001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2025 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.xpath;
021
022import com.puppycrawl.tools.checkstyle.xpath.iterators.DescendantIterator;
023import net.sf.saxon.Configuration;
024import net.sf.saxon.om.AxisInfo;
025import net.sf.saxon.om.GenericTreeInfo;
026import net.sf.saxon.om.NamespaceUri;
027import net.sf.saxon.om.NodeInfo;
028import net.sf.saxon.tree.iter.ArrayIterator;
029import net.sf.saxon.tree.iter.AxisIterator;
030import net.sf.saxon.tree.iter.EmptyIterator;
031import net.sf.saxon.tree.iter.SingleNodeIterator;
032import net.sf.saxon.type.Type;
033
034/**
035 * Represents root node of Xpath-tree.
036 */
037public abstract class AbstractRootNode extends AbstractNode {
038
039    /** Name of the root element. */
040    private static final String ROOT_NAME = "ROOT";
041
042    /** Constant for optimization. */
043    private static final AbstractNode[] EMPTY_ABSTRACT_NODE_ARRAY = new AbstractNode[0];
044
045    /**
046     * Creates a new {@code AbstractRootNode} instance.
047     */
048    protected AbstractRootNode() {
049        super(new GenericTreeInfo(Configuration.newConfiguration()));
050    }
051
052    /**
053     * Compares current object with specified for order.
054     * Throws {@code UnsupportedOperationException} because functionality not required here.
055     *
056     * @param nodeInfo another {@code NodeInfo} object
057     * @return number representing order of current object to specified one
058     */
059    @Override
060    public int compareOrder(NodeInfo nodeInfo) {
061        throw throwUnsupportedOperationException();
062    }
063
064    /**
065     * Returns attribute value. Throws {@code UnsupportedOperationException} because root node
066     * has no attributes.
067     *
068     * @param namespace namespace
069     * @param localPart actual name of the attribute
070     * @return attribute value
071     */
072    @Override
073    public String getAttributeValue(NamespaceUri namespace, String localPart) {
074        throw throwUnsupportedOperationException();
075    }
076
077    /**
078     * Returns local part.
079     *
080     * @return local part
081     */
082    @Override
083    public String getLocalPart() {
084        return ROOT_NAME;
085    }
086
087    /**
088     * Returns type of the node.
089     *
090     * @return node kind
091     */
092    @Override
093    public int getNodeKind() {
094        return Type.DOCUMENT;
095    }
096
097    /**
098     * Returns parent.
099     *
100     * @return parent
101     */
102    @Override
103    public NodeInfo getParent() {
104        return null;
105    }
106
107    /**
108     * Returns root of the tree.
109     *
110     * @return root of the tree
111     */
112    @Override
113    public NodeInfo getRoot() {
114        return this;
115    }
116
117    /**
118     * Determines axis iteration algorithm. Throws {@code UnsupportedOperationException} in case,
119     * when there is no axis iterator for given axisNumber.
120     *
121     * @param axisNumber element from {@code AxisInfo}
122     * @return {@code AxisIterator} object
123     */
124    @Override
125    public AxisIterator iterateAxis(int axisNumber) {
126        return switch (axisNumber) {
127            case AxisInfo.ANCESTOR,
128                 AxisInfo.PARENT,
129                 AxisInfo.FOLLOWING,
130                 AxisInfo.FOLLOWING_SIBLING,
131                 AxisInfo.PRECEDING,
132                 AxisInfo.PRECEDING_SIBLING -> EmptyIterator.ofNodes();
133
134            case AxisInfo.ANCESTOR_OR_SELF,
135                 AxisInfo.SELF -> SingleNodeIterator.makeIterator(this);
136
137            case AxisInfo.CHILD -> {
138                if (hasChildNodes()) {
139                    yield new ArrayIterator.OfNodes<>(
140                            getChildren().toArray(EMPTY_ABSTRACT_NODE_ARRAY));
141                }
142                yield EmptyIterator.ofNodes();
143            }
144
145            case AxisInfo.DESCENDANT -> {
146                if (hasChildNodes()) {
147                    yield new DescendantIterator(this, DescendantIterator.StartWith.CHILDREN);
148                }
149                yield EmptyIterator.ofNodes();
150            }
151
152            case AxisInfo.DESCENDANT_OR_SELF ->
153                new DescendantIterator(this, DescendantIterator.StartWith.CURRENT_NODE);
154
155            default -> throw throwUnsupportedOperationException();
156        };
157    }
158
159    /**
160     * Getter method for node depth.
161     *
162     * @return always {@code 0}
163     */
164    @Override
165    public int getDepth() {
166        return 0;
167    }
168
169    /**
170     * Returns UnsupportedOperationException exception.
171     *
172     * @return UnsupportedOperationException exception
173     */
174    private static UnsupportedOperationException throwUnsupportedOperationException() {
175        return new UnsupportedOperationException("Operation is not supported");
176    }
177
178}