/*******************************************************************************
 * Copyright (c) 2003, 2005 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 * Port to the D programming language:
 *     Frank Benoit <benoit@tionex.de>
 *******************************************************************************/
module dwtx.draw2d.graph.GraphUtilities;

import dwt.dwthelper.utils;
import dwtx.draw2d.graph.Subgraph;
import dwtx.draw2d.graph.Node;
import dwtx.draw2d.graph.NodeList;
import dwtx.draw2d.graph.DirectedGraph;
import dwtx.draw2d.graph.Rank;
import dwtx.draw2d.graph.Edge;
import dwtx.draw2d.graph.EdgeList;

/**
 * Some utility methods for graphs.
 * @author Eric Bordeau
 * @since 2.1.2
 */
class GraphUtilities {

static Subgraph getCommonAncestor(Node left, Node right) {
    Subgraph parent;
    if (auto p = cast(Subgraph)right )
        parent = p;
    else
        parent = right.getParent();
    while (parent !is null) {
        if (parent.isNested(left))
            return parent;
        parent = parent.getParent();
    }
    return null;
}

/**
 * Returns <code>true</code> if the given graph contains at least one cycle.
 * @param graph the graph to test
 * @return whether the graph is cyclic
 */
public static bool isCyclic(DirectedGraph graph) {
    return isCyclic(new NodeList(graph.nodes));
}

/**
 * Recursively removes leaf nodes from the list until there are no nodes remaining (acyclic)
 * or there are no leaf nodes but the list is not empty (cyclic), then returns the result.
 * @param nodes the list of nodes to test
 * @return whether the graph is cyclic
 */
public static bool isCyclic(NodeList nodes) {
    if (nodes.isEmpty())
        return false;
    int size = nodes.size();
    // remove all the leaf nodes from the graph
    for (int i = 0; i < nodes.size(); i++) {
        Node node = nodes.getNode(i);
        if (node.outgoing is null || node.outgoing.isEmpty()) { // this is a leaf node
            nodes.remove(node);
            for (int j = 0; j < node.incoming.size(); j++) {
                Edge e = node.incoming.getEdge(j);
                e.source.outgoing.remove(e);
            }
        }
    }
    //  if no nodes were removed, that means there are no leaf nodes and the graph is cyclic
    if (nodes.size() is size)
        return true;
    // leaf nodes were removed, so recursively call this method with the new list
    return isCyclic(nodes);
}

/**
 * Counts the number of edge crossings in a DirectedGraph
 * @param graph the graph whose crossed edges are counted
 * @return the number of edge crossings in the graph
 */
public static int numberOfCrossingsInGraph(DirectedGraph graph) {
    int crossings = 0;
    for (int i = 0; i < graph.ranks.size(); i++) {
        Rank rank = graph.ranks.getRank(i);
        crossings += numberOfCrossingsInRank(rank);
    }
    return crossings;
}

/**
 * Counts the number of edge crossings in a Rank
 * @param rank the rank whose crossed edges are counted
 * @return the number of edge crossings in the rank
 */
public static int numberOfCrossingsInRank(Rank rank) {
    int crossings = 0;
    for (int i = 0; i < rank.size() - 1; i++) {
        Node currentNode = rank.getNode(i);
        Node nextNode;
        for (int j = i + 1; j < rank.size(); j++) {
            nextNode = rank.getNode(j);
            EdgeList currentOutgoing = currentNode.outgoing;
            EdgeList nextOutgoing = nextNode.outgoing;
            for (int k = 0; k < currentOutgoing.size(); k++) {
                Edge currentEdge = currentOutgoing.getEdge(k);
                for (int l = 0; l < nextOutgoing.size(); l++) {
                    if (nextOutgoing.getEdge(l).getIndexForRank(currentNode.rank + 1)
                        < currentEdge.getIndexForRank(currentNode.rank + 1))
                        crossings++;
                }
            }
        }
    }
    return crossings;
}

private static NodeList search(Node node, NodeList list) {
    if (node.flag)
        return list;
    node.flag = true;
    list.add(node);
    for (int i = 0; i < node.outgoing.size(); i++)
        search(node.outgoing.getEdge(i).target, list);
    return list;
}

/**
 * Returns <code>true</code> if adding an edge between the 2 given nodes will introduce a
 * cycle in the containing graph.
 * @param source the potential source node
 * @param target the potential target node
 * @return whether an edge between the 2 given nodes will introduce a cycle
 */
public static bool willCauseCycle(Node source, Node target) {
    NodeList nodes = search(target, new NodeList());
    nodes.resetFlags();
    return nodes.contains(source);
}

static bool isConstrained(Node left, Node right) {
    Subgraph common = left.getParent();
    while (common !is null && !common.isNested(right)) {
        left = left.getParent();
        common = left.getParent();
    }
    while (right.getParent() !is common)
        right = right.getParent();
    return (left.rowOrder !is -1 && right.rowOrder !is -1)
      && left.rowOrder !is right.rowOrder;
}

}