/**

 * Back 2 Browser Bytecode Translator

 * Copyright (C) 2012 Jaroslav Tulach <jaroslav.tulach@apidesign.org>

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, version 2 of the License.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program. Look for COPYING file in the top folder.

 * If not, see http://opensource.org/licenses/GPL-2.0.

 */

package org.apidesign.vm4brwsr;

import java.io.IOException;

import java.io.InputStream;

import java.net.URL;

import java.util.Enumeration;

/** Build your own virtual machine! Use methods in this class to generate

 * a skeleton JVM in JavaScript that contains pre-compiled classes of your

 * choice. The generated script defines one JavaScript method that can

 * be used to bootstrap and load the virtual machine: <pre>

 * var vm = bck2brwsr();

 * var main = vm.loadClass('org.your.pkg.Main');

 * main.main__V_3Ljava_lang_String_2(null);

 * </pre>

 * In case one wants to initialize the virtual machine with ability to

 * load classes lazily when needed, one can provide a loader function to

 * when creating the virtual machine: <pre>

 * var vm = bck2brwsr(function(resource) { 

 *   return null; // byte[] for the resource

 * });

 * </pre>

 * In this scenario, when a request for an unknown class is made, the loader

 * function is asked for its byte code and the system dynamically transforms

 * it to JavaScript.

 * <p>

 * Instead of a loader function, one can also provide a URL to a JAR file.

 * The <code>bck2brwsr</code> system will do its best to download the file

 * and provide loader function for it automatically.

 * <p>

 * One can provide as many loader functions and JAR URL references as necessary.

 * Then the initialization code would look like:<pre>

 * var vm = bck2brwsr(url1, url2, fnctn1, url3, functn2);

 * </pre>

 * The provided URLs and loader functions will be consulted one by one.

 *

 * @author Jaroslav Tulach <jtulach@netbeans.org>

 */

public final class Bck2Brwsr {

    private Bck2Brwsr() {

    }

    /** Generates virtual machine from bytes served by a <code>resources</code>

     * provider.

     * 

     * @param out the output to write the generated JavaScript to

     * @param resources provider of class files to use

     * @param classes additional classes to include in the generated script

     * @throws IOException I/O exception can be thrown when something goes wrong

     */

    public static void generate(Appendable out, Resources resources, String... classes) throws IOException {

        StringArray arr = StringArray.asList(classes);

        arr.add(VM.class.getName().replace('.', '/'));

        try {

            ClosureWrapper.produceTo(out, resources, arr);

        } catch (IOException ex) {

            throw ex;

        } catch (Throwable ex) {

            VM.compile(resources, out, arr);

        }

    }

    /** Generates virtual machine from bytes served by a class loader.

     * 

     * @param out the output to write the generated JavaScript to

     * @param loader class loader to load needed classes from

     * @param classes additional classes to include in the generated script

     * @throws IOException I/O exception can be thrown when something goes wrong

     */

    public static void generate(Appendable out, final ClassLoader loader, String... classes) throws IOException {

        class R implements Resources {

            @Override

            public InputStream get(String name) throws IOException {

                Enumeration<URL> en = loader.getResources(name);

                URL u = null;

                while (en.hasMoreElements()) {

                    u = en.nextElement();

                }

                if (u == null) {

                    throw new IOException("Can't find " + name);

                }

                return u.openStream();

            }

        }

        generate(out, new R(), classes);

    }

    /** Provider of resources (classes and other files). The 

     * {@link #generate(java.lang.Appendable, org.apidesign.vm4brwsr.Bck2Brwsr.Resources, java.lang.String[]) 

     * generator method} will call back here for all classes needed during

     * translation to JavaScript.

     */

    public interface Resources {

        /** Loads given resource (class or other file like image). The 

         * resource name to load bytes for the {@link String} class

         * would be <code>"java/lang/String.class"</code>.

         * 

         * @param resource path to resource to load

         * @return the input stream for the resource 

         * @throws IOException can be thrown if the loading fails on some error

         *   or the file cannot be found

         */

        public InputStream get(String resource) throws IOException;

    }

}