/*______________________________________________________________________________
 * 
 * Copyright 2000-2001 Paul Cantrell
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * (1) Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 * (2) Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in
 *     the documentation and/or other materials provided with the
 *     distribution. 
 *
 * (3) The name of the author may not be used to endorse or promote
 *     products derived from this software without specific prior
 *     written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *_______________________________________________________________________________
 */

package net.innig.collect;

import java.util.*;

/**
    Graph utilities.

    <p align="center">
    <table cellpadding=4 cellspacing=2 border=0 bgcolor="#338833" width="90%"><tr><td bgcolor="#EEEEEE">
        <b>Maturity:</b>
        This is obviously a very immature API.
        The implementation of the single method in it, however, works quite well.
    </td></tr><tr><td bgcolor="#EEEEEE">
        <b>Plans:</b>
        In the future, innig-util will include more complete graph handling utilities.
    </td></tr></table>
    
    @author Paul Cantrell
    @version [Development version]
*/

public abstract class Graphs
    {
    /** Returns the set of all nodes reachable along directed paths
     *  from a given node in a given graph.  The implementation is
     *  smart about cycle detection. */
    
    public static <N> Set<N> reachableNodes(N initial, GraphWalker<N> walker)
        { return reachableNodesFromSet(Collections.singleton(initial), walker); }

    /** Returns the set of all nodes reachable along directed paths
     *  from a given set of nodes in a given graph.  The implementation
     *  is smart about cycle detection. */
    
    public static <N> Set<N> reachableNodesFromSet(Set<N> initial, GraphWalker<N> walker)
        {
        Set<N>
            nodes = new HashSet<N>(),
            newNodes = initial,
            newerNodes = new HashSet<N>();
        
        while(!newNodes.isEmpty())
            {
            nodes.addAll(newNodes);   // Put the new nodes in the current list.
            
            // Now put all the newly reachable nodes a list of even newer nodes.
            
            for(N newNode : newNodes)
                newerNodes.addAll(walker.getEdgesFrom(newNode));
            
            // Add unwalked newer nodes for next time
            
            newerNodes.removeAll(nodes);
            newNodes = newerNodes;
            newerNodes = new HashSet<N>();
            }
        
        return nodes;
        }
    
    public static <N> Set<List<N>> findCycles(N initial, GraphWalker<N> walker)
        {
        Set<List<N>> cycles = new HashSet<List<N>>(); //! change to IdentityHashSet
        findCycles(
            initial,
            cycles,
            walker,
            new ArrayList<N>(),
            new HashSet<N>()); //! change to IdentityHashSet
        return cycles;
        }
    
    private static <N> void findCycles(
            N node,
            Set<List<N>> cycles, 
            GraphWalker<N> walker,
            List<N> curPath,
            Set<N>  visited)
        {
        curPath.add(node);
        
        if(visited.contains(node))
            cycles.add(Collections.unmodifiableList(new ArrayList<N>(curPath))); //! wastes 10%
        else
            {
            visited.add(node);
            for(N neighbor : walker.getEdgesFrom(node))
                findCycles(neighbor, cycles, walker, curPath, visited);
            visited.remove(node);
            }
            
        curPath.remove(curPath.size() - 1);
        }
        
    private Graphs() { } // To prevent instantiation
    }