadata('topological-sort-level')][] =& $nodes[$key];

            $nodes[$key]->unsetMetadata('topological-sort-level');

        }

        return $result;

    }

    /* }}} */

}

/* }}} */

?>