/*
 * Copyright 2002,2004 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.commons.jelly.impl;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.MalformedURLException;
import java.net.URL;

import org.apache.commons.jelly.Jelly;
import org.apache.commons.jelly.JellyContext;
import org.apache.commons.jelly.Script;
import org.apache.commons.jelly.TagLibrary;
import org.apache.commons.jelly.XMLOutput;
import org.apache.commons.jelly.parser.XMLParser;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.xml.sax.SAXException;

/**
 * @author <a href="mailto:vinayc@apache.org">Vinay Chandran</a>
 *
 * <p><code>Embedded</code> provides easy means to embed JellyEngine <br/>
 * and use Jelly scripts within an application</p>
 * A typical usage:<br/>
 *  <code><br/>
 *     Embedded embedded = new Embedded();<br/>
 *     embedded.setOutputStream(new ByteArrayOutputStream());<br/>
 *     embedded.setVariable("some-var","some-object");<br/>
 *     .....<br/>
 *     embedded.setScript(scriptAsString);<br/>
 *     //or one can do.<br/>
 *     //embedded.setScript(scriptAsInputStream);<br/>
 *     <br/>
 *     boolean bStatus=embedded.execute();<br/>
 *     if(!bStatus) //if error<br/>
 *     {<br/>
 *         String errorMsg=embedded.getErrorMsg();<br/>
 *     }<br/>
 *  </code>  <br/>
 *
 * @author <a href="mailto:vinayc@apache.org">Vinay Chandran</a>
 */
public class Embedded {
    /** Jelly Engine */
    Jelly m_jellyEngine = new Jelly();
    /** JellyContext*/
    private JellyContext m_context = new JellyContext();
    /** Compiled Script Object*/
    private Script m_script;
    /** Input script as stream*/
    private InputStream m_inputStream;
    /** Output Stream */
    private OutputStream m_outputStream;
    /** Output(default System.out) */
    private XMLOutput m_output =
        XMLOutput.createXMLOutput(new OutputStreamWriter(System.out));
    /** Exception thrown during compilation of script*/
    Exception m_scriptCompilationException;
    /** boolean value indicating whether the script has been successfully compiled or NOT */
    boolean m_scriptCompiled = false;
    /** ErrorMsg*/
    private String m_errorMsg;
    /** The Log to which logging calls will be made. */
    private static final Log log = LogFactory.getLog(Embedded.class);

    /**
     * Default Constructor
     *
     */
    public Embedded() {
        //m_context.setClassLoader(new TagLibraryClassLoader(m_context));
    }

    /**
     * Method setContext.
     * @param context
     */
    public void setContext(JellyContext context) {
        m_context = context;
    }

    /**
     * Method getContext.
     * @return JellyContext
     */
    public JellyContext getContext() {
        return m_context;
    }

    /**
     * Set a new variable within the context for the script to use.
     * @param name
     * @param value
     */
    public void setVariable(String name, Object value) {
        m_context.setVariable(name, value);
    }

    /**
     * Set the input script
     * @param scriptAsString
     */
    public void setScript(String scriptAsString) {

        try {
            URL url = resolveURL(scriptAsString);
            m_inputStream = url.openStream();
        }
        catch (MalformedURLException e) {
            //Encapsulate the string within
            m_inputStream = new ByteArrayInputStream(scriptAsString.getBytes());
        }
        catch (IOException e) {
            //Error reading from the URL
            m_inputStream = null;
        }

        compileScriptAndKeep();

    }

    /**
     * @return the URL for the relative file name or absolute URL
     */
    private URL resolveURL(String name) throws MalformedURLException {
        File file = new File(name);
        if (file.exists()) {
            return file.toURL();
        }
        return new URL(name);
    }

    /**
     * Set the input stream
     * @param scriptAsInputStream
     */
    public void setScript(InputStream scriptAsInputStream) {
        m_inputStream = scriptAsInputStream;
        compileScriptAndKeep();
    }

    /**
     * Compile the script
     */
    private void compileScriptAndKeep() {
        XMLParser parser = new XMLParser();
        parser.setContext(m_context);
        m_scriptCompiled = false;
        try {
            m_script = parser.parse(m_inputStream);
            m_script = m_script.compile();
            m_scriptCompiled = true;
        }
        catch (IOException e) {
            m_scriptCompilationException = e;
        }
        catch (SAXException e) {
            m_scriptCompilationException = e;
        }
        catch (Exception e) {
            m_scriptCompilationException = e;
        }
    }

    /**
     * Method setOutputStream.
     * @param outputStream
     */
    public void setOutputStream(OutputStream outputStream) {
        m_outputStream = outputStream;
        m_output =
            XMLOutput.createXMLOutput(new OutputStreamWriter(m_outputStream));
    }

    /**
     * Registers the given tag library class name against the given namespace URI.
     * The class will be loaded via the given ClassLoader
     * This should be called before the parser is used.
     */
    public void registerTagLibrary(String namespaceURI, String className) {
        if (m_context != null)
            m_context.registerTagLibrary(namespaceURI, className);
    }

    /**
     * Registers the given tag library against the given namespace URI.
     * This should be called before the parser is used.
     */
    public void registerTagLibrary(String namespaceURI, TagLibrary taglib) {
        if (m_context != null)
            m_context.registerTagLibrary(namespaceURI, taglib);
    }

    /**
     * Returns the errorMsg.
     * @return String
     */
    public String getErrorMsg() {
        return m_errorMsg;
    }

    /**
     * Sets the errorMsg.
     * @param errorMsg The errorMsg to set
     */
    private void setErrorMsg(String errorMsg) {
        m_errorMsg = errorMsg;
    }

    /**
     * Execute the jelly script and capture the errors (ifany)within.
     *
     * @throws JellyException
     */
    public boolean execute() {
        if (log.isDebugEnabled())
            log.debug("Starting Execution");
        //If script has not been compiled then return the errorMsg that occured during compilation
        if (!m_scriptCompiled) {
            if (log.isErrorEnabled())
                log.error(m_scriptCompilationException.getMessage());
            setErrorMsg(m_scriptCompilationException.getMessage());
            return false;
        }
        if (m_inputStream == null) {
            if (log.isErrorEnabled())
                log.error("[Error] Input script-resource NOT accessible");
            setErrorMsg("[Error] Input script-resource NOT accessible");
            return false;
        }
        try {
            m_script.run(m_context, m_output);
            m_outputStream.close();
            m_output.flush();
        }
        catch (Exception e) {
            if (log.isErrorEnabled())
                log.error(e.getMessage());
            setErrorMsg(e.getMessage());
            return false;
        }
        if (log.isDebugEnabled())
            log.debug("Done Executing");
        return true;
    }

}