/* Copyright 2002-2004 Elliotte Rusty Harold
   
   This library is free software; you can redistribute it and/or modify
   it under the terms of version 2.1 of the GNU Lesser General Public 
   License as published by the Free Software Foundation.
   
   This library 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 Lesser General Public License for more details.
   
   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, write to the 
   Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
   Boston, MA 02111-1307  USA
   
   You can contact Elliotte Rusty Harold by sending e-mail to
   elharo@metalab.unc.edu. Please include the word "XOM" in the
   subject line. The XOM home page is located at http://www.xom.nu/
*/

package nu.xom.xslt;

/**
 * <p>
 *   Thrown when an XSL stylesheet fails to compile
 *   or an XSL transform fails.
 * </p>
 * 
 * @author Elliotte Rusty Harold
 * @version 1.0b3
 */
public class XSLException extends Exception {

    
    private Throwable cause;

    
    /**
     * <p>
     * Creates a new <code>XSLException</code> with the specified 
     * detail message and an underlying root cause.
     * </p>
     * 
     * @param message information about the cause of the exception
     * @param cause the nested exception that caused this exception
     */
    public XSLException(String message, Throwable cause) {
        super(message);
        this.initCause(cause);
    }
    
    
    /**
     * <p>
     * Creates a new <code>XSLException</code>
     * with the specified detail message.
     * </p>
     * 
     * @param message information about the cause of the exception
     */
    public XSLException(String message) {
        super(message);
    }

    
    // null is insufficient for detecting an uninitialized cause.
    // The cause may be set to null which may not then be reset.
    private boolean causeSet = false;

    /**
     * <p>
     * Sets the root cause of this exception. This may 
     * only be called once. Subsequent calls throw an 
     * <code>IllegalStateException</code>.
     * </p>
     * 
     * <p>
     * This method is unnecessary in Java 1.4 where it could easily be
     * inherited from the superclass. However, including it here
     * allows this  method to be used in Java 1.3 and earlier.
     * </p>
     *
     * @param cause the root cause of this exception
     * 
     * @return this <code>XSLException</code>
     * 
     * @throws IllegalArgumentException if the cause is this exception
     *   (An exception cannot be its own cause.)
     * @throws IllegalStateException if this method is called twice
     */
    public Throwable initCause(Throwable cause) {
        
        if (causeSet) {
            throw new IllegalStateException("Can't overwrite cause");
        } 
        else if (cause == this) {
            throw new IllegalArgumentException(
              "Self-causation not permitted"); 
        }
        else this.cause = cause;
        causeSet = true;
        return this;
        
    }

    
    /**
     * <p>
     * Returns the underlying exception that caused this exception.
     * </p>
     * 
     * @return the initial exception that caused this exception 
     *     to be thrown
     */
    public Throwable getCause() {
        return this.cause;  
    }

    
}
