/*
 * 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.behavior;

import java.io.Serializable;

import org.apache.wicket.AttributeModifier;
import org.apache.wicket.model.IModel;
import org.apache.wicket.util.string.Strings;

/**
 * AttributeModifier that appends the given value, rather than replace it. This is especially useful
 * for adding CSS classes to markup elements, or adding JavaScript snippets to existing element
 * handlers.
 * 
 * <pre>
 *     &lt;a href=&quot;#&quot; wicket:id=&quot;foo&quot; class=&quot;link&quot; onmouseover=&quot;doSomething()&quot;&gt;
 * </pre>
 * 
 * can be modified with these AttributeAppenders:
 * 
 * <pre>
 * link.add(new AttributeAppender(&quot;class&quot;, Model.of(&quot;hot&quot;)));
 * link.add(new AttributeAppender(&quot;onmouseover&quot;, Model.of(&quot;foo();return false;&quot;)).setSeparator(&quot;;&quot;));
 * </pre>
 * 
 * this will result in the following markup:
 * 
 * <pre>
 *     &lt;a href=&quot;#&quot; wicket:id=&quot;foo&quot; class=&quot;link hot&quot; onmouseover=&quot;doSomething();foo();return false;&quot;&gt;
 * </pre>
 * 
 * @see AttributeModifier#append(String, IModel)
 * @see AttributeModifier#append(String, Serializable)
 * @see AttributeModifier#prepend(String, IModel)
 * @see AttributeModifier#prepend(String, Serializable)
 * 
 * @author Martijn Dashorst
 */
public class AttributeAppender extends AttributeModifier
{
        private static final long serialVersionUID = 1L;

        /**
         * Separator between the current value and the concatenated value, typically a space ' ' or
         * colon ';'.
         */
        private String separator;

        /**
         * Creates an attribute modifier that concatenates the {@code replaceModel} to the attribute's
         * current value, optionally separated by the {@link #getSeparator() separator}.
         * 
         * @param attribute
         * @param replaceModel
         */
        public AttributeAppender(String attribute, IModel<?> replaceModel)
        {
                super(attribute, replaceModel);
        }

        /**
         * Creates an attribute modifier that appends the {@code value} to the attribute's current
         * value, optionally separated by the {@link #getSeparator() separator}.
         * 
         * @param attribute
         * @param value
         */
        public AttributeAppender(String attribute, Serializable value)
        {
                super(attribute, value);
        }

        /**
         * Creates an AttributeModifier that appends the value to the current value of the
         * attribute, and will add the attribute when it is not there already.
         *
         * @param attribute
         *            the attribute to append the appendModels value to
         * @param value
         *            the value to append
         * @param separator
         *            the separator string, comes between the original value and the append value
         */
        public AttributeAppender(String attribute, Serializable value, String separator)
        {
                super(attribute, value);
                setSeparator(separator);
        }

        /**
         * Creates an AttributeModifier that appends the appendModel's value to the current value of the
         * attribute, and will add the attribute when it is not there already.
         * 
         * @param attribute
         *            the attribute to append the appendModels value to
         * @param appendModel
         *            the model supplying the value to append
         * @param separator
         *            the separator string, comes between the original value and the append value
         */
        public AttributeAppender(String attribute, IModel<?> appendModel, String separator)
        {
                super(attribute, appendModel);
                setSeparator(separator);
        }

        /**
         * Gets the separator used by attribute appenders and prependers.
         * 
         * @return the separator used by attribute appenders and prependers.
         */
        public String getSeparator()
        {
                return separator;
        }

        /**
         * Sets the separator used by attribute appenders and prependers.
         * 
         * @param separator
         *            a space, semicolon or other character used to separate the current value and the
         *            appended/prepended value.
         * @return this
         */
        public AttributeAppender setSeparator(String separator)
        {
                this.separator = separator;
                return this;
        }

        @Override
        protected Serializable newValue(String currentValue, String appendValue)
        {
                // Short circuit when one of the values is empty: return the other value.
                if (Strings.isEmpty(currentValue))
                {
                        return appendValue;
                }
                else if (Strings.isEmpty(appendValue))
                {
                        return currentValue;
                }
                StringBuilder sb = new StringBuilder(currentValue);
                sb.append((getSeparator() == null ? "" : getSeparator()));
                sb.append(appendValue);
                return sb.toString();
        }

        @Override
        public String toString()
        {
                String attributeModifier = super.toString();
                attributeModifier = attributeModifier.substring(0, attributeModifier.length() - 2) +
                        ", separator=" + separator + "]";
                return attributeModifier;
        }
}