/*

 * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package com.sun.tools.javac.util;

/** <p><b>This is NOT part of any supported API.

 *  If you write code that depends on this, you do so at your own risk.

 *  This code and its internal interfaces are subject to change or

 *  deletion without notice.</b>

 */

public class GraphUtils {

    /**

     * This class is a basic abstract class for representing a node.

     * A node is associated with a given data.

     */

    public static abstract class Node<D> {

        public final D data;

        public Node(D data) {

            this.data = data;

        }

        public abstract Iterable<? extends Node<D>> getDependencies();

        public abstract String printDependency(Node<D> to);

        @Override

        public String toString() {

            return data.toString();

        }

    }

    /**

     * This class specialized Node, by adding elements that are required in order

     * to perform Tarjan computation of strongly connected components.

     */

    public static abstract class TarjanNode<D> extends Node<D> implements Comparable<TarjanNode<D>> {

        int index = -1;

        int lowlink;

        boolean active;

        public TarjanNode(D data) {

            super(data);

        }

        public abstract Iterable<? extends TarjanNode<D>> getDependencies();

        public int compareTo(TarjanNode<D> o) {

            return (index < o.index) ? -1 : (index == o.index) ? 0 : 1;

        }

    }

    /**

     * Tarjan's algorithm to determine strongly connected components of a

     * directed graph in linear time. Works on TarjanNode.

     */

    public static <D, N extends TarjanNode<D>> List<? extends List<? extends N>> tarjan(Iterable<? extends N> nodes) {

        ListBuffer<List<N>> cycles = ListBuffer.lb();

        ListBuffer<N> stack = ListBuffer.lb();

        int index = 0;

        for (N node: nodes) {

            if (node.index == -1) {

                index += tarjan(node, index, stack, cycles);

            }

        }

        return cycles.toList();

    }

    private static <D, N extends TarjanNode<D>> int tarjan(N v, int index, ListBuffer<N> stack, ListBuffer<List<N>> cycles) {

        v.index = index;

        v.lowlink = index;

        index++;

        stack.prepend(v);

        v.active = true;

        for (TarjanNode<D> nd: v.getDependencies()) {

            @SuppressWarnings("unchecked")

            N n = (N)nd;

            if (n.index == -1) {

                tarjan(n, index, stack, cycles);

                v.lowlink = Math.min(v.lowlink, n.lowlink);

            } else if (stack.contains(n)) {

                v.lowlink = Math.min(v.lowlink, n.index);

            }

        }

        if (v.lowlink == v.index) {

            N n;

            ListBuffer<N> cycle = ListBuffer.lb();

            do {

                n = stack.remove();

                n.active = false;

                cycle.add(n);

            } while (n != v);

            cycles.add(cycle.toList());

        }

        return index;

    }

    /**

     * Debugging: dot representation of a set of connected nodes. The resulting

     * dot representation will use {@code Node.toString} to display node labels

     * and {@code Node.printDependency} to display edge labels. The resulting

     * representation is also customizable with a graph name and a header.

     */

    public static <D> String toDot(Iterable<? extends TarjanNode<D>> nodes, String name, String header) {

        StringBuilder buf = new StringBuilder();

        buf.append(String.format("digraph %s {\n", name));

        buf.append(String.format("label = \"%s\";\n", header));

        //dump nodes

        for (TarjanNode<D> n : nodes) {

            buf.append(String.format("%s [label = \"%s\"];\n", n.hashCode(), n.toString()));

        }

        //dump arcs

        for (TarjanNode<D> from : nodes) {

            for (TarjanNode<D> to : from.getDependencies()) {

                buf.append(String.format("%s -> %s [label = \" %s \"];\n",

                        from.hashCode(), to.hashCode(), from.printDependency(to)));

            }

        }

        buf.append("}\n");

        return buf.toString();

    }

}