/*
 * 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.extensions.ajax.markup.html.autocomplete;

import org.apache.wicket.request.Response;
import org.apache.wicket.util.string.Strings;

/**
 * A renderer that abstracts auto-assist specific details and allows subclasses to only render the
 * visual part of the assist instead of having to also render the necessary auto-assist javascript
 * hooks.
 * 
 * @param <T>
 * 
 * @since 1.2
 * 
 * @author Igor Vaynberg (ivaynberg)
 */
public abstract class AbstractAutoCompleteRenderer<T> implements IAutoCompleteRenderer<T>
{
        private static final long serialVersionUID = 1L;

        @Override
        public void render(final T object, final Response response, final String criteria)
        {
                String textValue = getTextValue(object);
                if (textValue == null)
                {
                        throw new IllegalStateException(
                                "A call to textValue(Object) returned an illegal value: null for object: " +
                                        object.toString());
                }
                textValue = Strings.escapeMarkup(textValue).toString();

                response.write("<li textvalue=\"" + textValue + "\"");
                final CharSequence handler = getOnSelectJavaScriptExpression(object);
                if (handler != null)
                {
                        response.write(" onselect=\"" + handler + '"');
                }
                response.write(">");
                renderChoice(object, response, criteria);
                response.write("</li>");
        }

        @Override
        public void renderHeader(final Response response)
        {
                response.write("<ul>");
        }

        @Override
        public void renderFooter(final Response response, int count)
        {
                response.write("</ul>");
        }

        /**
         * Render the visual portion of the assist. Usually the html representing the assist choice
         * object is written out to the response use {@link Response#write(CharSequence)}
         * 
         * @param object
         *            current assist choice
         * @param response
         * @param criteria
         */
        protected abstract void renderChoice(T object, Response response, String criteria);

        /**
         * Retrieves the text value that will be set on the textbox if this assist is selected
         * 
         * @param object
         *            assist choice object
         * @return the text value that will be set on the textbox if this assist is selected
         */
        protected abstract String getTextValue(T object);

        /**
         * Allows the execution of a custom javascript expression when an item is selected in the
         * autocompleter popup (either by clicking on it or hitting enter on the current selection).
         * <p/>
         * The javascript to execute must be a javascript expression that will be processed using
         * javascript's eval(). The function should return the textvalue to copy it into the
         * corresponding form input field (the default behavior).
         * 
         * the current text value will be in variable 'input'.
         * 
         * If the function returns <code>null</code> the chosen text value will be ignored.
         * <p/>
         * example 1:
         * 
         * <pre>
         * protected CharSequence getOnSelectJavaScript(Address address)
         * {
         *      final StringBuilder js = new StringBuilder();
         *      js.append(&quot;Wicket.DOM.get('street').value ='&quot; + address.getStreet() + &quot;';&quot;);
         *      js.append(&quot;Wicket.DOM.get('zipcode').value ='&quot; + address.getZipCode() + &quot;';&quot;);
         *      js.append(&quot;Wicket.DOM.get('city').value ='&quot; + address.getCity() + &quot;';&quot;);
         *      js.append(&quot;arguments[0]&quot;); // &lt;-- do not use return statement here!
         *      return js.toString();
         * }
         * </pre>
         * 
         * example 2:
         * 
         * <pre>
         * protected CharSequence getOnSelectJavaScript(Currency currency)
         * {
         *      final StringBuilder js = new StringBuilder();
         *      js.append(&quot;val rate = ajaxGetExchangeRateForCurrency(currencySymbol);&quot;);
         *      js.append(&quot;if(rate == null) alert('exchange rate service currently not available');&quot;);
         *      js.append(&quot;rate&quot;);
         *      return js.toString();
         * }
         * </pre>
         * 
         * Then the autocompleter popup will be closed.
         * 
         * @param item
         *            the autocomplete item to get a custom javascript expression for
         * @return javascript to execute on selection or <code>null</code> if default behavior is
         *         intented
         */
        protected CharSequence getOnSelectJavaScriptExpression(final T item)
        {
                return null;
        }
}