/* $Id: ObjectParamRule.java,v 1.10 2004/05/10 06:52:50 skitching Exp $
 *
 * Copyright 2002-2004 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.commons.digester;

import org.xml.sax.Attributes;

/**
 * <p>Rule implementation that saves a parameter for use by a surrounding
 * <code>CallMethodRule<code>.</p>
 *
 * <p>This parameter may be:
 * <ul>
 * <li>an arbitrary Object defined programatically, assigned when the element pattern associated with the Rule is matched
 * See {@link #ObjectParamRule(int paramIndex, Object param)}
 * <li>an arbitrary Object defined programatically, assigned if the element pattern AND specified attribute name are matched
 * See {@link #ObjectParamRule(int paramIndex, String attributeName, Object param)}
 * </ul>
 * </p>
 *
 * @since 1.4
 */

public class ObjectParamRule extends Rule {
    // ----------------------------------------------------------- Constructors
    /**
     * Construct a "call parameter" rule that will save the given Object as
     * the parameter value.
     *
     * @param paramIndex The zero-relative parameter number
     * @param param the parameter to pass along
     */
    public ObjectParamRule(int paramIndex, Object param) {
        this(paramIndex, null, param);
    }


    /**
     * Construct a "call parameter" rule that will save the given Object as
     * the parameter value, provided that the specified attribute exists.
     *
     * @param paramIndex The zero-relative parameter number
     * @param attributeName The name of the attribute to match
     * @param param the parameter to pass along
     */
    public ObjectParamRule(int paramIndex, String attributeName, Object param) {
        this.paramIndex = paramIndex;
        this.attributeName = attributeName;
        this.param = param;
    }


    // ----------------------------------------------------- Instance Variables

    /**
     * The attribute which we are attempting to match
     */
    protected String attributeName = null;

    /**
     * The zero-relative index of the parameter we are saving.
     */
    protected int paramIndex = 0;

    /**
     * The parameter we wish to pass to the method call
     */
    protected Object param = null;


    // --------------------------------------------------------- Public Methods

    /**
     * Process the start of this element.
     *
     * @param attributes The attribute list for this element
     */
    public void begin(String namespace, String name,
                      Attributes attributes) throws Exception {
        Object anAttribute = null;
        Object parameters[] = (Object[]) digester.peekParams();

        if (attributeName != null) {
            anAttribute = attributes.getValue(attributeName);
            if(anAttribute != null) {
                parameters[paramIndex] = param;
            }
            // note -- if attributeName != null and anAttribute == null, this rule
            // will pass null as its parameter!
        }else{
            parameters[paramIndex] = param;
        }
    }

    /**
     * Render a printable version of this Rule.
     */
    public String toString() {
        StringBuffer sb = new StringBuffer("ObjectParamRule[");
        sb.append("paramIndex=");
        sb.append(paramIndex);
        sb.append(", attributeName=");
        sb.append(attributeName);
        sb.append(", param=");
        sb.append(param);
        sb.append("]");
        return (sb.toString());
    }
}