/*
 * Steps.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.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.Set;
import org.w3c.dom.Attr;
import org.w3c.dom.Node;

/**
 * A list of transitions between components in a location path.
 *
 * @author <a href='mailto:dog@gnu.org'>Chris Burdess</a>
 */
public final class Steps
  extends Path
{

  final LinkedList path;

  public Steps()
  {
    this(new LinkedList());
  }

  Steps(LinkedList path)
  {
    this.path = path;
  }

  public boolean matches(Node context)
  {
    // Right to left
    return matches(context, path.size() - 1);
  }

  boolean matches(Node context, int pos)
  {
    Pattern right = (Pattern) path.get(pos);
    if (!right.matches(context))
      {
        return false;
      }
    if (pos > 0)
      {
        Pattern left = (Pattern) path.get(pos - 1);
        Iterator j = possibleContexts(right, context).iterator();
        while (j.hasNext())
          {
            Node candidate = (Node) j.next();
            if (left.matches(candidate) &&
                matches(candidate, pos - 1))
              {
                return true;
              }
            // keep going, there may be another candidate
          }
        return false;
      }
    return true;
  }

  /**
   * Essentially the reverse of Selector.addCandidates.
   * The idea is to determine possible context nodes for a match.
   */
  Collection possibleContexts(Pattern pattern, Node context)
  {
    if (pattern instanceof Selector)
      {
        Selector s = (Selector) pattern;
        Collection candidates = new LinkedHashSet();
        switch (s.axis)
          {
          case Selector.PARENT:
            s.addChildNodes(context, candidates, false);
            break;
          case Selector.ANCESTOR:
            s.addChildNodes(context, candidates, true);
            break;
          case Selector.ANCESTOR_OR_SELF:
            candidates.add (context);
            s.addChildNodes(context, candidates, true);
            break;
          case Selector.CHILD:
            s.addParentNode(context, candidates, false);
            break;
          case Selector.DESCENDANT:
            s.addParentNode(context, candidates, true);
            break;
          case Selector.DESCENDANT_OR_SELF:
            candidates.add(context);
            s.addParentNode(context, candidates, true);
            break;
          case Selector.PRECEDING_SIBLING:
            s.addFollowingNodes(context, candidates, false);
            break;
          case Selector.FOLLOWING_SIBLING:
            s.addPrecedingNodes(context, candidates, false);
            break;
          case Selector.PRECEDING:
            s.addFollowingNodes(context, candidates, true);
            break;
          case Selector.FOLLOWING:
            s.addPrecedingNodes(context, candidates, true);
            break;
          case Selector.ATTRIBUTE:
          case Selector.NAMESPACE:
            if (context.getNodeType() == Node.ATTRIBUTE_NODE)
              {
                candidates.add(((Attr) context).getOwnerElement());
              }
            break;
          case Selector.SELF:
            candidates.add(context);
            break;
          }
        return candidates;
      }
    return Collections.EMPTY_SET;
  }

  public Object evaluate(Node context, int pos, int len)
  {
    //System.err.println(toString()+" evaluate");
    // Left to right
    Iterator i = path.iterator();
    Expr lhs = (Expr) i.next();
    Object val = lhs.evaluate(context, pos, len);
    //System.err.println("\tevaluate "+lhs+" = "+val);
    while (val instanceof Collection && i.hasNext())
      {
        Path rhs = (Path) i.next();
        val = rhs.evaluate(context, (Collection) val);
        //System.err.println("\tevaluate "+rhs+" = "+val);
      }
    return val;
  }

  Collection evaluate(Node context, Collection ns)
  {
    // Left to right
    Iterator i = path.iterator();
    Expr lhs = (Expr) i.next();
    if (lhs instanceof Path)
      {
        ns = ((Path) lhs).evaluate(context, ns);
      }
    else
      {
        Set acc = new LinkedHashSet();
        int pos = 1, len = ns.size();
        for (Iterator j = ns.iterator(); j.hasNext(); )
          {
            Node node = (Node) j.next();
            Object ret = lhs.evaluate(node, pos++, len);
            if (ret instanceof Collection)
              {
                acc.addAll((Collection) ret);
              }
          }
        ns = acc;
      }
    while (i.hasNext())
      {
        Path rhs = (Path) i.next();
        ns = rhs.evaluate(context, ns);
      }
    return ns;
  }

  public Expr clone(Object context)
  {
    int len = path.size();
    LinkedList path2 = new LinkedList();
    for (int i = 0; i < len; i++)
      {
        path2.add(((Expr) path.get(i)).clone(context));
      }
    return new Steps(path2);
  }

  public String toString()
  {
    StringBuffer buf = new StringBuffer();
    Iterator i = path.iterator();
    Expr expr = (Expr) i.next();
    if (!(expr instanceof Root))
      {
        buf.append(expr);
      }
    while (i.hasNext())
      {
        expr = (Expr) i.next();
        buf.append('/');
        buf.append(expr);
      }
    return buf.toString();
  }

}
