/**

 * 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;

/** 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:

 * <pre>

 * Writer w = new {@link java.io.StringWriter}();

 * {@link #newCompiler() Bck2Brwsr.newCompiler}()

 *   .{@link #resources(org.apidesign.vm4brwsr.Bck2Brwsr.Resources)}

 *   .{@link #addRootClasses(java.lang.String...)}

 *   .{@link #addClasses(java.lang.String...)}

 *   .{@link #addExported(java.lang.String...)}

 *   .{@link #generate(java.lang.Appendable) generate(w)};

 * System.out.{@link java.io.PrintStream#print(java.lang.String) print(w.toString())};

 * </pre>

 * 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.invoke('main');

 * </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

 * or a library JavaScript file generated with {@link #library(java.lang.String...)}

 * option on.

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

 * and provide loader function for it automatically. In order to use

 * the JAR file <code>emul.zip</code> module needs to be available in the system.

 * <p>

 * One can provide as many loader functions and 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.

 * <p>

 * The initialization of the <b>Bck2Brwsr</b> is done asynchronously since 

 * version 0.9. E.g. call to <pre>

 * var vm = bck2brwsr('myapp.js');

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

 * main.invoke('main');

 * </pre>

 * returns immediately and the call to the static main method will happen

 * once the virtual machine is initialized and the class available.

 *

 * @author Jaroslav Tulach

 */

public final class Bck2Brwsr {

    private final ObfuscationLevel level;

    private final StringArray exported;

    private final StringArray classes;

    private final StringArray resources;

    private final Resources res;

    private final Boolean extension;

    private final StringArray classpath;

    private Bck2Brwsr(

            ObfuscationLevel level, 

            StringArray exported, StringArray classes, StringArray resources, 

            Resources res, 

            Boolean extension, StringArray classpath

    ) {

        this.level = level;

        this.exported = exported;

        this.classes = classes;

        this.resources = resources;

        this.res = res;

        this.extension = extension;

        this.classpath = classpath;

    }

    /** 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 #newCompiler()}.{@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() {

        return new Bck2Brwsr(

            ObfuscationLevel.NONE, 

            new StringArray(), new StringArray(), new StringArray(), 

            null, false, null

        );

    }

    /** Adds exported classes or packages. If the string ends 

     * with slash, it is considered a name of package. If it does not,

     * it is a name of a class (without <code>.class</code> suffix).

     * The exported classes are prevented from being obfuscated. 

     * All public classes in exported packages are prevented from

     * being obfuscated. By listing the packages or classes in this 

     * method, these classes are not guaranteed to be included in

     * the generated script. Use {@link #addClasses} to include

     * the classes.

     * 

     * @param exported names of classes and packages to treat as exported

     * @return new instances of the Bck2Brwsr compiler which inherits

     *   all values from <code>this</code> except list of exported classes

     */

    public Bck2Brwsr addExported(String... exported) {

        return new Bck2Brwsr(

            level, this.exported.addAndNew(exported), 

            classes, resources, res, extension, classpath

        );

    }

    /** Adds additional classes 

     * to the list of those that should be included in the generated

     * JavaScript file.

     * These classes are guaranteed to be available in the

     * generated virtual machine code accessible using their fully 

     * qualified name. This brings the same behavior as if the

     * classes were added by {@link #addClasses(java.lang.String...) } and

     * exported via {@link #addExported(java.lang.String...)}.

     * 

     * @param classes the classes to add to the compilation

     * @return new instance of the Bck2Brwsr compiler which inherits

     * all values from <code>this</code>

     */

    public Bck2Brwsr addRootClasses(String... classes) {

        if (classes.length == 0) {

            return this;

        } 

        return addExported(classes).addClasses(classes);

    }

    /** Adds additional classes 

     * to the list of those that should be included in the generated

     * JavaScript file. These classes are guaranteed to be present,

     * but they may not be accessible through their fully qualified

     * name.

     * 

     * @param classes the classes to add to the compilation

     * @return new instance of the Bck2Brwsr compiler which inherits

     * all values from <code>this</code>

     * @since 0.9

     */

    public Bck2Brwsr addClasses(String... classes) {

        if (classes.length == 0) {

            return this;

        } else {

            return new Bck2Brwsr(level, exported, 

                this.classes.addAndNew(classes), resources, res,

                extension, classpath);

        }

    }

    /** These resources should be made available in the compiled file in

     * binary form. These resources can then be loaded

     * by {@link ClassLoader#getResource(java.lang.String)} and similar 

     * methods.

     * 

     * @param resources names of the resources to be loaded by {@link Resources#get(java.lang.String)}

     * @return new instance of the Bck2Brwsr compiler which inherits

     *   all values from <code>this</code> just adds few more resource names

     *   for processing

     * @since 0.9

     */

    public Bck2Brwsr addResources(String... resources) {

        if (resources.length == 0) {

            return this;

        } else {

            return new Bck2Brwsr(level, exported, this.classes, 

                this.resources.addAndNew(resources), res, extension, classpath

            );

        }

    }

    /** 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, exported, classes, resources, res, extension, classpath);

    }

    /** 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, exported, classes, resources, 

            res, extension, classpath

        );

    }

    /** Should one generate a library? By default the system generates

     * all transitive classes needed by the the transitive closure of

     * {@link #addRootClasses(java.lang.String...)} and {@link #addClasses(java.lang.String...)}.

     * By turning on the library mode, only classes explicitly listed

     * will be included in the archive. The others will be referenced

     * as external ones.

     * <p>

     * A library archive may specify its <em>classpath</em> - e.g. link to

     * other libraries that should also be included in the application. 

     * One can specify the list of libraries as vararg to this method.

     * These are relative URL with respect to location of this library.

     * The runtime system then prefers seek for ".js" suffix of the library

     * and only then seeks for the classical ".jar" path.

     * 

     * @param classpath the array of JARs that are referenced by this library -

     *   by default gets turned into 

     * @return new instance of the compiler with library flag changed

     * @since 0.9

     */

    public Bck2Brwsr library(String... classpath) {

        return new Bck2Brwsr(

            level, exported, classes, 

            resources, res, true, 

            StringArray.asList(classpath)

        );

    }

    /** Turns on the standalone mode. E.g. does the opposite of

     * calling {@link #library(java.lang.String...)},

     * but also allows to specify whether the <em>Bck2Brwsr VM</em> should

     * be included at all. If not, only the skeleton of the launcher is

     * generated without any additional VM classes referenced.

     * 

     * @param includeVM should the VM be compiled in, or left out

     * @return new instance of the compiler with standalone mode on

     * @since 0.9

     */

    public Bck2Brwsr standalone(boolean includeVM) {

        return new Bck2Brwsr(

            level, exported, classes, resources, 

            res, includeVM ? false : null, null

        );

    }

    /** 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(loader, false);

    }

    /** 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

     * @param ignoreBootClassPath <code>true</code> if classes loaded

     *    from <code>rt.jar</code> 

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

     *   different resources provider

     * @since 0.9

     */

    public Bck2Brwsr resources(final ClassLoader loader, boolean ignoreBootClassPath) {

        return resources(new LdrRsrcs(loader, ignoreBootClassPath));

    }

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

     * compiler.

     * 

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

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

     * @since 0.5

     */

    public void generate(Appendable out) throws IOException {

        if (level != ObfuscationLevel.NONE) {

            try {

                ClosureWrapper.produceTo(out, level, this);

                return;

            } catch (IOException ex) {

                throw ex;

            } catch (Throwable ex) {

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

                               + " */\n");

            }

        }

        VM.compile(out, this);

    }

    //

    // Internal getters

    // 

    Resources getResources() {

        return res != null ? res : new LdrRsrcs(Bck2Brwsr.class.getClassLoader(), false);

    }

    StringArray allResources() {

        return resources;

    }

    StringArray classes() {

        return classes;

    }

    StringArray exported() {

        return exported;

    }

    boolean isExtension() {

        return Boolean.TRUE.equals(extension);

    }

    boolean includeVM() {

        return extension != null;

    }

    StringArray classpath() {

        return classpath;

    }

    /** 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;

    }

}