/**

  * 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('.', '/'));

         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;

     }

 }