/*

 * Copyright 2000-2006 Sun Microsystems, Inc.  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.  Sun designates this

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

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package sun.security.provider.certpath;

import java.util.ArrayList;

import java.util.Collections;

import java.util.Iterator;

import java.util.List;

/**

 * An AdjacencyList is used to store the history of certification paths

 * attempted in constructing a path from an initiator to a target. The

 * AdjacencyList is initialized with a <code>List</code> of

 * <code>List</code>s, where each sub-<code>List</code> contains objects of

 * type <code>Vertex</code>. A <code>Vertex</code> describes one possible or

 * actual step in the chain building process, and the associated

 * <code>Certificate</code>. Specifically, a <code>Vertex</code> object

 * contains a <code>Certificate</code> and an index value referencing the

 * next sub-list in the process. If the index value is -1 then this

 * <code>Vertex</code> doesn't continue the attempted build path.

 * <p>

 * Example:

 * <p>

 * Attempted Paths:<ul>

 * <li>C1-&gt;C2-&gt;C3

 * <li>C1-&gt;C4-&gt;C5

 * <li>C1-&gt;C4-&gt;C6

 * <li>C1-&gt;C4-&gt;C7

 * <li>C1-&gt;C8-&gt;C9

 * <li>C1-&gt;C10-&gt;C11

 * </ul>

 * <p>

 * AdjacencyList structure:<ul>

 * <li>AL[0] = C1,1

 * <li>AL[1] = C2,2   =&gt;C4,3   =&gt;C8,4     =&gt;C10,5

 * <li>AL[2] = C3,-1

 * <li>AL[3] = C5,-1  =&gt;C6,-1  =&gt;C7,-1

 * <li>AL[4] = C9,-1

 * <li>AL[5] = C11,-1

 * </ul>

 * <p>

 * The iterator method returns objects of type <code>BuildStep</code>, not

 * objects of type <code>Vertex</code>.

 * A <code>BuildStep</code> contains a <code>Vertex</code> and a result code,

 * accessable via getResult method. There are five result values.

 * <code>POSSIBLE</code> denotes that the current step represents a

 * <code>Certificate</code> that the builder is considering at this point in

 * the build. <code>FOLLOW</code> denotes a <code>Certificate</code> (one of

 * those noted as <code>POSSIBLE</code>) that the builder is using to try

 * extending the chain. <code>BACK</code> represents that a

 * <code>FOLLOW</code> was incorrect, and is being removed from the chain.

 * There is exactly one <code>FOLLOW</code> for each <code>BACK</code>. The

 * values <code>SUCCEED</code> and <code>FAIL</code> mean that we've come to

 * the end of the build process, and there will not be any more entries in

 * the list.

 * <p>

 * @see sun.security.provider.certpath.BuildStep

 * @see sun.security.provider.certpath.Vertex

 * <p>

 * @author  seth proctor

 * @since   1.4

 */

public class AdjacencyList {

    // the actual set of steps the AdjacencyList represents

    private ArrayList<BuildStep> mStepList;

    // the original list, just for the toString method

    private List<List<Vertex>> mOrigList;

    /**

     * Constructs a new <code>AdjacencyList</code> based on the specified

     * <code>List</code>. See the example above.

     *

     * @param list a <code>List</code> of <code>List</code>s of

     *             <code>Vertex</code> objects

     */

    public AdjacencyList(List<List<Vertex>> list) {

        mStepList = new ArrayList<BuildStep>();

        mOrigList = list;

        buildList(list, 0, null);

    }

    /**

     * Gets an <code>Iterator</code> to iterate over the set of

     * <code>BuildStep</code>s in build-order. Any attempts to change

     * the list through the remove method will fail.

     *

     * @return an <code>Iterator</code> over the <code>BuildStep</code>s

     */

    public Iterator<BuildStep> iterator() {

        return Collections.unmodifiableList(mStepList).iterator();

    }

    /**

     * Recursive, private method which actually builds the step list from

     * the given adjacency list. <code>Follow</code> is the parent BuildStep

     * that we followed to get here, and if it's null, it means that we're

     * at the start.

     */

    private boolean buildList(List<List<Vertex>> theList, int index,

        BuildStep follow) {

        // Each time this method is called, we're examining a new list

        // from the global list. So, we have to start by getting the list

        // that contains the set of Vertexes we're considering.

        List<Vertex> l = theList.get(index);

        try {

            // we're interested in the case where all indexes are -1...

            boolean allNegOne = true;

            // ...and in the case where every entry has a Throwable

            boolean allXcps = true;

            for (Vertex v : l) {

                if (v.getIndex() != -1) {

                    // count an empty list the same as an index of -1...this

                    // is to patch a bug somewhere in the builder

                    if (theList.get(v.getIndex()).size() != 0)

                        allNegOne = false;

                }

                else

                    if (v.getThrowable() == null)

                        allXcps = false;

                // every entry, regardless of the final use for it, is always

                // entered as a possible step before we take any actions

                mStepList.add(new BuildStep(v, BuildStep.POSSIBLE));

            }

            if (allNegOne) {

                // There are two cases that we could be looking at here. We

                // may need to back up, or the build may have succeeded at

                // this point. This is based on whether or not any

                // exceptions were found in the list.

                if (allXcps) {

                    // we need to go back...see if this is the last one

                    if (follow == null)

                        mStepList.add(new BuildStep(null, BuildStep.FAIL));

                    else

                        mStepList.add(new BuildStep(follow.getVertex(),

                                                    BuildStep.BACK));

                    return false;

                } else {

                    // we succeeded...now the only question is which is the

                    // successful step? If there's only one entry without

                    // a throwable, then that's the successful step. Otherwise,

                    // we'll have to make some guesses...

                    List<Vertex> possibles = new ArrayList<Vertex>();

                    for (Vertex v : l) {

                        if (v.getThrowable() == null)

                            possibles.add(v);

                    }

                    if (possibles.size() == 1) {

                        // real easy...we've found the final Vertex

                        mStepList.add(new BuildStep(possibles.get(0),

                                                    BuildStep.SUCCEED));

                    } else {

                        // ok...at this point, there is more than one Cert

                        // which might be the succeed step...how do we know

                        // which it is? I'm going to assume that our builder

                        // algorithm is good enough to know which is the

                        // correct one, and put it first...but a FIXME goes

                        // here anyway, and we should be comparing to the

                        // target/initiator Cert...

                        mStepList.add(new BuildStep(possibles.get(0),

                                                    BuildStep.SUCCEED));

                    }

                    return true;

                }

            } else {

                // There's at least one thing that we can try before we give

                // up and go back. Run through the list now, and enter a new

                // BuildStep for each path that we try to follow. If none of

                // the paths we try produce a successful end, we're going to

                // have to back out ourselves.

                boolean success = false;

                for (Vertex v : l) {

                    // Note that we'll only find a SUCCEED case when we're

                    // looking at the last possible path, so we don't need to

                    // consider success in the while loop

                    if (v.getIndex() != -1) {

                        if (theList.get(v.getIndex()).size() != 0) {

                            // If the entry we're looking at doesn't have an

                            // index of -1, and doesn't lead to an empty list,

                            // then it's something we follow!

                            BuildStep bs = new BuildStep(v, BuildStep.FOLLOW);

                            mStepList.add(bs);

                            success = buildList(theList, v.getIndex(), bs);

                        }

                    }

                }

                if (success) {

                    // We're already finished!

                    return true;

                } else {

                    // We failed, and we've exhausted all the paths that we

                    // could take. The only choice is to back ourselves out.

                    if (follow == null)

                        mStepList.add(new BuildStep(null, BuildStep.FAIL));

                    else

                        mStepList.add(new BuildStep(follow.getVertex(),

                                                    BuildStep.BACK));

                    return false;

                }

            }

        }

        catch (Exception e) {}

        // we'll never get here, but you know java...

        return false;

    }

    /**

     * Prints out a string representation of this AdjacencyList.

     *

     * @return String representation

     */

    public String toString() {

        String out = "[\n";

        int i = 0;

        for (List<Vertex> l : mOrigList) {

            out = out + "LinkedList[" + i++ + "]:\n";

            for (Vertex step : l) {

                try {

                    out = out + step.toString();

                    out = out + "\n";

                }

                catch (Exception e) { out = out + "No Such Element\n"; }

            }

        }

        out = out + "]\n";

        return out;

    }

}