/**************************************************************************************
 * Copyright (c) Jonas BonŽr, Alexandre Vasseur. All rights reserved.                 *
 * http://aspectwerkz.codehaus.org                                                    *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the LGPL license      *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/
package org.codehaus.aspectwerkz.definition;

import org.codehaus.aspectwerkz.exception.DefinitionException;
import org.codehaus.aspectwerkz.exception.WrappedRuntimeException;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Iterator;
import java.util.List;

/**
 * Parses the XML definition file using <tt>dom4j</tt>.
 * 
 * @author <a href="mailto:jboner@codehaus.org">Jonas BonŽr </a>
 */
public class XmlParser {
    /**
     * The current DTD public id. The matching dtd will be searched as a resource.
     */
    private final static String DTD_PUBLIC_ID = "-//AspectWerkz//DTD 1.0//EN";

    private final static String DTD_PUBLIC_ID_ALIAS = "-//AspectWerkz//DTD//EN";

    /**
     * The timestamp, holding the last time that the definition was parsed.
     */
    private static File s_timestamp = new File(".timestamp");

    /**
     * The AspectWerkz definitions.
     */
    private static List s_definitions = null;

    /**
     * @param definitionFile the definition file
     * @return the definitions
     */
    public static List getAspectClassNames(final File definitionFile) {
        if (definitionFile == null) {
            throw new IllegalArgumentException("definition file can not be null");
        }
        if (!definitionFile.exists()) {
            throw new DefinitionException("definition file " + definitionFile.toString() + " does not exist");
        }
        try {
            return getAspectClassNames(definitionFile.toURL());
        } catch (MalformedURLException e) {
            throw new DefinitionException(definitionFile + " does not exist");
        }
    }

    public static List getAspectClassNames(final URL definitionURL) {
        if (definitionURL == null) {
            throw new IllegalArgumentException("definition file can not be null");
        }
        try {
            Document document = createDocument(definitionURL);
            return DocumentParser.parseAspectClassNames(document);
        } catch (DocumentException e) {
            throw new DefinitionException("XML definition file <" + definitionURL + "> has errors: " + e.toString());
        }
    }

    /**
     * @param stream the input stream containing the document
     * @return the definitions
     */
    public static List getAspectClassNames(final InputStream stream) {
        try {
            Document document = createDocument(stream);
            return DocumentParser.parseAspectClassNames(document);
        } catch (DocumentException e) {
            throw new DefinitionException("XML definition file on classpath has errors: " + e.toString());
        }
    }

    /**
     * Parses the XML definition file, only if it has been updated. Uses a timestamp to check for modifications.
     * 
     * @param loader the current class loader
     * @param definitionFile the definition file
     * @param isDirty flag to mark the the definition as updated or not
     * @return the definitions
     */
    public static List parse(final ClassLoader loader, final File definitionFile, boolean isDirty) {
        if (definitionFile == null) {
            throw new IllegalArgumentException("definition file can not be null");
        }
        if (!definitionFile.exists()) {
            throw new DefinitionException("definition file " + definitionFile.toString() + " does not exist");
        }

        // if definition is not updated; don't parse but return it right away
        if (isNotUpdated(definitionFile)) {
            isDirty = false;
            return s_definitions;
        }

        // updated definition, ready to be parsed
        try {
            Document document = createDocument(definitionFile.toURL());
            s_definitions = DocumentParser.parse(loader, document);
            setParsingTimestamp();
            isDirty = true;
            return s_definitions;
        } catch (MalformedURLException e) {
            throw new DefinitionException(definitionFile + " does not exist");
        } catch (DocumentException e) {
            throw new DefinitionException("XML definition file <" + definitionFile + "> has errors: " + e.toString());
        }
    }

    /**
     * Parses the XML definition file retrieved from an input stream.
     * 
     * @param loader the current class loader
     * @param stream the input stream containing the document
     * @return the definitions
     */
    public static List parse(final ClassLoader loader, final InputStream stream) {
        try {
            Document document = createDocument(stream);
            s_definitions = DocumentParser.parse(loader, document);
            return s_definitions;
        } catch (DocumentException e) {
            throw new DefinitionException("XML definition file on classpath has errors: " + e.getMessage());
        }
    }

    /**
     * Parses the XML definition file not using the cache.
     * 
     * @param loader the current class loader
     * @param url the URL to the definition file
     * @return the definition object
     */
    public static List parseNoCache(final ClassLoader loader, final URL url) {
        try {
            Document document = createDocument(url);
            s_definitions = DocumentParser.parse(loader, document);
            return s_definitions;
        } catch (Exception e) {
            throw new WrappedRuntimeException(e);
        }
    }

    /**
     * Merges two DOM documents.
     * 
     * @param document1 the first document
     * @param document2 the second document
     * @return the definition merged document
     */
    public static Document mergeDocuments(final Document document1, final Document document2) {
        if ((document2 == null) && (document1 != null)) {
            return document1;
        }
        if ((document1 == null) && (document2 != null)) {
            return document2;
        }
        if ((document1 == null) && (document2 == null)) {
            return null;
        }
        try {
            Element root1 = document1.getRootElement();
            Element root2 = document2.getRootElement();
            for (Iterator it1 = root2.elementIterator(); it1.hasNext();) {
                Element element = (Element) it1.next();
                element.setParent(null);
                root1.add(element);
            }
        } catch (Exception e) {
            throw new WrappedRuntimeException(e);
        }
        return document1;
    }

    /**
     * Creates a DOM document.
     * 
     * @param url the URL to the file containing the XML
     * @return the DOM document
     * @throws DocumentException
     * @throws DocumentException
     */
    public static Document createDocument(final URL url) throws DocumentException {
        SAXReader reader = new SAXReader();
        setEntityResolver(reader);
        return reader.read(url);
    }

    /**
     * Creates a DOM document.
     * 
     * @param stream the stream containing the XML
     * @return the DOM document
     * @throws DocumentException
     * @throws DocumentException
     */
    public static Document createDocument(final InputStream stream) throws DocumentException {
        SAXReader reader = new SAXReader();
        setEntityResolver(reader);
        return reader.read(stream);
    }

    /**
     * Sets the entity resolver which is created based on the DTD from in the root dir of the AspectWerkz distribution.
     * 
     * @param reader the reader to set the resolver in
     */
    private static void setEntityResolver(final SAXReader reader) {
        EntityResolver resolver = new EntityResolver() {
            public InputSource resolveEntity(String publicId, String systemId) {
                if (publicId.equals(DTD_PUBLIC_ID) || publicId.equals(DTD_PUBLIC_ID_ALIAS)) {
                    InputStream in = getClass().getResourceAsStream("/aspectwerkz.dtd");
                    if (in == null) {
                        System.err.println("AspectWerkz - WARN - could not open DTD");
                        return new InputSource();
                    } else {
                        return new InputSource(in);
                    }
                } else {
                    System.err.println("AspectWerkz - WARN - deprecated DTD "
                        + publicId
                        + " - consider upgrading to "
                        + DTD_PUBLIC_ID);
                    return new InputSource(); // avoid null pointer exception
                }
            }
        };
        reader.setEntityResolver(resolver);
    }

    /**
     * Checks if the definition file has been updated since the last parsing.
     * 
     * @param definitionFile the definition file
     * @return boolean
     */
    private static boolean isNotUpdated(final File definitionFile) {
        return (definitionFile.lastModified() < getParsingTimestamp()) && (s_definitions != null);
    }

    /**
     * Sets the timestamp for the latest parsing of the definition file.
     */
    private static void setParsingTimestamp() {
        final long newModifiedTime = System.currentTimeMillis();
        s_timestamp.setLastModified(newModifiedTime);
    }

    /**
     * Returns the timestamp for the last parsing of the definition file.
     * 
     * @return the timestamp
     */
    private static long getParsingTimestamp() {
        final long modifiedTime = s_timestamp.lastModified();
        if (modifiedTime == 0L) {
            // no timestamp, create a new one
            try {
                s_timestamp.createNewFile();
            } catch (IOException e) {
                throw new RuntimeException("could not create timestamp file: " + s_timestamp.getAbsolutePath());
            }
        }
        return modifiedTime;
    }
}