/*
 * ome.dsl.VelocityHelper
 *
 *   Copyright 2006 University of Dundee. All rights reserved.
 *   Use is subject to license terms supplied in LICENSE.txt
 */

package ome.dsl;

import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.StringWriter;
import java.io.Writer;

import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.apache.velocity.runtime.RuntimeConstants;

/**
 * utility class to setup a VelocityEngine and VelocityContext (with macros).
 * Makes methods availeble to parse a template to a String or a File (using
 * Writer)
 */
public class VelocityHelper {

    private String macros;

    private final VelocityEngine ve = new VelocityEngine();

    private final VelocityContext vc = new VelocityContext();

    /** setups up a VelocityEngine with no macros file */
    public VelocityHelper() {
        this(null);
    }

    /**
     * setups up a VelocityEngine with the given macros file. Error thrown if
     * the macros file is not available
     */
    public VelocityHelper(String base) {
        ve.setProperty(RuntimeConstants.RUNTIME_LOG_LOGSYSTEM_CLASS,
                "org.apache.velocity.runtime.log.SimpleLog4JLogSystem");
        ve.setProperty("runtime.log.logsystem.log4j.category", "velocity");
        ve.setProperty("resource.loader", "file, class");
        ve
                .setProperty("class.resource.loader.class",
                        "org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader");
        if (null != macros) {
            ve.setProperty(RuntimeConstants.VM_LIBRARY, macros);
        }
        try {
            ve.init();
        } catch (Exception e) {
            throw new RuntimeException("Velocity initialization exception.", e);
        }
    }

    /** adds an item to the VelocityContext */
    public void put(String key, Object value) {
        vc.put(key, value);
    }

    /** parses the given template and returns the results as a String */
    public String invoke(InputStream template) {
        StringWriter sw = new StringWriter();
        invoke(template, sw);
        return sw.toString();
    }

    /** parses the given template and writes the results to Writer */
    public void invoke(InputStream template, Writer w) {
        try {
            InputStreamReader r = new InputStreamReader(template);
            ve.evaluate(vc, w, "Running template: " + template, r);
        } catch (Exception e) {
            throw new RuntimeException("Error invoking Velocity template:"
                    + template, e);
        }
    }

}