/*
 * 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.
 */
package org.apache.cocoon.components.xslt;

import javax.xml.transform.ErrorListener;
import javax.xml.transform.TransformerException;

import org.apache.avalon.framework.logger.Logger;
import org.apache.cocoon.util.location.Location;
import org.apache.cocoon.util.location.LocationUtils;

/**
 * A smart error listener for <code>javax.xml.tranform</code> that does its best to provide
 * useful error messages.
 * 
 * @version $Id$
 * @since 2.1.8
 */
public class TraxErrorListener implements ErrorListener{

    private Logger logger;
    private String uri;
    
    /** The exception we had from warning() */
    private TransformerException warningEx;
    
    /** The exception we had from error() or fatalError() */
    private TransformerException exception;

    public TraxErrorListener(Logger logger, String uri) {
        this.logger = logger;
        this.uri = uri;
    }

    /**
     * Get the exception that was catched by this listener, if any.
     * 
     * @return the exception
     */
    public Throwable getThrowable() {
        if (exception == null) {
            return null;
        }
        
        Location loc = LocationUtils.getLocation(exception);
        if (LocationUtils.isKnown(loc)) {
            // Has a location: don't loose this precious information!
            return exception;
        }
        
        // No location: if it's just a wrapper, consider only the wrapped exception
        if (exception.getCause() != null) {
            return exception.getCause();
        }
        
        // That's the actual exception!
        return exception;
    }

    public void warning(TransformerException ex) throws TransformerException {
        // TODO: We may want here to allow some special formatting of the messages, such as
        // "DEBUG:A debug message" or "INFO:Transforming <foo> in mode 'bar'" to use the different
        // log levels. This can include also deprecation logs for system-defined stylesheets
        // using "DEPRECATED:WARN:Styling 'foo' is replaced by 'bar'".    

        if (logger.isWarnEnabled()) {
            Location loc = LocationUtils.getLocation(ex);
            logger.warn(ex.getMessage() + " at "+ loc == null ? uri : loc.toString());
        }
        // Keep the warning (see below)
        warningEx = ex;
    }

    public void error(TransformerException ex) throws TransformerException {

        // If we had a warning previoulsy, and the current exception has no cause, then use the warning.
        // This is how Xalan behaves on <xsl:message terminate="yes">: it first issues a warning with all
        // the useful information, then a useless "stylesheed directed termination" error.
        if (warningEx != null && ex.getCause() == null) {
            ex = warningEx;
        }
        warningEx = null;

        // Keep the exception for later use.
        exception = ex;
        // and rethrow it
        throw ex;
    }

    public void fatalError(TransformerException ex) throws TransformerException {
        if (warningEx != null && ex.getCause() == null) {
            ex = warningEx;
        }
        warningEx = null;

        exception = ex;
        throw ex;
    }
}