/*
 * 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.jelly.tags.xml;

import java.util.Iterator;
import java.util.List;
import java.util.Collections;

import org.apache.commons.jelly.JellyTagException;
import org.apache.commons.jelly.XMLOutput;
import org.apache.commons.jelly.xpath.XPathComparator;
import org.apache.commons.jelly.xpath.XPathSource;
import org.apache.commons.jelly.xpath.XPathTagSupport;

import org.jaxen.XPath;
import org.jaxen.JaxenException;

/** A tag which performs an iteration over the results of an XPath expression
  *
  * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
  * @version $Revision: 1.5 $
  */
public class ForEachTag extends XPathTagSupport implements XPathSource {

    /** Holds the XPath selector. */
    private XPath select;

    /** Xpath comparator for sorting */
    private XPathComparator xpCmp = null;

    /** If specified then the current item iterated through will be defined
      * as the given variable name. */
    private String var;

    /** The current iteration value */
    private Object iterationValue;


    public ForEachTag() {
    }

    // Tag interface
    //-------------------------------------------------------------------------
    public void doTag(XMLOutput output) throws JellyTagException {
        if (select != null) {
            List nodes = null;
            try {
                nodes = select.selectNodes( getXPathContext() );
            }
            catch (JaxenException e) {
                throw new JellyTagException(e);
            }

            // sort the list if xpCmp is set.
            if (xpCmp != null && (xpCmp.getXpath() != null)) {
                Collections.sort(nodes, xpCmp);
            }

            Iterator iter = nodes.iterator();
            while (iter.hasNext()) {
                iterationValue = iter.next();
                if (var != null) {
                    context.setVariable(var, iterationValue);
                }
                invokeBody(output);
            }
        }
    }

    // XPathSource interface
    //-------------------------------------------------------------------------

    /**
     * @return the current XPath iteration value
     *  so that any other XPath aware child tags to use
     */
    public Object getXPathSource() {
        return iterationValue;
    }

    // Properties
    //-------------------------------------------------------------------------
    /** Sets the XPath selection expression
      */
    public void setSelect(XPath select) {
        this.select = select;
    }

    /** Sets the variable name to export for the item being iterated over
     */
    public void setVar(String var) {
        this.var = var;
    }

    /** Sets the xpath expression to use to sort selected nodes.
     */
    public void setSort(XPath sortXPath) throws JaxenException {
        if (xpCmp == null) xpCmp = new XPathComparator();
        xpCmp.setXpath(sortXPath);
    }

    /**
     * Set whether to sort ascending or descending.
     */
    public void setDescending(boolean descending) {
        if (xpCmp == null) xpCmp = new XPathComparator();
        xpCmp.setDescending(descending);
    }

    /*
     * Override superclass so method can be access by IfTag
     */
    protected Object getXPathContext() {
        return super.getXPathContext();
    }

}