/*
 * @(#)$Id: BinaryExp.java,v 1.12 2001/07/13 17:57:30 Bear Exp $
 *
 * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */
package com.sun.msv.grammar;

import java.util.Iterator;

/**
 * Base implementation for those expression which has two child expressions.
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
 */
public abstract class BinaryExp extends Expression {
	
	public final Expression exp1;
	public final Expression exp2;
	
	public BinaryExp( Expression left, Expression right, int hashKey ) {
		super( hashCode(left,right,hashKey) );
		this.exp1 = left;
		this.exp2 = right;
	}

	public boolean equals( Object o ) {
		if( !this.getClass().equals(o.getClass()) )		return false;
		
		// every existing children are already unified.
		// therefore, == is enough. (don't need to call equals)
		return ((BinaryExp)o).exp1 == exp1
			&& ((BinaryExp)o).exp2 == exp2;
	}
	
	/**
	 * returns all child expressions in one array.
	 * 
	 * This method is similar to the children method but it returns an array 
	 * that contains all children instead of an iterator object.
	 */
	public Expression[] getChildren() {
		// count the number of children
		int cnt=1;
		Expression exp = this;
		while( exp.getClass()==this.getClass() ) {
			cnt++;
			exp = ((BinaryExp)exp).exp1;
		}
		
		Expression[] r = new Expression[cnt];
		exp=this;
		while( exp.getClass()==this.getClass() ) {
			r[--cnt] = ((BinaryExp)exp).exp2;
			exp = ((BinaryExp)exp).exp1;
		}
		r[0] = exp;
		
		return r;
	}
	
	/**
	 * iterates all child expressions.
	 * 
	 * Since expressions are binarized, expressions like A|B|C is modeled as
	 * A|(B|C).  This is may not be preferable for some applications.
	 * 
	 * <P>
	 * This method returns an iterator that iterates all children
	 * (A,B, and C in this example)
	 */
	public Iterator children() {
		final Expression[] items = getChildren();
		return new Iterator() {
			private int idx =0;
			
			public Object next() {
				return items[idx++];
			}
			public boolean hasNext() { return idx!=items.length; }
			public void remove() { throw new UnsupportedOperationException(); }
		};
	}
	
}