/*
 * 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.
 */
/*
 * $Id$
 */
package org.apache.xalan.lib;

import java.util.HashMap;
import java.util.Map;

import org.apache.xml.utils.DOMHelper;
import org.apache.xpath.NodeSet;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * This class contains EXSLT set extension functions.
 * It is accessed by specifying a namespace URI as follows:
 * <pre>
 *    xmlns:set="http://exslt.org/sets"
 * </pre>
 * 
 * The documentation for each function has been copied from the relevant
 * EXSLT Implementer page. 
 * 
 * @see <a href="http://www.exslt.org/">EXSLT</a>
 * @xsl.usage general
 */
public class ExsltSets extends ExsltBase
{   
  /**
   * The set:leading function returns the nodes in the node set passed as the first argument that
   * precede, in document order, the first node in the node set passed as the second argument. If
   * the first node in the second node set is not contained in the first node set, then an empty
   * node set is returned. If the second node set is empty, then the first node set is returned.
   * 
   * @param nl1 NodeList for first node-set.
   * @param nl2 NodeList for second node-set.
   * @return a NodeList containing the nodes in nl1 that precede in document order the first
   * node in nl2; an empty node-set if the first node in nl2 is not in nl1; all of nl1 if nl2
   * is empty.
   * 
   * @see <a href="http://www.exslt.org/">EXSLT</a>
   */
  public static NodeList leading (NodeList nl1, NodeList nl2)
  {
    if (nl2.getLength() == 0)
      return nl1;
      
    NodeSet ns1 = new NodeSet(nl1);
    NodeSet leadNodes = new NodeSet();
    Node endNode = nl2.item(0);
    if (!ns1.contains(endNode))
      return leadNodes; // empty NodeSet
      
    for (int i = 0; i < nl1.getLength(); i++)
    {
      Node testNode = nl1.item(i);
      if (DOMHelper.isNodeAfter(testNode, endNode) 
          && !DOMHelper.isNodeTheSame(testNode, endNode))
        leadNodes.addElement(testNode);
    }
    return leadNodes;
  }
  
  /**
   * The set:trailing function returns the nodes in the node set passed as the first argument that 
   * follow, in document order, the first node in the node set passed as the second argument. If 
   * the first node in the second node set is not contained in the first node set, then an empty 
   * node set is returned. If the second node set is empty, then the first node set is returned. 
   * 
   * @param nl1 NodeList for first node-set.
   * @param nl2 NodeList for second node-set.
   * @return a NodeList containing the nodes in nl1 that follow in document order the first
   * node in nl2; an empty node-set if the first node in nl2 is not in nl1; all of nl1 if nl2
   * is empty.
   * 
   * @see <a href="http://www.exslt.org/">EXSLT</a>
   */
  public static NodeList trailing (NodeList nl1, NodeList nl2)
  {
    if (nl2.getLength() == 0)
      return nl1;
      
    NodeSet ns1 = new NodeSet(nl1);
    NodeSet trailNodes = new NodeSet();
    Node startNode = nl2.item(0);
    if (!ns1.contains(startNode))
      return trailNodes; // empty NodeSet
      
    for (int i = 0; i < nl1.getLength(); i++)
    {
      Node testNode = nl1.item(i);
      if (DOMHelper.isNodeAfter(startNode, testNode) 
          && !DOMHelper.isNodeTheSame(startNode, testNode))
        trailNodes.addElement(testNode);          
    }
    return trailNodes;
  }
  
  /**
   * The set:intersection function returns a node set comprising the nodes that are within 
   * both the node sets passed as arguments to it.
   * 
   * @param nl1 NodeList for first node-set.
   * @param nl2 NodeList for second node-set.
   * @return a NodeList containing the nodes in nl1 that are also
   * in nl2.
   * 
   * @see <a href="http://www.exslt.org/">EXSLT</a>
   */
  public static NodeList intersection(NodeList nl1, NodeList nl2)
  {
    NodeSet ns1 = new NodeSet(nl1);
    NodeSet ns2 = new NodeSet(nl2);
    NodeSet inter = new NodeSet();

    inter.setShouldCacheNodes(true);

    for (int i = 0; i < ns1.getLength(); i++)
    {
      Node n = ns1.elementAt(i);

      if (ns2.contains(n))
        inter.addElement(n);
    }

    return inter;
  }
  
  /**
   * The set:difference function returns the difference between two node sets - those nodes that 
   * are in the node set passed as the first argument that are not in the node set passed as the 
   * second argument.
   * 
   * @param nl1 NodeList for first node-set.
   * @param nl2 NodeList for second node-set.
   * @return a NodeList containing the nodes in nl1 that are not in nl2.
   * 
   * @see <a href="http://www.exslt.org/">EXSLT</a>
   */
  public static NodeList difference(NodeList nl1, NodeList nl2)
  {
    NodeSet ns1 = new NodeSet(nl1);
    NodeSet ns2 = new NodeSet(nl2);

    NodeSet diff = new NodeSet();

    diff.setShouldCacheNodes(true);

    for (int i = 0; i < ns1.getLength(); i++)
    {
      Node n = ns1.elementAt(i);

      if (!ns2.contains(n))
        diff.addElement(n);
    }

    return diff;
  }
  
  /**
   * The set:distinct function returns a subset of the nodes contained in the node-set NS passed 
   * as the first argument. Specifically, it selects a node N if there is no node in NS that has 
   * the same string value as N, and that precedes N in document order. 
   * 
   * @param nl NodeList for the node-set.
   * @return a NodeList with nodes from nl containing distinct string values.
   * In other words, if more than one node in nl contains the same string value,
   * only include the first such node found.
   * 
   * @see <a href="http://www.exslt.org/">EXSLT</a>
   */
  public static NodeList distinct(NodeList nl)
  {
    NodeSet dist = new NodeSet();
    dist.setShouldCacheNodes(true);

    Map stringTable = new HashMap();
    
    for (int i = 0; i < nl.getLength(); i++)
    {
      Node currNode = nl.item(i);
      String key = toString(currNode);
      
      if (key == null)
        dist.addElement(currNode);
      else if (!stringTable.containsKey(key))
      {
        stringTable.put(key, currNode);
        dist.addElement(currNode);      	
      }
    }

    return dist;
  }
  
  /**
   * The set:has-same-node function returns true if the node set passed as the first argument shares 
   * any nodes with the node set passed as the second argument. If there are no nodes that are in both
   * node sets, then it returns false. 
   * 
   * The Xalan extensions MethodResolver converts 'has-same-node' to 'hasSameNode'.
   * 
   * Note: Not to be confused with hasSameNodes in the Xalan namespace, which returns true if
   * the two node sets contain the exactly the same nodes (perhaps in a different order), 
   * otherwise false.
   * 
   * @see <a href="http://www.exslt.org/">EXSLT</a>
   */
  public static boolean hasSameNode(NodeList nl1, NodeList nl2)
  {
    
    NodeSet ns1 = new NodeSet(nl1);
    NodeSet ns2 = new NodeSet(nl2);

    for (int i = 0; i < ns1.getLength(); i++)
    {
      if (ns2.contains(ns1.elementAt(i)))
        return true;
    }
    return false;
  }
  
}
