/*
 * Copyright (c) 2011, 2020, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.source.util;

import com.sun.source.doctree.*;


A DocTreeVisitor that visits all the child tree nodes.
To visit nodes of a particular type, just override the
corresponding visitXYZ method.
Inside your method, call super.visitXYZ to visit descendant
nodes.
The default implementation of the visitXYZ methods will determine
a result as follows:

If the node being visited has no children, the result will be null. 
If the node being visited has one child, the result will be the result of calling scan on that child. The child may be a simple node or itself a list of nodes. 
 If the node being visited has more than one child, the result will be determined by calling scan each child in turn, and then combining the result of each scan after the first with the cumulative result so far, as determined by the reduce method. Each child may be either a simple node of a list of nodes. The default behavior of the reduce method is such that the result of the visitXYZ method will be the result of the last child scanned. 
Here is an example to count the number of erroneous nodes in a tree:
 class CountErrors extends DocTreeScanner<Integer,Void> { @Override public Integer visitErroneous(ErroneousTree node, Void p) { return 1; } @Override public Integer reduce(Integer r1, Integer r2) { return (r1 == null ? 0 : r1) + (r2 == null ? 0 : r2); } } 
Since:
1.8/**
 * A DocTreeVisitor that visits all the child tree nodes.
 * To visit nodes of a particular type, just override the
 * corresponding visitXYZ method.
 * Inside your method, call super.visitXYZ to visit descendant
 * nodes.
 *
 * <p>The default implementation of the visitXYZ methods will determine
 * a result as follows:
 * <ul>
 * <li>If the node being visited has no children, the result will be {@code null}.
 * <li>If the node being visited has one child, the result will be the
 * result of calling {@code scan} on that child. The child may be a simple node
 * or itself a list of nodes.
 * <li> If the node being visited has more than one child, the result will
 * be determined by calling {@code scan} each child in turn, and then combining the
 * result of each scan after the first with the cumulative result
 * so far, as determined by the {@link #reduce} method. Each child may be either
 * a simple node of a list of nodes. The default behavior of the {@code reduce}
 * method is such that the result of the visitXYZ method will be the result of
 * the last child scanned.
 * </ul>
 *
 * <p>Here is an example to count the number of erroneous nodes in a tree:
 * <pre>
 *   class CountErrors extends DocTreeScanner&lt;Integer,Void&gt; {
 *      {@literal @}Override
 *      public Integer visitErroneous(ErroneousTree node, Void p) {
 *          return 1;
 *      }
 *      {@literal @}Override
 *      public Integer reduce(Integer r1, Integer r2) {
 *          return (r1 == null ? 0 : r1) + (r2 == null ? 0 : r2);
 *      }
 *   }
 * </pre>
 *
 * @since 1.8
 */
public class DocTreeScanner<R,P> implements DocTreeVisitor<R,P> {
    
Constructs a DocTreeScanner. /**
     * Constructs a {@code DocTreeScanner}.
     */
    public DocTreeScanner() {}

    
Scans a single node.
Params:
node – the node to be scanned
p – a parameter value passed to the visit method
Returns:
the result value from the visit method/**
     * Scans a single node.
     * @param node the node to be scanned
     * @param p a parameter value passed to the visit method
     * @return the result value from the visit method
     */
    public R scan(DocTree node, P p) {
        return (node == null) ? null : node.accept(this, p);
    }

    private R scanAndReduce(DocTree node, P p, R r) {
        return reduce(scan(node, p), r);
    }

    
Scans a sequence of nodes.
Params:
nodes – the nodes to be scanned
p – a parameter value to be passed to the visit method for each node
Returns:
the combined return value from the visit methods. The values are combined using the reduce method./**
     * Scans a sequence of nodes.
     * @param nodes the nodes to be scanned
     * @param p a parameter value to be passed to the visit method for each node
     * @return the combined return value from the visit methods.
     *      The values are combined using the {@link #reduce reduce} method.
     */
    public R scan(Iterable<? extends DocTree> nodes, P p) {
        R r = null;
        if (nodes != null) {
            boolean first = true;
            for (DocTree node : nodes) {
                r = (first ? scan(node, p) : scanAndReduce(node, p, r));
                first = false;
            }
        }
        return r;
    }

    private R scanAndReduce(Iterable<? extends DocTree> nodes, P p, R r) {
        return reduce(scan(nodes, p), r);
    }

    
Reduces two results into a combined result.
The default implementation is to return the first parameter.
The general contract of the method is that it may take any action whatsoever.
Params:
r1 – the first of the values to be combined
r2 – the second of the values to be combined
Returns:
the result of combining the two parameters/**
     * Reduces two results into a combined result.
     * The default implementation is to return the first parameter.
     * The general contract of the method is that it may take any action whatsoever.
     * @param r1 the first of the values to be combined
     * @param r2 the second of the values to be combined
     * @return the result of combining the two parameters
     */
    public R reduce(R r1, R r2) {
        return r1;
    }


/* ***************************************************************************
 * Visitor methods
 ****************************************************************************/

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitAttribute(AttributeTree node, P p) {
        return scan(node.getValue(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitAuthor(AuthorTree node, P p) {
        return scan(node.getName(), p);
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitComment(CommentTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitDeprecated(DeprecatedTree node, P p) {
        return scan(node.getBody(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitDocComment(DocCommentTree node, P p) {
        R r = scan(node.getFirstSentence(), p);
        r = scanAndReduce(node.getBody(), p, r);
        r = scanAndReduce(node.getBlockTags(), p, r);
        return r;
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitDocRoot(DocRootTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitDocType(DocTypeTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitEndElement(EndElementTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitEntity(EntityTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitErroneous(ErroneousTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitHidden(HiddenTree node, P p) {
        return scan(node.getBody(), p);
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitIdentifier(IdentifierTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitIndex(IndexTree node, P p) {
        R r = scan(node.getSearchTerm(), p);
        r = scanAndReduce(node.getDescription(), p, r);
        return r;
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitInheritDoc(InheritDocTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitLink(LinkTree node, P p) {
        R r = scan(node.getReference(), p);
        r = scanAndReduce(node.getLabel(), p, r);
        return r;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitLiteral(LiteralTree node, P p) {
        return scan(node.getBody(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitParam(ParamTree node, P p) {
        R r = scan(node.getName(), p);
        r = scanAndReduce(node.getDescription(), p, r);
        return r;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitProvides(ProvidesTree node, P p) {
        R r = scan(node.getServiceType(), p);
        r = scanAndReduce(node.getDescription(), p, r);
        return r;
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitReference(ReferenceTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitReturn(ReturnTree node, P p) {
        return scan(node.getDescription(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitSee(SeeTree node, P p) {
        return scan(node.getReference(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitSerial(SerialTree node, P p) {
        return scan(node.getDescription(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitSerialData(SerialDataTree node, P p) {
        return scan(node.getDescription(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitSerialField(SerialFieldTree node, P p) {
        R r = scan(node.getName(), p);
        r = scanAndReduce(node.getType(), p, r);
        r = scanAndReduce(node.getDescription(), p, r);
        return r;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitSince(SinceTree node, P p) {
        return scan(node.getBody(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitStartElement(StartElementTree node, P p) {
        return scan(node.getAttributes(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning
Since:
10/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     * @since 10
     */
    @Override
    public R visitSummary(SummaryTree node, P p) {
        return scan(node.getSummary(), p);
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning
Since:
12/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     * @since 12
     */
    @Override
    public R visitSystemProperty(SystemPropertyTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitText(TextTree node, P p) {
        return null;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitThrows(ThrowsTree node, P p) {
        R r = scan(node.getExceptionName(), p);
        r = scanAndReduce(node.getDescription(), p, r);
        return r;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitUnknownBlockTag(UnknownBlockTagTree node, P p) {
        return scan(node.getContent(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitUnknownInlineTag(UnknownInlineTagTree node, P p) {
        return scan(node.getContent(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitUses(UsesTree node, P p) {
        R r = scan(node.getServiceType(), p);
        r = scanAndReduce(node.getDescription(), p, r);
        return r;
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitValue(ValueTree node, P p) {
        return scan(node.getReference(), p);
    }

    
{@inheritDoc} This implementation scans the children in left to right order.
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation scans the children in left to right order.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitVersion(VersionTree node, P p) {
        return scan(node.getBody(), p);
    }

    
{@inheritDoc} This implementation returns null. 
Params:
node –  {@inheritDoc}
p –  {@inheritDoc}
Returns:
the result of scanning/**
     * {@inheritDoc} This implementation returns {@code null}.
     *
     * @param node  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of scanning
     */
    @Override
    public R visitOther(DocTree node, P p) {
        return null;
    }

}