<?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>                  |
// +-----------------------------------------------------------------------------+
//
/**
 * The Graph.php file contains the definition of the Structures_Graph class 
 *
 * @see Structures_Graph
 * @package Structures_Graph
 */

/* dependencies {{{ */
/** PEAR base classes */
require_once 'PEAR.php';
/** Graph Node */
require_once 'Structures/Graph/Node.php';
/* }}} */

define('STRUCTURES_GRAPH_ERROR_GENERIC', 100);

/* class Structures_Graph {{{ */
/**
 * The Structures_Graph class represents a graph data structure. 
 *
 * A Graph is a data structure composed by a set of nodes, connected by arcs.
 * Graphs may either be directed or undirected. In a directed graph, arcs are 
 * directional, and can be traveled only one way. In an undirected graph, arcs
 * are bidirectional, and can be traveled both ways.
 *
 * @author		Sérgio Carvalho <sergio.carvalho@portugalmail.com> 
 * @copyright	(c) 2004 by Sérgio Carvalho
 * @package Structures_Graph
 */
/* }}} */
class Structures_Graph {
    /* fields {{{ */
    /**
     * @access private
     */
    var $_nodes = array();
    /**
     * @access private
     */
    var $_directed = false;
    /* }}} */

    /* Constructor {{{ */
    /**
    *
    * Constructor
    *
    * @param    boolean    Set to true if the graph is directed. Set to false if it is not directed. (Optional, defaults to true)
    * @access	public
    */
    function __construct($directed = true) {
        $this->_directed = $directed;
    }
    /* }}} */

    /* isDirected {{{ */
    /**
    *
    * Return true if a graph is directed
    *
    * @return	boolean	 true if the graph is directed
    * @access	public
    */
    function isDirected() {
        return (boolean) $this->_directed;
    }
    /* }}} */

    /* addNode {{{ */
    /**
    *
    * Add a Node to the Graph
    *
    * @param    Structures_Graph_Node   The node to be added.
    * @access	public
    */
    function addNode(&$newNode) {
        // We only add nodes
        if (!is_a($newNode, 'Structures_Graph_Node')) return Pear::raiseError('Structures_Graph::addNode received an object that is not a Structures_Graph_Node', STRUCTURES_GRAPH_ERROR_GENERIC);
        // Graphs are node *sets*, so duplicates are forbidden. We allow nodes that are exactly equal, but disallow equal references.
        foreach($this->_nodes as $key => $node) {
            /*
             ZE1 equality operators choke on the recursive cycle introduced by the _graph field in the Node object.
             So, we'll check references the hard way (change $this->_nodes[$key] and check if the change reflects in 
             $node)
            */
            $savedData = $this->_nodes[$key];
            $referenceIsEqualFlag = false;
            $this->_nodes[$key] = true;
            if ($node === true) {
                $this->_nodes[$key] = false;
                if ($node === false) $referenceIsEqualFlag = true;
            }
            $this->_nodes[$key] = $savedData;
            if ($referenceIsEqualFlag) return Pear::raiseError('Structures_Graph::addNode received an object that is a duplicate for this dataset', STRUCTURES_GRAPH_ERROR_GENERIC);
        }
        $this->_nodes[] =& $newNode;
        $newNode->setGraph($this);
    }
    /* }}} */

    /* removeNode (unimplemented) {{{ */
    /**
    *
    * Remove a Node from the Graph
    *
    * @todo     This is unimplemented
    * @param    Structures_Graph_Node   The node to be removed from the graph
    * @access	public
    */
    function removeNode(&$node) {
    }
    /* }}} */

    /* getNodes {{{ */
    /**
    *
    * Return the node set, in no particular order. For ordered node sets, use a Graph Manipulator insted.
    *
    * @access   public
    * @see      Structures_Graph_Manipulator_TopologicalSorter
    * @return   array The set of nodes in this graph
    */
    function &getNodes() {
        return $this->_nodes;
    }
    /* }}} */
}
?>
