/**

 * 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;

/** 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 final boolean extension;

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

        this.level = level;

        this.classes = classes;

        this.res = resources;

        this.extension = extension;

    }

    /** 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(

                              Class.class.getName().replace('.', '/'),

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

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

    }

    /** 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,

                                 extension);

        }

    }

    /** 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, extension);

    }

    /** 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, extension);

    }

    public Bck2Brwsr extension(boolean extension) {

        return new Bck2Brwsr(level, classes, res, extension);

    }

    /** 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, extension);

                return;

            } catch (IOException ex) {

                throw ex;

            } catch (Throwable ex) {

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

                               + " */\n");

            }

        }

        VM.compile(out, r, classes, extension);

    }

    /** 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;

    }

}