/*
 * $Id: EmptyTag.java 54929 2004-10-16 16:38:42Z germuska $ 
 *
 * Copyright 1999-2004 The Apache Software Foundation.
 *
 * Licensed 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.struts.taglib.logic;

import java.util.Collection;
import java.util.Map;
import java.lang.reflect.Array;

import javax.servlet.jsp.JspException;

import org.apache.struts.taglib.TagUtils;

/**
 * Evalute the nested body content of this tag if the specified value
 * is empty for this request.
 *
 * @version $Rev: 54929 $ $Date: 2004-10-16 17:38:42 +0100 (Sat, 16 Oct 2004) $
 * @since Struts 1.1
 */
public class EmptyTag extends ConditionalTagBase {


    // ------------------------------------------------------ Protected Methods


    /**
     * Evaluate the condition that is being tested by this particular tag,
     * and return <code>true</code> if the nested body content of this tag
     * should be evaluated, or <code>false</code> if it should be skipped.
     * This method must be implemented by concrete subclasses.
     *
     * @exception JspException if a JSP exception occurs
     */
    protected boolean condition() throws JspException {

        return (condition(true));

    }


    /**
     * Evaluate the condition that is being tested by this particular tag,
     * and return <code>true</code> if the nested body content of this tag
     * should be evaluated, or <code>false</code> if it should be skipped.
     * This method must be implemented by concrete subclasses.
     *
     * @param desired Desired outcome for a true result
     *
     * @exception JspException if a JSP exception occurs
     */
    protected boolean condition(boolean desired) throws JspException {
        if (this.name == null) {
            JspException e =
                    new JspException(messages.getMessage("empty.noNameAttribute"));
            TagUtils.getInstance().saveException(pageContext, e);
            throw e;
        }

        Object value = null;
        if (this.property == null) {
            value = TagUtils.getInstance().lookup(pageContext, name, scope);
        } else {
            value = TagUtils.getInstance().lookup(pageContext, name, property, scope);
        }

        boolean empty = true;

        if (value == null) {
            empty = true;

        } else if (value instanceof String) {
            String strValue = (String) value;
            empty = (strValue.length() < 1);

        } else if (value instanceof Collection) {
            Collection collValue = (Collection) value;
            empty = collValue.isEmpty();

        } else if (value instanceof Map) {
            Map mapValue = (Map) value;
            empty = mapValue.isEmpty();

        } else if (value.getClass().isArray()) {
            empty = Array.getLength(value) == 0;

        } else {
            empty = false;
        }

        return (empty == desired);
    }

}