code: /*
   * 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.xsltc.compiler;
  
  import java.util.Vector;
  
  import org.apache.bcel.generic.ConstantPoolGen;
  import org.apache.bcel.generic.INVOKEINTERFACE;
  import org.apache.bcel.generic.INVOKESPECIAL;
  import org.apache.bcel.generic.INVOKEVIRTUAL;
  import org.apache.bcel.generic.InstructionList;
  import org.apache.bcel.generic.NEW;
  import org.apache.xalan.xsltc.compiler.util.ClassGenerator;
  import org.apache.xalan.xsltc.compiler.util.MethodGenerator;
  import org.apache.xalan.xsltc.compiler.util.Type;
  import org.apache.xalan.xsltc.compiler.util.TypeCheckError;
  import org.apache.xml.dtm.Axis;
  import org.apache.xml.dtm.DTM;
  
  /**
   * @author Jacek Ambroziak
   * @author Santiago Pericas-Geertsen
   */
  final class UnionPathExpr extends Expression {
  
      private final Expression _pathExpr;
      private final Expression _rest;
      private boolean _reverse = false;
  
      // linearization for top level UnionPathExprs
      private Expression[] _components;
      
      public UnionPathExpr(Expression pathExpr, Expression rest) {
  	_pathExpr = pathExpr;
  	_rest     = rest;
      }
  
      public void setParser(Parser parser) {
  	super.setParser(parser);
  	// find all expressions in this Union
  	final Vector components = new Vector();
  	flatten(components);
  	final int size = components.size();
  	_components = (Expression[])components.toArray(new Expression[size]);
  	for (int i = 0; i < size; i++) {
  	    _components[i].setParser(parser);
  	    _components[i].setParent(this);
  	    if (_components[i] instanceof Step) {
  		final Step step = (Step)_components[i];
  		final int axis = step.getAxis();
  		final int type = step.getNodeType();
  		// Put attribute iterators first
  		if ((axis == Axis.ATTRIBUTE) || (type == DTM.ATTRIBUTE_NODE)) {
  		    _components[i] = _components[0];
  		    _components[0] = step;
  		}
  		// Check if the union contains a reverse iterator
          if (Axis.isReverse(axis)) _reverse = true;
  	    }
  	}
  	// No need to reverse anything if another expression lies on top of this
  	if (getParent() instanceof Expression) _reverse = false;
      }
      
      public Type typeCheck(SymbolTable stable) throws TypeCheckError {
  	final int length = _components.length;
  	for (int i = 0; i < length; i++) {
  	    if (_components[i].typeCheck(stable) != Type.NodeSet) {
  		_components[i] = new CastExpr(_components[i], Type.NodeSet);
  	    }
  	}
  	return _type = Type.NodeSet;	
      }
  
      public String toString() {
  	return "union(" + _pathExpr + ", " + _rest + ')';
      }
  	
      private void flatten(Vector components) {
  	components.addElement(_pathExpr);
  	if (_rest != null) {
  	    if (_rest instanceof UnionPathExpr) {
  		((UnionPathExpr)_rest).flatten(components);
  	    }
  	    else {
  		components.addElement(_rest);
  	    }
  	}
      }
  
      public void translate(ClassGenerator classGen, MethodGenerator methodGen) {
  	final ConstantPoolGen cpg = classGen.getConstantPool();
  	final InstructionList il = methodGen.getInstructionList();
  
  	final int init = cpg.addMethodref(UNION_ITERATOR_CLASS,
  					  "<init>",
  					  "("+DOM_INTF_SIG+")V");
  	final int iter = cpg.addMethodref(UNION_ITERATOR_CLASS,
  					  ADD_ITERATOR,
  					  ADD_ITERATOR_SIG);
  
  	// Create the UnionIterator and leave it on the stack
  	il.append(new NEW(cpg.addClass(UNION_ITERATOR_CLASS)));
  	il.append(DUP);
  	il.append(methodGen.loadDOM());
  	il.append(new INVOKESPECIAL(init));
  
  	// Add the various iterators to the UnionIterator
  	final int length = _components.length;
  	for (int i = 0; i < length; i++) {
  	    _components[i].translate(classGen, methodGen);
  	    il.append(new INVOKEVIRTUAL(iter));
  	}
  
  	// Order the iterator only if strictly needed
  	if (_reverse) {
  	    final int order = cpg.addInterfaceMethodref(DOM_INTF,
  							ORDER_ITERATOR,
  							ORDER_ITERATOR_SIG);
  	    il.append(methodGen.loadDOM());
  	    il.append(SWAP);
  	    il.append(methodGen.loadContextNode());
  	    il.append(new INVOKEINTERFACE(order, 3));
  
  	}
      }
  }
  