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Wicket is a Java web application framework that takes simplicity, separation of concerns and ease of development to a whole new level. Wicket pages can be mocked up, previewed and later revised using standard WYSIWYG HTML design tools. Dynamic content processing and form handling is all handled in Java code using a first-class component model backed by POJO data beans that can easily be persisted using your favorite technology.

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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.wicket;

import java.io.Serializable;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.regex.Pattern;

import org.apache.wicket.behavior.AttributeAppender;
import org.apache.wicket.util.string.Strings;

/**
 * An AttributeModifier specialized in managing the CSS style
 * attribute
 */
public abstract class StyleAttributeModifier extends AttributeAppender
{
	private static final Pattern STYLES_SPLITTER = Pattern.compile("\\s*;\\s*");
	private static final Pattern KEY_VALUE_SPLITTER = Pattern.compile("\\s*:\\s*");

	/**
	 * Constructor.
	 */
	public StyleAttributeModifier()
	{
		super("style", null, ";");
	}

	@Override
	protected Serializable newValue(String currentValue, String appendValue)
	{
		String[] styles;
		if (Strings.isEmpty(currentValue))
		{
			styles = new String[0];
		}
		else
		{
			styles = STYLES_SPLITTER.split(currentValue.trim());
		}
		Map oldStyles = new LinkedHashMap<>();
		for (String style : styles)
		{
			String[] keyValue = KEY_VALUE_SPLITTER.split(style, 2);
			oldStyles.put(keyValue[0], keyValue[1]);
		}

		Map newStyles = update(oldStyles);

		String separator = getSeparator();
		StringBuilder result = new StringBuilder();
		for (Map.Entry entry : newStyles.entrySet())
		{
			result
				.append(entry.getKey())
				.append(':')
				.append(entry.getValue())
				.append(separator);
		}
		return result.length() > 0 ? result.toString() : VALUELESS_ATTRIBUTE_REMOVE;
	}

	/**
	 * Callback to update the CSS class values for a tag.
	 *
	 * @param oldStyles
	 *          A map with the old style key/values
	 * @return A map with the new style key/values
	 */
	protected abstract Map update(Map oldStyles);
}