001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.convert;
018
019import java.lang.reflect.Array;
020import java.nio.file.Path;
021import java.util.ArrayList;
022import java.util.Collection;
023import java.util.Iterator;
024import java.util.LinkedList;
025import java.util.Set;
026
027/**
028 * <p>
029 * An abstract base class for concrete {@code ListDelimiterHandler} implementations.
030 * </p>
031 * <p>
032 * This base class provides a fully functional implementation for parsing a value object which can deal with different
033 * cases like collections, arrays, iterators, etc. This logic is typically needed by every concrete subclass. Other
034 * methods are partly implemented handling special corner cases like <b>null</b> values; concrete subclasses do not have
035 * do implement the corresponding checks.
036 * </p>
037 *
038 * @since 2.0
039 */
040public abstract class AbstractListDelimiterHandler implements ListDelimiterHandler {
041
042    static Collection<?> flatten(final ListDelimiterHandler handler, final Object value, final int limit, final Set<Object> dejaVu) {
043        dejaVu.add(value);
044        if (value instanceof String) {
045            return handler.split((String) value, true);
046        }
047        final Collection<Object> result = new LinkedList<>();
048        if (value instanceof Path) {
049            // Don't handle as an Iterable.
050            result.add(value);
051        } else if (value instanceof Iterable) {
052            flattenIterator(handler, result, ((Iterable<?>) value).iterator(), limit, dejaVu);
053        } else if (value instanceof Iterator) {
054            flattenIterator(handler, result, (Iterator<?>) value, limit, dejaVu);
055        } else if (value != null) {
056            if (value.getClass().isArray()) {
057                for (int len = Array.getLength(value), idx = 0, size = 0; idx < len && size < limit; idx++, size = result.size()) {
058                    result.addAll(handler.flatten(Array.get(value, idx), limit - size));
059                }
060            } else {
061                result.add(value);
062            }
063        }
064        return result;
065    }
066
067    /**
068     * Flattens the given iterator. For each element in the iteration {@code flatten()} is called recursively.
069     *
070     * @param handler the working handler
071     * @param target the target collection
072     * @param iterator the iterator to process
073     * @param limit a limit for the number of elements to extract
074     * @param dejaVue Previously visited objects.
075     */
076    static void flattenIterator(final ListDelimiterHandler handler, final Collection<Object> target, final Iterator<?> iterator, final int limit,
077            final Set<Object> dejaVue) {
078        int size = target.size();
079        while (size < limit && iterator.hasNext()) {
080            final Object next = iterator.next();
081            if (!dejaVue.contains(next)) {
082                target.addAll(flatten(handler, next, limit - size, dejaVue));
083                size = target.size();
084            }
085        }
086    }
087
088    /**
089     * {@inheritDoc} This implementation checks whether the object to be escaped is a string. If yes, it delegates to
090     * {@link #escapeString(String)}, otherwise no escaping is performed. Eventually, the passed in transformer is invoked
091     * so that additional encoding can be performed.
092     */
093    @Override
094    public Object escape(final Object value, final ValueTransformer transformer) {
095        return transformer.transformValue(value instanceof String ? escapeString((String) value) : value);
096    }
097
098    /**
099     * Escapes the specified string. This method is called by {@code escape()} if the passed in object is a string. Concrete
100     * subclasses have to implement their specific escaping logic here, so that the list delimiters they support are
101     * properly escaped.
102     *
103     * @param s the string to be escaped (not <b>null</b>)
104     * @return the escaped string
105     */
106    protected abstract String escapeString(String s);
107
108    /**
109     * Performs the actual work as advertised by the {@code parse()} method. This method delegates to
110     * {@link #flatten(Object, int)} without specifying a limit.
111     *
112     * @param value the value to be processed
113     * @return a &quot;flat&quot; collection containing all primitive values of the passed in object
114     */
115    private Collection<?> flatten(final Object value) {
116        return flatten(value, Integer.MAX_VALUE);
117    }
118
119    /**
120     * {@inheritDoc} Depending on the type of the passed in object the following things happen:
121     * <ul>
122     * <li>Strings are checked for delimiter characters and split if necessary. This is done by calling the {@code split()}
123     * method.</li>
124     * <li>For objects implementing the {@code Iterable} interface, the corresponding {@code Iterator} is obtained, and
125     * contained elements are added to the resulting iteration.</li>
126     * <li>Arrays are treated as {@code Iterable} objects.</li>
127     * <li>All other types are directly inserted.</li>
128     * <li>Recursive combinations are supported, e.g. a collection containing an array that contains strings: The resulting
129     * collection will only contain primitive objects.</li>
130     * </ul>
131     */
132    @Override
133    public Iterable<?> parse(final Object value) {
134        return flatten(value);
135    }
136
137    /**
138     * {@inheritDoc} This implementation handles the case that the passed in string is <b>null</b>. In this case, an empty
139     * collection is returned. Otherwise, this method delegates to {@link #splitString(String, boolean)}.
140     */
141    @Override
142    public Collection<String> split(final String s, final boolean trim) {
143        return s == null ? new ArrayList<>(0) : splitString(s, trim);
144    }
145
146    /**
147     * Actually splits the passed in string which is guaranteed to be not <b>null</b>. This method is called by the base
148     * implementation of the {@code split()} method. Here the actual splitting logic has to be implemented.
149     *
150     * @param s the string to be split (not <b>null</b>)
151     * @param trim a flag whether the single components have to be trimmed
152     * @return a collection with the extracted components of the passed in string
153     */
154    protected abstract Collection<String> splitString(String s, boolean trim);
155}