/*
 * @(#)$Id: ValueExp.java,v 1.1 2001/10/18 23:52:10 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 org.relaxng.datatype.Datatype;
import org.relaxng.datatype.ValidationContext;
import com.sun.msv.util.StringPair;

/**
 * Expression that matchs a particular value of a {@link Datatype}.
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
 */
public final class ValueExp extends Expression implements DataOrValueExp {
	
	/** Datatype object that is used to test the equality. */
	public final Datatype dt;
	public Datatype getType() { return dt; }

	/** This expression matches this value only. */
	public final Object value;
	
	/**
	 * name of this datatype.
	 * 
	 * The value of this field is not considered as significant.
	 * When two TypedStringExps share the same Datatype object,
	 * then they are unified even if they have different names.
	 */
	public final StringPair name;
	public StringPair getName() { return name; }
	
	protected ValueExp( Datatype dt, StringPair typeName, Object value ) {
		super(hashCode(dt,HASHCODE_VALUE));
		this.dt=dt;
		this.name = typeName;
		this.value = value;
	}
	
	public boolean equals( Object o ) {
		// Note that equals method of this class *can* be sloppy, 
		// since this class does not have a pattern as its child.
		
		// Therefore datatype vocaburary does not necessarily provide
		// strict equals method.
		if(o.getClass()!=this.getClass())	return false;
		
		ValueExp rhs = (ValueExp)o;
		
		if(!rhs.dt.equals(dt))				return false;
		
		return dt.sameValue(value,rhs.value);
	}
	
	public Object visit( ExpressionVisitor visitor )				{ return visitor.onValue(this); }
	public Expression visit( ExpressionVisitorExpression visitor )	{ return visitor.onValue(this); }
	public boolean visit( ExpressionVisitorBoolean visitor )		{ return visitor.onValue(this); }
	public void visit( ExpressionVisitorVoid visitor )				{ visitor.onValue(this); }

	protected boolean calcEpsilonReducibility() {
		return false;
	}
}