/*
 * Copyright 1997-2004 The Apache Software Foundation
 * 
 * Licensed 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.avalon.framework.configuration;

import java.util.ArrayList;
import java.util.BitSet;
import org.xml.sax.Attributes;
import org.xml.sax.ErrorHandler;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.xml.sax.helpers.DefaultHandler;

/**
 * A SAXConfigurationHandler helps build Configurations out of sax events.
 *
 * @author <a href="mailto:dev@avalon.apache.org">Avalon Development Team</a>
 * @version $Id: SAXConfigurationHandler.java 30977 2004-07-30 03:57:54 -0500 (Fri, 30 Jul 2004) niclas $
 */
public class SAXConfigurationHandler
    extends DefaultHandler
    implements ErrorHandler
{
    /**
     * Likely number of nested configuration items. If more is
     * encountered the lists will grow automatically.
     */
    private static final int EXPECTED_DEPTH = 5;
    private final ArrayList m_elements = new ArrayList( EXPECTED_DEPTH );
    private final ArrayList m_values = new ArrayList( EXPECTED_DEPTH );
    /**
     * Contains true at index n if space in the configuration with
     * depth n is to be preserved.
     */
    private final BitSet m_preserveSpace = new BitSet();
    private Configuration m_configuration;
    private Locator m_locator;

    /**
     * Get the configuration object that was built.
     *
     * @return a <code>Configuration</code> object
     */
    public Configuration getConfiguration()
    {
        return m_configuration;
    }

    /**
     * Clears all data from this configuration handler.
     */
    public void clear()
    {
        m_elements.clear();
        m_values.clear();
        m_locator = null;
    }

    /**
     * Set the document <code>Locator</code> to use.
     *
     * @param locator a <code>Locator</code> value
     */
    public void setDocumentLocator( final Locator locator )
    {
        m_locator = locator;
    }

    /**
     * Handling hook for character data.
     *
     * @param ch a <code>char[]</code> of data
     * @param start offset in the character array from which to start reading
     * @param end length of character data
     * @throws SAXException if an error occurs
     */
    public void characters( final char[] ch, int start, int end )
        throws SAXException
    {
        // it is possible to play micro-optimization here by doing
        // manual trimming and thus preserve some precious bits
        // of memory, but it's really not important enough to justify
        // resulting code complexity
        final int depth = m_values.size() - 1;
        final StringBuffer valueBuffer = (StringBuffer)m_values.get( depth );
        valueBuffer.append( ch, start, end );
    }

    /**
     * Handling hook for finishing parsing of an element.
     *
     * @param namespaceURI a <code>String</code> value
     * @param localName a <code>String</code> value
     * @param rawName a <code>String</code> value
     * @throws SAXException if an error occurs
     */
    public void endElement( final String namespaceURI,
                            final String localName,
                            final String rawName )
        throws SAXException
    {
        final int depth = m_elements.size() - 1;
        final DefaultConfiguration finishedConfiguration =
            (DefaultConfiguration)m_elements.remove( depth );
        final String accumulatedValue =
            ( (StringBuffer)m_values.remove( depth ) ).toString();

        if( finishedConfiguration.getChildren().length == 0 )
        {
            // leaf node
            String finishedValue;
            if( m_preserveSpace.get( depth ) )
            {
                finishedValue = accumulatedValue;
            }
            else if( 0 == accumulatedValue.length() )
            {
                finishedValue = null;
            }
            else
            {
                finishedValue = accumulatedValue.trim();
            }
            finishedConfiguration.setValue( finishedValue );
        }
        else
        {
            final String trimmedValue = accumulatedValue.trim();
            if( trimmedValue.length() > 0 )
            {
                throw new SAXException( "Not allowed to define mixed content in the "
                                        + "element " + finishedConfiguration.getName() + " at "
                                        + finishedConfiguration.getLocation() );
            }
        }

        if( 0 == depth )
        {
            m_configuration = finishedConfiguration;
        }
    }

    /**
     * Create a new <code>DefaultConfiguration</code> with the specified
     * local name and location.
     *
     * @param localName a <code>String</code> value
     * @param location a <code>String</code> value
     * @return a <code>DefaultConfiguration</code> value
     */
    protected DefaultConfiguration createConfiguration( final String localName,
                                                        final String location )
    {
        return new DefaultConfiguration( localName, location );
    }

    /**
     * Handling hook for starting parsing of an element.
     *
     * @param namespaceURI a <code>String</code> value
     * @param localName a <code>String</code> value
     * @param rawName a <code>String</code> value
     * @param attributes an <code>Attributes</code> value
     * @throws SAXException if an error occurs
     */
    public void startElement( final String namespaceURI,
                              final String localName,
                              final String rawName,
                              final Attributes attributes )
        throws SAXException
    {
        final DefaultConfiguration configuration =
            createConfiguration( rawName, getLocationString() );
        // depth of new configuration (not decrementing here, configuration
        // is to be added)
        final int depth = m_elements.size();
        boolean preserveSpace = false; // top level element trims space by default

        if( depth > 0 )
        {
            final DefaultConfiguration parent =
                (DefaultConfiguration)m_elements.get( depth - 1 );
            parent.addChild( configuration );
            // inherits parent's space preservation policy
            preserveSpace = m_preserveSpace.get( depth - 1 );
        }

        m_elements.add( configuration );
        m_values.add( new StringBuffer() );

        final int attributesSize = attributes.getLength();

        for( int i = 0; i < attributesSize; i++ )
        {
            final String name = attributes.getQName( i );
            final String value = attributes.getValue( i );

            if( !name.equals( "xml:space" ) )
            {
                configuration.setAttribute( name, value );
            }
            else
            {
                preserveSpace = value.equals( "preserve" );
            }
        }

        if( preserveSpace )
        {
            m_preserveSpace.set( depth );
        }
        else
        {
            m_preserveSpace.clear( depth );
        }
    }

    /**
     * This just throws an exception on a parse error.
     * @param exception the parse error
     * @throws SAXException if an error occurs
     */
    public void error( final SAXParseException exception )
        throws SAXException
    {
        throw exception;
    }

    /**
     * This just throws an exception on a parse error.
     * @param exception the parse error
     * @throws SAXException if an error occurs
     */
    public void warning( final SAXParseException exception )
        throws SAXException
    {
        throw exception;
    }

    /**
     * This just throws an exception on a parse error.
     * @param exception the parse error
     * @throws SAXException if an error occurs
     */
    public void fatalError( final SAXParseException exception )
        throws SAXException
    {
        throw exception;
    }

    /**
     * Returns a string showing the current system ID, line number and column number.
     *
     * @return a <code>String</code> value
     */
    protected String getLocationString()
    {
        if( null == m_locator )
        {
            return "Unknown";
        }
        else
        {
            final int columnNumber = m_locator.getColumnNumber();
            return
                m_locator.getSystemId() + ":"
                + m_locator.getLineNumber()
                + ( columnNumber >= 0 ? ( ":" + columnNumber ) : "" );
        }
    }
}
