/**

  * 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 final ObfuscationLevel level;

     private final StringArray classes;

     private final Resources res;

     private Bck2Brwsr(ObfuscationLevel level, StringArray classes, Resources resources) {

         this.level = level;

         this.classes = classes;

         this.res = resources;

     }

     /** Helper method to generate 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 {

         newCompiler().resources(resources).addRootClasses(classes).generate(out);

     }

     /** Helper method to generate 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, ClassLoader loader, String... classes) throws IOException {

         newCompiler().resources(loader).addRootClasses(classes).generate(out);

     }

     /** Creates new instance of Bck2Brwsr compiler which is ready to generate

      * empty Bck2Brwsr virtual machine. The instance can be further

      * configured by calling chain of methods. For example: 

      * <pre>

      * {@link #createCompiler()}.{@link #resources(org.apidesign.vm4brwsr.Bck2Brwsr.Resources) resources(loader)}.{@link #addRootClasses(java.lang.String[]) addRootClasses("your/Clazz")}.{@link #generate(java.lang.Appendable) generate(out)};

      * </pre>

      * 

      * @return new instance of the Bck2Brwsr compiler

      * @since 0.5

      */

     public static Bck2Brwsr newCompiler() {

         StringArray arr = StringArray.asList(VM.class.getName().replace('.', '/'));

         return new Bck2Brwsr(ObfuscationLevel.NONE, arr, null);

     }

     /** Creates new instance of the Bck2Brwsr compiler which inherits

      * all values from <code>this</code> instance and adds additional classes 

      * to the list of those that should be compiled by the {@link #generate(java.lang.Appendable)} 

      * method.

      * 

      * @param classes the classes to add to the compilation

      * @return new instance of the compiler

      */

     public Bck2Brwsr addRootClasses(String... classes) {

         if (classes.length == 0) {

             return this;

         } else {

             return new Bck2Brwsr(level, this.classes.addAndNew(classes), res);

         }

     }

     /** Changes the obfuscation level for the compiler by creating new instance

      * which inherits all values from <code>this</code> and adjust the level

      * of obfuscation.

      * 

      * @param level the new level of obfuscation

      * @return new instance of the compiler with changed level of obfuscation

      * @since 0.5

      */

     public Bck2Brwsr obfuscation(ObfuscationLevel level) {

         return new Bck2Brwsr(level, classes, res);

     }

     /** A way to change the provider of additional resources (classes) for the 

      * compiler. 

      * 

      * @param res the implementation of resources provider

      * @return new instance of the compiler with all values remaining the same, just 

      *   with different resources provider

      * @since 0.5

      */

     public Bck2Brwsr resources(Resources res) {

         return new Bck2Brwsr(level, classes, res);

     }

     /** A way to change the provider of additional resources (classes) for the 

      * compiler by specifying classloader to use for loading them.

      * 

      * @param loader class loader to load the resources from

      * @return new instance of the compiler with all values being the same, just 

      *   different resources provider

      * @since 0.5

      */

     public Bck2Brwsr resources(final ClassLoader loader) {

         return resources(new LdrRsrcs(loader));

     }

     /** Generates virtual machine based on previous configuration of the 

      * compiler.

      * 

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

      * @since 0.5

      */

     public void generate(Appendable out) throws IOException {

         Resources r = res != null ? res : new LdrRsrcs(Bck2Brwsr.class.getClassLoader());

         if (level != ObfuscationLevel.NONE) {

             try {

                 ClosureWrapper.produceTo(out, level, r, classes);

                 return;

             } catch (IOException ex) {

                 throw ex;

             } catch (Throwable ex) {

                 out.append("/* Failed to obfuscate: " + ex.getMessage()

                                + " */\n");

             }

         }

         VM.compile(r, out, 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;

     }

 }