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Tools to assist in the reading of configuration/preferences files in various formats
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.configuration2.convert;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;

/**
 * 
 * An abstract base class for concrete {@code ListDelimiterHandler}
 * implementations.
 * 
 * 
 * This base class provides a fully functional implementation for parsing a
 * value object which can deal with different cases like collections, arrays,
 * iterators, etc. This logic is typically needed by every concrete subclass.
 * Other methods are partly implemented handling special corner cases like
 * null values; concrete subclasses do not have do implement the
 * corresponding checks.
 * 
 *
 * @since 2.0
 */
public abstract class AbstractListDelimiterHandler implements
        ListDelimiterHandler
{
    /**
     * {@inheritDoc} Depending on the type of the passed in object the following
     * things happen:
     * 
     * Strings are checked for delimiter characters and split if necessary.
     * This is done by calling the {@code split()} method.
     * For objects implementing the {@code Iterable} interface, the
     * corresponding {@code Iterator} is obtained, and contained elements are
     * added to the resulting iteration.
     * Arrays are treated as {@code Iterable} objects.
     * All other types are directly inserted.
     * Recursive combinations are supported, e.g. a collection containing an
     * array that contains strings: The resulting collection will only contain
     * primitive objects.
     * 
     */
    @Override
    public Iterable parse(final Object value)
    {
        return flatten(value);
    }

    /**
     * {@inheritDoc} This implementation handles the case that the passed in
     * string is null. In this case, an empty collection is returned.
     * Otherwise, this method delegates to {@link #splitString(String, boolean)}.
     */
    @Override
    public Collection split(final String s, final boolean trim)
    {
        if (s == null)
        {
            return new ArrayList<>(0);
        }
        return splitString(s, trim);
    }

    /**
     * {@inheritDoc} This implementation checks whether the object to be escaped
     * is a string. If yes, it delegates to {@link #escapeString(String)},
     * otherwise no escaping is performed. Eventually, the passed in transformer
     * is invoked so that additional encoding can be performed.
     */
    @Override
    public Object escape(final Object value, final ValueTransformer transformer)
    {
        final Object escValue =
                (value instanceof String) ? escapeString((String) value)
                        : value;
        return transformer.transformValue(escValue);
    }

    /**
     * Actually splits the passed in string which is guaranteed to be not
     * null. This method is called by the base implementation of the
     * {@code split()} method. Here the actual splitting logic has to be
     * implemented.
     *
     * @param s the string to be split (not null)
     * @param trim a flag whether the single components have to be trimmed
     * @return a collection with the extracted components of the passed in
     *         string
     */
    protected abstract Collection splitString(String s, boolean trim);

    /**
     * Escapes the specified string. This method is called by {@code escape()}
     * if the passed in object is a string. Concrete subclasses have to
     * implement their specific escaping logic here, so that the list delimiters
     * they support are properly escaped.
     *
     * @param s the string to be escaped (not null)
     * @return the escaped string
     */
    protected abstract String escapeString(String s);

    /**
     * Extracts all values contained in the specified object up to the given
     * limit. The passed in object is evaluated (if necessary in a recursive
     * way). If it is a complex object (e.g. a collection or an array), all its
     * elements are processed recursively and added to a target collection. The
     * process stops if the limit is reached, but depending on the input object,
     * it might be exceeded. (The limit is just an indicator to stop the process
     * to avoid unnecessary work if the caller is only interested in a few
     * values.)
     *
     * @param value the value to be processed
     * @param limit the limit for aborting the processing
     * @return a "flat" collection containing all primitive values of
     *         the passed in object
     */
    Collection flatten(final Object value, final int limit)
    {
        if (value instanceof String)
        {
            return split((String) value, true);
        }

        final Collection