content: package act.util;
  
  /*-
   * #%L
   * ACT Framework
   * %%
   * Copyright (C) 2014 - 2017 ActFramework
   * %%
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   * 
   *      http://www.apache.org/licenses/LICENSE-2.0
   * 
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   * #L%
   */
  
  import act.asm.AnnotationVisitor;
  import act.asm.MethodVisitor;
  import act.asm.Type;
  import org.osgl.$;
  import org.osgl.util.S;
  
  import javax.inject.Singleton;
  
  /**
   * If a certain non-abstract/public class extends {@link SingletonBase} ensure the class
   * has {@link javax.inject.Singleton} annotation, and generate {@link SingletonBase#instance()}
   * implementation
   */
  @SuppressWarnings("unused")
  public class SingletonEnhancer extends AppByteCodeEnhancer<SingletonEnhancer> {
  
      private boolean shouldEnhance = false;
      private boolean shouldAddAnnotation = true;
      private String typeName;
  
      public SingletonEnhancer() {
          super($.F.<String>yes());
      }
  
      @Override
      protected Class<SingletonEnhancer> subClass() {
          return SingletonEnhancer.class;
      }
  
      @Override
      protected void reset() {
          this.shouldAddAnnotation = true;
          this.shouldEnhance = false;
          this.typeName = null;
          super.reset();
      }
  
      @Override
      public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {
          super.visit(version, access, name, signature, superName, interfaces);
          this.typeName = name;
          if (SingletonBase.class.getName().equals(Type.getObjectType(superName).getClassName())) {
              if (isAbstract(access)) {
                  logger.warn("SingletonBase sub class is abstract: %s", name);
                  return;
              } else if (!isPublic(access)) {
                  logger.warn("SingletonBase sub class is not public: %s", name);
                  return;
              }
              shouldEnhance = true;
          }
      }
  
      @Override
      public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
          Type type = Type.getType(desc);
          if (Singleton.class.getName().equals(type.getClassName())) {
              shouldAddAnnotation = false;
              shouldEnhance = true;
          }
          return super.visitAnnotation(desc, visible);
      }
  
      @Override
      public void visitEnd() {
          if (shouldEnhance) {
              addAnnotationIfNeeded();
              addInstanceMethod();
          }
          super.visitEnd();
      }
  
      private void addAnnotationIfNeeded() {
          if (shouldAddAnnotation) {
              AnnotationVisitor av = super.visitAnnotation(Type.getType(Singleton.class).getDescriptor(), true);
              av.visitEnd();
          }
      }
  
      private void addInstanceMethod() {
          MethodVisitor mv = super.visitMethod(ACC_PUBLIC + ACC_STATIC, "instance", "()Ljava/lang/Object;", "<T:Ljava/lang/Object;>()TT;", null);
          mv.visitCode();
          mv.visitMethodInsn(INVOKESTATIC, "act/app/App", "instance", "()Lact/app/App;", false);
          mv.visitLdcInsn(Type.getType(instanceTypeDesc()));
          mv.visitMethodInsn(INVOKEVIRTUAL, "act/app/App", "singleton", "(Ljava/lang/Class;)Ljava/lang/Object;", false);
          mv.visitInsn(ARETURN);
          mv.visitMaxs(2, 0);
          mv.visitEnd();
      }
  
      private String instanceMethodReturnTypeDesc() {
          return S.fmt("()L%s;", typeName);
      }
  
      private String instanceTypeDesc() {
          return S.fmt("L%s;", typeName);
      }
  
  }
  