/*
 * Expr.java
 * Copyright (C) 2004 The Free Software Foundation
 * 
 * This file is part of GNU JAXP, a library.
 *
 * GNU JAXP is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * GNU JAXP is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Linking this library statically or dynamically with other modules is
 * making a combined work based on this library.  Thus, the terms and
 * conditions of the GNU General Public License cover the whole
 * combination.
 *
 * As a special exception, the copyright holders of this library give you
 * permission to link this library with independent modules to produce an
 * executable, regardless of the license terms of these independent
 * modules, and to copy and distribute the resulting executable under
 * terms of your choice, provided that you also meet, for each linked
 * independent module, the terms and conditions of the license of that
 * module.  An independent module is a module which is not derived from
 * or based on this library.  If you modify this library, you may extend
 * this exception to your version of the library, but you are not
 * obliged to do so.  If you do not wish to do so, delete this
 * exception statement from your version. 
 */

package gnu.xml.xpath;

import java.io.IOException;
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Set;
import java.util.StringTokenizer;
import javax.xml.namespace.QName;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * An XPath expression.
 * This can be evaluated in the context of a node to produce a result.
 *
 * @author <a href='mailto:dog@gnu.org'>Chris Burdess</a>
 */
public abstract class Expr
  implements XPathExpression
{

  protected static final Comparator documentOrderComparator =
    new DocumentOrderComparator();

  protected static final DecimalFormat decimalFormat =
    new DecimalFormat("####################################################" +
                      ".####################################################",
                      new DecimalFormatSymbols(Locale.US));

  public Object evaluate(Object item, QName returnType)
    throws XPathExpressionException
  {
    Object ret = null;
    Node context = null;
    if (item instanceof Node)
      {
        context = (Node) item;
        ret = evaluate(context, 1, 1);
        if (XPathConstants.STRING == returnType &&
            !(ret instanceof String))
          {
            ret = _string(context, ret);
          }
        else if (XPathConstants.NUMBER == returnType &&
                 !(ret instanceof Double))
          {
            ret = new Double(_number(context, ret));
          }
        else if (XPathConstants.BOOLEAN == returnType &&
                 !(ret instanceof Boolean))
          {
            ret = _boolean(context, ret) ? Boolean.TRUE : Boolean.FALSE;
          }
        else if (XPathConstants.NODE == returnType)
          {
            if (ret instanceof Collection)
              {
                Collection ns = (Collection) ret;
                switch (ns.size())
                  {
                  case 0:
                    ret = null;
                    break;
                  case 1:
                    ret = (Node) ns.iterator().next();
                    break;
                  default:
                    throw new XPathExpressionException("multiple nodes in node-set");
                  }
              }
            else if (ret != null)
              {
                throw new XPathExpressionException("return value is not a node-set");
              }
          }
        else if (XPathConstants.NODESET == returnType)
          {
            if (ret != null && !(ret instanceof Collection))
              {
                throw new XPathExpressionException("return value is not a node-set");
              }
          }
      }
    return ret;
  }

  public String evaluate(Object item)
    throws XPathExpressionException
  {
    return (String) evaluate(item, XPathConstants.STRING); 
  }

  public Object evaluate(InputSource source, QName returnType)
    throws XPathExpressionException
  {
    try
      {
        DocumentBuilderFactory factory =
          new gnu.xml.dom.JAXPFactory();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(source);
        return evaluate(doc, returnType);
      }
    catch (ParserConfigurationException e)
      {
        throw new XPathExpressionException(e); 
      }
    catch (SAXException e)
      {
        throw new XPathExpressionException(e); 
      }
    catch (IOException e)
      {
        throw new XPathExpressionException(e); 
      }
  }

  public String evaluate(InputSource source)
    throws XPathExpressionException
  {
    return (String) evaluate(source, XPathConstants.STRING);
  }

  public abstract Object evaluate(Node context, int pos, int len);

  public abstract Expr clone(Object context);
  
  /* -- 4.1 Node Set Functions -- */

  /**
   * The id function selects elements by their unique ID.
   * When the argument to id is of type node-set, then the result is
   * the union of the result of applying id to the string-value of each of
   * the nodes in the argument node-set. When the argument to id is of any
   * other type, the argument is converted to a string as if by a call to
   * the string function; the string is split into a whitespace-separated
   * list of tokens (whitespace is any sequence of characters matching the
   * production S); the result is a node-set containing the elements in the
   * same document as the context node that have a unique ID equal to any of
   * the tokens in the list.
   */
  public static Collection _id(Node context, Object object)
  {
    Set ret = new HashSet();
    if (object instanceof Collection)
      {
        Collection nodeSet = (Collection) object;
        for (Iterator i = nodeSet.iterator(); i.hasNext(); )
          {
            String string = stringValue((Node) i.next());
            ret.addAll(_id (context, string));
          }
      }
    else
      {
        Document doc = (context instanceof Document) ? (Document) context :
          context.getOwnerDocument();
        String string = _string(context, object);
        StringTokenizer st = new StringTokenizer(string, " \t\r\n");
        while (st.hasMoreTokens())
          {
            Node element = doc.getElementById(st.nextToken());
            if (element != null)
              {
                ret.add(element);
              }
          }
      }
    return ret;
  }

  /**
   * The local-name function returns the local part of the expanded-name of
   * the node in the argument node-set that is first in document order. If
   * the argument node-set is empty or the first node has no expanded-name,
   * an empty string is returned. If the argument is omitted, it defaults to
   * a node-set with the context node as its only member.
   */
  public static String _local_name(Node context, Collection nodeSet)
  {
    Node node = (nodeSet == null || nodeSet.size() == 0) ? context :
      firstNode(nodeSet);
    return node.getLocalName();
  }

  /**
   * The namespace-uri function returns the namespace URI of the
   * expanded-name of the node in the argument node-set that is first in
   * document order. If the argument node-set is empty, the first node has
   * no expanded-name, or the namespace URI of the expanded-name is null, an
   * empty string is returned. If the argument is omitted, it defaults to a
   * node-set with the context node as its only member.
   */
  public static String _namespace_uri(Node context, Collection nodeSet)
  {
    Node node = (nodeSet == null || nodeSet.size() == 0) ? context :
      firstNode(nodeSet);
    return node.getNamespaceURI();
  }
  
  /**
   * The name function returns a string containing a QName representing the
   * expanded-name of the node in the argument node-set that is first in
   * document order. The QName must represent the expanded-name with respect
   * to the namespace declarations in effect on the node whose expanded-name
   * is being represented. Typically, this will be the QName that occurred
   * in the XML source. This need not be the case if there are namespace
   * declarations in effect on the node that associate multiple prefixes
   * with the same namespace. However, an implementation may include
   * information about the original prefix in its representation of nodes;
   * in this case, an implementation can ensure that the returned string is
   * always the same as the QName used in the XML source. If the argument
   * node-set is empty or the first node has no expanded-name, an empty
   * string is returned. If the argument it omitted, it defaults to a
   * node-set with the context node as its only member.
   */
  public static String _name(Node context, Collection nodeSet)
  {
    Node node = (nodeSet == null || nodeSet.size() == 0) ? context :
      firstNode(nodeSet);
    switch (node.getNodeType())
      {
      case Node.ATTRIBUTE_NODE:
      case Node.ELEMENT_NODE:
      case Node.PROCESSING_INSTRUCTION_NODE:
        return node.getNodeName();
      default:
        return "";
      }
  }

  /**
   * Returns the first node in the set in document order.
   */
  static Node firstNode(Collection nodeSet)
  {
    List list = new ArrayList(nodeSet);
    Collections.sort(list, documentOrderComparator);
    return (Node) list.get(0);
  }

  /* -- 4.2 String Functions -- */

  /**
   * Implementation of the XPath <code>string</code> function.
   */
  public static String _string(Node context, Object object)
  {
    if (object == null)
      {
        return stringValue(context);
      }
    if (object instanceof String)
      {
        return (String) object;
      }
    if (object instanceof Boolean)
      {
        return object.toString();
      }
    if (object instanceof Double)
      {
        double d = ((Double) object).doubleValue();
        if (Double.isNaN(d))
          {
            return "NaN";
          }
        else if (d == 0.0d)
          {
            return "0";
          }
        else if (Double.isInfinite(d))
          {
            if (d < 0)
              {
                return "-Infinity";
              }
            else
              {
                return "Infinity";
              }
          }
        else
          {
            String ret = decimalFormat.format(d);
            if (ret.endsWith (".0"))
              { 
                ret = ret.substring(0, ret.length() - 2);
              }
            return ret;
          }
      }
    if (object instanceof Collection)
      {
        Collection nodeSet = (Collection) object;
        if (nodeSet.isEmpty())
          {
            return "";
          }
        Node node = firstNode(nodeSet);
        return stringValue(node);
      }
    throw new IllegalArgumentException(object.toString());
  }

  /* -- 4.3 Boolean Functions -- */
  
  /**
   * Implementation of the XPath <code>boolean</code> function.
   */
  public static boolean _boolean(Node context, Object object)
  {
    if (object instanceof Boolean)
      {
        return ((Boolean) object).booleanValue();
      }
    if (object instanceof Double)
      {
        return ((Double) object).doubleValue() != 0.0;
      }
    if (object instanceof String)
      {
        return ((String) object).length() != 0;
      }
    if (object instanceof Collection)
      {
        return ((Collection) object).size() != 0;
      }
    return false; // TODO user defined types
  }

  /* -- 4.4 Number Functions -- */

  /**
   * Implementation of the XPath <code>number</code> function.
   */
  public static double _number(Node context, Object object)
  {
    if (object == null)
      {
        object = Collections.singleton(context);
      }
    if (object instanceof Double)
      {
        return ((Double) object).doubleValue();
      }
    if (object instanceof Boolean)
      {
        return ((Boolean) object).booleanValue() ? 1.0 : 0.0;
      }
    if (object instanceof Collection)
      {
        // Convert node-set to string
        object = stringValue((Collection) object);
      }
    if (object instanceof String)
      {
        String string = ((String) object).trim();
        try
          {
            return Double.parseDouble(string);
          }
        catch (NumberFormatException e)
          {
            return Double.NaN;
          }
      }
    return Double.NaN; // TODO user-defined types
  }

  /**
   * Computes the XPath string-value of the specified node-set.
   */
  public static String stringValue(Collection nodeSet)
  {
    StringBuffer buf = new StringBuffer();
    for (Iterator i = nodeSet.iterator(); i.hasNext(); )
      {
        buf.append(stringValue((Node) i.next()));
      }
    return buf.toString();
  }

  /**
   * Computes the XPath string-value of the specified node.
   */
  public static String stringValue(Node node)
  {
    return stringValue(node, false);
  }
  
  static String stringValue(Node node, boolean elementMode)
  {
    switch (node.getNodeType())
      {
      case Node.DOCUMENT_NODE: // 5.1 Root Node
      case Node.DOCUMENT_FRAGMENT_NODE:
      case Node.ELEMENT_NODE: // 5.2 Element Nodes
        StringBuffer buf = new StringBuffer();
        for (Node ctx = node.getFirstChild(); ctx != null;
             ctx = ctx.getNextSibling())
          {
            buf.append(stringValue(ctx, true));
          }
        return buf.toString();
      case Node.TEXT_NODE: // 5.7 Text Nodes
      case Node.CDATA_SECTION_NODE:
        return node.getNodeValue();
      case Node.ATTRIBUTE_NODE: // 5.3 Attribute Nodes
      case Node.PROCESSING_INSTRUCTION_NODE: // 5.5 Processing Instruction
      case Node.COMMENT_NODE: // 5.6 Comment Nodes
        if (!elementMode)
          {
            return node.getNodeValue();
          }
      default:
        return "";
      }
  }

}
