/**

  * Back 2 Browser Bytecode Translator

  * Copyright (C) 2012-2015 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 org.apidesign.bck2brwsr.core.JavaScriptBody;

 import org.apidesign.vm4brwsr.ByteCodeParser.ClassData;

 import org.apidesign.vm4brwsr.ByteCodeParser.FieldData;

 import org.apidesign.vm4brwsr.ByteCodeParser.MethodData;

 /** Generator of JavaScript from bytecode of classes on classpath of the VM.

  *

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

  */

 abstract class VM extends ByteCodeToJavaScript {

     protected final ClassDataCache classDataCache;

     private final Bck2Brwsr.Resources resources;

     private final ExportedSymbols exportedSymbols;

     private final StringBuilder invokerMethods;

     private final StringArray asBinary;

     int exportedCount;

     private VM(

         Appendable out, Bck2Brwsr.Resources resources, 

         StringArray explicitlyExported, StringArray asBinary

     ) {

         super(out);

         this.resources = resources;

         this.classDataCache = new ClassDataCache(resources);

         this.exportedSymbols = new ExportedSymbols(resources, explicitlyExported);

         this.invokerMethods = new StringBuilder();

         this.asBinary = asBinary;

     }

     static {

         // uses VMLazy to load dynamic classes

         boolean assertsOn = false;

         assert assertsOn = true;

         if (assertsOn) {

             VMLazy.init();

             ClassPath.init();

         }

     }

     @Override

     boolean debug(String msg) throws IOException {

         return false;

     }

     static void compile(Appendable out, 

         Bck2Brwsr config

     ) throws IOException {

         String[] both = config.classes().toArray();

         final StringArray fixedNames = new StringArray();

         boolean addThree = false;

         VM vm;

         if (config.isExtension()) {

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

             vm = new Extension(out, 

                 config.getResources(), both, config.exported(),

                 config.allResources(), config.classpath()

             );

             addThree = true;

         } else {

             if (config.includeVM()) {

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

                 addThree = true;

             }

             vm = new Standalone(out, 

                 config.getResources(), config.exported(),

                 config.allResources()

             );

         }            

         if (addThree) {

             fixedNames.add(Object.class.getName().replace('.', '/'));

             fixedNames.add(Class.class.getName().replace('.', '/'));

             fixedNames.add(ArithmeticException.class.getName().replace('.', '/'));

         }

         vm.doCompile(fixedNames.addAndNew(both));

     }

     private void doCompile(StringArray names) throws IOException {

         generatePrologue();

         append("\n  var invoker = {};");

         append("\n  function registerClass(vm, name, fn) {");

         append("\n    if (!vm[name]) vm[name] = fn;");

         append("\n    return vm[name];");

         append("\n  }");

         generateBody(names);

         append(invokerMethods);

         for (String r : asBinary.toArray()) {

             append("\n  ").append(getExportsObject()).append("['registerResource']('");

             append(r).append("', '");

             InputStream is = this.resources.get(r);

             int avail = is.available();

             if (avail <= 0) {

                 avail = 4096;

             }

             byte[] arr = new byte[avail];

             int offset = 0;

             for (;;) {

                 if (offset == arr.length) {

                     byte[] tmp = new byte[arr.length * 2];

                     System.arraycopy(arr, 0, tmp, 0, arr.length);

                     arr = tmp;

                 }

                 int len = is.read(arr, offset, arr.length - offset);

                 if (len == -1) {

                     break;

                 }

                 offset += len;

             }

             if (offset != arr.length) {

                 byte[] tmp = new byte[offset];

                 System.arraycopy(arr, 0, tmp, 0, offset);

                 arr = tmp;

             }

             append(btoa(arr));

             append("');");

         }

         append("\n");

         generateEpilogue();

     }

     @JavaScriptBody(args = { "arr" }, body = "return btoa(arr);")

     private static String btoa(byte[] arr) {

         return javax.xml.bind.DatatypeConverter.printBase64Binary(arr);

     }

     protected abstract void generatePrologue() throws IOException;

     protected abstract void generateEpilogue() throws IOException;

     protected abstract String getExportsObject();

     protected abstract boolean isExternalClass(String className);

     protected abstract void lazyReference(Appendable out, String n) throws IOException;

     @Override

     protected final void declareClass(ClassData classData, String mangledName)

             throws IOException {

         if (exportedSymbols.isExported(classData)) {

             append("registerClass(").append(getExportsObject()).append(",'")

                                                .append(mangledName)

                                                .append("',")

                             .append(mangledName)

                .append(")");

             exportedCount++;

         } else {

             append(mangledName);

         }

     }

     protected String generateClass(String className) throws IOException {

         ClassData classData = classDataCache.getClassData(className);

         if (classData == null) {

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

         }

         return compile(classData);

     }

     @Override

     protected void declaredField(FieldData fieldData,

                                  String destObject,

                                  String mangledName) throws IOException {

         if (exportedSymbols.isExported(fieldData)) {

             exportMember(destObject, mangledName);

         }

     }

     @Override

     protected void declaredMethod(MethodData methodData,

                                   String destObject,

                                   String mangledName) throws IOException {

         if (isHierarchyExported(methodData)) {

             exportMember(destObject, mangledName);

         }

     }

     private void exportMember(String destObject, String memberName)

             throws IOException {

         append("\n").append(destObject).append("['")

         .append(memberName)

         .append("'] = m;\n");

     }

     private void generateBody(StringArray names) throws IOException {

         StringArray processed = new StringArray();

         StringArray initCode = new StringArray();

         StringArray skipClass = new StringArray();

         for (String baseClass : names.toArray()) {

             references.add(baseClass);

             for (;;) {

                 String name = null;

                 for (String n : references.toArray()) {

                     if (skipClass.contains(n)) {

                         continue;

                     }

                     if (processed.contains(n)) {

                         continue;

                     }

                     name = n;

                 }

                 if (name == null) {

                     break;

                 }

                 InputStream is = resources.get(name + ".class");

                 if (is == null) {

                     lazyReference(this, name);

                     skipClass.add(name);

                     continue;

                 }

                 try {

                     String ic = generateClass(name);

                     processed.add(name);

                     initCode.add(ic == null ? "" : ic);

                 } catch (RuntimeException ex) {

                     throw new IOException("Error while compiling " + name + "\n", ex);

                 }

             }

             for (String resource : scripts.toArray()) {

                 while (resource.startsWith("/")) {

                     resource = resource.substring(1);

                 }

                 requireResourceImpl(resource);

                 asBinary.remove(resource);

             }

             scripts = new StringArray();

             StringArray toInit = StringArray.asList(references.toArray());

             toInit.reverse();

             for (String ic : toInit.toArray()) {

                 int indx = processed.indexOf(ic);

                 if (indx >= 0) {

                     final String theCode = initCode.toArray()[indx];

                     if (!theCode.isEmpty()) {

                         append(theCode).append("\n");

                     }

                     initCode.toArray()[indx] = "";

                 }

             }

         }

     }

     final void requireResourceImpl(String resource) throws IOException {

         InputStream emul = resources.get(resource);

         if (emul == null) {

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

         }

         append("\n// resource from ").append(resource).append("\n");

         append("\neval(\"");

         readResource(emul, this);

         append("\");\n");

     }

     private static void readResource(InputStream emul, Appendable out) throws IOException {

         try {

             for (;;) {

                 int ch = emul.read();

                 if (ch == -1) {

                     break;

                 }

                 if (ch < 0 || ch > 255) {

                     throw new IOException("Invalid char in emulation " + ch);

                 }

                 switch (ch) {

                     case '"':

                         out.append("\\\"");

                         break;

                     case '\\':

                         out.append("\\\\");

                         break;

                     case '\n':

                         out.append("\\n\"\n + \"");

                         break;

                     case '\t':

                         out.append("\\t");

                         break;

                     case '\r':

                         out.append("\\r");

                         break;

                     default:

                         out.append((char)ch);

                 }

             }

         } finally {

             emul.close();

         }

     }

     static String toString(String name) throws IOException {

         StringBuilder sb = new StringBuilder();

 //        compile(sb, name);

         return sb.toString().toString();

     }

     private StringArray scripts = new StringArray();

     private StringArray references = new StringArray();

     @Override

     protected boolean requireReference(String cn) {

         return references.addIfMissing(cn);

     }

     @Override

     protected void requireScript(String resourcePath) {

         scripts.add(resourcePath);

     }

     @Override

     String assignClass(String className) {

         return "vm." + className + " = ";

     }

     @Override

     String accessClass(String className) {

         return "vm." + className;

     }

     @Override

     protected FieldData findField(String[] fieldInfoName) throws IOException {

         FieldData field = classDataCache.findField(

             fieldInfoName[0], fieldInfoName[1], fieldInfoName[2]

         );

         return field != null && canAccessDirectly(field.cls) ? field : null;

     }

     @Override

     protected String accessField(String object, FieldData field, String[] fieldInfoName)

     throws IOException {

         if (field != null && !field.isStatic()) {

             return "fld_" + object + "_" + field.getName();

         } else {

             String mangledName = "_" + fieldInfoName[1];

            return accessNonVirtualMember(

                object, mangledName, field != null ? field.cls : null

            );

          }

     }

     @Override

     protected String accessStaticMethod(

                              String object,

                              String mangledName,

                              String[] fieldInfoName) throws IOException {

         final MethodData method =

                 classDataCache.findMethod(fieldInfoName[0],

                                           fieldInfoName[1],

                                           fieldInfoName[2]);

         return accessNonVirtualMember(object, mangledName,

                                       (method != null) ? method.cls : null);

     }

     @Override

     protected String accessVirtualMethod(

             String object, 

             String mangledName, 

             String[] fieldInfoName, 

             int params

     ) throws IOException {

         final ClassData referencedClass =

                 classDataCache.getClassData(fieldInfoName[0]);

         final MethodData method =

                 classDataCache.findMethod(referencedClass,

                                           fieldInfoName[1],

                                           fieldInfoName[2]);

         if ((method != null)

                 && !isExternalClass(method.cls.getClassName())

                 && (((method.access & ByteCodeParser.ACC_FINAL) != 0)

                         || ((referencedClass.getAccessFlags()

                                  & ByteCodeParser.ACC_FINAL) != 0)

                         || !isHierarchyExported(method))) {

             return object + "." + mangledName + '(';

         }

         return accessThroughInvoker(object, mangledName, params);

     }

     private String accessThroughInvoker(String object, String mangledName, int params) 

     throws IOException {

         String def = "\n  invoker." + mangledName + " = function(target";

         if (invokerMethods.indexOf(def) == -1) {

             invokerMethods.append(def);

             for (int j = 0; j < params; j++) {

                 invokerMethods.append(", p").append(j);

             }

             invokerMethods.append(") {\n    return target['").

                 append(mangledName).append("'](");

             for (int j = 0; j < params; j++) {

                 if (j > 0) {

                     invokerMethods.append(",");

                 }

                 invokerMethods.append("p").append(j);

             }

             invokerMethods.append(");\n  };");

         }

         return "invoker." + mangledName + '(' + object + (params > 1 ? "," : "");

     }

     private boolean isHierarchyExported(final MethodData methodData)

             throws IOException {

         if (exportedSymbols.isExported(methodData)) {

             return true;

         }

         if ((methodData.access & (ByteCodeParser.ACC_PRIVATE

                                       | ByteCodeParser.ACC_STATIC)) != 0) {

             return false;

         }

         final ExportedMethodFinder exportedMethodFinder =

                 new ExportedMethodFinder(exportedSymbols);

         classDataCache.findMethods(

                 methodData.cls,

                 methodData.getName(),

                 methodData.getInternalSig(),

                 exportedMethodFinder);

         return (exportedMethodFinder.getFound() != null);

     }

     private boolean canAccessDirectly(ClassData declaringClass) {

         if (declaringClass == null) {

             return false;

         }

         final String className = declaringClass.getClassName();

         if (

             "java/lang/Object".equals(className) ||

             "java/lang/reflect/Array".equals(className) ||

             isExternalClass(className)

         ) {

             return false;

         }

         return true;

     }

     private String accessNonVirtualMember(

         String object, String mangledName, ClassData declaringClass

     ) {

         return canAccessDirectly(declaringClass) ?

             object + "." + mangledName :

             object + "['" + mangledName + "']";

     }

     private final class ExportedMethodFinder

             implements ClassDataCache.TraversalCallback<MethodData> {

         private final ExportedSymbols exportedSymbols;

         private MethodData found;

         public ExportedMethodFinder(final ExportedSymbols exportedSymbols) {

             this.exportedSymbols = exportedSymbols;

         }

         @Override

         public boolean traverse(final MethodData methodData) {

             try {

                 if (

                     exportedSymbols.isExported(methodData) ||

                     isExternalClass(methodData.cls.getClassName())

                 ) {

                     found = methodData;

                     return false;

                 }

             } catch (final IOException e) {

             }

             return true;

         }

         public MethodData getFound() {

             return found;

         }

     }

     private static final class Standalone extends VM {

         private Standalone(Appendable out,

             Bck2Brwsr.Resources resources, 

             StringArray explicitlyExported, StringArray asBinary

         ) {

             super(out, resources, explicitlyExported, asBinary);

         }

         @Override

         protected void generatePrologue() throws IOException {

             append("(function VM(global) {var fillInVMSkeleton = function(vm) {");

         }

         @Override

         protected void generateEpilogue() throws IOException {

             append(

                   "  return vm;\n"

                 + "  };\n"

                 + "  var extensions = [];\n"

                 + "  function replaceAll(s, target, replacement) {\n"

                 + "    var pos = 0;\n"

                 + "    for (;;) {\n"

                 + "      var indx = s.indexOf(target, pos);\n"

                 + "      if (indx === -1) {\n"

                 + "        return s;\n"

                 + "      }\n"

                 + "      pos = indx + replacement.length;\n"

                 + "      s = s.substring(0, indx) + replacement + s.substring(indx + target.length);\n"

                 + "    }\n"

                 + "  }\n"

                 + "  function mangleClass(name) {\n"

                 + "    name = replaceAll(name, '_', '_1');\n"

                 + "    name = replaceAll(name, '.', '_');\n"

                 + "    return name;\n"

                 + "  };\n"

                 + "  var pending = [];\n"

                 + "  var pendingClasses = [];\n"

                 + "  function extensionLoaded(ev) {\n"

                 + "    var at = pending.indexOf(ev.target);\n"

                 + "    pending.splice(at, 1);\n"

                 + "    if (pending.length === 0) {\n"

                 + "      for (var i = 0; i < pendingClasses.length; i += 3) {\n"

                 + "        invokeMethod(pendingClasses[i], pendingClasses[i + 1], pendingClasses[i + 2]);\n"

                 + "      }\n"

                 + "      pendingClasses = [];\n"

                 + "    }\n"

                 + "  }\n"

                 + "  function invokeMethod(vm, n, args) {\n"

                 + "    var clazz = vm.loadClass(n);\n"

                 + "    if (args) {\n"

                 + "      var seek = args[0];\n"

                 + "      var prefix = seek.indexOf('__') == -1 ? seek + '__' : seek;\n"

                 + "      args = Array.prototype.slice.call(args, 1);\n"

                 + "      var found = '';\n"

                 + "      for (var m in clazz) {\n"

                 + "        if (m.indexOf(prefix) === 0) {\n"

                 + "          return clazz[m].apply(null, args);\n"

                 + "        }\n"

                 + "        found += m.toString() + '\\n'\n"

                 + "      }\n"

                 + "      throw 'Cannot find ' + seek + ' in ' + n + ' found:\\n' + found;\n"

                 + "    }\n"

                 + "  }\n"

                 + "  function extensionError(ev) {\n"

                 + "    console.log('error loading ' + ev.target.src);\n"

                 + "    extensionLoaded(ev);\n"

                 + "  }\n"

                 + "  function loadExtension(url) {\n"

                 + "      if (url.substring(url.length - 4) == '.jar')\n"

                 + "        url = url.substring(0, url.length - 4) + '.js';\n"

                 + "      var script = document.createElement('script');\n"

                 + "      script.type = 'text/javascript';\n"

                 + "      script.src = url;\n"

                 + "      script.onload = extensionLoaded;\n"

                 + "      script.onerror = extensionError;\n"

                 + "      document.getElementsByTagName('head')[0].appendChild(script);\n"

                 + "      pending.push(script);\n"

                 + "  }\n"

                 + "  global.bck2brwsr = function() {\n"

                 + "    var args = Array.prototype.slice.apply(arguments);\n"

                 + "    var resources = {};\n"

                 + "    function registerResource(n, a64) {\n"

                 + "      var frm = atob || window.atob;\n"

                 + "      var str = frm(a64);\n"

                 + "      var arr = [];\n"

                 + "      for (var i = 0; i < str.length; i++) {\n"

                 + "        var ch = str.charCodeAt(i) & 0xff;\n"

                 + "        if (ch > 127) ch -= 256;\n"

                 + "        arr.push(ch);\n"

                 + "      }\n"

                 + "      if (!resources[n]) resources[n] = [arr];\n"

                 + "      else resources[n].push(arr);\n"

                 + "    }\n"

                 + "    var vm = fillInVMSkeleton({ 'registerResource' : registerResource });\n"

                 + "    function initVM() {\n"

                 + "      var clsArray = vm['java_lang_reflect_Array'];\n"

                 + "      if (clsArray) clsArray(false);\n"

                 + "    }\n"

                 + "    for (var i = 0; i < extensions.length; ++i) {\n"

                 + "      extensions[i](vm);\n"

                 + "    }\n"

                 + "    vm['registerResource'] = null;\n"

                 + "    var knownExtensions = extensions.length;\n"

                 + "    var loader = {};\n"

                 + "    var classPath;\n"

                 + "    var loadBytes = function(name, skip) {\n"

                 + "      skip = typeof skip == 'number' ? skip : 0;\n"

                 + "      var arr = resources[name];\n"

                 + "      if (arr) {\n"

                 + "        var arrSize = arr.length;\n"

                 + "        if (skip < arrSize) return arr[skip];\n"

                 + "        skip -= arrSize;\n"

                 + "      } else {\n"

                 + "        var arrSize = 0;\n"

                 + "      };\n"

                 + "      for (var i = 0; i < args.length; i++) {\n"

                 + "        var at = args[i];\n"

                 + "        if(!at) continue;\n"

                 + "        var ret;\n"

                 + "        if (typeof at === 'string' && at.substring(at.length - 3) === '.js') {\n"

                 + "          loadExtension(at);\n"

                 + "          args[i] = null;\n"

                 + "        } else if (typeof at === 'function') ret = at(name, skip);\n"

                 + "        else {\n"

                 + "          if (classPath === undefined) {\n"

                 + "             classPath = null;\n"

                 + "             try {\n"

                 + "               classPath = vm.loadClass('org.apidesign.vm4brwsr.ClassPath');\n"

                 + "             } catch (err) {\n"

                 + "             }\n"

                 + "           }\n"

                 + "          if (!classPath) {\n"

                 + "            if (name !== 'org/apidesign/vm4brwsr/ClassPath.class') {\n"

                 + "              throw 'Core Java library not registered. Cannot load from ' + at;\n"

                 + "            }\n"

                 + "            ret = null;\n"

                 + "          } else {\n"

                 + "            ret = classPath['loadBytes___3BLjava_lang_String_2Ljava_lang_Object_2II'](name, args, i, skip);\n"

                 + "          }\n"

                 + "        }\n"

                 + "        if (ret) return ret;\n"

                 + "      }\n"

                 + "      while (knownExtensions < extensions.length) {\n"

                 + "        vm['registerResource'] = registerResource;\n"

                 + "        extensions[knownExtensions++](vm);\n"

                 + "        vm['registerResource'] = null;\n"

                 + "        initVM();\n"

                 + "      }\n"

                 + "      var arr = resources[name];\n"

                 + "      return (arr && arr.length > arrSize) ? arr[arrSize] : null;\n"

                 + "    }\n"

                 + "    var reload = function(name, arr, keep) {\n"

                 + "      if (!arr) throw 'Cannot find ' + name;\n"

                 + "      var err = null;\n"

                 + "      try {\n"

                 + "        var lazy = loadClass('org.apidesign.vm4brwsr.VMLazy');\n"

                 + "      } catch (e) {\n"

                 + "        err = e;\n"

                 + "      }\n"

                 + "      if (!lazy) {\n"

                 + "         throw 'No bck2brwsr VM module to compile ' + name + ':\\n' + err;\n"

                 + "      }\n"

                 + "      if (!keep) {\n"

                 + "        var attr = mangleClass(name);\n"

                 + "        delete vm[attr];\n"

                 + "      }\n"

                 + "      return lazy['load__Ljava_lang_Object_2Ljava_lang_Object_2Ljava_lang_String_2_3Ljava_lang_Object_2_3B']\n"

                 + "        (vm, name, args, arr);\n"

                 + "    };\n"

                 + "    var loadClass = function(name) {\n"

                 + "      var attr = mangleClass(name);\n"

                 + "      var fn = vm[attr];\n"

                 + "      if (fn) return fn(false);\n"

                 + "      try {\n"

                 + "        var arr = loadBytes(replaceAll(name, '.', '/') + '.class');\n"

                 + "        return reload(name, arr, true);\n"

                 + "      } catch (err) {\n"

                 + "        fn = vm[attr];\n"

                 + "        if (fn) return fn(false);\n"

                 + "        throw err;\n"

                 + "      }\n"

                 + "    }\n"

                 + "    if (vm['loadClass']) {\n"

                 + "      throw 'Cannot initialize the bck2brwsr VM twice!';\n"

                 + "    }\n"

                 + "    vm['loadClass'] = loadClass;\n"

                 + "    vm['_reload'] = reload;\n"

                 + "    vm['loadBytes'] = loadBytes;\n"

                 + "    initVM();\n"

                 + "    loader.loadClass = function(name) {\n"

                 + "      if (pending.length === 0) {\n"

                 + "        try {\n"

                 + "          var c = loadClass(name);\n"

                 + "          c['invoke'] = function() {\n"

                 + "            return invokeMethod(vm, name, arguments);\n"

                 + "          };\n"

                 + "          return c;\n"

                 + "        } catch (err) {\n"

                 + "          if (pending.length === 0) throw err;\n"

                 + "        }\n"

                 + "      }\n"

                 + "      pendingClasses.push(vm);\n"

                 + "      pendingClasses.push(name);\n"

                 + "      pendingClasses.push(null);\n"

                 + "      return {\n"

                 + "        'invoke' : function() {\n"

                 + "          if (pending.length === 0) {\n"

                 + "            invokeMethod(vm, name, arguments);\n"

                 + "            return;\n"

                 + "          }\n"

                 + "          pendingClasses.push(vm);\n"

                 + "          pendingClasses.push(name);\n"

                 + "          pendingClasses.push(arguments);\n"

                 + "        }\n"

                 + "      };\n"

                 + "    }\n"

                 + "    return loader;\n"

                 + "  };\n");

             append(

                   "  global.bck2brwsr.register = function(config, extension) {\n"

                 + "    if (!config || config['magic'] !== 'kafčo') {\n"

                 + "      console.log('Will not register: ' + extension);\n"

                 + "      return false;\n"

                 + "    }\n"

                 + "    var cs = typeof document == 'undefined' ? null : document['currentScript'];\n"

                 + "    var csUrl = cs ? cs['src'] : null;\n"

                 + "    var prefix = csUrl ? csUrl['replace'](/\\/[^\\/]*$/,'/') : '';\n"

                 + "    extensions.push(extension);\n"

                 + "    var cp = config['classpath'];\n"

                 + "    if (cp) for (var i = 0; i < cp.length; i++) {\n"

                 + "      loadExtension(prefix + cp[i]);\n"

                 + "    }\n"

                 + "    return null;\n"

                 + "  };\n");

             append("}(this));");

         }

         @Override

         protected String getExportsObject() {

             return "vm";

         }

         @Override

         protected boolean isExternalClass(String className) {

             return false;

         }

         @Override

         protected void lazyReference(Appendable out, String n) throws IOException {

             String cls = n.replace('/', '_');

             String dot = n.replace('/', '.');

             out.append("\nvm.").append(cls).append(" = function() {");

             out.append("\n  var instance = arguments.length == 0 || arguments[0] === true;");

             out.append("\n  delete vm.").append(cls).append(";");

             out.append("\n  var c = vm.loadClass('").append(dot).append("');");

             out.append("\n  return vm.").append(cls).append("(instance);");

             out.append("\n}");

         }

         @Override

         protected void requireResource(String resourcePath) throws IOException {

             requireResourceImpl(resourcePath);

             super.asBinary.remove(resourcePath);

         }

     }

     private static final class Extension extends VM {

         private final StringArray extensionClasses;

         private final StringArray classpath;

         private Extension(Appendable out, Bck2Brwsr.Resources resources,

             String[] extClassesArray, StringArray explicitlyExported,

             StringArray asBinary, StringArray classpath

         ) throws IOException {

             super(out, resources, explicitlyExported, asBinary);

             this.extensionClasses = StringArray.asList(extClassesArray);

             this.classpath = classpath;

         }

         @Override

         protected void generatePrologue() throws IOException {

             append(

                   "bck2brwsr.register({\n"

                 + "  'magic' : 'kafčo'"

             );

             if (classpath != null && classpath.toArray().length > 0) {

                 append(

                   ",\n  'classpath' : [\n"

                 );

                 String sep = "    ";

                 for (String s : classpath.toArray()) {

                     append(sep).append("'").append(s).append("'");

                     sep = ",\n    ";

                 }

                 append(

                   "\n  ]"

                 );

             }

             append(

                   "\n}, function(exports) {\n"

                 + "  var vm = {};\n");

             append("  function link(n, assign) {\n"

                 + "    function replaceAll(s, o, n) {\n"

                 + "      var pos = 0;\n"

                 + "      for (;;) {\n"

                 + "         var indx = s.indexOf(o, pos);\n"

                 + "         if (indx === -1) {\n"

                 + "           return s;\n"

                 + "         }\n"

                 + "         pos = indx + n.length;\n"

                 + "         s = s.substring(0, indx) + n + s.substring(indx + o.length);\n"

                 + "      }\n"

                 + "    }\n"

                 + "    return function() {\n"

                 + "      var no_ = replaceAll(n, '_', '_1');\n"

                 + "      var cls = replaceAll(no_, '/', '_');\n"

                 + "      var dot = replaceAll(n, '/', '.');\n"

                 + "      exports.loadClass(dot);\n"

                 + "      assign(exports[cls]);\n"

                 + "      return exports[cls](arguments);\n"

                 + "    };\n"

                 + "  };\n"

             );

         }

         @Override

         protected void generateEpilogue() throws IOException {

             append("});");

             if (exportedCount == 0) {

                 throw new IOException("Creating library without any exported symbols is useless!");

             }

         }

         @Override

         String accessClass(String className) {

             if (this.extensionClasses.contains(className.replace('_', '/'))) {

                 return className;

             }

             return super.accessClass(className);

         }

         @Override

         protected String generateClass(String className) throws IOException {

             if (isExternalClass(className)) {

                 final String cls = className.replace("_", "_1").replace('/', '_');

                 append("\n").append(assignClass(cls))

                    .append("link('")

                    .append(className)

                    .append("', function(f) { ").append(assignClass(cls)).append(" f; });");

                 return null;

             }

             return super.generateClass(className);

         }

         @Override

         protected String getExportsObject() {

             return "exports";

         }

         @Override

         protected boolean isExternalClass(String className) {

             return !extensionClasses.contains(className);

         }

         @Override

         protected void lazyReference(Appendable out, String n) throws IOException {

             String cls = n.replace('/', '_');

             out.append("\nvm.").append(cls).append(" = function() {");

             out.append("\n  var instance = arguments.length == 0 || arguments[0] === true;");

             out.append("\n  delete vm.").append(cls).append(";");

             out.append("\n  return link('").append(n).append("', function(f) { vm.");

             out.append(cls).append(" = f;})(instance);");

             out.append("\n}");

         }

         @Override

         protected void requireResource(String resourcePath) throws IOException {

             requireResourceImpl(resourcePath);

             super.asBinary.remove(resourcePath);

         }

     }

 }